The forming quality of metal bipolar plate(BPP)flow channels in proton exchange membrane fuel cells(PEMFCs)is a key factor affecting battery performance.A flow channel with straight sidewalls and a low thinning rate c...The forming quality of metal bipolar plate(BPP)flow channels in proton exchange membrane fuel cells(PEMFCs)is a key factor affecting battery performance.A flow channel with straight sidewalls and a low thinning rate can enhance battery output.Roll forming,as a new technology for BPP production,offers advantages such as a low thinning rate and high efficiency.However,existing roll curve design methods struggle to accommodate both low thinning rates and straight sidewall angles simultaneously.This study aims to develop flow channels with right-angled sidewalls,which provide benefits such as a low thinning rate,reduced residual stress,and high accuracy.A roller tooth profile was designed to achieve a flow channel with right-angled sidewalls and minimal thinning.Simulations and experiments were conducted to validate the feasibility of this novel design method for the roll forming process.The study investigated the effects of roller tooth parameters on sidewall angle,thinning rate,and residual stress.A multifactor evaluation method was developed to optimize the tip fillet radius and the tooth profile backlash of the roller.The results indicated that the tip fillet radius and the tooth profile backlash were negatively correlated with the sidewall angle.As the tip fillet radius and tooth profile backlash increased,the thinning rate and residual stress decreased.With a tip fillet radius of 0.25 mm and a tooth profile backlash of 0.19 mm,the flow channel achieved an approximately right-angled sidewall,a maximum thinning rate of 7.7%,a 29.6%reduction in maximum residual stress,and maximum and average residual stress imbalance values of 7.1%and 3.2%,respectively.This study proposes a new design method for a right-angled sidewall runner roller gear profile,facilitating the roll forming of metal BPPs with right-angled sidewalls and minimal thinning.This method provides theoretical support for the large-scale application of roll forming in the manufacture of PEMFC BPPs.展开更多
Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated...Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated wall was assumed. The numerical program code interms of vorticity, stream function, axial velocity com ponent and energy equations was written based on a finite volume method. Based on the numerical results, the flow and temperature field were given, and the effects of Dean and Prandtl numbers on flow and heat transfer were ex amined, and the correlations of flow resistance and mean Nusselt number were developed for the jacket. The results show that the structure of secondary flow is steady two vortices in the investigated range of dimensionless curvatureratio and Reynolds number. Two peaks of local Nusselt number increase significantly with Prandtl and Dean num ber increasing, but the local Nusselt numbers near two ends and at the center of the heated wall increase only slightly. The center and two ends of heated wall are the poor positions for heat transfer in the jacket. Compared with the outer half coil jacket at the same area of heated wall, curvature radius, Reynolds number and Prandtl number, e jacket of triangular flow chmnel has lower flow resistance and less mean Nusselt number.展开更多
The electroosmotic flow of a micropolar fluid in a microchannel bounded by two parallel porous plates undergoing periodic vibration is studied. The equations for conservation of linear and angular momentums and Gauss...The electroosmotic flow of a micropolar fluid in a microchannel bounded by two parallel porous plates undergoing periodic vibration is studied. The equations for conservation of linear and angular momentums and Gauss＇s law of charge distribution are solved within the framework of the Debye-Hückel approximation. The fluid velocity and microrotation are assumed to depend linearly on the Reynolds number. The study shows that the amplitude of microrotation is highly sensitive to the changes in the magnitude of the suction velocity and the width of the microchannel. An increase in the micropolar parameter gives rise to a decrease in the amplitude of microrotation. Numerical estimates reveal that the microrotation of the suspended microelements in blood also plays an important role in controlling the electro-osmotically actuated flow dynamics in microbio-fluidic devices.展开更多
Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optim...Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optimum level for proton conductivity.Water management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and degradation.This process requires the study and understanding of internal two-phase flows.Different experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel cells.However,the experiments have limitations in in situ measurements;they are also expensive and time exhaustive.In contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel cells.This paper introduces the recent design of flow channels.It reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop models.Furthermore,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected aspects.Finally,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.展开更多
The estimate of flow resistance in vegetated channels is a challenging topic for programming riparian vegetation management,controlling channel conveyance and flooding propensity,for designing soil bioengineering prac...The estimate of flow resistance in vegetated channels is a challenging topic for programming riparian vegetation management,controlling channel conveyance and flooding propensity,for designing soil bioengineering practices.In this paper,measurements collected by Gualtieri et al.(2018),in a flume where rigid cylinders were set in two arrangements(staggered,aligned)at high submergence ratios(ratio between the water depth and the vegetation height greater than 5),were used to study the effect of rigid submerged vegetation on estimating flow resistance.The theoretical flow resistance equation,obtained by integrating the power flow velocity distribution,was first summarized.Then,this flow resistance equation was calibrated and tested by measurements of Gualtieri et al.(2018).In particular,a relationship between theΓfunction of the power velocity distribution,the channel slope,the flow Froude number,and the submergence ratio was established by using the available measurements carried out for the two arrangements with different stem concentrations.The calibration of this relationship was carried out by(i)distinguishing measurements corresponding to different vegetation arrangements(staggered,aligned),(ii)joining all available data,and(iii)using only a scale factor representing the effect of vegetation arrangements.For the cases(ii)and(iii),the analysis demonstrated that the theoretical flow resistance equation allows an accurate estimate of the Darcy–Weisbach friction factor,which is characterized by errors that are always less than 5%and less than or equal to 2.5%for 88%of the investigated cases.展开更多
Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under d...Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K<0.1); transitional flow(0.1< k/K<1); and turbulent flow(k/K>1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow.展开更多
In order to make the numerical calculation of viscous flows more convenient for the flows in channel with complicated profile governing equations expressed in the arbitrary curvilinear coordinates were derived by mean...In order to make the numerical calculation of viscous flows more convenient for the flows in channel with complicated profile governing equations expressed in the arbitrary curvilinear coordinates were derived by means of Favre density-weighted averaged method, and a turbulent model with effect of curvature modification was also derived. The numerical calculation of laminar and turbulent flown in divergent curved channels was carried out by means of parabolizeil computation method. The calculating results were used to analyze and investigate the aerodynamic performance of talor cascades in compressors preliminarily.展开更多
Power batteries serve as key components of new energy vehicles and are distinguished by their large capacity,long lifespan,high energy density,and stable operation.The strict temperature demands of power battery packs...Power batteries serve as key components of new energy vehicles and are distinguished by their large capacity,long lifespan,high energy density,and stable operation.The strict temperature demands of power battery packs necessitate the development of highly efficient thermal management systems.In this study,a converging-diverging liquid cooling channel featuring a wave shaped structure was designed and analyzed for 18,650-type lithium-ion batteries.To investigate the design methodology for flow channel structure,a thermal model for the heat generation rate of the 18,650-type battery was developed.A comparative analysis of four geometrical configurations of convergingdiverging channels.It identified the flat-bottomed channel achieves a maximum reduction of 20.6%in peak internal temperature compared to the other designs.Subsequently,the effects of the arc depth,cell spacing,and Reynolds number on the heat dissipation of the flat-bottomed flow channel were comprehensively investigated.The results demonstrated that increasing the Reynolds number,maximizing the arc depth of the converging-diverging structure,and reducing cell spacing considerably improved the cooling heat dissipation efficiency.Based on the particle swarm optimization algorithm,the optimal parameter combination of the battery pack was obtained at a discharge rate of 2C,comprising an arc depth of 8.5 mm,cell spacing of 1 mm,and Reynolds number of 700.The study provides valuable guidance and references for the practical design and implementation of thermal management systems in new energy vehicles.展开更多
To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of opt...To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of optimal spatial distribution,a multi-physics simulation model of the resulting Sunflower Bionic Flow Field(SBFF)was developed.Building upon this foundation,an enhanced configuration was introduced by integrating an annular channel,yielding a modified variant referred to as Modified Sunflower Bionic Flow Field(MSBFF).For comparative purposes,a conventional Traditional Parallel Flow Field(TPFF)was also analyzed under identical conditions.Simulation results underscore the superior gas distribution performance of the bionic configurations.Both SBFF and MSBFF significantly improved the homogeneity of reactant gas molar concentration throughout the flow domain.Relative to the TPFF,the SBFF achieved a 13.32%increase in current density,while the MSBFF reached an enhancement of 15.09%.Correspondingly,peak power densities rose by 14.07%and 16.55%,respectively.Furthermore,these bio-inspired structures contributed to improved thermal regulation,as evidenced by a reduction in average electrolyte temperature by 3.22%for the SBFF and 2.92%for the MSBFF.To further optimize performance,the influence of Fibonacci spiral channel count within the MSBFF design was systematically investigated.Results reveal a strong positive correlation between the number of spiral channels and electrochemical output.In particular,the MSBFF with 16 spiral channels(MSBFF-16)demonstrated the most favorable electrical and thermal characteristics.At an operating voltage of 0.7 V,MSBFF-16 exhibited a current density increase of 1.27%and 0.94%over MSBFF and MSBFF-12,respectively.Likewise,peak power density improved by 2.69%and 1.67%.Finally,the study examined the impact of varying inlet mass fractions of oxygen and hydrogen on SOFC performance.Distinct trends were observed:increasing the oxygen mass fraction markedly enhanced heat transfer and current density,while greater hydrogen mass fractions significantly boosted fuel utilization.These findings highlight the crucial role of reactant composition and flow field topology in governing the electrochemical and thermal efficiency of SOFC systems.展开更多
Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity str...Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel,seriously affecting the flow performance of oil.Based on the new design space provided by additive manufacturing technology,the internal hydraulic flow channel of valve block is optimized by using B-spline curve.Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop.The weight reduction of hydraulic valve block is carried out through topology optimization.According to the results of topology optimization,using the method of selective laser melting(SLM),the printing of the hydraulic valve block is completed.The optimized hydraulic channel reduces the pressure loss by 31.4%compared with the traditional hydraulic channel.Compared with the traditional valve block,the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%.Therefore,the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.展开更多
