Final Report Summary - DEMOS (DEsign and Manufacturing of a pitch-Oscillating System for gurney flap testing)
Executive Summary:
The DEMOS project aimed at developing an electromechanical set up for Wind Tunnel test.
The system is composed of a pitch oscillating system, an Active Gurney Flap (AGF) system and a balance system.
The baseline design for the pitch oscillating system is composed by a 2D airfoil (c=0.4m) driven by a 1FW3 Siemens torque motor remotely controlled to generate the desired pitch-oscillating motions. From a technical point of view, the pitch-oscillating system has been designed to generate a pitch-oscillating motion of the 2D model with the following laws:
Sinusoidal Law and Ramp Law
In order to study the effectiveness of the Active Gurney Flap (AGF) system in the mitigation of the dynamic stall problem, the 2D pitching oscillating model is equipped with an AGF (maximum protrusion length 1%c) installed on the lower surface of the model at the 95% of model chord.
The baseline configuration for the Active Gurney Flap (AGF) system is composed by a full span T-shape gurney flap driven by two magnetic Linear Motors (Siemens) remotely controlled to generate (during the pitch-oscillating motion of the airfoil) the following motion law:
Sinusoidal Law and Non Harmonic Law
DEMOS System is instrumented to perform loads measurement, steady and unsteady, using suitable load cells and is also instrumented to perform steady surface pressure measurements.
Project Context and Objectives:
The DEMOS project is structured in 4 work packages (WP):
WP1: Consortium management
This work package dealt the issues related to the administration of the project, e.g. cost and time controlling, management of meetings and reports, communication with the European Commission, with the Clean Sky GRC partner and with the WP and Task leaders.
WP2: Design, procurement, manufacturing and integration of Dynamic Systems
Pitch oscillating system
The design for the pitch oscillating system is a full span model with a model chord of 0.4m (the airfoil is installed wall to wall into the wind tunnel test section) activated by one power system (torque motor); motor performances has been evaluated taking into account aerodynamic loads and rotational inertial loads.
The airfoil has two interface disks, one for each side of the test section. One of these interface disk is connected to the pitching oscillating motor and the other one to a mechanical support.
The connection between profile and disks is done by means of bolts distributed on the root of the profile; stress is distributed on bolts and the connection is a multi point constrain.
A huge number of pipes is cabled for static pressure measurements on the model.
Concerning loads measurements a balance system (load cells) for lift, drag and momentum recovery has been adopted.
During the activity special care has been given to the design of support frames, those that connect the pitch-oscillating mechanism to the wind tunnel frame, in particular as far as it concerns the interface and the loads path.
Concerning the remote control system (RCS) for the pitching oscillation mechanism, it is able to remotely control several parameters depending on the motion law (sinusoidal or ramp) set for the airfoil:
For the sinusoidal law, the operator can control:
- the frequency (in the operative range)
- the mean angle of attack
- the oscillation amplitude
for the ramp law, the operator can control:
- ramp velocity
- the initial angle of attack
- the angle variation
Active Gurney Flap system
The pitching oscillating model is equipped with an Active Gurney Flap (AGF) able to perform harmonic or non harmonic motion laws with the possibility to modify: AGF frequency and AGF protrusion length.
The solution for the gurney flap system is a full span T-shape gurney flap driven by two magnetic linear motors (Siemens) located on the external face of interface disks.
From a technical point of view, the design of the AGF system involved several critical aspects:
the evaluation of AGF actuating force: has been considered the weight of the movable part, its inertia and the friction.
the Active Gurney Flap protrusion length: the maximum length of the gurney flap is limited by the model thickness at 95% of chord length (where the gurney flap is located); in particular for the geometry of the airfoil chosen from Agusta Westland the maximum protrusion length is 4mm (1%c).
Concerning the remote control system (RCS) for Active Gurney Flap mechanism, it is able to remotely control several parameter depending on the motion law of the AGF:
For the harmonic law, the operator can control:
- the motion frequency (the same of the pitch oscillating system)
- the protrusion length of the Gurney flap
for the non harmonic law, the operator can control:
- non harmonic period
- the protrusion length of the Gurney flap
- time instant of protruding and retracting of Gurney flap
Balance system
The Balance system allows measuring dynamic aerodynamic loads; aerodynamic forces on the airfoil can be measured by 2 bi-axial load cells for lift and drag force measurements and 1 torque load cell for the pitching moment measurement. Load cells are positioned in axis with the airfoil support shaft.
Despite load cells are usually calibrated for static loads, within the DEMOS project, they are used to perform both static and dynamic loads measurements. For this reason a dynamic calibration has been requested to the manufacturer.
Remote Control and Data Acquisition System
A control System (RCS) has been designed and manufactured to remote control and synchronize all DEMOS devices. The RCS during test in IWT (CIRA) will be located at a distance of 20 meters far from the wind tunnel test section so cables length is compliant with this requirement. RCS is equipped with an emergency button that is able to shut down the whole DEMOS system in case of unexpected problems.
