水泵水轮机转轮叶片低压边相比其他部位更具有空蚀的危险性。首先基于低比转速混流式转轮设计程序，设计了3种具有不同厚度的叶片，厚度差异主要在叶片低压边位置；然后采用数值模拟方法对3种翼型转轮分别进行了3个不同出力的水轮机工况以及3个不同流量的水泵工况的全流道定常数值计算，对比分析了各计算工况下具有不同叶片低压边厚度的转轮的空化形态及流动特征；最后采用有限元方法对转轮叶片强度进行了校核。研究表明：3种叶片低压边厚度分布规律的转轮均满足强度要求。空化性能方面，水轮机42%出力工况下，翼型2转轮不发生空化；88%出力工况、100%出力工况和水泵大流量工况下，随着叶片低压边的厚度的增大，空化越剧烈；水泵小流量工况与设计工况下，转轮的空化程度并不因低压边厚度的增大而加剧，而是水泵设计工况下，低压边厚度相对最大的翼型3叶片头部绕流平顺，空化性能相对较好，其他2种翼型由于头部出现脱流和漩涡，出现严重空化。%Because flow separation of blade entrance region and low pressure area are located in the inlet of runner at pump mode, and the low pressure of blade at turbine mode usually occurs in the outlet of runner, the low pressure edges of runner are more risks of cavitation compared with other parts for pump-turbine. In this research, first of all, a two-order polynomial was proposed to describe the blade setting angle distribution law along the meridional streamline in the streamline equation. The runner was designed by the point-to-point integration method with a specific blade setting angle distribution with a consideration of the working condition of turbine and the working condition of pump by adjusting the blade setting angle of heading-edge and trailing-edge. Three blades with different thickness distributions of the low pressure edge were obtained in this method. The main difference was located in the relative chord length 0.8-1.0 position. Secondly, in order to analyze and evaluate the performance of designed runners, structured meshes were adopted to describe the geometries such as scroll case, stay vanes, guide vanes, runner and draft tube. Base on Reynolds Averaged Navier Stokes (RANS) equation, steady state numerical simulations of the Francis pump turbine at three turbine operations with different outputs and at three pump operations with different discharges were completed. The computational boundary conditions were applied at the inlet and outlet surfaces of the computational domain. For the inlet boundary condition, the uniform velocity distribution was assumed. As for the outlet boundary condition, the average pressure was set to constant. For the surface of a wall, the non-slip boundary conditions was prescribed, the velocity components were set to zero. Furthermore, for the interaction of the flow between a stator and rotor passage, Frozen Rotor interfaces were used. Comparisons of cavitation morphology and flow characteristics between runners with different thickness distributions of low pressure edge were analyzed. Finally, the finite element method was employed for checking the strength of runner blades, and the maximum equivalent stress values and positions of runner blades were confirmed. The research results showed that the strengths of three kinds of hydrofoil met the design requirement. For cavitation performance, airfoil 2 cavitation did not occur at 42% output operational condition. However, at 88% output, and 100% output and large discharge pump conditions, cavitation became more intense with the increase of the thickness distribution of low pressure edge of runner. At small discharge and design conditions, cavitation was not more intense with the increase of the thickness of low pressure edge of runner. Under the pump design condition, the airfoil3 with the largest thickness distribution of low pressure edge had the better cavitation performance due to the flow around the head of blade was smoothly compared to the other two airfoil runners which had severe cavitation as result of flow separation and vortices.
展开▼
