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Due to high power consumption and low energy efficiency of the hydrogenation feed multistage pump, conducting structural optimization design and reducing energy losses for this pump is necessary. In this study, an optimization method based on the particle swarm optimization (PSO) algorithm and least squares support vector regression (LSSVR) surrogate model is proposed. The head and efficiency are taken as the optimization objectives of the multistage pump, and the optimization design of the two impellers is carried out. Through the optimization of the surrogate model, the head and efficiency of the multistage pump are increased by 3.99% and 2.91%, respectively. It is found that the optimized impeller has more stable flow characteristics than original impeller. Further, the entropy production method is introduced to analyze the energy loss of pump. The result shows that the pump optimized by PSO-LSSVR surrogate model can reduce 9% energy consumption under nominal flow rate. It is attributed to the inhibitory effect of the optimization scheme on the horseshoe vortex at leading edge and the wake vortex at trailing edge of impeller. This study provides a new idea for the optimization design of high efficiency and low energy consumption of multistage centrifugal pumps.

Hydrodynamic cavitation (HC) has emerged as a promising technology for water disinfection. Interestingly, when subjected to specific cavitation pressures, jet pump cavitation reactors (JPCRs) exhibit effective water treatment capabilities. This study investigated the cavitation flow and vorticty transport in a JPCR with various area ratios by utilizing computational fluid dynamics. The results reveal that cavitation is more likely to occur within the JPCR as the area ratio becomes smaller. While as the area ratio decreases, the limit flow ratio also decreases, leading to a reduced operational range for the JPCR. During the cavitation inception stage, only a few bubbles with limited travel distances are generated at the throat inlet. A stable cavitation layer developed between the throat and downstream wall during the limited cavitation stage. In this phase, the primary flow carried the bubbles towards the outlet. In addition, it was found that the vortex stretching, compression expansion, and baroclinic torque terms primarily influence the vorticity transport equation in this context. This work may provide a reference value to the design of JPCRs for water treatment.

Blade wrap angle is one of the main parameters of centrifugal pump, which has an important influence on the internal flow characteristic and pump performance. In this work, five impeller models with different blade wrap angles (85°, 95°, 105°, 115°, and 125°) are established on the condition of other impeller parameters remain unchanged, whose external characteristic, internal flow, and wear were analyzed by numerical simulation method. The results show that the influence of blade wrap angle on efficiency is more significant than head, has a certain effect on the internal flow field of the centrifugal pumps and effects the wear position of pressure surface. With the increasing of blade wrap angle, the pump efficiency increases companied by the pump head decreases slightly, the area of higher speed at the outlet of the impeller tends to decrease, the higher speed wake area at the end of the blade pressure surface breaks and shrinks, the vortex in the impeller passage is fewer and smaller, the turbulent kinetic energy and morphology of vortex inside the pump decreases gradually, and the wear rate of the flow passage components shows a pattern of first decreasing and then increasing.

The multi-size group (MUSIG) model is employed in this paper to simulate the gas–liquid two-phase flow in pump as turbine (PAT) since the traditional Eulerian–Eulerian two-fluid model is unable to take into account the phenomena of breakup and coalescence of bubbles. First, the simulation of gas–liquid two-phase flow in a square column is compared with the experiment to verify the accuracy of the MUSIG model. Then, the results of gas–liquid two-phase flow in PAT simulated by the MUSIG model are compared with those by the conventional uniform bubble (UB) model and find that the MUSIG model is more favorable to capture the flow pattern at high gas content compared to the UB model. Based on the MUSIG model, the internal flow characteristics, pressure fluctuation, and bubble size distribution of the PAT are analyzed. The rotation of the blades breaks a part of big bubbles into small bubbles in the volute, resulting in a smaller diameter of the bubbles entering the impeller. As the gas content increases, the number and size of vortices in the impeller flow channel increase. The vortex is formed at locations where the gas phase distribution in the impeller flow channel is concentrated. The outlet of the impeller is more prone to bubble consolidation under high gas content conditions. In conclusion, the MUSIG model can well predict the complex flow characteristics of gas–liquid two-phase inside the PAT and identify the key influencing factors of energy acquisition, which can provide support for improving the performance of the PAT design.

An inducer is a key component in a cryogenic pump to improve its cavitation performance. The thermodynamic effects of the cryogenic medium make the cryogenic cavitation flow extremely complicated. For this reason, it is crucial to investigate the cryogenic cavitation flow of the inducer which is equipped upstream of the cryogenic pump. In this paper, the isothermal cavitation model is modified based on the law of heat conduction, and the cryogenic cavitation model of the inducer is developed by considering thermodynamic effects. The turbulence model is also modified to account for the compressibility of cryogenic cavitation flow. The methods of numerical calculations are performed to investigate the influence of thermodynamic effects on cryogenic cavitation of the inducer. The law of the spatio-temporal evolution of cryogen cavitation in the inducer is clarified. The initial position, development and collapse phenomenon of cavitation are obtained. The relationship between the generation and collapse of the cavitation and the work capacity of the inducer’s blade, the relationship between thermodynamic effects and the influence of the inducer’s blade tip leakage vortex and thermodynamic on cryogenic cavitation of the inducer are revealed.

We have employed the large eddy simulation (LES) approach to investigate the cavitation noise characteristics of an unsteady cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil by employing an Eulerian-Lagrangian based multiscale cavitation model. A volume of fluid (VOF) method simulates the large cavity, whereas a Lagrangian discrete bubble model (DBM) tracks the small bubbles. Meanwhile, noise is determined using the Ffowcs Williams-Hawkings equation (FW-H). Eulerian-Lagrangian analysis has shown that, in comparison to VOF, it is more effective in revealing microscopic characteristics of unsteady cavitating flows, including microscale bubbles, that are unresolvable around the cloud cavity, and their impact on the flow field. It is also evident that its evolution of cavitation features on the hydrofoil is more consistent with the experimental observations. The frequency of the maximum sound pressure level corresponds to the frequency of the main cavity shedding for the noise characteristics. Using the Eulerian-Lagrangian method to predict the noise signal, results show that the cavitation noise, generated by discrete bubbles due to their collapse, is mainly composed of high-frequency signals. In addition, the frequency of cavitation noise induced by discrete microbubbles is around 10 kHz. A typical characteristic of cavitation noise, including two intense pulses during the collapsing of the cloud cavity, is described, as well as the mechanisms that underlie these phenomena. The findings of this work provide for a fundamental understanding of cavitation and serve as a valuable reference for the design and intensification of hydrodynamic cavitation reactors.

