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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.

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.

Axial flow pumps are widely used in water conservancy, petrochemical and agricultural industries. Efficient operation is crucial for energy conservation and emission reduction. Improving efficiency under severe conditions requires studying the internal flow of axial-flow pumps, particularly at low flow rates where backflow vortices form near the impeller inlet. This study investigates the unsteady flow characteristics of backflow vortices at different flow rates in an axial-flow pump. Results show that backflow vortices form when the flow rate decreases to 0.59 Q d . As the flow rate further declines, the backflow vortex progresses upstream, contracts, and rebounds. The flow rate range is divided into three stages: Stage I with no backflow vortex, stage II with initial vortex development extending upstream and relatively fragmented, and stage III with vortex contraction and rebound forming a more coherent structure. Besides, backflow vortices induce significant pressure fluctuations and velocity oscillations with the primary frequency being 0.5 f b . They exhibit a three-dimensional spiral motion involving changes in axial length, self-rotation, and revolution around the pump axis, with an angular velocity of approximately half the impeller’s rotational speed. This work enhances insights into backflow vortex behaviors, which is essential for optimizing pump design and improving operational stability in challenging environments.

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.

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.

With the full construction of the South to North Water Diversion Project and the renovation of pumping stations, vertical axial flow pump devices have been widely used in various pumping station projects. This article uses the streamlined method to design the impeller and guide vanes of a vertical axial flow pump device. To analyze the hydraulic and structural characteristics, this paper uses CFD numerical simulation and fluid-structure interaction calculation methods. And the trend of output power change under different flow conditions was divided into three stages, elucidating the reasons for the sudden change in output power under flow conditions of 0.8 Q -1.0 Q . This article focuses on analyzing the internal flow state of the designed lower height guide vane segment to explore the problem of low guide vane height that is prone to occur during the design process. According to the research results, it is found that the lower height guide vane can also play a good role in stabilizing flow and recovering circulation under certain operating conditions. This article also studied the structural characteristics of the impeller and guide vanes, explaining the stress and strain distribution under design flow conditions.

This paper investigates the influence of cascade density on energy dissipation in the impeller of a multi-blade axial-flow pump. Three-dimensional transient numerical simulations were conducted using the SST k-ω turbulence model for impeller schemes with different cascade density, corresponding to different blade chord length and pitch. Entropy production theory was applied to locate the regions with high energy loss in the impeller. The relationships between local entropy generation, energy loss, and unsteady flow were analyzed for different cascade density. The results indicate that impeller entropy output of the multi-blade axial-flow pump is highly consistent with the head loss during testing. Turbulence dissipation accounts for more than 50% of the total energy loss, followed by wall friction, while direct dissipation is the smallest contributor. The relative loss of the impeller can be minimized by decreasing the number of blades or increasing the blade chord length. By comparing energy dissipation in blade rotation with different chord length and pitch, it is found that turbulent dissipation ability can be controlled more effectively by changing chord length, while the ability of direct dissipation can be controlled more effectively by changing the pitch.

Submersible axial flow pump is capable of generating large flow rate at high efficiency and is widely used in agriculture, irrigation, water supply and drainage in factories, urban areas, etc. Pumps are always designed to operate at the designed conditions of flowrate and head, but in certain practical applications, their off- design operation seems to be more important, like if there is waterflooding due to heavy rainfall or in case of variable flowrate, variable head operations or long-distance water supply. These situations arise for limited operation (time) and hence it is not economical to change the existing pumping system. The present work deals with the analysis of submersible axial flow pump at design as well as off-design conditions. This off-design operation was controlled by the variable inlet guide vane (VIGV) with the task of making it energy efficient for all conditions. The scope of this work was to investigate the performance of selected pump at designed rotational speed, at designed flowrate ( Q/Q d =1) as well as Q/Q d =0.8 and Q/Q d =1.2, using Computational Fluid Dynamics (CFD) and at various VIGV angles in the range of ±25°. The fluid flow analysis was performed using commercial CFD tool ANSYS CFX v 17.0. From the numerical study, it was concluded that the performance of the considered AFP significantly increased due to the presence of VIGV at positive rotation angles. The best performance was observed for IGV angle of +25° for all flowrates. As compared to the reference case of 0° IGV rotation, the performance of the AFP increased by 28.42% in terms of head ratio and 0.235% in terms of hydraulic efficiency, for +25° IGV angle, at the designed flowrate. Also, an increment of 69.05% in terms of head ratio and 14.49% in terms of hydraulic efficiency was observed at overload condition of Q/Q d =1.2.

Fluid-structure interaction (FSI) was used to determine the structural mechanical characteristics of full tubular and axial-flow pumps. The results showed that as the flow rate increases, the total deformation and equivalent stress are significantly reduced. The max total deformation (MTD) and the max equivalent stress (MES) of the full tubular pump impeller occur on the outer edge of the blade. There are two stress concentrations in the full tubular pump impeller, one of which is located in the outlet area of the rim, and the other is located in the outlet area of the hub. However, the MES of the axial-flow pump appears in the center of the blade hub. The performance difference between the full tubular pump and the axial-flow pump is mainly caused by the clearance backflow. The natural frequency of the full tubular pump is lower than that of the axial-flow pump on the basis of the modal results. The MES of the full tubular pump is mainly concentrated at the junction of the blade and the motor rotor, and the max thickness of the rim is 6mm, which can be more prone to cracks and seriously affect the safety and stability of the pump.

To reveal the cavitation forms of tip leakage vortex (TLV) of the axial flow pump and the flow mechanism of the flow field, this research adopts the partially-averaged Navier-Stokes (PANS) model to simulate the cavitation values of an axial flow pump, followed by experimental validation. The experimental result shows that compared with the shear stress transport (SST) k - ω model, the PANS model significantly reduces the eddy viscosity of the flow field to make the vortex structure clearer and allow the turbulence scale to be more robustly analyzed. The cavitation area within the axial flow pump mainly comprises of TLV cavitation, clearance cavitation and tip leakage flows combined effect of triangular cloud cavitation formed. The formation and development of cavitation are accompanied by the formation and evolution of vortex, and variations in vortex structure also generate and promote the development of cavitation. In addition, an in-depth analysis of the relationship between the turbulent kinetic energy (TKE) transport equation and cavitation patterns was also conducted, finding that the regions with relatively high TKE are mainly distributed around gas/liquid boundaries with serious cavitation and evident gas-liquid change. This phenomenon is mainly attributed to the combined effect of the pressure action term, stress diffusion term and TKE production term.