Simulation of Turbulent Wind Noise Reduction by Porous Windscreens Using High-Order Schemes

Abstract

The purpose of the study is to investigate the wind noise reduction provided by microphone windscreens at different frequencies of the impinging turbulence. The windscreen is assumed to be a cylindrically shaped porous medium. This paper uses a high-order scheme to improve the accuracy at the interface between air and porous medium. The computational scheme is based on a modified immersed-boundary method with distributed forcing terms. The simulation results show that, for low-frequency turbulence, the windscreens with low flow resistivity are more effective in noise reduction, while for high-frequency turbulence, the windscreens with high flow resistivity are more effective.

A computational study of the effect of windscreen shape and flow resistivity on turbulent wind noise reduction

“…At this high-Reynolds number, a relatively broad spectrum of pressure fluctuations is generated with flow over the upstream circular cylinder, in contrast to a low-Reynolds number flow, where only very tonal pressure fluctuations, related to the von Karman vortex shedding frequency, are generated. The shape of the broadband spectrum of the unscreened case (to be shown shortly) is very similar to those of wind noise in the literature [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] that follow the À5/3-frequency power decay of the spectrum of atmospheric turbulent pressure.…”

“…Such pressure fluctuations sensed by the microphone, which is assumed to be the pressure at the center of the cylinder representing the microphone, result from near-field, incompressible disturbances. The flow fluctuations, both internal and external to the windscreen, have been investigated with a coupled flow simulation between the outside and inside of the windscreen utilizing an IB method 10 on a Cartesian grid, as the IB methods for fluid-structure interaction problems typically discretize the equations of motion for fluid on a Cartesian grid. 14,15 The model equations are the Navier-Stokes (NS) equations for incompressible flow outside the porous medium, with a modified ZK equation 11 medium.…”

“…Recently, a finite-difference, time-domain (FDTD) method was developed to simulate turbulence-induced pressure fluctuations around a porous microphone windscreen. 10 In this approach, the unsteady, incompressible fluid flow equations were solved for the air flow, whereas an incompressible form of the Zwikker-Kosten (ZK) 11 equation was solved within the porous medium under low-Reynolds number flow condition with a third-order upwind scheme implemented around the interface zone between the air and the porous medium. The simulation results showed that, for low-frequency turbulence, windscreens with low flow resistivity were more effective in noise reduction, while for high-frequency turbulence, windscreens with high flow resistivity were more effective.…”

“…One of the most effective ways to overcome the discontinuity is to apply high-order schemes. 10 Hence, in this study, a WENO scheme 12,13 is used in the regions near the interface between the fluid and porous media and is combined with a modified immersed-boundary (IB) method 14,15 to solve the governing equations. The use of a WENO scheme enables simulation of high-Reynolds number flow through different media; this is important, as Reynolds numbers for atmospheric turbulence are ordinarily quite large [O (10 5 ) or greater].…”

Simulation of sound propagation over porous barriers of arbitrary shapes

“…However, the ability and accuracy to include irregular geometries and realistic wind profiles is limited. We have previously developed immersed-boundary (IB) methods [10][11][12] that can be used to accommodate complex geometries with irregular shapes, multiple objects with different media, and even moving objects. These methods have been successfully implemented to compute the flow induced pressure fluctuations.…”