射水减弱混流式水轮机尾水管内压力脉动的数值模拟

Numerical Simulation of Elimination of Pressure Fluctuation in Francis Turbine Draft Tube Using Water Jet

摘要:

选用RNG k—ε湍流模型，对一台混流式模型水轮机在部分负荷工况下的流动进行了全流道三维瞬态湍流数值模拟。数值计算结果与模型试验结果进行了比较，成功预测了水轮机尾水管内压力脉动的幅值与频率特性。从混流式水轮机泄水锥处向尾水管内射水可减弱尾水管内低频压力脉动，对射水后水轮机内的流动进行了数值模拟。计算结果表明，通过射水可以有效减弱尾水管内的压力脉动，减小压力脉动幅值。随着射水量的增加，压力脉动幅值减小更加明显，但是同时会导致水轮机效率的下降。为了尽可能大的减小压力脉动幅值，并兼顾水轮机效率，建议选择0.03~0.05倍该工况流量的射水量。此时，水轮机压力脉动幅值降低明显，而水轮机效率下降不大。

Abstract:

3-D unsteady turbulent flow simulation with RNG k—ε turbulence model of complete flow passage on Francis turbine at partial load condition was performed. The simulation results were compared with the test data. The simulation predicted the pressure fluctuation magnitude and frequency characteristic in the draft tube successfully. A method injecting water from the crown tip to the turbine draft tube to weaken the pressure fluctuation was introduced. Simulation of the flow with water jet was performed, showing that the water jet weakened the pressure fluctuation in the turbine draft tube effectively. With the increase of the jet flow rate, a greater reduction of pressure fluctuation magnitude was detected, but a decrease of efficiency was found. To keep a balance between pressure fluctuation mitigation and efficiency requirement, 0.03~0.05 times of flow rate at the calculated operating condition was suggested.