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European Strategic Wind Tunnels Improved Research Potential

Final Report Summary - ESWIRP (European Strategic Wind Tunnels Improved Research Potential)

Executive Summary:
“European Strategic Wind tunnel Improved Research Potential” ESWIRP is a project in the EU 7th Framework program (FP7) and it is designed to improve the performance capabilities of the three strategic wind tunnels in Europe by intensifying the cooperation between three key wind tunnels in a new consortium. The research consortium members are ONERA operating the S1MA as its largest transonic wind tunnel, DNW operating the LLF as its largest low speed wind tunnel and ETW operating its cryogenic transonic wind tunnel. Together these wind tunnels cover a wide range of experimental situations of relevance for civil aviation and other research.

The project started on October 2009 for a period of 5 years. The European financial contribution is € 7.2 million.

The contents of the project consist of two major components, the improvements to the testing infrastructure and the provision of access to research groups which do not usually have the means to access such large scale testing capabilities. These are flanked by public dissemination and information activities.

Although the tunnels covered in this project are of complementary nature, the infrastructure activities are joined together by a common representation of and approach to the tunnel performance characteristics. For this a generic model of a virtual wind tunnel was developed, enabling operators to assess the effect of the control parameters upon the testing conditions. The final aim of all participants is to provide the user community an improved capacity to test their innovative ideas and to be able to do this with increased reliability.

In the provision of access to those major wind tunnels, mainly research groups from European universities have been targeted. The approach taken has been that of maximum transparency of process and support of the researchers by the organizations responsible for the tunnels. And when possible, bringing research groups together to obtain full benefit of economies of scale in the research projects is encouraged.

ESWIRP responds to the so-called targeted approach of the Integrating Activities of the FP7 Capacities Work Programme:

* Networking activities, essentially focused around 4 topics:
1- Organisation of information campaigns, lectures and workshops to disseminate knowledge between the partners and future users,
2 - Opening of a website for the consultation of wind tunnel standards,
3 - Exchange of personnel between the Consortium partners to foster spreading of good practices and exchange technical know-how,
4 - Joint development of a reference wind tunnel parameter database.

* Trans-national access and/or testing services: after the call for proposals by the facility providers, groups of researchers had the opportunity to have a free access to wind tunnel services, including technical assistance to support the corresponding scientific research team.

* Joint research activities: By innovative modeling of wind tunnels to help designers to make better decisions before the implementation of novel hardware. This is the first time that mathematic modeling will create a standard for wind tunnels. The infrastructure improvements are targeting the capability to obtain unsteady test data at high accuracy in the ETW, to improve the capability to simulate aircraft behavior in ground proximity in the LLF and to establish a reliable closed loop Mach number control in the S1MA wind tunnel.

ESWIRP is a European support for strategic wind tunnels, key research infrastructures in the development process of current and future aircrafts. This is the first time that Europe offers such support. After this first step, the ESWIRP Consortium wishes for the long term support complementary to existing European national support to maintain these wind tunnels at the highest level.

Project Context and Objectives:
Ever since the start of aviation, in addition to flight testing, the need to have ground test facilities to understand flight physics phenomena and to investigate flight characteristics of future flying vehicles, has been recognized by flight physics researchers & aircraft designers. The most commonly used type of ground test facilities for aviation by researchers and development engineers are wind tunnels.

A wind tunnel is a tool for simulating flight physics phenomena encountered when an aircraft moves in air. Typically, it uses scaled models of the projected aircraft under scrutiny. The very purpose of a wind tunnel is to contribute to the development of new aircraft by providing characteristic data at low technical & economical risks as compared to real flight testing. Throughout all stages of aircraft development, from basic research of aerodynamic phenomena to applied research and optimisation of components and eventually validation of the end configuration, wind tunnel testing has always been an indispensable tool for researchers and designers. Although predictions of aircraft performance and characteristics through Computational Fluid Dynamics (CFD) calculations have been progressing tremendously, until now the development of an aircraft without wind tunnel testing has been unheard of because of risks and costs and will remain so for at least the next decades to come. Moreover, wind tunnel testing itself is an important contributing element to the ongoing development of sophisticated computational tools by validation and verification of numerical codes and data.

The demand for modern wind tunnel testing requires wind tunnels of excellent performance and quality and sophisticated aircraft models provided with up-to-date instruments and interference free flow measurement techniques, and above all, highly skilled personnel. Over the years, models, testing techniques and associated instrumentation have become more and more sophisticated in order to meet the ever increasing requirements of the aeronautic community in terms of accuracy and repeatability of results.

The activities planned under ESWIRP project aim to optimise the utilisation of specific research infrastructures and to improve their performance. Three strategic facilities for Europe are concerned by this project:

ONERA S1MA wind tunnel

The ONERA S1MA wind tunnel facility is a closed circuit atmospheric wind tunnel with a maximum speed near Mach 1, which provides unique capabilities for testing large models at cruising speed and above. The tunnel is located near Modane, France, and was erected after the Second World War. The tunnel has three exchangeable test sections with a diameter of 8m, which can be transformed into five different test section configurations. The benefit of having large models is essential for testing new concepts and having enough room within the models for housing various devices such as boundary layer control devices, remotely actuated mechanisms, drag reduction devices; aircraft control mechanisms both for handling qualities and efficiency improvement, laminar flow concepts, etc.

Civil transport aircraft developed over the last decades have been designed with a consistently increasing maximum cruise speed. The benefits retrieved from experimental work performed at S1MA are essential for future high-speed research. The S1MA represents a strategic facility which must be closely looked at in terms of capabilities to fulfill the increasing complex requirements of its users.

The design of the next generation of aircraft will be strongly influenced by environmental impacts considerations. Future aircraft configurations will have to compromise between fuel consumption reduction, low noise levels (cabin noise and noise nuisances to the surroundings) and performances. The trade-off between various options at high speed will ideally be determined at S1MA, which has already a long-term experience with motorized models, with high-pressure air supply necessary to study engine installation effects. In that respect the accumulated experience with testing propeller driven aircraft at S1MA will serve for testing rear mounted open rotors configurations for instance.

The large facility S1MA is need by aircraft manufacturers worldwide and by a number of researchers, which are taking benefit of its large size, and thus large models where very innovative ideas can be tested.

Amongst the leading criteria to use S1MA are:
* Its access cost,
* Its availability.

The ESWIRP project objectives for S1MA are to save 30 to 35% of the time necessary for an experiment by the way of providing improved quality data with no necessity to repeat data acquisition.

This will have a double impact:
* Better quality of the data provide because the aerodynamic parameters will be acquired in perfectly stable conditions,
* Possibility to test more new ideas for the researchers for a given budget.

Large Low speed Facility DNW-LLF

The DNW-LLF is a closed circuit low-speed wind tunnel with a maximum speed near Mach 0.4. The tunnel is located near Marknesse in the Netherlands. The tunnel has been in operation since 1980. The LLF has two interchangeable test sections of 9.5m x 9.5m and 6m x 8m (height x width), respectively, with which four test section configurations including one open jet can be realized. The LLF has an internal balance sting system for model support and is further equipped with a Moving Belt Ground Plane (MBGP) with a maximum speed of 40 m/s. The MBGP is provided with a boundary layer removal system that scoops and re-injects the floor boundary layer air into the tunnel. The demand for further improvements in aircraft fuel efficiency as well as for reduction in noise generation around airports makes an upgrade of facility a necessity. Since landing and take-off phases of the aircraft flight are the major factor affecting population, the availability of the best possible experimental simulation capabilities for this phase, where the quality of tunnel, air flow and ground simulation perform an integral part in providing data in the exploration of new possibilities, is essential for progress.

The proposed technical upgrade of the LLF in the framework of ESWIRP foresees major improvements on the existing Moving Belt Ground Plane. Higher relative speeds than achieved today will be obtained. Therefore, the quality of the simulation of the relative motion between an aircraft and the runway will be higher and consequently a considerable increase in data reliability can be reached.

ESWIRP opens the possibility to initiate joint research activities with the Consortium partners to study the impact of the planned upgrade on flow simulation, to prepare the detailed design and to familiarise the aeronautics research community with the improvements in potential obtainable design from improved ground simulation.

Cryogenic wind tunnel ETW

The ETW uniquely achieves real flight Mach and Reynolds numbers for transport aircraft at model scale. This unique capability is gained by cryogenic pressurized operation of the wind tunnel from low speed to a maximum speed of Mach 1.3 at real-flight Reynolds numbers. Using ETW, researchers are able to check scientific concepts for applicability at real-flight conditions effectively and efficiently at low risk. Therefore, ETW contributes to increase aeronautic innovation speed, and enables research to provide breakthrough technologies for ecological and economical optimization of future air transport. The ETW is in operation since 1994. Its test section dimensions are 2.0m x 2.4m (height x width). The test medium nitrogen gas can be pressurized up to 4.5 bar and cooled down to 110K.

Currently ETW has two exchangeable model support modules, so-called model carts for full model support that enable testing at Mach 0.8 up to 50 and 85 million in Reynolds number, matching flight conditions of aircraft as large as the Airbus A340 and A380, respectively. One of the model carts is adapted to allow as well half-model testing. By variation of pressure and temperature flow parameters like Mach number, Reynolds number and dynamic pressure can be varied independently. This enables a distinct separation of compressibility effects, Reynolds number and model deformation effects. Flow separation and its interaction with e.g. the model deformation or shock waves in the flow field in general is highly Reynolds number dependent. Unsteady interaction may occur which then initiates model vibrations. These physical phenomena often determine the flight envelope boundary of aircraft, and thus its understanding and control is subject to aeronautical research. Compared with CFD and conventional wind tunnels, the ETW wind tunnel circuit itself uniquely facilitates to take into account these phenomena at flight relevant conditions.

The proposed improvements will enable researchers to make better use of these capabilities due to the increased flexibility in tunnel access. The availability of a tool for unsteady force and moment investigations up to real flight conditions additionally opens a new unique area of wind tunnel testing.

Description of the infrastructure improvements of the participating facilities


The proposed upgrade of S1MA aims at improving the wind tunnel quality and productivity by implementation of a closed loop Mach number control system. The work has been to determine the best control strategy via a modeling of the flow behavior and then to design and implement a control mechanism.
To reach an acceptable situation the Mach number fluctuation should be limited to +/-0.001 which is an improvement by a factor 5 according to the existing situation. To achieve this goal it has been necessary to design and implement a flow control device at a station to be defined in the wind tunnel circuit.

DNW-LLF improvements

A main topic for which the tunnel has been designed is to test the take-off and landing configurations of aircraft. For this purpose, an important available simulation technique is the so-called ground simulation. The runway is simulated by a Moving Belt Ground plane (MBGP) with a current maximum belt speed of about 40 m/s. The MBGP is provided with a boundary layer removal system that scoops and re-injects the floor boundary layer air into the tunnel.

The proposed upgrade of DNW-LLF foresees in a major improvement of the MBGP. The adaptations will enable an improved simulation of the relative motion between a powered aircraft model and the simulated runway.

ETW Improvements

To fulfill advanced research and development requirements for unsteady force and moment measurements at transonic speeds in terms of data quality, availability, and costs efficiency, sophisticated state-of-the-art instrumentation is needed beside the global tunnel capability. Enhanced balance stiffness combined with a high-end signal conditioning and high-speed data acquisition system allowing to record high-frequency unsteady data. The proposed upgrade targets to design and establish such a unique test capability allowing unsteady force and moment measurements at flight Reynolds numbers.

As such type of measurement is usually performed using half-models vertically installed in the test-section while full model testing is done in horizontal model alignment; either side–wall slots or top/bottom slots have to be opened in the walls. In this way, the wind-tunnel wall boundary condition can be varied which impacts not only the steady mean flow about the model but also the unsteady flow field, e.g. by changing the reflection of pressure waves. To increase the flexibility of changing the wind-tunnel wall boundary condition while enhancing productivity by avoiding access to the tunnel for a manual modification a cost-saving remotely controlled mechanism for slot opening and closure will be developed and installed. The performance of the considered activities will consequently consist of the following steps:

* Design, manufacturing, calibration and commissioning of a new balance, update of the signal conditioning and data-acquisition system for recording high-frequency unsteady data;
* Design, manufacturing and installation of a remotely controlled mechanism for opening and closure of the slots in the floor and sidewalls of the test section for a fast change of the tunnel configuration.

