On the higher hydrodynamic modes and the onset of whistling in self-sustained cavity oscillations

Abstract

Aeroacoustic power generation due to a self-sustained oscillation by an axisymmetric cavity exposed to a low Mach number grazing flow is studied both experimentally and numerically. The feedback effect is produced by the velocity fluctuations resulting from a coupling with acoustic standing waves in a coaxial pipe. A hybrid computational aeroacoustic methodology that combines incompressible flow simulations with Vortex Sound Theory is used to predict the time averaged acoustic source power generated by the cavity. The effect of the cavity width on the whistling is addressed while keeping the cavity depth and momentum thickness of the approach flow fixed. A particular attention is given to higher hydrodynamic modes within the same acoustic mode and the onset of whistling. The onset of whistling is determined by the Strouhal number based on the momentum thickness of the approaching flow.