轴流泵叶顶泄漏涡及其空化的数值模拟与可视化试验

Numerical simulations and visualized experiments of tip leakage vortex and associated cavitation in axial-flow pump

为了研究叶顶泄漏涡的三维结构及其空化特性,该文以某一轴流泵模型为研究对象,利用修正的滤波器模型(Modified Filter-based Model,MFBM)对轴流泵叶顶间隙流动进行数值模拟,并与试验进行对比。结果表明修正后的湍流模型可以很好地预测泵的水力性能和空化性能。该文通过轴向速度和湍动能分布,详细地解释了不同工况下叶顶间隙内的流场结构。利用最小张量法则,可以判别叶顶区的空化初生现象,且结果与利用最大旋涡准则预测的涡心涡量和压力分布相一致。通过叶顶区的三维涡量分布,揭示了叶顶泄漏涡的三维卷吸过程,表明了叶顶泄漏涡的空间结构。利用数值模拟和可视化试验,说明了叶顶空化涡的类型及其演变过程,尤其是叶片出口处几乎垂直于叶片吸力面的大尺度空化云结构,其初生机理及其诱导的流动失稳等现象将是今后研究的重点。

In order to investigate the three-dimensional structure of tip leakage vortex and associated cavitation, the tip clearance flow of an axial-flow pump model was simulated using an improved filter-based model and the results were compared with experiments. It shows that the modified turbulence model can predict the hydraulic and cavitation performance well. By the distributions of axial velocity and turbulence kinetic energy, the flow structure in the tip clearance for different flow rates can be clarified in detail. The cavitation inception in the tip region can be predicted using minimum tension criterion, corresponding to the vorticity and pressure distributions in the vortex core which is detected using maximum strength method. With the distribution of vorticity layers in the tip regon, the mean three-dimensional roll-up process of tip leakage vortex is shown, which can reveal the spatial structure of the vortex. With the aid of simulations and visualized observations, the type of tip cavitating vortices and the revolution can be revealed, especially the large-scale cavitation cloud moving in the direction that is nearly perpendicular to the blade suction side at the blade outlet. Definitely, some phenomena, such as the inception mechanism and induced flow instabilities, would be of significant importance in the future work.