Simulation of pressure oscillations in a combustion chamber under periodic inlet disturbances

Abstract

The working process of a solid rocket motor (SRM) is a transient problem. The burning rate of the propellant is related to several factors, which results in variations in the mass injection rate. To date, the simulation of the flow field in an SRM generally comprises the use of constant inlet boundary conditions, a simulation that does not consider inlet disturbance conditions. This paper is mainly concerned with the influence of periodic disturbances on the pressure oscillation. In this study, a numerical simulation was performed with a periodic disturbance inlet based on the typical Von Karman Institute for Fluid Dynamics subscale motor without an obstacle. It was found that the inlet conditions of the periodic disturbance greatly affect the amplitude and frequency of the pressure oscillation in the combustion chamber. When the mass flow inlet disturbance frequency is close in value to the acoustic modal frequency of the combustion chamber, the amplitude of the pressure oscillations increases. Similarly, when the disturbance frequency is far in value from the acoustic modal frequency, the amplitude of the pressure oscillation decreases. When the inlet disturbance changes from 650 Hz to 400 Hz, the amplitude of the pressure oscillation increases by 451.5%. In addition, at certain frequencies, the inlet disturbance can excite pressure oscillations at acoustic modes near the disturbance frequency in the combustion chamber.