Some Influences of Noise on Combustion Instabilities and Combustor Dynamics

The chief purpose of this paper is to investigate the influences of noise, more generally stochastic sources of any sort, on linear and nonlinear unsteady motions in combustion chambers. To be definite, our primary applications here relate to combustion instabilities in solid propellant rockets, particularly linear stability. Two aspects are especially relevant to practical applications: the direct effects of noise on stability; and extraction of information about stability margin from noisy pressure records taken for stable motors. However, the formulation and results are relevant to combustors generally. A fundamental issue is the distinction between and relative importance of self-excited (linearly unstable) oscillations on the one hand and forced oscillation on the other. This has been a controversial and occasionally misunderstood topic for many years. The essential ideas can be clarified unambiguously within the context of global dynamics treated here. We are not so concerned with the details of data processing as with the physical interpretation of the results.