高超声速进气道低马赫数不起动和再起动试验

Test of low Mach number unstart and restart processes of hypersonic inlet

为拓展对高超声速进气道不起动机理的认识,对一截短的二元高超声速进气道的低马赫数不起动现象和再起动现象进行了风洞试验研究。试验中分别通过改变进气道攻角和在通道下游设置堵锥形成流动壅塞的方法来模拟进气道来流马赫数的改变和燃烧室内释热导致的流动壅塞。试验中采用高速纹影技术和动态压力测量技术对上述动态过程中的瞬态流动结构和壁面动态压力信号特征进行了记录。研究发现,当进气道处于低马赫数不起动时,其口部分离包诱导激波受分离包自身振荡特性的影响,在唇口附近连续的小幅振荡,进而给整个进气道通道内引入了一类无基频的小幅压力扰动。而该扰动随着马赫数的增加,进气道恢复起动后逐渐消失。此外,还捕捉到了进气道再起动过程中分离包吞入的迟滞现象,进气道从"小喘"阶段恢复至起动状态时,由于下游高压的存在使得分离包未能完全吞回,并出现了类似低马赫数不起动时的无基频小幅振荡。该振荡直至通道下游完全敞开、口部分离包被吞入才逐渐消失,至此进气道也顺利地恢复到了起动状态。

To enrich the understanding of the mechanism for hypersonic inlet unstart,a wind tunnel test is conducted to investigate the low Mach number unstart and restart of a truncated two-dimensional hypersonic inlet.By varying the inlet angle of attack and the downstream choking degree,the variation of the inlet flow Mach number and heat release of combustion in real flight conditions are simulated in this test.The high-speed Schlieren imaging technology and time-resolved pressure measurements are used to record the instantaneous flow pattern and surface pressure signals.The results show that during the unstart process at low Mach number,the separation bubble induced oblique shock is influenced by the oscillation characteristic of the separation bubble,and oscillates slightly around the cowl lip to introduce a type of small-amplitude disturbance without base frequency.This disturbance gradually disappears with the increase of the Mach number and restart of the inlet.Hysteresis of swallow of separation bubble is also observed in the test.When the inlet recoveries from the little buzzle state to the start state,the separation bubble cannot be fully swallowed due to the presence of high pressure downstream during the restart process,and exhibits as a small-amplitude oscillation similar to the one in low Mach number unstart process.The oscillation does not disappear until the inlet exit is fully open and the separation bubble in the entrance is swallowed simultaneously,and then the inlet returns to start successfully.