Tip clearance is the distance required between the blade tip and the pump body wall of an impeller in a helicon-axial multiphase pump, which tends to induce tip leakage flow. The tip leakage vortex formed by the interaction of tip leakage flow with the mainstream can seriously affect the performance of the multiphase pump. To minimize the adverse effects of tip leakage flow in the multiphase pump, a method to design a squealer tip on the impeller blade is proposed in this paper. The effect of the squealer tip on external characteristics, tip clearance flow characteristics, and energy dissipation of the multiphase pump is analyzed. Research results indicate that the blade squealer tip can effectively improve hydraulic efficiency of the multiphase pump. At the optimal efficiency point, the head and hydraulic efficiency of the multiphase pump with a squealer tip increased by 3.62% and 4.15%, respectively, compared with the original model. The influence of tip leakage flow in the axial rear half passage of the multiphase pump impeller is far greater than that in the axial forward half passage, especially on the back position in the middle of the impeller passage. The squealer tip can restrain the reverse of leakage flow from the pressure side to the suction side of the impeller blade, and the clearance leakage flow of the model with a squealer tip is smaller than that of the original model. The squealer tip on blade will reduce the energy dissipation caused by unsteady flow in the mainstream. The research results in this paper can provide theoretical support for effectively restraining the influence of the tip leakage vortex on the mainstream of the helicon-axial multiphase pump and contribute to engineering practice value of improving the performance of the multiphase pump.

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.

The flow is extremely complex within the main flow passage during the operation of the multiphase pump, which results in constant changes in vortex structure, and interferes with the orderly flow of flow field present, thus, reducing the pump performance. Numerical calculations, supplemented by experimental verification, are used as the main method for investigating influencing factors that affects the vortex structure in impeller passage of pump, and vortex structure present on isosurfaces is selected based on Q criterion to study the evolution of vortex structures under different working conditions. Results indicate that the flow rate affects vortex structure generation on the suction side and trailing edge of the blade. With an increase in flow rate, the vortex becomes complete from fine broken structures. Speed has a greater influence on vortex structures in inlet and outlet areas: the higher the speed, the larger the vortex structure attached to the impeller leading edge. The vortex structure is separated from blade surface at 2/3 of the impeller under gas-liquid two-phase working condition, with an increase in inlet gas void fraction (IGVF) the vortex structrue expands to the center of impeller passage. Therefore, exploring evolutions of the vortex structure can provide a certain theoretical basis for improving the stability of multiphase pump internal flow.

Tip-leakage flow occurs in the tip-clearance region of helico-axial multi-phase pumps, and this reduces their working performance. In this study, a structural modification, in the form of the inclusion of “squealers” on the impeller blade tips, was adopted to reduce the tip-leakage flow in a helico-axial multi-phase pump, thereby improving its working performance. Numerical simulations were conducted to examine the impact patterns of geometric parameters such as the depth, shape, and size of the squealer on the external characteristics and tip-leakage flow. The results of this study show that the presence of squealer tips has significant effect on the performance of a multi-phase pump. The depth of the squealer and the ratio of the squealer length to the blade-tip length were found to be the critical structural parameters of the squealer. There is an optimal value for the relative squealer depth, and this was found to be 9%. Larger ratios of squealer length to blade-tip length were also found to be more favorable for improving the performance of the multi-phase pump. The width and location of the squealer were found to have relatively low impacts on the performance of the multi-phase pump considered in this study. The presence of squealer reduced the tip-leakage flow rate and also alter the structure of the flow field in the impeller blade-tip region, changing the periodic distribution pattern of tip-leakage flow to some extent. The results of this study have important guiding significance for improving the performance of helico-axial multi-phase pumps.

The architecture of real dandelion seeds is diverse. Previous studies have primarily focused on the flow patterns and drag coefficients of dandelion seeds with a pappus angle no greater than 180°, but have paid less attention to the cases of the pappus angle larger than 180°. This work therefore numerically investigated the flow patterns and drag coefficients of dandelion seeds with the pappus angle larger than 180° when the speed of incident flow is 0.2 m/s, using double-layered models consisting of two oppositely oriented filament layers. The simulated results were then compared to those obtained from single-layered models consisting of identical number of but leeward-oriented filaments (the pappus angle lower than 180°). It reveals that, either single-layered or double-layered models, the length (L) and width (W) of separated vortex rings increase, drag coefficients (CD) increase, but the shape index (L/W) and the relative location of separated vortex rings (zu) decrease, as the number of filaments increases. At a given filament number, L, W, and zu in double-layered models are smaller than those in single-layered models, but L/W and CD in double-layered models are larger than those in single-layered models, attributed to the windward-oriented filaments. In double-layered models, thanks to small difference in the drag force but significant difference in the projected area, CD is significantly higher when both windward-oriented and leeward-oriented filaments are installed at identical locations on the central disk's perimeter compared to cases where windward-oriented and leeward-oriented filaments are installed at different locations.

The helical-bladed multiphase pump demonstrates significant advantages in transporting complex media. However, the presence of solid particles complicates the fluid–structure interaction mechanism, posing challenges to studying solid–liquid two-phase flow within the pump. This research focuses on a self-developed three-stage helical-bladed multiphase pump, employing numerical simulation with experimental validation, to systematically investigate the effect of particle mass concentration (Cm = 1‰, 5‰, and 1%) on particle motion characteristics. The results indicate particle velocity distribution follows similar trends under different Cm conditions. In the impeller flow passage, the circumferential velocity of particles increases significantly while axial velocity changes marginally. Upon entering the guide vanes, circumferential velocity decreases, whereas axial velocity increases. The absolute velocity rises axially along each impeller stage but declines axially in each guide vane stage. As Cm increases, particle backflow intensifies, leading to aggravated flow blockage in the reflux zone at the first-stage impeller inlet. Under high-concentration conditions, particles aggregate into clusters within the flow passage, elevating collision probability. Particle distribution shifts from low-speed to medium-speed regions: dispersed at low Cm but concentrated toward medium-speed zones at medium-to-high Cm. Particle collision frequency rises with Cm, with increased proportions of collisions against the shroud and hub but decreased proportions against blades. The total particle–wall contact force escalates with higher Cm, with impeller-wall forces exceeding guide-vane-wall forces. In the guide vane region, contact forces distribute as blades > shroud > hub. These findings elucidate the kinetic characteristics of solid particles, providing a basis for the optimal design of multiphase pumps.