Analysis of far-field coherence of subsonic jet noise

Abstract

© 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Measurements of the sound radiated by subsonic jets with Mach numbers ranging from 0.3 to 0.9 are carried out, with a view to examining the two-point statistics of the far-field sound, and, in particular, the two-point coherence. It is seen that the cross-correlation between neighbouring microphones in a polar arc decreases with increasing Mach number. The same happens with the two-point coherence, a feature predicted by wave-packet models including jitter.1 The far-field coherence results are shown to be consistent with the mentioned wave-packet model. In particular, a collapse of coherence results for all Mach numbers is obtained once measurements are plotted as a function of the angular dependence expected by the model. The results show that the far-field is consistent with a jittering wave-packet source model, which explains the observed decrease of coherence for higher Mach numbers.