WP3: Design and Manufacturing of the 2D Airfoil Model
The whole design activity has been performed in two phases: a design phase and a structural analysis phase, strictly connected each other. The first one dealt with 3D CAD models design and drawings whereas the second one was dedicated to structural (dynamics and aero-elasticity) and stress analyses. The partner in charge of manufacturing (Revoind Industriale) has provided support to the design team in order to prevent unfeasible technical choices by better addressing the entire design process in an efficient and proficient way.
The mechanical design was mainly focus on dynamic characteristics of the system.
This strategy has allowed reaching the required oscillating motion for obtaining the target in terms of dynamic performance. This goal has been achieved by means of an optimization process taking into account stiffness, inertia and strength characteristics of the entire system and, at the same time, by assuring the system safety.
2D model manufacturing
The model has been roughed through several stages in order to keep internal stresses as low as possible; more in detail, the raw material has been fixed on a dedicated fixture then four steps of roughing have been performed. In parallel with the previous task all the covers have been prepared on different machines.
Before the finishing phase, the covers’ slot have been suitably calibrated in such a way to avoid gaps between the slots themselves and the covers. Several checks have been performed in process in order to calibrate the gurney flap’s components such as the flap itself, the fixed and the interchangeable covers as well as to ensure the gurney flap sliding through the slot via different tools designed and manufactured ad hoc.
The model finishing has been done through two different steps (a pre-finishing and a finishing) with the covers mounted in place: in that way a uniform and a smooth surface had come out from the milling. The wing model has been checked during the manufacturing, by measuring the position of several points spread out on the surface, after the pre-finishing and the finishing phases respectively. The last performed task was the drilling of the pressure tap holes.
In order to fulfill the required roughness the model has been smoothed by hand using a fine sand paper.
WP4: DEMOS system Installation and Validation
After all parts have been manufactured, integrated and verified, the subsystems have been assembled on a dedicated test rig.
Preliminary ground tests have been performed in house, than DEMOS system has been shipped to CIRA facility where the system has been tested for acceptance.
Main objectives of DEMOS project are:
Design objectives:
Perform design of pitch-oscillating system
Perform design of the Gurney flap system
Perform design of the Balance System
Perform design of the Remote Control and Data Acquisition System
Perform the Design of the 2D Wind Tunnel Model
Procurement and Manufacturing objectives:
Procurement and manufacturing of pitch-oscillating assembly
Procurement and manufacturing of Active Gurney Flap assembly
Procurement and manufacturing of Balance System
Procurement and manufacturing of Remote Control and Data Acquisition System
Procurement and manufacturing of the 2D Wind Tunnel Model
Assembly and testing of the whole DEMOS System (Active Gurney Flap + 2D Model + Pitch-oscillating + RCS):
Assembly in house to perform a preliminary test and acceptance of DEMOS System
Installation of DEMOS System on the test rig
Test acceptance of DEMOS System on ground (system integrated on the test rig) and performance recovery
Project Results:
1 DEMOS System
1.1 Generality
The activities of the European research project CleanSky – JTI Green Rotorcraft “Innovative Rotor Blade” - GRC1, are aiming at the development of active and passive technologies for the design of innovative blades able to provide the greatest possible reduction in rotor noise and fuel consumption. In the framework of the project, task 1.1.5 “Testing of GRC Technology” is dedicated to component and/or wind tunnel testing of the technologies developed in the task 1.1.4 “Technology Development”. In particular, CIRA proposed a wind tunnel test campaign for the analysis of the dynamic stall over an airfoil both in clean configuration as well as equipped with an active Gurney flap (AGF). The overall experimental setup has been designed and manufactured by the DEMOS consortium under Cfp.
The pitch-oscillating system is composed by a wall-to-wall full span model (1.1m) with a chord of 0.4m activated by one power system (electric motor) with a reduction gear system able to generate the required pitch-oscillation motion around the model quarter-chord axis. The airfoil is integrated in the wind tunnel test section by means of two interface disks, one for each side of the test section, one connected to the pitch-oscillating motor and the other to a mechanical support. A general view of the pitch-oscillating system is reported in Figure 1 while Figure 2 shows the system integrated into the STS-IWT.
1.1.1 Pitching Oscillating System
From a technical point of view, according with the given requirements, the pitch-oscillating system has been designed to generate a pitch-oscillating motion of the 2D model with the following laws (see Figure 3).
The system technical capabilities in terms of pitching oscillating frequencies-amplitude angle operative envelope are graphically summarized in Figure 4. As expected, due to limitations related to the control/accuracy in the pitching angle well as to the allowable loads acting on the system, for value of fp higher than 9Hz, it is necessary to reduce the maximum allowable amplitude angle. Nevertheless, the system capabilities completely fulfil system requirements, see Figure 4 for sinusoidal law and Figure 5 for ramp law.
In particular for a given angle of attack, the system is able to cover the test conditions reported in Figure 5.
