title: Transfer impedance of microperforated materials with tapered holes.
abstract: 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. By using those procedures, Bolton and Kim extended Maa's classical theory to include a resistive end correction for sharp-edged cylindrical holes which differs from those previously proposed by the inclusion of a static component. Here it is shown that CFD models can also be used to compute end corrections for tapered holes. Since practical experimental characterization of perforated materials often involves measurement of the static flow resistance, a closed form empirical equation for that quantity has been developed. Finally, it is shown that configurations having equivalent static flow resistances can yield different acoustic absorptions.
authors: Predictive Engineering, 3M Company, St. Paul, Minnesota 55144.
authors: Thomas
authors: T
authors: Herdtle
authors: Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University, 140 S. Martin Jischke Drive, West Lafayette, Indiana 47907-2031.
authors: J Stuart
authors: JS
authors: Bolton
authors: Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University, 140 S. Martin Jischke Drive, West Lafayette, Indiana 47907-2031.
authors: Nicholas N
authors: NN
authors: Kim
authors: Automotive Division, 3M Company, St. Paul, Minnesota 55144.
authors: Jonathan H
authors: JH
authors: Alexander
authors: Division Engineering, 3M Company, St. Paul, Minnesota 55144.
authors: Ronald W
authors: RW
authors: Gerdes