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

This is the published version. Copyright 2011 Acoustical Society of AmericaIn this paper, numerical simulations are used to study the turbulentwind noise reduction effect of microphone windscreens with varying shapes and flow resistivities. Typical windscreen shapes consisting of circular, elliptical, and rectangular cylinders are investigated. A turbulent environment is generated by placing a solid circular cylinder upstream of the microphone. An immersed-boundary method with a fifth-order weighted essentially non-oscillatory scheme is implemented to enhance the simulation accuracy for high-Reynolds number flow around the solid cylinder as well as at the interface between the open air and the porous material comprising the windscreen. The Navier–Stokes equations for incompressible flow are solved in the open air. For the flow inside the porous material, a modified form of the Zwikker–Kosten equation is solved. The results show that, on average, the circular and horizontal ellipse windscreens have similar overall wind noise reduction performance, while the horizontal ellipse windscreen with medium flow resistivity provides the most effective wind noise reduction among all the considered cases. The vertical ellipse windscreen with high flow resistivity, in particular, increases the wind noise because of increased self-generation of turbulence

The effect of realistic ground impedance on the accuracy of ray tracing

The heuristic model of sound propagation in the atmosphere has been developed by L'Esp\ue9rance et al. [Appl. Acoust. 37, 111\u8211139 (1992)] to provide rapid calculation of sound-pressure levels. This model uses an analytic ray trace method to calculate ray paths from the source to the receiver. The effects of finite ground impedance are treated by calculating the spherical wave reflection factor as if the atmosphere was homogeneous. The actual reflection angles and times of flight are used in this formulation. Since the speed of sound varies linearly with height, no focusing factors are calculated. The heuristic model has been compared to full wave calculations and is found to agree well at long ranges. In this paper the agreement between the heuristic model and the fast field program is investigated in detail. Criteria for the accuracy of ray tracing are discussed. It is demonstrated that the heuristic model produces realistic predictions even though certain criteria are violated. The finite ground impedance is shown to remove those rays for which the ray tracing criteria do not hold.NRC publication: Ye

Acoustic end corrections for micro-perforated plates

© 2019 Acoustical Society of America. Micro-perforated plates (MPPs) are acoustically important elements in micro-electro-mechanical systems (MEMS). In this work an analytical solution for perforated plates is combined with finite element method (FEM) to develop formulas for the reactive and resistive end effects of the perforations on the plate. The reactive end effect is found to depend on the hole radius and porosity. The resistive end effect is found to depend on hole radius only. FEM is also used to develop an understanding of the loss mechanism that corresponds to the resistive end effects. The developed models can be used in optimization studies of the MEMS and MPPs