1.1.2 Active Gurney Flap System
In order to study the effectiveness of the Active Gurney Flap (AGF) system in the mitigation of the dynamic stall problem, the 2D pitching oscillating model is equipped with an AGF (maximum protrusion length 1%c) installed on the lower surface of the model at the 95% of model. The baseline configuration for the Active Gurney Flap (AGF) system is composed by a full span T-shape gurney flap driven by two magnetic Linear Motors (Siemens), see Figure 6.
From a technical point of view, according with the given requirements, the AGF system will be remotely controlled to generate (during the pitch-oscillating motion of the airfoil) the motion laws:
- sinusoidal Law (see Figure 7)
- non-harmonic deployment law (see Figure 7)
Similarly to the Pitching oscillating systems, some limitations related to the control/accuracy in the GF positioning as well as to the allowable loads acting on the system are envisaged for the GF non-harmonic motion. In particular, for values of frequency higher than 7Hz, it is necessary to increase the GF deployment/re-entry times.
The complete operative envelope for the AGF non harmonic motion law is reported in Table 1.
1.1.3 2D WT Model
The 2D WT model has been designed to meet an adequate structural integrity under aerodynamic and inertial loads as well as model modularity to allow the setting of the different configurations. An overview of the 2D model is reported in Figure 8. The airfoil has been designed to guarantee sufficient access to the instrumentation installed inside the model, by minimizing the number of removable components and mitigating the risk of steps, gaps and/or imperfections on external skin which can affect the natural flow development. At this regard, removable panels have been manufactured on the lower part of the surface, by leaving the upper surface of the model clean. The model has been designed to allow different configurations (Figure 8):
- Clean configuration (absence of GF),
- No. 3 model configurations having a fixed GF with 1%, 2%, 3% of protrusion length respectively, with GF located on the lower surface at 95% of the model chord,
- Model equipped with the AGF located on the lower surface at the 95% of the chord.
In order to measure the aerodynamic coefficients during steady tests (no oscillating motion) the model has been equipped with no. 57 steady pressure taps located on the upper and lower surface of the airfoil. The steady pressure taps are located streamwise at the mid-span of the model surface. Further steady pressure taps (no. 16 taps) are positioned along the model span to check the flow dimensionality in wind tunnel during tests.
The model has been designed to host a suitable number (44) of high frequency pressure transducers. High frequency pressure measurement points are located, on the airfoil, along a line parallel to the mid-span line (where steady pressure taps are located).
1.1.4 Material Data
The material used on DEMOS system are listed in Tab. 1.
1.2 Test Configuration for Acceptance Tests
Acceptance tests have been performed on ground. A special test rig has been therefore designed and manufactured for the purpose.(Figure 9). The test rig assembled with DEMOS system is shown in Figure 10.
2 ACCEPTANCE TESTS
2.1 Tests Acceptance
Acceptance tests are aimed to verify the correct functioning of the DEMOS sub-systems as well as to validate the overall DEMOS test capabilities. Table 2 summarizes the different cheeks categories.
2.2 CHECK A - DEMOS setup and Documentation
The following documentations has been shared/checked with/by the CIRA topic manager:
• DEMOS deliverables
• Drawings and CAD files
• Technical datasheets related to the engine motor, load cells, encoder and magnetic linear encoders
• Assembling, installation and maintenance procedures
While the 2D pitching oscillating model and the DEMOS system have been previously checked from a manufacturing and assembling point of view, the correct setting of the 2D model in terms pitch angle and the AGF protrusion length has been performed. See PHASE A ) BASIC GEOMETRICAL CHECKS.
2.3 CHECK B - Pitch-Oscillating system – Sinusoidal law
For different test conditions in terms of amplitude angle alfa_0 and pitching frequency, the pitching oscillating sinusoidal motion of the DEMOS system has been dynamically checked comparing the “real” DEMOS behavior with reference curves.
Figure 11 reports the performed test points within the nominal DEMOS operative envelope:
The testing procedure was aimed to check the Pitching oscillating signal as acquired by the NI-PXI-1044 compared with the reference sinusoidal curve. Checks have been performed in terms of pitching mean angle, maximum amplitude angle and pitching oscillating frequency. In particular, to qualitatively assess system performances the following constrains have been agreed with the topic manager:
2.4 CHECK C - Pitch-Oscillating system – Ramp law
Table 3 reports the checked test points (evidenced in red) within the nominal DEMOS operative envelope:
Note that the ramp starting angle (being not significant for this specific tests) has been fixed 0° for all test points. The testing procedure was aimed to check the quality of the ramp signal as acquired by the NI-PXI-1044 compared with the reference ramp curve. Checks have been performed in terms of ramp velocity and maximum amplitude angle. In particular, the following check conditions were agreed with the topic manager to qualitatively assess the system performances.
2.5 CHECK D – Active Gurney Flap
As reported in paragraph 1.1.2 the AGF system has been purposely designed to generate (during the pitch-oscillating motion of the airfoil) harmonic and non-harmonic motion laws. For each AGF motion law, the AGF system capabilities has been dynamically checked comparing “real” DEMOS behavior with reference curves.