Wall-bounded turbulent flow involves the development of multi-scale turbulent eddies, as well as a sharply varying boundary layer. Its theoretical descriptions are yet phenomenological. We present here a new framework...Wall-bounded turbulent flow involves the development of multi-scale turbulent eddies, as well as a sharply varying boundary layer. Its theoretical descriptions are yet phenomenological. We present here a new framework called structural ensemble dynamics （SED）, which aims at using systematically all relevant statistical properties of turbulent structures for a quantitative description of ensemble means. A new set of closure equations based on the SED approach for a turbulent channel flow is presented. SED order functions are defined, and numerically determined from data of direct numerical simulations （DNS）. Computational results show that the new closure model reproduces accurately the solution of the original Navier-Stokes simulation, including the mean velocity profile, the kinetic energy of the streamwise velocity component, and every term in the energy budget equation. It is suggested that the SED-based studies of turbulent structure builds a bridge between the studies of physical mechanisms of turbulence and the development of accurate model equations for engineering predictions.展开更多
The structural features of fiber suspensions are dependent on the fiber alignment in the flows. In this work the orientation distribution function and orientation tensors for semi-concentrated fiber suspensions in ...The structural features of fiber suspensions are dependent on the fiber alignment in the flows. In this work the orientation distribution function and orientation tensors for semi-concentrated fiber suspensions in converging channel flow were calculated, and the evolutions of the fiber alignment and the bulk effective vis-cosity were analyzed. The results showed that the bulk stress and the effective viscosity were functions of therate-of-strain tensor and the fiber orientation state ; and that the fiber suspensions evolved to steady alignment and tended to concentrate to some preferred directions close to but not same as the directions of local stream-lines. The bulk effective viscosity depended on the product of Reynolds number and time. The decrease of ef-fective viscosity near the boundary benefited the increase of the rate of flow. Finally when the fiber alignment went into steady state, the structural features of fiber suspensions were not dependent on the Reynolds numberbut on the converging channel angle.展开更多
The concentration and orientation of fiber in a turbulent T-shaped branching channel flow are investi-gated numerically. The Reynolds averaged Navier-Stokes equations together with the Reynolds stress turbulent model ...The concentration and orientation of fiber in a turbulent T-shaped branching channel flow are investi-gated numerically. The Reynolds averaged Navier-Stokes equations together with the Reynolds stress turbulent model are solved for the mean flow field and the turbulent kinetic energy. The fluctuating velocities of the fluid are assumed as a random variable with Gaussian distribution whose variance is related to the turbulent kinetic energy. The slender-body theory is used to simulate the fiber motion based on the known mean and fluctuating velocities of the fluid. The results show that at low Reynolds number, fiber concentration is high in the flow separation regions, and fiber orientation throughout the channel is widely distributed with a slight preference of aligning along the horizontal axis. With increasing of Re, the high concentration region disappears, and fiber orientation becomes ho-mogeneous without any preferred direction. At high Reynolds number, fiber concentration increases gradually along the flow direction. The differences in the distribution of concentration and orientation between different fiber aspect ratio are evident only at low Re. Both Re and fiber aspect ratio have small effect on the variance of orientation angle.展开更多
Drag reduction features in the transition regime of channel flow with fibre suspension were analyzed in terms of the linear stability theory. The modified stability equation was obtained based on the slender-body theo...Drag reduction features in the transition regime of channel flow with fibre suspension were analyzed in terms of the linear stability theory. The modified stability equation was obtained based on the slender-body theory and natural closure approximation. Results of the stability analysis show attenuating effects of fibre additives to the flow instability. For the cases leading to transition, drag reduction rate increases with the characteristic parameter H of fibres. The mechanism of drag reduction by fibres is revealed through the variation of velocity profile and the decrease of wall shear stress. The theoretical results are qualitatively consistent with some typical experiments.展开更多
The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influ...The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.展开更多
The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow...The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow regime, more fibres orient to the flow direction as the Reynolds number increases. The shear rate of fluid around a fibre plays an important role in determining the orientation distribution of fibres, while the fibre density and the fibre aspect-ratio have marginal influence on the orientation distribution. In the turbulent regime, the orientation distribution of fibres becomes more homogeneous with the increase of Reynolds number, and the concentration profile is flatter than that in the laminar regime. The fluctuating intensity of fibre velocity in the downstream direction is larger than that in the lateral directions.展开更多
