Scale-Resolving Simulation of Pressure Oscillations in a Radial-Inflow Solid Rocket Motor

Abstract

Combustion instability in solid rocket motors (SRMs) arises from the coupling of unsteady pressure oscillations with chamber acoustic modes and can threaten structural integrity and operational reliability. This study examines how replacing a conventional axial inlet with a radial inlet affects internal flow dynamics, vortex-acoustic coupling, and pressure fluctuations in an SRM combustion chamber. Radial inflow introduces a circumferential velocity component that increases tangential shear near the walls, promotes earlier vortex roll-up around the inhibitor, and produces denser, more three-dimensional vortical structures, thereby strengthening vortex-acoustic interactions. Two-dimensional axisymmetric simulations were performed using scale-resolving simulation (SRS) and unsteady Reynolds-averaged Navier-Stokes (URANS) approaches. Pressure histories recorded at two monitoring points were analyzed using the fast Fourier transform (FFT) to identify dominant acoustic frequencies and normalized amplitudes. The SRS models agreed closely with the experimental data, accurately capturing the first four acoustic modes and the monotonic decrease in normalized amplitude with increasing mode number; LES with the WALE model produced the most reliable overall results. By contrast, the URANS models smoothed small-scale fluctuations, underpredicted higher-frequency modes, and misrepresented amplitude levels, particularly when the scale-adaptive simulation model was used. These findings show that the radial-inlet configuration substantially alters SRM flow physics and instability characteristics and demonstrate the value of advanced SRS approaches for inlet-specific designs intended to mitigate combustion instability.