隔舌安放角对旋流泵内非稳态流动特性的影响

为明确隔舌安放角对旋流泵性能及非定常流动特性的影响，该研究设计了不同隔舌安放角的蜗壳模型，基于Navier-Stokes方程和RNG k-?湍流模型对旋流泵进行了全流场数值模拟，并通过能量性能和压力脉动试验对数值模拟方法进行了验证。能量性能预测结果表明，存在最优隔舌安放角使泵扬程和效率均达到极大值。流场分析结果表明，隔舌安放角对蜗壳隔舌及扩散段的流态具有较大的影响：较小的隔舌安放角会减小蜗壳喉部的过流面积，使无叶腔内流体的旋转运动受阻，致使循环流与隔舌的动静干涉作用增强；过大的隔舌安放角会造成扩散段产生大尺度的漩涡和回流。压力脉动分析表明，隔舌处压力脉动分布特征受安放角和测点位置共同影响：随隔舌安放角的增大，隔舌处的压力脉动先降低后增大，安放角由30°增大至45°时，2倍轴频（fn）的脉动最大降幅约47%，安放角继续增大至50°时，（0.25～0.5）fn的低频脉动最大增幅约86%；随着测点与叶轮轴向距离增大，隔舌处的压力脉动逐渐减小，叶轮一侧的脉动幅值约为泵体进口一侧的2倍。涡量场分析表明：蜗壳隔舌处频率为2fn的压力脉动由入口螺旋状入流发展扩散产生；隔舌处涡核分布的不对称性是导致蜗壳隔舌处压力分布不对称的原因。适当增大隔舌安放角能有效改善旋流泵隔舌处内流的稳定性，并一定程度提升旋流泵扬程和效率。综合各项性能表明该模型泵隔舌安放角45°时性能最优。研究结果可为旋流泵优化设计提供理论参考。

Effects of volute tongue angels on unsteady flow characteristics in a vortex pump

Abstract: A vortex pump is totally different from the centrifugal pump in physical and flow structure. Since the current vortex pump is developed from the centrifugal pump, many structural parameters cannot be suitable for the vortex pumps. Therefore, it is necessary to determine the structural parameters of the vortex pump in particular. In this study, five groups of volute models with different tongue angles were designed to clarify the effect of volute tongue angle on the performance and unsteady flow characteristics in a vortex pump. The numerical calculation was performed on the vortex pump using the commercial software ANSYS CFX. The full flow field of the vortex pump was simulated using the Navier-Stokes equations and the RNG k-? turbulence model. The energy test and pressure pulsation test were conducted and the test results were applied to verify the numerical simulation method. The energy performance showed that there was an optimal angle for the best pump performance. The flow field showed that the volute tongue angle posed a great influence on the flow state of the volute tongue and the diffuser section. Specifically, the relatively smaller tongue angle significantly reduced the flow area of the volute throat, and then blocked the rotational movement of the fluid in the non-vane cavity for the higher dynamic and static interference between the circulation flow and the volute tongue. By contrast, the larger tongue angle caused the large-scale vortex and backflows in the diffuser section. Furthermore, the tongue angle and the position of the measuring point also determined the distribution characteristics of pressure pulsation at the volute tongue during operation. The pressure pulsation at the volute tongue decreased first and then increased with the increase of the tongue angle. The pulsation amplitude at twice the axial frequency was significantly higher than that at other angles when the volute tongue angle was 30°. After that, the pulsation amplitude at twice the axial frequency decreased significantly at the volute tongue angle of 40° and 45°. Once the volute tongue angle reached 50°, there was a great increase in amplitude of low-frequency pulsation at 0.25-0.5 times the axial frequency. Meanwhile, the pressure pulsation of all frequencies decreased gradually with the increase of the axial distance between the measuring point and the impeller. The vortices field demonstrated that the pressure pulsation with twice the axial frequency at the volute tongue was produced by the development and diffusion of spiral inlet flow. The asymmetry pressure distribution was attributed to the vortex core distribution at the volute tongue. Consequently, the higher tongue angle can be expected to effectively improve the stability of the internal flow at the volute tongue of the vortex pump for a higher head and efficiency than before. The best volute tongue angle of 45° was also achieved for the performance of the improved model. This finding can also provide a promising theoretical reference to optimize the vortex pump.