Numerical investigation of cavity self-oscillation and noise radiation induced by turbulent flow at non-zero inclination angle.

A hybrid numerical approach was used on a three-dimensional cavity at a non-zero inclination angle of the upstream section to reveal the mechanism of self-oscillation and the characteristics of far-field sound field. In this hybrid approach, the unsteady flow physics was captured by a compressible large eddy simulation, and the far-field sound field was calculated by the FW-H integral equation, with the noise source provided by near-field calculation. The mechanism of self-oscillation was revealed based on the instantaneous flow field structure and the pressure inside the cavity. The effects of the position of opening, inclination angle and neck thickness on the frequency and amplitude of the fluctuation pressure inside the cavity were examined. Results showed that the frequency and the amplitude were sensitive to the inclination angle but not to the position of the opening. Under varying neck thicknesses, the fundamental frequencies changed, but the amplitude remained almost constant. The influences of the boundary layer thickness on the amplitude of the fluctuation pressure was also investigated. Results revealed that the oscillation was suppressed once the boundary layer thickness reached a critical value. The findings could provide a reference for a quiet car with a low sunroof buffeting noise.