高压涡轮封严流与主流相互作用的机理研究

Investigation on Interaction Mechanism Between Rim Sealing Flow and Mainstream Flow in High-Pressure Turbine

为探究高压涡轮轮毂封严流与主流相互作用的机理,借助经过实验校核的数值模拟方法,详细分析了封严流对主流端区二次流结构的影响以及封严流与主流的相互作用过程。研究发现:一方面,主流从叶片前缘位置侵入封严结构内部,在封严出口处形成封严回流涡,并在封严结构内部诱导出一个反向涡,这两个涡直接影响封严结构的封严效率;另一方面,封严出口处封严回流涡与叶片通道内的马蹄涡压力面分支在流向上旋转方向一致,互相融合并增强通道涡强度。封严结构决定了封严回流涡流出的位置和速度方向,直接影响封严回流涡与马蹄涡压力面分支的相互作用过程,从而决定了损失的大小。研究还发现,当封严流和主流在封严出口交界面上流量相当且存在一定的周向速度差时,封严出口会发生Kelvin-Helmholtz不稳定现象。此时伴随大量边界层低能流体进入封严结构内,封严流周向速度减小,马蹄涡的压力面分支和封严回流涡随之减弱,继而使端区二次流损失减小。

In order to advance the understanding of the fundamental mechanism of the interaction between rim sealing flow and mainstream flow in a high-pressure turbine, the influence of sealing flow on the structure of the hub secondary flow and the interaction process between them were analyzed in detail. The numerical simulation method has been verified by experiment to guarantee the accuracy. The study shows that, on the one hand,the mainstream flow ingress occurred at the leading edge of the blade, which leads to a recirculation zone at the outer part of the rim seal and a reverse vortex below it. The position and size of these two vortices influences sealing effectiveness directly. On the other hand, the pressure side leg of horse-shoe vortex and the leakage slot vortex would get merged and develops into passage vortex in the blade passage later, which has the same sense of rotation in streamwise direction. The sealing configuration determines the outflow position and velocity direction of the leakage slot vortex, which affects the loss caused by sealing flow. At the same time, the Kelvin-Helmholtz instability phenomenon is observed to occur at the seal outlet, resulting from a certain circumferential velocity difference between the sealing flow and the mainstream flow with almost the same scale massflow at the interface of the seal outlet. With lots of low-energy boundary layer fluid ingested into the rim seal, the circumferential velocity of the sealing flow would decrease. The pressure side leg of horse-shoe vortex and the leakage slot vortex would subsequently get weakened, which contributes to reducing losses.