EXPERIMENTAL INVESTIGATION ON FLOWFIELD AROUND BLUNT BODY WITH FORWARD-FACING JET AND SPIKE

The characteristics of the flow around a blunt body with the combination of forward-facing jet and spike are investigated through wind tunnel experiments, which include the mechanism of steady mode and unsteady mode. The dynamic-force measurement, the dynamic-pressure measurement and the schlieren photograph are involved. The results indicate that there are the steady mode and the unsteady mode for the flow field around the blunt body with the combination of forward-facing jet and spike. The flow is steady as the pressure ratio of the supersonic jet is higher than the critical pressure ratio, while it is unsteady as the pressure ratio of the supersonic jet is lower than the critical pressure ratio. The drag of the blunt body decreases with the increasing of the length of the spike until the length of the spike reaches a certain value. With the enhancement of jet pressure ratio the strength of the reattachment shock waves is weakened significantly, which is beneficial to the eliminating of the hot spot on the shoulder of the blunt body. The pressure on the surface surrounded by the reattachment shock waves is fluctuating intensively under the unsteady mode, which is induced by the self-excited oscillations of shock waves around the blunt body. The dominant frequency of the self-excited oscillation decreases with the increasing of the jet pressure ratio. The mechanism of self-excited oscillation is that the ambient pressure around the jet exit cannot be balanced persistently when the jet pressure ratio is lower than the critical pressure ratio.