When the multiphase pump is running, the internal medium often exists as bubble flow. In order to investigate the bubble occurrence characteristics in the pressurization unit of the multiphase pump more accurately, this paper couples computational fluid dynamics (CFD) with a population balance model (PBM) to investigate the bubble size distribution law of the multiphase pump under different operating conditions, taking into account the bubble coalescence and breakup. The research shows that the mean bubble size in the impeller domain gradually decreases from 1.7013 mm at the inlet to 0.6179 mm at the outlet along the axis direction; the average bubble diameter in the diffuser domain fluctuates around 0.60 mm. The bubbles in the impeller region gradually change from the trend of coalescence to the trend of breakup along the axial and radial directions, and the bubbles in the diffuser tend to be broken by the vortex entrainment. The bubble size development law is influenced by the inlet gas volume fraction (IGVF) and the rotational speed, showing a more obvious rule, where the gas phase aggregation phenomenon enhanced by the increase in IGVF promotes the trend of bubble coalescence and makes the bubble size gradually increase. The increased blade shearing effect with the increase in rotational speed promotes the trend of bubble breakup, which gradually reduces the size of the bubbles. In addition, increasing the bubble coalescence probability is a key factor leading to changes in bubble size; the bubble size development law is not very sensitive to changes in flow, and the bubble size is at its maximum under design conditions. The research results can accurately predict the performance change of the multiphase pump and provide technical guidance for its safe operation and optimal design.

Tip clearance inevitably exists in helico-axial flow multiphase pumps, which generates a great impact on flow characteristics. To select a reasonable tip clearance and improve the transporting efficiency, different tip clearances (R_tc = 0.5, 1.0, and 1.5 mm) are chosen to investigate the flow behaviors and hydraulic characteristics. Based on the shear stress transport k-ω turbulence model, the unsteady Reynolds averaged Navier–Stokes equations are applied to solve the unsteady flow. Results show that when the tip clearance increases, the tip leakage vortex (TLV) near the tip gradually becomes obvious and the pressure fluctuation near the TLV also becomes larger. The spatial–temporal evolution is divided into three stages: split stage, contraction stage, and recurrence stage. Besides, the rotor–stator interaction is still the primary cause for the pressure fluctuation.

A spiral axial-flow blade pump (SABP), as the core piece of equipment in the oil and natural gas closed-gathering and transportation process, can not only transport gas–liquid mixtures with a high gas content, but can also transport gas–liquid–solid mixtures containing small amounts of sand. However, due to the complexity of the distribution of transport media groups and the uncertainty of internal flow processes, large vortices often appear in the passage of the pumps, and the existence of vortices can easily induce the occurrence of pump cavitations. In the present work, a self-developed SABP was taken as the research object, and the cavitation performance of the SABP was numerically calculated. The pressure load variation under different tip clearances and different cavitation stages was analyzed, and the characteristics of the axial and radial forces were also analyzed in detail.

Inlet gas void fraction (IGVF) affects the cavitation evolution in a multiphase pump and easily results in a drop of the head and efficiency when cavitation is more serious. In this paper, a numerical method was performed to qualitatively and quantitatively analyze the effect of the inlet gas void fraction on the pressure and velocity characteristics of the multiphase pump at different cavitation stages. The results show that with the increase of IGVF and the development of cavitation, the pressure in the impeller flow passage is reduced, and the pressure corresponding to the cavitation region drops sharply to the saturated vapor pressure. With the decrease of the cavitation coefficient, and due to the expulsion effect of the cavitation bubbles, the relative velocity in the cavitation region becomes larger. Because of the large pressure gradient at the end of the cavitation bubbles, the kinetic energy of the fluid is insufficient to overcome the effect of the inverse pressure gradient, resulting in a backflow vortex. Investigations on cavitation evolution in the multiphase pump at different IGVFs are of great significance for improving its performance.

In oilfield operations, produced fluids consist of complex mixtures including heavy oil, sand, and water. Variations in sand particle parameters and operational conditions can significantly impact the performance of multiphase pumps. To elucidate the movement patterns of sand particles within a vane-type multiphase pump, this study employs the Discrete Phase Model (DPM) to investigate the effects of different sand particle parameters and operational conditions on the internal flow characteristics. The study found that: sand particle diameter, flow rate, rotational speed, and oil content significantly influence the trajectories of the solid–liquid two-phase flow, the motion characteristics of sand particles, and the vortices in the liquid flow field. As sand particle diameter increases, their radial and axial momentum first rise and then decline. Both radial and axial momentum are positively correlated with sand concentration. An increase in flow rate, higher rotational speed, and lower oil content all lead to greater fluctuations in the radial momentum curve of sand particles inside the impeller. Larger sand particles are predominantly distributed near the inlet, while smaller particles are more concentrated at the outlet. Higher sand concentrations and non-spherical particles increase particle distribution within the flow passages, with the guide vane channels exhibiting the most pronounced accumulation—reaching a maximum concentration of 6260 kg/m³ due to elevated sand loading. Increasing flow rate, rotational speed, or oil content significantly reduces sand concentration in the flow channel, promoting more efficient particle transport. Conversely, lower inlet sand concentration, non-spherical particles, reduced flow rate, decreased rotational speed, and higher oil content all result in fewer large particles in the flow passage. The findings provide important guidance for improving the wear resistance of vane-type multiphase pumps.

A spiral axial-flow blade pump (SABP) is an indispensable device in the closed gathering and transporting technology of oil and natural gas exploitation; it can not only transport a gas–liquid mixture with a high gas content, but also transport a gas–liquid–solid mixture containing a small amount of sand. However, due to the large vortices that often appear in the flow channel of the SABP, cavitation is induced extremely easily. This paper presents a numeric calculation of the cavitation performance of an SABP to reveal the law governing the impact of cavitation on its internal flow. The impact of tip clearance with different sizes on the dynamic and static head of the SABP was analyzed, and the change rules of the absolute velocity, relative velocity, and dynamic and static head were revealed under different cavitation stages, too.