Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

FP7

ACcTIOM Streszczenie raportu

Project ID: 298187
Źródło dofinansowania: FP7-JTI
Kraj: France

Periodic Report Summary 1 - ACCTIOM (Advanced Pylon Noise Reduction Design and Characterization through flight worthy PIV)

Project Context and Objectives:
This 37-month research project is part of the JTI-CS-2011-2-SFWA programme. It first aims to optimize the pylon shape of a Counter Rotating Open Rotor (CROR) propeller and to design an associated active flow control system dedicated to the reduction of noise emission through the mitigation of the pylon wake. Second, it aims to develop an advanced experimental methodology, based on vibration-controlled stereoscopic Particle Image Velocimetry (3C-PIV), able to be flight-operated and that will serve in validating the above mentioned pylon design and associated active flow control system when operated on the Flying Test Bench (FTB).
In this context, the ACcTIOM project is divided into 6 work packages hereafter denoted WP#. The aerodynamic design of the pylon and of the active flow control system is conducted in WP2. WP3 is dedicated to the conception and manufacturing of the pylon and of its associated active flow control system, and to the validation of its efficiency in mitigating the pylon wake, through wind tunnel (WT) tests. WP4 and WP5 are devoted to the definition of hybrid -passive/active, software/hardware- correction methodologies for vibration-disturbed PIV measurements, and to their validation through WT tests in vibrating environment respectively. Two complementary work packages are dedicated to the coordination of the project and of the ISAE/AAE consortium (WP1), and to the project valorization (WP6) respectively.

