Numerical Simulation And Experimental Research On Volute Of Mixed-Flow Pump As Turbine

The small hydropower system with hydraulic turbine as the main equipment has the advantages of low investment cost,convenient operation,easy maintenance,and small influence on environment.It is widely used in industrial residual pressure recovery system and remote rural where electricity is scarce.Under the condition of large flow and low head,the mixed-flow pump as turbine(MPAT)is more suitable for hydraulic power generation.At present,the research and improvement on mixed-flow pump as turbine is mainly focused on the impeller.However,the research of volute is hardly to be found.Due to radial dimension limitation,the mixed-flow pump as turbine usually works without guide vane,which leads to water flows directly from the volute outlet to the impeller inlet.The geometry of the volute largely affects the inflow state of the impeller and the performance of the unit.Therefore,the research on the volute of the mixed flow pump as turbine has important practical significance for improving the comprehensive energy efficiency of the small hydropower system.In this dissertation,the external characteristics,internal flow state and structure design of the mixed-flow pump are studied by means of numerical simulation and experimental investigation,on the basis of related theories.The main work and creative achievements of this dissertation were:(1)A mixed-flow pump as turbine with specific speed of 288 was designed and manufactured,and a test-rig was built for external characteristics testing.The effects of grid number and turbulence model on the external characteristics of the mixed-flow pump in the numerical calculation process are studied.The calculated results are compared with the experimental results,and a more accurate numerical calculation scheme for mixed-flow pump for turbine is obtained.The internal flow state and energy conversion process of the mixed-flow pump as turbine have been simulated,which lays a foundation for the structure research of the volute.(2)The mixed-flow pump as turbine volute components is redesigned.By means of numerical simulation,the influence of main geometric of volute on mixed-flowpump as turbine such as the shape of volute section,the type of volute profile,the area of volute cross section and the width of volute outlet has been discussed.Furthermore,the variation rule about external characteristics,internal flow and hydraulic loss of the mixed-flow pump are obtained.In this dissertation,the design method of mixed-flow pump as turbine is discussed in terms of volute,which provides a certain theoretical reference for practical engineering application.(3)The whole domain is divided into main flow zone,transition zone and cavity zone.The flow of the cavity zone has been numerically simulated,correspondingly,the internal flow state and the effect on the external performance were analyzed.The back cavity is modified by filling plate and tested on the test-rig.The numerical calculations and experimental results show that the head,shaft power and efficiency of the mixed-flow pump as the turbine are increased when the gap is filled.(4)The inclined volute outlet is innovatively proposed to improve the efficiency of mixed-flow pump as turbine.After the calculation,the external characteristic and the internal flow rule of the mixed-flow pump as turbine in the case of the outlet inclined spiral case are obtained.Compared with the conventional volute,the head,shaft power and efficiency of the mixed-flow pump as turbine with inclined volute are increased by 10.41%,17.64% and 5.2%,respectively.An outlet inclined volute is designed and manufactured for experiment,and the experiment results are compared with traditional volute case.The experimental results show that the outlet inclined volute case can significantly improve the operating efficiency and provide a new design idea for the design and application of the mixed-flow pump as turbine.