Project Results:
Work package 1 - Management activities

The management activities comprise the formation of a joint Board of Directors which first task was to compile a Consortium Operation Manual to lay down the objectives of the Consortium and to settle the legal aspects and responsibilities of the partners.

The second task was to appoint Project Managers for the various Tasks defined in ESWIRP, to (re)allocate budgets and to monitor the justification of these budgets. At individual level, an important aspect of this task is to control the embedment of ESWIRP activities into the planned investments for the three facilities so that the objectives of the cooperation in terms of enhancement of the complementary facilities, closer interaction between operators and users (scientists and industry) and improved services in terms of quality, capabilities, productivity and costs are met.

The third task was to have regular meetings to monitor the progress of ESWIRP.

General assembly

The General Assembly is the decision-making body of the ESWIRP Consortium. The General Assembly consist of one representative of each Party (Director of DNW, Director of ETW and Director of the wind tunnel division, ONERA).

Number Dates Place

Reporting period#1
General assembly 1 10/11/2009 Modane -France
General assembly 2 16/06/2010 Brussels – Belgium
General assembly 3 16/02/2011 Brussels – Belgium

Reporting period#2
General assembly 4 25/08/2011 Brussels – Belgium
General assembly 5 22/03/2012 Brussels – Belgium

Reporting period#3
General assembly 6 05/09/2012 Brussels – Belgium
General assembly 7 04/09/2013 Brussels – Belgium
General assembly 8 05/02/2014 Brussels – Belgium
General assembly 9 15/05/2014 Brussels – Belgium

Technical meeting (technical detail meetings excluded – essentially done for WP4.2 activities, company by company)

Regular meetings to monitor the technical progresses of ESWIRP have been done. Usually during these meetings, WP 1, 2, 3 and 4 are discussed.

List of the meetings, representatives and WP concerned during each meeting:

# Dates Place Country ONERA DNW ETW WP1-WP2-WP3-WP4
Reporting period#1
1 02/02/2010 Brussels B x x x x x x
2 08/04/2010 Cologne G x x x x x x
3 01/06/2010 Chatillon F x x x x x x x
4 06/10/2010 Amsterdam NL x x x x x x x
5 25/01/2011 Brussels B x x x x x x x

Reporting period#2
6 26/05/2011 Brussels B x x x x x x x
7 20/09/2011 Brussels B x x x x x x x
8 22/02/2012 Amsterdam NL x x x x x x x

Reporting period#3
9 31/10/2012 Brussels B x x x x x x x
10 20/03/2013 Brussels B x x x x x x x
11 26/11/2013 Amsterdam NL x x x x x x x
12 27/02/2014 Cologne G x x x x x x x

Project planning and status

Some adjustments were made on Work packages 3 and 4, including:

WP3: Due to the wind tunnel occupancy and the complexity of TNA test preparation, the 4 TNA tests have been done in 2014, between February and September 2014.

WP4.1: Planned work on mathematical modelling of the 3 wind tunnels was also refined in the light of technical difficulties: including the fact that the development of module S1MA has taken longer than originally planned. The development of LLF and ETW wind tunnel modules was originally planned in parallel, they are now shifted to better take into account the specificities of each facility. We also change of programming language, the initial one not well adapted for LLF and ETW model (heavier than S1MA module)

WP4.2: Detailed schedules of the 3 wind tunnel improvements (WP 4.2) were also refined in the light of the progresses made during the preliminary design: the choice of technical solutions proposed and the first contacts with suppliers have enabled the Consortium to refine this development plan.

All these changes alter the overall project duration (initially 48 months) and the Consortium requested an amendment to modify the total duration up to 60 months. This change was accepted by the EC (letter ARES(2013)815205).

These changes didn’t modify the project objectives.

Work package 2

Task 2.1 Organisation of information campaigns, lectures and workshops

A series of three workshops have been organised in order to give maximum opportunity to research groups to propose and discuss potential projects with the three ESWIRP consortium members.

Via email, invitations for the workshops were sent out to experts at aeronautic university faculties and industry from the European Union and its Associated Members.

All of these three ESWIRP workshops took place near one of the participating wind tunnels and lasted for two days. The participation was free and included a reception/dinner at the evening before the start of the workshop, the accommodation in a hotel single room for two days, access to the conference room, a social event (presenting aspects of the hosting country) and a visit to one of the three wind tunnels.

The participant lists and proposal abstracts of these workshops have been reported in the deliverables D2.3 D2.6 and D3.3.

The ESWIRP website presented all relevant information for the workshops (i.e. topics, deadlines, workshop announcements etc.) including an expert system generated within task 3.5 enabling potential users of the facilities matching their needs with the Consortium’s capabilities.

At all workshops both the ESWIRP wind tunnel experts and the independent experts, who later on formed the “ESWIRP review team” (task 3.3) were present to advice and support the project teams.

Shortly after the accomplishment of each workshop its complete documentation was published on the TNA webpage of the ESWIRP website

The Consortium has organised 3 workshops with a progressive approach.

First workshop – Cologne – ETW facility – November 2010
To collect a first panel of ideas, and confront various test objectives
30 participants including the ESWIRP team attended the first workshop. 15 project ideas were presented.

Second workshop – Modane/Bardonecchia – S1MA facility – March 2011
To consolidate the ideas for the projects for forming potential consortia
25 participants including the ESWIRP team took part in this second workshop. 11 projects were presented.

Third workshop – Zwolle/Marknesse – LLF facility - October 2011
To prepare answers to the call for proposal and to implement consolidation of the interested partners
32 participants visited the third ESWIRP workshop including the ESWIRP team.

During these 3 workshops tours to each of the participating wind tunnel were organised, all participants had the opportunity for discussing measurement techniques and tunnel capabilities with local experts. This clearly contributed to a better understanding.

It was the opportunity for the participants to gather sufficient information to be able to answer the TNA call for proposal. Technical information on wind tunnel capabilities, through technical presentations and visits, were given during these 3 meetings and mail exchanges between the workshops. During the meetings, it was also possible for them to ask the Consortium about administrative rules for this TNA.

During the 3 workshops, the Consortium reached more than 80 persons, coming from 12 countries.

After the third Workshop, the Consortium has issued the Call for Test Proposals.

Task 2.2 Opening of a website

The ESWIRP website has been designed to be efficient and simple to use. It a good tool for providing information to the aerodynamics community concerning the TNA test performance opportunity and a very useful and easy to use data base for the members.
The ESWIRP web-site is frequently used by its members to retrieve and share information regarding the ESWIRP project, the workshops, presentations and other informational documents.

The website gives also the opportunity for any potential candidate to use tools that have been developed within this project to better investigate their need and the potential answer of the different wind tunnels.

This website is till on line and will be maintain on line for the next 5 years.

A member section includes all the project items dealing with organisation, project management, report writing and validation tool. Only members from the consortium can be logged to this section of the website.

A detailed description of the ESWIRP website is written in the deliverable D2.5

Task 2.3: Exchange of personnel between the Consortium partners

The three ESWIRP partners planned the personnel exchange to foster the spreading of good practices and exchange technical know-how, e.g. the development of common standards for data acquisition and processing and the implementation of novel testing methods and techniques.

The staff exchange was typically mapped out as a medium term secondment of project engineers and key personnel, i.e. scientists, project managers, engineers, technicians and non-technical personnel.

DNW, ETW and ONERA agreed not to define a fixed work program for every personnel exchange stay, but to offer the welcomed person the opportunity to take part in the on-going activities of the hosting team.

Some of the sojourns were scheduled to take place during the experimental testing of the selected four ESWIRP TNA projects in 2014.
ONERA, DNW and ETW named 5 exchange participants each - most of them young engineers, who as test engineers, designers and instrumentation technicians covered the whole range of technical wind tunnel personnel.

The exchanges started in 2011 up to September 2014. The duration of these exchanges are 2 weeks minimum up to 2 months, except for exchanges during TNA tests (limited in this case to the TNA test duration, usually between 1 to 2 weeks).

All employees, who participated in the exchange, wrote reports afterwards, which are included in the deliverable D2.8. They were asked to cover not only technical topics, but also to give their opinion on the organisation, quality and personal effects of their stay abroad.

All the participants, who took part in the wind tunnel attendances, welcomed the opportunity for a professional exchange with the wind tunnel experts of the hosting facility. They agreed that meeting the hosting wind tunnel experts on site improved the understanding of the facility capacities and the different technical approach of projects.

Despite the differences in the excellences and proceedings of the three wind tunnels, the common ground stayed visible, which was clearly worded more than once in the reports.

The occupation during their stay diversified: some worked in their field of expertise and enjoyed the opportunity to meet other experts. Others were integrated in the development of new systems, which might prove interesting for their own wind tunnel sometime in the future. By taking part in the integration of these systems, they could also broaden their management abilities. Some participants got acquainted with new software or techniques, which are not used at their home wind tunnel. Others had the opportunity not only to stay and work at the partner wind tunnel, but to visit also other facilities of the welcoming organisation.

Regardless of their kind of occupation during their stay, all employees praised the good cooperation with their foreign colleagues and integration in the welcoming team.

Task 2.4 : Joint development of a reference wind tunnel parameter database necessary for wind tunnel simulation and modelling

The task has been completed on April 1st 2010, as scheduled. The associated deliverable is D2.2 Wind Tunnel Database.

This document is a reference wind tunnel parameter database giving the characteristics of each ESWIRP consortium wind tunnel (i.e DNW-LLF, ETW and ONERA-S1) according to the following items:
- main characteristics
- overview
- test sections size
- model handling
- instrumentation
- typical tests

It includes only information classified “public access” and can be downloaded on ESWIRP website ( / facilities / DNW-LLF (or ETW or ONERA-S1) / datasheet).

A detailed description of the ESWIRP reference wind tunnel parameter database is written in the deliverable D2.2.

Work package 3

Task 3.1 Call for proposals

The methodology for the TNA selection was:
- 3 Workshops for advertising on ESWIRP opportunity – Nov 2010 to Oct 2011
- Call for proposal – October 2011 to January 2012
- Evaluation and selection – January and February 2012
- Test preparation and test - March 2012 to September 2014

After the third Workshop, the Consortium has issued the Call for Test Proposals. The call form specified criteria like period of performance, scope of budget and access units, and gives guidelines as to preferences such as links to the proposed Joint Research Activities, transparency, trans-national cooperation, interrelated use of all three facilities and publication of results.

The call was also published on the websites of ESWIRP, the EU as well as on the website of the consortium partners and the national research institutes.

6 Proposals have been received (see task 3.3). The detailed process and the proposals are in the deliverable D3.1.

Task 3.2 Internet Networking Service

The ESWIRP forum page (Internet Networking Service) is a feature which can be used by members to share information and experiences, and to support discussions amongst the registered members. The members have to register first before they can participate and post messages on the ESWIRP forum page.

The Internet Networking Service is realised via the website. Members of the ESWIRP consortium can publish and update information about several topics, e.g. wind tunnel features or workshop activities.

This forum was not really used by the participants themselves. They used direct e mail exchanges with the various technical point of contact of each wind tunnel.

A detailed description of this tool is written in the deliverable D3.2.

Task 3.3: Evaluation and final Selection

The following list of 6 proposals was received:

2 projects for ETW
> Time-Resolved Wake Measurements of Separated Wing Flow & Wall Interference Investigations (JL Godard – ONERA - France) – selected
> Reynolds number influence on delta wing vortex flows (Dr. Simon Prince - City University London – UK) – not selected

3 projects for LLF
> Experimental Investigation of the acoustic Field of a Realistic Wing Section with Slat and Flaps in High Lift Configuration (Dr. Ronald Abstiens - Aerodynamic Institute RWTH Aachen University – Germany) - selected
> New-Mexico (Helge Aagaard Madsen - Technical University of Denmark) – selected
> Optimization of Algorithms for Simulation Procedures (Vlamos Panayiotis - Dept. of Informatics, Ionian University, Greece) – LLF – not selected

1 project for S1MA
> Investigation of the small scale statistics of turbulence in the Modane S1MA wind-tunnel (Peinke Joachim - University of Oldenburg – Germany) – S1MA - selected

During the TNA selection meeting of February 12, 2012 in Amsterdam, with participation of both the ESWIRP representatives and (external) expert team, the proposals have been reviewed based on the criteria defined and published during the first reporting period.

