混流式水轮机偏工况运行的大涡模拟方法验证

Verification of large eddy simulation(LES) applied in Francis hydro-turbine under partial flow conditions

为更准确地预测混流式水轮机在偏离最优工况时的内部流动特性和外特性,采用大涡模拟方法(LES)对其进行数值研究,针对LES方法,对比单相流计算和空化模型计算的结果.结果表明:基于空化模型的LES预测混流式水轮机内部流场比单相LES更为精确,偏工况下,多相流LES计算能捕捉到更准确的叶道涡结构和尾水管涡带结构.对比模型实验结果表明,LES计算能更好地预测水轮机的外特性,包括流量曲线和效率曲线.基于非定常的水轮机内部流动的LES,使用Q方法提取转轮区的空化叶道涡和尾水管涡带,研究叶道涡的高频运动和涡带的低频演化规律,在活动导叶开度10 mm、单位转速64.9 r/min工况下,叶道涡演化频率为转频的15倍,而涡带演化频率为转频的0.4倍,和实验结果相符合,验证了在复杂三维流动中LES方法的准确性.

To precisely predict the internal flow characteristics and external features of Francis hydro-turbine when running off the optimal flow conditions,numerical computation based on large eddy simulation（ LES）method was performed. For LES method,the results from both single-phase model and cavitation model were compared. It is revealed that LES is capable of providing better depiction for inner flow field of Francis hydroturbine,and also,at partial flow conditions,LES method accompanying with cavitation model can capture more accurate structures for channel vortices and draft tube vortices. Moreover,LES method shows advantages for predicting the external characteristics,including the trends of flow rate and working efficiency,which are verified by the experimental results. Based on the transient simulation on the internal flow,the cavitating vortices in the runner and draft tube are captured by using Q method,and their evolutions with certain frequency are re-generated. For the condition of a = 10 mm and n11= 64. 9 r / min,the frequencies of channel vortex and vortex rope are 15 times and 0. 4 times of rotating frequency,respectively. The results are in agreement with the experimental ones,thus the LES method is proved to be accurate for the complicated threedimensional simulation.