Research on the effect of cowl lip angle on the accelerating start process of a two-dimensional hypersonic inlet

摘要

The effect of the cowl lip angle on the accelerating start process of a hypersonic inlet was investigated. A self-sustaining mechanism of the large-scale separation zone in the start process was studied. The inlet was a simplified, two-dimensional, one-side converging, hypersonic inlet. The movements of the large-scale separation zone of different cowl lip angles were compared and analyzed. The results show that: (1) Cowl lip angle influences the startability of a twodimensional hypersonic inlet dramatically. With the same contraction ratio, the start Mach number of different cowl lip angles varies. First, it decreases to a minimum value at 4 degrees, and then increases. (2) Large-scale separation zones are the common features of all cowl lip angles in unstart status. Their different development is the main cause of the different start characteristics. (3) The pressure stress is the main factor of the balance of the large-scale separation zone, and the viscous shear stress around it is of little impact. (4) The separation zone sustains itself mainly by the reflection shock of separation shock at the upper wall which is movable and adaptive with the change of Mach number. This is the reason that the separation zone gets a new balance when the incoming flow condition changes.