Project Results:
WP2 tasks performed

During this first period and following Airbus recommendations in terms of integration and manufacturing constraints as well as robustness in a given flight domain with a low drag impact, the flow control strategy to be developed for the pylon wake attenuation has first been identified. It will consist in an innovative scooping/blowing coupled active flow control system. Due to pylon mechanical constraints, the implementation area of the flow control system has to be restricted to the aft part of the pylon, beyond a downstream-to-stagnation point position equal to 75% of the pylon chord c. Furthermore the active flow control system has to be optimized for standard takeoff and landing flight conditions, i.e. for a Mach number M=0.23 at ambient pressure (101325Pa) and temperature (288K), a Reynolds number per meter equal to 4.3x10^6, with no incidence of the pylon relative to the upstream airflow (alpha = 0°).
The evaluation of the optimization process of the design of the aft part of the pylon and of the associated flow control system is based on the computation of the C2 acoustic criterion. This criterion quantifies the distortion of the total pressure profile measured or numerically computed at a given transverse station in the wake of the pylon. It has to range below the target value C2t = 0.25 x 10^-10 when computed at the location of the first blade stage of the CROR (X/c=15%). Here it is computed at midway between the pylon trailing edge and the first blade stage of the CROR (X/c=7.5%, vertical blue line on figure (a)). This imposes a more critical and binding optimization process.
First, on the basis of the original 1:1 scaled reference geometry of the pylon provided by Airbus (black profile on figure (a)), the wake resulting from the {M= 0.23, Re/m = 4.3 x 10^6, alpha=0°} airflow was numerically predicted and the corresponding C2 criterion, computed at X/c=7.5%, was estimated to 6 x 10^-8. This clearly demonstrates that the reference geometry of the CROR pylon fails to comply with imposed vibro acoustic requirements. Complementary series of Reynolds Average Navier Stokes (RANS) computations were then conducted. They have permitted to define a new 1:2 chord-based scaled geometry as the reference geometry of the ACcTIOM project (red profile on figure (a)).
This new geometry takes over the key characteristics from the aft part of the original Airbus geometry. Moreover its global specifications comply with the WT size and maximum flow velocity constraints.
This new geometry, from now on considered as the reference (or baseline) geometry for the ACcTIOM project (hereafter denoted WTT geometry), ensures the reliability of the optimization process. Moreover the geometrical coherence of its aft part with the original Airbus geometry guarantees flow control system integration similarity between the WT model and the future 1:1 scaled aircraft-dedicated pylon, and optimization consistency for the design, positioning and operability parameters of both the scooping and blowing devices.
The optimization process was then determined. It relies on 2D RANS computations with a Spalart- Allmaras turbulence model (CFD++ software) of the {M= 0.23, Re/m = 4.3 x 10^6, alpha=0°} airflow past the 1:2 scaled reference geometry. Several input parameters are considered for the optimization process: streamwise and normal-to-wall positions of the scooping and blowing devices, height of the scooping and blowing slots, boat tail angle and size of the trailing edge (design optimization parameters of the aft part of the pylon), scooping and blowing mass flow rates. Complementary prospective concepts are also studied, such as trailing edge blowing or the influence of the blowing jet temperature on the wake. The optimum configuration is then selected by minimizing the following criteria:
- value of the acoustic criterion C2 computed at the streamwise position X/c = 7.5% downstream of the trailing edge of the WTT geometry,
- WTT model and full-scale, aircraft-dedicated pylon integration constraints,
- drag impact,
- optimum scooping and blowing mass flow rates (MFR).
Once this optimum configuration has been determined for the {M= 0.23, Re/m = 4.3 x 10^6, alpha=0°} airflow, the optimum scooping and blowing mass flow rates are then estimated for the WT airflow conditions {M= 0.12, Re/m = 2.7 x 10^6, alpha=0°}. This complementary database will complete the validation of the CFD approach through the correlation between computational results and WTT measurements.
The aerodynamic shapes of the WTT geometry and of the scooping and blowing devices obtained from the optimization process are illustrated on figure (b). The location of these devices has been determined to 80% of chord c for the scooping inlet slot and 95% of chord c for the blowing outlet slot.
Considering the {M= 0.23, Re/m = 4.3 x 10^6, alpha=0°} flow conditions, the optimum scooping MFR (required to ingest the boundary layer) is 3.4kg/s/m (global mass flow rate for both sides of the WTT geometry). The optimum blowing MFR value associated with the above-mentioned optimum scooping MFR is 0.4kg/s/m. It is interesting to notice the high ratio between blowing and scooping optimum MFR. This tends to indicate that a flow control system that would solely use the energy of the blowing MFR in order to generate the scooping MFR, through a Venturi effect apparatus for instance would probably not be sufficiently efficient to ensure the target scooping MFR. One should also notice the high sensitivity of the C2 criterion to blowing MFR variations. As a consequence the target maximum value C2t may not be guaranteed beyond blowing MFR variation the order of ±4g/s/m around the optimum value. The operational MFR has thus to be precisely managed.
Considering the optimized geometry and optimum scooping and blowing MFR, the resulting WTT geometry wake topology, in terms of normalized total pressure transverse profiles at X/c = 7.5% and X/c = 15% is presented on figure (c) (red curve: actuation off, green curve: actuation on). Corresponding C2 criteria are also provided.
The actuation of the flow control system with the optimized parameters (size, positioning, design of the scooping and blowing devices, MFR, etc.) promotes a dramatic mitigation of the distortion of the wake. It results to very low C2 values, much lower than the target value C2t.
This promising results tend to indicate that the proposed aft part design of the CROR-propeller pylon associated with the innovative scooping/blowing active flow control system developed during this WP will be efficient in complying with the Airbus acoustic requirements.

