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The paper aims to analyse the flow characteristics of a rotating, isothermally heated circular cylinder with a downstream vertical arc-shaped control plate. The study employs the stream function–vorticity ( ψ - ω ) formulation of 2-D Navier–Stokes equations, considering different distances of the control plate (0.5, 1, 2, 3) and rotational rates (0.5, 1, 2.07, 3.25) at Prandtl number 0.7 and Reynolds number 150. Higher-order compact (HOC) scheme discretizes the governing equations, and the resulting algebraic equations are solved using the bi-conjugate gradient stabilized approach. Including a control plate at a distance, d / R 0 = 0.5 , reduces the peak values of aerodynamic forces, such as drag and lift coefficients, and enhances the heat transfer rate from the upper half of the rotating cylinder compared to the case without a plate. The peak drag coefficient diminishes by approximately 12 % , while the peak lift coefficient experiences a notable reduction of around 91 % with α = 0.5 . The arc-shaped plate effectively delays vortex shedding and mitigates its impact. The rotational motion of the cylinder shifts the vortex shedding plane upward from the centreline of the flow domain. The wake structure varies based on the control plate position. Vortex size significantly reduces when the control plate is at d / R 0 = 3 with a high rotational rate. The impact of varied plate positions is substantial at greater rotational rates. Cylinder rotation and plate location can be manipulated to adjust drag, lift coefficients, and surface heat transfer. The maximum drag coefficient value, approximately 3, is achieved for d / R 0 = 2 and α = 3.25 . [ABSTRACT FROM AUTHOR]

Few studies have focused on abutments located on curved channels; previous studies have typically focused on straight channels. The present study experimentally examined the local scour that occurs around abutments of different lengths placed on inner and outer banks along a curved channel under clear-water scour flow conditions. The local scour around an abutment in a curved channel is a function of the upstream Froude number, flow intensity, the angle of the bend curvature and the ratios of abutment length to flow depth, abutment length to abutment width and abutment length to channel width. The maximum scour depth around the abutments placed on the outer bank was 1.45 times the scour depth on the inner bank. An empirical equation was developed containing all the dimensional parameters for equilibrium scour depth. The average percentage error of the proposed equation was 2%. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration of a regulating valve not only wastes the energy of the control system, but also causes serious damage to the valve trims. It is very important to suppress vortex-induced vibration of the flow field in a valve by optimizing the valve trim structure. In this paper, a multistage pressure-reducing valve is proposed, and the flow fields in the valve with the lightweight, flat bottom, circular truncated cone and cylinder valve plug are simulated using the ANSYS Workbench. To verify the reliability of the simulation, a flow test device for the valve is established and the flow rates at different openings are measured. The test result shows that the valve designed by simulation conforms to the specified flow characteristics. By monitoring the lift coefficient of the vortex cross flow, the amplitude and main frequency of vortex-induced vibration are evaluated. The effect of the valve plug shapes on the vortex-induced vibration characteristics is studied. The results show that the shape of the valve plug has an obvious effect on the amplitude of vortex-induced vibration. The conical valve plugs can play the role of flow guiding, the amplitude of vortex-induced vibration of the valve is smallest, it is about 1/4 of that of other valve plugs at medium and high openings. This work is of significance for suppressing the vortex-induced vibration of the multistage pressure-reducing valve. [ABSTRACT FROM AUTHOR]

In order to recover the waste heat of high temperature metallic granules to produce steam for hydrogen production, a waste heat recovery cooling cylinder with cooling water channel is innovatively developed. The simulation is carried out based on DEM and soft sphere model to study the flow characteristics of ternary size metallic granules. The model of cooling cylinder is established and verified by comparing to the experiment data. The change rule of bed shape in the waste heat recovery cooling cylinder is examined, and the inclination angle, rotational speed and filling rate are assessed to find their influence on the flow characteristics of ternary size metallic granules. The results indicated that, with the increase of inclination angle, the axial velocity increases by 482.76%, which means the reduce of residence time of granules. With the increase of rotational speed, the axial velocity has an increase of 161.54%, the sum velocity increases by 158.49%, leading to a decrease of residence time. As the filling rate increases from 1.5% to 15.5%, the contact number has an increase of 91.53%, which lead to the increase of heat transfer area. The residence time and heat transfer area will directly affect the waste heat recovery efficiency, so a proper arrangement of granule flow is significant for enhancing the heat transfer efficiency. • The combination of waste heat recovery and hydrogen production was put forward. • A new cooling cylinder with cooling water channel was put forward. • The change rule of bed shape in the waste heat recovery cooling cylinder was examined. • The flow characteristics of ternary size metallic granules was revealed. [ABSTRACT FROM AUTHOR]

A new circular-arc epitrochoid rotor profile is proposed and initially applied to a hydrogen circulation pump for hydrogen fuel cells. This paper presents a mathematical model and generation method for the "AVEC" epitrochoid rotor profile, along with a geometric evolution analysis of this profile. The study systematically examines the evolution process of the rotor tooth shape relative to the angle between two epitrochoids, and the root-to-tip radius ratio of the teeth. The variation in the area utilization rate with geometric parameters has also been analyzed. Using CFD methods, the internal transient flow field characteristics and pump performance of the proposed new rotary lobe pump are comprehensively simulated. Compared to traditional external cycloidal rotary pump, the outlet flow rate of the new design has increased by 14.28%. Additionally, the performance of the new rotary lobe pump has been significantly improved, with flow pulsation controlled within 10.27% and pressure pulsation controlled within 1.14%, showcasing the superiority of the new rotor profile. Beyond hydrogen circulation pumps, this rotor profile can also be applied to compressors, vacuum pumps, roots pumps, and multiphase pumps. [Display omitted] • A new rotor profile is designed. The geometric evolution of the new profile is demonstrated, and the relationship between design parameters and area utilization rate is quantified. • The corresponding flow characteristics of the new design are comparatively analyzed by three-dimensional CFD modelling. • The new rotor profile achieves better flow characteristics than traditional cycloid profile. • The new rotor profile can be applied to hydrogen circulation pumps, as well as rotary lobe pumps, compressors and vacuum pumps. [ABSTRACT FROM AUTHOR]