In this paper, several methods about the active noise control (ANC) system are studied. The common adaptive recognition system based on the variable step filter x least mean square (FxLMS) algorithm are elaborated. By introducing the momentum term into the variable step algorithm, the value range of the variable step is increased, so as to speed up the convergence of the algorithm and improve the effect of noise reduction. The weight of the control filter based on the improved logarithmic function variable step size least mean square (VSSLMS) algorithm is updated in the improved second channel online recognition algorithm. The initial smooth noise signal, the noise signal of increasing amplitude, and the abrupt noise signal are utilized to verify the convergence speed and the noise reduction effect of the modified ANC method. Numerical results show that the improved algorithm structure could improve the convergence speed and reduce the noises of the whole system at three different primary noises. The initial smooth noise signal, the noise signal of increasing amplitude, and the abrupt noise signal are utilized to verify the convergence speed and the noise reduction effect of the modified ANC method. Numerical results under three different primary noises show that the improved algorithm structure could improve the convergence speed and reduce the noise of the whole system.

Simulation of cavitation considering bubble dynamics is challenging due to the wide range of length and time scales. As the volume of fluid (VOF) method is suited for resolving the cavity and the discrete bubble model (DBM) in the Lagrangian frame is better for simulating micro-scale bubbles, the present work develops an Eulerian–Lagrangian multiscale cavitating flow solver with two-way transition in OpenFOAM. The growing and collapsing of discrete bubbles are solved using the Rayleigh–Plesset equation or the simplified Rayleigh–Plesset equation, and the adaptive mesh refinement is also available. Simulation tests of different cavitation conditions demonstrate the accuracy of the solver.

A transient computational fluid dynamics (CFD) method based on dynamic mesh is adopted to investigate the static and dynamic performances of an annular seal with a tilted rotor. The reliability of the CFD method is verified by the experimental data, and then the variations of dynamic performance and sealing performance under different length-diameter ratios and misalignment angles are investigated by the method. The results show that the leakage flowrate of the tilted annular seal decreases with the increasing length-diameter ratio, while the whirl frequency ratio increases with the length-diameter ratio. The increase of misalignment angle has little detrimental effect on the stability of long shaft system in the three misalignment modes. In addition, the misalignment mode for the tilted position at the half-length of the annular seal can reduce the leakage flowrate.

A fluid food conveying pump is used to convey edible or nutritional fluids and semi-fluids (containing suspended soft and hard particles and with different viscosities), such as water, glycerin, yogurt, and juice concentrate. Since different fluid food have different viscosities, the internal flow characteristics and conveying performance of food conveying pump are greatly affected by viscosity. To obtain the influence law of fluid food viscosity on the internal flow characteristics of the pump, the internal flow characteristics of food conveying pump when conveying food of 4 different viscosities (water, glycerin, 67.2 °Bx wild jujube juice, and 71.0 °Bx haw juice) were compared and observed in this study. The results showed that, with the increase in food viscosity, the overall flow loss in the pump, the entropy generation, and the proportion of total entropy generation in the pump chamber increase, but the conveying performance of the food conveying pump gets worse; however, the pressure pulsation intensity caused by static and dynamic interferences decreases with the increase in viscosity.

Traditional centrifugal pump performance prediction (CPPP) employs the semi-theoretical and semi-empirical approaches; however, it can lead to many prediction errors. Considering the superiority of deep learning when applied to nonlinear systems, in this paper, a method combining hydraulic loss and convolutional neural network (HLCNN) is applied to CPPP. Head and efficiency were selected as two variables for demonstrating the energy performance of the centrifugal pump in order to reflect the prediction ability of the proposed model. The evaluation results indicate that the predicted head and efficiency are accurate, compared with the experimental results. Furthermore, the HLCNN prediction model was compared against machine learning methods and the computational fluid dynamic method. The proposed HLCNN model obtained a better AREmean, root mean square error, sum of squares due to error, and mean absolute error for centrifugal pump energy performance. The research revealed that the HLCNN model achieves accurate energy performance prediction in the design of centrifugal pumps, reducing the development time and costs.

Annular seals can induce fluid excitation forces that severely affect the stability of the pump rotor systems. In this paper, a transient computational fluid dynamic method with a mesh deformation technique is used to study the fluid excitation forces generated on the long annular seal caused by cylindrical whirls and conical whirls. The reliability of the method is verified by comparing the simulation results with the experimental results. The whirl motion, composed of cylindrical and conical whirls, is realized by the phase difference between the whirl movements at the annular seal inlet and outlet, and the effects of the phase difference and inlet preswirl on the fluid excitation forces are studied numerically. The results show that the fluid excitation forces significantly depend on the phase difference of the rotor whirl movement, and tangential force acts as a stabilizing force only when the phase difference approaches 45°. The tangential forces of the cylindrical whirl, the conical whirl and the form of cylindrical and conical combined whirl are sensitive to inlet preswirl, while the effect of inlet preswirl on the radial forces becomes obvious only when the rotor whirls in the form of combined whirls.

In the field of food processing, the processing of liquid foods has always played an important role. Liquid foods have high requirements for the processing environment and equipment. As the core equipment in liquid foods processing, food transport pumps are widely used in liquid foods production, processing and transportation. Most liquid foods are non-Newtonian and vulnerable to vibration, noise, and temperature rise produced by rotary motions of food transport pumps in operation, which can finally affect foods safety. Therefore, this review summarizes the impact of mechanical vibration, noise, and temperature rise on liquid food products, with the aim of ensuring food safety while designing a cleaner, safer and more reliable food transport pumps in the future.