Criterion for Selection Weight (%)
Technical intrinsic value and interest
- Innovative potential and scientific value for the community
- Potential added value to the understanding of flow physics 50

Quality (and cohesion) of proposing team(s)
- Number of users
- Number of nationalities
- European representativity 15

Importance and relevance to the upgrades to the ESWIRP programme 15

Adequacy with facility capabilities 20


To evaluate the submitted proposals the Consortium appointed a review team consisting of three experts from the academic, research and industry community covering aeronautics and wind tunnel techniques:
* For industrial: Jean-Jacques Degeilh - Airbus – Aerodynamic senior expert
* For academic: Piotr Doerffer - Polish Academy of Sciences - Head of department: Transonic Flows and Numerical Methods - Institute of Fluid Flow Machinery
* For research: Horst Körner - retired from the DLR (Professor)

The outcome (projects for which testing time will be made available / funded in the framework of the ESWIRP project) of the assessment is as follows:

* DNW LLF: Experimental Investigation of the acoustic Field & New Mexico (2 projects).
* ETW: Time resolved wake measurements.
* ONERA - S1 Modane: Investigation of the small scale statistics.

The evaluation process and the final selection are written in the deliverable D3.3.

Several months after this process, the team for "Experimental Investigation of the acoustic Field" cancelled his participation. The ESWIRP Consortium selected a backup team for each facilities. In this case, the back-up was selected: it is the APIAN-INF TNA test (see detailed description below).

Task 3.4: Test preparation, performance and analysis

3.4.1 Project for S1MA wind tunnel

Title of Proposal: Investigation of the small scale statistics of turbulence in the Modane S1MA wind-tunnel

The proposal aims at a detailed experimental investigation of the statistical properties of turbulent flows at large Reynolds numbers. Though computational fluid dynamics has known impressive progress in the last decades, so have the requirements in terms of modelling accuracy.
Effects of turbulence are among the most difficult to simulate and predict and they still require fundamental investigations and experiments to be better apprehended. As recently discussed during a dedicated session of the French Academy of Science dedicated to advances in fluid mechanics research, one crucial and well identified challenge concerns the comprehension of energy cascade and dissipative mechanisms of turbulence which have important consequences in practical situations as aerodynamics, combustion, pollutant dispersion, etc.

The primary goal is to take advantage of the unequalled large scale dimensions of the ONERA S1MA wind tunnel facility in Modane, to make available to the broad scientific community experimental turbulence data with unprecedented resolution (both spatial and temporal) and accuracy (in terms of statistical convergence quality).

The experiment focuses the study on grid generated turbulence. A large scale grid (10m in diameter, with a mesh size of 0.625m) was used as turbulence generator, as it is known to produce canonical homogeneous and isotropic turbulence. This is an academic flow known to produce almost perfectly homogeneous and isotropic turbulence (HIT) which remains a unique playground to investigate fundamental properties of turbulent flows. The characteristics of turbulence were measured downstream by different instruments mounted on a mobile cart in the test section from X ~ 0 to X ~ 15 m. Measurements were performed during some fifteen hours, at six X positions of the mobile cart and for velocities in the test section ranging from 20 m/s to 45 m/s.

The objective is to produce a database as complete as possible, in terms of characterization of the turbulence, which will help the research community to get a better insight in longstanding mysteries which still limit the capacity to understand and accurately model turbulent flows.

These include, among others, turbulence intermittency, mixing and dispersion properties, and the link between Eulerian and Lagrangian descriptions of turbulence. For this purpose, several measurements have been implemented:
- Hot-wire anemometry
- Laser cantilever anemometry
- Lagrangian particle tracking
- Vortical acoustic scattering
- Micro-pitot tubes

To achieve this ambitious project, a large international consortium of 22 scientists with complementary expertise allowing to span a large spectrum in terms of measurement techniques, high resolution instrumentation and signal processing has been selected.
The laboratories involved are given below:
- Laboratory LEGI - Laboratoire des Ecoulements Géophysiques et Industriels (Grenoble)
- Institut de recherche en sciences et technologies pour l'environnement et l'agriculture - IRSTEA (Rennes)
- Neel Institute(Grenoble)
- LEGI (Grenoble)
- ENS-Lyon
- Laboratory PPRIME (Poitiers)
- Laboratory COmplexe de Recherche Interprofessionnel en Aérothermochimie - CORIA (Rouen)
- Academy of Science of the Czech republic
- University of Oldenburg
- Max Planck Institute (Gottingen)
- Royal Institute of Technology - KTH (Stockholm)

From a scientific point of view, although the acquired data just started to be processed, the ESWIRP TNA team says the campaign has been successful. The first analysis shows indeed that the smallest scales of the flow were well resolved what the main challenge was. The different diagnoses are consistent within each other, with different levels and ranges of noise. The combination of the data recorded with the several instrument should improve the overall quality of the measurements. The coming months will be devoted to a deep quality assessment of the acquired data, in order to quantify precisely the actual resolution of the several performed measurements and to build a complete database, ought to become open to the scientific community within a period 2 years starting from the completion of the database.


Title of Proposal: Experimental Investigation of the acoustic Field of a Realistic Wing Section with Slat and Flaps in High Lift Configuration

To gain a better understanding of the mechanisms that result in noise production, numerical studies of a wing-slat configuration will be performed. Noise, however, is not only produced by the high-lift devices of the wing, but also by any kind of additions to the wing such as tracks to move the flaps and the slats. Since the noise is strongly influenced by the geometry of the body exposed to the flow modelling the configuration in detail results in a very complex geometry the flow field of which is difficult to compute. To validate computations high Reynolds-number measurements are necessary. Due to the limited size of the test section area and the limited free stream velocity of the wind tunnel at the AIA and for example the AWB in Braunschweig, measurements in a wind tunnel of greater size and higher velocity are a great step forward.
Due to this fact it would be necessary to use a large wind-tunnel like the DNW LLF in the Netherlands with the capability for acoustic measurements. Additional PIV measurements at the DNW-LLF will be conducted by the Institute of Aerodynamics Aachen (AIA). The flow data from PIV measurements and the acoustic data could be used to validate numerical simulations done by all partners of the consortium.

After the selection procedure this project, under the leadership of a researcher from the RWTH Aachen, unfortunately folded due to the departure of the leading investigator. It was scheduled to take place in the spring of 2014.

In an effort to replace the proposed project within the spirit of the TNA, a number of discussions has been held with two of the leading Universities in Aeronautical Engineering – The TU Braunschweig in Germany and the TU Delft in the NL. As a result of the discussions a proposal is emerging on the topic of Aero-acoustic and aerodynamic performance of a single open rotor (propeller) in non-uniform inflow conditions.
Consideration has been given to the remaining time frame in the ESWIRP project, the scientific interest of potential participants and the capability of DNW to provide test hardware and essential instrumentation.

Title of Proposal: Investigation of the APIAN propeller in non-uniform flow (APIAN-INF) in the German-Dutch Wind-tunnel LLF

Because of their high propulsive efficiency compared to turbofans, propellers are generally considered as an interesting option for the propulsion system of future generations of passenger transport aircraft. The large rotor diameter(s) combined with interior noise constraints have driven possible propeller aircraft lay-outs towards a rear-fuselage mounted pusher propeller configuration. In this setup, the propeller blades operate in the wake of the upstream pylon, leading to non-uniform inflow on the propeller disk, hence unsteady blade loads and associated increased propeller noise emissions. Literature has shown that pylon blowing can mitigate this noise penalty due to the pylon wake interaction by re-filling the pylon wake deficit. The proposal aims at experimental and numerical investigations of the aerodynamic and aero-acoustic response of an isolated propeller in a non-uniform flow field caused by an upstream installed pylon model. For this purpose the existing and well investigated propeller model from the European APIAN project is reused.

The primary goal is to take advantage of the large scale dimensions of the German-Dutch Large Low speed Facility (DNW-LLF) wind tunnel facility in the Netherlands, to make experimental aero-acoustic and aerodynamic data with high quality available to the scientific community. Especially the large open jet test section with the acoustic absorbing treatment on the walls is suitable for acoustic far-field measurement.

The first objective of the experiment focuses the study on aero-acoustic measurements of far-field data with different measurement techniques. For the measurement of unbiased narrow band data a large number of inflow microphones could be traversed over a wide range of 10 m in stream wise direction to the propeller model. With another large set of fixed microphones outside of the flow the directivity of the propeller noise could be measured over a wide directivity range at a distance of up to 20 m from the source. By means of 3 phased microphone arrays the distribution of the noise sources is localized from different observer positions outside of the open jet flow.

Acoustic measurements with the propeller model were performed during some twenty four hours, at several positions upstream and downstream of the propeller model and for a range of velocities between 40 m/s and 70 m/s and a range for the angle of attack between +-6 deg.

The second objective of the experiment focuses the study on aerodynamic flow around the propeller by means of three components participle image telemetry (PIV) measurements. PIV-measurements were performed during some twenty four hours, at several positions upstream and downstream of the propeller model and for a constant velocity of 60 m/s and a range for the angle of attack between +/-6 deg.

For both the acoustic and aerodynamic measurements three main configurations were investigated:
1. Isolated propeller
2. Propeller with pylon installed upstream of the propeller
a. With several pylon blowing rates
3. Propeller without pylon and installed swirl recovery vanes (SRV)

The third objective of the experiment focuses on the calibration of the inflow and out-of-flow measurement systems by means of two artificial acoustic calibration noise sources.
• Plasma noise source based on spark technology (provided and operated by ONERA)
• Calibration noise source based on loudspeaker technology (provided and operated by Airbus)

After the removal of the propeller model these sources are placed at the former location of the propeller. Acoustic calibration measurements were performed during some twenty four hours, at several positions of the sources and different signal types. The sources are operated for a range of velocities between 40 m/s and 80 m/s.

For this purpose, several measurements have been implemented:
- Acoustic measurements:
o Inflow far-field microphone technique
o Out-of-flow microphone technique
o Phased microphone array techniques
o Plasma spark calibration noise source (by ONERA)
o Loudspeaker calibration noise source (by Airbus)
- Rotor performance measurements
o Rotating shaft balance (RSB) technique
o Torque meter
o blade pressure sensors (27 Kulites)
o RPM signals
- Flow measurements
o Standard wind tunnel parameter
o Model position
o 3 components particle image velocimetry (PIV) technique

To achieve this project, an international consortium of about 20 scientists with complementary expertise allowing to span a large spectrum in terms of measurement techniques, high resolution instrumentation and signal processing has been selected.

The test has been performed in DNW-LLF from 15 September 2014 to 30 September 2014.

The laboratories and people involved are given below:
Technical University of Delft (The Netherlands): Leo Veldhuis, Georg Eitelberg, Tomas Sinnige, Kirk Scheper, Anwar Malgoezar, Kyle Lynch, Daniele Ragni, Mirjam Snellen
Research institute INCAS (Romania): Corneliu Stoica
Research institute TsAGI (Russia): Victor Kopiev, Mikhail Zaytsev, Ivan Belyaev, Ivan Pankratov, Nikolay Butura, Viacheslav Verkhovskiy
University of Cambridge (United Kingdom): William Graham
Technical University of Braunschweig (Germany): Alexander Skorpel, R. Radespiel, Jens Friedrichs
Research institute DLR Braunschweig (Germany): Carlo Marquez, Oscar Sitges, Arne Stuermer
Research institute ONERA (France): Renaud Davy, Fabien Mery
Airbus industries (France): Emmanuel Julliard, Jean-Marc Prosper


Although the acquired data could only be online processed and preliminary reviewed, the ESWIRP TNA team say the campaign has been successful. The amount of acquired data is much larger as hoped for to be realized. For a research test the productivity of the PIV and acoustic measurements was surprisingly high and is comparable to an industrial test program. The first analysis of the acoustic data and the PIV data show indeed that the pylon wake interaction noise with the propeller can successfully be reduced by means of controlled pylon blowing. Furthermore it could be demonstrated that by means of a static rotor installation, like the applied swirl recovery vane system some characteristics of a counter rotating open rotor (CROR) propeller system could be investigated by a more experimental simplified test setup.