As electro-hydrostatic actuator(EHA)technology advances towards lightweight and integration,the demand for enhanced internal flow pathways in hydraulic valve blocks intensifies.However,owing to the constraints imposed...As electro-hydrostatic actuator(EHA)technology advances towards lightweight and integration,the demand for enhanced internal flow pathways in hydraulic valve blocks intensifies.However,owing to the constraints imposed by traditional manufacturing processes,conventional hydraulic integrated valve blocks fail to satisfy the demands of a more compact channel layout and lower energy dissipation.Notably,the subjectivity in the arrangement of internal passages results in a time-consuming and labor-intensive process.This study employed additive manufacturing technology and the ant colony algorithm and B-spline curves for the meticulous design of internal passages within an aviation EHA valve block.The layout environment for the valve block passages was established,and path optimization was achieved using the ant colony algorithm,complemented by smoothing using B-spline curves.Three-dimensional modeling was performed using SolidWorks software,revealing a 10.03%reduction in volume for the optimized passages compared with the original passages.Computational fluid dynamics(CFD)simulations were performed using Fluent software,demonstrating that the algorithmically optimized passages effectively prevented the occurrence of vortices at right-angled locations,exhibited superior flow characteristics,and concurrently reduced pressure losses by 34.09%-36.36%.The small discrepancy between the experimental and simulation results validated the efficacy of the ant colony algorithm and B-spline curves in optimizing the passage design,offering a viable solution for channel design in additive manufacturing.展开更多
We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events, it is verified on water and drag-reduci...We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events, it is verified on water and drag-reducing surfactant solution flows investigated by particle image velocimetry in experiments. It is obtained that the turbulent contribution to the skin friction factor is linearly proportional to the product of the spatial frequency and strength of turbulent bursts originated from the wall.展开更多
A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vort...A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vorticity gradient tensor(or the so-called vorticity strain rate tensor).The new subgrid-scale stress model is taken into account the effect of the vortex motions in turbulence,which is reflected on the anti-symmetric part of the velocity gradient tensor.In addition,the eddy viscosity of the new model reproduces the proper scaling as O(y^3)near the wall.Then,the new SGS model is applied in large-eddy simulation of the spanwise rotating turbulent channel flow.Different simulating cases are selected to test the new model.The results demonstrate that the present model can well predict the mean velocity profiles,the turbulence intensities,and the rotating turbulence structures.In addition,it needs no a second filter,and is convenient to be used in the engineering rotational flows.展开更多
Direct simulation of 3-D MHD(magnetohydrodynamics) flows in liquid metal fusion blanket with flow channel insert(FCI) has been conducted.Two kinds of pressure equilibrium slot (PES) in FCI,which are used to balance th...Direct simulation of 3-D MHD(magnetohydrodynamics) flows in liquid metal fusion blanket with flow channel insert(FCI) has been conducted.Two kinds of pressure equilibrium slot (PES) in FCI,which are used to balance the pressure difference between the inside and outside of FCI,are considered with a slot in Hartmann wall or a slot in side wall,respectively.The velocity and pressure distribution of FCI made of SiC/SiC_f are numerically studied to illustrate the 3-D MHD flow effects,which clearly show that the flows in fusion blanket with FCI are typical three-dimensional issues and the assumption of 2-D fully developed flows is not the real physical problem of the MHD flows in dual-coolant liquid metal fusion blanket.The optimum opening location of PES has been analyzed based on the 3-D pressure and velocity distributions.展开更多
基金Supported by Major Special Projects of Public Bidding in Shanxi Province of China(Grant No.20201101020)Central Guidance on Local Science and Technology Development Fund Project of China(Grant No.YDZJSX2022A053)Open Fund Subjectof National Key Laboratory of Material Forming and Mold Technology of China(Grant No.P2024-002)。
文摘The forming quality of metal bipolar plate(BPP)flow channels in proton exchange membrane fuel cells(PEMFCs)is a key factor affecting battery performance.A flow channel with straight sidewalls and a low thinning rate can enhance battery output.Roll forming,as a new technology for BPP production,offers advantages such as a low thinning rate and high efficiency.However,existing roll curve design methods struggle to accommodate both low thinning rates and straight sidewall angles simultaneously.This study aims to develop flow channels with right-angled sidewalls,which provide benefits such as a low thinning rate,reduced residual stress,and high accuracy.A roller tooth profile was designed to achieve a flow channel with right-angled sidewalls and minimal thinning.Simulations and experiments were conducted to validate the feasibility of this novel design method for the roll forming process.The study investigated the effects of roller tooth parameters on sidewall angle,thinning rate,and residual stress.A multifactor evaluation method was developed to optimize the tip fillet radius and the tooth profile backlash of the roller.The results indicated that the tip fillet radius and the tooth profile backlash were negatively correlated with the sidewall angle.As the tip fillet radius and tooth profile backlash increased,the thinning rate and residual stress decreased.With a tip fillet radius of 0.25 mm and a tooth profile backlash of 0.19 mm,the flow channel achieved an approximately right-angled sidewall,a maximum thinning rate of 7.7%,a 29.6%reduction in maximum residual stress,and maximum and average residual stress imbalance values of 7.1%and 3.2%,respectively.This study proposes a new design method for a right-angled sidewall runner roller gear profile,facilitating the roll forming of metal BPPs with right-angled sidewalls and minimal thinning.This method provides theoretical support for the large-scale application of roll forming in the manufacture of PEMFC BPPs.
