Acoustic longitudinal mode linear combustion instabilities in 3D solid fuel grain

The combustion instabilities in solid rocket motor (SRM) are abiding predicament since their inception seven decades ago. The availability of large amount of energy in SRM combustion in comparison to small amount required to generate the combustion instabilities ensue the likely occurrence of the problem. This entails the SRM combustion instability prediction. This paper deals with the prediction of acoustic longitudinal mode linear combustion instabilities in 3D grain SRM. The stability history of SRM is predicted during motor burn time. This necessitates the performance (pressure/thrust) analysis. The FEA based solver is employed for the acoustic analysis of the grain port cavity as the grain burns. This is followed by determination of propellant response function. The computer code developed using approximate stability analysis results based on spatial and temporal averaging of the equations of two phase flow is used to predict the stability history. The results are presented and discussed for various longitudinal acoustic modes of SRM. The study evinces the decrease in stability margin with time and increase with mode number.