超声速层流/湍流压缩拐角流动结构的实验研究

在Ma=3.0的超声速风洞中, 分别对上游边界层为超声速层流和湍流, 压缩角度为25°和28°的压缩拐角流动进行了实验研究. 采用纳米粒子示踪平面激光散射(NPLS)技术获得了流场整体和局部区域的精细结构, 边界层、剪切层、分离激波、回流区和再附激波等典型结构清晰可见, 测量了超声速层流压缩拐角壁面的压力系数. 从时间平均的流场结构中测量出分离激波、再附激波的角度和再附后重新发展的边界层的增长情况, 通过分析时间相关的流场NPLS图像, 可以发现流场结构随时间的演化特性. 实验结果表明: 在25°的压缩角度下, 超声速层流压缩拐角流动发生了典型的分离, 边界层迅速增长失稳转捩, 并引起一道诱导激波, 流场中出现了K-H涡、剪切层和微弱压缩波结构, 而超声速湍流压缩拐角流动没有出现分离, 湍流边界层始终表现为附着状态; 在28° 的压缩角度下, 超声速层流压缩拐角流动进一步分离, 回流区范围明显扩大, 诱导激波、分离激波向上游移动, 再附激波向下游移动, 分离区流动结构复杂, 相比之下, 超声速湍流压缩拐角流动的回流区范围明显较小, 边界层增长缓慢, 流场中没有出现诱导激波、K-H涡和压缩波, 流动分离区域的结构也相对简单, 但分离激波的强度则明显更强. 关键词： 压缩拐角 层流 湍流 流动结构

Experimental investigations on structures of supersonic laminar/turbulent flow over a compression ramp

Experimental investigations of supersonic laminar/turbulent flow over a compression ramp are carried out in a Mach 3.0 wind tunnel, the angles of ramp are 25 degrees and 28 degrees. Fine structures of holistic flow field and local regions are visualized via nanoparticle-tracer based planar laser scattering (NPLS) technique, some typical flow structures such as boundary layer, shear layer, separation shock, recirculation zone and reattachment shock are visible clearly, and the wall pressure coefficient of laminar flow is measured. The angle of separation shock and reattachment shock, the development of boundary layer after reattachment are measured by time-averaged flow field structures. The analyses of time-relevant NPLS images reveal the spatio temporal evolution characteristics of flow field. The experimental results indicate that when the ramp angle is 25 degrees, a typical separation appearing in the supersonic laminar flow with boundary layer increases and is converted into turbulence quickly, at the same time, a shock is induced by developing boundary layer; K-H vortexes, shear layer and compression waves arise in the flow field. But the supersonic turbulent flow does not show separation, and the turbulent boundary layer always adhers to the wall. When the ramp angle is 28 degrees, the range of recirculation zone expanded obviously in supersonic laminar flow which is separated further, induces shock and separation shock moves upstream, reattachment shock moves downstream. Therefore the structures of separated region is complicated. By comparison with laminar flow, the range of recirculation zone in supersonic turbulent flow is obviously small, boundary layer increases slowly, and there are not any induced shock, K-H vortexes, compression waves in the flow field. The structures of separated region is simple, but the strength of separation shock is much stronger.
Keywords： compression ramp laminar flow turbulent flow flow structrures