汽轮机高压级叶顶间隙泄漏流的掺混作用分析

Analysis on mixing process of tip shroud leakage flow in high-pressure stage of steam turbine

对某带有高低齿汽封的汽轮机高压1.5级模型进行数值计算,分析了不同叶顶间隙下汽封出口腔内泄漏流的涡系变化以及泄漏流与主流掺混对下游静叶气动性能的影响,并定量计算了泄漏流引起的相关损失。结果表明:泄漏流与主流在周向速度和径向速度上存在较大差异,二者掺混将导致动叶出口处汽流方向发生偏转,对下游静叶产生负攻角,引起级效率的下降。在泄漏流引起的相关损失中,掺混损失占主要部分。叶顶间隙的大小直接影响汽封腔内回流涡的尺寸,回流涡与汽封腔内泄漏流动能的耗散程度密切相关。因此,在叶顶汽封设计中,应尽量减小叶顶间隙,增强密封腔内汽流扰动,减小泄漏流与主流的速度差异,以便提高汽轮机经济性。

A numerical calculation was attempted based on a high-pressure1.5-stage steam turbine with rotor labyrinth seal.The variation of leakage vortex system in shroud exit cavity and the effect of main flow mixing with leakage flow on the aerodynamic characteristics of downstream stator were analyzed.Besides,the related losses generated by leakage flow were calculated.Results showed that there were large differences between main flow and leakage flow in the circumferential velocity and radial velocity.Main flow was deflected at the rotor blade exit when it mixed with the leakage flow,which led to the negative angles of incidence on the subsequent stator and the decrease of the stage efficiency.The mixing loss was the main part among the related losses generated by leakage flow.The tip clearance directly affected the size of backflow vortex which was closely related to the kinetic energy dissipation of leakage flow.Therefore,during the structure design process of the blade tip seal,it is necessary to reduce the tip clearance,enhance the disturbance of leakage flow in seal cavity,and decrease the velocity difference between leakage flow and main flow to improve the economy of steam turbine.