半开式径向叶轮上游预旋流动研究

叶轮进口上游的预旋流动是影响流体机械水力及空化性能的重要因素，主要采用粒子成像测速（PIV）技术对半开式径向叶轮上游的预旋流动进行试验研究。通过对比不同转速和流量工况下的PIV试验结果，发现在叶轮上游吸入管内均存在与叶轮旋转方向一致的预旋流动，且偏离设计工况越远、距离叶轮越近、其预旋速度相应也越大。同时，叶轮旋转的影响还可通过流道向上游传播，继而在吸入管内诱导产生涡量场。因此，有必要基于RANS方程组及RNG k-ε湍流模型进行叶轮全流道三维湍流流场的数值模拟。结合试验和数值模拟的结果，可发现吸入管内部预旋流动主要为沿旋转方向的周向流动，而沿半径方向的径向流动很小，且径向速度在数值上要比周向速度小一个量级。

Investigation on the Upstream Pre-Swirl Flow of a Semi-Open Radial Impeller

The upstream pre-swirl flow of an impeller inlet has a crucial effect to the hydraulic and cavita-tion performance of fluid machinery. In this paper,the upstream pre-swirl flow of a semi-open radial im-peller is investigated by using the Particle Image Velocimetry（PIV）method. Based on the PIV experimen-tal results at different revolution speeds and flow rates conditions,it is observed that the pre-swirl flow whose direction coincides with the impeller rotation exists in upstream suction pipe. Besides,the pre-swirl velocity is greater at smaller flow rate condition,at the location of impeller inlet,or when the overall de-sign deviates from the original. The influence of impeller revolution could transport to upstream along the flow passage and thus induce vortex in the suction pipe. Also,the three dimensional turbulent flow for the full flow passage of the impeller is simulated based on RANS equations combined with RNG k-ε turbu-lence model. With the combination of experimental and numerical results,it is indicated that the pre-swirl flow in the suction pipe is mainly tangential flow along the revolution direction,while the radial flow along the impeller radius direction is negligible as its velocity is much smaller than that of the tangential velocity.