A numerical study of unsteady gas-dynamic processes in controllable solid-propellant rocket motors with a central body

This study presents a numerical investigation of unsteady gas-dynamic processes in axisymmetric solid-propellant rocket motors equipped with a movable central body for thrust regulation. Three motor configurations with identical burning-surface areas but different chamber volumes and grain geometries were analyzed, including a design with a recessed nozzle. The nonstationary Euler equations were solved using the control-volume Godunov scheme on moving meshes incorporating a hybrid algorithm combining grid smoothing and local remeshing to track the motion of the flow-control element. Calculations were performed for two propellants with different burning-rate characteristics at varying velocity of the throttling mechanism. The results show that rapid changes in the throat area induce strong transient restructuring of the flow in the transonic and supersonic zones, leading to short-term thrust overshoots or undershoots caused by the mismatch between chamber-pressure evolution and instantaneous critical-area variation. The magnitude of these thrust excursions increases with the throttling rate, whereas the duration of the transient process decreases. Transients during throttling from the maximum to the minimum thrust were 2-2.5 times shorter than in the reverse mode. For all configurations, the maximum difference in thrust-overshoot amplitude at a fixed throttling rate reached 5.5-7% of the initial thrust.

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