Adaptation of the impedance tube technique for the measurement of combustion process admittances

Abstract

This paper describes the development and application of the impedance tube technique in the measurement of localized combustion process admittances. The latter are needed for combustor stability analyses. The experimental set-up consists of a tube with the combustion process to be investigated at one end and an acoustic driver at the other end. The latter is used to excite a standing wave in the tube whose structure depends upon its interaction with the combustion process. The needed combustion process admittance is determined from acoustic pressure measurements taken at several locations along the tube. The paper discusses the theoretical foundation of the experiment and the developed data reduction procedure which accounts for the presence of steady state temperature gradient, mean flow gradient and gas-phase losses in the tube. Results showing the applicability of the developed experimental technique are provided.