Search Results (19)

This paper focuses on a vertical axial flow pump and employs a 1D-3D coupling method to investigate the effects of different gate pre-opening angles on the internal and external flow characteristics of the axial flow pump during startup. Through comparative analysis, the following conclusions are drawn: In the study, a fully open gate is defined as 1, while a fully closed gate is defined as 0. When starting the axial flow pump with different valve pre-opening degrees, backflow occurs within the first 20 s of startup, and the backflow rate inside the pump gradually increases with the increase in the valve pre-opening degree. At a valve pre-opening degree of 0.6, the maximum backflow rate inside the pump reaches 5.89% of the rated flow rate. When starting the pump with the valve fully open, the maximum backflow rate reaches 10.98% of the rated flow rate, and the efficiency is affected by the backflow rate. The valve pre-opening degree has little impact on the axial force acting on the impeller during startup. When starting with a valve pre-opening degree of 0.6, the internal pressure difference in the pump is minimized. Within the first 20 s of startup, the internal pressure difference in the impeller is 28.96% higher and the flow velocity is 14.62% higher with valve pre-opening degrees of 0.8 and 1.0 compared to a 0.6 degree opening. During the initial stage of pump startup, with valve pre-opening degrees of 0.8 and 1.0, the pressure fluctuation amplitude inside the pump is minimal, with maximum relative amplitudes of only 0.621 and 0.525, which are 41.00% and 28.51% lower than the maximum amplitudes at 0 and 0.2 degrees, respectively. In summary, the peak pressure inside the pump is minimized when the valve pre-opening degree is around 0.8, while the pressure difference and flow velocity are relatively lower at a pre-opening degree of 0.6. It is recommended to start the pump with a valve pre-opening degree of around 0.6 to 0.8. Full article

Axial-flow pumps consider both the conventional pump mode and the pump as turbine (PAT) mode operation and put forward higher requirements for long-term operation stability and structural strength; therefore, it is of great engineering significance to evaluate the structural strength and fatigue life of the rotor under full operating conditions. In this study, based on computational fluid dynamics and the one-way fluid-structure interaction algorithm, the structural strength and fatigue life of the rotor system of a large vertical axial-flow pump under full operating conditions were evaluated and studied. The results show that blade deformation and equivalent stress are generally higher in the PAT mode than in the pump mode. The maximum deformation in both modes occurs at the tip of the blade, while the area of stress concentration is at the root of the blade. Both the deformation and the equivalent stress increase with increasing flow rate. The minimum safety factor occurs at the blade root in both modes, and the safety factor in the PAT mode is relatively smaller than that in pump mode. Therefore, when designing and manufacturing axial flow pumps for turbine duties, priority should be given to material strength at the blade root during PAT mode operation to ensure safe and stable operation. The aim of this study is to provide technical references and theoretical foundations for evaluating the service cycle of axial-flow pumps and the influence on pump life under different operation modes. Full article

The paper uses a hydraulic performance analysis method to support the design of stock production multistage pumps. The method relies on a hybrid numerical–experimental approach conceived as a trade-off between accuracy and cost. It is based on CFD analyses incorporating experimental data of leakage flows across the sealing elements to obtain accurate predictions without the need of inclusion in the CFD model of small-scale features, which strongly increase the model complexity and computational effort. The aim of the paper is to present and validate this method. To this end, a 6-stage vertical pump manufactured by the stainless-steel metal-sheets-forming technique was considered as the benchmark. A series of experimental tests were performed to hydraulically characterize the impeller and return-channels-sealing elements by means of an “ad hoc” designed test rig. The characteristic curves of the sealing elements were embedded on the CFD model implemented in accordance with the strategy proposed in a previous authors’ work to obtain satisfactory predictions of multistage pumps’ hydraulic performance with minimum computational effort with the analytical correction of single-stage single-channel computations to account for the interaction between adjacent stages. To further explore the capabilities of the hybrid model, axial thrust measurements were performed by means of another “ad hoc” designed experimental apparatus. The application of the method to the benchmark pump shows that the hybrid model predicts the static head and efficiency with an error value lower than 1% at its best efficiency operation, and estimates the axial thrust with a 5% average error in the operating range from approximately 70% to 120% of the best efficiency duty. Full article

