超临界二氧化碳向心涡轮泄漏特性计算与分析

Calculation and analysis of leakage characteristics of supercritical carbon dioxide radial-inflow turbine

针对超临界二氧化碳(SCO2)向心涡轮轮背空腔泄漏流,采用典型的迷宫密封,对设计参数进行参数化研究与流场分析,并计算轴向力.首先建立迷宫密封泄漏流动CFD模型,运用NUMECA软件对迷宫密封的可靠性进行验证,进而从气动参数和结构参数两方面对SCO2向心涡轮轮背泄漏特性进行研究.结果表明,涡轮泄漏量和轴向力随密封出口压力的升高而减少,在一定间隙范围内线性增大,当密封齿高较小时,泄漏量和轴向力随齿高的增加而减小,当密封齿高超过6.3 mm时,泄漏量和轴向力不再随之变化;在密封轴向长度给定的情况下,齿数为6时能实现最佳的密封效果;通过改变密封齿的形状,得到一种密封性较好的等腰梯形齿.

Using a typical labyrinth seal for the leakage flow of the impeller backface cavity of a supercritical carbon dioxide(SCO2) radial-inflow turbine, the parametric research and flow field analysis are conducted for design parameters, and the axial-force is calculated. Firstly, the CFD model of labyrinth seal leakage flow is established, and the reliability of labyrinth seal is verified by NUMECA software. Then the impeller backface leakage characteristics of the SCO2 radial-inflow turbine are studied from two aspects, namely aerodynamic parameters and structural parameters. The results indicate that the leakage mass flow and the axial-force of the turbine decrease with increasing seal outlet pressure, and increase linearly over a range of clearances. When the height of the seal tooth is small, the leakage mass flow and the axial-force decrease with increase in the height. When the tooth height exceeds a certain value(6.3 mm for the studied case), the leakage mass flow and the axial-force no longer change. In the case where the axial length of the seal is given, an optimum sealing effect can be achieved with a number of teeth of 6. By changing the shape of seal teeth, an isosceles trapezoidal tooth is obtained which has a better sealing performance.