叶片数对高比转数轴流泵空化特性的影响

Effects of Number of Blades on Cavitation of High Specific Speed Axial Flow Pump

摘要:

基于shear stress transport（SST）k-ω湍流模型和Zwart空化模型，针对某一高比转数轴流泵模型，对叶片数分别为3、4和5的3组叶轮方案，分别进行了空化流场模拟和实验，计算了不同叶片数下的流量-扬程曲线、流量-效率曲线和空化性能曲线，得到了3组叶轮的临界空化余量NPSHc分别为6.19m、5.122m和4.765m。与叶片数为3的叶轮方案对比，另外2组叶片数方案的NPSH值分别降低了17.25%和23.02%。在空化充分发展的工况范围，发现叶片数多的叶轮的扬程对NPSH降低较敏感；针对轴流泵叶片背面的固定空化和叶顶间隙的旋涡空化，用空泡分布来表征空化的程度，分析了其在不同空化余量下空泡分布的变化规律。通过对比得到，相同NPSH下，叶片数Z=5的叶轮，叶片背面空泡分布体积较少，即空化的程度较低；但其空化严重区的空泡体积增幅较大，即空化发展的速度较快；叶顶区域的叶顶涡诱导的低压区随叶片数减少，范围逐渐向上游扩大，轮缘的空泡体积也随之增大，叶顶泄漏空化更加严重。即叶片数对不同类型空化情况，以及相同类型的不同程度的空化情况影响不同。

Abstract:

Based on turbulence model of shear stress transport(SST) k-ω, homogeneous multiphase model, and Zwart cavitation model, numerical simulations for high specific speed axial flow pumps with three difference blade number impellers were conducted. External characteristic curves and head performances of cavitation were obtained. Through the analysis, critical NPSHc of three impellers, whose blade number were 3, 4, 5, was respectively 6.19m, 5.122m and 4.765m. In severe cavitation area, the more blades the impeller had, the faster head declined with NPSH reducing. Aiming at the two cavitation type in axial flow pump: fixed cavitation on suction side and vortex cavitation in tip region, the cavitating distribution rule in different NPSH value was found. Compared among three impellers, in the same NPSH, the five blades impeller got smaller cavitating distribution on suction side, which meant lower cavitation degree. However, this impeller would get a sharp head decline when it came to severe cavitation area. Low pressure zone caused by tip leakage vortex moved and expanded to upstream with the decreasing number of impeller blades. Moreover, cavitating volume in the impeller with smaller blade number was larger than the others, and it indicated that this impeller’s cavitation degree was severer than others. So the effect of blades number on different cavitation types and different NPSH was not the same.