The internal flow field of the hydrogen circulation pump becomes more complex and flow process becomes more intense during the stopping process, strong vibration is generated to the pump and the working life of the pump is shortened. Therefore, the pressure pulsation at the inlet and outlet section, the radial force characteristics of the active rotor and the transient flow mechanism of the internal flow under different stopping modes are studied in this paper. The results show that the intake pressure and exhaust flow change greatly in exponential stopping mode, while the pressure pulsation amplitude decreases with the increase of stopping time in linear stopping mode. In addition, the radial force value of the active rotor in the exponential stopping mode is significantly smaller than that in the linear stopping mode, and the direction of the radial force F x and F y point to the negative direction of their respective axes. In this paper, the dynamic mesh technology is used to design the corresponding rotating speed UDF according to different stopping functions, and then the transient simulation of the hydrogen circulation pump under different stopping modes is completed. Finally, the change law of pressure and flow pulsation, radial force characteristics and internal flow field under different stopping modes are analyzed. [Display omitted] • Effects of different stopping modes on flow characteristics are studied. • Pressure variation under different stopping modes are discussed. • Radial force of the rotor under different stopping modes are analyzed. • Working process is researched from the pressure and velocity distribution. [ABSTRACT FROM AUTHOR]

Liquid hydrogen plays a critical role in large-scale hydrogen storage and long-distance transport. The primary cost associated with liquid hydrogen supply is attributed to the liquefaction consumption. The hydrogen turbo-expander, a pivotal component in industrial hydrogen liquefaction plants, is instrumental in determining liquefaction costs. Improving the efficiency of the expander offers a significant opportunity for cost reduction. This paper commences by validating the loss model employed to assess the hydrogen turbo-expander using numerical simulation results. Subsequently, a regional division model is introduced for the expander impeller passage to identify the locations of various losses. Under diverse operational conditions, the boundaries of regions are determined through a comparison between the loss model and numerical simulation. Finally, an examination of losses in the hydrogen turbo-expander is conducted using Computational Fluid Dynamics (CFD) results under varying operating conditions, yielding the following insights. With an increase in the expansion ratio of the hydrogen turbo-expander, the isentropic efficiency initially rises and then declines. Among the various losses observed under variable working conditions, incidence loss emerges as the most critical factor. When the expansion ratio is small, a negative attack angle forms at the impeller inlet, causing chaotic flow within the channel and an increase in passage loss. • Correlations in loss model are validated for hydrogen turbo-expanders. • The proposed regional division model enables a quantitative loss analysis. • Efficiency decays more severely with the expansion ratio lower than design value. • Incidence loss is the primary driver for efficiency decline far from design condition. [ABSTRACT FROM AUTHOR]

To address the limited consideration of coarse particles in existing studies on gravity flow of caved ore and rock, this study conducted physical and numerical draw tests. The purpose was to investigate the flow characteristics of caved ore and rock under the influence of different numbers, relative positions, and spacing of coarse particles. The analysis focused on the perspective of interparticle interaction, considering the evolution laws of unbalanced force, void fraction, and force chains. The main research findings are as follows: (1) As the number of coarse particles increases from one to four, the size ratio of coarse and fine particles, which has similar effects on the shape of IMZ, decreases from 6.0 to 4.0. (2) When two coarse particles are arranged vertically and in contact, there is no significant separation between them, and the agglomeration effect of the force chain is the most prominent. [ABSTRACT FROM AUTHOR]

The consumption of aquaculture products and, in turn, the importance of the aquaculture industry are increasing with the depletion of global fishery resources. In the flow-through aquaculture systems used in Korea, olive flounders are overcrowded near the central outlet, causing stress, and the sharp central outlet hole injures the olive flounders. Therefore, in this study, we propose a central outlet cap that can prevent overcrowding and injuries in olive flounders near the central outlet in a flow-through aquaculture system. An L27(35) orthogonal array was constructed using five central outlet cap design variables, and computational fluid dynamics (CFD) analysis was performed for each experimental point. The pressure drop between the tank inlet and the central outlet was evaluated, and the experimental point with the highest pressure drop was identified. In addition, the internal fluid velocity of the experimental point with the highest pressure drop value was confirmed to be improved compared to the initial flow-through aquaculture system. The central outlet cap designed in this study is expected to be economically beneficial to aquaculture by reducing the overcrowding of olive flounder and preventing injury to olive flounder while improving the internal fluid velocity. [ABSTRACT FROM AUTHOR]

The flow characteristics around the frontal face of a square cylinder with a frontal jet injection were experimentally studied in a closed-loop wind tunnel using the PIV technique. Four characteristic flow modes were identified based on the injection ratio: swinging jet, deflected oscillating jet, deflection jet, and penetrating jet. At low injection ratio, the flow mode denoted as the swinging jet is characterised by two recirculation regions and a four-way saddle point. At moderate injection ratio, the flow mode termed deflected oscillating jet is characterised by a recirculation region and a counterclockwise rotating vortex within the recirculation region. At moderately high injection ratio, the flow mode is denoted as deflection jet, where a clockwise rotating vortex appears in the flow field. At high injection ratio, the flow mode is termed as penetrating jet, with no vortex formation in the flow field. The strength of the turbulence intensities increases considerably with high injection ratios. The time histories of instantaneous velocity for non-injection case, swinging jet, and deflected oscillating jet modes show periodic oscillations, whereas those of deflection jet and penetrating jet modes do not show periodic oscillations. The study presents and discusses the time-averaged velocity vectors, and streamlines, vorticity contours, velocity properties, velocity time histories, and power spectral density function under different flow modes. [ABSTRACT FROM AUTHOR]

AbstractCharacterization of pore structures and flow simulation are essential to spatial migration of coalbed methane. In this paper, coal samples from Xinjing and Xinzhuang coal mines are collected and a comprehensive characterization method by using computed tomography (CT) technique and experiments of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) is proposed. Pore structure parameters are finely characterized and analyzed. Moreover, the flow process for coal samples is visualized and flow characteristics are analyzed. The result shows that pore structures of coal samples are strongly heterogeneous and are dominated by micropores, and filled with kaolinite, calcium monofluorophosphate, pyrite, etc. The flow velocity increases obviously in micropores and narrow throats. The flow is greatly affected by the pore structure. This study is of practical significance for the coalbed methane recoverability evaluation and exploration. [ABSTRACT FROM AUTHOR]

