Self-priming pump is a kind of special centrifugal pump, which is widely used in irrigation and drainage, construction, mine drainage, city fire fighting, military, petrochemical industry, food industry and so on. The self-priming pumps produced in China have some problems such as complex structure, large size, difficulty for casting, low suction height, long self-priming time, and the design methods of the self-priming pump have still stayed in the semi-empirical theories stage, which can not meet the demand of predicting properties and the requirement of new products design. In order to know the flow rule, it becomes very important to research the inner flow of the self–priming pump. The self-priming transient process in self-priming pump is complex gas-liquid two-phase flow, gas-liquid mixing and separation performances play a crucial role during self-priming process. The self-priming pump typed 65ZB-40C was chosen as the numerical model. The three-dimensional model was generated in Pro/E software, and the three-dimensional unstructured grid was adopted in meshing in ICEM software because of the complexity of the geometric model. The gas-liquid two-phase flow field in a self-priming pump was simulated in FLUENT software by using VOF multiphase model, sliding mesh, and combined with the rotational speed curve of the impeller and the pressure curve of the pump outlet from tests. The PISO algorithm was used to handle the pressure-velocity coupling, and governing equations were discrete with second order upstream scheme. The model was initialized before computing, set the lower part of the pump for water, and the rest of the pump for air. Gas-liquid mixing and separation phenomena were simulated and the air volume fraction curves during starting period were obtained from monitoring points on the gas-liquid separation chamber inlet, the reflux hole, the cross-sections of volute and impeller. Results show that a gas-liquid mixing layer appeared at the outer edge of the impeller after running, the phenomena of gas-liquid mixing and separation is obviously at the gas-liquid separation chamber inlet, the air volume fraction curve of the gas-liquid separation chamber inlet fluctuated strongly due to the unstable operation at the early stage of the starting period, the air volume fraction curve of the impeller fluctuated strongly due to the bubbles constantly generating and breaking. The results suggest that this approach is good in simulating the gas-liquid two-phase flow of the self-priming pump during starting period. It plays an important role in the further study of gas-liquid mixing and separation phenomenon in the self-priming pump.% 自吸泵的自吸过程是一个十分复杂的瞬态气液两相流动过程，自吸过程中气水混合及分离效果的好坏，是决定自吸泵自吸性能的关键。该文运用 VOF 多相流模型结合滑移网格技术，加载试验所获得启动过程中叶轮的转速变化曲线及泵出口压力变化曲线，模拟了启动过程中气液混合现象及气液分离现象，获得了气液分离室进口、回流孔、蜗壳各断面及叶轮内监测点的含气率变化曲线。结果表明，叶轮外缘出现了明显的气液混合层，气液分离室进口回流现象明显，启动过程初期泵运行的不稳定，使气液分离室进口及蜗壳隔舌处含气率出现明显的振荡，气泡在叶轮中不断地生成及溃灭是造成叶轮上监测点含气率振荡的原因。该文采用的模拟方法能够较好地模拟自吸泵启动过程内部气液两相流动，为进一步研究自吸泵内部气液混合及分离提供参考。
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