可逆式水泵水轮机转轮的三维反问题优化设计

Optimal design of reversible pump-turbine runner

与常规的水泵或水轮机转轮相比,可逆式水泵水轮机转轮要兼顾水泵和水轮机2种工况下的性能,设计要求高、难度大,且影响转轮性能的设计参数较多,很难通过设计-修正-试验的方法获得2种运行工况下性能均优的可逆式水泵水轮机转轮。针对这些困难,该文将三维反问题设计、CFD计算与多目标优化策略相结合,构建了可逆式水泵水轮机转轮的优化设计系统。该设计系统不仅可缩短转轮设计周期,且能对多个运行工况下的多个目标同时进行优化。利用该优化设计系统,以叶片载荷和叶片倾角为优化变量,以水泵设计工况点的转轮效率和水轮机额定工况点的转轮效率为优化目标,以水泵设计工况的扬程为约束,对某一抽水蓄能电站的水泵水轮机转轮进行了优化设计。结果表明利用该优化设计系统能够设计出在水泵和水轮机2种运行工况下转轮水力效率均高于95%的可逆式水泵水轮机转轮,其中水泵设计工况下转轮效率提高了0.15%,水轮机额定工况下转轮效率提高了2%,表明了该优化设计系统在提高可逆式水泵水轮机转轮性能方面的可行性和有效性。该研究可为水力机械,包括水泵水轮机、常规水轮机、水泵的设计开发提供参考。

As a key component of a reversible pump-turbine unit, a pump-turbine runner rotates at two opposite directions under the pump and turbine modes. The flow states in the runner are quite different under the pump and turbine modes, which creates a great challenge for the design of a pump-turbine runner. Nowadays, a pump-turbine runner is always designed in one mode and verified with the other mode. Since there are several parameters affecting the runner＇s performances and one parameter might have contrary effects on runner performances under the pump and turbine modes, it is hard to obtain a runner with high performance at both the pump and turbine modes by a trial and error method. In the present paper, a 3D inverse design method, CFD calculations, and multi-objective optimization strategy were coupled, and an optimal design system was built to improve the performances of a reversible pump-turbine runner. In the system, by using a 3D inverse design method, the runner shape was obtained by inputting corresponding parameters. A validated CFD method was used to estimate runner performances under different operating conditions. A multi-objective optimization strategy was then adopted to search runners with good performances at both operating modes in the design space based on a response surface model between input parameters and runner performances. The optimal design system was capable of solving some difficulties in pump-turbine runner design, such as a long design cycle and difficulties in obtaining good performances at both pump and turbine modes. The system was used to optimally design a middle-high head reversible pump-turbine runner, in which blade loading and blade lean were chosen as the input parameters, runner efficiency at the pump design point and the turbine rated point were set as optimization objectives, and the head at pump design point was set as a constraint. Since the optimization calculations were based on a response surface model, performances of nearly 10 000 runners under different operating modes were estimated in several minutes. Three runners from the Pareto frontier were chosen for detailed validation. CFD results showed that the optimal runner had a high hydraulic efficiency of over 95% at both the pump and turbine modes, which indicated a great improvement in runner efficiency in the turbine mode and the maintenance of high efficiency at the pump mode as compared with the initial design. The effects of the input parameters on runner interior characteristics under different operating modes were also analyzed in this paper. The results showed that fore-loaded blade loading distribution on the shroud was helpful in improving the flow state at the inlet under the pump mode by reducing the low-pressure area on the suction side. The blade lean at the high pressure side not only changed the work distribution along the span wise direction, but also improved the flow state by bringing down the pressure difference at the inlet in the turbine mode, and played an important role in improving runner efficiency, especially in the turbine mode.