Ellipticity has a significant impact on the flow and heat transfer performance of microchannel heat exchangers (MHEs) with elliptical concave cavities. In this study, five types of MHEs with different elliptical concave cavities (ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2) were designed. The influence of ellipticity on the flow and heat transfer performance of MHEs was numerically investigated using ANSYS Fluent 21.0 R1. Moreover, MHEs with corresponding elliptical concave cavities structures were processed and manufactured, and then an experimental platform was designed and built for experimental verification. The results showed that the fluid velocity distribution in MHEs with elliptical concave cavities was symmetrical, and the formation of secondary flow in the elliptical concave cavities led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel, which is conducive to mass and heat transfer in the MHEs with elliptical concave cavities. The inlet and outlet pressure drop of MHEs with elliptical concave cavities increased as the inlet flow rate increased. At the same inlet flow rate, the inlet and outlet pressure drop of the MHE with elliptical concave cavities first increased and then decreased with increasing ellipticity. At an ellipticity of 1.0, the inlet and outlet of MHE exhibited the lowest pressure drop indicating that the MHE with an ellipticity of 1.0 featured the highest pressure drop performance. The cold‐water outlet temperature of the MHEs with elliptical concave cavities first decreased and then increased as the inlet flow rate increased. At the same inlet flow rate, the cold‐water outlet temperature of the MHEs with elliptical concave cavities first increased and then decreased with increasing ellipticity, while the hot‐water outlet temperature of the MHEs first decreased and then increased with increasing flow rate. This indicated that the MHE with an ellipticity of 1.0 exhibited excellent heat transfer performance. [ABSTRACT FROM AUTHOR]

After transporting oil with a mobile pipeline, it is necessary to empty the oil within the pipeline. A common method is to inject water into the inlet to push the oil out. However, due to the effects of buoyancy and surface tension, the oil within the pipeline tends to accumulate at the elevated section, forming a stagnant oil layer, which will limit the evacuation efficiency. Based on the multiphase flow theory, a hydrodynamic model of oil–water flow was utilized to describe the pressure distribution and the thickness of the stagnant oil layer within the pipeline. A numerical model for oil-carrying water flow in a downward-inclined mobile pipeline was established, and the model was solved under given initial and boundary conditions to obtain the characteristics of the oil-carrying water flow within the pipeline. The calculation results indicate that the initial water phase velocity has a promoting effect on the oil-carrying capacity of water flow. The pipe diameter is negatively correlated with the capacity. The initial thickness of the oil is not directly related to the capacity but can increase the oil phase front velocity, which can enable the oil phase to be emptied more quickly. When the initial water phase velocity is lower than the critical water phase velocity, an increase in the inclination angle will weaken the capacity of water flow to carry oil. Conversely, when the velocity of the initial water phase is higher than the critical water phase velocity, an increase in the inclination angle will enhance the capacity. [ABSTRACT FROM AUTHOR]

The pressure ratio of a compressor increases when the engine performance is improved, which leads to a higher air velocity in the combustion chamber. This aggravates the pressure loss in a conventional diffuser, which is proportional to the square of the inlet velocity. It is, therefore, an urgent need for a new diffuser technology. Regardless of whether high-temperature, or low-pollution, combustion chambers are being used, the significant difference when compared with other chambers is the notable increase in the combustion air and its entry through the dome of the flame tube. However, the increased amount of air in the dome causes a mismatch between the diffuser outlet and the dome intake of the flame tube. Therefore, to solve the problem of an excessive total pressure loss and a mismatch of the intake air in the combustor, a novel air-bleeding aerodynamic diffuser has here been proposed. The effects of various parameters (including the number of air-bleed holes, the position of the first row of holes, and the position of the second row of holes) and their interactions on the performance of this diffuser have then been investigated by using the experimental design presented by Taguchi. The maximum static pressure recovery was achieved by using a genetic algorithm combined with the CFD method. Among the three parameters, the results revealed that the position of the first row of holes had the largest impact on the performance of the diffuser. Also, the optimal values of the three parameters varied for the inlet Mach numbers 0.10, 0.15, and 0.20. The relative difference between the predicted values and the values obtained by the numerical simulations were all below 3%, which showed the reliability of the predictions. As compared with the reference case, the optimized results for the three working conditions increased by 19.16%, 21.38%, and 40.62%, respectively. [ABSTRACT FROM AUTHOR]

Currently, the primary method for controlling red tides in the ocean involves spraying water solutions with special chemicals as solutes. High-pressure spraying results in the formation of typical jet structures. In this study, numerical simulation methods are employed to investigate the velocity variations, turbulent characteristics, and gas content distribution of jet flow fields under different initial jet flow pressures, cone angles, and nozzle diameters. Based on practical application scenarios, cluster analysis is used to explore the similarities and differences in jet equivalent diameters under different parameter conditions. The research findings indicate the following. (1) The difference of jet velocity distribution at the far field exit will be enlarged with the increase in the nozzle cone angle. When the nozzle cone angle is 4 mm, the velocity uniformity at the outlet is the best. (2) The TKE of the flow field has no consistent change law along the central axis. At the jet exit, the TKE shows an obvious multi-peak structure. (3) The gas content demonstrates a typical "double-valley" feature at the jet outlet cross-section. Increasing the initial pressure leads to a decrease in the gas content within the jet due to reduced entrainment, while the entrainment range remains largely constant. (4) Cluster analysis reveals that the similarity of jet flow width when it reaches the water surface is minimal compared to other operating conditions when the initial pressure is 0.36 MPa, the cone angle is 115°, and the nozzle diameter is 2 mm. All conditions can be categorized into two or three groups to ensure jet effectiveness. The study results provide scientific guidance for selecting spray devices for controlling red tides in the ocean. [ABSTRACT FROM AUTHOR]

Based on one-dimensional water hammer theory and combined with an engineering example, the selection of the flow characteristics of the end control valve of gravity flow system with wide-range flow variation is numerically studied from three aspects: the influence of flow characteristics of control valve on its steady-state opening-degree, the determination of the most unfavorable flow conditions of valveclosing water hammer, and the influence of flow characteristics of contrive valve on valve-closing water hammer. And the flow characteristics of linear type, parabola type and equal percentage type are compared. The results show that: 1 The equal percentage flow characteristic is more conducive to the stable operation of the control valve under the low flow condition. Under this condition, the steady-state opening-degree of the equal percentage type control valve is larger, which can avoid cavitation and vibration caused by too small opening. 2 The most unfavorable flow condition of the valve-closing water hammer should consider the minimum initial flow condition, under which the water hammer pressure of the input point of the control valve is largest because of the largest initial pressure and the shortest closing time. 3 The equal percentage flow characteristic is more conducive to reducing the control valve-closing water hammer pressure. Under the same initial flow rate and valve closing rate, the control valve with equal percentage type flow characteristics has a larger initial opening-degree, a longer actual closing time, and a smaller change gradient of flow coefficient in the small opening-degree range, so the extreme value of the valve-closing water hammer pressure is smaller, which is more conducive to pipeline safety. [ABSTRACT FROM AUTHOR]

