Resonance Frequencies and Damping of a Combustor Acoustically Coupled to an Absorber

Abstract

The coupled acoustic system of a cylindrical combustor and an absorber cavity has been investigated experimentally in hot-fire and cold-flow tests. The addition of an absorber volume to the combustor is shown to result in eigenfrequencies of the coupled system systematically different from that of a pure cylindrical resonance volume. The general behavior of the coupled system is explained based on an analytical one-dimensional analysis of the problem. Numerical simulations in two dimensions result in very good agreement with experimental observations. A three-dimensional simulation of a cylinder equipped with 40 absorbers demonstrates the relevance of the reported phenomena for rocket engines equipped with absorber rings. Experimental data on the damping behavior of an absorber are given and the damping of absorbers is discussed based on the numerically obtained acoustic eigenmodes of the coupled system.