Characteristics of the pressure relief slot on the start performance of the hypersonic inlet

Numerical study was carried out to investigate the effect of the pressure relief slot on the start property of a hypersonic inlet. By setting the pressure relief slot on the compression wall, the inlet start property can be significantly improved. The mechanism of the pressure relief slot on improving the start property and the influence of the parameters of the slot operating efficiency were summarized. By bleeding the back flow within the bubble and decreasing the backpropagation of the back pressure, the separation region can be divided into several parts, and thus, the flow separation is limited and the size of the bubble is reduced. Meanwhile, the suction effect of the low-speed and low-momentum flow within the boundary layer enhanced the airflow against the flow separation, which is beneficial to delay the inlet unstart. On the other hand, the results revealed that the inlet start property is sensitive to the slot parameters. The location is the most important parameter which decides the way that the separation bubble is divided and the type of shock/boundary interaction in the internal contraction part. By increasing the slot amount, the start property can also be significantly promoted only if the slot location is reasonable. In contrast, the width and the aspect ratio show weak influence on the start property. Therefore, the slots should be arranged carefully based on the location of the cowl and separation bubble.