WP3 tasks performed

In agreement with the previously determined flow control strategy and due to ISAE/S4 WT maximum flow velocity conditions {M=0.12 at ambient pressure (101325Pa) and temperature (288K), Re/m = 2.7 x 10^6, alpha}, WTT geometry has also been numerically assessed at Mach 0.12 (2D computations) with adapted scooping and blowing MFR in order to provide relevant data for the correlation with WTT measurements. Results reveal that this configuration is still efficient regarding the target value C2t. However, because of scooping operational limitation imposed by the S4 WT, the total pressure profiles (not presented here) exhibit two local pressure drop peaks. Ideally scooping MFR should be increased such as to suppress these peaks. However this non-strictly flattened total pressure profile is not an issue for the future definition of the flight-operated optimized pylon and flow control system. The present configuration is dedicated first to the validation of the scooping/blowing system design and to the definition of its modus operandi, second to the validation of the numerical approach through the correlation of CFD database with WT experimental results.
The proposed design of the WT model is illustrated on figure (d). It consists in a 1.5m wingspan, 1.5m chord length profile complemented with two tip-wall sets at the two ends of the model. In order to ensure uniform flow rates of the scooping and blowing devices along the span of the model, the scooping and blowing device slots are split into separated flow control modules of shorter span, distributed along the wingspan of the model. The WT model is thus primarily composed of three flow control system-equipped modules, each 333mm span, positioned in the central part of the WT model. The advantage of this strategy relies in its possible transposition to the future aircraft-dedicated pylon. Moreover, since the aircraft-dedicated pylon will probably not incorporate scooping and blowing slots on its whole span, due to integration issues close to the fuselage and nacelle junctions, it is interesting to reproduce and to study the potential impact of the local mixing of controlled/non controlled wakes via experiments on the WT model. To this avail 2 complementary passive end-modules ensure the junction of the active part of the pylon with the 2 tip-wall sets.
The initial objectives of the ACcTIOM project, WP2 and WP3, as defined in the Description of Work (DoW) associated with Grant Agreement n°298187, were to design an optimized pylon shape and a dedicated active flow control system able to mitigate the wake of the CROR-propeller pylon in order to comply with Airbus acoustic requirements for {M= 0.23, Re/m = 4.3 x 10^6, alpha=0°} flow conditions. However, considering actual low velocity flight conditions, such as those encountered during takeoff and landing phases, it is legitimate to consider that the pylon can temporarily be submitted to locally slipped airflow. In order to guarantee the profitability of the present work for the future CROR-propelled aircraft, the consortium ISAE/AAE has accepted Airbus request to partially re define the specifications of the WT model into a more complex operability domain imposed by {M= 0.23, Re/m = 4.3 x 10^6, alpha=”few °”} slipped flows, out of the scope of the project at its starting date. This re orientation of the demonstrator specifications has increased its technical complexity, in particular in terms of scooping/blowing modules internal design, parts of the aeraulics circuits, pneumatics elements and MFR control.
In order to comply with potentially slipped flow configurations, the differential treatment of the two sides of the pylon in terms of flow control strategy results in the splitting of each active flow control system-equipped module into two sub-modules, distributed on each side of the pylon (illustrated on figure (e)). As a consequence the active control of the wake is provided thanks to 12 devices, divided into 2 groups dedicated to the scooping and blowing respectively. Each group is thus composed of 6 identical devices, independent from each other and managed thanks to independent control valves. The aeraulics circuits of both scooping and blowing devices were optimized via 3D RANS computations in order to minimize the pressure losses from the supply valves of the scooping and blowing (vacuum valves and compressed air valves respectively) up to the scooping and blowing slots.
The WT model on-board instrumentation consists in 163 wall pressure taps, uniformly distributed along 4 lines, positioned at mid span of each of the 3 active flow control system-equipped modules and of one of the passive module, along the chord and on both sides of the WT model. Each scooping and blowing device is equipped with a total temperature sensor. The blowing devices are also equipped with total pressure sensors. This instrumentation will allow characterizing the pressure distribution on the surface of the WT model, for CFD/WTT correlation purposes. It will also serve the scooping and blowing MFR monitoring and will permit to check for scooping and blowing homogeneity along the span of each active module.

WP6 tasks performed

At the completion of WP2, an exhaustive description of the work achieved and results was provided in the deliverable D2.1 delivered to the JU the 24th of August 2012. A complementary technical note TN1 was provided at the same date. This report aimed to describe, in the form of guidelines, the optimization process of the aft pylon shape and of the flow control system. A second technical note was provided to Airbus the 21th of July 2012. It consisted in a design guide describing the design and conception of the WT model.
At last, the strategic monitoring for patent licensing of the optimized, flow control system-equipped CROR-propeller pylon has been initiated.

Potential Impact:
As previously mentioned, the expected final results are dual. First the definition, manufacturing and validation of an optimized CROR-propeller pylon shape and of its associated active flow control system will permit to mitigate the wake of the pylon before it impacts the first blade stage of the CROR propeller. As such it should alleviate the fluid-structure interaction-induced emission of noise of the future CROR-propelled aircraft. This work will eventually serve the potential certification of this new generation of more energy-efficient aircrafts. Second, the development of an advanced experimental methodology, based on vibration-controlled stereoscopic Particle Image Velocimetry (3C-PIV) able to be flight-operated, will enhance knowledge on the mechanisms driving the wake mitigation by the active flow control system. It will also participate to the certification process of this innovative flow control technology. Moreover mastery of this advanced measurement technique in harsh flight conditions will have widespread applications both for the characterization of complex airflows past specific airframe elements (wing/pylon/nacelle interaction for instance) or for other certification issues.

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