水泵水轮机泵工况旋转失速压力脉动特性及转动机理

水泵水轮机在泵工况部分负荷下运行,叶道内易发生旋转失速,可诱发剧烈的低频压力脉动,严重影响水电站的安全稳定运行。本文采用尺度自适应(SST-SAS)湍流模型对某模型水泵水轮机泵工况进行全流道非定常数值模拟,得到不同工况点下旋转失速引起的压力脉动特性及失速涡团的周向转动机理。结果显示,在40%~80%设计流量下运行时,导叶区发生旋转失速,失速涡团的转动频率为叶轮转频的3.3%~8.1%。旋转失速发展强度越剧烈,转动越慢。旋转失速周向转动的机理是:失速与非失速相邻导叶流道内存在较大压力梯度,在其作用下,失速流道内流体从活动导叶与固定导叶之间通道流向非失速流道,加剧非失速流道内流动分离。被阻碍的水流与无叶区主流叠加流向下一流道,并在活动导叶吸力面进口前缘产生局部低压,导致当前非失速活动导叶流道在进口与出口之间的逆压梯度增强,使流体反向流动,流道产生失速。

Pressure fluctuations characteristics and rotating stall propagation mechanism of a pump-turbine in pump mode

The pump-turbines have to be operated under off-design conditions to maintain the stability of the grid. The rotating stall usually occurs at part load in pump mode,which can cause severe pressure fluc-tuations and strong vibrations. To understand the pressure fluctuations and the stall cells propagation mecha-nism within turbine, the Scale adaptive simulation (SST-SAS) turbulence model and unsteady RANS ap-proach were adopted to simulate a mode pump-turbine with different flow rate. The results show that the simulated characteristics curves are in good agreement with the experiment results. The rotating stall occurs in the region from 40% to 80% of the best efficiency point (BEP) flow rate. The stall cells rotating along the circumference and their rotating frequency is 3.3%~8.1% of the runner rotating frequency. The propaga-tion of the stall cells is driven by the growth and the decay of the stall cell. The pressure gradient be-tween the stalled and un-stalled channels make the fluids flow from the stalled channel into the un-stalled channel through the gap between the corresponding guide vane and stay vane, which will increase the flow separations in the un-stalled channel. The growth of flow blockage in the un-stalled channel will make the inflow deviate toward the downstream channel and pressure decrease around the leading edge of the guide vane suction side. Further, the adverse pressure gradient between the leading and the trailing edges of the un-stalled guide vane is enhanced. Consequently,the flow blockage continues to grow until the vortices oc-cupy the entire un-stalled channel.