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%.

To investigate the internal ballistics characteristics of the variable thrust solid motor during the operation process with pintle ablation, a variable thrust solid rocket motor with rear-mounted pintle was designed in this paper, and the hot firing test of the motor was carried out. The test results show that the pintle ablation was severe near the throat, with a maximum average radial ablation rate of 1.31 mm/s. An internal ballistic model considering pintle ablation was established, and the calculation results were in good agreement with the experimental data. Compared with the model without considering pintle ablation, the maximum deviation of the calculation results was reduced from 12.9% to less than 3%. The pintle ablation led to a significant reduction in the regulating capacity of the motor, and the pressure regulating range decreased by 43.4%. The influences of the onset time and the rate of ablation on the internal ballistics were studied. It was found that the delay of the onset time of pintle ablation can cause the pressure change rate and the pressure peak in the pressure boosting section to increase first and then remain unchanged, while the pressure change rate in the pressure reduction section and the pressure fluctuation in the platform section to increase first and then decrease. With the increase of the ablation rate, the pressure change rate and the pressure peak in the pressure rising and dropping sections decreased, the pressure change rate in the pressure reduction section gradually decreased to zero, the pressure fluctuation in the platform section increased first and then decreased, and the pressure deviation monotonically increased and then tended to a constant value.

Solid rocket motors often experience complex overload conditions during flight, and sudden internal ballistic lift or oscillations occur occasionally. To study the pressure characteristics in the combustion chamber of solid rocket motors under dynamic overload conditions, the relationship curves between overload and mass flow rate of the propellant combustion surface are obtained using the Greatrix burning rate enhancement model and the zero-dimensional internal ballistic model considering the combustion surface recession. Based on the relationship, simulation of the internal flow field for a cylindrical cone bore charge is carried out under composite overload. The effects of lateral overload acceleration, lateral vibration and vibration frequency on the dynamic characteristics of the motor and vortex flow are investigated. The results show that with the increase of lateral overload acceleration and lateral vibration, the equilibrium pressure rises and pressure oscillation amplitude in the combustion chamber increases, and the lateral overload acceleration can increase the pressure amplitude and equilibrium pressure by 0.02% and 0.35%, respectively, with per 1g increase in acceleration at the working pressure of 10.54 MPa. As the lateral vibration frequency rises from 7 to 320 Hz, the amplitude of pressure oscillation decreases. But it is amplified by resonance near the intrinsic frequency of the combustion chamber acoustic cavity, and the first-order resonance（160 Hz）raises the amplitude of the pressure from 0.16% to 0.30%, which is twice the original amplitude. When the composite overload frequency resonates with the combustion chamber acoustic cavity, the energy transfer from the propellant surface into the combustion chamber is more orderly.