Investigation of the composite amplitude in solid rocket motor combustion chamber pressure oscillations

To date, a well developed nonlinear combustion instability theory remains elusive. Flandro developed a nonlinear theory using the concept of an acoustic energy balance. The theory expresses the pressure and velocity oscillations in a rocket motor chamber as a superposition of acoustic modes and models growth and decay responses using a differential equation to describe the composite wave amplitude. This work attempted to apply the theory developed by Flandro to some data from a recent test program done by the Naval Warfare Center (NWC). Two different data reduction methods were used. Both methods were only partially successful and a parameter study was carried out to investigate the equations and solution behavior which were being fit to the data. It was concluded that multiple pulse responses must be combined into a single data set to determine a set of triggering and limit-cycle oscillations, and this data set must include both growth and decay responses to reliably estimate triggering and limit-cycle amplitudes in a third-order or higher system. This work recommends that future test programs should be more focused on a particular motor geometry and propellant combination with greater repetition and less variation in the testing than the NWC test program.