This work aimed to study the bubble distribution in a multiphase pump. A Euler-Euler inhomogeneous two-phase flow model coupled with a discrete particle population balance model (PBM) was used to simulate the whole flow channel of a three-stage gas-liquid two-phase centrifugal pump. Comparison of the computational fluid dynamic (CFD) simulation results with experimental data shows that the model can accurately predict the performance of the pump under various operating conditions. In addition, the liquid phase velocity distribution, gas-phase distribution, and pressure distribution of the second stage impeller at a 0.5 span of blade height under three typical working conditions were compared. Results show that the region with high local gas volume fraction (LGVF) mainly appears on the suction surface (SS) of the blade. With the increase in inlet gas volume fraction (IGVF), vortices and low velocity recirculation regions are generated at the impeller outlet and SS of the blade, the area with high LGVF increases, and gas–liquid separation occurs at the SS of the blade. The liquid phase flows out of the impeller at high velocity along the pressure surface of the blade, and the limited pressurization of fluid mainly happens at the impeller outlet. The average bubble size at the impeller outlet is the smallest while that at the impeller inlet is the largest. Under low IGVF conditions, bubbles tend to break into smaller ones, and the broken bubbles mainly concentrate at the blade pressure surface (PS) and the impeller outlet. Bubbles tend to coalesce into larger ones under high IGVF conditions. With the increase in IGVF, the bubble aggregation zone diffuses from the blade SS to the PS.

For the purpose of improving the transport capability of the mixed transport pump, a new self-made three-stage deep-sea multiphase pump was taken as the research object. Based on the Euler-Euler heterogeneous flow model, liquid (water) and gas (air) are used as the mixed media to study the external characteristics and internal flow identities of the mixed pump under different gas volume fraction (GVF) conditions. According to the simulation results, a local optimal design scheme of the diversion cavity in the dynamic and static connection section is proposed. The numerical results before and after the optimization are compared and analyzed to explore the effect of the diversion cavity optimization on the performance, blade load and internal flow identities of the pump. The results show that the head and efficiency are obviously improved when the inner wall of the diversion cavity is reduced by 4 mm along the radial direction. After optimization, under the condition of 10% gas content, the head and efficiency is increased by 3.73% and 2.91% respectively. Meanwhile, the hydraulic losses of the diversion cavity and diffuser are reduced by 9.11% and 4.32% respectively. The gas distribution in the impeller is improved obviously and the phenomenon of a large amount of gas phase accumulation is eliminated in the channel. In addition, the abnormal pressure load on the blade surface is eliminated and the turbulent flow energy intensity is reduced. The average turbulent kinetic energy ( ${\mathrm{T}}_K$ ) at i = 0.51 of the first stage impeller passage is reduced by 35%. Finally, the reliability of the numerical method is verified by the experimental results. To sum up, the performance and internal flow identities of the optimized mixed transport pump are improved, which verifies the availability and applicability of the optimization results. This provides a reference for the research and design of a multiphase mixed transport pump in the future.

The paper deals with the influence of the tongue shape on the flow characteristics at the near-tongue region of the volute in the double suction centrifugal pump with long-tongue, middle-tongue and short-tongue respectively. For this study, the computational fluid domains including suction chamber, impeller and volute was simulated by means of the commercial CFD software that solved the Navier-Stokes equations for three-dimensional steady flow. The results show that the tongue shape has a significant impact on the pump head and efficiency in a range of 0.4Q_d-1.4Q_d flow rate. Under small flow conditions, the head and efficiency of the short-tongue model are higher than that of the middle-tongue model and long-tongue model. Under large flow conditions, the head and efficiency curves of the three models are relatively close. In addition, the tongue shape has a great influence on the pressure and the streamline distribution in the near-tongue region. Therefore, effectively changing the tongue shape can improve the internal flow pattern of the double suction centrifugal pump and reduce the pressure pulsations. The tongue shape also has a great influence on the turbulent kinetic energy distribution. By changing the tongue shape the numerical value of the turbulent kinetic energy can be effectively reduced, thus the generation of the turbulent vortex and the energy loss of the pump will be reduced. It is shown that the tongue shape has a great influence on the performance of the double suction centrifugal pump. This study has certain reference value to improve the pressure pulsation of the double suction centrifugal pump.

The development of oil and gas resources towards the deep sea is an inevitable trend in international energy development. Due to its advantages of high production and transportation efficiency, good flow safety and low investment cost, oil and gas mixed transportation technology has become the preferred technology for deep-sea oil and gas production and transportation system. The core device of the oil-gas mixed transportation system is the gas-liquid two-phase flow pump. Under the gas-liquid two-phase condition, the pressure surging will occur with the increase of the inlet gas volume fraction (IGVF) in the pump. At this time, the pressurization capacity of the pump decreases significantly, accompanied by violent vibration, resulting in extremely unstable operation. To solve this problem, the numerical simulation and experiment of the two-phase operation characteristics of a centrifugal pump and a semi-open mixed-flow pump were carried out in this study. The influence of operating parameters on its pressurization capacity was clarified, and the internal gas-liquid distribution was visually tested, revealing the distribution and its spatiotemporal evolution of gas-phase in the impeller. Finally, the unsteady characteristics of pressure surging were analyzed in detail.