Transfer impedance of microperforated materials with tapered holes.

It has been previously shown that relatively simple computational fluid dynamics (CFD) models can be used to calculate the transfer impedances, including the associated end corrections, of microperforated panels. The impedance is estimated by first calculating the pressure difference across a single hole when a transient input velocity is imposed, and then Fourier transforming the result to obtain the impedance as a function of frequency. Since the size of the hole and the dimensions of the inlet and outlet channels are very small compared to a wavelength, the flow through the hole can be modeled as incompressible.