Numerical simulation on the nonlinear acoustic properties of an orifice

An axisymmetric potential model is presented in this paper to study the nonlinear acoustic properties of an orifice in a plate. The vortex shedding process connected closely with the nonlinear acoustic phenomena is described by the discrete vortex method. Some flow details, such as the rolling up of the vortex sheet and the forming of the Vena Contracta, are simulated. For a sinusoidal pressure variation, both the time-history and spectrum of the average velocity through the orifice are computed. The nonlinear distortion of the velocity is clearly demonstrated by its calculated distribution of the harmonic components, which is consistent with the previous experiment. In terms of the fundamental component of the velocity, the nonlinear impedance is calculated. It is found that the resistance is in excellent agreement with the quasi-steady models, and the reactance decreases with the increasing sound pressure amplitude as revealed by the previous experiments.