Numerical modeling of microperforated acoustical materials
Abstract
As technology makes people's lives more convenient and makes the quality of their life higher, people now desire clean and eco-friendly environments. This tendency is also shown in the acoustics area, where there is renewed interest in sound absorber design. Microperforated panels, one of these sound absorbing materials, can be designed in many ways. These panels feature many small (sub-millimeter) holes and typically small surface porosities on the order of 1 percent. The classical Maa theory, one of the most popular theories for microperforated materials, was initially formulated for constant diameter cylindrical holes. Since then, a number of ad hoc corrections have been suggested to account for different hole shapes, in particular, rounding of the aperture. These ad-hoc end corrections create a discrepancy with experimental results, especially in the low frequency range. In this thesis, more accurate end corrections have been calculated by using computational fluid dynamics (CFD). It is shown that the resistance and reactance of small apertures may be calculated using relatively simple CFD models in which a single hole is modeled. The fluid is assumed to be viscous but incompressible, and the hole geometry is assumed to be axisymmetric. It will be shown that this approach essentially reproduces the classical theory of Maa for circular apertures. However, it will also be shown that the empirical correction to the resistive end correction, in particular, exhibits a clear dependence on frequency and geometrical parameters that is not accounted for in conventional microperforated material models. In this thesis, a more convenient equation for the end correction, especially for the dynamic flow resistance, is formulated as a function of frequency and geometrical parameters. For the geometrical parameters, sharp-edged holes, round-edged holes and tapered holes were considered to create standard equations.
Degree
M.S.M.E.
Advisors
Bolton, Purdue University.
Subject Area
Materials science|Acoustics
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