In this paper, the flow characteristics of a continuous-type liquid–liquid pintle injector are described, focusing on the differential impact of a non-uniform center-flow distribution on single- and bi-injection methodologies as well as the cavitation effect on the spray angle. Using cold-flow experiments, jet-type flows of the center propellant caused by a non-uniform flow distribution were observed during a single injection. This resulted in an augmented pressure drop, as opposed to the flow characteristics of uniform single-film injection. By contrast, bi-injection modalities exhibited a substantial reduction in the pressure drop of the center propellant, underscoring a more equitable flow distribution. Moreover, the occurrence of cavitation in the center propellant was found to markedly affect the spray angle. By considering the injection exit area reduction caused by cavitation, the spray-angle prediction accuracy increased. The findings of this study are expected to reveal the interplay between flow distribution and pressure drop as well as that between cavitation and the spray angle in pintle injectors. Through this understanding, this study provides crucial considerations for the development of more efficient propulsion systems. [ABSTRACT FROM AUTHOR]

• The flow characteristic parameters of the regenerator were studied experimentally. • A method for improving permeability and inertial resistance accuracy was presented. • The effect of temperature and pressure on flow characteristic parameters was studied. • The harmonic mean of density and viscosity was used to simplify gradient data. • The flow characteristic correlations for wire mesh and powder filler were derived. A method was proposed to improve the accuracy of permeability and inertial resistance coefficient measurements for the flow characteristics of a regenerator, considering density and dynamic viscosity. Given the thickness of the porous medium at only 2 mm, and to simplify gradient data processing, the harmonic mean of the fluid density and dynamic viscosity was utilized. Various mesh counts of wire mesh and sintered powder filler were tested. The results showed that permeability decreased for both types of fillers as mesh count increased. Due to the high randomness inherent in the sintered powder, repeated tests were conducted, with errors being within 17 %. The inertial resistance coefficient fluctuated between 300 and 600 mesh counts, with a significant increase at 700 mesh. In contrast, the inertial resistance coefficient of the wire mesh increased consistently with the mesh count. The significant inertial resistance within the sintered powder was due to its irregularity, and a high positive correlation was observed between the regularity of the filler microstructure and the pressure drop across the regenerator. The flow characteristic correlations for two types of fillers were derived, applicable within the Reynolds number ranges of 6.54 to 99.17 for the wire mesh filler and 0.86 to 15.91 for the powder filler, with both exhibiting a goodness of fit exceeding 95 % being achieved. [ABSTRACT FROM AUTHOR]

The fluid oscillator, relying on the Coanda effect, is a flow control device that can alter the direction or velocity of a jet both spatially and temporally. The fuel injection device based on a fluid oscillator significantly enhances atomization and spatial dispersion performance compared to a direct-spray nozzle. However, when used in high heat load afterburners with aviation kerosene as the working medium, oxidative coking issues may arise. To address this, it is recommended to use premixed rich fuel-vapor as the working fluid in order to reduce the residence time of fuel in the oscillator. This study investigates the flow rate and frequency variation of ideal air (simulated gas phase fuel) as it moves through a double feedback channel fluid oscillator with varying thicknesses and outlet throat widths. Experimental and numerical simulation methods are employed. And the influence mechanism is analyzed through an examination of the flow field structure within the cavity of the fluid oscillator. The results indicate that increasing the thickness of the fluid oscillator leads to a higher outlet tangential velocity and deflection angle, while simultaneously decreasing the oscillation frequency. Conversely, widening the fluid oscillator throat results in a decrease in tangential velocity, deflection angle, and oscillation frequency. The performance of the fluid oscillator reaches a critical threshold when the outlet throat is square. As thickness increases, the rate of decrease in oscillation frequency and the rate of increase in tangential velocity both slow down. Furthermore, the maximum deflection angle of the airflow at the oscillator outlet reaches a critical value at a thickness of 3.375 mm, beyond which the trend of increasing deflection angle also slows. When the thickness of the oscillator is less than 3.375 mm, mass flow is the predominant driving factor for airflow deflection in the mixing chamber. In contrast, when the thickness is greater than or equal to 3.375 mm, pressure becomes the primary driving factor for this deflection. [ABSTRACT FROM AUTHOR]

Enhanced pipe surfaces offer greater heat transfer enhancement due to increased turbulence levels, leading to improved heat exchange performance. This study combines numerical simulations and experimental work to identify the best geometric design of enhanced tubes for thermal–hydraulic performance, flow structure, and pressure drop, and the simulations are validated with experimental data. Water is a working fluid with Reynolds numbers ranging from 4000 to 15,000, q = 25,500 W/m2, and an inlet temperature of 298 K with constant fluid property, steady state, and no‐slip condition. The three‐dimensional steady incompressible turbulent flow in the concavity dimpled shape‐enhanced tubes is numerically studied. This research found that pipes with a concave shape transfer heat most effectively. The overall heat transfer is significantly influenced by the shape of the dimples, their arrangement in rings, the size of these rings, and the number of rings. However, the number of cylindrical dimples does not seem to impact heat transfer much. The increase in heat transfer performance was by 9.8%–61% for dimple rings = 2ring performed best compared with a smooth pipe and by 8.21%–38.49% at the effect of ring numbers as grouping, also the dimple ring diameters by 5%–38% and by 7%–39% at dimple numbers. The performance evaluation factor (PEF) assesses overall performance by considering both the pressure drop penalty and improved heat transfer. The optimal configuration achieving the highest performance (PEF = 1.295) at a flow rate (Re) of 4000 involves a single dimple ring with a 2‐mm diameter, spaced 10‐mm apart, containing four dimples. Furthermore, discussing the different parameters of thermal and hydraulic performances to obtain the best thermal performance, and increasing the number and size of dimples gives a better guide for engineering to obtain better thermohydraulic performances for heat exchangers. [ABSTRACT FROM AUTHOR]

