| It has the advantages of low cost, quick effect and considerable economic benefits for the hydropower stations with the capacity of expansion. Some small and medium power plants that run for many years have backward technical indicators,poor manufacturing quality, serious wear and capacity decreasing and so on. Such problems not only waste a lot of water resources, but also affect the safe operation of the power stations. At present, the CFD technology has developed rapidly and has got remarkable achievements. It is of great practical significance to explore how to use CFD to improve the capacity of turbines in old power plants.As for the actual problems of HL741-WJ-84 turbine that belongs to Gulangdi hydropower station in Qinghai province, a reform scheme has been developed. At first,preliminarily select a target runner by analyzing many excellent model runners, then appropriately modify the selected runner in order to make the runner keep itself good performance and meet the requirements of power reform. In view of the small hydraulic turbine runner jams frequently in the flood season so that affects the normal operation, uprating of the turbine by reducing three blades in modified target runner.Use CFD to explore numerical simulation and hydraulic performance estimation method that can be used to transformation of turbine. Validate the results of reform and analyze the reasonability of flow pattern after transformation to evaluate the improvement objective.The research based on the numerical calculation of flow field to analyze the flow of water before and after the retrofit of the turbine, and predict the performance of the unit. By solving the Reynolds equations, and selecting the standard κ-ε turbulence model and SIMPLE algorithm to calculate the entire flow passage of the turbine before and after the modification in the FLUENT. The information of flow in the whole passage of turbine and each component at four typical conditions is gained.Through the analysis for the calculation results to get the different characteristics of hydrodynamics, and the change law of the efficiency and output with the guide vane is given.After the reform, the flow of the turbine is uniform, and the flow distribution is reasonable, and there is no disturbance of the flow field. In the spiral case, the flow of water becomes more soother, and flow capacity is enhanced. The pressure and speed of water flow is steady; the results of numerical simulation for blades show that reduce the number of blades has great effect on pressure distribution at the back of the blades, and the airfoil cavitation of blades under different working conditions is better than the original HL741, but the cavitation at the back of the blade near the inlet ring becomes worse. For the sake of safety, some measures that anti cavitation need to be taken; in the draft tube , the flow of water is steady and uniform between the original optimal condition and larger opening condition. The eccentric vortex is weakened,and the overall flow becomes smooth. The hydraulic performance is better than former turbine. The optimal working conditions tend to large flow area, the capacity increased by up to 13%, and the efficiency reached 91% after transformation of the hydraulic turbine. The results can be used in the actual transformation of HL741-WJ- 84 turbine and guide the operation of power plant. |
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