Analysis of contra rotating open rotors flyover noise data by beamforming techniques

For the preparation of forthcoming flyover CROR noise tests, CROR noise data are first simulated by a hybrid CFD/CAA solver and are then analyzed by a beamforming technique. The CROR is a realistic full-size CROR flying over a ground microphone array in take-off conditions. For the blade passage frequency of each rotor, the de-Dopplerized spectral density is well recovered by the beamforming technique from the microphone array data. However, the spectral density at the interaction frequencies is wrongly estimated. In this case, the beamforming technique, based on an acoustic model consisting of uncorrelated monopoles, should be modified in order to take into account the strong correlation of the acoustic sources between each rotor.