A curved channel is a common flow form in nature, often hosting aquatic vegetation along rivers. The stem thickness of this vegetation affects its resistance to flow and subsequently influences flow characteristics. To explore the impact of stem thickness on river flow in curved channels, we developed a Reynolds stress model based on real river flow conditions and vegetation data. The flow characteristics were analyzed in terms of flow velocity, Reynolds stress and turbulence intensity by varying the stem thickness of the vegetation in the vegetated area. The results of the study reveal that: (1) Water velocity in the vegetated area is significantly reduced compared to the non-vegetated area, with a greater reduction observed for thicker stems. Increasing the vegetation diameter by 3 mm resulted in a velocity decrease of 2.31–26.55%. (2) Thicker vegetation stems lead to more intense energy exchange in water flow. A 3 mm increase in vegetation diameter increased Reynolds stress by 91.81–139.70%. (3) Turbulent kinetic energy in the vegetated area is significantly higher than in the non-vegetated area, with greater turbulence intensity observed for thicker vegetation stems. Increasing the vegetation diameter by 3 mm resulted in a turbulent kinetic energy increase of 115.19–218.55%. HIGHLIGHTS Less research has been done on the effect of vegetation stem thickness on water flow in curved channels.; The feasibility of studying the flow characteristics of curved river channels through simulation is verified.; Analysis of sedimentation by comparing concave and convex shores.; The results can guide the construction of river channels and the design of aquatic systems.; It can provide relevant data for the subsequent research on the influence of vegetation stem coarseness on water flow characteristics.;

Concerning dual-carbon applications, establishing a new energy-dominated power system to achieve carbon peaking and carbon neutrality objectives is imperative. Pumped storage units excel in this context, owing to their unique advantages. During the load-shedding process of the pump turbine, the intricate flow patterns and cavitation phenomena substantially influence the flow field. This study introduces a cavitation model to perform numerical simulations of load rejection processes in pumped storage power plants, aiming to thoroughly investigate the impact of cavitation phenomena on the units. The results indicate that as the rotational speed increases, the dynamic and static interference within the no-blade region becomes notable, resulting in pressure pulsations within the guide vane region and exacerbating structural deformation and fatigue failures. Moreover, deviations from the designated operational point disrupt the symmetry of the flow field, leading to irregular changes in radial forces. Accounting for the mass disturbance and changes in wave velocity attributable to a cavitation phase transition, pressure fluctuation amplitude increases within the draft tube, consequently engendering complex flow phenomena. These findings offer indispensable guidance for the optimal design and safe operation of pump turbines within new power systems.

The pressure ratio of a compressor increases when the engine performance is improved, which leads to a higher air velocity in the combustion chamber. This aggravates the pressure loss in a conventional diffuser, which is proportional to the square of the inlet velocity. It is, therefore, an urgent need for a new diffuser technology. Regardless of whether high-temperature, or low-pollution, combustion chambers are being used, the significant difference when compared with other chambers is the notable increase in the combustion air and its entry through the dome of the flame tube. However, the increased amount of air in the dome causes a mismatch between the diffuser outlet and the dome intake of the flame tube. Therefore, to solve the problem of an excessive total pressure loss and a mismatch of the intake air in the combustor, a novel air-bleeding aerodynamic diffuser has here been proposed. The effects of various parameters (including the number of air-bleed holes, the position of the first row of holes, and the position of the second row of holes) and their interactions on the performance of this diffuser have then been investigated by using the experimental design presented by Taguchi. The maximum static pressure recovery was achieved by using a genetic algorithm combined with the CFD method. Among the three parameters, the results revealed that the position of the first row of holes had the largest impact on the performance of the diffuser. Also, the optimal values of the three parameters varied for the inlet Mach numbers 0.10, 0.15, and 0.20. The relative difference between the predicted values and the values obtained by the numerical simulations were all below 3%, which showed the reliability of the predictions. As compared with the reference case, the optimized results for the three working conditions increased by 19.16%, 21.38%, and 40.62%, respectively.

This study aimed to investigate the critical suction velocity required for lifting sediment off the bed under hydrosuction. Flow characteristics below the suction pipe under unbound and bound conditions were studied experimentally and numerically, and the effects of various parameters on the critical suction velocity, such as suction pipe diameter, suction discharge, suction inlet height, and sediment size, were investigated. The results showed all the parameters significantly affect the critical suction velocity, with suction inlet height being the most influential. Unbound and bound conditions yielded divergent flow characteristics beneath the suction pipe, revealing distinct flow patterns. Interdependency among the parameters affecting critical suction velocity have been studied statistically, and empirical relations are developed to compute the critical suction velocity, its resultant centerline velocity, and the associated flow profile. A proposed relation for critical suction velocity showcased a ±10% error margin, while equations computed resultant centerline velocities and flow profiles with ±15% accuracy, representing satisfactory agreement. These findings can also be helpful in designing efficient suction systems in various sediment-laden water environments. Practical Applications: The current study on hydrosuction sediment removal presents practical solutions for addressing the persistent challenge of reservoir sedimentation. Hydrosuction is an efficient and cost-effective method of sediment removal with minimum disturbance to the connecting structures and surrounding ecosystem and aquatic life, ensuring sustainable reservoir management. The study focuses on providing detailed insight into the behavior of the flow below the suction pipe under varying conditions, which is responsible for sediment movement during hydrosuction. The study also investigates the minimum suction velocity required to lift the sediment off the bed surface. Applicability of hydrosuction is not limited to the desilting of a reservoir; it also holds potential for various applications in multiple fields, such as river and canal restoration, dredging of navigational channels, irrigation canal cleaning, dewatering and slurry removal, contaminant cleanup, trench excavation, flood control, and wastewater management. [ABSTRACT FROM AUTHOR]

Concerning dual-carbon applications, establishing a new energy-dominated power system to achieve carbon peaking and carbon neutrality objectives is imperative. Pumped storage units excel in this context, owing to their unique advantages. During the load-shedding process of the pump turbine, the intricate flow patterns and cavitation phenomena substantially influence the flow field. This study introduces a cavitation model to perform numerical simulations of load rejection processes in pumped storage power plants, aiming to thoroughly investigate the impact of cavitation phenomena on the units. The results indicate that as the rotational speed increases, the dynamic and static interference within the no-blade region becomes notable, resulting in pressure pulsations within the guide vane region and exacerbating structural deformation and fatigue failures. Moreover, deviations from the designated operational point disrupt the symmetry of the flow field, leading to irregular changes in radial forces. Accounting for the mass disturbance and changes in wave velocity attributable to a cavitation phase transition, pressure fluctuation amplitude increases within the draft tube, consequently engendering complex flow phenomena. These findings offer indispensable guidance for the optimal design and safe operation of pump turbines within new power systems. [ABSTRACT FROM AUTHOR]

