Effects of baffle designs on damping acoustic oscillations in a solid rocket motor

Abstract

The baffle is a practical and promising passive damping method of dissipating acoustic energy and increasing acoustic losses in a solid rocket motor (SRM). In this study, numerical studies were conducted conjunction with the acoustic pulse response method (PRM) to evaluate the acoustic damping performance of a full-scale SRM with a baffle. The forced pulse function was imposed according to the frequency of the longitudinal acoustic mode. We comparatively evaluated the acoustic damping performance of the SRM with and without a baffle. The performances were characterized by (1) acoustic growth rate, (2) damping rate, and (3) acoustic energy. The PRM was first validated using data available in the literature. Several numerical investigations were conducted to develop geometry design criteria, which were subsequently used to ensure the effective operation of the baffle to suppress combustion-driven acoustic modes in the SRM. The effects of 1) the baffle axial location (x/L) and 2) the relative diameter (d/D) on acoustic damping performance were examined in detail. The results indicated that the baffle is effective in suppressing acoustic oscillations only when placed at 1/4 ≤x/L ≤1/2. Furthermore, when the baffle was placed at x/L=1/2, a relative improvement of approximately 51% and 15.3% in the growth and damping rates, respectively, was achieved compared with those in the SRM without a baffle. In addition, an annular baffle with a smaller inner diameter was observed to have a good design. A baffle with d/D=1/2 was observed to be associated with a favorable damping effect. This research elucidates the effective design of a baffle in stabilizing combustion in an SRM.