汽轮机高压缸小容积流量工况数值模拟

Numerical Simulation of High Pressure Steam Turbine Cylinder under Low Volume Flow Condition

建立了某汽轮机高压缸的两级叶栅通道的数值模型,并且通过减小背压降低流量以达到模拟高压缸小流量工况的目的。对不同流量工况进行流场分析可以得到,小流量工况下高压缸的动叶顶部间隙处由于速度分布和间隙流的影响最易形成涡流,其随流量的减小,逐渐向流道底部发展。并且容积流量的减少会导致负攻角的产生,导致级内的分离流动。在小流量下分离流动存在于整个叶高通道,阻塞主流。通过分析级的焓降变化可以得出,当级的流量为设计流量的50%时即将进入鼓风工况前的过渡工况,这与一些文献中所推导的结论一致。同时鼓风工况会使得级内的温度场发生较大的变化,在20%设计流量下,排汽温度比设计工况提高了30K,危害汽轮机的安全运行。

In this paper,a numerical model of the two-stage cascade channel of a high-pressure cylinder of a steam turbine is established,and the flow is reduced by increasing the back pressure to achieve the purpose of simulating the small flow condition of the high-pressure cylinder.The flow field analysis of different flow conditions shows that the gap at the top of the rotor blade of the high-pressure cylinder under small flow conditions is most likely to form a vortex due to the influence of the velocity distribution and the clearance flow,which gradually moves to the bottom of the flow channel as the flow decreases.And the reduction of the volume flow will lead to the generation of negative angles of attack,leading to separate flow within the stage.In a small flow,the separated flow exists in the entire leaf height channel,blocking the main flow.By analyzing the enthalpy drop change of the stage,it can be concluded that when the flow of the stage is 50%of the design flow,it will enter the transitional condition before the blast condition,which is consistent with the conclusions derived in some documents.At the same time,the blast working condition will make a big change in the temperature field in the stage.At 20%of the design flow,the exhaust steam temperature is 30K higher than the design working condition,which endangers the safe operation of the steam turbine.