Hydrodynamic Performance and Cavitation Characteristics of an Integrated Pump-Gate

With the pressure decreasing, the process of cavitation in a centrifugal pump could be summarized as incipient cavitation, quasi-steady cavitation and unsteady cavitation. Quasi-steady cavitation is the condition that is between the incipient cavitation and unsteady cavitation in a centrifugal pump. Under this condition, the intensity of cavitation is relatively weak, and the head of the pump almost remains unchanged, but the cavitation exists, causing damage to the impeller by pitting and erosion. So it is important to investigate the quasi-steady cavitation. In this paper, both the numerical and experimental methods had been carried out to investigate the characteristics of quasi-steady cavitation. The internal flow in the pump, the performance of cavitation and the inlet and outlet pressure pulsation of the pump measured through experimental method have been studied under different NPSHa conditions. It was found that the head decreases about 0.77%-1.38% from non-cavitation condition and it could be regarded as the quasi-steady cavitation. Little change has been found from the internal flow between non-cavitation condition and quasi-steady cavitation condition. The period of inlet pressure pulsation changes from the time that the blade passes by to the period of shaft rotating with the development of cavitation. The dominant frequency of the inlet pressure pulsation is two times of shaft frequency whose amplitudes decrease firstly and then increase to a peak value, followed by a decrease to a low value in quasi-steady cavitation conditions. The dominant frequency of the outlet pressure pulsation is blade passing frequency whose amplitudes increase firstly and then decrease gradually with the decrease of NPSHa.

This study investigates trapezoidal (scheme A) and triangular (scheme B) bionic structures, inspired by the leading edge pectoral fin of a humpback whale, arranged at the impeller blade leading edge of a guide vane mixed-flow pump. The effects of them on the cavitation performance and internal flow were compared through numerical simulation, and the accuracy of the numerical simulation was verified by experimental test. Entropy production analysis quantified and visualized flow losses induced by cavitation and bionic structures. Results show both schemes suppress cavitation development, with scheme B exhibiting slightly better hydraulic performance: 0.78% head increase at critical cavitation (NPSHa = 9.46 m) and 15.35% at severe cavitation (NPSHa = 8.27 m). Entropy production analysis indicates that after adding the bionic structures, at the severe cavitation stage turbulence dissipation is reduced by 21.9%–22.8% and wall entropy production is decreased by 10.6%–11.2% by suppressing large-scale vortexes and inducing secondary flows. The bionic structures optimize leading-edge pressure distribution, delay flow separation, and disperse cavitation bubble collapse, enhancing cavitation resistance and stability. The findings offer theoretical and engineering insights for bionic optimization in hydraulic machinery.

The sealing gaskets of multistage centrifugal pumps are prone to wear during operation. This study investigates the influence of gasket wear rate on hydraulic performance and internal flow field through numerical simulations. As the wear rate of the gasket increases, both the efficiency and head coefficient of the pump gradually decrease. When the gasket is completely worn out, the efficiency decreases by 5.6% and the head coefficient decreases by 9.5% compared to the unworn gasket condition. Analysis of the internal flow field reveals that the front side chamber is most significantly affected by gasket wear. As the gasket wears, the flow velocity within the front side chamber increases gradually, and the high-entropy production zone expands, thereby affecting the hydraulic performance of the pump. The findings of this study provide practical engineering insights for enhancing the operational performance of multistage centrifugal pumps.

Axial-flow axial fan is used as fire fighting parts in the axial-flow pneumatic extinguisher. The shape of axial impeller is the key factor affecting the internal flow field structure of fire-fighting fan, outlet Total pressure and flow velocity. In order to understand the flow pattern of axial-flow fire-fighting fan thoroughly, according to N-S equations and k-ɛ turbulence model, the internal three-dimensional viscous flow field of axial-flow fire-fighting fan was numerically simulated and many internal flow details, rules and performance parameters of axial-flow fan under the design working conditions was obtained. Numerical analysis shows that under the design working conditions, gas takes parallel flow from inlet and helically outflows from outlet as a whole, vortex generates at the blade tip area, some gas have reversed flow and lead to loss. The simulation results provide a theoretical basis for performance improvements of axial-flow fire-fighting fan.

