气液两相离心泵受力特性研究

离心泵在气液两相流工况运行时，叶轮内部流动极不稳定，为了研究叶轮在该工况下的受力情况，该文采用计算流体动力学的方法对某一气液两相离心泵进行了研究。基于欧拉-欧拉非均相流模型及SST湍流模型求解气液两相流离心泵的三维湍流流场，并将数值模拟结果与试验数据对比，两者吻合较好。通过对不同含气率工况下的离心泵瞬态特性进行分析发现，叶轮所受轴向力的大小随着时间的变化而波动，进口含气率达到3%时，轴向力脉动出现明显的峰值，这些峰值所对应的频率均为叶轮转频，随着进口含气率的增加，出现了2个及以上的峰值，进口含气率为7%工况的轴向力脉动峰值是3%工况的3倍，是5%工况的2倍；叶轮所受径向力大小及径向力脉动幅值均随进口含气率的增加呈先增加后减小的趋势，各工况下径向力脉动峰值所对应的频率均为叶片转频的倍数；通过分析进口含气率分别为1%、3%及7%工况下叶轮中间截面的含气率分布、涡量分布以及静压分布可得，叶轮内含气率较高区域的涡量也较大，而该区域的压力分布也不均匀，由此可见，叶轮内气液分布不均导致了叶轮内的压力分布不均，从而使叶轮受力不均。

Research on force characteristics of gas-liquid two-phase centrifugal pump

Centrifugal pumps are widely used in various fields because of their high head, high efficiency and simple structure. It will be accompanied by instability phenomena, such as vibration and noise, when a centrifugal pump is operated at gas-liquid two-phase conditions. Uneven force on impeller is an important reason for these unstable phenomena of pump. The variable radial force will make the bearing of pump subject to alternating stress and produce directional deflection of pump shaft, so that the clearances of seal become uneven, leading to leakage.The impeller is also moved axially by axial force. Therefore, it is very important to study the force acting on gas-liquid two-phase centrifugal pump. In this study, a gas-liquid two-phase centrifugal pump was studied by computational fluid dynamics (CFD) to analyze the unsteady force characteristics. The CFX-18.0 was used to solve the three-dimensional turbulent flow field of the gas-liquid two-phase centrifugal pump. The inhomogeneous Eulerian-Eulerian two-fluid model was used to capture the distribution of each phase and its influence on the pressure and velocity fields. The SST (Shear Stress Transmission) model was adopted as turbulence model in the process of numerical simulation. The transient characteristics of the pump under different gas volume fraction conditions were studied. The results showed that the numerical simulation results were coincident with the experimental data. IGVF affected the magnitude of the axial force. The magnitude of axial force at gas-liquid two-phase flow conditions was 2.4 times that of water single-phase flow condition. Under gas-liquid two-phase conditions, the unsteady axial force acting on the impeller was produced a large amplitude fluctuation under some frequency. And the magnitude of the amplitude was increased exponentially with the increase of the IGVF. IGVF had a great influence on the magnitude and direction of radial force. Under water single-phase condition, the magnitude of the radial force on the impeller was the largest, and the direction of radial force on the impeller''s rotating circle distributed in an elliptical shape. Under gas-liquid two-phase condition, the impeller radial force magnitude changed dramatically, and the vector diagram of each working condition had an irregular polygonal distribution. IGVF affected the number of radial force fluctuation period. There were 5 wave peaks and troughs of periodic fluctuation for one impeller cycle which was the same as the number of impeller blades at the condition of 0, 1% and 7% IGVF, while it was four for the condition of 3% and 5% IGVF. IGVF also affected the radial force fluctuation of impeller. The peak value of radial force coefficient at 7% IGVF was 1.6 times that of 0 IGVF and 2.6 times that of 1% IGVF. IGVF affected the gas liquid two phase flow pattern. It was isolated bubble flow at the 1% IGVF, the flow pattern was unstable gas-pocket formed by the aggregation of some small bubbles under the3% and 5% IGVF, and the gas-pocket becomed large and more stable which occupying most of the area of the flow channel as IGVF increased to 7%. Therefore, the impeller flow field had undergone a process from stability to slight oscillation, then to drastic change and finally to stability as IGVF increased from 0 to 7%, which was accompanied by the change of radial force. In addition, the distribution law of vorticity in impeller was consistent with that of gas-liquid two-phase distribution. The large vorticity in gas accumulation area resulted in uneven pressure gradient distribution in impeller and uneven force distribution in impeller.