The Performance Prediction And Numerical Simulation Of Hydraulic Turbine Based On Multi-stage Centrifugal Pump

The hydraulic turbine equipment transforms the pressure energy into mechanical energy or electrical energy.Using multistage pump as hydraulic tutrbine is a waste energy saving technology in industrial preocess. There are some problems in the practise for reverse pump using as turbine, such as the unaccurate performance prediction at turbine mode, the difficulty for choosing the right pump, the lower efficiency and so on. Many scholars have studied the voluted single-stage centrifugal pump by the theorial and trial methods.Recently, with the application and development of computer science, making use of CFD numerical simulation to research on the characters of hydraulic turbine is becoming a new method. In this article, the concents studied about the hydraulic turbine are as follows:1,Performance prediction of hydraulic turbine. Predicts the performance of hydraulic turbine by the theorial and numerical methods.For the theorial method ,the main ideas are as follow: derivates the dynamic equation sets of hydraulic turbine from the energy equation and character equation of cascade ,and builds the relationship of head coefficientεand the geometrical parameters; Analysises the hydraulic loss in the passage and calculates the loss coefficientΦ;Expresses the efficiency with the head and loss coefficient because of the highest efficiency is corresponding with the minimumΦ/ε. Solves those equation sets,and definites the coefficient of them,and finally gets the unit flow Q11 ,unit speed n11 and efficiencyη.Then takes the ns=68 multistage centrifugal pump for example, estimates the parameters and calculates the loss of whole passage,and gets the values by calculating these equations one by one.For the numerical method, sets up the whole passage 3D modle of five stages centrifugal pump of which the specific speed is 68 with radial diffuser, meshes the geometry, and discretes the flow equation of liquid with the RNG K-εturbulence modle of FLUENT software. In the case of the constant head and the varial speed, gets a serials of numerical caculated data, draws the speed character curves of hydraulic turbine.Transfers the parameters to unit flow Q11and unit speed n11, and gets the the highest efficiency point in the graphy of comprehensive character curves. At last, compares the two results and gets that the numerical method is more accurate while the theorial method is simple and convenient to predict the performance. 2,Numerical simulation of the whole passage of multistage hydraulic turbine. For the model of multistage centrifulgal pump set above, simulates the whole flow passage by changing the flow while the speed constant.Gets the performance curves by changing flow and analysises the influence by the head and flow. Treats the post-proceeding with Tecplot software.Observes the flow field distributions of velocity and pressure in the middle surfaces of impeller-diffuser set, inlet case, outlet case, and the suction and pressure surfaces of impeller at the modes of the best efficiency point, high flow point and small flow point.Then analysises the flow mechanism in the interior passage, as well as the phenomenon and causes of hydraulic losses in each flow component. Compares the velocity and pressure distributions on the interface surface of each stage, and analysises the variation rules of performance parameters in the turbine passage parts.In order to eliminate the impact loss in the head of impeller,vortex in the back diffuser,impact and mixed loss at the bottom of the annulus part of inlet case and the vortex sets at the two sides of the tongue in the outlet case, some measures are proposed to improve the hydraulic efficiency.3,Character research on hydraulic turbine.Reasearch is focusing on the energy and force characters.For the multistage centrifugal pump modle with ns =68, compares the performances of the power, head, efficiency at pump and turbine modes. Analysises the influences on the turbine performance by the rotation speed. Studies the characters of radial force and axile force for the five stages impellers in variable flow at turbine mode, and the trends of force character curves while the flow is changed in the middle stage.Sets up the one stage 3D modle of ns=35, 60, 68, 100 multistage pumps to research the curve trends of mensionless parameters characters at different specific speeds. Studies the trends ofηt/ηp, Ht/Hp, Qt/Qp, Frt/Frp and Fzt/Fzp varied with the specific speeds. Compares the differences of performances at pump and turbine modes, and derivates the relationships of character parameter ratios at the two modes. Discusses the causes of both radial and axile forces, and compares the trends of force curves varied with flow in one stage at the two modes.