Modeling perforates

Abstract

A number of computational and analytical tools are available to model perforated elements by treating the perforate interface as a distribution of localized reacting sources. Since the unsteady flow through an orifice exhibits a wide range of behavior, the results of such analyses depend strongly on the perforate model. Frequency-domain techniques are the most common approach for perforated element analysis and, correspondingly, nearly all available experimental data are presented in terms of frequency-domain parameters. Nonlinear behavior is generally addressed through a nonlinear orifice impedance, defined at a single frequency. While the frequency-domain approach is clearly justified for linear physics, or for nonlinear cases with a single driving frequency (the frequency is a natural scaling parameter), the use of this technique for nonlinear behavior caused by multifrequency disturbances may become questionable. The present study investigates unsteady flow through a circular orifice from a time-domain perspective. Development of an empirical perforate model based on relationships obtained from time-domain experimental data is discussed. The orifice model is incorporated into a time-domain computational scheme for perforated tube silencers and numerical predictions are compared to experimental data. The relative benefits and limitations of the present approach are addressed.