基金Supported by the Speciai Pogram forLocal Universities Development of Central Finance of China （2050205）, the National Natural Science Foundation of China （21106086）, and the Program for Liaoning Excellent Talents in University （LJQ2012035）.
文摘Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated wall was assumed. The numerical program code interms of vorticity, stream function, axial velocity com ponent and energy equations was written based on a finite volume method. Based on the numerical results, the flow and temperature field were given, and the effects of Dean and Prandtl numbers on flow and heat transfer were ex amined, and the correlations of flow resistance and mean Nusselt number were developed for the jacket. The results show that the structure of secondary flow is steady two vortices in the investigated range of dimensionless curvatureratio and Reynolds number. Two peaks of local Nusselt number increase significantly with Prandtl and Dean num ber increasing, but the local Nusselt numbers near two ends and at the center of the heated wall increase only slightly. The center and two ends of heated wall are the poor positions for heat transfer in the jacket. Compared with the outer half coil jacket at the same area of heated wall, curvature radius, Reynolds number and Prandtl number, e jacket of triangular flow chmnel has lower flow resistance and less mean Nusselt number.
文摘The electroosmotic flow of a micropolar fluid in a microchannel bounded by two parallel porous plates undergoing periodic vibration is studied. The equations for conservation of linear and angular momentums and Gauss＇s law of charge distribution are solved within the framework of the Debye-Hückel approximation. The fluid velocity and microrotation are assumed to depend linearly on the Reynolds number. The study shows that the amplitude of microrotation is highly sensitive to the changes in the magnitude of the suction velocity and the width of the microchannel. An increase in the micropolar parameter gives rise to a decrease in the amplitude of microrotation. Numerical estimates reveal that the microrotation of the suspended microelements in blood also plays an important role in controlling the electro-osmotically actuated flow dynamics in microbio-fluidic devices.
基金supported under the program of the top project unveiled by the Inner Mongolia Autonomous Region(Grant No.22JBGS0027).
文摘Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optimum level for proton conductivity.Water management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and degradation.This process requires the study and understanding of internal two-phase flows.Different experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel cells.However,the experiments have limitations in in situ measurements;they are also expensive and time exhaustive.In contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel cells.This paper introduces the recent design of flow channels.It reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop models.Furthermore,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected aspects.Finally,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.
文摘The estimate of flow resistance in vegetated channels is a challenging topic for programming riparian vegetation management,controlling channel conveyance and flooding propensity,for designing soil bioengineering practices.In this paper,measurements collected by Gualtieri et al.(2018),in a flume where rigid cylinders were set in two arrangements(staggered,aligned)at high submergence ratios(ratio between the water depth and the vegetation height greater than 5),were used to study the effect of rigid submerged vegetation on estimating flow resistance.The theoretical flow resistance equation,obtained by integrating the power flow velocity distribution,was first summarized.Then,this flow resistance equation was calibrated and tested by measurements of Gualtieri et al.(2018).In particular,a relationship between theΓfunction of the power velocity distribution,the channel slope,the flow Froude number,and the submergence ratio was established by using the available measurements carried out for the two arrangements with different stem concentrations.The calibration of this relationship was carried out by(i)distinguishing measurements corresponding to different vegetation arrangements(staggered,aligned),(ii)joining all available data,and(iii)using only a scale factor representing the effect of vegetation arrangements.For the cases(ii)and(iii),the analysis demonstrated that the theoretical flow resistance equation allows an accurate estimate of the Darcy–Weisbach friction factor,which is characterized by errors that are always less than 5%and less than or equal to 2.5%for 88%of the investigated cases.
