超声速喷管起动过程激波结构演化特征

Research on evolution of starting shock in a supersonic nozzle

通过改变进出口压比,对马赫数2.7的二维对称拉瓦尔喷管流动进行了试验研究,给出了超声速喷管起动过程中的激波结构演化特征。在试验过程中,固定喷管喉道出口面积比,改变喷管上下游压比,使喷管起动激波从喉道发展到喷管出口处,逐渐过渡到设计工况。在起动激波向下游发展的过程中,喷管内流动经历了教科书上给出的理论过程:喉道正激波、扩张段内正激波、喷管出口马赫反射、喷管出口规则反射、设计工况等;但由于附面层的存在,每一个过程与无粘情况下的激波示意图都有所不同。比如,试验中捕捉到的激波串在向下游的移动过程中,出现的由λ型激波向Х型激波的转变,以及激波串非对称现象的出现等。基于纹影和剪切敏感液晶摩阻显示技术获得了起动激波串的首道激波的三维特征。

The starting process of the flow in a Mach 2.7 supersonic nozzle is experimentally investigated. The starting shock moves from the throat to the exit of the nozzle when the incoming total pressure is gradually increased. The flow in the nozzle undergoes the process of normal shock at the throat, normal shock at the expansion duct, oblique shock at the expansion duct, Mach reflection at the exit of the nozzle, regular reflection at the exit of the nozzle and the design conditions. The transformation from the Mach reflection to the regular reflection is observed based on the experimental result of schlieren and PIV. The three-dimensional flow structure of the leading shocks of the shock train has been rebuilt by using the schlieren image system and the shear-sensitive liquid crystal technology.