Table 4 reports the checked test points:
The testing procedure was aimed to check the quality of the gurney flap signal as acquired by the NI-PXI-1044 compared with the reference ramp curve sinusoidal/non-harmonic curves. In particular, to qualitatively assess the system performances the following constrains have been agreed with the topic manager.
2.6 CHECK E - DEMOS Functional Tests
For different test conditions in terms of pitching oscillating and AGF parameters, the overall DEMOS system has been dynamically checked comparing the “real” DEMOS behavior with reference curves. The testing procedure was aimed to check the Pitching oscillating and active Gurney flap signals and protrusion lenght as acquired by the NI-PXI-1044 compared with the reference curve. Checks have been performed in terms of pitching mean angle, maximum amplitude angle and pitching oscillating frequency. In particular, to qualitatively assess system performances the following constrains have been agreed with the topic manager:
2.7 CHECK F – Load Cell Functional Tests
DEMOS bi-axial and torsional load cells have been dynamically checked in different test conditions in terms of pitching oscillating parameters. In this regard, calibrated weights (20Kg) have been installed on the model to simulate desired Lifts and pitching Moments during the pitching oscillating motion of the airfoil.
See PHASE F) Load Cell Functional Tests.
Several test points were checked see PHASE F) Load Cell Functional Tests.
Potential Impact:
DEMOS system has developed an advanced large-scale ground demonstrators able to characterize the dynamic stall phenomenon acting on a retreating rotor blade section. The DEMOS system will be, thus, used to validate the effectiveness of the Active Gurney Flap system in the mitigation of the dynamic stall problem in real flight conditions (referred to a medium size helicopter) giving benefits both in terms of drag and vibration reduction. This clearly represents the most effective way to reduce fuel usage, CO2/NOx emissions, and rotorcraft generated noise levels.
As far as it concerns the impact of DEMOS project, it will work on several different levels:
a) each partner that contributed to the project has had several advantages:
- Development of advanced technologies both for design and manufacturing for helicopters.
- A reference project that has shown competence at an international level by winning the CfP against international competitors as well as having successfully worked together as a multidisciplinary team.
- All partners in the consortium have had the opportunity to further increase their know-how by working in synergy and in an international context, therefore to enrich their expertise. Because of all partners are SMEs this can be further exploited by transferring IP generated in this project into industrial applications. DEMOS project has strengthen partner's competence in their field of work.
b) DEMOS system will contribute to increase the competitiveness of the European aeronautical industries because an upgrade of a facility (CIRA Icing Wind Tunnel) will be performed providing the possibility to test, the application of realistic flow control devices on helicopter blades for the control of the dynamic stall.
c) Regarding GRC JTI-Cleansky this project will help in solving important questions about the dynamic stall of helicopters offering the possibility to improve their aerodynamics performance. In fact, the project aim to investigate the gurney flap performance on a blade that realistically simulate the airfoil helicopter motion. The success of this type of devices will bring to its installation on the future helicopters. On an international level this increases Europe’s competitiveness in the development of the future helicopters having an improved behaviour to dynamic stall. A reduction of the dynamic stall phenomenon will contributes to further decrease the drag and the noise emission. These issues are therefore in line with the ACARE-goals.
DISSEMINATION ACTIVITIES
Up to now 2 different papers have been presented to international conferences:
- STAI (Supersonic Tunnel Association International) 122nd meeting in Paris/Modane, France 2014
title: DEsign and Manufacturing of a Pitch-Oscillating System for Gurney Flap Testing
- 6R Green Aviation Conference in Paris, France 2014
title: Design and Development of an innovative Pitch-Oscillating System for the study of the AGF Effectiveness in Mitigating the Dynamic stall Phenomenon
in both of them Mr. Antonello Marino (CIRA) presented the paper.
A paper in preparation will be presented to the international conference:
- AIDAA (Italian Association of Aeronautics and Astronautics) 23rd meeting in Turin, Italy 2015
title: DESIGN AND MANUFACTURING OF A PITCH-OSCILLATING SYSTEM FOR HELICOPTER ROTOR BLADE DYNAMIC STALL TESTING
Mr. Antonello Marino (CIRA) will present the paper.
SCIENTIFIC PUBLICATIONS
Some papers will be presented at the end of 2015 and during 2016 on the most important international Journals, such as:
- AIAA Journal
- Journal of Aircraft
List of Websites:
NHOE S.r.l.
Operative site:
Via Luigi Perna, 51
00142 Roma (RM) Italy
Tel. +39 06/83.60.83.49
Fax +39 06/91.65.93.92
http://www.nhoe.it/
Mr. Luca Flamini (Coordinator)
Tel. +39 06/83.60.83.49
Cell. +39 349/10.50.567
luca.flamini@nhoe.it
Revoind Industriale S.r.l.
