Experimental source characterization techniques for studying the acoustic properties of perforates under high level acoustic excitation

Abstract

This paper discusses experimental techniques for obtaining the acoustic properties of in-duct samples with non-linear acoustic characteristic. The methods developed are intended both for studies of non-linear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems and for samples accessible from both sides such as perforates or other top sheets. When harmonic sound waves are incident on the sample nonlinear energy transfer results in sound generation at higher harmonics at the sample (perforate) surface. The idea is that these sources can be characterized using linear system identification techniques similar to one-port or two-port techniques which are traditionally used for obtaining source data for in-duct sources such as IC-engines or fans. The starting point will be so called polyharmonic distortion modeling which is used for characterization of nonlinear properties of microwave systems. It will be shown how acoustic source data models can be expressed using this theory. Source models of different complexity are developed and experimentally tested. The results of the experimental tests show that these techniques can give results which are useful for understanding non-linear energy transfer to higher harmonics.

Aeroacoustics research in Europe: The CEAS-ASC report on 2011 highlights

“…New experimental techniques have been developed for obtaining the acoustic properties of in-duct samples with nonlinear acoustic characteristics [38]. The methods developed are intended both for studies of nonlinear energy transfer to higher harmonics for samples only accessible from one side such as wall treatment in aircraft engine ducts or automotive exhaust systems, and for samples accessible from both sides such as perforates or other top sheets.…”

Experimental Investigation of an In-Duct Orifice with Bias Flow under Medium and High Level Acoustic Excitation

“…In Ref. [32][33][34] two or multi-load methods were used to study nonlinear harmonic interaction effects for perforates without bias flow. The additional condition which should be added is to keep the same magnitude of acoustic pressure difference or the same magnitude of acoustic flow velocity in the orifice.…”