基金supported by the Open Foundation of Key Laboratory of Mountain Hazards and Earth Surface Process, Chinese Academy of Sciences (Grant No. 201503)the Key Research Program of the Chinese Academy of Sciences (Grant No. KZZD-EW-05-01)+1 种基金the National Natural Science Foundation of China (Grant No. 51579163)the Open Foundation of State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (Grant No. SKHL1426)
文摘Particle Image Velocimetry(PIV) technique was used to test the analogues of hyperconcentrated flow and dilute debris flow in an open flume. Flow fields, velocity profiles and turbulent parameters were obtained under different conditions. Results show that the flow regime depends on coarse grain concentration. Slurry with high fine grain concentration but lacking of coarse grains behaves as a laminar flow. Dilute debris flows containing coarse grains are generally turbulent flows. Streamlines are parallel and velocity values are large in laminar flows. However, in turbulent flows the velocity diminishes in line with the intense mixing of liquid and eddies occurring. The velocity profiles of laminar flow accord with the parabolic distribution law. When the flow is in a transitional regime, velocity profiles deviate slightly from the parabolic law. Turbulent flow has an approximately uniform distribution of velocity and turbulent kinetic energy. The ratio of turbulent kinetic energy to the kinetic energy of time-averaged flow is the internal cause determining the flow regime: laminar flow(k/K<0.1); transitional flow(0.1< k/K<1); and turbulent flow(k/K>1). Turbulent kinetic energy firstly increases with increasing coarse grain concentration and then decreases owing to the suppression of turbulence by the high concentration of coarse grains. This variation is also influenced by coarse grain size and channel slope. The results contribute to the modeling of debris flow and hyperconcentrated flow.
文摘In order to make the numerical calculation of viscous flows more convenient for the flows in channel with complicated profile governing equations expressed in the arbitrary curvilinear coordinates were derived by means of Favre density-weighted averaged method, and a turbulent model with effect of curvature modification was also derived. The numerical calculation of laminar and turbulent flown in divergent curved channels was carried out by means of parabolizeil computation method. The calculating results were used to analyze and investigate the aerodynamic performance of talor cascades in compressors preliminarily.
基金funded by the National Nature Science Foundation of China,grant number 52406024.
文摘Power batteries serve as key components of new energy vehicles and are distinguished by their large capacity,long lifespan,high energy density,and stable operation.The strict temperature demands of power battery packs necessitate the development of highly efficient thermal management systems.In this study,a converging-diverging liquid cooling channel featuring a wave shaped structure was designed and analyzed for 18,650-type lithium-ion batteries.To investigate the design methodology for flow channel structure,a thermal model for the heat generation rate of the 18,650-type battery was developed.A comparative analysis of four geometrical configurations of convergingdiverging channels.It identified the flat-bottomed channel achieves a maximum reduction of 20.6%in peak internal temperature compared to the other designs.Subsequently,the effects of the arc depth,cell spacing,and Reynolds number on the heat dissipation of the flat-bottomed flow channel were comprehensively investigated.The results demonstrated that increasing the Reynolds number,maximizing the arc depth of the converging-diverging structure,and reducing cell spacing considerably improved the cooling heat dissipation efficiency.Based on the particle swarm optimization algorithm,the optimal parameter combination of the battery pack was obtained at a discharge rate of 2C,comprising an arc depth of 8.5 mm,cell spacing of 1 mm,and Reynolds number of 700.The study provides valuable guidance and references for the practical design and implementation of thermal management systems in new energy vehicles.
基金supported by a grant from National Key R&D Plan of China(Grant No.2023YFB2504503).
文摘To advance the performance of solid oxide fuel cells(SOFCs),this work proposes a novel biomimetic flow field architecture inspired by the geometric arrangement of sunflower florets.Drawing on natural principles of optimal spatial distribution,a multi-physics simulation model of the resulting Sunflower Bionic Flow Field(SBFF)was developed.Building upon this foundation,an enhanced configuration was introduced by integrating an annular channel,yielding a modified variant referred to as Modified Sunflower Bionic Flow Field(MSBFF).For comparative purposes,a conventional Traditional Parallel Flow Field(TPFF)was also analyzed under identical conditions.Simulation results underscore the superior gas distribution performance of the bionic configurations.Both SBFF and MSBFF significantly improved the homogeneity of reactant gas molar concentration throughout the flow domain.Relative to the TPFF,the SBFF achieved a 13.32%increase in current density,while the MSBFF reached an enhancement of 15.09%.Correspondingly,peak power densities rose by 14.07%and 16.55%,respectively.Furthermore,these bio-inspired structures contributed to improved thermal regulation,as evidenced by a reduction in average electrolyte temperature by 3.22%for the SBFF and 2.92%for the MSBFF.To further optimize performance,the influence of Fibonacci spiral channel count within the MSBFF design was systematically investigated.Results reveal a strong positive correlation between the number of spiral channels and electrochemical output.In particular,the MSBFF with 16 spiral channels(MSBFF-16)demonstrated the most favorable electrical and thermal characteristics.At an operating voltage of 0.7 V,MSBFF-16 exhibited a current density increase of 1.27%and 0.94%over MSBFF and MSBFF-12,respectively.Likewise,peak power density improved by 2.69%and 1.67%.Finally,the study examined the impact of varying inlet mass fractions of oxygen and hydrogen on SOFC performance.Distinct trends were observed:increasing the oxygen mass fraction markedly enhanced heat transfer and current density,while greater hydrogen mass fractions significantly boosted fuel utilization.These findings highlight the crucial role of reactant composition and flow field topology in governing the electrochemical and thermal efficiency of SOFC systems.
