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Rotor-stator interaction in axial pumps can produce pressure fluctuations and further vibrations even damage to the pump system in some extreme case. In this paper, the influence of tip clearance on pressure fluctuations in an axial flow water pump has been investigated by numerical method. Three-dimensional unsteady flow in the axial flow water pump has been simulated with different tip clearances between the impeller blade tip and the casing wall. In addition to monitoring pressure fluctuations at some typical points, a new method based on pressure statistics was proposed to determine pressure fluctuations at all grid nodes inside the whole pump. The comparison shows that the existence of impeller tip clearance magnifies the pressure fluctuations in the impeller region, from the hub to shroud. However, the effect on pressure fluctuation in the diffuser region is not evident. Furthermore, the tip clearance vortex has also been examined under different tip clearances.

The spiral axial flow gas-liquid mixed pump has some problems, such as unsteady flow and sharp decline in performance, when it runs in the biased condition with high gas content. Based on the principle of fluid flow and the design concept of slot drainage, a slit blade is proposed in this study to improve the degree of gas-liquid separation inside the mixing pump. The slit connects the pressure surface of the blade of the mixing pump with the suction surface. The pressure difference between the pressure surface and the suction surface leads to the generation of slit jet, which plays a “blowing” role in the adhesion of the gas phase on the suction surface inside the mixing pump. And make the stagnant air mass in the flow passage move again, so as to slow down the gas-liquid separation in the mixed transport pump. This study provides theoretical reference for the design and optimization of spiral axial flow gas-liquid mixed pump.

With the onset of the fossil energy crisis, demand for oil has skyrocketed, and the spiral axial flow gas-liquid mixing pump has emerged as the primary piece of equipment for deep-sea oil extraction. However, at high gas content, the problems of separation of mixed media from hydraulic components, gas-liquid separation and gas phase aggregation are faced. The difficulties of gas-phase aggregation and bubble trajectory in the impeller channel have received much attention, while the problem of increased medium flow resistance induced by flow separation has received less attention. The spiral axial gas-liquid mixing pump is numerically calculated using the Eulerian multiphase flow model and the SST k- turbulence model in this work. The pump is designed with the design flow rate Q = 100 m 3 /h, rotational speed n = 4500 rmin, and head H = 30m by arranging guide slots with different relative depths and different number of slots to reduce the dissipative vortices, thus reducing the flow resistance in the 1/5 region behind the suction surface. The findings reveal that when the relative depth of the slots is 1/7 and the number of guide slots arranged is 5, the highest drag reduction rate in this location is 69.6% under the design flow condition. When the relative depth of the guide channel is1/7 and the number of guide channels is 3, the performance of the mixing pump is improved most, with an efficiency increment of 1.9% and a head increment of 4.2%, which can provide technical support for the flow resistance reduction of gas-liquid mixing pumps.

Easy implementation and considerable equipment cost savings, encourage the engineers to use pump as a turbine for both water supply systems and small-scale hydroelectric plants. Flow dynamics in the pumps which are used as turbines are not considered well, and one important disadvantage of them is their incapacity to control flow. This study investigates the mixed-flow dynamics of axial pumps under five operational conditions, from optimal (1.0 QBEP) to the QBEP plus value (20 l/min). In addition, three angles are considered, namely − 3°, 0°, and 3°, to examine the effects of blade angle on them. The flow stability of the axial pump deteriorated as the flow decreased, while pressure pulsations in different flow regions became more intense. Increasing the runner blade angle from − 3° through 0° to 3° influenced the machine's flow and pressure field characteristics. As a result of this increased blade angle, flow unsteadiness and pressure pulsation levels also increased, and the rotor–stator interaction frequencies became dominant in most flow regions. Researchers and engineers will greatly benefit from this study since it contributes to a more thorough understanding of pump flow dynamics.

Axial flow pumps often experience uneven distribution of axial force on the blades when deviating from design conditions, which can easily lead to local damage to the pump blades. In response to this issue, this article conducts a detailed study on the hydraulic and axial force characteristics of large vertical axial flow pumping stations in China based on constant and non-constant numerical simulation research methods. Research has found that under biased operating conditions, due to the angle between the water flow direction inside the impeller and the impeller blades, the water body collides with the blades, resulting in concentrated pressure distribution on both sides of the inlet side of the impeller blades. Under low flow conditions, the high axial force area of the impeller blade is concentrated in the middle and rear position of the suction surface, while under high flow conditions, the high axial force area is widely distributed. Under the conditions of 0.8 Q to 1.4 Q , the fluctuation of axial force on the impeller blades is mainly affected by the rotation of the impeller blades. However, under low flow conditions, due to the turbulence of the flow state, there is no obvious pattern of axial force variation on the impeller blades. In addition, under different flow conditions, there is no obvious pattern in the fluctuation of axial force on the guide vanes. This also proves that there are problems such as uneven axial force distribution and no periodic changes in the impeller blades under low flow conditions, which can easily lead to damage to the impeller blades. The above analysis can provide some reference for the design of impeller blades.

