某低水头混流式水轮机叶道涡特性数值分析

Numerical analysis of blade passage vortex characteristics in a low head mixed flow turbine

采用数值模拟手段,研究低水头混流式水轮机叶道涡的水力特性,依托某低水头混流式水轮机模型转轮试验结果和数值计算结果,选取三个单位转速下出现叶道涡的工况,基于N-S方程及SST湍流模型对水轮机进行单流道、全流道、定常和非定常流动数值模拟,分析叶道涡复杂流动的水力特性和压力脉动。结果表明,在叶道涡初生工况,叶片上冠正背面均有部分脱流现象,随着水流在叶片内部运动,转轮出口处,靠近上冠区域有较明显的脱流漩涡和失速区,这部分区域也是叶道涡产生的集中区域。分析转轮内部各个监测点的压力脉动数据,发现转轮内部各个测点会出现有规律的1倍转频的低频脉动和24倍高频脉动,1倍低频脉动与转轮自身转速有关,24倍高频脉动与活动导叶数量有关,是动静干涉影响的结果。测点位置的流态越差,该测点的压力脉动幅值会越高。

By means of numerical simulation, the hydraulic characteristics of blade passage vortex of the low-head mixed flow turbine are studied. Based on runner test results and numerical calculation results of a low-head mixed flow turbine model, three working conditions with blade passage vortex at unit speed are selected. Based on the N-S equation and SST turbulence model, the hydraulic characteristics and pressure pulsation of complex flow of blade passage vortex are analyzed. The results show that under the initial condition of blade passage vortex, there are partial flow separation phenomena on both the front and back of upper crown of the blade. With the flow moving inside the blade, there are obvious flow separation vortex and stall areas near upper crown at the runner outlet, which are also the concentrated areas where blade passage vortex generates. By analyzing the pressure pulsation data of each monitoring point inside the runner, it is found that there will be regular low-frequency pulsation of 1 time the rotating frequency and 24 times highfrequency pulsation at each measuring point inside the runner. The low-frequency pulsation of 1 time is related to the speed of the runner itself, and the 24 times high-frequency pulsation is related to the number of movable guide vanes, which is the result of dynamic and static interference. The worse the flow pattern at the measuring point is, the higher the pressure fluctuation amplitude at the measuring point will be.