Vortex Shedding and its Nonlinear Acoustic Effect Occurring at a Slit

Abstract

This paper presents a theoretical study of the nonlinear acoustic properties of a slit in a thin plate subjected to highintensity sound excitation. In the present model, the conventional discrete vortexmethod is employed to simulate the near-field two-dimensional unsteady flow in order to capture the mechanism of the sound–vortex interaction, which is in combination with a spanwise-averaged three-dimensional Green’s function method used to connect the nearfield flow quantities with the far-field sound pressure. This model is compared with an existing particle image velocimetry flow visualization and a direct numerical simulation model, showing good qualitative agreement. It is revealed that the oscillatory slitflow is dominated by a pair of spiral-like counter-rotating vorticesmoving away from the slit and eventually colliding into each other. Because of the vortical flow effect, increases in the sound pressure level result in significant increases in acoustic resistance and modest decreases in acoustic reactance. For the parametric range in this study, increases in the aspect ratio of the slit result in slight increases in acoustic resistance but unnegligible reductions in acoustic reactance. However, the influence of the aspect ratio on acoustic impedance tends to be less important when the sound pressure level exceeds a certain high value.