The solid–liquid two-phase centrifugal pump is one of the core power equipment of solid phase material hydraulic transportation, widely used in hydraulic engineering, petrochemical industry, marine metal mineral exploitation, urban sewage treatment, and other sectors of the national economy. There is a significant increase in the need to transport dense fine particle slurry in industrial production. Under this condition, the influence of particle parameters on the performance of the centrifugal pump is still not clear. In order to study the flow and wear characteristics of dense fine particle solid–liquid two-phase transported by an open impeller centrifugal pump, the Re-Normalization Group k − ε and dense discrete phase models in Fluent were used to describe the characteristics of the solid–liquid two-phase flow. The numerical model is validated with the experimental data of the pump’s performance. The study indicates that the particle size and concentration have great influence on the wear of the impeller. The wear of the blade pressure surface is the most serious. With the increase of particle concentration and size, the wear area expands to the leading edge and the upper surface of the blade. These results can provide supporting theories for the design of a dense fine particle solid–liquid two-phase medium conveying pump.

This study performed external characteristics, dynamic pressure, and vibration tests on the closed impeller model, semi-open type impeller model, and open impeller model in order to study the influence of the impeller structure on the operational stability of the pump. According to the research findings, the external characteristics of the three impellers enjoyed favorable stability with flat curves under low flow rates. As the flow increases, the stability of the external characteristics weakens, and the poorest stability can be observed in the open impeller, while the enclosed impeller has the best stability under a large flow rate. In addition, intense pressure fluctuations arise near the casing tongue due to the dynamic and static interference between the blade and the casing tongue, causing a large amplitude of pressure pulsation near the casing tongue and the pump outlet. It can be seen that the stability of pressure pulsation of the closed impeller in the casing tongue area was the best, whereas the stability of pressure pulsation of the open impeller was the poorest. The minimum casing vibration can be found in the closed impeller, followed by the semi-open impeller, and the open impeller, with the maximum vibration. In addition, the optimum stability of rotor vibration can be observed in the closed impeller, semi-open impeller, and open impeller with similar stability of rotor vibration.

A wear-ring is an important part of the centrifugal pump. The leakage flow in the wear-ring clearance and main flow at the impeller inlet form crossed mixed flows perpendicular to each other. Large eddies and shocks are produced at the intersection of the two flows due to great velocity difference and different directions, resulting in flow losses, unsteady flow, and even flow-induced vibration. Consequently, the pump performance, pressure pulsation and vibration, and other characteristics will be greatly affected. In this paper, 5 incident angles between the incident section of the wear-ring clearance and the circumferential direction of impeller inlet, i.e., the original angle (90°), 75°, 60°, 45°, and 30°, were formed with a low-specific-speed centrifugal pump as the study object. Unsteady flow calculation and fluid–structure interaction calculation were performed on centrifugal pumps with different wear-ring clearances; the effect of the incident angle of the wear-ring clearance on the distribution of pressure pulsation and vibration performance of centrifugal pump was analyzed. The results showed that the improved efflux angle of the wear-ring clearance could effectively weaken the impact disturbance of the leakage flow in the wear-ring clearance to the main flow at the inlet. Accordingly, the flow status at the inlet of the centrifugal pump was improved, flow losses were reduced, the efficiency of the centrifugal pump was improved, and the vibration amplitude and vibration energy of the pump were also reduced.

The efficiency of the impeller machinery can be improved by the inlet guide vanes, but the relationship between the external characteristics of the centrifugal pump and the internal flow state needs further study. In this paper, the flow characteristics of the centrifugal pump with different offset angles of inlet guide vanes (IGVs) are simulated based on the SST k-ω turbulence model. The influence of the offset angle of the IGV on the internal flow and energy dissipation of the centrifugal pump is analyzed by using the entropy generation theory and Q-criterion. The research results show that the increase of the offset angle is beneficial to reducing the intensity of vortex in the volute and impeller, while the energy loss is reduced by 21.12 and 17.82% at 0.6Qd and 0.8Qd, respectively. However, the excessive offset angle of the IGV tends to cause greater energy loss in the inlet pipe, thus reducing the head and efficiency of the centrifugal pump. In terms of external characteristics, the pump with 25° IGVs has the best head and efficiency improvement. Under three small operating points, the pump with 25° IGVs increased the head by 2.11, 0.95, and 0.73% and the efficiency by 2.51, 1.67, and 1.25%, respectively, compared with the pump with 0° IGVs. The research in this paper contributes to the performance improvement of centrifugal pumps operating at low flow conditions.

Time-resolved particle image velocimetry (TR-PIV) measurements were conducted to analyze the unsteady flow field developing in a centrifugal pump. The flow structures in the impeller passage under different flow rates were investigated. The overall statistical characteristics of the flow were obtained with the study of relative phase-averaged flow field, phase-averaged turbulent kinetic energy (TKE), and the analysis of frequency. Through the study of the first few proper orthogonal decomposition (POD) modes of the flow field, the coherent flow structures under several flow rates were revealed, consequently, the flow fields were reconstructed by the POD modes. Results show that the main flow structures could be reflected by the first few modes of the flow field: when the fluid follows the blade contour well, the first few modes corresponded to the “jet-wake” structures; when the large-scale flow structures appear in the passage, the 1st and 2nd modes were associated in pairs and corresponded to the stall cells, the 3rd and 4th modes corresponded to the “jet-wake” structures, and the 5th and 6th modes corresponded to the passage vortexes or the “jet-wake” structures (for the extreme part-load conditions). The flow structures that were reflected by the first few modes change as the decrease of flow rate, especially, at the extreme part-load condition, not only the shapes of the flow structures changed, but also the flow direction is reversed. This indicates that the generation mechanism of turbulent kinetic energy in the flow passage changed at the extreme part-load conditions.

