Combustion instabilities in liquid-fuelled propulsion systems
Combustion of reactants in a confined volume favors excitation of unsteady motions over a broad range of frequencies. A relatively small conversion of the energy released will produce both random fluctuations or noise, and, under many circumstances, organized oscillations generically called combustion instabilities. Owing to the high energy densities and low losses in combustion chambers designed for propulsion systems, the likelihood of combustion instabilities is high. The accompanying heat transfer to exposed surfaces, and structural vibrations are often unacceptable, causing failure in extreme cases. This paper is a brief review of combustion instabilities in liquid-fueled propulsion systems-rockets, ramjets, and thrust augmentors-with emphasis on work accomplished during the past decade. To provide a common framework for discussing the wide range of works, a theory of two-phase flow is reviewed as the basis for an approximate analysis of combustion instabilities. The analysis is directed primarily to treatment of linear stability; it is sufficiently general to accommodate all processes occurring in actual systems. A new result has been obtained for an extended form of Rayleigh's criterion and its relation to the growth constant for unstable waves. The chief mechanisms for combustion instabilities in liquid-fueled systems are reviewed, followed by a summary of the common methods of analysis and applications to the three classes of propulsion systems. Control of instabilities by passive and active means is examined briefly.
© 1988. During preparation of this paper I have benefitted from numerous conversations (and arguments) with my colleagues Professors Marble and Zukoski. This work has been supported partly by the California Institute of Technology; by the Office of Naval Research; by the Air Force Office of Scientific Research; by the Naval Weapons Center under a Personal Services Contract; and by Hersh Acoustical Engineering under contract to the Air Force Astronautics Laboratory. I am indebted to Mmes. Cynde Herman, Jan Patterson, Elizabeth Wood, and Dana Young for all the extraordinary help they gave me in the typing and preparation of this manuscript.
Reprint - 307_Culick_FEC_1988.pdf