Thermal design and the choice of turbulence models are crucial for motors. In this project, the geometrical model of the vertical shielding induction motor for a small nuclear main pump was established by SolidWorks software and the finite volume method was adopted to investigate the temperature of the motor, especially the temperatures of bearings lubricated water. To make the numerical simulation of flow and heat transfer in the rotating clearance of the shielding induction motor more accurate, the effects of four types of different two equation turbulence models on the temperature field of the shielding induction motor were studied. The results showed that different choices of turbulence models had little effect on the temperature of the winding insulation but influenced the temperature of the lower guide bearing lubricating water and the secondary cooling water outlet. The SST k-ω model showed the lowest relative error result of the temperature of the winding insulation and the bearing lubricating water in the primary loop system of the shielding induction motor. The temperature of the clearance water, the spiral tube water and the spiral groove water increased approximately linearly along the axial direction. Full article

A bi-directional pump is designed by using S-shaped hydrofoil, is the most convenient way to achieve bi-directional operation. In this paper, high-speed photography is used to visualize the flow field characteristics of the bidirectional pump under different cavitation numbers, and the flow field changes caused by cavitation are quantitatively analyzed in combination with the pressure pulsation sensor. The results show that the operation efficiency of the bidirectional pump in reverse operation is lower than that in forward operation. Tip clearance cavitation occurs on both suction and pressure surfaces of the impeller under reverse operation and large flow. In reverse operation, the influence of guide vane on the main frequency of pressure pulsation in the impeller is obvious. The quasi-periodic vertical cavitation flow phenomenon increases the amplitude of pressure pulsation in the impeller and becomes the main component of the internal flow in the bidirectional axial flow pump. Full article

The aim of this paper is to study the influence of non-uniform suction flow on the transient characteristics of a vertical axial-flow pump device. The unsteady calculation is employed to forecast the unstable flow structure with three inlet deflection angles $\alpha$, and the calculation accuracy under uniform inlet flow is verified by the external characteristic test. The results depict that a promotion in the $\alpha$ will increase the head and shaft power and thus improve the stress and fatigue failure risk of the impeller. At the impeller inlet, the pressure pulsation intensity (PPI) with $\alpha$ = 40° is lower than that with $\alpha$ = 0° caused by a decline in the axial velocity. The dominant frequency of the unsteady pressure signal is the blade-passing frequency (BPF), and the dominant frequency amplitude rises with the increase in $\alpha$ due to the improvement of the pre-rotation impact intensity. At the guide vanes inlet, the dominant frequency of the unsteady pressure signal at the guide vane inlet is also the blade-passing frequency. An improvement in $\alpha$ magnifies the angle between the trailing edge jet of the impeller and the leading edge of the guide vanes under 0.8Q_des and 1.0Q_des, while it diminishes the angle under 1.2Q_des. Thus, the PPI and dominant frequency amplitude with $\alpha$ = 40° are higher than that with $\alpha$ = 0° under 0.8Q_des and 1.0Q_des, but these are lower than that with $\alpha$ = 0° under 1.2Q_des. Full article