In this paper, the numerical simulation was used to study the flow and heat transfer characteristics for twisted oval and two-start twisted helically wound tubes with Reynolds numbers 4000–16,000. The significant factors that affect the flow and heat transfer characteristics were analyzed. The range of twist pitch p is 0.02–0.10 m, and ellipse ratio r is 1.2–2 for twisted oval tube, the groove depth e is 0.4–2 mm for two-start twisted tube. The result showed that the relative friction coefficient and Nusselt number increased with the increase of ellipse ratio r and decreased with the increase of twist pitch p for twisted oval helically wound tube. With the growth of Reynolds number, the effects of twist pitch p and ellipse ratio r on the flow characteristics decreased. In addition, the average level of the thermal enhancement factor TEF of the two-start twisted was higher than that of the twisted oval helically wound tube. The maximum enhancements factor TEF of 1.1312 is obtained with groove depth of 2.0, twisted pitch of 0.02, and Reynolds number of 4000 for the two-start twisted tube. Finally, new empirical formulas for flow and heat transfer in helically wound tubes were proposed for two kinds of enhanced tubes.

The cavitation characteristics and load distributions of the inducer have great influences on the vibration characteristics of the rotating system and the whole pump. In this paper, the numerical simulations of the flow field within different inducers were carried out based on the Shear Stress Transfer (SST) k–ω turbulence model combined with the hybrid cavitation model to investigate the effects of blade numbers on the internal flow and cavitation characteristics of the model inducers. The simulation results were compared with the experimental results obtained using a closed inducer performance test rig to verify the accuracy and applicability of the numerical simulation method. The comparisons show that the three-blade inducer has better cavitation performances than the two-blade one. The simulation results of the bubble and load distributions suggest that the cavitation at low flow rates within the two model inducers occurs mainly near the leading edge of the blade tip, but at the design flow rates or higher flow rates, the cavitation within the two-blade inducer occurs along the suction surfaces near the inlet and the cavitation within the three-blade inducer occurs mainly on the inlet suction surfaces near the blade root.

In the energy conversion device and fluid transport equipment, the solid–liquid two-phase centrifugal pump occupies a large proportion, but the transport mechanism of dense fine particles has not been studied in detail. In this work, the solid–liquid two-phase flow in a centrifugal pump was numerically simulated by the mixture model. Two-phase performance tests with different particle concentrations and particle sizes at a low flow rate (0.6Qd) were conducted, and dimensionless analysis on the effect of particle concentrations and particle sizes on head and efficiency was conducted. The results show that the increase in particle size and particle concentration can increase the influence coefficient of head and efficiency and the influence of the two parameters on efficiency is greater than that on the head on the whole. The increase in particle size and concentration will lead to more uneven distribution of the solid volume fraction in the pump. The transport of dense fine particles absorbs a large amount of energy, which leads to the relative decrease in the kinetic energy of the liquid phase and inhibits the generation of the vortex in the impeller passage.

Ball valve is an important control component in the pipeline transportation system. It is widely used in pipeline transportation systems to control the pressure and flow parameters of the conveying medium. Based on the user-defined UDF technology and the standard k- ε turbulence model using computational fluid dynamics techniques, the transient numerical simulation of the internal flow field of the ball valve under the variable speed law and different opening degrees is carried out, and the flow coefficient characteristics, resistance coefficient characteristics, inlet and outlet pressure drop, and internal flow field distribution of the ball valve are analyzed and studied. The results show that by designing the curve function of the ball valve actuator movement process with different structure forms, different types of ball valve flow coefficient and resistance coefficient curve can be obtained, which makes the ball valve as a flow regulating valve more widely used; Modifying the motion law of ball valve electric actuator has little influence on the distribution of ball valve flow field. As long as the motion law of ball valve actuator is optimized within a reasonable range, the purpose of pipeline flow control can be achieved, the inconvenience of valve replacement can be reduced, and the economic cost can be saved.

Membrane filtration is an efficient wastewater treatment technology. However, sludge particles will easily aggregate and deposit upon the membrane surface, which will decrease the water productivity of membrane filaments. Focusing on the influence of velocity on particle behavior, experimental and numerical research was carried out. The k−ε turbulent model, porous media model and DPM model were adopted in the simulation. The flow characteristics including pressure, velocity and particle concentration contour are discussed using different inlet velocities of 0.6, 0.8, 1 m/s. The effects of gravity were also investigated. The final evaluation suggests the best working conditions in three scenarios, which could help to suppress membrane pollution. The results indicate that when the inlet velocity is about 1 m/s, particle deposition is weakest, resulting in better water productivity.

In order to study the effect of tip clearance on the internal cavitation stability of a shunt blade inducer, an external characteristics experiment of a centrifugal pump with a shunt blade inducer was carried out. Based on the turbulence model and mixture model, the cavitating flow in a centrifugal pump with the inducer was numerically simulated. The influence of tip clearance on the cavitating flow in a shunt inducer was studied and analyzed. Through the research, it was found that tip clearance has a certain influence on the critical cavitation coefficient. The existence of the tip clearance caused a significant leakage vortex near the inducer’s inlet and a strong transient effect was shown. The location and degree of cavitation caused by the tip leakage are clarified in this paper. Tip clearance has a great impact on the pressure distribution on a shunt blade inducer. The influence law of tip clearance on an inducer’s blade load distribution was clarified. The results showed that tip clearance has a significant effect on the cavitation of a shunt blade inducer under low flow rate conditions.

