Influence of structure on two-phase flow in visual nozzle of solid rocket motor

To investigate the velocity distribution in the two-phase flow field of the solid rocket motor nozzle, a two-dimensional planar visual nozzle was designed, and an online system for measuring velocity of the nozzle flow field was established. The hot-firing test was carried out using a low combustion temperature solid propellant containing alumina particles. The flow field velocity in the expansion section inside the nozzle was obtained by the Particle-Image Velocimetry (PIV). The influence of the truncated length of the side cover and shape of the visual nozzle on the two-phase flow field is studied by numerical simulation method. The research results show that the experimentally measured maximum axial velocity within the nozzle reached 1 850 m/s. The internal flow field contained a mixture of soot agglomerates and aluminum oxide particles, and as the soot concentration increased in the streamwise direction, the image grayscale intensity of the flow field gradually decreased from bright to dark. The numerical results indicate that reducing the truncated length of the side cover plate of the visual nozzle, thereby shifting the truncated position farther away from the nozzle throat, decreases the diffusion angle of particles from 24.3° to 21.5°, leading to a stronger concentration of particle trajectories toward the straight-line wall. The nozzle geometry was found to exert a pronounced influence on particle transport within the Laval nozzle. In the converging section and near the throat of the half-square nozzle, particles experienced repeated collisions with the straight wall due to geometric confinement, leading to a temporary residence or “particle trapping” phenomenon in the throat region. When the nozzle configuration was modified from a half-square to a full-square geometry, the maximum velocity lag of the particles relative to the gas was decreased by 46.9%.