Frequency Analysis and Combustion Instability of Solid Rocket Motor

During static testing of two identical large segmented solid rocket motors (SRM-3 & 4), unanticipated small amplitude pressure oscillations and consequent thrust oscillations were observed for certain duration. The purpose of this paper is to give an overview of the pressure and thrust data obtained and the frequency analysis carried out on the test data. The probable cause of the oscillations is also discussed. Frequency analysis was carried out by means of Fast Fourier Transform software. A major part of this work was carried out on frequency analysis of the data by using FFT software. The analysis revealed that the frequency of oscillations in both motors were very close, i.e., 54.29 Hz for SRM-3 and 55.17 Hz for SRM-4. The fundamental axial acoustic mode frequency is also calculated for these motors to find its matching with the analyzed frequency.