Numerical Simulation And Experimental Research On Hump District Of Francis Pump-turbine

On the characteristic curve of the pump mode of pump-turbine there is a hump district,which will affect the stable operation of the pump mode.For this reason,in the pump-turbine tenders and contracts strict rules were usually made for the hump safety margin of the pump mode. In order to avoid the operation in the pump mode of pump-turbine getting into the hump zone,it is necessary to conduct an deep research on this.In this paper,experimental study and numerical simulation were used to make a detailed study for the internal flow of the runner as well as the effects to the unit when pump-turbine was operated at the hump zone.Firstly,energy characteristics and the pressure fluctuation test were made in pump mode of the pump-turbine at different openings of the guide vanes.The energy characteristic curve was drawn in pump mode of the pump-turbine,and the image of the flow pattern at the runner inlet was obtained at a certain guid vanes opening. Pressure fluctuation test was made at the outlet of the volute,between runner and guide vanes,between head cover and runner,at the upstream and downstream of cone, at the upstreamand downstream of the elbow when the pump-turbine was operated at hump zone.Secondly,three-dimensional turbulent flow field calculation and analysis of both one flow passage and whole flow passage in pump mode of pump-turbine were finished by using permanent and incompressible three-dimensional Navier-Stokes equations and the RNG k-εmodel,the delivery lift in pump mode of pump-turbine was predicted and was compared with the test results at relevant guide vanes openings. Analysis pointed out that:with the reducing of flow,the flow separation near the crown of the runner outlet of pump-trbine,the senondary flow from the inlet of guide vanes to the outlet of runner, the positive rotary at the cone of the draft tube near the runner inlet and the size and direction of relative velocity changes at the outlet of the suction surface of the runner blades had an important impact on the formation of the hump zone on the characteristic curve in the pump mode of pump-turbine.If the design of the molded line of the guide vanes and crown is optimized in the design of pump-turbine, at the same time, measures to delay or reduce the appearance and the development of the back flow at the inlet of the runner are taken, the performance in pump mode of the pump-turbine in the hump are may be greatly improved.The results of this study provided a basis for further research of hump area characteristics and improving the hydraulic characteristics of pump-turbine runner in pump mode.