Abstract: To reveal the influence of the inlet and outlet angles of positive guide vanes on the performance of a multistage hydraulic turbine, a three-stage centrifugal pump is examined in this study. These angles are derived analytically from the geometric parameters of the impeller and reverse guide vanes by using the equal velocity moment; three kinds of guide vane models are designed. Then, these three new schemes and the initial scheme are numerically simulated and compared based on the computational fluid dynamics code CFX. The results show that the new schemes significantly improve the efficiency under various flow conditions, and widen the range of high-efficiency operation. Among them, Scheme C of the new designs has the best performance, with an efficiency increase by 2.2% under the optimal operating condition. The new schemes also improve the internal flow state of a multistage hydraulic turbine－ more uniform pressure distributions between its positive guide vanes and impeller; smaller vortex area near the inlet of the impeller blades in all 4stages; a significant reduction of the high turbulent kinetic energy area near the inlet. This study would help the design and further optimization of multistage hydraulic turbine guide vanes.

Key words: positive guide vane, multistage pump as hydraulic turbine, velocity moment, numerical simulation, turbulent kinetic energy