Combustion Instabilities In Solid Propellant Rocket Motors

Abstract : These notes for two lectures are intended to provide the basic ideas for understanding and interpreting coherent oscillations is solid propellant rocket motors. The discussion is concerned mainly with the dynamics of a system consisting of two coupled sub-systems: the chamber containing combustion products; and the combustion processes con ned almost entirely to a thin region adjacent to the surface of burning propellant. Coupling between the sub-systems is always present due to the sensitivity of the ocmbustion processes to local values of pressure and velocity. Thus the primary mechanisms for instabilities in solid rockets are related to those interactions. A second mechanism involves vortex shedding, a cause of instabilities mainly in large motors, notably the Space Shuttle and Ariene V boost motors. Following a brief review of the history of combustion instabilities in solid rockets, the mechanisms and their quantitative representations are discussed. The remainder of the lectures is devoted to an approximate analysis providing a general framework convenient for understanding, predicting and interpreting combustion instabilities.