Experimental study on internal flowfield characteristics and start-unstart behaviour in a two-dimensional variable geometry inlet

The present paper experimentally investigates the flow field characteristics, starting and a unstarting process of a high-speed air inlet, when the cowl is opened from the fully closed condition at three different cowl rotation rates. High-Speed schlieren image synchronized with the pressure data is used to better understand the changes in internal flow behavior of the inlet. By employing a simple variable geometry inlet, inlet starting is realized even at low free stream Mach number by movement of separation bubble inside the inlet and attachment of cowl lip shock in the cowl lip. Separation bubble formed at the cowl hinge junction and in the expansion corner majorly alters the internal shock structure. As cowl moves further up the separation bubble at the cowl hinge location grows leading to aerodynamic blockage and resulting in inlet unstart. For the present inlet model, unstart is detected earlier by two pressure ports, one located in the throat and another in the middle of the isolator compared to other ports and hence helps in preventing inlet to unstart by sending signals to the feedback system.