The different acoustic measurement techniques, like the inflow and out-of-flow far-field measurements and the phase microphone array measurements are consistent within each other, with different approaches and observer positions. The combination of the data recorded with the several instrument should improve the overall quality of the measurements. The coming months will be devoted to a deep quality assessment of the acquired data, in order to quantify precisely the actual resolution of the several performed measurements and to build a complete database, ought to become open to the scientific community within a period 2 years starting from the completion of the database.

Title of Proposal: New Mexico

The wind energy community is still in demand of high quality data on wind turbines to validate CFD simulations and design codes. This holds true for performance data, flow field information and certification load cases. In 2006 such a data set was gathered during a wind tunnel test campaign at DNW-LLF financed by the EU and designated Mexico. This data-set has been used extensively worldwide and is part of Energy Technology Network (IEA) Wind Task 29 Mexnext ( During the last decade the technology involved in wind turbine design and manufacturing has evolved strongly giving rise to a need for more detailed wind turbine data. Amongst others, noise has become an important aspect of wind turbine design. Since it is hard to gather these data on a full scale rotor in controlled conditions a controlled test environment is needed.

The primary goal is to take advantage of the available of an existing wind turbine model (Mexico) in combination with the large scale dimensions of the German-Dutch Large Low speed Facility (DNW-LLF) wind tunnel facility in the Netherlands, to gather experimental aero-acoustic and aerodynamic data with high quality and make them available to the scientific community. Especially the large open jet test section with the acoustic absorbing treatment on the walls is suitable for acoustic far-field measurement. Moreover the 9.5 x 9.5 open jet with Seifert Flügel offers the possibility to test a large scale wind turbine model in a controlled environment.

The test combined several objectives into one experiment in which several test and measurement techniques were combined. Since the wind tunnel configuration and set-up for this experiment (9.5 x 9.5 m open jet with Seifert Flügel) is unique and is solely in use for the Mexico wind turbine rotor, special care had to be taken to verify the quality of the wind tunnel flow.

For the various purposes of the test, several measurements techniques have been implemented:
- Flow measurements
o Standard wind tunnel parameters
o Pitot-static tube at wind tunnel centre-line
o Pitot-static tube at PIV-plane
o Model position
- Yaw of attack variations
o 3 components particle image velocimetry (PIV) technique.
o Static pressure at the collector
- Acoustic measurements:
o Out-of-flow microphone technique
o Phased microphone array techniques
- DNW array technique installed upstream of the wind turbine rotor
- Rotor performance measurements
o Wind turbine loads (external balance)
o Torque (power adsorbed by the controller - brake)
o Blade pressure sensors (Kulites)
o RPM signals
o Blade angles
o Blade strain gauges (individual blade loads)

To achieve these measurements an international team was formed.

The test has been performed in DNW-LLF from 20 June 2014 to 4 July 2014.

The laboratories and people involved are given below:
-Technical University of Denmark (DTU): Helge Aagard Madson, Niels Sørensen
-Energy research Centre of the Netherlands (ECN): Koen Boorsma, Gerard Schepers, Erwin Werkhoven
-Technical University of Delft (The Netherlands): Giel Hermans, Nando Timmer, Gerard van Bussel
-Technology Institute of Israel (Technion): Aviv Rosen, Arie Wolf, Doron Ben-Shmuel


The data analysis done until now indicates that the data is of high quality. All priority 1 test conditions have been measured as well as some priority 2 and 3 test conditions. Independent verification of the wind tunnel calibration and wind turbine set-up blockage effect showed good agreement between pressure and PIV data, establishing confidence in the wind tunnel calibration and simulation. Detailed flow fields have been recorded for future validation of CFD codes. Extensive acoustic data has been gathered for validation of design codes. The overall comprehensive data set is made available to the involved parties and will become available to the scientific community within the coming years.


The TNA test in the European Transonic Windtunnel ETW performed world-wide unique unsteady measurements of the wake flow field by time-resolved PIV (Particle Image Velocimetry) and unsteady deformation measurements for a cruise aircraft configuration at real-flight Reynolds and Mach numbers. These conditions can be achieved only by the combination of cryogenic temperatures (115K) and a tunnel pressure of approx. 300kPa in ETW. The study is needed to further the understanding of the occurring phenomena and the validation of CFD codes (Computational Fluid Dynamics).
The results of this scientific test are expected to give valuable insights in the development and downstream propagation of wing wake flows as well as the resulting effects on the empennage. These scenarios are of high interest to the international aircraft industry due to the potentially heavy unsteadiness of separated wing flow at the borders of the flight regime that may cause an excitation of the empennage.
The main objectives of this test campaign were as follows:
• Time-resolved PIV investigations of separated wing flow (operated by DLR).
• Wall Interference Investigations.
• Acquisition of validation data for numerical calculations.
• Investigations of unsteady HTP inflow at stall conditions (low and high speed).
• Buffet investigations at limits of flight envelope.
• Acquisition of data to be compared with existing CRM wind tunnel data.

More than 40 international aerodynamic specialists from various European institutions, US NASA, Russian TsAGI and Japanese JAXA met at ETW to attend the experimental test entry of the project "Time-resolved Wake measurement of Separated Wing Flow & Wall Interference Investigations".



Tests were performed with the NASA CRM full model, which was provided by NASA. This model was previously tested in the NASA NTF and AMES 11ft. wind tunnels several times and was also used in the NASA Drag Prediction Workshop. For this model a comprehensive data base is available in the public domain and enables the comparison of the ETW wind tunnel data to both numerical calculations obtained by CFD and other wind tunnel data bases. For the integration of the NASA model ETW designed and manufactured interface components to enable the mounting of the ETW Balance B004 and the AVS system in the sting line.

PIV Measurement System

One of the main objectives for this test was the visualisation of the vortices behind the wing by means of PIV. Due to the nature of this high speed separated flow a new time resolved PIV system was implemented in ETW and operated by DLR Göttingen.

For the current tests the existing cryoPIV system especially developed for applications at ETW in the past, was equipped with high-speed PIV components providing a temporal resolution of 2 kHz in the velocity data. The cryoPIV system consists of optical modules for a placement of cameras and light-sheet optics behind test section windows. Because of the cryogenic environment, these modules are placed in heated housings and are remotely controllable. The PIV laser is placed outside the wind tunnel and the laser beam is directed via laser mirrors through a small window in the plenum pressure shell to an optical module (containing the light-sheet-forming optics) installed in the test section wall.

To compensate for laser light beam deflections due to optical and mechanical effects when changing the tunnel temperature or pressure, a beam monitor is employed in this module which permits automatic repositioning and redirection of the laser beam using motorised mirrors. To produce flow tracers tiny ice crystals are used that are generated by injecting a small amount of water aerosol into the saturated cryogenic environment of the wind tunnel.

The light sheet is aligned parallel to the direction of the free stream velocity for a good dynamic range of the measured velocities. Different measurement positions are achieved by pivoting the light-sheet using motorised laser mirrors inside the light-sheet module. Also the field-of-view of the camera can be adjusted accordingly using a mirror setup and an especially designed lens adapter inside the camera module.

Further Measurement Equipment
Among the huge number of measurement techniques applied following peculiarities should be pointed out:
• The model was well equipped with 253 pressure tappings on the wings, which were recorded with five scanners installed in the model nose.
• Markers for the Stereo Pattern Tracking (SPT) System were attached on both the port lower wing and HTP surface. Based on wind-off reference measurements over the entire incidence range of the model, the system can identify the displacement between loaded and unloaded conditions, which then can be finally transformed into wing twist and bending information. For the illumination of the SPT markers LED lights were installed at several positions in the test section.
• The model was mounted on the ETW B004 six-component strain gauge balance.
• The model support system attached to the MC2 sting boss flange comprised the conical stub sting incorporating the AVS anti-vibration unit. The new bent strut sting component was attached to the ETW stub sting using a flange joint. The NASA Upper Swept Strut sting component was attached to the ETW bent strut using a conical joint with setting screws.
• The model incidence and sideslip were derived from on-board instrumentation combined with the Sector Roll System (SRS) instrumentation. The on-board instrumentation measured the angle between the model reference axis and the horizontal plane irrespective of the model roll, pitch (and yaw) angles.
• The model attitude was measured directly by an on-board inclinometer attached to the inclinometer bracket, which, in turn, was mounted to the balance adapter.
• A three-axis Entran accelerometer, installed within the model inclinometer heated package, was attached to the model adapter in the front fuselage to monitor model dynamics. Two additional accelerometers were installed in the fuselage nose and in the rear fuselage to provide additional information on the model dynamics characteristics.


Tests were performed at Mach numbers in the range of 0.25 to 0.87 and at Reynolds numbers between 2.9 and 30.0 million. The tunnel temperature varied between 300 and 115 K and pressure levels from 111 to 445 kPa were achieved.
Two configurations of the NASA CRM full model were tested. Testing of the first configuration at ambient conditions up to a Reynolds number of 5.0 million included transition fixing on model nose, wing and HTP surfaces. The second configuration was dedicated to transition free testing at high Reynolds numbers. Overall model forces and moments were measured together with 253 wing pressures. Performance data were acquired using the continuous traverse technique with sufficient repeat polars performed to confirm data quality and repeatability.
The TR-PIV measurements were performed at fixed model incidences operated by DLR Göttingen. The SPT model deformation polars were performed in the pitch/ pause mode of operation at selected model incidences.


The test results have been made available to the involved scientists and the evaluation and the comparison between CFD and other experimental results is still going on. As a brief summary it can be stated:

Pressure measurement
Repeat polars at Mach 0.85 were built into the test programme to establish the levels of repeatability and to provide information on possible model contamination effects due to the PIV seeding. The performance polars derived for this assessment are showing excellent short term repeatability for a Reynolds number of 30.0 million, tested at 115 K.

Same applies for levels for lift, drag and pitching moment. It shall be noted that the repeatability levels provided were acquired for the same model configuration, but tested as separate blocks with an overnight break and the reconditioning/ cooldown of tunnel and model in between.
Even if extensive PIV testing with a relatively high amount of seeding injection was performed it can be seen that lift, drag, and pitching moment characteristics are shown to have good repeatability within the accuracy levels defined by ETW
The chordwise wing pressure distribution along the span for a Mach number of 0.85 and a lift coefficient of 0.5 for the three Reynolds numbers 5.0 19.8 and 30.0 million Reynolds are in agreement with measurements ant NTF and a good base for CFD validation.

Model Dynamic Characteristics
The AVS III sting based system was incorporated in the sting line and the system was activated at all requested test conditions. Separate AVS tunings were derived and applied for both each model configurations and all test temperatures.
For the high incidences achieved during the continuous traverses it can be seen that relatively high levels of dynamics were encountered in the vertical model orientation (Z-axis), which in turn forced the abortion of the pitch sweep, whereby the model movement system returned the model to a pre-defined safe position.

Model Deformation Measurements
At selected test conditions model deformation data were acquired and processed to produce wing deformation data in terms of bending and twist (relative to 50 % chord).
Two SPT systems were operated simultaneously for the assessment of the overall wing deformation and the HTP deformation.

PIV Measurements
The PIV results achieved both at sub- and transonic stall conditions show turbulent flow structures in the wake of the wing providing an insight to turbulent energies and frequency spectra. For the first time PIV measurements have been successfully carried out at such high Ma- (up to 0.85) and Re-numbers (Re up to 30 Mio.).

The assessment and analysis of the Time-Resolved PIV data was performed by DLR Göttingen. The figure above provides a preliminary result for a Mach number of 0.85 which was presented at the ESWIRP workshop at ETW on 24 & 25 September 2014. The plot provides the instantaneous velocity field for a spanwise position of 56.5 %, a Reynolds number of 30.0 million, a cryogenic temperature of 116 K and a model incidence of 4.5 deg. In addition a second image obtained 500µs later is included to illustrate the changes of the velocity fields. A more comprehensive analysis of the TR-PIV data will be provided by DLR.