Via Casale Marcangeli, 13
67063 - Oricola (AQ)
Loc. Colle Marcangeli Italy
Tel. +39 0863/99.59.97
http://www.revoind.it/
Mr. Paolo Lautizi
Chief Executive Officer
Tel. +39 0863/99.59.97
Cell. +39 331/62.47.985
paolo.lautizi@revoind.it
STEP SUD MARE S.r.l.
Operative site:
Via Ex Aeroporto c/o Consorzio Il Sole
80038 Pomigliano d'Arco (NA) Italy
Tel. +39 081/80.36.677
Fax +39 081/31.77.513
http://www.stepsudmare.com/
Mr. Marco Bellucci (Contact point)
Tel. +39 081/80.36.677
Cell. +39 393/98.67.172
marco.bellucci@stepsudmare.com
The DEMOS project aimed at developing an electromechanical set up for Wind Tunnel test.
The system is composed of a pitch oscillating system, an Active Gurney Flap (AGF) system and a balance system.
The baseline design for the pitch oscillating system is composed by a 2D airfoil (c=0.4m) driven by a 1FW3 Siemens torque motor remotely controlled to generate the desired pitch-oscillating motions. From a technical point of view, the pitch-oscillating system has been designed to generate a pitch-oscillating motion of the 2D model with the following laws:
Sinusoidal Law and Ramp Law
In order to study the effectiveness of the Active Gurney Flap (AGF) system in the mitigation of the dynamic stall problem, the 2D pitching oscillating model is equipped with an AGF (maximum protrusion length 1%c) installed on the lower surface of the model at the 95% of model chord.
The baseline configuration for the Active Gurney Flap (AGF) system is composed by a full span T-shape gurney flap driven by two magnetic Linear Motors (Siemens) remotely controlled to generate (during the pitch-oscillating motion of the airfoil) the following motion law:
Sinusoidal Law and Non Harmonic Law
DEMOS System is instrumented to perform loads measurement, steady and unsteady, using suitable load cells and is also instrumented to perform steady surface pressure measurements.
Project Context and Objectives:
The DEMOS project is structured in 4 work packages (WP):
WP1: Consortium management
This work package dealt the issues related to the administration of the project, e.g. cost and time controlling, management of meetings and reports, communication with the European Commission, with the Clean Sky GRC partner and with the WP and Task leaders.
WP2: Design, procurement, manufacturing and integration of Dynamic Systems
Pitch oscillating system
The design for the pitch oscillating system is a full span model with a model chord of 0.4m (the airfoil is installed wall to wall into the wind tunnel test section) activated by one power system (torque motor); motor performances has been evaluated taking into account aerodynamic loads and rotational inertial loads.
The airfoil has two interface disks, one for each side of the test section. One of these interface disk is connected to the pitching oscillating motor and the other one to a mechanical support.
The connection between profile and disks is done by means of bolts distributed on the root of the profile; stress is distributed on bolts and the connection is a multi point constrain.
A huge number of pipes is cabled for static pressure measurements on the model.
Concerning loads measurements a balance system (load cells) for lift, drag and momentum recovery has been adopted.
During the activity special care has been given to the design of support frames, those that connect the pitch-oscillating mechanism to the wind tunnel frame, in particular as far as it concerns the interface and the loads path.
Concerning the remote control system (RCS) for the pitching oscillation mechanism, it is able to remotely control several parameters depending on the motion law (sinusoidal or ramp) set for the airfoil:
For the sinusoidal law, the operator can control:
- the frequency (in the operative range)
- the mean angle of attack
- the oscillation amplitude
for the ramp law, the operator can control:
- ramp velocity
- the initial angle of attack
- the angle variation
Active Gurney Flap system
The pitching oscillating model is equipped with an Active Gurney Flap (AGF) able to perform harmonic or non harmonic motion laws with the possibility to modify: AGF frequency and AGF protrusion length.
The solution for the gurney flap system is a full span T-shape gurney flap driven by two magnetic linear motors (Siemens) located on the external face of interface disks.
From a technical point of view, the design of the AGF system involved several critical aspects:
the evaluation of AGF actuating force: has been considered the weight of the movable part, its inertia and the friction.
the Active Gurney Flap protrusion length: the maximum length of the gurney flap is limited by the model thickness at 95% of chord length (where the gurney flap is located); in particular for the geometry of the airfoil chosen from Agusta Westland the maximum protrusion length is 4mm (1%c).
Concerning the remote control system (RCS) for Active Gurney Flap mechanism, it is able to remotely control several parameter depending on the motion law of the AGF:
For the harmonic law, the operator can control:
- the motion frequency (the same of the pitch oscillating system)
- the protrusion length of the Gurney flap
for the non harmonic law, the operator can control:
- non harmonic period
- the protrusion length of the Gurney flap
- time instant of protruding and retracting of Gurney flap
Balance system
The Balance system allows measuring dynamic aerodynamic loads; aerodynamic forces on the airfoil can be measured by 2 bi-axial load cells for lift and drag force measurements and 1 torque load cell for the pitching moment measurement. Load cells are positioned in axis with the airfoil support shaft.
