轴流泵叶轮进口流场PIV试验与数值计算

轴流泵内部流场较为复杂,尤其是端璧区的叶顶泄漏,不仅能破坏叶轮进口流场,而且对叶轮流道内流场也有较大的影响.采用CFD数值计算与PIV试验研究相结合的手段,对叶轮进口附近流场进行研究,以揭示其流动机理.PIV结果表明：在1.2Qopt和1.0Qopt工况下的流线及速度云图分布较为均匀,而0.8Qopt工况下,外缘壁面靠近叶片进口边处出现低速区,且流线向轮毂侧偏转.数值计算结果表明：预测外特性结果与试验相吻合,叶轮进口的流场也与PIV结果一致;另外,在1.2Qopt工况下,5%叶顶高处的间隙内部流动方向与主流一致;1.0Qopt工况下,流体基本沿周向运动;当流量减小到0.8Qopt时,出现叶顶泄漏,并在间隙内靠压力面侧形成分离后再附着的现象,在吸力面一侧受泄漏流与主流碰撞及相互卷吸的影响,形成一个逆时针方向的旋涡.

PIV measurement and numerical calculation for impeller inlet flow field in axial flow pump

The internal flow field for axial flow pumps is complex,especially the tip leakage in the end-wall region.This phenomenon can not only disturb the flow field at impeller inlet,but also play an important role in the flow within impeller passage.Therefore,the flow field close to impeller inlet was investigated using an approach combining CFD numerical method with the PIV measurement system to reveal the flow mechanism.The results of PIV show that：the distributions of streamlines and velocity contour are relatively uniform at 1.2Qopt and 1.0Qopt conditions,while at 0.8Qopt condition,a region with low velocity appears near the outer wall close to blade leading edge and the streamlines deflect to hub-side.Numerical results reveal that the predicted pump performance curves agree well with the experimental results,and the flow field at impeller inlet is consistent with the PIV results.Moreover,it is found that the flow direction in clearance for 5%blade tip height at 1.2Qopt condition is as the same as that for mainstream.For the case of 1.0Qopt,fluid within tip clearance mainly migrates along the circumference direction.Tip leakage flow arises as the flow rate decreases to 0.8Qopt,with separation phenomenon followed by adhesion in the clearance close to pressure surface side,forming a counterclockwise vortex due to the effect of collision and entrainment of leakage flow and mainstream on suction suzface side.