Numerical Evidence of Mode Switching in the Flow-Induced Oscillations by a Cavity

Abstract

A Direct Noise Computation (DNC) has been performed for a turbulent boundary layer past a rectangular cavity, matching one configuration of Karamcheti1 experiments. An LES approach with periodic boundary conditions in the spanwise direction is used to evaluate the solution at a reasonable computational cost. The two components in the pressure spectra found experimentally are well reproduced. The acoustic field appears to be dominated by the low-frequency component whereas the experimental visualization indicates a radiation at the higher frequency. The mechanism giving rise to the lower frequency is investigated providing evidence on the possibility of switching between two cavity modes and that the strong coupling of the separated shear layer with the recirculation flow within the cavity is likely to participate to the low-frequency modulation. Moreover, an extrapolation method is proposed and applied to obtain the far-field from the near acoustic field.