Despite load cells are usually calibrated for static loads, within the DEMOS project, they are used to perform both static and dynamic loads measurements. For this reason a dynamic calibration has been requested to the manufacturer.
Remote Control and Data Acquisition System
A control System (RCS) has been designed and manufactured to remote control and synchronize all DEMOS devices. The RCS during test in IWT (CIRA) will be located at a distance of 20 meters far from the wind tunnel test section so cables length is compliant with this requirement. RCS is equipped with an emergency button that is able to shut down the whole DEMOS system in case of unexpected problems.
WP3: Design and Manufacturing of the 2D Airfoil Model
The whole design activity has been performed in two phases: a design phase and a structural analysis phase, strictly connected each other. The first one dealt with 3D CAD models design and drawings whereas the second one was dedicated to structural (dynamics and aero-elasticity) and stress analyses. The partner in charge of manufacturing (Revoind Industriale) has provided support to the design team in order to prevent unfeasible technical choices by better addressing the entire design process in an efficient and proficient way.
The mechanical design was mainly focus on dynamic characteristics of the system.
This strategy has allowed reaching the required oscillating motion for obtaining the target in terms of dynamic performance. This goal has been achieved by means of an optimization process taking into account stiffness, inertia and strength characteristics of the entire system and, at the same time, by assuring the system safety.
2D model manufacturing
The model has been roughed through several stages in order to keep internal stresses as low as possible; more in detail, the raw material has been fixed on a dedicated fixture then four steps of roughing have been performed. In parallel with the previous task all the covers have been prepared on different machines.
Before the finishing phase, the covers’ slot have been suitably calibrated in such a way to avoid gaps between the slots themselves and the covers. Several checks have been performed in process in order to calibrate the gurney flap’s components such as the flap itself, the fixed and the interchangeable covers as well as to ensure the gurney flap sliding through the slot via different tools designed and manufactured ad hoc.
The model finishing has been done through two different steps (a pre-finishing and a finishing) with the covers mounted in place: in that way a uniform and a smooth surface had come out from the milling. The wing model has been checked during the manufacturing, by measuring the position of several points spread out on the surface, after the pre-finishing and the finishing phases respectively. The last performed task was the drilling of the pressure tap holes.
In order to fulfill the required roughness the model has been smoothed by hand using a fine sand paper.
WP4: DEMOS system Installation and Validation
After all parts have been manufactured, integrated and verified, the subsystems have been assembled on a dedicated test rig.
Preliminary ground tests have been performed in house, than DEMOS system has been shipped to CIRA facility where the system has been tested for acceptance.
Main objectives of DEMOS project are:
Design objectives:
Perform design of pitch-oscillating system
Perform design of the Gurney flap system
Perform design of the Balance System
Perform design of the Remote Control and Data Acquisition System
Perform the Design of the 2D Wind Tunnel Model
Procurement and Manufacturing objectives:
Procurement and manufacturing of pitch-oscillating assembly
Procurement and manufacturing of Active Gurney Flap assembly
Procurement and manufacturing of Balance System
Procurement and manufacturing of Remote Control and Data Acquisition System
Procurement and manufacturing of the 2D Wind Tunnel Model
Assembly and testing of the whole DEMOS System (Active Gurney Flap + 2D Model + Pitch-oscillating + RCS):
Assembly in house to perform a preliminary test and acceptance of DEMOS System
Installation of DEMOS System on the test rig
Test acceptance of DEMOS System on ground (system integrated on the test rig) and performance recovery
Project Results:
1 DEMOS System
1.1 Generality
The activities of the European research project CleanSky – JTI Green Rotorcraft “Innovative Rotor Blade” - GRC1, are aiming at the development of active and passive technologies for the design of innovative blades able to provide the greatest possible reduction in rotor noise and fuel consumption. In the framework of the project, task 1.1.5 “Testing of GRC Technology” is dedicated to component and/or wind tunnel testing of the technologies developed in the task 1.1.4 “Technology Development”. In particular, CIRA proposed a wind tunnel test campaign for the analysis of the dynamic stall over an airfoil both in clean configuration as well as equipped with an active Gurney flap (AGF). The overall experimental setup has been designed and manufactured by the DEMOS consortium under Cfp.
The pitch-oscillating system is composed by a wall-to-wall full span model (1.1m) with a chord of 0.4m activated by one power system (electric motor) with a reduction gear system able to generate the required pitch-oscillation motion around the model quarter-chord axis. The airfoil is integrated in the wind tunnel test section by means of two interface disks, one for each side of the test section, one connected to the pitch-oscillating motor and the other to a mechanical support. A general view of the pitch-oscillating system is reported in Figure 1 while Figure 2 shows the system integrated into the STS-IWT.
1.1.1 Pitching Oscillating System
From a technical point of view, according with the given requirements, the pitch-oscillating system has been designed to generate a pitch-oscillating motion of the 2D model with the following laws (see Figure 3).