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The characteristics of flow field and the brine distribution will greatly affect the cavern expansion and final cavern shape in the process of constructing salt cavern gas storage, while the flow characteristics and concentration distribution can’t be monitored by technical means. To study flow characteristics, brine concentration distribution and their impact on cavern shape expansion during the multi-step salt cavern construction, numerical simulation calculations were conducted based on the established multi-physics coupled flow model, and the results were compared with field data of two storage wells in Jintan. The simulation results were consistent with the field data, which verified the accuracy of the model. Based on the simulation results and data, the flow field characteristics and brine concentration distribution in each stage of solution mining were analyzed, and how flow characteristics and brine concentration distribution affect the cavern expansion was analyzed. The results show that there will form a vortex in cavern during positive circulation, which mainly cause erosion and inhibits dissolution during solution mining. There will form two vortices in cavern during reverse circulation. The one in lower part promoting the discharge of brine and the another one in upper part promoting dissolution Forced convection will cause vortex, and the strength of vortex will gradually decrease with the expansion of the cavern. The vortex makes the fluid flow in the cavern, and promotes the process of convection diffusion, thus affecting the distribution of brine concentration, and ultimately affecting the expansion of the cavern. The shape expansion of the cavern can be controlled by adjusting the positive and negative circulation mode, the position of the tube, the position of the oil cushion, and the injection rate. In the early stages of cavern construction, erosion plays a dominant role, which resulting in high cavern construction efficiency, resulting in a slower cavity making rate because of the small surface area of the cavern. The cavern mainly extends towards the middle and lower parts. In the later stages, as the cavity expands, the main effect is dissolution, and the rate of cavern construction is high. The cavity mainly expands towards the middle and upper parts. The research results and rules provide a certain theoretical basis for cavern construction design in field, and have guiding significance for improving construction efficiency and optimizing parameters. [ABSTRACT FROM AUTHOR]

The rapid development of new energy vehicles demands significant improvements in connector structures and performance standards. Wire harness connectors, crucial for linking various electrical components, face challenges due to their small size and thin-walled structure, which can lead to dimensional shrinkage and warping during injection molding. To address these issues, this study optimizes the injection molding process by fine-tuning parameters such as melt temperature, mold temperature, injection time, holding pressure/time, and cooling time. By integrating the Taguchi method with grey relational analysis, the study enhances the molding process for thin-walled composite connectors. This combined approach provides a comprehensive framework for optimizing multiple quality objectives and improving the overall performance of injection-molded composite components. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fishways act as ecological corridors, enabling migratory fish species to surmount barriers such as weirs or dams, which are crucial for the restoration of river ecosystems. The island-type fishway is a novel design that utilizes a combination of island structures and valvular configurations to dissipate the kinetic energy of water flow, decelerate the water velocity, and thus reduce the challenge faced by fish attempting to ascend the watercourse. The impact of valvular configurations on the hydrodynamic characteristics within an island-type fishway was explored. The results showed that the main high-velocity flow exhibits a nearly "S"-shaped characteristic, while a low-velocity region develops downstream of the valvular. The valvular configuration has a significant effect on the internal flow dynamics of the island-type fishway. Specifically, the smaller the valvular arc angle, the broader the high-velocity main flow becomes, and the smaller the area of the low-velocity region. When the valvular arc angle is set at 180°, the area dominated by low flow velocities maintains a coverage of over 60%. As the valvular arc angle decreases, turbulent kinetic energy rises, leading to an approximate 70% increase in the maximum turbulent kinetic energy across different water layers relative to the model with the initial angle setting. Within the range of valvular arc angles studied, an island-type fishway with a 180° valvular arc angle is most conducive to supporting the upstream migration of fish. This study can provide a reference for the further development of island-type fishways. [ABSTRACT FROM AUTHOR]

The long-term effects of the centrifugal force of water flow in a curved river channel result in the scouring of the concave bank and the silting of the convex bank. This phenomenon significantly impacts the stability of bank slopes and the surrounding ecological environment. A common hydraulic structure, the spur dike, is extensively employed in river training and bank protection. Focusing on a 180° bend flume as the research subject, this study examines the effects of spur dike placement on the concave bank side of the bend. To this end, a second-order accurate computational format in computational fluid dynamics (CFD) and the RNG k-ε turbulence model were employed. Specifically, the influence mechanism of the pick angle and the river-width-narrowing rate on the flow dynamics and eddy structures within the bend were investigated. The results indicated that both the river-width-narrowing rate and pick angle significantly influence the flow structure of the bend, with the pick angle being the more dominant factor. The vortex scale generated by a positive pick angle of the spur dike is the largest, while upward and downward pick angles produce smaller vortex scales. Both upward and positive pick angles have larger areas of influence, and the maximum value of turbulent kinetic energy occurs at the back of the secondary spur dike. In contrast, the downward pick angle has a smaller area of influence for turbulent kinetic energy, resulting in a smaller vortex at the back of the spur dike and leading to smoother water flow overall. In river-training and bank-protection projects, the selection of the spur dike angle is crucial for controlling scour risk. The findings provide valuable insights for engineering design and construction activities. [ABSTRACT FROM AUTHOR]

The blade fracture of horizontal centrifugal pump will not only affect the hydraulic performance of the pump, but also affect the safety and stability of the whole unit. In this paper, for horizontal centrifugal pumps, five single-blade fracture schemes are designed and numerical simulations are carried out under different operating conditions. The results show that with the increase of fracture size, the influence on the hydraulic characteristics of the pump shows a decreasing trend, and it will also affect the turbulent kinetic energy distribution near the impeller inlet, so that the internal flow becomes complex and the flow loss increases. The radial force on the impeller changes periodically, and its magnitude shows a nonlinear decreasing change with the increase of the fracture size. The pressure pulsation analysis of several monitoring points in the worm shell shows that as the fracture size increases, the amplitude of the lobe frequency slowly rises, and the shaft frequency, which is second only to the lobe frequency, becomes higher and higher and begins to dominate. A study of the rotor system shows that the maximum deformation of the impeller occurs at the edge of the impeller cover and the maximum equivalent stress occurs at the blade exit; blade fracture causes a significant reduction in the latter third-order intrinsic frequency. [ABSTRACT FROM AUTHOR]

