Aircraft Noise: New Aspects on Lateral Sound Attenuation

Abstract

The lateral attenuation of sound for different aircraft was investigated with the help of a spectral three-dimensional model of the sound source. This model allows an independent analysis of the directivity of the sound source and the attenuation due to sound propagation, including ground effects. The sound immission at lateral receiver points has been calculated for different geometries and for hard and soft ground. Sound levels calculated with the three-dimensional model were compared with corresponding values resulting by the rotationally symmetric model implemented in Flula2. The differences arising from the two models were applied in a comparison of the sound directivity of six different aircraft with the engine installation corrections proposed in the revised Doc 29 3rd edition. For aircraft with fuselage-mounted engines good agreement was found between our results and the proposed engine installation corrections. Poor agreement was observed only for aircraft with wing-mounted engines. Moreover our results suggest that the lateral directivity may differ even for aircraft with identical engine configurations. In the second part of the paper the overall influence of the ground effect on A-weighted sound levels is analysed. Results for different receiver heights and ground impedances are presented.