The system technical capabilities in terms of pitching oscillating frequencies-amplitude angle operative envelope are graphically summarized in Figure 4. As expected, due to limitations related to the control/accuracy in the pitching angle well as to the allowable loads acting on the system, for value of fp higher than 9Hz, it is necessary to reduce the maximum allowable amplitude angle. Nevertheless, the system capabilities completely fulfil system requirements, see Figure 4 for sinusoidal law and Figure 5 for ramp law.
In particular for a given angle of attack, the system is able to cover the test conditions reported in Figure 5.
1.1.2 Active Gurney Flap System
In order to study the effectiveness of the Active Gurney Flap (AGF) system in the mitigation of the dynamic stall problem, the 2D pitching oscillating model is equipped with an AGF (maximum protrusion length 1%c) installed on the lower surface of the model at the 95% of model. The baseline configuration for the Active Gurney Flap (AGF) system is composed by a full span T-shape gurney flap driven by two magnetic Linear Motors (Siemens), see Figure 6.
From a technical point of view, according with the given requirements, the AGF system will be remotely controlled to generate (during the pitch-oscillating motion of the airfoil) the motion laws:
- sinusoidal Law (see Figure 7)
- non-harmonic deployment law (see Figure 7)
Similarly to the Pitching oscillating systems, some limitations related to the control/accuracy in the GF positioning as well as to the allowable loads acting on the system are envisaged for the GF non-harmonic motion. In particular, for values of frequency higher than 7Hz, it is necessary to increase the GF deployment/re-entry times.
The complete operative envelope for the AGF non harmonic motion law is reported in Table 1.
1.1.3 2D WT Model
The 2D WT model has been designed to meet an adequate structural integrity under aerodynamic and inertial loads as well as model modularity to allow the setting of the different configurations. An overview of the 2D model is reported in Figure 8. The airfoil has been designed to guarantee sufficient access to the instrumentation installed inside the model, by minimizing the number of removable components and mitigating the risk of steps, gaps and/or imperfections on external skin which can affect the natural flow development. At this regard, removable panels have been manufactured on the lower part of the surface, by leaving the upper surface of the model clean. The model has been designed to allow different configurations (Figure 8):
- Clean configuration (absence of GF),
- No. 3 model configurations having a fixed GF with 1%, 2%, 3% of protrusion length respectively, with GF located on the lower surface at 95% of the model chord,
- Model equipped with the AGF located on the lower surface at the 95% of the chord.
In order to measure the aerodynamic coefficients during steady tests (no oscillating motion) the model has been equipped with no. 57 steady pressure taps located on the upper and lower surface of the airfoil. The steady pressure taps are located streamwise at the mid-span of the model surface. Further steady pressure taps (no. 16 taps) are positioned along the model span to check the flow dimensionality in wind tunnel during tests.
The model has been designed to host a suitable number (44) of high frequency pressure transducers. High frequency pressure measurement points are located, on the airfoil, along a line parallel to the mid-span line (where steady pressure taps are located).
1.1.4 Material Data
The material used on DEMOS system are listed in Tab. 1.
1.2 Test Configuration for Acceptance Tests
Acceptance tests have been performed on ground. A special test rig has been therefore designed and manufactured for the purpose.(Figure 9). The test rig assembled with DEMOS system is shown in Figure 10.
2 ACCEPTANCE TESTS
2.1 Tests Acceptance
Acceptance tests are aimed to verify the correct functioning of the DEMOS sub-systems as well as to validate the overall DEMOS test capabilities. Table 2 summarizes the different cheeks categories.
2.2 CHECK A - DEMOS setup and Documentation
The following documentations has been shared/checked with/by the CIRA topic manager:
• DEMOS deliverables
• Drawings and CAD files
• Technical datasheets related to the engine motor, load cells, encoder and magnetic linear encoders
• Assembling, installation and maintenance procedures
While the 2D pitching oscillating model and the DEMOS system have been previously checked from a manufacturing and assembling point of view, the correct setting of the 2D model in terms pitch angle and the AGF protrusion length has been performed. See PHASE A ) BASIC GEOMETRICAL CHECKS.
2.3 CHECK B - Pitch-Oscillating system – Sinusoidal law
For different test conditions in terms of amplitude angle alfa_0 and pitching frequency, the pitching oscillating sinusoidal motion of the DEMOS system has been dynamically checked comparing the “real” DEMOS behavior with reference curves.
Figure 11 reports the performed test points within the nominal DEMOS operative envelope:
The testing procedure was aimed to check the Pitching oscillating signal as acquired by the NI-PXI-1044 compared with the reference sinusoidal curve. Checks have been performed in terms of pitching mean angle, maximum amplitude angle and pitching oscillating frequency. In particular, to qualitatively assess system performances the following constrains have been agreed with the topic manager:
2.4 CHECK C - Pitch-Oscillating system – Ramp law
Table 3 reports the checked test points (evidenced in red) within the nominal DEMOS operative envelope:
Note that the ramp starting angle (being not significant for this specific tests) has been fixed 0° for all test points. The testing procedure was aimed to check the quality of the ramp signal as acquired by the NI-PXI-1044 compared with the reference ramp curve. Checks have been performed in terms of ramp velocity and maximum amplitude angle. In particular, the following check conditions were agreed with the topic manager to qualitatively assess the system performances.
