High speed flight effects on noise propagation
Abstract
An experimental study to investigate the effects of source motion on sound propagation at high Mach numbers was devised to determine, in particular, if the large amplifications in the forward arc to high speeds, predicted by the 'convective amplification' factors normally used for low speeds, are realistic. An acoustic point source and a microphone, both immersed in flows up to a Mach number of 0.8, were used to obtain the convective amplification factors for comparison with predictions. The results confirmed the existence of high levels of noise propagating ahead of an aircraft flying at high speed. The commonly adopted prediction formula, namely (1  M sub 0 cos theta sub E) exp 4, was categorically confirmed by the data for frequencies up to 5 kHz and Mach numbers of 0.2 to 0.8. At higher frequencies, the predictions are followed up to emission angles of 120 deg, but then deviate downward towards the direction of flight.
 Publication:

25th AIAA Aerospace Sciences Meeting
 Pub Date:
 January 1987
 Bibcode:
 1987aiaa.meetR....B
 Keywords:

 Aerodynamic Noise;
 Aircraft Noise;
 High Speed;
 Noise Prediction (Aircraft);
 Noise Propagation;
 Data Acquisition;
 Data Reduction;
 Directivity;
 Far Fields;
 Fast Fourier Transformations;
 Mach Number;
 Microphones;
 Noise Measurement;
 Spectral Energy Distribution;
 Wind Tunnel Tests;
 Acoustics