Pulsed instability in rocket motors - A comparison between predictions and experiments

A series of 18 pulsed motor tests was conducted in heavy-wall solid rocket motors having an internal case diameter of 8.38 cm. The motor length was varied from 0.61 -1.22 m. Three related reduced-smoke propellants and four different grain designs were tested. All of the motors were linearly stable and all were pulsed into nonlinear instability. The data from this test series were used to evaluate the validity of previously developed pulser models and to evaluate the ability of a previously developed nonlinear instability analysis to predict the observed trends in the data. In most cases, the combined pulser and chamber stability models were found to be capable of predicting measured pulse amplitudes to within 10%. The ejecta pulser model had to be modified to account for the effect of internal wave reflection when propellant grain extended up to the nozzle entrance plane. The nonlinear instability analysis demonstrated the ability to predict many of the observed wave amplitude and shift trends in the data as a function of propellant and grain design. This combined analytical/experimental investigation also provides additional insight into the nature of nonlinear pulse triggered instability and the factors that influence its occurrence and severity.