Starting characteristics restrict the operation limits of a hypersonic inlet. Enhancement of the starting ability thus serves as one of the most serious issues in propulsion system. In the present work, we propose a simple adaptive slot control method, which expands the working range of hypersonic inlets to a lower Mach number and shows very weak losses. Our simulation results applying the five parallel slot geometrical design show a substantial reduction of the starting Mach number. The air flow inside the parallel slot channels is self-driven by the pressure gradient located near the separation shock under unstart mode, whereas it is strongly suppressed when the inlet is restarted. Surprisingly, all the inlet configurations are almost restarted at the same Mach 3.0, regardless of the individual width of the slot and the number of slot. This confirms the self-adapted nature of the pressure gradient inside the channel which shows prospect for the potential engineering applications of the simple slot control method. However, the location of the slots shows a big influence on the control efficiency, indicating that these slots need to be arranged carefully on the compression surface based on the location of the separation bubble.
Numerical study of unsteady starting characteristics of a hypersonic inlet