Normal incidence acoustic insertion loss of perforated plates with bias flow

Abstract

The transmission of sound at normal incidence through perforated plates with bias flow is investigated experimentally and theoretically over a large parameter space. A specially designed experimental apparatus enabled the measurement of insertion loss with bias flow Mach number up to 0.25. A theoretical model for insertion loss was constructed based on inviscid, one-dimensional wave propagation with mean flow through a single contraction/expansion chamber. The mass end correction of the contraction is modified for hole interaction effects and mean flow. Hydrodynamic losses are modeled using a vena contracta coefficient dependent on both perforation geometry and Reynolds number. Losses in acoustic energy that occur in the mixing region downstream of the perforations are modeled as fluctuations in entropy. The proposed model was validated experimentally over a range of plate thickness, porosity, and hole size. The experimental results indicate an increase in insertion loss with increasing frequency, followed by saturation and decline as resonant conditions are established in the perforations. The insertion loss at low frequency increases with increasing Mach number through the perforation. The proposed model captures these trends and its predictions are shown to be more accurate than those of past models.

Characterization of a novel sound absorption material derived from waste agricultural film

“…As an acoustic structure, perforated plates show excellent abilities for low-and middle-frequency noise control. Perforated plates [10,11] and mic-perforated plates [12,13] have been used to control noise in extensive ranges for years. Researchers filled porous materials into the back air layer of perforated plates to improve their sound absorption properties in highfrequency range [14,15].…”