The formation conditions of maximum- and minimum-wave jumps were experimentally investigated. A total of 110 wave-type jump experiments were carried out for several discharges, supercritical upstream and subcritical downstream water depths and drop heights. The experimental results revealed that the influential parameters on wave-type jumps are the upstream Froude number and the relative drop height. As the classical hydraulic jump equation is not sufficient to define conjugate depths of wave-type flow, empirical equations were developed for defining the conjugate depths of maximum-wave jumps and minimum-wave jumps (for which insufficient experimental data are available in the literature). The agreement between calculated and measured conjugate depths was good. It was also found that the value of the lower limit for the upstream Froude number is not constant for the formation of a maximum-wave jump – it depends on the relative drop height. Furthermore, the experimental results showed that the energy-dissipation ratios of maximum- and minimum-wave jumps are equal to or larger than those of classical hydraulic jumps. For this reason, wave-type jumps may be preferred at stilling basins with drops along with A-jumps. [ABSTRACT FROM AUTHOR]

Vortex has attracted attention because it is the main factor affecting the flow characteristics around offshore structures. This paper researches the flow field variations around a semi-submerged rectangular cylinder (SRC) under four aspect ratios, thereby revealing the bottom vortex effects on the flow field at Reynolds number = 36,300. According to the particle image velocimetry (PIV) data, the renormalization group (RNG) k-ε model is selected as an applicable turbulence model for studying SRC flow characteristics. From the results, the bottom vortex generation and streamwise velocity are inseparable. As the draft increases, the increased range of the bottom vortex would directly interfere with the flow characteristic around the SRC. Since the wake vortex forms a reattachment state when the SRC pierces the free surface, its flow field could be disturbed by the bottom vortex. Furthermore, the bottom vortex also affects the extreme point position of the boundary layer characteristic at the SRC bottom. [ABSTRACT FROM AUTHOR]

In order to study the flow characteristics of an integrated natural circulation reactor under inclined conditions, a typical three-dimensional analysis model of natural circulation was established. The natural circulation under inclined conditions was numerically simulated using the computational fluid dynamics method, and the velocity and temperature distribution characteristics of heat exchangers and mixed-flow channels with different inclined angles were analyzed. The results show that as the inclination angle of the heat exchanger flow rate increases, there is a spatial migration phenomenon corresponding to the direction of the average flow rate. A large inclination angle will lead to a serious deterioration of the natural circulation capacity in the lower channel. Under inclined conditions, there is a phenomenon of temperature stratification in the mixed-flow channel. [ABSTRACT FROM AUTHOR]

In this study, the motion of wet particles in the drying unit of a vertical powder dryer is investigated by using a Discrete element method (DEM) coupled with a liquid bridge force. In particular, by varying parameters such as the particle mass flow rates, the superficial gas velocities, and superficial gas temperatures, the influence of the moisture content on the flow behavior is examined. The results show that when the moisture content increases, the mean particle velocity decreases while the bed mean solid "holdup" and the mean residence time (MRT) of particles grow. It is also found that the local solid holdup is relatively higher in the near-wall region and decreases towards the near-fluid region. Two regression models are introduced accordingly for the mean particle velocity and the bed mean solid holdup by means of the RSM-BBD (Response surface methodology-Box-Behnken design) method to obtain the optimal combination of parameters for flooding prevention. Finally, the optimal results are compared with numerical observations. As the relative error is less than 10%, this demonstrates that the proposed methodology can accurately describe the particle flow dynamics in the drying unit. Graphic Abstract [ABSTRACT FROM AUTHOR]

Kaplan turbine units can adjust their blades to achieve wider outputs without a significant loss of efficiency. The combination of guide vane angle (GVA) and blade angle (BA) is selected based on efficiency curves obtained from cam tests. However, the vibration characteristics are not considered in the test. The vibration and flow characteristics are complex with different combinations of guide vane and blade angles. Different cam relation selection principles lead to varying machine vibration and flow characteristics. In this research, the flow and vibration characteristics were obtained by means of field test and numerical simulation. Vibration, pressure pulsation, and other stability indicators have been extracted and investigated under off-cam conditions. The flow and variation rules of different indicators have been thoroughly researched. The findings suggest that the magnitude of vibration in the X direction surpassed that in the Y direction for the head cover, upper frame, and lower frame under 22 experimental conditions. The disparity between the head cover and upper frame in both directions was not significant, whereas a substantial contrast existed between the lower frame in the X and Y directions. The calculation results indicate that when the guide vane angle was small, vortices appeared near the high-pressure edge of the runner in the vaneless region and caused disorganized flow lines in the runner, and this complex vortex behavior led to multiple frequency components in the pressure pulsation frequency domain. The conclusions provide references for the designers of Kaplan turbine units and improves the operating safety of Kaplan turbine power stations. [ABSTRACT FROM AUTHOR]

In recent years, jacket foundations have been increasingly employed in offshore wind farms. Their complex design comprising piles and trusses poses challenges for conducting comprehensive flow field measurements using physical experiments. Consequently, the influence of the flow field on local scour around these foundations remains unclear. Therefore, numerical simulation methods are essential to depict the surrounding flow characteristics. This study utilizes large eddy simulation (LES) turbulence models within OpenFOAM to simulate the flow field around jacket foundations on flat-bed and equilibrium scour bathymetry. A flume experiment was conducted for numerical model establishment and validation. The close agreement between experimental and numerical results indicates that the LES model accurately reflects the flow patterns around the jacket foundation. Time-averaged and instantaneous flow characteristics, average kinetic energy (AKE), turbulence structure, and bed shear stress were analyzed. The results indicate that flow intensity is reduced due to the shielding effect and energy dissipation by the truss structure of the jacket foundation. Furthermore, the AKE of the flow upstream of the rear piles decreases by 18.9% in the flat-bed state and 28.0% in the equilibrium state, indicating more energy dissipation and less scour at the rear piles in the equilibrium state. The research findings offer valuable insights into the design and scour protection strategies for jacket foundations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Fuzhou University is the property of Journal of Fuzhou University, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Graphene foam composite is a promising candidate for advanced thermal management applications due to its excellent mechanical strength, high thermal conductivity, ultra-high porosity and huge specific surface area. In this study, a three-dimensional physical model was developed in accordance with the dodecahedral structure of graphene foam composite. A comprehensive numerical simulation was carried out to investigate the fluid flow and convective heat transfer in open-cell graphene foam composite by using ANSYS Fluent 2021 R1 commercial software. Research results show that, as porosity increases, the pressure gradient for graphene foam composite with circular and triangular cross-section struts is reduced by 65% and by 77%, respectively. At a given porosity of 0.904, when the inlet velocity increases from 1 m/s to 5 m/s, the pressure gradient is increased by 11.3 times and 13.8 times, and the convective heat transfer coefficient is increased by 54.5% and 43% for graphene foam composite with circular and triangular cross-section struts, respectively. Due to the irregularity of the skeleton distribution, the pressure drop in Y direction is the highest among the three directions, which is 8.7% and 17.4% higher than that in the Z and X directions at the inlet velocity of 5 m/s, respectively. The convective heat transfer coefficient in the Y direction is significantly lower than that along the X and Z directions. Furthermore, triangular cross-section struts induce a greater pressure drop but offer less effective heat transfer compared to circular struts. The research findings may provide critical insights into the design and optimization of graphene foam composites, and promote their potential for efficient thermal management and gas/liquid purification in engineering applications. [ABSTRACT FROM AUTHOR]