Task 3.5: Service activity - the interactive Expert System:

One of the main objectives of ESWIRP is the provision of trans-national access to the three engaged infrastructures: the wind tunnels S1MA in France, LLF in The Netherlands and ETW in Germany. Targeting by its nature at European researchers at relevant organisations and Universities, those people may not have the detailed knowledge about the facilities and their capabilities with respect to the realisation of proposed innovative ideas. Although, a comprehensive database has been established for each tunnel in task 2.4 it was considered worth to provide an additional tool allowing a pre-selection of the facility best matching the requests on performance and test capabilities as well as available measurement techniques. This led to the creation of the so called “Expert Tool” accessible to public on the website of ESWIRP under trans-national access.

The core of the tool is the database available in the project holding technical details, specifications and information about capabilities, operational limits and available measurement techniques. The tool itself is a web based programme realised in PHP in combination with MySQL for execution on a web server. The internal logical structure is based on “Nassi Schneiderman Diagrams”. A user may distinguish between an interest to test an aerodynamic model, to perform an aerodynamic study or to evaluate a new measurement technique. Further input on the model and its requested test conditions or, alternatively, scaling down from a real aircraft to match tunnel dimensions have to be entered. In the next input level information has to be provided on the type of testing (e.g. ground testing) and the considered choice of instrumentation.

If the subject of interest refers to an evaluation of a measurement technique, details have to be entered on the pressure and temperature range to be covered. Finally, a result page informs about the facility best matching the requests; but additionally data are provided, why or where it does not fit the capabilities of the other facilities. Parts of the sample output sheets are given in the 2 figures below. These sheets may be printed or saved for future use.

A detailed description of this tool is written in the deliverable D3.5.

Work package 4

Task 4.1 : Development of a generic numerical simulation model

The objective behind this approach is that before such far going decisions as to the implementation of novel hardware are being made, the tunnel operator should have a model at his disposal that simulates the interaction between control inputs and physical phenomena in the tunnels and that gives maximum confidence that the new features will work satisfactorily and thus justify the scope of investments. In principle, the proposed model should be universal for all three facilities to demonstrate the complementarities but takes account of the peculiar properties of each. To achieve this it is foreseen that in addition to a generic numerical model three extra modules are required to cope with these diversities.

The mathematical model will consider the existing tunnel geometry, and will aim at a realistic representation of the physical phenomena in the flow. The tunnel will be divided in a number of single volumes defined by an entry station and an exit station (axially). The basic thermodynamic behaviour such as: temperature exchanges, pressure loss, mass flow equation (injection or blow-off), will be considered at different stations along the circuit. The main drive of the facility (compressor or fan) will also be simulated, and the tunnel characteristics which are essential to the flow behaviour (plenum volume, nozzle, fixed contraction, diffuser, second throat if any, test section, etc.). In the initial phase of the model development, the methodology will be similar for all 3 facilities, although each specific feature shall have to be addressed in a second phase.

The task for the generic modelling has been completed on April 1st 2010, as scheduled. The associated deliverable is D4.1 Numerical WT Module.

This document describes the numerical simulation model of a virtual wind tunnel of same size as ONERA-S1, but with some simplifications: the air exchanges with the atmosphere are not simulated and flow temperature is controlled by the mean of an internal heat exchanger.
The circuit is divided into 40 individual volumes in which the time dependant equations are resolved.

The individual circuit volumes are characterised by their geometry (mean diameter, length and wetted area), their pressure loss coefficient and the thermal exchange coefficient through the walls.

The numerical model calculates the outputs values and the wall temperature by applying the physical laws of aerodynamics and heat exchanges to the inputs at each time step.

The main control parameters of the generic model are the fan rotational speed (RPM) and the water mass flow through the heat exchanger.
A graphical Human Machine Interface (HMI) has been developed to:
- adapt the internal parameters of the model
- define time variations of control parameters to perform simulations (rpm, water mass flow, …)
- define variables to be outputted and stored in files for future processing
- provide in line processing of main data

The generic numerical model has been delivered to the ESWIRP consortium member in March 2010 and was used as a base to be adapted to the specificities of each wind tunnel.

Task 4.1.1 : Numerical simulation model – ONERA-S1MA Module

The ONERA-S1MA Module development started in July 2010 up to March 2011.

It has been built by adapting the generic module to S1MA characteristics mainly with:
- the suppression of the cooler and replacement by one inlet at the head of the second diffuser and one outlet and the contraction entrance;
- the addition of one inlet upstream the fan to simulate the wake blowing device of the first fan supports;
- the addition of one inlet with adjustable mass flow upstream corner n°1 to simulate one device studied within WP4.2 –S1MA to control the Mach Number into the test section;
- the addition of an adjustable pressure loss section combined to the test section, to simulate the effects of angle of attack changes;
- the addition of an adjustable pressure loss section at the head of diffuser n°1 to simulate the second device studied within WP4.2 S1MA to control the Mach Number into the test section.

The number of individual circuit volume has been reduced from 40 to 20, in order to shorten the computing time.

The software is made of:
- an editor (ESWIRP_gm_editor) which enables the user to adapt the geometrical characteristics of the model. The data are stored in the file “config.dat”;
- the model itself (ESWIRP_genmod) that performs the simulation, by starting to read the inputs in “config.dat”.

The HMI of the generic model has been adapted to the S1MA wind tunnel model.

Comparison between experimental data and model results

The agreement between the simulation results and the experimental data is satisfying.

During the second period, after the completion of LLF module, S1MA was updated to be in accordance with LLF module (harmonization process).

A detailed description of S1MA module is given deliverable D4.2 and results given in deliverable D4.5.

Task 4.1.2 : Numerical simulation model – DNW-LLF Module

The generic numerical model has been adapted to the specifics of the DNW-LLF wind tunnel. The model is based on the equations of the physical phenomena present in the wind tunnel circuit. Only macroscopic low frequencies phenomena (< 10 Hz) are represented; boundary layers and turbulence are out of the scope of such a model.

The following characteristics of the LLF circuit are introduced in the representation:
- size of the overall circuit
- fan characteristics
- cooler
- heat exchanges with the concrete walls
- breathing with the tunnel hall
- test section, only the 8x6 m2 test section is represented in the model.

In each box, the flow equations are solved to determine the actual temperatures, pressures and mass flows. In above figure, the blue elements correspond to the highest total pressure zones and the yellow elements to the lowest total pressure zones; the red element corresponds to the test section.

The circuit has been divided into 15 elements with:
- the fan located between elements 14 and 0
- the test section represented by the element 9
- the cooler located in element 7.

The numerical results of the simulation model have been compared with experimental results of the tunnel calibration of the LLF closed 8mx6m test section.

In below figures the following comparison plots are shown:
- Tunnel dynamic pressure as a function of fan rotational speed
- Consumed fan power as a function of rotational speed.

The agreement for steady conditions turns out to be very good. Discrepancies are only due to inaccuracy/approximations in the specifications of the characteristics of the LLF circuit elements.

A detailed description of DNW-LLF module is given deliverable D4.3 and results given in deliverable D4.6.

Task 4.1.3 : Numerical simulation model – ETW Module

Following the same process as the two first modules (S1MA and LLF), the ETW module was developed from the generic module, taking account of the experience of the other modules.

The flow equations are solved to determine the actual temperatures, pressures and mass flows. The green volumes correspond to the highest total pressures zone and the yellow volumes to the lowest total pressures zone.

The circuit has been divided into 14 elements with:
- compressor/drive upstream of the element 0
- blow-off located at location 4
- adjustable nozzle at location 8
- test section/2nd throat at location 9
- LN2 injection system at location 12

The plenum is represented by a volume in parallel with the test section.

The numerical results of the simulation model have been compared with experimental results.

After this third wind tunnel modelling, the HMI was frozen.

A detailed description of ETW module is given deliverable D4.4 and results given in deliverable D4.7.

Task 4.2 : ESWIRP Consortium Wind Tunnel upgrades and task 4.3 Dissemination of results

ONERA - S1MA Upgrade

The ONERA S1MA wind tunnel facility is the largest transonic wind tunnel in the world. It is a closed circuit atmospheric wind tunnel with a maximum speed near Mach 1. The ONERA S1MA provides unique capabilities for testing large models at cruising speed and above. The tunnel was erected after the Second World War and has three exchangeable test sections with a diameter of 8m. The air in the tunnel is propelled by two large fans each connected by means of a shaft to a Pelton turbine outside the tunnel circuit. The installed power output is 88 MW.

The major benefits of S1MA are:

* Its size: The S1MA facility (the biggest in the world for its velocity range) can accommodate in its test section very large models. The benefit of having large models is essential for testing new concepts and having enough room within the models for housing various devices such as boundary layer control devices, remotely actuated mechanisms, drag reduction devices; aircraft control mechanisms both for handling qualities and efficiency improvement, laminar flow concepts etc.
* Its performances: The S1MA facility can operate up to sonic Mach number at atmospheric pressure. Civil transport aircraft developed over the last decades have been designed with a consistently increasing maximum flying speed.

The benefits retrieved from experimental works performed at S1MA are essential to the researchers and aircraft manufacturers, to the future of the European aeronautic and all together to the harmonious development of Europe and the welfare of its citizens. In that respect it represents a strategic facility which must be closely looked at in terms of capabilities to fulfil the increasing complex requirements for progress of its users.

The existing Mach number control process of the ONERA S1MA is not sufficiently accurate to maintain a perfect constant Mach number in the test section during a test run resulting in long and expensive procedures to obtain high quality test data. The Mach number in the test section varies as a result of both the natural flow instabilities of the tunnel and the continuous variation of model attitude. The goal of the proposed upgrade within ESWIRP Project is to make this top quality testing available to the users on more permanent basis, and at reduced costs.

The proposed upgrade of S1MA aims at improving the wind tunnel quality and productivity with the implementation of a new closed loop Mach number control system. The work done in this WP is to design and implement a control mechanism demonstrator, and test it to demonstrate its capabilities/performances. This new mechanical device implemented inside or outside the wind tunnel has to improve significantly the Mach number regulation.

For S1MA new Mach controller, the objective is very ambitious since it aims to obtain Mach number stability during a pitch polar within ± 0.001 at least up to Mach 0.9.

Solutions studied:

Three solutions have been studied :
1. A mast fitted out with flaps located inside the main diffuser. In this case the pressure losses variations in the test section are compensated by the pressure losses variations due to the flaps.
2. An air inlet with flaps called EAR inlet (“Entrée d’Air de Régulation” – additional air inlet for Mach regulation) which is located above the corner #1 of the wind tunnel at the exit of the main diffuser. With this device a small mass flow rate is injected, goes through the fans and goes out by the annular outlet of the wind tunnel located just upstream the convergent.
3. A by-pass of the fans which breathed a small air flow rate of the wind tunnel just upstream the fan #1 and threw it back inside the wind tunnel just downstream the fan #2.

Only a preliminary study of the solution #3 was made because it appeared quickly that the implantation of such a by-pass circuit will be very difficult in the S1MA surroundings and also the cost for its manufacturing and its mounting would be too expensive.

On the opposite the solutions #1 and #2 seemed realistic from a technical and cost point of view and then they have been studied in detail which means that all drawings and technical specifications of both solutions were made.

Choice of the solution

At the end of the preliminary studies, in order to make the choice between the solutions 1 and 2, the following table was established including the main advantages and disadvantages of each solution.

This table listed the most important criterions of the project; a group of ONERA wind tunnel division experts gave a note on 10 for each criterion and selected the solution which had the best total note.

The solution 2 obtained the best note without contest and that was the reason why ONERA finally decided to manufacture and mount the EAR inlet.

Criterions Solution 1 Solution 2
Mast EAR inlet

1 Compared price for the manufacturing and mounting of the solution 7 10
2 Technical risk i.e. reliability of the solution in order not to decrease
the present availability of S1MA 6 10
3 Reversibility of the solution i.e. easiness to come back to the present
running of S1MA in a short delay 4 10
4 Easiness of the maintenance i.e. access to the mechanical parts
supposed to be changed and delay to repair or to change them 5 10
5 Impact on the flow in the test section or in the circuit of S1MA 6 9
6 Impact on the existing structures of S1MA i.e. risk to damage
these structures in case of breaking of a
mechanical device part 6 9
Total note 34 58

Description of the EAR inlet (solution 2 selected by ONERA)

The purpose of the EAR is to compensate the variation of the pressure losses ΔP coming from the model mounting by injecting a small air mass flow rate ΔQEAR just upstream the fans of the wind tunnel. The EAR has been then located on the corner #1 of the wind tunnel which is just upstream the fans.

