Multiphase rotodynamic pumps are used by the oil and gas industry to transport mixed media in pipelines. The characteristics of gas–liquid–solid flow in such pumps are significantly affected by the rotor–stator axial spacing so that further investigation is required. Based on the Euler multi-fluid model, the Computational Fluid Dynamics simulations were conducted in this study on the gas–liquid–solid multiphase rotodynamic pump at the rotor–stator axial spacings of 8, 10, 12, 14, and 16 mm, respectively. Changes in the pump's characteristics of external, multiphase flow, and pressure fluctuation were systematically analyzed by using ANSYS-CFX. The results showed that, an overall decreasing trend for the efficiency and head of the multiphase rotodynamic pump were demonstrated with increases in the rotor–stator axial spacing from 8 to 16 mm, which can be categorized into plummets I, moderation, and plummets II. As the rotor–stator axial spacing increased, the pressurization decreased from the inlet to outlet of guide vane while the aggregation of gas and solid increased. Additionally, vorticity increased and vortex structure was found to be more significant. As a result, the overall performance of the multiphase rotodynamic pump deteriorated. The pressure fluctuation in the multiphase rotodynamic pump was determined by the rotor–stator interaction and multiphase flow under gas–liquid–solid flow conditions, resulting in a non-positive correlation between the pressure fluctuation and the pump's external and internal flow characteristics. The location of maximum pressure fluctuation in the multiphase rotodynamic pump was changed from the impeller outlet to the guide vane inlet with increases in rotor–stator axial spacing.

Flow and phase separation in gas–liquid multiphase pumps is easy to occur, which deteriorates their performance and mixed transportability. Many research achievements have been made in the experiment, CFD simulation and performance improvement of multiphase pumps. However, there are many challenges for the test technology, accurate numerical model development and gas–liquid flow control. This paper is mainly aimed at critically reviewing various technologies for experimental observation, flow calculation and analysis, and the optimization design of gas–liquid multiphase pumps. In this regard, the experimental results including the energy performance, flow pattern and bubble movement in the multiphase pump are presented in detail. Discussions on the turbulence model, multiphase flow model and bubble balance model are carried out for the flow prediction in such pumps. Various numerical results are presented, including energy performance, bubble distribution, vorticity, phase interaction and pressure fluctuation. Moreover, the flow control and optimization strategy are briefly introduced. Having carried out an extensive literature review of flow characteristics in multiphase pumps, the deficiencies of relevant fields and suggestions for future research direction are given.

The multiphase rotodynamic pump is crucial for the multiphase blending transportation process. However, desigining such pump with high hydraulic performance and good blending transportation ability is quite challenging because of its unique structure. This study constructed a multi-objective optimization design system, which combines the 3D inverse design theory, response surface methodology, genetic algorithm, computational fluid dynamics simulation, and multi-objective optimization strategy, to improve the multiphase pump performance. Five optimization variables, namely the impeller loading parameters ( m_1,S, m_1,H, k_S, k_H) and the high-pressure edge angle ( θ), were selected in this study. Furthermore, two optimization objectives were considered at inlet gas void fraction ( IGVF) = 10%, namely the pump efficiency and the gas uniformity at the impeller outlet. The optimization results demonstrated that the pump efficiency and blending transportation ability would improve if the impeller blades had for-loaded loading distribution and the negative high-pressure edge angle. After optimization, the pump efficiency and the gas uniformity for the optimized impeller Opt1 improved by 2.6% and 18.2% at IGVF = 10%, respectively. Moreover, the internal flow pattern in the impeller was improved significantly, resulting in the maximum amplitude of pressure fluctuation in impeller Opt1 being 0.42 times that in the original test impeller.

In the chemical and petroleum industry, the axial flow pump is widely used for the circulation pipeline system, and most of the transportation mediums are the shear-thinning non-Newtonian fluids. However, previous investigations on axial flow pumps are focused on water, which leads to a considerable deviation between the actual application and the research finding. In this work, shear-thinning non-Newtonian fluid (CMC solution) and viscous Newtonian fluid (the viscosity equals the apparent viscosity of CMC solution as the flow index is 1) are selected as the working medium. Based on the research output, lower apparent viscosity occurs in the near-wall and rotor–stator interaction region due to the larger velocity gradient. The shear-thinning property results in an increased tip leakage flow rate, and a sharp decline in friction loss. Compared to the viscous Newtonian fluid, the head and efficiency of the pump improves substantially for the shear-thinning fluid. The discrepancy is observed to increase with a higher flow rate. The comprehensive analysis of flow field and energy performance reveals that friction loss is still the main part of the total loss in the shear-thinning fluid.

With the large-scale integration of renewable energy, pumped storage, as a globally recognized reliable peak-shaving power source, has become increasingly prominent. However, frequent operating condition transitions inevitably force pump-turbines to pass through the hump region, or even the double-hump region during start-stop or load regulation processes, which seriously affects the stable operation of the unit. In this study, to reveal the formation mechanism of double-hump region, the energy loss characteristics of a pump-turbine are thoroughly investigated by a combination of experiment and unsteady simulations. The characteristics of energy conversion, pressure fluctuation, and internal flow in the double-hump region are also elaborated in detail. The results show that the decline rate of unit hydraulic loss energy curve increases significantly under the double-hump conditions. The runner work energy curve initially shows a downward trend in the first hump region, and then the energy coefficient continues to increase rapidly with the decrease in flow rate. The characteristic frequencies in the double-hump region exhibit complex evolutionary patterns. In the first hump region, the pressure fluctuation frequencies in the runner disperse across multiple frequency bands with enhanced nonlinear superposition effects. In the second hump region, the pressure fluctuation amplitudes in the guide vane increase significantly. Additionally, the formation of the first hump region is primarily attributed to the emergence of a large-scale flow separation region near the band side of the runner inlet. This leads to a sharp increase in runner's energy losses, acting as the primary factor, and a decline in its work capacity, both of which contribute to the formation of the first hump region. The formation of the second hump region is mainly due to the significant increase in rotating stall intensity within the guide vane. The dynamic evolution of Dean vortices in the draft tube also has a certain promoting effect on its formation.

The spiral separator is an efficient gravity separation device widely used in mineral processing because of its environmental friendliness and low maintenance requirements. The downward bevel angle is a key structural parameter of the spiral separator. However, its impact mechanism on multiphase flow characteristics and separation performance remains unclear. This study employs the volume of fluid multiphase flow model and the Renormalization Group k–ε turbulence model to conduct numerical simulations on spiral separators with four different downward bevel angles. The results show that the flow film thickness gradually increases from the inner to the outer trough. The tangential velocity positively correlates with water depth and radial distance. The secondary flow is more concentrated in the outer trough and exhibits turbulent flow, while it is weaker and laminar flow in the inner trough. As the downward bevel angle increases, the flow film thickness in the inner and middle troughs increases, which is beneficial for enhancing the tangential velocity at the same position. Conversely, a thinner flow film in the outer trough reduces the tangential velocity at the same position. The overall scope and intensity of the secondary flow increase, which expands its range inward and effectively facilitates the inward aggregation of the concentrate. However, this also reduces the laminar flow range in the inner trough, which decreases the stability of the flow within the concentrate band. Additionally, the expansion of the secondary flow range increases the turbulent flow range, making fine-grained heavy minerals easier to separate from the tailings and enhancing their tendency to move inward.