超临界二氧化碳轴流透平级流动损失评估

Flow loss assessment for a supercritical carbon dioxide axial turbine stage

为进一步探究超临界二氧化碳透平内部的损失机制,针对某透平级采用数值方法研究了其流动特性,将静叶与动叶通道内的损失进行分解,定量计算了各项损失大小及其占比,明晰了超临界二氧化碳透平级的损失大小序列。结果表明,超临界二氧化碳介质密度大和透平叶高小导致其隔板密封和叶顶密封的泄漏损失巨大,级负荷为0.93,静叶间隙相对高度为0.012,动叶间隙相对高度为0.010时,泄漏损失占级总损失的38.23%,其中隔板密封泄漏损失占比为21.94%,叶顶密封泄漏损失占比为16.29%。除泄漏损失外:静叶栅通道内,叶片平均最大厚度比弦长为0.33,展弦比为2.07时,型面损失远高于端壁损失和尾迹损失,占级总损失的9.68%;动叶栅通道内,叶片平均最大厚度比弦长为0.28,展弦比为1.73时,型面损失、端壁损失和尾迹损失相差不大,型面损失仍然占比最高,达到级总损失的15.39%;动叶通道内的二次流影响范围更大,导致其端壁损失远高于静叶端壁损失,其壁面附近流体的黏性耗散和马蹄涡、通道涡等造成的二次流损失是端壁损失的主要来源。研究结果可为超临界二氧化碳透平的优化设计提供方向指引和数据支撑。

In order to further investigate the loss mechanism in supercritical carbon dioxide turbines,the flow characteristics in a turbine stage were studied by numerical method.The losses in the passage of stator and rotor blades were decomposed,and the various loss values and their proportions were quantitatively calculated.The loss sequence of the supercritical carbon dioxide turbine stage was clarified.The results show that,the high density of supercritical carbon dioxide and low blade height result in a very large leakage loss in turbine stage.When the stage load coefficient is 0.93,the relative height of the stator clearance is 0.012 and the relative height of the rotor clearance is 0.010,the leakage loss accounts for 38.23% of the total loss,including 21.94% of the diaphragm seal leakage loss and 16.29% of the tip seal leakage loss.Except for leakage loss,when the average maximum thickness divided by chord length is 0.33 and the aspect ratio is 2.07 in stator passage,the profile loss is much higher than the endwall loss and trailing edge loss,accounting for 9.68% of the total loss.In rotor passage,when the average maximum thickness divided by chord length is 0.28 and the aspect ratio is 1.73,the difference among endwall loss,profile loss,and trailing edge loss is not significant,and the profile loss has the highest proportion,accounting for 15.39%of the total loss.The influence range of secondary flow in rotor is even wider,and its endwall loss is much higher than that of the stator.The main sources of endwall loss are viscous dissipation of fluid near the end wall and secondary loss caused by horseshoe vortices,passage vortices,etc.The research results will provide direction guidance and data support for the design and optimization of supercritical carbon dioxide turbines.