尾迹对低压涡轮边界层稳定性的影响

在低压涡轮内部上游周期性扫过的尾迹是下游叶片排内最重要的非定常扰动源,会对边界层的失稳和转捩过程产生决定性的影响.在施加低压涡轮负荷分布的平板上,采用热线对雷诺数为130000工况下,有/无尾迹作用时分离剪切层中的速度波动进行了测量.通过对比两种工况下分离剪切层中的扰动发展,分析了尾迹对分离泡稳定性的影响.结果表明:在无尾迹来流工况下,扰动在分离泡前部的增长符合线性不稳定机制,扰动增长至饱和后非线性机制开始起作用.主导分离剪切层的失稳过程的为K-H(Kelvin-Helmholtz)无黏不稳定机制.尾迹与分离剪切层的相互作用产生的扰动的增长在分离泡前部同样满足线性不稳定机制.尾迹加速了分离剪切层的失稳转捩进程,从而抑制了分离. 

Influence of wakes on boundary layer stability in low-pressure turbines

As the most important disturbance source, the wakes dominate the instability and transition process of boundary layer in low-pressure turbines. A detailed experimental study on the velocity fluctuation in a laminar separated shear layer on the flat plate of low-pressure turbine pressure distribution with the hot-wire probe at Reynolds number of 130000 were presented. The disturbance development under stable and instable incoming conditions was compared to analyze the influence of the wakes on the destabilization mechanism. Results show that the disturbance grows linearly in the former part of the separation bubble, and nonlinear interaction appears when the disturbance saturates, leading to vortex shedding at the maxima height of the bubble. Inviscid K-H(Kelvin-Helmholtz) mechanism dominates the instability process in the separation bubble. The occurrence of convective linear instability mechanisms was also revealed when amplifying the velocity fluctuations carried by wakes while propagating downstream. This accelerated the transition process and suppressed the separation bubble.