带喷流激波针流动特性实验研究

采用动态测力、动态测压和纹影等风洞实验技术，对加装了带喷流激波针的钝头体的绕流特性、稳定和非稳模态的形成条件和机理进行了研究.结果表明:带喷流激波针流场存在稳态和非稳态两种模态，超声速喷流的压比大于临界压比时流动处于稳定模态，反之则为非稳模态；增大激波针长度可减小钝头体阻力，但达到一定长度后，进一步减阻的效果不再显著；增大喷流压比能够有效减弱再附激波强度，有利于缓解单独激波针的肩部热斑问题；非稳模态下波系自激振荡对再附激波在钝头体表面所围的区域影响剧烈，振荡是周期性的，且存在确定的主导频率，主导频率随喷流压力比增大而减小；自激振荡的产生是由于喷流出口周围的反压在喷流压比小于临界压比时无法获得持续的平衡而导致. 

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.