Englacial radar reflectors in the ablation zone of the Greenland Ice Sheet are derived from layering deposited in the accumulation zone over past millennia. The original layer structure is distorted by ice flow toward the margin. In a simplified case, shear and normal strain incurred between the ice divide and terminus should align depositional layers such that they closely approximate particle paths through the ablation zone where horizontal motion dominates. It is unclear, however, if this relationship holds in western Greenland where complex bed topography, three dimensional ice flow, and historical changes to ice sheet mass and geometry since layer deposition may promote a misalignment between present-day layer orientation and the modern ice flow field. We investigate this problem using a suite of analyses that leverage ice sheet models and observational datasets. Our findings suggest that across a study sector of western Greenland, the radiostratigraphy of the ablation zone is closely aligned with englacial particle paths, and is not far departed from a state of balance. The englacial radiostratigraphy thus provides insight into the modern, local, internal flow field, and may serve to further constrain ice sheet models that simulate ice dynamics in this region.

Integrated pump-gates serve as crucial infrastructure in hydraulic engineering, urban flood control, and water transfer projects, playing a key role in enhancing engineering efficiency and ensuring public safety. However, the complex pressure pulsations induced by internal flow often result in reduced operational efficiency, structural vibrations, and fatigue damage. Therefore, it is essential to conduct systematic research aimed at optimizing their design and operational stability. This study utilizes the SST k-ω turbulence model to conduct numerical simulations analyzing pressure pulsation characteristics and radial force distributions under rotational speeds of 485 r/min and 590 r/min across varying flow conditions. The results reveal that at low-flow conditions, relatively strong pressure pulsations are observed on the impeller's suction side, whereas at high-flow conditions, more complex frequency-domain features emerge, likely linked to intensified turbulence or flow impact. As flow rates increase, the radial force distribution becomes more uniform, whereas higher rotational speeds yield larger absolute radial forces with reduced sensitivity to flow variations. These findings provide theoretical insights into improving hydraulic stability and mitigating structural fatigue risks, offering practical insights to enhance operational efficiency, prolong service life, and ensure the safety and sustainability of integrated pump-gate systems in water conservancy projects.

The low-pressure edge of a pump-turbine runner blade is more prone to cavitation than other parts. The installation angle of the blade’s low-pressure edge is one of the key parameters affecting the cavitation performance of the pump-turbine. Based on the installation angle of the blade’s low-pressure edge obtained by the principle of normal outflow of the turbine runner, two other installation angles of the low-pressure edge are constructed by increasing the installation angle of the low-pressure edge toward the band direction. Three types of blades are designed based on the parametric design program of the pump-turbine runner. The Zwart cavitation model is adopted to carry out full-channel steady numerical simulations for the three runners. The efficiencies and internal flow fields of the draft tube under turbine operating conditions are compared. The cavitation characteristics in pump mode, the distribution of the turbulent flow field, and the pressure distribution on the blade surface are analyzed. The influence laws of the installation angle of the blade’s low-pressure edge on pump-turbine performance is summarized. A design method for anti-cavitation of Francis pump-turbine runners has been explored. The results show that the LP1 blade can achieve normal outflow under the turbine’s rated operating condition, but due to the large inflow attack angle under pump operating conditions, the cavitation performance in pump mode is very poor. By increasing the installation angle of the blade’s low-pressure edge toward the band direction, the efficiencies and cavitation performances of the pump mode can be improved. The LP3 blade reduces the inflow attack angle while optimizing the pressure distribution on the blade’s suction surface, thereby reducing the superimposed effect of two phenomena under large-discharge pump operating conditions with low cavitation numbers: flow separations on the pressure surface caused by inflow impact, and flow separations on the suction surface of adjacent blades caused by cavitation. As a result, the cavitation performance of the LP3 blade is significantly better than that of the LP1 and LP2 blades. The proposed anti-cavitation design method is simple and effective and can be applied to the research and modification design of Francis pump-turbine runners.

