An in situ method of wall acoustic impedance measurement in flow ducts

Abstract

A novel method of local wall acoustic impedance measurement has been proved both feasible and viable for application to the walls of flow ducts with particular reference to the gas turbine environment. This technique is shown to be capable of impedance evaluations over a range of flow conditions to an accuracy of 10% or better. The problems of measurement have been thoroughly investigated and the relative importance of the sources of errors in the measurement technique has been made clear.