基金supported by the National Natural Science Foundation of China(No.51775273)the Jiangsu Province Science and Technology Support Plan Project(No.BE2018010-2)+2 种基金the National Defence Basic Scientific Research Program of China(No.JCKY2018605C010)the Frontiers of Science and Technology Program of China (No.1816312ZT00406301)the Aeronautical Science Foundation of China(No.2020Z049052002)
文摘Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel,seriously affecting the flow performance of oil.Based on the new design space provided by additive manufacturing technology,the internal hydraulic flow channel of valve block is optimized by using B-spline curve.Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop.The weight reduction of hydraulic valve block is carried out through topology optimization.According to the results of topology optimization,using the method of selective laser melting(SLM),the printing of the hydraulic valve block is completed.The optimized hydraulic channel reduces the pressure loss by 31.4%compared with the traditional hydraulic channel.Compared with the traditional valve block,the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%.Therefore,the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.
基金supported by the National Natural Science Foundation of China (90716008)the MOST under 973 project (2009CB724100)
文摘Wall-bounded turbulent flow involves the development of multi-scale turbulent eddies, as well as a sharply varying boundary layer. Its theoretical descriptions are yet phenomenological. We present here a new framework called structural ensemble dynamics （SED）, which aims at using systematically all relevant statistical properties of turbulent structures for a quantitative description of ensemble means. A new set of closure equations based on the SED approach for a turbulent channel flow is presented. SED order functions are defined, and numerically determined from data of direct numerical simulations （DNS）. Computational results show that the new closure model reproduces accurately the solution of the original Navier-Stokes simulation, including the mean velocity profile, the kinetic energy of the streamwise velocity component, and every term in the energy budget equation. It is suggested that the SED-based studies of turbulent structure builds a bridge between the studies of physical mechanisms of turbulence and the development of accurate model equations for engineering predictions.
文摘The structural features of fiber suspensions are dependent on the fiber alignment in the flows. In this work the orientation distribution function and orientation tensors for semi-concentrated fiber suspensions in converging channel flow were calculated, and the evolutions of the fiber alignment and the bulk effective vis-cosity were analyzed. The results showed that the bulk stress and the effective viscosity were functions of therate-of-strain tensor and the fiber orientation state ; and that the fiber suspensions evolved to steady alignment and tended to concentrate to some preferred directions close to but not same as the directions of local stream-lines. The bulk effective viscosity depended on the product of Reynolds number and time. The decrease of ef-fective viscosity near the boundary benefited the increase of the rate of flow. Finally when the fiber alignment went into steady state, the structural features of fiber suspensions were not dependent on the Reynolds numberbut on the converging channel angle.
基金Supported by the Major Program of the National Natural Science Foundation of China (No.10632070).
文摘The concentration and orientation of fiber in a turbulent T-shaped branching channel flow are investi-gated numerically. The Reynolds averaged Navier-Stokes equations together with the Reynolds stress turbulent model are solved for the mean flow field and the turbulent kinetic energy. The fluctuating velocities of the fluid are assumed as a random variable with Gaussian distribution whose variance is related to the turbulent kinetic energy. The slender-body theory is used to simulate the fiber motion based on the known mean and fluctuating velocities of the fluid. The results show that at low Reynolds number, fiber concentration is high in the flow separation regions, and fiber orientation throughout the channel is widely distributed with a slight preference of aligning along the horizontal axis. With increasing of Re, the high concentration region disappears, and fiber orientation becomes ho-mogeneous without any preferred direction. At high Reynolds number, fiber concentration increases gradually along the flow direction. The differences in the distribution of concentration and orientation between different fiber aspect ratio are evident only at low Re. Both Re and fiber aspect ratio have small effect on the variance of orientation angle.
基金the National Natural Science Foundation of China (No. 10372090 and No. 10102017).
文摘Drag reduction features in the transition regime of channel flow with fibre suspension were analyzed in terms of the linear stability theory. The modified stability equation was obtained based on the slender-body theory and natural closure approximation. Results of the stability analysis show attenuating effects of fibre additives to the flow instability. For the cases leading to transition, drag reduction rate increases with the characteristic parameter H of fibres. The mechanism of drag reduction by fibres is revealed through the variation of velocity profile and the decrease of wall shear stress. The theoretical results are qualitatively consistent with some typical experiments.
