Three types of previously used numerical methods are revisited for computing the streamfunctionψand velocity potentialχfrom the horizontal velocity v in limited domains.The first type,called the SOR-based method,use...Three types of previously used numerical methods are revisited for computing the streamfunctionψand velocity potentialχfrom the horizontal velocity v in limited domains.The first type,called the SOR-based method,uses a classical successive over-relaxation(SOR)scheme to computeψ(orχ)first with an arbitrary boundary condition(BC)and thenχ(orψ)with the BC derived from v.The second type,called the spectral method,uses spectral formulations to construct the inner part of(ψ,χ)-the inversion of(vorticity,divergence)with a homogeneous BC,and then the remaining harmonic part of(ψ,χ)with BCs from v.The third type,called the integral method,uses integral formulas to compute the internally induced(ψ,χ)-the inversion of domain-internal(vorticity,divergence)using the free-space Greenꞌs function without BCs and then the remaining harmonicψ(orχ)with BCs from v minus the internally-induced part.Although these methods have previously been successfully applied to flows in large-scale and synoptic-scale domains,their accuracy is compromised when applied to complex flows over mesoscale domains,as shown in this paper.To resolve this problem,two hybrid approaches,the integral-SOR method and the integral-spectral method,are developed by combining the first step of the integral method with the second step adopted from the SOR-based and spectral methods,respectively.Upon testing these methods on real-case complex flows,the integral-SOR method is significantly more accurate than the integral-spectral method,noting that the latter is still generally more accurate than the three previously-used methods.The integral-SOR method is recommended for future applications and diagnostic studies of complex flows.展开更多
Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymer chain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense in continuum m...Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymer chain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense in continuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to as envelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, a phenomenological viscoelastic model is derived. The model is tested in simple shear flow, simple elongational flow, oscillatory shear flow, and relaxation process after flow suddenly stopped. The results show that the model works well to predict the change of internal structure and viscoelastic performance of polymer melts in flow fields.展开更多
A finite difference method for computing the axisymmetric, transonic flows over a nacelle is presented in this paper. By use of the conservative full-potential equation, body-fitted grid, and the exact boundary condit...A finite difference method for computing the axisymmetric, transonic flows over a nacelle is presented in this paper. By use of the conservative full-potential equation, body-fitted grid, and the exact boundary conditions, a new AF scheme is constructed according to the criterion of optimum convergence. The proposed scheme has been applied to transonic nacelle flow problems. Computation for several nacelles shows the rapid convergence of this scheme and excellent agreement with the experimental results.展开更多
The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The sismulation is based on the two-equation RNG κ-ε turbulence model...The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The sismulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, and a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall; the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.展开更多
This article aims at building an electromagnetic and fluid model, based on the Maxwell equations and Navier-Stokes equations, in TiAl melt under two electric fields.FEM (Finite Element Method) and APDL (ANSYS Parametr...This article aims at building an electromagnetic and fluid model, based on the Maxwell equations and Navier-Stokes equations, in TiAl melt under two electric fields.FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed to perform the simulation, model setup, loading and problem solving.The melt in molds of same cross section area with different flakiness ratio (i.e.width/depth) under the load of sinusoidal current or pulse current was analyzed to obtain the distribution of electromagnetic field and flow field.The results show that the induced magnetic field occupies sufficiently the domain of the melt in the mold with a flakiness ratio of 5:1.The melt is driven bipolarly from the center in each electric field.It is also found that the pulse electric field actuates the TiAl melt to flow stronger than what the sinusoidal electric field does.展开更多
A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS?Fluent via a user-defined function(UDF)and applied to the dissipation of liquid slugs in the inlet pipe of a gas–liqui...A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS?Fluent via a user-defined function(UDF)and applied to the dissipation of liquid slugs in the inlet pipe of a gas–liquid cylindrical cyclone(GLCC)separator while varying the expanding diameter ratio and angle of inclination.The dissipation of liquid slug in inlet pipe is analyzed under different expanding diameter ratios and inclination angles.In the inlet pipe,it is found that increasing expanding diameter ratio and inclination angle can reduce the liquid slug stability and enhancing the effect of gravity,which is beneficial to slug flow dissipation.In the cylinder,increasing the expanding diameter ratio can significantly reduce the liquid carrying depth of the gas phase but result in a slightly increase of the gas content in the liquid phase space.Moreover,increasing the inclination angle results in a decrease in the carrying depth of liquid in the vapor phase,but enhances gas–liquid mixing and increases the gas-carrying depth in the liquid phase.Taking into consideration the dual effects of slug dissipation in the inlet pipe and carrying capacity of gas/liquid spaces in the cylinder,the optimal expanding diameter ratio and inclination angle values can be determined.展开更多
