小流量工况汽轮机末级流动不稳定数值研究

Numerical Investigation of the Flow Instability of Steam Turbine Last Stage under Low Mass Flow Condition

针对汽轮机低压末级在小负荷工况下出现的流动不稳定现象,进行了非定常数值模拟研究和分析。对末三级叶片耦合排气缸进行建模,其中末级采用整圈形式,对17%设计质量流量工况进行非定常计算,小流量工况下汽轮机末级表现出类似于压气机旋转失速的现象,对流场监控数据进行周向模态分解及相关分析,确定了扰动的数目为30个,其周向传播速度约为转子转速的56%。最后,结合内部流动特征对非稳定现象的形成机理进行了探讨,小流量下由于径向流动阻塞了通道,并在叶顶间隙射流的作用下形成了通道内的周期性高压区,而前缘溢流和叶顶间隙射流耦合作用促成了叶顶进口附近周期性低压区的形成。

An unsteady simulation work of low pressure steam turbine is performed to study the flow instability in last stage moving blades(LSMBs) under low mass flow condition.Upon the basic of preliminary study,unsteady simulation under 17% mass flow is calculated.The instable features are found under this flow condition;the stator-rotor interaction near tip is broken.The circumferential mode and propagation characteristics of the perturbation,determined by Fourier Transform,are captured.The results show that there are 30 vortex cells in annulus with about 56% rotational speed of rotors,and this phenomenon is similar to the rotating stall in axial compressor.Finally,the underneath mechanism is discussed by combining the streamline characteristics.