The gear transmission system is widely used in high-speed centrifugal pump to improve the operating speed and hydraulic performances of the whole pump. Vibration characteristics and the stability of these high-speed rotor systems with gear transmission have great impacts on the stability of the whole fluid transmission system of the plant. Based on the lumped-mass method and the principle of displacement equilibrium of the rotor system, a coupled lateral-torsional dynamic model describing the gear-rotor-seal-bearing (GRSB) system of high-speed centrifugal pumps which has considered the nonlinear factors within the gear pair, nonlinear forces of bearings, and those of the seals is proposed. Then, the stability and nonlinear vibration responses of a model GRSB system under different gear transmission ratios (i) have been studied. The following conclusions are drawn from the results: (1) The components with frequencies like fp, fg, fm, and 2fm have great impacts on the vibration responses of the gear pair, especially the fm component; moreover, the amplitude of fm first increases and then decreases with the ratio increase and reaches the maximum value under the ratio of 3. (2) A jump motion state will occur when the ratio i is 1.25 and the stability of the system is obviously worse than the bifurcation state. Quite different from those under the other states, under this jump motion state, the 0.2fg component and 0.5fp component will appear in the vibration responses of both gears and become the most contributed two factors to the responses of the driven gear. (3) In the design process, the transmission ratio of a high-speed centrifugal pump with a simplified GRSB system should be specially designed to avoid the jump-point state and the maximum-amplitude-of-fm state to ensure the stability of the system as well as reduce the mechanical impacts and noises.

To study the effect of fine particle size and volume concentration on the performance of solid-liquid two-phase centrifugal pump, the mixture multiphase flow model, RNG k-ε turbulence model, and SIMPLEC algorithm were used to simulate the two-phase flow of the centrifugal pump. The effects of particle size and volume concentration on internal pressure distribution, solid volume distribution, and external characteristics were analyzed. The results show that under the design discharge conditions, with the increase of particle size and volume concentration, the internal pressure of the flow field will decrease, and the volume fraction of solid phase in the impeller passage will also decrease as a whole. The solid particles gradually migrate from the suction surface to the pressure surface, and the particles in the volute channel are mainly concentrated in the flow channel near the outlet side of the volute. With the increase of particle size and volume concentration, the negative pressure value at the inlet of centrifugal pump increases, the total pressure difference at the inlet and outlet decreases, and the head and efficiency decrease accordingly.

As the core device of the deep-sea mining transport system, the slurry pump and its internal solid-liquid two-phase flow are extremely complicated; especially, the migration characteristics of particles have a great influence on the flow and wear of the pump. In order to grasp the particle motion law inside the slurry pump, this paper took into consideration the collision effects of the particles with particles and particles with walls and calculated the unsteady flow of the solid-liquid two-phase by CFD-DEM coupling algorithm. Then, the focus was put on the spatial distribution and movement characteristics of different particle diameters (namely, 5 mm, 10 mm, and 15 mm, while volume concentration Cv is constant 5%). The results show that the stratification phenomenon gradually disappears with the increase of particle diameter, and the intensity and scale of the vortex in the guide vane also increase obviously. Besides, as the particle diameter increases, the velocity changes more drastically, and the intensity and scale of the vortex increase significantly. Under low concentration conditions, the presence of particles has a limited influence on the hydraulic performance of the pump. By comparing with the experimental results, the simulation results are in good agreement with it, which proves that the CFD-DEM simulation in this paper is effective, and the conclusions can provide theoretical support for the design and analysis of the slurry pump in engineering application.

Static characteristics and leakage flow rates of liquid annular seals have great influences on the hydraulic efficiency of turbomachinery. In this paper, a two-dimensional (2D) mathematical model for predicting the leakage flow rates and static characteristics of liquid seal is established, based on the lattice Boltzmann method (LBM) combined with the D2G9 velocity model for incompressible fluid and large eddy simulation (LES) turbulence model, in which the transformation equation of reference pressure is developed with the Bernoulli equation. Moreover, the proposed model is validated by comparing with the experimental results, calculation results based on the finite volume method (FVM), and the results based on the empirical method of three seals under different operating conditions. The comparisons show that the maximum deviation in leakage prediction of the calculating model based on 2D LBM is 4%, and this calculating model will effectively improve the leakage prediction accuracy of the seals compared with the FVM and theoretical method.

This work analyzes the causes of the slip phenomenon in the impeller on the basis of the internal flow mechanism. Detailed optical measurements of the flow inside the rotation passages of a five-bladed centrifugal pump impeller are obtained through particle image velocimetry (PIV). On the basis of experimental data, the deviation coefficient of slip velocity is proposed and then revised according to the slip factor calculation formula of Stechkin. Results show that, at the same rotation speed, the slip factor increases with the flow rate and reaches the maximum value at 1.0 QBEP flow rate. At different rotation speeds, the slip factor increases with the rotation speed and shows a relatively large variation range. Moreover, a revised slip factor formula is proposed. The modified model is suitable for the correction of slip factor at part-load flow rates and serves as a guide for the hydraulic performance design and prediction of centrifugal pumps.

Along with the pressing demand for the long-distance transportation of coarse particles in the deep-sea mining industry, evaluating the slurry pump’s passing through and erosive wear by studying the particle motion characteristics and the slurry behavior is becoming increasingly important. Research on the influence of leakage flow through the clearance and balancing devices on the motion characteristic of granular grain flow is of great significance but has been seldom studied. This study coupled the discrete element method with the CFD method to investigate the comprehensive effect of a double-stage slurry pump’s main flow and leakage flow on the motion characteristics of particles with a 10 mm diameter. Results show that the leakage flow occupation in main flow falls from 26%–27% to 8%–9% for the two stages, with the flow rate increasing from 80 m3/h to 200 m3/h. In the first stage with leakage, accumulation of coarse particles was observed at the impeller eye, which should be paid much attention to slurry pumps’ operation to eliminate the chance of blockage. In the nonleak situation, although the increment of the average kinetic energy of particles through the impeller is more significant than in the leak case, most of them dissipate primarily by more than 10% collision in the bowl diffuser. In the leak or nonleak case, the average kinetic energy of particles was more than twice through the first stage but only 1.1 times through the second stage. The selection of stages in the slurry pump design should consider the limitation of particle velocity improvement.