2.5 CHECK D – Active Gurney Flap
As reported in paragraph 1.1.2 the AGF system has been purposely designed to generate (during the pitch-oscillating motion of the airfoil) harmonic and non-harmonic motion laws. For each AGF motion law, the AGF system capabilities has been dynamically checked comparing “real” DEMOS behavior with reference curves.
Table 4 reports the checked test points:
The testing procedure was aimed to check the quality of the gurney flap signal as acquired by the NI-PXI-1044 compared with the reference ramp curve sinusoidal/non-harmonic curves. In particular, to qualitatively assess the system performances the following constrains have been agreed with the topic manager.
2.6 CHECK E - DEMOS Functional Tests
For different test conditions in terms of pitching oscillating and AGF parameters, the overall DEMOS system has been dynamically checked comparing the “real” DEMOS behavior with reference curves. The testing procedure was aimed to check the Pitching oscillating and active Gurney flap signals and protrusion lenght as acquired by the NI-PXI-1044 compared with the reference curve. Checks have been performed in terms of pitching mean angle, maximum amplitude angle and pitching oscillating frequency. In particular, to qualitatively assess system performances the following constrains have been agreed with the topic manager:
2.7 CHECK F – Load Cell Functional Tests
DEMOS bi-axial and torsional load cells have been dynamically checked in different test conditions in terms of pitching oscillating parameters. In this regard, calibrated weights (20Kg) have been installed on the model to simulate desired Lifts and pitching Moments during the pitching oscillating motion of the airfoil.
See PHASE F) Load Cell Functional Tests.
Several test points were checked see PHASE F) Load Cell Functional Tests.
Potential Impact:
DEMOS system has developed an advanced large-scale ground demonstrators able to characterize the dynamic stall phenomenon acting on a retreating rotor blade section. The DEMOS system will be, thus, used to validate the effectiveness of the Active Gurney Flap system in the mitigation of the dynamic stall problem in real flight conditions (referred to a medium size helicopter) giving benefits both in terms of drag and vibration reduction. This clearly represents the most effective way to reduce fuel usage, CO2/NOx emissions, and rotorcraft generated noise levels.
As far as it concerns the impact of DEMOS project, it will work on several different levels:
a) each partner that contributed to the project has had several advantages:
- Development of advanced technologies both for design and manufacturing for helicopters.
- A reference project that has shown competence at an international level by winning the CfP against international competitors as well as having successfully worked together as a multidisciplinary team.
- All partners in the consortium have had the opportunity to further increase their know-how by working in synergy and in an international context, therefore to enrich their expertise. Because of all partners are SMEs this can be further exploited by transferring IP generated in this project into industrial applications. DEMOS project has strengthen partner's competence in their field of work.
b) DEMOS system will contribute to increase the competitiveness of the European aeronautical industries because an upgrade of a facility (CIRA Icing Wind Tunnel) will be performed providing the possibility to test, the application of realistic flow control devices on helicopter blades for the control of the dynamic stall.
c) Regarding GRC JTI-Cleansky this project will help in solving important questions about the dynamic stall of helicopters offering the possibility to improve their aerodynamics performance. In fact, the project aim to investigate the gurney flap performance on a blade that realistically simulate the airfoil helicopter motion. The success of this type of devices will bring to its installation on the future helicopters. On an international level this increases Europe’s competitiveness in the development of the future helicopters having an improved behaviour to dynamic stall. A reduction of the dynamic stall phenomenon will contributes to further decrease the drag and the noise emission. These issues are therefore in line with the ACARE-goals.
DISSEMINATION ACTIVITIES
Up to now 2 different papers have been presented to international conferences:
- STAI (Supersonic Tunnel Association International) 122nd meeting in Paris/Modane, France 2014
title: DEsign and Manufacturing of a Pitch-Oscillating System for Gurney Flap Testing
- 6R Green Aviation Conference in Paris, France 2014
title: Design and Development of an innovative Pitch-Oscillating System for the study of the AGF Effectiveness in Mitigating the Dynamic stall Phenomenon
in both of them Mr. Antonello Marino (CIRA) presented the paper.
A paper in preparation will be presented to the international conference:
- AIDAA (Italian Association of Aeronautics and Astronautics) 23rd meeting in Turin, Italy 2015
title: DESIGN AND MANUFACTURING OF A PITCH-OSCILLATING SYSTEM FOR HELICOPTER ROTOR BLADE DYNAMIC STALL TESTING
Mr. Antonello Marino (CIRA) will present the paper.
SCIENTIFIC PUBLICATIONS
Some papers will be presented at the end of 2015 and during 2016 on the most important international Journals, such as:
- AIAA Journal
- Journal of Aircraft
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