The Research Of Relationship Among Multistage Hydraulic Turbine Parameters

The hydraulic turbines can recover the energy from liquid with high pressure and convert the energy into shaft power which can further be used directly to generate electricity or to drive others energy consumption machine, so the development and utilization of high pressure liquid has been brought into effect. One of the main forms for the hydraulic turbines is pump working as turbine. The PAT has many advantages such as mass production, simple construction and wide spread application, including the single stage hydraulic turbine and multi-stage the single stage hydraulic turbine. The single stage hydraulic turbine work in medium or low power level conditions, and the multi-stage the single stage hydraulic turbine work in high power conditions. The relationship of the parameters between the pump and the multistage centrifugal pump for turbine were studied, and the hydraulic performance of the multistage centrifugal pump for turbine was forecasted. In this thesis, the pumps with the specific speed of60,68.6and112.5are selected. The above mentioned problems are studied by taking advantage of theoretical derivation and numerical simulation.1、The theoretical analysis. The loss of the multistage centrifugal pump in the direct and reverse mode includes mechanical friction loss, leakage loss and hydraulic loss. Mechanical efficiency and volumetric efficiency can be obtained by theoretical calculations, so the multistage centrifugal pump hydraulic efficiency can be achieved. hydraulic loss mainly includes the hydraulic loss of suction chamber、the hydraulic loss of pressure chamber、hydraulic loss in the impeller、the hydraulic loss in guide vane and the interstage hydraulic loss. the hydraulic loss of suction chamber and the hydraulic loss of pressure chamber can be neglected, hydraulic loss in the impeller、 the hydraulic loss in guide vane and the interstage hydraulic loss can be obtained by the theoretical calculation, then hydraulic efficiency of the impeller and guide vane can be obtained in direct mode, so the hydraulic efficiency in the impeller and guide vane can be obtained in reverse mode, combined with the interstage loss, the hydraulic efficiency of the turbine mode can be achieved; the the relationship of the flow in direct and reverse mode can be obtained by analysis of import and export velocity triangle; The relationship between the head and the pressure head can be obtained in direct and reverse mode through principle of momentum moment; Through three relation above, it’s obtained for the pressure head、flow and the hydraulic efficiency. If mechanical efficiency and volumetric efficiency in reverse mode were calculated, the total efficiency can be calculated in reverse mode.2、Numerical analysis and performance prediction. Through numerical analysis of multistage centrifugal pump with the specific speed of60、68.6and112.5, the characteristic curves of multistage centrifugal pump in the working condition of turbine and pump working condition were obtained. From the curves, it’s known that when the multistage centrifugal pump works as turbine, the flow rate and head are higher than them in the pump conditions at the best efficiency point, but the efficiency is lower. The flow ratio、the head ratio、power ratio and efficiency ratio at best efficiency point along with the change of specific speed was analyzed respectively, and the ratio of the flow rate decreases with the specific speed increasing, but the ratio of the head increase with the specific speed increasing. Compared the theoretical results with the numerical results, the best efficiency was in an acceptable coincidence with the numerical datas for turbine mode.3、The flow field of the hydraulic turbine. The distribution of relative velocity and static pressure in the suction chamber and the delivery chamber are not homogeneous, and the hydraulic loss in them increases with the flow rate increasing, but the hydraulic loss is so small at the best efficiency point that it can be ignored. At return guide vanes, the relative velocity are not homogeneous, it is higher at the concave surface than it at the convex surface, and there are in a large number of vortex. At the guide vane, the relative velocity are homogeneous in the expansion section, and static pressure is gradually reduced; In the spiral section, static pressure is not homogeneous, the hydraulic loss in the guide vane increases with the flow rate increasing, there are not shock loss at1.5times the design flow of the pump; Static pressure from import to export gradually reduces from entrance to exit, the pressure at the impeller blade suction is lower than that of the pressure side. There are a massive low speed area on the working plane area, and there is the lowest point about the hydraulic loss. The best efficiency point in the impeller does not coincide exactly with the best efficiency point in pump.