水泵水轮机临界空化系数的数值预测

Numerical prediction of critical cavitation number in pump-turbine

为了研究水泵水轮机空化系数对内部非定常流动的影响,采用SST k-ω模型对一模型水泵水轮机进行数值模拟,对机组在不同空化系数下的性能及内流场进行分析.结果表明,空化系数的大小可以改变水泵水轮机内部的流动状况,临界空化系数反映了水泵水轮机机组的能量特性.空化初生时,水泵水轮机的水头降低并且效率提高;随着空化的发展,机组水头显著增大,效率却快速减小;水泵水轮机的空化主要发生在叶片出口边吸力面靠近下环处;空化系数的改变对转轮内部流动稳定性的影响不明显.水泵水轮机的水头在空化系数较大时基本保持不变;当空化系数为0.075~0.150时,水头随空化系数的减小而略有减小;当空化系数小于0.075时,水头随空化系数的减小而增大.

The hydraulic performance and internal flow in a pump-turbine model were analyzed under different cavitation numbers to study effects of the coefficient on unsteady flow in the model by using the SST k- ω turbulence model. The results show that cavitation number can alter the flow pattern in the pump-turbine and the critical cavitation number reflects the energy performance of a pump-turbine.The head of pump-turbine decreases and the efficiency rises at cavitation inception; with development of the cavitation,the head increases considerably,while the efficiency decreases quickly. The cavities are located at the blade suction side near the runner outlet and ring. The change of cavitation number has less effect on the instability of flow in the pump-turbine runner only. If cavitation number is larger,the head of pump-turbine will remain unchanged essentially. Moreover,the head decreases slightly with decreasing cavitation number when cavitation number is in the range of 0. 075- 0. 150. However,the head increases with decreasing cavitation number as the coefficient is less than 0. 075.