Aeroacoustic characteristics of a shrouded helicopter tail rotor

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In order to reduce the aerodynamic noise emission from a shrouded tail rotor, an in-depth understanding of flow phenomena associated with the noise generation is necessary. For this purpose, a hybrid method combining unsteady Reynolds-averaged Navier-Stokes simulations with the Ffowcs Williams and Hawkings acoustic analogy is employed. The investigation exemplarily indicates that active flow control via boundary layer suction effectively eliminates the inlet flow distortion, thus reducing the far field noise level by about 5 dB in the forward flight condition.