Propagation of sound in a gas-particle mixture and acoustic combustion instability.

Abstract

The theory of the attenuation and dispersion of sound in a gas-particle mixture is examined from the viewpoint of its relevance to acoustic instability in rocket motors. Damping of acoustic instabilities by particles distributed throughout the motor cavity along with the gaseous products of combustion can represent an important acoustic loss factor in the highfrequency range, and is the one spatially distributed loss mechanism that can be tailored to attenuate a given frequency of excitation. Theoretical predictions of the influence of finite mass fraction of particles and of the presence of polydispersed sizes are described. The addition of inert particles of a given size to attenuate an instability of a predetermined frequency is compared with the addition of fuel components that produce a particulate product of combustion. The particulate dispersion of sound has an important role in determining the frequency of acoustic instability. The relationship between particulate damping and the elimination of catastrophic increases in burning rates of solid propellants subjected to acoustic instability is discussed.