The energy loss of the vertical axial flow pump device increases due to the unstable internal flow, which reduces the efficiency of the pump device and increases its energy consumption of the pump device. The research results of the flow loss characteristics of the total internal conduit are still unclear. Therefore, to show the internal energy loss mechanism of the axial flow pump, this paper used the entropy production method to calculate the energy loss of the total conduit of the pump device to clarify the internal energy loss mechanism of the pump device. The results show that the energy loss of the impeller is the largest under various flow conditions, accounting for more than 40% of the total energy loss of the pump device. The variation trend of the volume average entropy production and the energy loss is similar under various flow coefficients (K_Q). The volume average entropy production rate (EPR) and the energy loss decrease first and then increase with the increase of flow, the minimum volume average entropy production is 378,000 W/m³ at K_Q = 0.52, and the area average EPR of the impeller increases gradually with the increase of flow. Under various flow coefficient K_Q, the energy loss of campaniform inlet conduit is the smallest, accounting for less than 1% of the total energy loss. Its maximum value is 63.58 W. The energy loss of the guide vane and elbow increases with the increase of flow coefficient K_Q, and the maximum ratio of energy loss to the total energy loss of the pump device is 29% and 21%, respectively, at small flow condition K_Q = 0.38. The energy loss of straight outlet conduit reduces first and then increases with the increase of flow coefficient K_Q. When flow coefficient K_Q = 0.62, it accounts for 27% of the total energy loss of the pump device, but its area average entropy production rate (EPR) and volume average entropy production rate (EPR) are small. The main entropy production loss in the pump device is dominated by entropy production by turbulent dissipation (EPTD), and the proportion of entropy production by direct dissipation (EPDD) is the smallest. Full article

Low-head vertical axial-flow pump as turbine (PAT) devices play a vital part in the development of clean energy for hydropower in plain areas. The traditional method of evaluating the flow loss in hydraulic machinery is calculated by the pressure drop method, the limitation of which is that the location of the occurrence of large losses cannot be accurately determined. In this paper, entropy production theory is introduced to evaluate the irreversible losses in the axial-flow PAT from the perspective of the second law of thermodynamics. A three-dimensional model of the axial-flow PAT is established and solved numerically using the Reynolds time-averaged equation, and the turbulence model is adopted as Shear Stress Transport–Curvature Correction (SST-CC) model. The validity of the entropy production theory to evaluate the energy loss distribution of the axial-flow PAT is illustrated by comparing the flow loss calculated by the pressure drop and the entropy production theory, respectively. The entropy production by turbulent dissipative dominates the total entropy production in the whole flow conduit, and the turbulent dissipative entropy accounts for the smallest percentage of the whole conduit entropy production at the optimal working condition Q_bep, which is 51%. The impeller and the dustpan-shaped conduit are the essential sources of hydraulic loss in the entire flow conduit of the axial-flow PAT, and most of the energy loss of the impeller occurs at the blade leading edge, the trailing edge, and the flow separation zone near the suction surface. The energy loss of the dustpan-shaped conduit results from the high-speed flow from the impeller outlet to dustpan-shaped conduit to form a vortex, backflow and other chaotic flow patterns. Flow impact, flow separation, vortex and backflow are the main causes of high entropy production and energy loss. Full article

The complex flow inside the axial-flow pump device will cause the problem of hydraulic noise; in order to explore the influence of the law of rotation speed on the internal flow characteristics and hydraulic noise of the axial-flow pump conduit, a combination of Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) was used to numerically solve the flow field and internal sound field in the pump device. The results showed that the flow in the elbow inlet conduit was smooth at different rotation speeds, and there was no obvious unstable flow. The higher the rotation speed, the more disordered the flow pattern in the left half of the elbow, which intensifies the unstable flow in the straight outlet conduit. The impeller is the main sound source of the internal hydrodynamic noise of the vertical axial-flow pump device. When the sound source propagates upstream and downstream along the conduit, the Total Sound Source Intensity (TSSI) gradually decays with the increase of distance; the greater the rotation speed is, the faster the Total Sound Source Intensity (TSSI) decays. When the rotation speed was increased from 1450 r/min to 2200 r/min, the TSSI in the straight outlet conduit was attenuated by 8.9 dB, 13.9 dB, and 16.0 dB respectively, and the TSSI in the elbow inlet conduit was attenuated by 11.0 dB, 13.5 dB, and 25.9 dB respectively. The vortex structure in the conduit induces flow noise and delays the attenuation of TSSI in the propagation process; with the increase of rotation speed, this delay will be more obvious. Full article