In this research, to investigate the impact of the guide vanes on the flow analysis in the axial pump, unsteady numerical turbulence field simulations with and without guide vanes are simulated using the model of standard κ–ε turbulence with the technique of sliding mesh (SM). The numerical results are firstly validated and compared with experimental outcomes. Different detailed information data regarding flow analysis, for instance, static, dynamic, total pressures, turbulent kinetic energy, shear stress, and velocity magnitude are qualitatively analysed. Then pressure at varying regions in the pump is qualitatively investigated under different operating conditions. The results have shown that the flow field and performance of the pump are highly affected by adding the guide vane to the axial impeller. The impeller with guide vane can lead to enhance the pump performance. Moreover, results show that the pressure, kinetic energy, shear stress, and velocity are increased by adding a guide vane to the axial impeller. This study will provide good information and guidance to enhance and improve the axial flow pump design operation.

In axial flow pump systems constrained by limited internal space, the advantages of axial flow tandem pumps are high space utilization, strong power capacity, and great thrust. The onset of cavitation during the rapid starting period poses a classic issue for tandem axial flow pumps, resulting in issues like noise, vibration, cavitation breakdown, and material damage. This article aims to investigate the transient cavitation characteristics of each flow passage component of an axial flow tandem pump during the rapid starting period by numerical simulation method. It is compared that the evolution laws of the cavity of each flow passage component. The evolution of the cavity in all flow passage components is strongly correlated with the flow rate change rate in each stage of the rapid starting period. Among all flow passage components, the first impeller firstly experiences cavitation, and its cavitation severity is also the most severe. The Effective Net Positive Suction Head ( NPSH a ) can reduce the influence of transient effects on cavity prediction and better characterize the details of the cavity evolution in different impellers than the cavitation number σ during the rapid starting period. Meanwhile, The NPSH a of the second impeller inlet is always higher than that of the first impeller inlet, indicating superior cavitation performance for the second impeller.

Computational fluid dynamics (CFD) was applied to investigate the flow characteristics in an industrial polymerization tank with double layer helical coils. Herschel-Bulkley model was applied to describe the rheology of Bingham-pseudoplastic fluid. The effect of Bingham property on the flow was revealed. The helical coils were found to affect the flow pattern, making the axial flow impeller present shortage in overall mixing performance, especially in the area between the coils. The combined impeller, which consists of an axial flow impeller and a large blade radial flow impeller, was proposed to improve the flow close to coils and overall mixing. The comparison results indicated that under the same operational condition, the combined impeller provide a higher average shear rate than the original axial flow impeller, resulting in a decrease in viscosity but a corresponding increase in power consumption. The combined impeller generates effective radial flow through the coils and the axial circulation flow ensures the overall mixing efficiency. In addition, appropriately increasing the impeller diameter ratio is beneficial for further promoting the fluid flow between coils. Effective guidance for the industrial coiled stirred tank with complex rheological properties may be obtained based on the impeller optimization.

When an axial-flow pump works in low flow rate conditions, rotating stall phenomena will probably occur, and the pump will enter hydraulic unsteady conditions. The rotating stall can lead to violent vibration, noise, turbulent flow, and a sharp drop in efficiency. This affects the safety and stability of the pump unit. To study the rotating stall flow characteristics of an axial-flow pump, the steady and unsteady internal flow field in a large vertical axial-flow pump was investigated using 3D computational fluid dynamic (CFD) technology. Numerical calculations were carried out using the Reynolds-averaged Navier–Stokes (RANS) solver and Menter's shear stress transport (SST) k-ω turbulence model. Steady flow characteristics including streamline, velocity vector, pressure and turbulent kinetic energy are presented and analyzed. Unsteady flow characteristics are described using post-processing signals for pressure monitoring points in the time and frequency domains. Using Q-criterion, the locations and evolution rules of the core region of the vortex structure in guide vanes under deep stall conditions were investigated. The reliability of the numerical simulation results was verified using the experimental prototype pressure fluctuation test. In this way, typical flow structure and pressure fluctuation characteristics in an axial-flow pump were analyzed, with contrastive analysis in design condition and stall conditions. Finally, the mechanism of low-frequency pressure fluctuation in a pump unit under the stall condition was revealed.

Helical axial-flow multiphase (HAFM) pumps experience intermittent gas-blocking events, which negatively impact performance and threaten the stability of the overall pump and pipeline systems. This study applies jet flow field method to HAFM pumps. Active intervention in the gas-liquid separation process, utilizing external energy, results in the reorganization of the flow field within HAFM pumps. The effect of jet location on improving the efficiency of HAFM pumps is assessed, with a focus on the active flow control mechanism through jet influence. The study indicates that the region sensitive to jet site distribution affecting pump performance is 0.5Lc≤ xr ≤ 0.7Lc, while the weakly sensitive region is 0.15Lc ≤ xr ≤ 0.5Lc. When xr ≤ 0.15Lc, the improvement in head and efficiency under high gas content conditions is reduced. Jet flow field control technology obviously decreases the gas phase accumulation in the downstream flow channel of the moving blade cascade. The optimal position for reducing gas phase agglomeration in the impeller channel is 0.3Lc. The jet site arrangement significantly affects the pressure structure near the cascade trailing edge. Appropriate jet hole positioning significantly improves the pressure structure at the cascade trailing edge, decreases reflux caused by separation vortices at the impeller outlet, and enhances the hydraulic performance in the multiphase pump.