2种隔舌模型对离心泵性能模拟的影响

Influence of two types of cut-water shapes on simulated performance of centrifugal pump

为了提高离心泵性能预测的精确度,降低水泵研发成本,对2种影响泵性能较大的隔舌模型进行了对比研究.通过Ansys ICEM CFD软件对离心泵3个结构部分进口、叶轮、蜗壳进行网格划分,利用商业软件CFX进行数值模拟.进口边界设定为均匀来流,出口边界设定为压力出口,进口段与叶轮壁面粗糙度0.02 mm,蜗壳壁面粗糙度0.05 mm,采用k-ε湍流模型并计算机械损失11%,容积损失4%,将模拟结果与试验数据进行对比发现:在各流量工况下,圆角隔舌模拟结果与试验数据误差较小且保持稳定;矩形隔舌模拟结果在小流量工况下接近试验数据,在大流量下则误差较大.通过压力分布和流线图发现随着流量的增大,圆角隔舌的高压区和流线分布都较为稳定,矩形隔舌在额定流量和大流量下高压区扩散,并且有旋涡产生,旋涡随流量增大而增强,影响了蜗壳内部流动,使得模拟误差变大.研究对比了2种隔舌模型外特性的差异,并通过流场分析找到了产生差异的原因,表明对隔舌进行圆角处理能明显地改善内部流场,从而提高泵的性能.

A comparative study was conducted between two types of cut-water shapes which significantly affect the performance of a centrifugal pump to improve the accuracy of performance prediction and reduce development costs for the pump.The computational fluid domains include suction pipe,impeller and volute,which were meshed with Ansys ICEM CFD code to generate a structured mesh and the numerical simulation of flow in the pump was accomplished with Ansys CFX.There is the normal velocity boundary condition at the inlet to the suction pipe,and there exists the outlet pressure condition at the discharge of the volute diffuser.The mechanical and volumetric efficiencies were considered to be 89% and 96%,respectively.It was found that the simulated performance for the pump with round cut-water shape is close to the test data at various flow rates.The simulated performance for the pump with rectangular cut-water shape is near the measured result at low flow rates,but shows a relatively noticed difference from the measured one at a high flow rate.According to the pressure contours and streamline plots,the high pressure zone on the round cut-water is relatively stable and the streamlines around it are smooth with increasing flow rate.For the rectangular cut-water shape,however,the high pressure zone is unstable to shed a series of vortices at the design condition and high flow rate.Those vortices alter flow patterns in the volute and eventually result in that the predicted performance differs from the measurement considerably.The reason,why there is a significant difference in the perfor-mance exists between two types of cut-water shapes,has been clarified by analyzing the flow field in the volute.It is confirmed that a round cut-water can make flow pattern in the volute smoother and subsequently improves the pump performance.