Environmental pollution as a result of urban and industrial wastewater has become an increasingly prominent issue. Rivers, lakes, and oceans that have become eutrophicated or polluted by suspended solids and hazardous substances in wastewater have endangered the environment. A root cause of this is the discharge of untreated urban and industrial wastewater into the ecosystem. As a solution to the pollution, wastewater treatment facilities have seen increasingly rapid development. Sewage pumps are designed to transport urban and industrial wastewater containing solid particles or hazardous substances to water treatment centers for purification and treatment. Sewage pumps are of great importance in the entire wastewater treatment system. Sewage in the environment where sewage pumps work usually contains sands, suspended particles, and plenty of saline ions. Flow passage components and sealing elements of the pump become vulnerable to abrasion and chemical corrosion, which further challenges operational stability of the pump. Research has remained focused on how to improve reliability of sewage pumps under severe conditions. Because of advances in materials science, the application of an increasing number of new materials has been witnessed, such as carbon-based composite materials and carbon nanomaterials, thanks to their fine self-lubrication performance, heat resistance, thermal and electrical conductivity, chemical stability, heat and seismic resistance, as well as plasticity. These properties contribute to enormous potential that new carbon-based composite materials and carbon nanomaterials have to offer in terms of corrosion resistance. This paper outlines application scenarios, research progress, and the prospect of new materials in sewage pumps.

The effect of inclined volute tongue on the aerodynamic noise and performance of a centrifugal fan was investigated by experimental test in this article. The present work highlights that the effect of both the clearance and the radius of the volute tongue has an influence on the performance and noise. The experimental tests of various models aim to obtain the aerodynamic noise and performance characteristics of several fan models. First, the experimental results of centrifugal fan performance are tested by the standard test equipment of aerodynamic performance. The experimental results of centrifugal fan aerodynamic noise are measured by the standard test equipment of experimental noise. Our experimental results mainly show that the generation of aerodynamic noise is significantly correlated with the clearance and radius of the volute tongue. Certain geometries of the volute tongue could reduce the noise of the centrifugal fan without decreasing the performance. It is experimentally demonstrated that the high A-weighted sound pressure levels mainly concentrate on a range of from 700 to 7000 Hz frequency by observing the each 1/3 octave band frequency for four fan models. The comparison of aerodynamic noise results also demonstrates that the inclined volute tongue may not only produce a deceasing of about 1.58 dB compared to that of the baseline model. We further obtain that the properly inclined volute tongue not only has positive performance features compared with the baseline model but also effectively controls the broadband frequency noise of single-inlet centrifugal fan.

The blade load distributions reflect the working characteristics of centrifugal impellers, and the vortexes in the impeller channel affect the blade load distribution, but the mechanism of this phenomenon is still unclear. In this study, particle image velocimetry (PIV) was adopted to clarify the correlation between the internal flow pattern and the blade load distribution. The internal flow pattern and the blade load distribution were presented under different working conditions to study the influence of the internal flow pattern on the blade load. Results showed that the vortexes in the flow channel redistributed the blade load. The clockwise vortex made the position of the maximum blade load closer to the outlet, while the counterclockwise vortex had the opposite effect. Meanwhile, the vortexes caused the blade load distribution to be steeper, which reduced energy conversion efficiency. Moreover, the mean absolute flow angle was introduced to explain the mechanism of the effects of vortexes on blade load. The results can be used as a theoretical basis for the design of high-performance impellers.

Multistage pumps with blade-type guide vanes are widely used in offshore oil production, the petrochemical and coal-chemical industries, and nuclear power fields for its advantages of large flow rate, high pressure, and excellent operation stability. However, the internal flow of this kind of pump is complex; in particular, the hydraulic, flow, and pressure pulsation characteristics of the different stages are quite different, which has a great impact on the design and performance predictions of this kind of pump. Thus, in this paper, the hydraulic performance, unsteady flow characteristics, evolution of vortex structures and pressure pulsation characteristics in a 10 stage centrifugal pump are investigated numerically. The results show that inverse flow, jet-wake flow, and rotor-stator interaction flow are the key factors causing energy loss and efficiency decline at every stage and in the whole pump. The vortex evolution at the rotor–stator interaction regions is actually the process that the vortex structures fall off and impact on the pressure surface at the leading edge of the guide vane blade at a frequency that equals to the impeller blade passing frequency. Furthermore, under the actions of the guide vane with confluence cavity, the pressure pulsation within the final-stage guide vane contains low-frequency components with large bandwidths, which mainly results from the confluence flow disturbance at the outlet of the cylindrical guide passage.

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

This work presents an experimental study to investigate the influence of step volute tongue on aerodynamic performance and aeroacoustic behavior of a forward-curved fan. The noise characteristics are analyzed and controlled based on measured acoustic pressures for various stepped tongues; meanwhile, fan performance is detected and optimized. The design parameters of the stepped tongues are presented to provide significant physical insight into increasing the static pressure as well as the efficiency of static pressure and reducing the fan noise generation. The comparison of the test results indicates that the improved static pressure and its efficiency of the HLHL model have increased by 15.67 Pa and 3.57%, respectively, by comparing with those of the baseline model. At 740 m 3 /h, a great correlation between different arrays of stepped tongue and the noise generation was observed. The tonal noise level of the HLHL model is a better optimization scheme because it decreases as much as 1.2 dB for the noise generation of forward-curved fan. In particular, it is found that some stepped tongues of the volute tongue achieved the goal of reducing noise generation and improving the performance of fan by experimental measurement at the same time.

Detailed optical measurements for the flow inside rotating passages of a five-bladed centrifugal impeller were performed by particle image velocimetry (PIV). The flow in mid-plane perpendicular to the pump axis was measured at 1400 r/min rotation speed. Seven flow rates, namely, 1.2, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 Qd, were surveyed. The averaged PIV velocity maps and streamline were analyzed. Results show that when flow rate decreases to 0.8 Qd, the flow separation forms initially at the blade suction side in passage 1. With decreasing of flow rate, the flow separation appears in much more passage, the separation region enlarges, and the flow at the pressure side begins to form flow separation. All passages are gradually occupied by the vortices generated by flow separation, until the passages are finally blocked. The scale of vortex along the stream-wise direction at the suction side is larger than that at the pressure side, whereas the scale of vortex along the span-wise direction is smaller than that at the pressure side. With the decrease in flow rate, the scales of vortices at the suction and pressure sides increase, and the vortices at both sides move toward the inlet and outlet, respectively. Moreover, the effect of vortices on the tangential and radial components of the absolute velocity was analyzed.

