A priori assessment of the effect of small scales on sound radiation from a subsonic axisymmetric jet

Abstract

The effect of small scales on sound generated from a subsonic axisymmetric jet was investigated by filtering near-field data from a direct numerical simulation to determine the accuracy of the large eddy simulation technique for jet sound predictions. Lighthill’s acoustic analogy was employed to predict the far-field sound. The direct numerical simulation results were in agreement with published results [Mitchell et al., J. Fluid Mech. 383, 113–142 (1999)]. A new approach to handle the large spatial extent of the Lighthill source term yielded predictions of the far field in good agreement with the simulation results at low frequencies even for shallow angles from the jet axis. It was found that the small scales have little effect on the low-frequency sound, which is dominant in this case. The levels computed from both the filtered and unfiltered computed sound pressure field were in good agreement with those predicted by direct computations. As expected, filtering removed the small scale fluctuations in the near field, thereby reducing the magnitude of the source term for the high-frequency sound. [Work supported by NIH DCO 3577-02, RO1 grant from NIDCD.]