In order to determine the recommended flow velocity for the safe and energy-saving transport of ice-slurry-type light particle slurries, it is necessary to study the flow characteristics of light particle slurries, especially the critical flow velocity. Therefore, in this paper, a numerical simulation method based on the mixed turbulence model with the RANS (Reynolds averaged Navier Stokes) equation is used, and a new concentration distribution method is proposed for the first time to derive the critical flow velocity, as follows: the flow velocity of the light particle slurry when the ratio of the solid volume fraction vf at the position of 0.08D above the bottom of the pipeline to that at the center of the pipeline, vf/vf(y) = 0.75, is taken as the critical flow velocity. The flow changes in the slurry (polyethylene particles with a density of 922 kg/m3 and water) under 0.1–1.0 m/s (at intervals of 0.1 m/s) were investigated experimentally, and the pressure drop data obtained from the experiments were used to determine the recommended flow rate for safe and energy-saving transportation of the light particle slurry. The pipe diameter used for the experiments and simulations was 28 mm, and the solid-phase particle sizes were 0.3 mm, 0.4 mm, and 0.5 mm, with solid-phase contents of 5 vol%, 10 vol%, 15 vol%, and 20 vol%. In addition, the experimental and numerical simulation results show that an increase in solid-phase content and particle size leads to an increase in critical flow velocity. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The optimization of film-unloading and film–soil separation components can effectively improve the residual film unloading rate and reduce impurity content. So, the DEM models of soil and residual film were established and the suspension and flow characteristics under fluid action were analyzed based on the CFD—DEM coupling simulation in this article. The matching parameters of the film-unloading and film-lifting device were optimized with the Box–Behnken test. When the wind velocity was between 1.65 and 10.54 m · s − 1 , the film–soil separation effect was the best, with a film–impurity separation rate of 96.6%. The optimized parameter combination of the film-unloading device and film-lifting device is A = 9°, B = 40 mm, and C = 40 mm (A, B, and C represent the angle between the teeth and the normal of the air inlet, the minimum distance between the teeth and the air inlet, and the width of the air inlet, respectively). With the optimized parameter, the best film unloading effect is achieved, the minimum wind velocity of film unloading is 2.6 m · s − 1 . This article provides theoretical and simulation methods for assessing the flow characteristics of flexible particles and parameter optimization of air suction devices, which is conducive to the high-purity recovery of residual film. [ABSTRACT FROM AUTHOR]

A coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach is used to calculate the interaction of a flexible rag transported by a fluid current with a fixed solid cylinder. More specifically a hybrid Eulerian-Lagrangian approach is used with the rag being modeled as a set of interconnected particles. The influence of various parameters is considered, namely the inlet velocity (1.5, 2.0, and 2.5 m/s, respectively), the angle formed by the initially straight rag with the flow direction (45°, 60° and 90°, respectively), and the inlet position (90, 100, and 110 mm, respectively). The results show that the flow rate has a significant impact on the permeability of the rag. The higher the flow rate, the higher the permeability and the rag speed difference. The angle has a minor effect on rag permeability, with 45° being the most favorable angle for permeability. The inlet position has a small impact on rag permeability, while reducing the initial distance between the rag an the cylinder makes it easier for rags to pass through. [ABSTRACT FROM AUTHOR]

The thermal state of plate–fin heat exchangers with bilateral coolant supply is studied. The heat exchangers considered are rectangular in cross section and trapezoidal in longitudinal section. Coolant is supplied from both sides (models M1 and M2) or from one side only (in model M3). Heat escapes though a hole in the smaller side of the trapezium. The flow and thermal characteristics of the heat exchangers are compared. In bilateral coolant supply, a larger area of the heat exchanger is cooled, while retaining high rates of heat transfer. [ABSTRACT FROM AUTHOR]

A variable-speed pump-turbine is the core component of a hydraulic storage and energy generation station. When the pump-turbine operates at a constant speed, its response to the power grid frequency is poor. In order to improve the hydraulic efficiency of the pumped storage unit, variable-speed units are used. However, there has been no numerical study on the effect of the rotational flow characteristics within the gap of a variable-speed pump-turbine. This paper calculates the flow characteristics within the gap of a variable-speed pump-turbine under three typical pump modes (maximum head minimum flow condition, minimum head maximum flow condition, and maximum speed condition). The research results indicate that the rotational speed significantly affects the pressure distribution, velocity distribution, and turbulent kinetic energy distribution within the crown and band gaps. The higher the speed, the larger the area of the high-pressure region before the runner inlet compared to other operating conditions, and similarly, the low-pressure area after the runner outlet is also larger than in other operating conditions. The change in speed mainly affects the internal flow field of the crown gap, with the most noticeable changes occurring in the pressure and flow velocity at the inlet and outlet of the crown gap. There is a clear trend of pressure drop and velocity increase within the gap as the speed increases. However, with the increase in speed, the pressure distribution and flow velocity within the band gap remain almost the same. In addition to speed changes, it is observed that the pressure within the gap and the flow velocity within the passages are also related to the head, especially in the condition of maximum head, where this relationship becomes more noticeable. [ABSTRACT FROM AUTHOR]

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Copyright of Water Conservancy Science & Techonlogy & Economy is the property of Water Conservancy Science & Technology & Economy Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)