A planar laser scattering system is built and then verified in a shock tunnel with a nominal Mach number of 6.A proper amount of water vapor is added into the test gas before the experiment,and then the water vapor condenses into tiny particles when it goes through the shock tunnel nozzle.The condensed H2O particles are used as tracers for the planar laser scattering.With the help of this flow visualization method and sophisticated arrangements of the optical path,the flow field of a hypersonic inward-turning inlet with a transition from the elliptical-like to circular shape is observed in experiments,and the preliminary flow structure in the inlet forebody and the isolator are obtained.The results show that the nominal diameter of the condensate tracers is approximately 67 nm with good following performances in the flow field.The forebody shock is curved and inflected obviously,and is concaved near the symmetry and raised at the sides.Based on several laser scattering images,the three-dimensional forebody shock is rebuilt using a spline interpolation method.As a result,the forebody shock looks like an oblique scoop.There are two pairs of streamwise vortices in the isolator.One vortex-pair near the bodyside is large and the other vortex-pair near the cowl-side is small,and both are unsteady.The high-speed flow concentrates in the core region of the isolator and inclines slightly to the cowl-side,whereas the low-speed flow accumulates on the bodyside.The flow field of the isolator is thus nonuniform.%在名义马赫数为6的激波风洞中,通过预先在试验气体中加入适量的水蒸气,利用水蒸气流经喷管时凝结产生的粒子作为示踪粒子,搭建并验证了平面激光散射系统.采用该流场显示技术,结合适当的光路布置,对类椭圆形转圆形高超声速内转式进气道进行了试验观测,初步得到了进气道前体及隔离段的流场结构.结果表明:水蒸气凝结产生的示踪粒子平均直径约为67 nm,在流场中具有较好的跟随性;内转式进气道前体激波有明显的凹凸性和拐点,前体激波靠近对称面的部分向内凹,而两侧的边缘向外凸出;基于多个流场截面的激光散射图像进行样条插值,重构出的三维前体激波面呈倾斜的糖勺形;隔离段顶板一侧和唇口板一侧各有一对反转流向涡,顶板一侧的涡流区较大,而唇口板一侧的较小,两对流向涡存在一定的非定常性;高速气流区集中在隔离段中心,并且偏向唇口板一侧,而大量的低速气流堆积在顶板一侧,使得隔离段流场的不均匀性显著.
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