This paper presents a large eddy simulation of a centrifugal pump impeller during a transient condition. The flow rate is sinusoidal and oscillates between 0.25Qd (Qd indicates design load) and 0.75Qd when the rotating speed is maintained. Research shows that in one period, the inlet flow rate will twice reach 0.5Qd, and among the impeller of one moment is a stall state, but the other is a non-stall state. In the process of flow development, the evolution of low-frequency pressure fluctuation shows an obviously sinusoidal form, whose frequency is insensitive to the monitoring position and equals to that of the flow rate. However, inside the impeller, the phase and amplitude in the stall passages lag behind more and are stronger than that in the non-stall passages. Meanwhile, the strongest region of the high-frequency pressure fluctuation appears in the stall passages at the transient rising stage. The second dominant frequency in stall passages is 2.5 times to that in non-stall passages. In addition, similar to the pressure fluctuation, the evolution of the low-frequency head shows a sinusoidal form, whose phase is lagging behind that by one-third of a period in the inlet flow rate.

The slurry transport pump is the key equipment of deep-ocean mining systems. The motion law of coarse particles in the pump is not clear enough. In this paper, a hydraulic model of a laboratory-scale two-stage slurry transport pump is constructed, and the motion characteristics of coarse particles in the pump are numerically studied by using the computational fluid dynamics–discrete element method (CFD-DEM) method. The performance curve of the pump is obtained by experimental measurement, and the reliability of the calculated results is verified. Due to the application of the amplification flow rate design method, the optimum efficiency point of the pump is shifted to the large flow rate condition. Differences in particle swarm within two stages are compared. The position distribution, velocity variation and trajectory of particles in the impeller and bowl diffuser are studied in detail. The velocity of particles leaving the impeller depends on whether they collide with the impeller blade. The motion of particles in the bowl diffuser is divided into three periods. Collision between particles and blades in the bowl diffuser not only leads to energy loss but also gradually transforms the circumferential velocity of particles into axial velocity in the second period. This work can provide a reference for the study of wear and blockage prevention of slurry transport pumps.

Flow separation is undesirable and lowers the efficiency of centrifugal impellers. In this study, the evolution characteristics of separated vortices in a centrifugal impeller are studied under the off-designed flow rate condition. Unsteady Reynolds-Averaged Navier–Stokes (URANS) with standard k-ε turbulent model is applied to simulate the alternating stall in the six-blade centrifugal impeller. We present and analyze the distributions of pressure gradient (either adverse or favorable) and skin friction coefficients on both sides of the blade for the stalled and unstalled passages to study the relationship between pressure gradient and separation of boundary layer flow. The evolution of skin friction coefficient is also presented at various axial cross sections. Numerical results reveal that, for the stalled passage, the increase in adverse pressure gradient on the pressure surface near the middle of the blade (S/S0 = 0.4) is much larger than that of the suction surface during a vortex formation cycle. The skin friction coefficient on the pressure surface also increases in magnitude sharply and the variation shows a peak-valley trend, while the coefficient on the suction surface increases slowly. Comparing the distribution of skin friction coefficient on the pressure surface of the same blade at different axial cross sections, it is found that the skin friction coefficient notably increases at S/S0 = 0.6 on the middle axial cross section (Z/b2 = 0.5). For the unstalled passage, both the pressure and suction surfaces produce favorable pressure gradients. The skin friction coefficient on the pressure surface shows an increasing trend around S/S0 = 0.5, and a large vortex can be seen at the exit of the impeller. The variation of skin friction coefficient on the suction surface is relatively mild; thus, the flow is relatively stable. It is clarified that the effect of adverse pressure gradient and wall shear stress jointly cause separation of the boundary layer; thus, the separated vortices are generated in the rotating impeller and deteriorate the performance of the impeller.

The parameters of blade trailing edge have an important influence on the performance of centrifugal pump and internal unstable flow. In this study, the influences of cutting angles of blade trailing edge on unstable pressure pulsation and unstable flow structure are investigated using a centrifugal pump under off-design conditions through large eddy simulation. Three typical blade trailing edges, namely, original trailing edge (OTE), 15° cutting angle of blade trailing edge (OBS15) and 30° cutting angle of blade trailing edge (OBS30), are analysed. Results show that the cutting angle of blade trailing edge has a certain effect on the performance of the centrifugal pump. Under part-load conditions, the OBS30 impeller evidently contributes to the reduction in pressure pulsation intensity. By contrast, the OBS15 impeller has opposite effect because of the increase in wake vortex intensity. The OBS30 impeller can effectively improve the unstable vortex structure caused by backflow at the centrifugal pump tongue using a new Ω method. Consequently, reduction in the unstable flow structure mainly contributes to the reduction in pressure pulsation used by the proper cutting angle of blade trailing edge.

Direct numerical simulations (DNS) of high–temperature supersonic turbulent channel flow of equilibrium air are conducted at constant dimensional wall temperature 1733.2 K. The Mach number based on the bulk velocity and the speed of sound at the isothermal wall is 3.0, and the Reynolds number based on the bulk density, bulk velocity, channel half–width, and viscosity at the isothermal wall is 4880. Bidirectional coupling (BC) and unidirectional influence (UI) conditions are investigated, conditions which take account, respectively, of the influence of turbulence on chemistry and the influence of chemistry on turbulence, and just the influence of turbulence on chemistry. The reliability of the DNS data for the UI condition is verified by comparison with the results of Coleman et al. [J. Fluid Mech. 305, 159–183 (1995)]. The results of present research show that the many turbulent statistics and instantaneous structures which hold for calorically perfect gas also hold for equilibrium air, even for the BC condition. The coupling condition has no significant influence on the van Driest transformed mean velocity and turbulent kinetic energy budget. The magnitudes of the mean and fluctuating specific heat and enthalpy for the BC condition are larger than those for the UI condition. An inverted trend is observed for the temperature and dissociation degree. Compared with the UI condition, the near–wall streaks for the BC condition are arranged in a more spanwise manner, owing mainly to the increase in anisotropy ratios. The large–scale structures become small, sharp, and chaotic for the BC condition.

