Effect of pintle on the acoustic field and stability factors of a solid-propellant rocket motor with variable pintle thruster

The acoustic modes and combustion instability within a solid rocket combustion chamber are predicted and analyzed in the presence of a movable pintle in the nozzle. The prediction of acoustic field is performed with a commercial finite element method code, and a combustion instability diagnosis is conducted with the classical acoustic analysis by investigating the stability factors (alphas). The effect of pintle position on the acoustic modes is analyzed by comparing the acoustic modes of cylindrical chambers with and without a pintle. A stability integral and alphas survey is carried out between the annular type chamber (resulting from the presence of the pintle) and the cylindrical chamber. Emphasis is placed on the changes in the nozzle throat area and on their respective stability integral when pintle position varies. The stability behavior according to the presence of the pintle is analyzed using two major driving and damping factors. The stability analysis reveals that the acoustic mode with the pintle is more sensitive to the fourth longitudinal mode compared with the acoustic mode without the pintle. Meanwhile, other modes show analogous acoustic fields, and the second mode is highly dependent on pintle position.