This study investigated the influence of the change in blade tip clearance on the internal flow characteristics of a vertical axial flow pump. Taking the actual running vertical axial flow pump of a pumping station as the research object, based on the SST k-ω turbulent flow model, the numerical simulation technology was used to study the effects of different tip clearances on the pressure, turbulent kinetic energy, Z–X section pressure and flow state of the impeller at the middle section. Furthermore, the impact of clearance layer tip leakage was also analyzed. Unsteady calculations of flow characteristics under the design conditions were performed. The research results showed that the variation trend of the pressure in the impeller was basically the same under different tip clearance values. With the increase in the clearance value, the pressure gradient along the water inlet direction of the blade decreased and the leakage vorticity increased. Observing the leakage vorticity distribution of the gap layer under the flow condition of $0.6Q_0$, it was found that when the tip clearance was smaller than 1 mm, the leakage flow was small and easily assimilated by the mainstream, and the leakage flow and mainstream had a certain ability to compete, which caused adverse effects on the performance of the pump device. The pressure pulsation characteristics showed that the leakage flow caused by the tip clearance caused a high-frequency distribution, and the clearance obviously influenced the pressure pulsation characteristics. Full article

The RANS equation and the RNG k-ε turbulence model were used in the three-dimensional non-constant numerical simulations of the full flow path of a vertical axial-flow pump which was carried out by applying CFX software. The velocity characteristics of the flow field and the pressure distribution of the impeller under different operating conditions were analyzed and verified by external characteristic tests. The fluid–structure interaction research was conducted for the stress distribution and deformation features of different surfaces of the blade under different working conditions. The result shows that where stress is most concentrated is at the point of the root of the blade near the hub. The low-pressure zone on the suction surface is mainly distributed near the rim, and the low-pressure area on the pressure side is mainly distributed near the hub. Full article

Increasing extreme rainfall events caused by global climate change have had a significant impact on urban drainage systems. As a critical component of a pumping station, a large-scale slanted axial-flow pump (SAFP) featuring high specific speed plays a critical role in mitigating urban flooding and waterlogging. In this study, to reveal the transient characteristics of a SAFP at shut-off conditions, a computational fluid dynamics (CFD) based approach with dynamic mesh was proposed. Multiple shut-off conditions with various shut-down speeds of the sluice gate (SG) were modeled. Our analysis demonstrated that both the shut-off conditions and the slanted structure have conspicuous impacts on the hydrodynamic performance of a SAFP. Reducing the shut-down speed leads to a greater reverse flow rate and higher runner speed. The water hammer effect was simulated with different shut-down speeds, increasing the water head by 5.07–10.42 m, the axial force by 163.46–297.06 kN∙m, and the axial moment by 116.05–224.01 kN∙m. Compared with the axial direction, moments in the radial directions were found with more obvious oscillation as a result of stronger rotor–stator interaction. Due to the gravitational effect of the slanted structure, the fluctuation of the runner in vertical direction presented an off-axis characteristic compared with the horizontal one. As the SG speed increased, pressure fluctuations gradually decreased at various locations across the SAFP. Full article

The internal flow in a vertical axial-flow pump is a complex unsteady three-dimensional viscous flow. An unstable flow often produces complex flow phenomena such as flow separation, vortices, and secondary reflux, which reduces the operating efficiency of the pump and can endanger safety and stability. In this paper, computational fluid dynamics is used to calculate the flow characteristics in an axial-flow pump using the shear stress transport and curvature correction (SST-CC) model for turbulence modified to account for the rotational curvature. Furthermore, the dependability of the numerical results was confirmed by a test with an actual model of a pump. The transient deviation angle at the impeller inlet of the pump, the stream field attributes in various spanwise parts of the impeller and guide vane, and the velocity distributions at the impeller inlet and outlet were analyzed. The omega method was utilized to recognize the vortex structure inside the guide vane. Moreover, the development of the transient vortex structure inside the guide vane was studied. As the flow rate increased, the scale and turbulent kinetic energy of the vortex structure gradually decreased. The time-domain graph for the impeller inlet is clearly periodic, with three peaks and three troughs in an impeller rotational period. The dominant frequency in the spectrum at each monitoring point was basically the blade frequency, and the secondary dominant frequency was twice the blade frequency. Full article