Liquid annular seals are primarily used to control the leakage in high-speed turbomachinery, especially in nuclear and petrochemical pumps. In this paper, a theoretical analysis method for dynamic characteristics of liquid seals with herringbone grooves on the stator is proposed based on bulk-flow theory. Steady-state velocities and leakage rates within the upstream and downstream spiral parts and the middle plain part taking account of the pumping effects are figured out first with the inertia term of the fluid within the whole seal. Then, the dynamic characteristics of the whole seal are solved based on Childs’ finite-length solutions and verified by comparing with experimental hydraulic forces. Moreover, characteristic coefficients and instability parameters of the herringbone-grooved teeth-on-stator (TOS) seals and teeth-on-rotor (TOR) seals of the same size under different pressure differences are predicted and compared in detail. The influences of the lengths of constituent parts on the dynamic characteristics and instability parameters of the model seals are theoretically investigated. The results show that the stability of the TOS seal is much better than that of the TOR seal under most operating conditions. And the lengths of the middle plain part significantly affect the dynamic characteristics and the stability parameter.

Due to the characteristics of unsteady flow in the centrifugal pump at low flow rate is not revealed well, a simulation of the internal flow at different flow rates is carried out with renormalization group k–ε turbulence model and multiple reference frame. For analyzing the influence of flow rate, ratios of flow rate ( Q / Q d ) are set to 0.1, 0.3, 0.6, and 1.0 at this study. The hydraulic performance of the centrifugal pump obtained by numerical calculation has matched well with the corresponding experimental result. From the characteristics of the internal flow captured by the numerical simulation, it can be seen that backflow occurs in the inlet of impeller at low flow rate, which prevents fluid discharging into impeller passages and leads to vortical structures in suction region. With further decrease in flow rate, the strength of backflow has been intensified, and the number of vortex has significantly increased. A visualization experiment of the backflow evolution in suction pipe is carried out to validate the unsteady simulated results. Results show that the prerotation is an important factor for the deterioration of centrifugal pump performance.

For the stable and reliable operation of centrifugal pump, the transient flow must be studied and the separation region should be avoided. Three-dimensional, incompressible, steady, and transient flows in a centrifugal pump at specific speed within 74 were numerically studied using shear stress transport k - ω turbulence model, and an improved explicit algebraic Reynolds stress model–rotation-curvature turbulence model was proposed by considering the effects of rotation and curvature in the impeller passages in this work. Steady and transient computations were conducted to compare with the experiments. The comparison of pump hydraulic performance showed that the explicit algebraic Reynolds stress model–rotation-curvature turbulence model was better than the original model, especially between 0.6 Q BEP and 1.2 Q BEP ; the improved model could enhance the head prediction of pump by about 1%–7% than that with the original model. Then, the visualization of the vortex evolution was observed to validate the unsteady simulations. Good agreement was investigated between calculations and visualizations. It is indicated that the explicit algebraic Reynolds stress model–rotation-curvature model can successfully capture the separation flow.

Statistics of heat transfer in two-dimensional (2D) turbulent Rayleigh-Bénard (RB) convection for Pr=6,20,100 and 106 are investigated using the lattice Boltzmann method (LBM). Our results reveal that the large scale circulation is gradually broken up into small scale structures plumes with the increase of Pr, the large scale circulation disappears with increasing Pr, and a great deal of smaller thermal plumes vertically rise and fall from the bottom to top walls. It is further indicated that vertical motion of various plumes gradually plays main role with increasing Pr. In addition, our analysis also shows that the thermal dissipation is distributed mainly in the position of high temperature gradient, the thermal dissipation rate εθ already increasingly plays a dominant position in the thermal transport, εu can have no effect with increase of Pr. The kinematic viscosity dissipation rate and the thermal dissipation rate gradually decrease with increasing Pr. The energy spectrum significantly decreases with the increase of Pr. A scope of linear scaling arises in the second order velocity structure functions, the temperature structure function and mixed structure function(temperature-velocity). The value of linear scaling and the 2nd-order velocity decrease with increasing Pr, which is qualitatively consistent with the theoretical predictions.

Size-based particle filtration has become indispensable in numerous biomedical and environmental applications. In this study, bioinspired by the filter-feeding mechanism (lobe filtration) of manta rays, we designed a U-shaped biomimetic gill rake filter that combined lobe filtration and Dean flow to filter monodisperse suspensions, bi-disperse suspensions and yeast cells. Compared with other equipment using the inertial focusing technology, our equipment can perform high-throughput (up to 8 mL min-1) and high-efficiency filtration of particles (maximum filtration efficiencies of 96.08% and 97.14% for 10 and 15 µm monodisperse suspensions at the optimum flow rate of 6 mL min-1). The complex velocity field of the micro-fluidic flow within the filter is numerically simulated, and in combination with experiments, a threshold for the flow rate is identified. When the inlet flow rate exceeds the threshold value, the efficiency of particle filtration is increased rapidly. Afterwards, by analysing the filtration mechanism, we develop three novel filtration processes. The equilibrium positions of the particles and yeast cells in the main channel are close to the outer wall at high flow rate, which diminishes the likelihood of particles and yeast cells entering the side channel. This configuration establishes a self-cleaning mechanism, ensuring prolonged and efficient operation of the filter with high-throughput processing. Furthermore, the influence of the filter lobe angle and channel width on the filtration efficiency and outlet flow rate ratio are explored, and an optimisation plan is prepared. [ABSTRACT FROM AUTHOR]