Amplification and Attenuation of Acoustic Waves in Non-homogeneous Steady Flows

Abstract

An investigation of the interaction between acoustic waves and steady-flow fields was stimulated by the problem of combustion instability in rocket engines. A one-dimensional analysis of traveling acoustic waves in flows of an inviscid, nonconducting, perfect gas, containing mass and heat sources, reveals the existence of a coupling between acoustic waves and non-homogeneous steady-flow fields. This coupling allows energy transport between the wave and the flow field, resulting in either amplification or attenuation of the wave, depending on the gradients of the steady-flow variables and on the propagation direction. Results of experiments with nonuniform velocity fields are in agreement with theoretical predictions. In particular, an air jet discharging into a straight organ pipe and a converging air flow through a tapered pipe, are found to attenuate waves propagating through the pipes. [This work was supported by the U. S. Air Force Office of Scientific Research.]