This paper presented an addendum rotational hydrodynamic cavitation reactors (ARHCR) that enabled circumferential shear cavitation, axial cavitation, and the Venturi effect, thus increasing cavitation efficiency. The experiments on hydroxyl (·OH) release and chemical oxygen demand (COD) removal demonstrate the feasibility of cavitation performance characterization and COD removal rate. The findings indicate that the COD removal rate can reach a maximum value of 28% or 30% with an increase in flow rate or rotating speed, respectively. Specifically, the maximum values were achieved at a rotation speed of 2,500 rpm or a flow rate of 1.0 m3·h−1. Based on the mechanism of the addendum cavitation, the wedge angles, and the crucial structural parameters, were examined for optimizing cavitation performance. The results revealed that the cavitation number and cavitation bubble were significantly influenced by wedge angles, as well as the efficiency of cavitation energy. The mechanical shear of fluid was enhanced by wedge angles, resulting in constant compression and release of fluid with increased kinetic energy. This led to stronger effects on bulge blocks, and the formation of vortexes that rebounded constantly, resulting in lower pressure areas and expanded regions of cavitation. Among the wedge angles tested, the wedge angle of 15° exhibited the highest cavitation bubbles with a maximum value of 46%. This was 31% higher than the grooves‐type cavitator reported. Furthermore, the cavitation performance was extremely improved with a wedge angle of 15°, as corresponding with the maximum efficiency of cavitation energy. These explorations provide references for the removal of COD in industrial and agricultural wastewater, as well as the development of novel reactors for wastewater treatment.

To improve the cavitation performance of the centrifugal pump, a new kind of centrifugal pump impeller with slot is proposed. The slot is on the impeller shroud near the suction side of the blade leading edge. So, the fluid with high energy in the impeller front side chamber is drained to the lowest pressure area. The jet flow would compensate the blade inlet flow with a certain energy. With numerical simulations, the pump’s inner flows for 5 different slot sizes and their hydraulic performances are compared with those of the prototype pump. The slot jet would result in the increase of the impeller flow rate and the volute area ratio, leading to the head decrease within the whole flow rate range. The slot jet can suppress the reverse flow remarkably at a low flow rate, and the pump efficiency is improved. The slot jet improves the pump cavitation performance effectively, especially at a low flow rate. To some extent, the smaller the slot size is, the better the pump cavitation performance is. The cavitation performance of the slot impeller with a size of 2 mm×1.75 mm is much better than that of the prototype impeller. Compared with the prototype impeller, the lowest pressure near the slot impeller blade inlet and even the pressure in all forepart regions are improved significantly. The slot impeller is shown to be effective in suppressing the cavitation, and the available net positive suction head is improved.

To investigate the performance of engine cooling water pump in automobile with variable rotating speed, experimental tests and numerical simulation are carried out on an engine cooling water pump under the rotating speed of 2650, 2960, 3700, and 4300 r/min. The hydraulic performance under 3700 r/min rotating speed and the cavitation performance under 340 L/min flow rate are tested and analyzed. The predicted results agree well with the experimental results, indicating that the simulation has high accuracy. The results show that the head of engine cooling water pump increases gradually and the best-effective region moves toward high flow rate condition with the increase in rotating speed. The augment of rotating speed would deteriorate the internal flow fields and causes more energy losses, which is due to the increase in tip leakage flow and enhancement of rotor–stator interaction effects. And, the rotor–stator interaction effect is sensitive to the temperature under various rotating speeds. Furthermore, the required net positive suction head increases with the increase in rotational speed and anti-cavitation performance is weakened during cavitation conditions.

The transient process of a centrifugal pump existed in a variety of occasions. There were a lot of researches in the external characteristic in startup process and stopping process, but internal characteristics were less observed and studied. Study of the internal flow field had significant meanings. The performance of a pump could be evaluated and improved by revealing the flow field. In the other hand, the prediction of external characteristic was based on the correct analysis of the internal flow. In this paper, theoretical method and numerical simulation were used to study the internal characteristic of a centrifugal pump. The theoretical study showed that the relative flow in an impeller was composed of homogeneous flow and axial vortex flow. The vortex intensity was mainly determined by angular velocity of impeller, flow channel width and blade curvature. In order to get the internal flow field and observe the evolution of transient internal flow in the impeller, Computational Fluid Dynamics(CFD) were used to study the three-dimensional unsteady incompressible viscous flows in a centrifugal pump during starting period. The Dynamic Mesh (DM) method with non-conformal grid boundaries was applied to get the external characteristic and internal flow field. The simulate model included three pumps with different blade numbers and the same blade curvature. The relative velocity vector showed that there was a big axial vortex in impeller channel. At the beginning, the vortex was raised in the pressure side of the impeller outlet and with time went on, it shifted to the middle flow channel of the impeller and the vortex intensity increased. When the speed and flow rate reached a definite value, the influence of the axial vortex began to get smaller. The vortex developed faster when the flow channel got narrower. Due to the evolution of axial vortex, the slip factor during starting period was smaller than that in quasi-steady condition. As a result, transient head was lower than quasi-steady head in startup process.

