基于PIV的低比转数离心泵网格无关性

Grid-independence in low specific speed centrifugal pump based on PIV

针对小流量工况采用计算流体动力学(CFD)对离心泵的性能进行数值模拟的精度问题,以一低比转数离心泵为例对其进行整体结构化网格划分,采用ANSYS CFX 14.5软件对模型离心泵的进口管路流道、叶轮流道以及蜗壳流道组成的流场进行定常数值计算.从改变整体网络数量与叶轮网格数量的角度分别进行网格无关性验证对0.6及1.0倍设计流量下的模拟精度进行比较研究.准确性评价指标采用外部特性扬程值及PIV得到的叶轮和蜗壳内部分区域的绝对速度,具有较强的说服性.分析表明:对总体网格数增加的方法进行的无关性分析即可满足要求;网格数量的增加对叶轮内绝对速度影响较大,而对蜗壳内绝对速度影响很小;在设计工况下,蜗壳和叶轮内部绝对速度的预测精度都比0.6Q_d工况下的高,因而在进一步小流量流动特性分析时,需要更精密的网格.通过对外特性和内流场速度的对比,最终选择网格模型为网格IGD.

In general, the flow in centrifugal pumps are exceedingly complex, especially under part- load condition in which rotation stall, flow separation and secondary flow are involved. The accuracy of CFD simulation of internal flow in a centrifugal pump under part-load condition is very important. However, this issue is rarely mentioned in literature. In this paper, a structured mesh in a low specific speed centrifugal pump is generated and the turbulent flow in the pump including suction pipe, impel- ler and volute is simulated by means of software ANSYS CFX 14.5. A grid-independence check is con- ducted when total number of cells and the number of cells in the impeller fluid domain are changed at 0.6 and 1.0 times the design flow rate. The head and absolute velocities in the impeller and volute ob- tained by PIV are adopted as more reasonable indexes to evaluate the CFD accuracy. It is shown that the grid-independence analysis can be performed satisfactorily by increasing total number of grid ceils, but increasing the number of mesh cells of the impeller fluid domain is unnecessary. The number of grid cells has a great effect on the absolute velocity of fluid in the impeller, but a little impact on the absolute velocity in the volute. The accuracy of predicted absolute velocity in the volute and impellerunder the design condition is higher than that at O. 6Qd. Comparisons in flow field and performance curve suggest the mesh model should be IGD eventually. These results will be helpful to the study on unstable cha-racteristics of internal flow in a low specific speed centrifugal pump under part-load condi- tion by making use of numerical simulation technique.