Main characteristics of the EAR

The EAR inlet is running by natural aspiration because the flow pressure inside the wind tunnel circuit in running is always lower than the outside atmospheric pressure. Its location on the corner 1 just upstream the fans is the best favourable one because the internal pressure there is the lowest of the circuit.

The difference of pressure used for the intake is usually included between 2000 and 6000 Pa according to the Mach number and to the pressure losses of the model mounting in the test section. The maximum air rate of the intake is estimated by aerodynamic calculation at 250 kg/s.

From upstream to downstream the aerodynamic EAR inlet circuit consists of :
- A rectangular convergent with an inlet protection grid of section 4,50 m x 1,60 m which aspirates the air below the existing roof of the so called “air inlet 1” of the S1MA wind tunnel.
- A central caisson of section 2,50 x 1,05 m including two vertical flaps. The aperture angle of the flaps can continuously change between 0° (open position) and 75° (closed position).
- An bend at 45° including 4 blades in order to guide the flow.

The complete circuit is mounted on a big frame of about 7 m x 3 m. Upstream the frame is fixed on a large ring of the wind tunnel and downstream it is fixed on a small ring by mean of elastic dampers in order to filter the mechanical vibrations that occurred when the wind tunnel is in operation.

The motorization of the flaps is mounted above the central caisson and includes an electric motor with a central screw and two rod-crank mechanisms. The motorization is protected by a shelter which includes also the electric closet. The EAR includes also a footbridge at each side of the circuit for the maintenance.

The total mass of the EAR is about 15 tons. It has been verified by mechanical calculations that this addition of mass has no significant impact on the mechanical behaviour of the wind tunnel circuit.

The design of the EAR circuit has included finite element calculations of all mechanical parts of the circuit and also of the shelter with the maximum efforts applied on them.

Tests performed to qualify the new Mach number regulation system

Tests were performed in November 2012 using a civil aircraft model at a scale of 1/26 in test section n° 2 – 45 m2 of the ONERA S1MA wind tunnel in order to qualify the new Mach number regulation obtained with the help of the EAR air inlet.

Measurements were performed on one hand with the classical Mach number regulation with the EA2 air inlet and on the other hand with a new regulation, specially developed in accordance with this new additional air inlet (based on the previous developments with large air intake, the idea was to use fan's RPM control to compensate large pressure losses with some time delay in association with a device which can generate limited but fast pressure variations in phase opposition with those of the model during its pitch motion).

The efficiency and the effect on the model of the EAR air inlet were evaluated.

Test programme to evaluate the EAR efficiency

Measure of the Mach number change during continuous variations of the model incidence or at stabilized incidences for different positions of the EAR air inlet and different settings of the Mach number regulation automaton, for M = 0.35 to 0.96.

The test conditions were:
- Mach number : 0.35 to 0.96;
- Stagnation pressure : about 0.9 bar (atmospheric pressure);
- Stagnation temperature : 300 K to 330 K;
- Model incidence : - 6° to + 8°.


A detailed description of S1MA improvements and the results obtained is given deliverable D4.9.

Impressive improvements achieved on S1MA Mach number controller could be observed. Indeed, nearly no drifts are observed for all the Mach numbers, even at negative angle of attack.

To conclude these experiments it was checked that activation of the ESWIRP air intake, in steady conditions, doesn't induced penalty on Mach number stability. Mach number fluctuations, over a period of 6 minutes, with and without air intake activation, are presented on figures below. No penalty is observed; on the contrary a mild improvement is obtained with air intake activation.

DNW- LLF Upgrade

Introduction / Objectives

In order to perform good ground simulation tests for aircraft during start and landing in the DNW-LLF 8 m x 6 m test section, the following aspects should be taken into account:
1. Ground proximity effects
2. Negligible/thin ground boundary layer at aircraft wing, engine intake and exhaust flow, landing gears and tail location
3. Aerodynamic effects due to velocity difference between aircraft and ground

In the past DNW has selected the moving belt system as ground simulation technique to meet these requirements. This report describes the activities to upgrade this system.

Description DNW-LLF

The Large-Low-Speed-Facility (LLF) of DNW is an atmospheric, closed circuit wind tunnel with a contraction ratio of 9. It is a concrete structure in a metal frame and has a drive power of about 14 MWh, which drives a constant pitch fan with variable speed. The wind tunnel has two exchangeable closed test section arrangements and it can be operated in an open jet mode as well. Each test section configuration consists of three elements: a nozzle, the test section itself and the transition. The overall length of the arrangement is 45 m. The largest test section has a cross section of 9.5 m x 9.5 m; the smaller test section has a cross section of either 8 m x 6 m or 6 m x 6 m. For the open jet arrangement the 8 mx6 m nozzle is used together with the 9.5 m x 9.5 m transition. Instead of a fixed floor, the test sections have removable and exchangeable floor sections. For ground effect testing a Moving Belt Ground Plane (MBGP) with boundary layer control is available.

Existing LLF Fabric Belt System


The model is supported via a dorsal sting set-up which is mounted to the torpedo and the sword. The variation in model height is set via the sword. Angle of attack is set via a joint between sting set-up and torpedo. Angle of yaw is set via two joints between sting set-up and torpedo as well as between torpedo and sword.

Ground effect testing is conducted in the 8 m x 6 m test section with an MBGP with boundary layer control as depicted in the figure below. When installed in the test section, the MBGP replaces a removable floor section but the upper surface of the MBGP is 200 mm higher than the fixed part of the test section floor. Because of this step in height, the oncoming tunnel floor boundary layer flow can be completely scooped out of the test section. At the downstream end of the MBGP the scooped mass flow is sucked into the tunnel again. The MBGP can be equipped with a belt with an exposed surface (width x length) of 6.3 m x 7.6 m.

- Limited belt speed (45 m/s) Complicated operation (manual controls, cooling, tension)
- Poor life-time
- Large aerodynamics forces act on the belt due to:
* Strong vortices induced by high angle of attack and lift
* Engine jet flow (e.g. thrust reverser) impingement, possibly resulting in local deformations of the belt

Requirements and Layout Improved LLF Belt

- Belt size 7.92 m x 6 m
- Maximum belt speed Mach 0.25 (80 m/s)
- Longer life-time
- The belt remains flat under the influence of aerodynamic forces introduced by models above the belt
- The flatness of the belt can be measured to enable an automated reaction by the air suction/pressure system
- Boundary layer removal by existing ground-plane (200 mm scoop)

In December 2009 the MTS metal belt was ordered and the system was aimed to become operational in September 2012.

- Detail design and manufacture of new metal belt and ground-plane (copy) at MTS - Assembly
- Factory Acceptance Test 1 (February 2012, see figure below)
- Factory Acceptance Test 2 (July 2012)
- Shipment to DNW (August 2012)

- Upgrades at DNW - Test section (higher belt weight)
- Elevator (higher belt weight)
- (dedicated) Air compressors

- Delivery at DNW - (Re-)assembly (September – November 2012)
- Commissioning/Site acceptance (December 2012 – February 2013)


The considered highest belt loadings are introduced during aircraft ground proximity investigations with engine simulation. The specified aerodynamic point loading is as follows:
- Over pressure 20 kPa
- Suction pressure -1.5 kPa

The belt should remain flat during this loading.

Aerodynamic point loading on the belt during site acceptance test is generated by two blown
nacelles pointing to the belt. The loading has been verified earlier in a separate set-up using an instrumented plate mounted on the floor (see figure at the right side).

To derive the requested loading the nozzle exits should be located 500 mm above the floor. The settings of each blown nacelle are:
- NPR = 1.5
- Mass flow = 1


The same checks as performed during the Factory Acceptance Test at MTS were repeated after the re-assembly of the MBGP at DNW site.

The acceptance test inside the LLF test section consisted of the following sequence of checks:
- Wind-off: with belt speed up to 80 m/s
- Wind-on: with belt speed up to 80 m/s and tunnel speed up to 80 m/s
- Wind-on and point loading: belt speed 80 m/s, tunnel speed 80 m/s and specified point loading by blown nacelles (symmetrical and asymmetrical) above the belt
.5 kg/s

LLF Test Section Calibration

Finally the LLF 8 m x 6 m test section was calibrated versus the tunnel reference system, with metal belt and optimized ground-plane settings.

Therefore the following instrumentation was used:
- Pitot-static tube at tunnel center and mounted to tunnel ceiling
- Tunnel reference instrumentation (total pressures, static pressures and total temperatures) in settling chamber

Conclusions / Outlook

- The new belt became available about half a year after the initial planning
- The new belt system is a superior ground simulation technique, which meets all DNW requirements
- Improved flat static pressure distribution toward belt nose
- The first industrial test has already been performed in April 2013

4.2.1 ETW Upgrade

The design and development of modern high quality transport aircrafts implies the needs of operating closer to the physical flight boundaries. As the flow fields in these regions are characterised by complex 3‐dimensional and unsteady behaviour the industry is expecting from the
wind tunnel performers also accurate and reliable test data from such areas. Those requirements can only be satisfied by providing sophisticated modern instrumentation, ideally non‐intrusive one, validated for the cryogenic pressurised operating range of ETW, which is representing the prerequisite for simulations at flight conditions.

Task 4.2 of the DoW is addressing relevant subjects by focussing on the provision and verification of appropriate tools and techniques with respect to improve / enhance the test capabilities of ETW and ,therefore,extending the portfolio for their customers.


In the frame of the present project 12 individual topics have been identified to be considered for implementation or upgrade which can globally be structured in two main categories, namely the “Enhancement of unsteady/aeroelastic Test Capability & operational Productivity” and the
“Development and conceptual Proof of an RC‐Slot System”. The first one is further split in 11 individual projects:
- Extension of operating range with respect to the maximum Eigenfrequency (E‐range)
- Increase of dynamic model deformation system speed up to 1kHz (D‐SPT)
- Transition detection by conditional sampling (CS‐TSP)
- Upgrade from standard CRYO‐PIV to time‐resolved CRYO‐PIV (TR‐PIV)
- Increase of input channels for the unsteady Data Acquisition System (UDAS)
- New half‐model balance for redundancy and fast exchange (new HMB)
- 2nd anti‐vibration System for redundancy and time saving (new AVS)
- Extension of glass‐fibre Network (GFN)
- Upgrading the conditioning Units (ECUs)
- Time synchronisation for multiple measuring systems using a single central clock (CS)
- Increase of unsteady Data Storage Capacity (CUDS)

I. Enhancement of unsteady/aeroelastic Test Capability & operational Productivity


Using a half model for aeroelastic testing is typically striving for an assessment of the unsteady behaviour of aerodynamic forces and moments, pressures and the corresponding model shape. While the base frequency is mostly below 100 Hz first and second harmonics, often stronger amplified, appear at frequencies of a few hundred Hertz. Hence, allowing for a proper analysis and assessment
of aeroelastic characteristics the Eigenfrequency of the model/balance support system should be acceptably higher.

On the way determining the status, the half model balance has been meshed and subsequently calculated for Eigenfrequencies by a finite element (FEM) code while the mechanical structure itself has been equipped with a series of accelerometers for in situ measurements during testing in the
tunnel .

The calculated Eigenfrequency (230Hz) reveals lower than the measured one of 300Hz. In the follow –on considerations no feasible solution for a reinforcement of the frame structure could be worked out. An improvement of the situation by modifying the structure of the complete model cart has not been considered as an acceptable option in the frame of the project.


With respect to a tracking of the unsteady deformations of wings or high‐lift model components the recording capacity of the existing SPT systems was completely inadequate. Hence, a new system based on more modern cameras with increased frame rates but acceptable resolution had to be
found and combined with according optical components like objectives, cables, connectors, light sources etc. Following the procurement and software adaptations provided by the supplier basic system trials have been performed in the lab.

