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Final Report Summary - HILAMBIZ (HiLamBiz)

Executive Summary:
The “Vision 2020” goals, introduced in 2001 by the European Union, require breakthrough achievements related to drag reduction and propulsion efficiency. Laminar flow technology was identified as a promising candidate to contribute to this objective, as the extended laminar flow region allows a strong decrease in skin friction drag. Laminar flow may be achieved by shape modification (Natural Laminar Flow, NLF) or surface -suction (Hybrid Laminar Flow Control, HLFC).
In the past, a number of flight demonstrators were successfully used in the USA and Europe. Flight tests were selected as they allow full system demonstration at flight Reynolds numbers, which were not achievable in conventional wind tunnels, e.g. the maximum chord Reynolds number in a transition test in transonic flow in the ONERA S1MA wind‐tunnel facility was about 10 million. On the other hand, such flight tests were much too expensive to allow for extensive parametric exploration and optimization.
As the ETW cryogenic wind tunnel allows for full model testing chord Reynolds numbers up to 50 million by combining testing at cryogenic temperatures (down to 110 K) and increased pressures (up to 4.5 bar), the European Research project TELFONA, led by Airbus, was launched to demonstrate the use of ETW for NLF wing design validation at high Reynolds numbers.

Project Context and Objectives:
The HiLamBiz project aims to move existing NLF flow control technology up to higher Technology Readiness Levels (TRL) with the overall aim of validation in a flying test bed and subsequent implementation in next generation aircraft. ETW, with its TELFONA background in laminar testing, aims to contribute to these goals by applying and further developing its associated capabilities. Within HiLamBiz these capabilities will be used to visualise the extent of laminar flow on the wings, to quantify the drag improvements and assess the buffet boundaries of an innovative laminar configuration Bizjet.

Project Results:
HiLamBiz covered the preparation and performance of a wind tunnel test using an innovative business jet configuration with two sets of NLF wings and a remotely Controlled HTP.

Model design, manufacturing and instrumentation were supported in order to achieve a high quality model suitable for a test in a cryogenic environment. The wind tunnel was instrumented for performance tests of a Z-sting mounted full model acquiring forces, moments as well as steady and unsteady pressure data.

The transition location on the wings was assessed using the mature cryogenic Temperature Sensitive Paint technique (cryo‐TSP), which has been developed and tuned for industrial application at ETW in cooperation with DLR over the last 8 years.

The wing shape was determined with the ETW stereo camera system SPT.

The objectives of HiLamBiz represent a next step towards the Technology Readiness Level 6 of the Natural Laminar Flow technology. Basic knowledge had already been gathered some years ago in the EC project TELFONA. Further relevant work got carried out for CleanSky (HiReLF and NLF-WingHiPer) using a big half-model devoted to work out the acceptable manufacturing tolerances for relevant wings. Now the existing test capabilities were used for the first time for investigating a full model of a business jet equipped with sophisticated wings designed for Natural Laminar Flow development. Beside the primary target assessing flight performance characteristics especially of drag, unsteady flow features like buffet boundaries were also subject of the investigations. These aims required additional specific instrumentation on the model in addition to the well proven transition monitoring technique by coating the wings with Temperature Sensitive Paint (TSP).
Striving to acquire high quality performance data it had to be proven at first that those data can also be gathered with a sting mounted full model being tested at cryogenic conditions in ETW. Referring to recently gained experience upgraded model handling and cleaning procedures have been performed in combination with tuned coating processes for the temperature sensitive paint. The achieved surface finish represents the highest presently achievable quality providing the prerequisite for transition investigations at high Reynolds number flow conditions.

The ETW expertise on cryogenic model design and remotely controlled devices contributed to the availability of a high quality test articles suitable for achieving the specified goals.
On the facility side the new enhanced manual cleaning and air filtering procedures as well as specific coating of insulation material generating “Clean Room” conditions in critical areas developed for NLF-WingHiPer were also validated for this type of models representing a substantial prerequisite for high quality data acquisition.
Two pairs of wings have been successfully tested applying a transition fixing on each for gaining reference conditions before generating high Reynolds number conditions. The according wing twist and bending mandatory for complementary CFD work has been assessed using the ETW Stereo Pattern Tracking System (SPT). A second SPT system proved its capability for setting and monitoring the remotely controlled HTP during the wind tunnel entries.

The performed campaign has remarkably contributed to improve the understanding on how to design laminar flow aircrafts but certainly further steps are required to achieve this challenging goal.

Potential Impact:
Within the HiLamBiz tests the NLF design of two different wing shapes was validated at flight Reynolds numbers. The full model set-up enabled the assessment of the overall drag improvements achieved by the NLF design. The tests considerably enhanced the knowledge about the sensitivity of laminar flow over the wings at high lift coefficients for cruise Mach numbers. The experimental data acquired during the tests will be used as a unique platform for the validation of modern industrial CFD codes which incorporate prediction of the laminar/turbulent boundary layer transition.

Since the complete chain from model design via manufacturing up to the test performance at flight conditions in the cryogenic environment has been tracked, unique experience was gained regarding the processes to be adopted for future aircraft models as well as real aircraft equipped with NLF wings.
With regard to the wind tunnel the experiences gathered will help to improve both the model preparation and the test procedures for such types of laminar flow investigations and therefore expand the unique competence of the wind tunnel facility.

With respect to the ACARE 2020 goals the development of aircrafts with a substantial extent of laminar flow on their wings exhibits a promising approach for reducing drag and, hence, being a “green” concept. Starting with the EC project TELFONA and progressed by the CleanSky projects HiReLF and NLF-WingHiPer ETW has continuously improved its test capabilities with respect to laminar wing investigations up to flight Reynolds numbers. While NLF-Wing HiPer had impressively demonstrated the presently existing status allowing high quality performance measurements on large laminar wing half-models, HiLamBiz has proven the availability of these capabilities also for full models. The testing of full- and half-models can now be offered as a worldwide unique capability to engagements in the design of future laminar wing transport and business aircrafts by providing a qualified test facility.
Regarding exploitation and dissemination a press release will be published on the ETW website The performed Clean Sky project is going to be incorporated in the company profile listing ongoing and completed European research projects. As a major dissemination item a video clip is under production providing an overview on the performed project activities at ETW. Here, special emphasis is given in more detail to the development, application and processing of Temperature Sensitive Paint. This technique continuously enhanced to a mature status for cryogenic environment represents the key for laminar flow investigations in wind tunnels capable of flight Reynolds number simulations.
A further relevant activity is a more comprehensive article published in the periodically released “ETW-News” available for download on the ETW-website.
Despite of the fact that due to the confidentiality of data and results the scope of publishable content had to be approved, a representative of the responsible industrial Clean Sky partner has given an invited oral presentation at the SkyTech conference in San Diego in January 2016. Further publications are presently under discussion.

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