基于NPLS的静压比对高超声速光学头罩冷却气膜影响作用研究

Ratio of static pressure influence on cooling film of hypersonic optical dome based on NPLS

超声速冷却气膜是应用于高超声速成像制导飞行器上的一项关键技术,静压比是影响超声速冷却气膜流场发展的重要因素。为研究静压比对该流场的影响规律,在M6高超声速风洞中采用基于纳米粒子的平面激光散射技术,对不同静压比下的马赫数3超声速冷却气膜流场进行了实验研究,获得了流场的瞬态流动显示图像。通过瞬态流动显示图像分析,研究了高超声速主流与超声速喷流之间边界面的发展过程;通过分形维数及间歇性分析,研究了静压比对湍流化程度的影响。结果表明在波系结构、喷流厚度及湍流化程度等方面,静压比对超声速冷却气膜产生了明显的影响:气膜总体厚度和静压比正相关,欠压状态和匹配状态气膜厚度增长先慢后快,过压状态先快后慢;欠压状态和匹配状态湍流破碎因子在流场前段普遍小于过压状态,但其沿流向增长较快,最终压力匹配状态湍流破碎因子最大,湍流化程度最高。

Supersonic cooling gas film is a key technique applied to hypersonic imaging guided vehicle. For ratio of static pressure (RSP) is a major factor affecting the development of supersonic cooling film,it has great engineering significance to carry out a systematic research on the RSP. In this view,flow visualization tests of supersonic cooling film at different RSP levels based on nano-tracer planar laser scattering (NPLS) were carried out in a M6 hypersonic wind tunnel. Through the analysis of transient flow visualization images,the development process of the shear layer between the hypersonic mainstream and supersonic jet was studied. With the analysis of fractal dimension and intermittency,the distributions were,respectively,obtained of fractal dimension along the flow direction and intermittency factor along the normal direction,and the effect of RSP on turbulence development was analyzed. The evolution of supersonic gas flow field mainly includes four stages which can be characterized by laminar shear layer,disturbance occurrence,mixing of “mainstream-jet” shear layer and jet boundary layer,and formation of “large boundary layer”. RSP has obvious influence on the wave structures,the film thickness and the turbulence degree of the flow field. The overall thickness of the gas film is positively related to the static pressure ratio along with the “condense” for a under-match RSP and the “inflation” for a over-match RSP. The film thickness of under-match state and match state increases slow first but then fast,meanwhile it is just opposite under over-match state. The turbulence breaking factor of under-pressure state and match state is generally smaller than that of the over-pressure state in the forepart of flow field,but it increases rapidly along the flow direction. Moreover,the match state has the largest turbulence breaking factor and the highest degree of turbulence level compared with the other states.