Combined aeroacoustic and flow diagnostic analysis of the motion induced sound generation by an oscillating airfoil with active flap

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Flow induced noise generated by wing profiles with unsteady change of the angle of attack is of crucial importance for a variety of open questions in the field of aeroacoustics. Examples include rotor blades of pitch-controlled wind turbines and active trailing edge flaps for flow control. By the movement of the wings or blades, the trajectories of sound producing flow structures vary and these flow structures interact with the moving wing. This complicates both the localization and characterization of the sound source as well as the modelling of the sound generation process. Within the framework of the proposed project here a flow diagnostic methodology, recently developed by one of the applicants, has to be extended to the application for the aeroacoustic investigation of moving wings. The methodology combines microphone measurements in the acoustic far-field with flow measurements and provides insights into the spatial and temporal development of flow structures, being involved in the sound generation process. The procedure is based on the calculation of the correlation coefficient between turbulent fluctuations and pressure fluctuations, which radiate as sound waves in the acoustic far field. The trajectories of aeroacoustic relevant flow structures can be identified by a space-time analysis of the resulting coefficient matrix. The novelty of this project is the application of this methodology to the aeroacoustic phenomenon of complex flows around moving wings with variable trailing edge flap. The correlation coefficients are strongly influenced by the movement of the wing. Despite a clear interpretation of the correlation coefficients and the characterization of sound production, a detailed analysis of the characteristic coherent flow structures and their dynamics is necessary. The ultimate goal of this project is to make a contribution to an improved prediction-model for aerodynamically induced noise of moving wings. This should include both the aerodynamic characterization of the noise and the influenced to the sound propagation by the moving wing.