The nuclear reactor coolant pump (RCP) is the core piece of equipment of a nuclear power plant (NPP). The energy performance and internal flow characteristics of RCPs are revealed by effective measurement methods, which are helpful to understand the flow mechanism of RCPs. The present work is intended to conduct an integrated study based on the energy performance test and Particle Image Velocimetry (PIV) flow-field non-contact measurement of the RCP. In addition, the prediction results of different turbulence models are compared with experimental results in detail. Through energy performance measurement and numerical calculation analysis, it can be found that various turbulence models have the ability to predict the performance of RCPs in engineering applications. At 0.8~1.2 Φd operating conditions, the maximum error is less than 10% and the minimum error is less than 0.1% by analyzing the energy performance of numerical calculations and experimental results. The PIV results show that the velocity of the discharge nozzle varies greatly from right (outlet of diffuser channel 2) to left (outlet of diffuser channel 12) due to different flow structures. Through the qualitative and quantitative comparison of the internal flow field, it can be concluded that, except for the low flow rate, compared with other computational models, the Realizable k-ε model can better predict the internal flow field of an RCP. The reasons for the experimental error and numerical calculation error are analyzed in detail, and the results can provide a reference for forecasting an RCP internal flow field with a special and complex structure.

In order to figure out the priority order of factors affecting centrifugal pump cavitation performance, the author carried out an orthogonal experiment on impeller geometric parameters which affects its cavitation performance, designed different impeller hydraulic models with the help of PCAD software, and used CFX software to conduct numerical stimulation calculation about its hydraulic and cavitation performance. The cavitation model used in this paper accurately predicted the centrifugal pump NPSH, in accordance with the experimental results of the prototype. The calculation result of the centrifugal pump cavitation performance was analyzed by the range analysis method. The influence of impeller inlet diameter, impeller exit width, outlet installing angle of impeller and blade numbers on centrifugal pump's cavitation performance weakens successively.

The multi-stage centrifugal pump run instability at the original design point, and the running operating point deviated far from the design point during the run. In order to better meet the multi-stage centrifugal pump operational requirements, through hydraulic model modification, changing the multi-stage pump design point, while the performance curve before and after the modification can be interchangeable in the flow of 150m3/h~320m3/h. The original program used 3 blades impeller. Taking into account the matching problem with pressurized water chamber, modification plan used 5 blades impeller. Analysis on the internal flow field before and after the modification was made. Through comparison the internal and external characteristics of the two plans, the analysis found that in the double volute pressurized water chamber, the flow field symmetry of 5 blades is better than the 3 blades’. The flow field symmetry can be well balanced radial force, and help to improve the instability phenomenon in operation.

Cavitation behavior is very important in pumps for long time operation. However, there is difficulty in predicting the cavitation phenomena of pumps by Computational fluid dynamics (CFD). In order to accurately ascertain cavitation behavior, a comparison between CFD and experimental data is a significant and essential process. The purpose of this study is to analyze cavitating behavior in multistage centrifugal pumps numerically and experimentally. For this investigation an experimental set up was used to obtain cavitation performance results. The CFD method was used to investigate the multistage centrifugal pump performance under developed cavitating conditions. The Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was adopted to account for turbulent flows. Numerical data were validated with experimental data and a good comparison of results was achieved. Numerically, cavitation performances were obtained for different pump stages and the effects on cavitation were described according to different NPSH (Net positive suction head). The occurrence of cavitation was also described according to NPSH3% in the head drop lines and water vapor volume fraction on the impeller blade. The rapid drop in head at low NPSH was captured for different flow conditions. It was found that for stage to stage performance, the head drop changes could be related to losses inside the pump. It was also shown that the simulation results can truly represent the development of the attached sheet cavitation in the impeller.