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.

The influence of edge geometry on end-correction coefficients in micro perforated plates

“…Bolton and Kim 6 proposed an expression for the resistive endcorrection coefficient in the dimensions of (Hz À0.5 ). Furthermore, using Bolton and Kim's CFD approach, 6 Herdtle et al 7 have computeed the end-corrections for tapered perforations.…”

Perfect electromagnetic and sound absorption via subwavelength holes array

“…In the following, the effective impedance of micro-perforated plate (MPP) is utilized in the design of various acoustic absorbers. It should be noted that although the MPP absorbers have been intensively studied after its invention by Maa in 1970s [22][23][24] , its intrinsic similarity with electromagnetic absorber such as Salisbury and Jaumann absorbers has seldom been studied [25][26][27] . In this paper, we show that the concept borrowed from electromagnetics is very efficient in the design of acoustic devices.…”

A finite-element formulation for room acoustics simulation with microperforated panel sound absorbing structures: Verification with electro-acoustical equivalent circuit theory and wave theory

“…There have been proposed various sound absorbing structures using MPPs and their absorption characteristics were studied theoretically, experimentally and computational experimentally [1][2][3][4][5][6][7][8][9][10][11]. As the conventional absorbing structure, an MPP is placed in front of a rigid wall with an air-cavity in-between to form the Helmholtz resonator [1].…”

“…Also, there proposed light-weight three-dimensional space sound absorbers such as CMSA [6] and RMSA [7] for providing further flexibility in the installation location and in the design. More recently, numerical methods such as computational fluid dynamics (CFD) and finite element method (FEM) have been used to model the MPPs with the consideration of advantage in handling arbitrary geometries [8][9][10][11]. CFD analysis has been used to calculate the acoustic impedance of the MPP having arbitrary hole geometry and to construct more accurate impedance model according to the hole type [8,9].…”

“…More recently, numerical methods such as computational fluid dynamics (CFD) and finite element method (FEM) have been used to model the MPPs with the consideration of advantage in handling arbitrary geometries [8][9][10][11]. CFD analysis has been used to calculate the acoustic impedance of the MPP having arbitrary hole geometry and to construct more accurate impedance model according to the hole type [8,9]. An FE model based on a porous material model [10] and a vibroacoustic FEM [11] using plate elements for bending vibration and acoustic impedance for the effect of the micro-perforation have also been presented to model the MPP absorbers with complex configurations.…”