This tested system revealed a reliable operation with a frame rate up to 386 Hz providing full resolution and viewing field. It has been installed and operated in the TNA entry for monitoring the behaviour of the HTP of the CRM full model.


The boundary layer transition detection by Temperature Sensitive Paint (TSP) has been successfully developed in cooperation with DLR more than a decade ago and permanently enhanced and automated for cryogenic operation so, that it may be considered as a mature technique. Regarding
unsteady measurements the implementation of a phase sampling capability was looking essential and feasible. Unfortunately, all TSP hardware including the paint, the processing and post‐processing software as well as the operational knowledge was owned by DLR, hence, their special team had to be recruited each time when an application in ETW had been required. This situation in the present period of increasing demands on laminar flow investigation at near flight Reynolds numbers is causing an inacceptable reduction in operational flexibility due to the naturally limited availability of the DLR team.

Consequently, the sub‐project CS‐TSP was settled aiming for the upgrade to conditional sampling as mentioned above as well as for the transfer of hardware, knowledge and software to ETW including staff training, hence, providing a high level of independence to ETW. Hardware has been procured including cameras, objectives, heated boxes and PCs for image control and data processing. Nowadays, the system can be operated by ETW staff leaving the provision of paint by purchase order to DLR.


The general application of the Particle Image Velocimetry (PIV) for non‐intrusive flow field measurements in wind tunnels is considered mature for operations at and near environmental test conditions. Also with respect to the approved TNA‐entry in the wind tunnel the developed and
operated system had to be upgraded for allowing unsteady PIV measurements of wake flows at cryogenic pressurised conditions at low and high Mach numbers. Applying the technique to the according full model revealed the need for a) the design and manufacturing of a new smaller
temperature controlled housing for the optical module to be placed below the test section floor, b) the design and manufacturing of a similar large box for the only suitable high speed camera and c) the implementation of a complex new light path for the laser beam. All those challenging tasks have
successfully been achieved on time for serving the TNA‐entry in ETW, hence, fulfilling the mandatory prerequisite for the relevant project objective.


The formerly existing unsteady data acquisition system limited the number of input channels to 64.
Based on experiences gathered in recent test campaigns this low number is not adequate for fulfilling client’s needs on signals to be acquired in a typical aeroelastic test. Further on, the capacities on electronic filtering units was insufficient too as well as the complete lack of an individual excitation capability for each channel. Comprehensive discussions with the provider of the old system revealed the general possibility of extending the number of input channels but without being able to upgrade the existing hardware to the required standard. Hence, a new 128 channel system has been designed according to ETW’s specification, tested for acceptance and finally integrated into the measurement pool.


The existing ETW balance for half model testing has been procured in the last century. Installed in the ceiling of a model cart it can only be accessed after having removed the test section ceiling. Regarding half model testing no other balance is available for substitution in case of a defect or
failure requiring a long period out of service. A critical careful analysis of operations and experiences gathered over more than a decade paved the
platform for a new specification containing a set of selected modifications and improvements. In this context the major item has been the provision of a capability to install the new balance without removal of the test section ceiling (a part of a model cart) for time saving reasons. Regarding the load capacities, sensitivities and accuracy no modifications have been made. The raw material for the manufacturing of the frame could be taken from the ETW stock; instrumentation was kept in the responsibility of ETW experienced staff and installed outside the project. These activities
are presently still ongoing to be followed by a careful calibration.


For supressing model vibrations due to Eigenfrequencies and, hence, being able testing up to higher angles of attack ETW is operating an in house developed anti‐vibration system named ERAS due to the cooperation with an industrial company. While one system is located between the balance and the sting, another system based on linear motors fighting pitch and heave modes is embedded in stub‐stings. Unfortunately, a single system is available only but this sensitive piece of equipment has to be removed and installed in different stub‐stings depending on the individual test requirements. To overcome this bottleneck the provision of a 2nd exchangeable system had been considered simultaneously providing a redundancy in case of need for avoiding down times when testing full models.

First considerations did only aim for the provision of a 2nd AVS identical to the existing one but the manufacturer informed that the supplier of the linear motor did not exist anymore. When finally going for an alternative motor this one was not compatible anymore with the existing old drive and
control system and had to be replaced and adapted to the new systems. At the end two identical exchangeable AVS no. 2 systems have been ordered and delivered together with the new corresponding control unit.


The high operating costs of cryogenic wind tunnels demand a high level of reliability and quality of data transfer for all systems being activated in a test. This requirement is of major importance in ETW where the tunnel is about 70m away from the main tunnel control‐room and series of cables
and fibres are running through cryogenic and ambient environment directly to it or to the instrumentation cabin at first and subsequently down to the control units and PCs. Having started tunnel operations in the 90ties by using classical copper cables the capabilities of modern
measurement and control systems cannot be adequately supported by this type of cable but requiring glass‐fibre connections.
The developed and realised concept is based on using 50/125μ glass‐fibres of the premium quality OM3. Regarding the hardware components it is at first compiled of 2 pairs of analogue/digital converters, each located in the instrumentation cabin on top of the model cart and in the main
control room.

In a similar arrangement at the same locations 10Gb/48Gb switches for data reduction and video data purposes have been installed.
The unit in the main tunnel control room may be connected either to the test section, tunnel hall or to one of the 3 cart rigging bays or 2 variable temperature check out rooms depending on the model location or the test engineers individual request.
The key unit in this arrangement is represented by a 24 port fibre‐optic switch making any manual interface on the sensitive network connections superfluous. All components could be implemented in a single rack in the control room providing easy and simple access in case of need.


Since the early 90’s ETW is operating about 160 conditioning units (CUs) developed by the Dutch research organisation NLR mainly used for the digitisation of analogue signals. Nowadays, their capabilities are not appropriate anymore and some specific features are simply missed. Contacting
the original provider and discussing present needs it turned out that no complete replacement of the devices is required rather than individual upgrades by exchanging the main circuit boards to be newly developed. Following the distribution of an RFP the finally settled modification went for a
replacement of all these boards for enhancing the capabilities, focussing on a replacement of the data bus by a modern Ethernet bus, the integration of a “True RMS” function and adding a certain number of DAS Hubs for connecting unmodified DAS‐bus data acquisition equipment.
In a first step the NLR developed a new circuit board in cooperation with ETW for comprehensive validation testing of the prototype by ETW experts. Following its acceptance all new boards have been provided and installed in the existing units.


Along the performance of unsteady measurements using individual systems no synchronisation of signals is applied as sketched in the upper part of
any reliable analysis and a deeper understanding of the flow field behaviour. Moreover, the individual measurement system may be subject of time‐wise drifts.

It was concluded that for a clock synchronisation system high precision is required on one side but accessibility and individual adaptivity is to be provided on the other hand with respect to the wide range of applications specified by ETW and, consequently, a relevant system could only be developed in house.

For the technical approach a suitable clock generator was considered sufficient being able for generating pulses between 0.01 Hz and 10MHz, hence, covering the data acquisition needs and allowing the simulation of an oscillator.

Beside the capability of synchronising input signals in time the system will also allow generating precise signals and time‐stamps by itself for triggering external devices.


Initiating activities for improving the capabilities for investigations of unsteady effects is typically attended by the needs for an enhanced data storage capacity. In the present case the acquisition of e.g. dynamic model deformation data and time‐/phase resolved TSP and PIV data are pushing for the
availability of modular data acquisition and analysis systems for gathering and storing significant amounts of data. Hence, appropriate data storage is the key to provide reliable and rapid “turnaround”, i.e. quick saving and access of data for allowing ad hoc detection of testing errors,
discrepancies, failures or loss of data. Further on, the operated system has to ensure reliability by automatic health monitoring combined with the capability of being configured for supporting a wide range of individual test setups with different modular measuring techniques and their according

Having performed a thorough evaluation of offered systems with respect to the above requirements a specific unified scalable Gigabit‐connected Network Attached Storage (NAS) solution has been selected. This high performance system is using a special operating system providing quick data‐read and –write access, inherent redundancy for high access availability and application aware backup/recovery/cloning. Its particular strength is an intelligent use of caching to decouple storage performance from the underlying physical disk‐array layout. It uses Non‐Volatile Random‐Access Memory (NVRAM) as a journal of incoming write requests allowing the system to commit write
requests to non‐volatile memory responding to writing hosts without delay. Beside other unique features the data acquisition may continue writing a stream of data while preliminary data analysis starts checking consistency and quality of the acquired data. Intelligent continuously running cloning/backup algorithms will significantly reduce the risk of losing valuable test data.

II. Development and conceptual Proof of a RC‐Slot System

Wind tunnel walls may be solid, slotted or perforated. Striving for a transonic wind tunnel with low wall interference the original ETW configuration for testing full models is characterised by longitudinal slots in the floor and ceiling of the test‐section. By the end of the last century the
capability of testing half‐models has been added requiring the attachment of such models to the ceiling for keeping the capability of transporting the model in and out by taking the benefit of the model cart concept. For this type of testing all walls may be closed or, for high speed operation,
slotted but then with the top and bottom wall closed. The slot configuration is achieved by using prefabricated inserts being manually bolted to the wall structure. Logically, the relevant work requires access to the tunnel under environmental conditions.

Depending on the individual test scenarios and the tunnel status at the end of a campaign (cold or warm) the nitrogen gas in the tunnel has to be released and the tunnel warmed up and purged before getting access. Additionally to this time consuming and costly procedure the test section will be
blocked by the slot exchange team for any parallel work. Several approaches to overcome this bottleneck and saving cost and time have been initiated without finding an efficient and acceptable technical solution. The re‐consideration in ESWIRP targeted to investigate new concepts and
performing a proof of concept in the cold at the end.

An essential aspect for the design has been the requirement of not affecting in any way the flow around the test object, which would lead to a complete recalibration of the tunnel over the full operating range. On this basis a step‐wise approach had been defined:
1. Developing an remotely controlled insert driven by electric motors
2. Calculating by CFD the effect of the insert inside the slot in maximum retracted position compared to the no‐insert configuration
3. Investigating experimentally the effect of all inserts in place on the flow field and the pressure distribution of a 2d‐airfoil in the cryogenic pilot facility PETW
4. Validating a motor for reliable operation at cryogenic conditions
5. Building a full scale mock‐up of a single slot channel with inserts and drives and including appropriate control soft‐ and hardware
6. Running validation test of the mock‐up under deep cryogenic condition for proving the system reliability.

Driven by structural requirements and the aim of supressing any cross‐flow in the plenum the depth of each slot channel in ETW is about 600mm. Design considerations revealed that the insert (plug) may only be retracted by 200 mm into the slot channel.

As the PETW test section is a copy of ETW scaled down by a factor of 8.8 tiny details including any drive cannot be perfectly modelled. Nevertheless, the individual inserts were placed in the correct position when comparing the surface pressure distribution on the walls and a 2d‐airfoil. Keeping in mind that 2d airfoils are characterised by huge interference levels

In the next step a suitable motor including gear has been validated in operation and output power at cryogenic conditions. Figure II.3 shows the selected device placed in a small cryo‐chamber. The experiments were conducted loading the motor by connecting proper weights for simulating realistic conditions including friction.

Potential Impact:
The ESWIRP project is fully responsive to the objectives of the Capacities – Research Infrastructure Program. It will enhance research and innovation capacities throughout Europe and contribute to ensuring their optimal use. The activities planned under this project aim at optimizing the utilization of the three strategic wind tunnels and improving their performance by new long-term investments for the benefit of scientists and customer industries.

The demand for modern wind tunnel testing requires wind tunnels of excellent performance and quality and sophisticated aircraft models provided with up-to-date instruments and interference free flow measurement techniques, and above all, highly skilled personnel. Over the years, models, testing techniques and associated instrumentation have become more and more sophisticated in order to meet the ever-increasing requirements of the aeronautic community in terms of accuracy and repeatability of results. High quality is mandatory to enable exchange of data with a high degree of accuracy, while high productivity is necessary to reduce the cost of data.

The activities planned under this project aim to optimize the utilization of specific research infrastructures and to improve their performance.

Improvements of S1MA:

Improvement of the S1MA Mach number controller was requested to increase the quality of the aerodynamic data base and the productivity of this unique large transonic wind tunnel.

