Numerical study on the influence of inlet cover opening process on the stage transition performance of solid propellant ducted rockets

The stage transition process of solid propellant ducted rockets represents a critical phase to ensure the successful initiation and stable operation of the ramjet mode. This transition, from the booster phase to the ramjet phase, requires a rapid and stable flow field adaptation within a short time frame. In this study, unsteady numerical simulations employing dynamic mesh techniques are conducted to investigate the influence of varying inlet cover opening durations and transition Mach numbers on the internal flow characteristics of the inlet during stage transition. The results reveal that the interaction between shock waves and boundary layers governs the evolution of the internal flow structure and pressure distribution. The duration of inlet cover opening is shown to significantly affect shock strength, flow reattachment behavior, and pressure fluctuation intensity. Prolonged opening durations lead to an extended separation region near the inlet lip, which inhibits inlet restart and degrades transition performance. The optimal inlet cover opening duration for the given inlet configuration is identified to be 10 ms. Furthermore, the timing of the outlet cover opening also plays a crucial role in the stage transition process. Opening the outlet cover during the early to mid phase of the filling process effectively shortens the transition duration and enhances total pressure recovery, thereby facilitating a more rapid and stable establishment of ramjet operation. This study provides theoretical insight into the aerodynamic mechanisms underlying the stage transition and offers valuable guidance for optimizing the performance of solid propellant ducted rockets.