| With the rapid development of economic construction and the increasing of industrial demand, the pumped-storage energy units are the large device of the currently commercial energy storage, and which have many advantages such as the hydroelectric equipment high speed starting and stopping, flexible adjustment and so on. The units can effectively cope with the change of the load, optimize the power structure, ensure the safety of the grid, and increase the economic benefits, etc. At present, the construction and development of the pumped-storage energy station is imperative, and the construction of domestic large pumped storage power station also has been started.The pump-turbine is the core equipment of pumped-storage energy plant. 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. 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 under the low head. The prevailing and effective solution to this problem is misaligned guide vanes (MGV) technique. But the application of it brought a new hydrodynamic research topic. Through the analysis of the improvement and effect in case of the guide vanes are not synchronized action, it is a great significance for in-depth understanding of the inherent mechanism of pump-turbine vibration, improving the operation stability of pump-turbine.Accordingly, this paper chooses a pump-turbine model of pumped-storage power station in China as the research object. Through build the three dimensional model of pump-turbine, and then simulate the whole flow passage. Analyze the internal flow characteristics and external characteristics of the pump-turbine under the use of the MGV-when it at different position and opening angle. Here is what the calculation results show:(1) A comparison of the CFD results of the pump-turbine used the MVG with the not shows that in the low flow conditions, centrifugal force and large incident angle cause the formation of large-scale vortex flows inside the runner and between the guide vanes and runner entrance, and that these vortices should be the major factors causing the S-shaped characteristics. (2) Asynchronous vane device can improve the S" characteristics of the pump-turbine unit. The results about the external characteristics of the unit under different asynchronous vanes arranged programs show that under the same open position and the same number of pre-opening vanes, the improvement of the characteristic curve changed better with the pre-opening angle increased; when the number of the asynchronous vanes is over two pairs (including two pairs), decentralized arrangement is better than centralized arrangement; for one pair of pre enlighten vane, the layout of7#-17#is better than2#-12#,so it is not the number of pre enlighten vane is more the improving effect of the S" features is better; Conversely,when the number of pre-enlighten vane is three pairs, the improving effect decreases, but it get the best effect if it has two pairs.(3) Analyzing the internal flow characteristics of unit under the different layout plans of the MGV. The result shows that the S-shaped characteristics of the pump-turbine are improved because the flow is increased, the inlet incidence angle is reduced and the eddy between the entrance of runner and the blade is weakened when the MGV is sed. The MGV disrupts the flow of the scroll case, damages the eddy’s symmetry structure and affects the stress distribution of the runner. The unit running stability is affect by the wheels were forced the different impact of flow.(4) Compared the results of numerical analysis, the study shows that the unit is most optimal when asynchronous guide vane number is two, arrange symmetrical(the corresponding wrap angle is333.18°、243.18°、153.18°、63.18°) and the pre-opening angle of the asynchronous guide vanes is30°. |
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