Intermittency of the azimuthal components of the sound radiated by subsonic jets

Resumo

We apply a filtering procedure, based on a continuous wavelet transform, to acoustic pressure and to the velocity field of an experimental Mach 0.6 jet in order to extract the intermittent bursts in the signals. With an intermittency measure based on this filter, it is possible to quantify the significance of these events in the total acoustic intensity. The acoustic pressure is measured by a ring of six azimuthal microphones, allowing decomposition of the sound field into azimuthal Fourier modes. The wavelet filtering is applied to each azimuthal mode, and the results show that the intermittent bursts occur mostly for the axisymmetric mode and for low polar angles. When high energy thresholds are used for the filtering, so as to retain only the most energetic bursts, more than 80 percent of the intermittent radiation is axisymmetric. © 2011 by P. Jordan. Published by the American Institute of Aeronautics and Astronautics, Inc.