高负荷低压涡轮边界层转捩的实验研究

Experimental Investigation on Boundary Layer Transition Process in High-Lift Low-Pressure Turbines

为了研究高负荷低压涡轮边界层的非定常转捩过程及雷诺数对尾迹边界层相互作用机制的影响,采用热线和表面热膜测试技术在高负荷叶栅实验台上对吸力面边界层的非定常时空演化进行了实验测试。结果表明:高负荷叶型的吸力面边界层在没有来流尾迹作用的情况下会不可避免地发生分离。分离剪切层中的K-H无粘不稳定机制主导了失稳转捩过程;来流尾迹的逆射流会与边界层相互作用,产生卷起涡结构,从而促进分离剪切层的转捩过程。边界层的分离被转捩产生的湍流条带及其后的寂静区抑制;随着雷诺数降低,分离点向上游移动11.4%吸力面弧长,分离泡的流向和法向范围扩大,尾迹引起的卷起涡结构尺度也随之变大。雷诺数通过改变分离剪切层的状态对转捩机制产生影响。

Detailed experimental investigations are carried out in order to study the interaction between unsteady wakes and boundary layer and the effects of Reynolds number on the wake induced transition mechanisms in high-lift low-pressure turbines. Extensive measurements about the unsteady time-spatial evolution of the suction surface boundary layer are conducted on a high-lift profiles cascade using hot-film and hot-wire methods.The results show that the boundary layer on the suction surface of the high-lift profile will separate inevitably under strong adverse pressure gradient. Transition occurs in the separated shear layer which is dominated by the inviscid K-H instability mechanism. The negative jet of the incoming wakes interact with the separation bubble,resulting in roll-up vortices and promotes the transition process. The flow separation is suppressed by the induced turbulent strip and the following calmed region. As the Reynolds number decreases,the separation point moves11.4% suction surface length upstream and the separation flow region extends in both streamwise and normal directions. At lower Reynolds number condition,the scale of roll-up vortices increases as the separation bubble grows. The Reynolds number affects transition process through influencing the status of the separated shear layer.