Vertical axial flow pump device has the characteristics of large flow and low head, which is widely used in pumping station projects with head of 3–9 m. In order to study the influence of the timing effect of the impeller relative flow channel and guide vane on the flow field and pulsation in the axial flow pump device, the whole flow channel of the vertical axial flow pump device was taken as the research object. The reliability of the numerical simulation was verified by physical model test. The flow field characteristics and pressure pulsation characteristics of the inlet and outlet regions of the impeller, the guide vane and the campaniform inlet conduit at different timing positions of the impeller under different flow rates were analyzed. The results show that the pressure coefficient distribution of the impeller inlet of the vertical axial flow pump device presents four high-pressure areas and four low-pressure areas with the rotation of the impeller. The pressure pulsation at the inlet and outlet of the impeller is mainly affected by the rotation of the impeller, and the main frequency is 4 times the rotation frequency amplitude of pressure pulsation decreases with the increase of flow rate. When the flow rate increased from 0.8 Q_bep to 1.2 Q_bep, the average velocity circulation at the guide vane outlet decreased by 12%; there is an obvious negative value region of the internal regularized helicity of the guide vane. When the flow rate increases from 0.8 Q_bep to 1.2 Q_bep, the amplitude of the pressure pulsation coefficient at the outlet of the guide vane decreases gradually, with a decrease of 94%. When the flow rate is 1.2 Q_bep, the main frequency and the secondary frequency of the pressure pulsation are both low-frequency, with obvious low-frequency pulsation characteristics. Under the small flow condition of 0.8 Q_bep, the outlet flow fluctuation of seven guide vane was 18.9% on average, and the flow variation of each guide vane was large. Under the optimal flow condition of 1.0 Q_bep and large flow condition of 1.2 Q_bep, the outlet flow fluctuation of 7 guide vane is 4.7% and 0.56% on average, and the flow change of each guide vane is stable. The outlet flow of the guide vane is mainly concentrated in two guide vane slots of the guide vane, and the flow ratios are 30.56%, 30.14% and 29.16% under three flow conditions, respectively. The research results provide a scientific basis for the optimization design and stable operation of vertical axial flow pump device. Full article

The deflection flow of inlet passage seriously affects the performance of axial flow pump devices, and reduces the operation efficiency and stability of pumping station systems. In this paper, the influence of different deflection angles on the internal flow characteristics and outlet pulsation characteristics of the inlet passage of the vertical axial flow pump are studied. Based on the Reynolds time-averaged N-S equation of the three-dimensional incompressible fluid and the standard k-ε turbulence model, the model axial flow pump device was numerically simulated. Under optimal working conditions (Q_bep = 31.04 L/s), the internal flow field of the axial flow pump was analyzed to study the change law of the axial flow pump performance under different deflection angles. Under the flow conditions of 0.6 Q_bep, 1.0 Q_bep and 1.2 Q_bep, the pulsation characteristics of the outlet of inlet passage in axial flow pump at different deflection angles were analyzed. The result shows that with the increase of the deflection angle, the flow pattern of the inlet passage becomes turbulent, forming vortices of different sizes, the hydraulic loss of the inlet passage increases continuously, and the uniformity of the outlet flow velocity of the inlet passage increases first and then decreases. The time-domain waveform of outlet of the inlet passage at the pressure pulsation monitoring point has obvious periodicity, and the dominant frequency of the monitoring point is four times the rotation frequency, which corresponds to the number of impeller blades. It shows that the numerical calculation is in good agreement with the experimental results, which proves the reliability and validity of the numerical simulation calculation. Full article