Research On The ’S’characteristics Of Prediction Methods Of The Pump Turbine

As the operation conditions of pump turbine are very complicated and various, the "S" characters of pump turbine are the most important part in the transient process of pump turbine. It is the key factor to restrict pump turbine to operate safely and stably. The serious "S" characters of pump turbine may result in the failure from no load of units to on load directly, so it is hard to connect the grid with start-up in the turbine mode. If "S" characters of pump-turbine are obvious, no load condition in the turbine mode will be unstable after the load rejection. Therefore, to research the "S" characters of pump-turbine are significant to develop the pumped storage.According to the test principle of hydraulic machinery, it is proposed that a new prediction method of "S" characters of pump-turbine is formed based on CFD Numerical prediction of "S" characters of pump-turbine is performed at the initial conditions of constant speed and constant head. Then unit speed is calculated by numerical calculated head and the corresponding relationship of unit speed and unit discharge for "S" characters is obtained. Comparing the results between the calculation and the "S" character of pump turbine, it is proved that the new prediction method is feasible.However, there is deficiency to predict "S" characters of pump turbine with above predicted method at constant speed and constant head. A rectification formula for unit speed and unit discharge at "S" character zone is proposed. It is proved that mathematical rectification is effective and feasible by the way of numerical calculation. From the comparative results between modified "S" character and test, it is shown that the rectification formula can significantly reduce the error of numerical prediction; especially it can play a great role to operate condition at low speed and large discharge. It is very significant to predict the "four quadrants" character at the transient process of pump turbine.Based on the "S" character prediction method of pump turbine, two profile structures of guide vane of space curved surface are computed to study their effects to "S" characters of pump turbine. Comparing with corrected results between guide vane of space curved surface for two profile structures and convention guide vane, it is confirmed that guide vane of space curved surface plays a significant role to improve "S" characters of pump turbine. The guide vane of space curved surface with profile structure NACA₁can improve and even eliminate the "S" character of pump turbine. The paper presents the formative principle of "S" character on the basis of "S" characters computer results by two profile structures of guide vane of space curved surface.By the initial condition of constant speed and constant head, numerical calculation of start-up condition of pump turbine is performed by boundary layer mesh refinement with SST k-w model. The relation of unit speed and unit flow at start-up operation condition is reflected by numerical head, and then the "S" characters of pump turbine can be predicted. As the deficiency of computation method, the rectification formula of numerical prediction method is proposed and it has been proved by numerical computation. According to the comparison of the correct results with test results, both of them have good approximation relationships and the former can reflect the "S" characters of pump turbine well. Thus, it is obtained that the accurate prediction method is used to predict "S" characters of low specific speed pump turbine. It is confirmed that profile NACA₁of guide vane of space curved surface can remarkably improve the "S" characters by calculating two profile structures of guide vane of space curved surface with the prediction method of "S" characters of pump turbine. The formative principle of "S" characters is discussed.