Progresses achieved on those two topics (data base quality and test productivity) are detailed in the next two sub chapters.

Improvement of data base quality

Since 2006 pressure measurements were recorded during continuous pitch polar (no pitch pause) which already generated significant productivity gains.

However, as one can see on the black curve on figure below, Mach number drifts were still significant in 2006 and Clients had to keep in mind this, during their analyses of the pressure data. With the new Mach number controller (pink curve), Mach number drifts can be considered as negligible when exploiting model pressure distributions. This Mach number stability considerably increases the data base quality and generates productivity gains on our Clients activity since it is not necessary to check, for each incidence, if the reached Mach number is not too far from the requested value, inducing possible false interpretation of the aerodynamic behaviour. It is important also to underline that this improvement of the data base quality applied not only for the pressure measurements but also for all the measurements for which interpolation is not adequate: dynamic measurements, acoustics measurement.

Furthermore, this improved Mach number control will be of great interest for wake survey tests and laminarity tests for which aerodynamic stability is crucial.

Improvement of test productivity

In a period in which competitiveness is enhanced, gains of productivity on wind tunnel tests are a major concern. With the new Mach number controller, which leads a high Mach number stability, loads interpolations are "easier" leading to the cancel of all the pitch polar which were requested for load interpolations purposes only.

To determine accurately the drag evolution at high Mach numbers, interpolations of load measurements are still done but now a step in Mach of 0.025 is possible compared to a step of 0.01 in the past. This generates very important productivity gains with and without the new Mach number controller, to carry out a typical run for a civil aircraft configuration, is realised.

Before 2013, additional pitch polar were added for load interpolations only and wind on time was around 115 minutes.

With the new Mach number controller, as Mach number drifts are considerably decreased leading to a step in Mach of 0.025 between two consecutive Mach numbers used for interpolation, it is necessary to add only one extra polar at Mach number 0.96 to interpolate the results at Mach number 0.95. Time necessary to acquire the same Client data base is reduced from 80 to 55 minutes in this example (≈ -30%).


The Large Low-speed Facility (LLF) in Marknesse (the Netherlands) is an industrial wind tunnel for the low-speed domain. It is a closed circuit, atmospheric, continuous low-speed wind tunnel with one closed wall and one configurable (slotted) wall test section and an open jet. The DNW-LLF is a closed circuit , low noise, low-speed wind tunnel with a maximum speed upto appr. 130 m/s. The tunnel originally was equipped with a fabric Moving Belt Ground Plane with a maximum speed of 45 m/s. The MBGP is provided with a boundary layer removal system that scoops and re-injects the floor boundary layer air into the tunnel.

The demand for further improvements in aircraft fuel efficiency during the last decades as well as for reduction in noise generation around airports made an upgrade of the facility a necessity. Since landing and take-off phases of the aircraft flight are the major factor affecting the population around airports, the availability of the best possible experimental simulation capabilities for these flight phases, where the quality of tunnel, air flow, background noise levels and ground simulation perform an integral part in providing data in the exploration of new possibilities, is essential for progress.

Improvement of ground simulation (upgrade of moving belt)

To improve the major shortcomings of the old fabric belt system, being its limited belt speed (45 m/s), complicated manual operation, poor life-time and flexibility under large aerodynamics loading by a near-by wind tunnel model, feasibility studies have been conducted in the framework of ESWIRP focused on potential improvements on the existing Moving Belt Ground Plane.

Feasibility studies were performed detailing potential benefits and making cost trade-offs. They indicated that the required ground simulation improvements cannot be realised with the existing system (multi-layered fabric belt). The potential benefits could only be realised by implementing a metal belt system. The costs of such a metal belt system, however, are outside of the available ESWIRP budget. A solution has been found in getting external to ESWIRP funds for the procurement of a metal belt system itself. The ESWIRP budget has been applied for integrating the metal belt system in the DNW-LLF infrastructure. In this way all of the original required ground simulation improvements could be realized.

MTS succeeded in developing the system for DNW-LLF, based on technology specifically used in automotive wind tunnels (that only have a width of 1.1 – 3.2 m as compared to the DNW requirements of 6 m). The 1 mm thick sheet runs on large hardened steel rollers. A sophisticated suction/blowing system keeps the belt flat under large aerodynamic loading when testing aircraft in ground proximity. A boundary layer removal system and the reinjection scoop complement the system. By optimizing scoop, breather and flap settings of the new system, a homogeneous static pressure distribution above the major part of the belt has been achieved for the whole belt speed range.

The new system has been successfully taken into operation in spring 2013 and applied for various industrial tests at DNW LLF. Feedback of these customers confirmed that the realization of the improvements have increased the fidelity of the in-ground-effect simulation cap[abilities of the DNW-LLF on one hand and based on own experience significantly increased improved system control and reduced cost of operation, since the metal belt in principle has an unlimited lifetime.

Reduction of background noise (acoustic upgrade)

The second major upgrade program related to the acoustic capabilities of the DNW-LLF.
Initially three distinct components with potential for improvements were identified. Two of these concern the wind tunnel circuit and one the test section. The test section upgrade focused on reducing the reflections of the original aeroacoustic noise from the parts of the wind tunnel infrastructure, making the test environment more anechoic. Most of the issues have been addressed, like wall sections have been refurbished, model mounting devices have been acoustically treated, components of the floor sections have been renewed and the diffusor entrances have been modified.

The other two components are the turning vanes before and after the wind tunnel drive fan and modifications in the settling chamber.
In the framework of ESWIRP feasibility studies were conducted into technical solutions of reducing background noise levels of the wind tunnel. Similarly to the upgrade of the ground simulation system, the costs for the actual system improvements were outside of the available ESWIRP budget. A solution has been found in getting external to ESWIRP funds to realize the acoustic upgrade.

The acoustic treatment of the corner vanes has been realized by following a design procedure established together with the DLR. These turning vanes succeed in turning the flow around the corners without introducing new disturbances into the flow and isolate a significant part of the fan noise from the upstream and downstream sections of the wind tunnel.

The last component of the acoustic upgrade took place in the settling chamber of the LLF. Here the original arrangement of the wind tunnel cooler, the flow straightener and the anti-turbulence screens was a source of non-negligible background noise. Extensive tests in a pilot facility were conducted in order to find an acoustically beneficial arrangement of these elements without incurring a penalty in turbulence levels. The settling chamber was refurbished without changing the heat exchanger configuration. The arrangement of the flow straightener and the anti-turbulence screens downstream of the heat exchanger was changed according to the results of the studies performed.

The shifting and redesigning of the two most downstream components of the settling chamber resulted in reducing the turbulence levels in the pre-determined calibration reference points by approximately 50% compared to the previous arrangement. The total background noise reduction achieved varies between 7 and 10 dB (a reduction by a factor of two would correspond to a 3 dB);

This very significant reduction and valuable achievement as already confirmed by the partners of the CleanSky project. In the framework of the Clean Sky project for Smart Fixed Wing Aircraft (SFWA), low-speed aerodynamic and aeroacoustic wind tunnel tests have been carried out on a large scale Contra-Rotating Open Rotor aircraft model. The Airbus wind tunnel model, equipped with hundreds of static pressure ports on the fuselage, wings, and tailplanes, also contained a large amount of unsteady pressure sensors on the air-motor driven CROR blades, powered by the DNW air supply system. An innovative NLR Rotating Shaft Balance RSB and telemetry system facilitated a step-change in data stream acquisition; approximately 50 terabytes of data were collected (equivalent to an MP3 playlist that would take 48 years to get through!).


Workpackage 4 of the DoW addresses the design, procurement and installation of new components for contributing to an improved performance, quality and productivity of the facility as well as a reduction of operating costs.

With respect to ETW a set of 12 individual smaller projects has been defined referring to the specific needs identified for the facility taking into account priorities, feasibility and budget for a successful realisation in the frame of ESWIRP:
1) Extension of operating range with respect to the maximum Eigenfrequency (E-range)
2) Increase of dynamic model deformation system speed up to 1kHz (D-SPT)
3) Transition detection by conditional sampling (CS-TSP)
4) Upgrade from standard CRYO-PIV to time-resolved CRYO-PIV (TR-PIV)
5) Increase of input channels for the unsteady Data Acquisition System (UDAS)
6) New half-model balance for redundancy and fast exchange (new HMB)
7) 2nd anti-vibration System for redundancy and time saving (new AVS)
8) Extension of glass-fibre Network (GFN)
9) Upgrading the conditioning Units (ECUs)
10) Time synchronisation for multiple measuring systems using a single central clock (CS)
11) Increase of unsteady Data Storage Capacity (CUDS)
12) Development and conceptual proof of a remotely controlled slot system.

While the first 11 subjects refer to an upgrade and enhancement of unsteady test capabilities, item no. 12 focusses on an overall productivity increase and saving of operational costs.

A critical assessment of the achievements is hard to be given at this early stage for the individual subjects as applications of the upgraded/enhanced tools and techniques have not yet been performed for all of them under hard industrial conditions. Nevertheless, some evaluation case by case has been tried with respect to the goals defined above.

1) A careful numerical and experimental structural analysis regarding an increase of the Eigenfrequency of the half model balance and its supporting structure did not reveal any feasible technical solution within the frame of the project rather than requiring major financial efforts.

2) The developed and successfully in the TNA-wind tunnel entry operated new dynamic model deformation measurement system is perfectly fulfilling the defined objectives offering a unique extension of measurement capabilities for unsteady testing.

3) The upgrades have successfully be integrated in the system. As the outcome of the completed scheduled actions ETW staff is now in the position of installing, setting-up and operating the system without further external support leading to a substantial flexibility in the timing of test preparations and performance.

4) It has never been the intention of ETW performing complex PIV investigations by ourselves. The targeted operation of time-resolved PIV applied at low and high speed conditions in cryogenic environment had been the key prerequisite for the approved and accepted TNA-entry. Although the status is a bit away from a maturity for industrial application the general feasibility could successfully be demonstrated in the entry mentioned above. This capability presents an important extension of measurement capabilities especially for RTD investigations.

5) The unsteady data acquisition system with its new enhanced capabilities is already fully integrated in the day to day tool cluster e.g. used for recording balance, accelerometer and strain-gauge data during testing.

6) The new half-model balance is presently still subject of further enhancement in instrumentation, handling and accuracy to comply with the most modern equipment ensuring accuracy, reliability and easy handling, all activities outside the ESWIRP frame.

7) The new set of anti-vibration systems no. 2 has successfully been checked out in the tunnel. Its availability is not only reducing the time for swapping over from an installation in one stub-sting to the other but especially remarkably reducing the risk of damage by having now one dedicated system per stub-sting. Further-on an exchange capability exists in case of damage.

8) Nearly all measurement, control and monitoring systems in and around the tunnel profit by this fast, powerful and less sensitive network. A further substantial gain has been achieved by cancelling the need for manual swapping of connections in the control room depending on the locations to be linked.

9) Although not all conditioning units have been supplied yet, with the new components (the replacement was not part of ESWIRP) the performed validation tests on the upgraded units impressively demonstrated the achieved improvements and the benefit for the reliability of these systems.

10) In a recently performed EU funded test 4 different measurement systems have been operated in unsteady mode. Not all of them could already be synchronised at that time but the realised system was able demonstrating successfully its new capabilities with respect to reliability and accuracy. The clock synchronisation tool will be mandatory when going for future aeroacoustic aerodynamic coupling investigation e.g. combining PIV and acoustic measurements.

11) The performed enhancement of the data storage capacity represents a key prerequisite for all unsteady measurements. The procured system is successfully integrated in the ETW data system working up to now with perfect fulfilment of the specification without being operated at its limits yet.

12) Finding a technically viable concept must already be considered as success with respect to the challenging objective. This fact was exemplarily demonstrated by the long and expiring searches for getting a suitable drive. Although the practical operating period inside the tunnel will be short, the reliability has to be proven by long term runs in the cold as any malfunction at cryogenic conditions would require warming up the tunnel and purging it. In case of a reliable and faultless operation substantial saving in time and costs are expected.

Focussing on an extension of unsteady measurement capabilities for improving the service for customers as well as an increase in efficiency and productivity of the facility the documented achievements contribute to these targets, although, no long time experience could be gathered so far.

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