基金supported by the National Natural Science Foundation of China (Grants No.50879019,50909036,and 50879020)the Research Fund for the Doctoral Program of Higher Education (Grants No.200802940001 and 200802941028)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No.2010B02214,2009B08014,and 2010B14214)the Natural Science Foundation of Hohai University(Grant No. 2008426411)the Jiangsu "333" Program for High Level Talents (Grant No. 2017-B08038)the National Undergraduate Innovation Training Plan (Grant No.G20101106)
文摘The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.
基金Project supported by the National Natural Science Foundation （Grant No 10372090） and the Doctorate Program of Higher Education of China （Grant No 20030335001）.
文摘The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow regime, more fibres orient to the flow direction as the Reynolds number increases. The shear rate of fluid around a fibre plays an important role in determining the orientation distribution of fibres, while the fibre density and the fibre aspect-ratio have marginal influence on the orientation distribution. In the turbulent regime, the orientation distribution of fibres becomes more homogeneous with the increase of Reynolds number, and the concentration profile is flatter than that in the laminar regime. The fluctuating intensity of fibre velocity in the downstream direction is larger than that in the lateral directions.
基金Supported by National Natural Science Foundation of China(Grant No.51890881)。
文摘As electro-hydrostatic actuator(EHA)technology advances towards lightweight and integration,the demand for enhanced internal flow pathways in hydraulic valve blocks intensifies.However,owing to the constraints imposed by traditional manufacturing processes,conventional hydraulic integrated valve blocks fail to satisfy the demands of a more compact channel layout and lower energy dissipation.Notably,the subjectivity in the arrangement of internal passages results in a time-consuming and labor-intensive process.This study employed additive manufacturing technology and the ant colony algorithm and B-spline curves for the meticulous design of internal passages within an aviation EHA valve block.The layout environment for the valve block passages was established,and path optimization was achieved using the ant colony algorithm,complemented by smoothing using B-spline curves.Three-dimensional modeling was performed using SolidWorks software,revealing a 10.03%reduction in volume for the optimized passages compared with the original passages.Computational fluid dynamics(CFD)simulations were performed using Fluent software,demonstrating that the algorithmically optimized passages effectively prevented the occurrence of vortices at right-angled locations,exhibited superior flow characteristics,and concurrently reduced pressure losses by 34.09%-36.36%.The small discrepancy between the experimental and simulation results validated the efficacy of the ant colony algorithm and B-spline curves in optimizing the passage design,offering a viable solution for channel design in additive manufacturing.
文摘We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events, it is verified on water and drag-reducing surfactant solution flows investigated by particle image velocimetry in experiments. It is obtained that the turbulent contribution to the skin friction factor is linearly proportional to the product of the spatial frequency and strength of turbulent bursts originated from the wall.
基金supported by the National Natural Science Foundation of China(Grants 91852203 and 11472278)the National Key Research and Development Program of China(Grant 2016YFA04-01200)+1 种基金Science Challenge Project(Grant TZ2016001)Strategic Priority Research Program of Chinese Academy of Sciences(Grants XDA17030100 and XDC01000000)。
文摘A new subgrid-scale(SGS)stress model is proposed for rotating turbulent flows,and the new model is based on the traceless symmetric part of the square of the velocity gradient tensor and the symmetric part of the vorticity gradient tensor(or the so-called vorticity strain rate tensor).The new subgrid-scale stress model is taken into account the effect of the vortex motions in turbulence,which is reflected on the anti-symmetric part of the velocity gradient tensor.In addition,the eddy viscosity of the new model reproduces the proper scaling as O(y^3)near the wall.Then,the new SGS model is applied in large-eddy simulation of the spanwise rotating turbulent channel flow.Different simulating cases are selected to test the new model.The results demonstrate that the present model can well predict the mean velocity profiles,the turbulence intensities,and the rotating turbulence structures.In addition,it needs no a second filter,and is convenient to be used in the engineering rotational flows.
基金supported by National Natural Science Foundation of China with grant Nos.10872212,50936006National Magnetic Confinement Fusion Science Program in China with grant No.2009GB10401
文摘Direct simulation of 3-D MHD(magnetohydrodynamics) flows in liquid metal fusion blanket with flow channel insert(FCI) has been conducted.Two kinds of pressure equilibrium slot (PES) in FCI,which are used to balance the pressure difference between the inside and outside of FCI,are considered with a slot in Hartmann wall or a slot in side wall,respectively.The velocity and pressure distribution of FCI made of SiC/SiC_f are numerically studied to illustrate the 3-D MHD flow effects,which clearly show that the flows in fusion blanket with FCI are typical three-dimensional issues and the assumption of 2-D fully developed flows is not the real physical problem of the MHD flows in dual-coolant liquid metal fusion blanket.The optimum opening location of PES has been analyzed based on the 3-D pressure and velocity distributions.
