It is proposed in this research programme to optimize the pylon shape of a Counter Rotating Open Rotor (CROR) propeller and its embedded flow control system, in order to reduce the noise emission through pylon wake attenuation, by means of advanced experimental methodology, such as 3CHD-PIV, adapted to in-flight tests.
It is proposed to decompose the project into subtasks of increasing complexity. Each task falls within the scope of either ISAE or AAE. Thus, ISAE and AAE offer to join their different skills to elaborate a work-plan based on well-defined responsibilities.
The subtasks are summarized below:
- Optimization of the flow control device for the 2D pylon.
- Detailed design and manufacturing of the 2D type pylon wind tunnel model and its instrumentation.
- Low speed wind tunnel tests of the 2D pylon without open rotor, in a non vibrating environment, including parametric studies on the advanced flow control devices parameters and boundary layer transition effects.
- Comparison between experimental results and numerical prediction. Analysis of the results, physical understanding and recommendation for further improvement of the concept.
- Definition of vibration environment simulators (VES), in compliance with Airbus inputs from in flight tests.
- Detailed definition and manufacturing of VES applicable to the different PIV subsystems (cameras, laser, laser sheet generation devices) as implemented in the wind tunnel.
- Characterization of the limits of the vibration spectrum supported by the PIV subsystems, beyond which vibration-induced errors on PIV measurements impose corrections on raw data or on PIV subsystems attitude.
- Definition of correction methodology to correct PIV measurements, through raw data manipulation or PIV subsystems vibration attenuation, in order to recover a non disturbed PIV measurement.
- Validation of the correction methodology in wind tunnel by replicating subtask 3.
Clean Sky, the most ambitious European aerospace research programme ever, is focused on developing future concepts for aircraft with substantially reduced environmental impact. The CROR engine with uncased blades on two stages that rotate in opposite directions could cut fuel consumption and associated carbon dioxide emissions by 30 %. Despite its promise, previous development efforts have been hampered by higher noise levels.
EU-funded scientists from the ISAE-SUPAERO and Aéroconseil consortium, in association with Airbus, have been working on the project 'Advanced pylon noise reduction design and characterization through flight worthy PIV' (ACcTIOM). They have addressed this challenge by inventing new active flow control strategies aiming at minimising CROR-induced noise through a combination of aerodynamic optimisation of the propeller pylon shape and the development of an innovative active flow control system to erase the pylon wake before it interacts with the CROR blades.
During the first phase of the ACcTIOM project, the active flow control system, a combination of scooping/blowing strategies, was designed and optimised via a coupled approach combining exhaustive Computational Fluid Dynamics (Reynolds-averaged Navier-Stokes) simulations and test bench experiments. The wind tunnel (WT) test model of the CROR pylon, including equipment, instrumentation and equipped with the so-developed embedded prototype of the active flow control system, was finalised as well.
Exhaustive series of WT tests were completed for the operating validation of the WT model of the CROR pylon equipped with its embedded flow control system, on-board instrumentation, and data acquisition and control systems. The WT tests were comprised of wall pressure coefficient taps, transverse profiles of total pressure at various streamwise and spanwise positions in the wake of the pylon and on stereoscopic Particle Image Velocimetry (3C-PIV) transverse plane measurements at various streamwise positions in the wake of the pylon. These WT tests confirmed the strong efficiency of the developed embedded active flow control system in erasing the pylon wake, when operated in the region of optimal flow control parameters numerically and experimentally identified by the consortium scientists in charge of ACcTIOM. They have also highlighted the robustness of the flow control system in mitigating the wake of the pylon despite moderate variations of the flow conditions. This embedded active flow control system acts as an aerodynamic stealth system.
In the second phase of the ACcTIOM project, the objectives of the consortium scientists have been to develop advanced optical methodologies, based on vibration-controlled 3C-PIV, able to be in-flight operated and dedicated to the validation of the efficiency of the above mentioned CROR pylon design and associated active flow control system in erasing the pylon wake on the CROR-propelled Flying Test Bench (FTB). To this avail they have first developed numerical models of the expected vibratory environment inside the cabin of the FTB. These models have permitted to design experimental test benches, hereafter denoted Vibrational Environment Simulator or VES, able to reproduce, in laboratory, the vibrational environment of the FTB and its influence on the optical misalignment of the different 3C-PIV subsystems and resulting 3C-PIV measurement issues. Further, the team has defined the hybrid, passive/active, vibration control strategy and required equipment for the design of a Vibration Correction Methodology (VCM) dedicated to the implementation and confident operation of in-flight 3C-PIV. The VCM will attenuate vibrations experienced by the 3C-PIV subsystems under VES influence during testing.
ACcTIOM technologies for active reduction of noise associated with the innovative CROR engine design will speed up certification and commercialisation of more energy-efficient aircraft. In-flight use of advanced vibration-controlled 3C-PIV will enhance understanding of mechanisms in other airframe elements as well. The outcomes should significantly reduce the environmental impact of air travel.