Nonlinear Slit Resonator

Application ID: 47171

In many applications, acoustic waves interact with surfaces that have small perforations or slits. This can be in muffler systems; in soundproofing structures; in liners for noise suppression in jet engines; or in grilles and meshes in front of, for example, miniature speakers in mobile devices.

At medium to high sound pressure levels, the local particle velocity in the narrow region of the perforate or slit can be so large that the linear assumptions of acoustics break down. Typically, vortex shedding takes place in the vicinity of that region. This leads to nonlinear losses and in audio applications also nonlinear distortion of the sound signal. The nonlinear effects are sometimes included through semiempirical parameters in analytical transfer impedance models for perforates.

In this tutorial, a narrow slit is located in front of a resonator volume and the losses are modeled directly. The model couples the Pressure Acoustics, Transient and the Thermoviscous Acoustics, Transient interfaces in a transient simulation. In order to model the complex nonlinear losses associated with the vortex shedding the Nonlinear Thermoviscous Acoustics Contributions feature is used. The incident acoustic field has an amplitude corresponding to 155 dB SPL.

This model example illustrates applications of this type that would nominally be built using the following products: