压力脉动对尾水管进口空化腔影响的CFD模拟分析

An Analysis of the Influence of Pressure Pulsations to the Cavitation Cavity at Draft Tube Inlet of Turbine Based on CFD

水电站过渡过程计算中水轮机尾水管进口最小压强须控制在-8 m H2O以上,以防止危险的水柱分离。对于水泵水轮机,压力脉动大且成份复杂,确定此最小压强时应该计入哪些压力脉动尚无明确答案。针对某直锥尾水管水泵水轮机模型,在转轮进口施加不同脉动流速,分析尾水管进口空化腔生成发展规律。发现尾水管最大空化腔体积与进口脉动流速频率相关;随频率增大,空腔体积有先快速增大后缓慢减小变化趋势;空化腔变化周期受压力脉动频率和尾水管出口压强波动共同影响。在实际转轮进口可能的压力脉动频率对尾水管空化腔波动都有较大影响,但频率与尾水涡频率一致时会有共振效应。尾水管水锤波动是产生空腔涡的根本因素。

The minimum pressure at the draft tube inlet of turbine should be controlled above-8 m H2O in the calculation of transient pro⁃cesses of hydropower station to prevent dangerous water column separation.For the pump-turbine,the magnitude of pressure pulsations is large and their composition is complex.There is no clear answer to which pressure pulsation components should be included in the calcula⁃tion of the minimum pressure.In this study,a pump-turbine model with straight cone draft tube is considered,and different velocity pulsa⁃tions are applied to the runner inlet to analyze the changing laws of cavitation cavity at the draft tube inlet.It is found that the maximum cavi⁃tation cavity volume of the draft tube is related to the inlet velocity pulsation frequency.With the increase in frequency,the cavity volume in⁃creases rapidly first and then decreases slowly.The variation period of cavitation cavity is affected by the pressure pulsation frequency and the pressure fluctuation of the draft tube outlet.The possible pressure pulsation frequency at the actual runner inlet has a great influence on the fluctuation of the cavitation cavity at the draft tube,but the resonance effect occurs when frequency is consistent with the frequency of the draft tube vortex.The fluctuation of the water hammer in the draft tube is the fundamental factor of cavity vorticity.