混流式水轮机部分负荷下的叶片动载荷模拟

Simulation of dynamic loads on Francis blades at partial load

通过求解三维不稳定Reynolds平均Navier-Stokes方程,并采用RNGk-ε模型实现方程的封闭,对3个不同转轮在部分负荷下进行了包括导叶、转轮、尾水管在内的三维不稳定流动计算。结果表明:由于水轮机转轮的旋转,在部分负荷工况下,由尾水管内涡带引起的转轮内的压力脉动主要频率fr是转频fn与涡带压力脉动频率fd之差;同时转轮内压力脉动还有导叶通过频率和转频及其倍频等成分;在66%左右开度下叶片上压力脉动幅值一般大于80%左右开度下的值;在同一工况下,叶片背面的压力脉动幅值一般大于叶片正面的值。

The pressure oscillations on Francis blades were analyzed numerically for partial loads by solving the 3-D Reynolds-averaged Navier-Stokes （RANS） equations with the RNG k-ε turbulence model. The calculational domain included the guide vanes, the runner, and the draft tube, The results show that with the runner rotating relative to the draft tube, tube at partial load that causes a vortex rope appears in the draft pressure fluctuations inside the runner with a frequency of - fn＋ fd. This frequency is usually dominant. Other frequencies such as the guide vane blade passing frequency, the rotational frequency and it＇s higher order harmonics can also be observed at some points near the inlet. The peak-to-peak amplitudes on the blades tend to be higher at 66% of the optimum opening than at 80% of the optimum opening. The pressure fluctuations on the suction side tend to be stronger than on the pressure side.