A metallic interconnect plate with a flow channel array is one of the most important elements in a solid oxide fuel cell(SOFC). Electrochemical machining(ECM) is considered to be an adoptable technology for fabricatin...A metallic interconnect plate with a flow channel array is one of the most important elements in a solid oxide fuel cell(SOFC). Electrochemical machining(ECM) is considered to be an adoptable technology for fabricating flow channels in an interconnect plate on account of its efficiency and low cost. With respect to the traditional electrolyte flow mode in ECM cross-channel array, the electrolyte usually flows from one side to the opposite side of the rectangular processing area. However, obvious flow marks are typically formed at the bottom of channels perpendicular to the flow. According to multiphysical simulation analysis, the low electrolyte velocity in the channels perpendicular to the flow leads to uneven distribution of electrolyte products. To improve the uniformity of the flow field, two new electrolyte flow modes, “two-in and two-out” and “three-in and one-out”, are proposed. By adding one or two additional electrolyte inlets to the sides of the traditional flow field, the electrolyte flow velocity in the channels perpendicular to the traditional flow will be increased. Corresponding simulations and experiments were performed and the results showed that the “three-in and one-out” flow mode can produce a flatter bottom surface for the cross-channel array. Parameter optimization experiments for the preferred flow mode were undertaken and the optimal flow field parameters were determined.展开更多
A model was established based on Maxwell's equations and Navier-Stokes' equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1. The ...A model was established based on Maxwell's equations and Navier-Stokes' equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1. The FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed for the model to execute the modeling, meshing, load applying and solving. The Ti-Al alloy melt was selected to illustrate and validate the effects of the harmonic field frequency on the distribution of the physical fields in the mold. The simulated results demonstrate that with an increasing frequency the electric current forms an ellipsoid cavity where it becomes much weaker, and that the melt flows more intensely with low frequency (less than 5 kHz) than with high frequency (more than 5 kHz). The melt is pinched from the central part in the mold to bipolar parts in which it forms two vortexes in each side. The maximum value of fluid velocity exists near the bipolar zone.展开更多
Designing bio-inspired flow fields holds great potential in improving the performance of Proton Exchange Membrane Fuel Cell(PEMFC).Two kinds of biological prototypes are widely used:plant prototype and animal prototyp...Designing bio-inspired flow fields holds great potential in improving the performance of Proton Exchange Membrane Fuel Cell(PEMFC).Two kinds of biological prototypes are widely used:plant prototype and animal prototype.It remains a question which one of these prototypes is more appropriate for the scenario of PEMFC.Here,a comparative study was conducted to compare bionic flow fields based on animal and plant prototypes.First,a Corn Leaf Vein Mathematical Model(CLMM)was established by extracting structural parameters from corn leaves of two growth stages.Then the obtained CLMM and well-known Murray’s law were employed to design bionic flow fields corresponding to the plant and animal prototypes,respectively,which have been subsequently compared by numerical investigations.The results demonstrate that the flow field guided by Murray’s law outperforms the counterpart based on the structural parameters of CLMM in terms of PEMFC net output power,mass transport,water management and pressure drop,suggesting that animal circulation system is more suitable to the bionic flow field design of PEMFC than plant leaf veins.The work may also offer valuable insights into the design of other flow fields related to electrochemical energy conversion.展开更多
In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence inten...In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.展开更多
The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine ...The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.展开更多
Atmospheric and oceanic drag are the main environmental forces controlling sea ice drift. Oceanic drag includes the form drag generated by water pressure gradients on the side of ice floes or on ice ridges, and the sk...Atmospheric and oceanic drag are the main environmental forces controlling sea ice drift. Oceanic drag includes the form drag generated by water pressure gradients on the side of ice floes or on ice ridges, and the skin friction generated by viscous flow on the bottom of ice floes. In this study, we carried out a two-dimensional numerical simulation using FLUENT software to investigate the characteristics of dynamic flow under ice with a smooth undersurface. We studied water drag and flow field distribution below the ice under different conditions of ice draft and flow velocity, and the results agreed well with data from laboratory-based physical modeling tests, demonstrating the ability of the numerical model to reproduce the dynamic interactions between sea ice and the flow field. The degree of distortion in the flow field caused by ice increased as the ice draft increased. Vortexes occurred in the wake field of the floe, and the centers of the vortexes moved away from the ice with increasing ice draft. The simulated drag of water on ice showed a clear linear relationship with the square of the flow velocity.展开更多
Proton exchange membrane fuel cells(PEMFCs)are largely used in various applications because of their pollution-free products and high energy conversion efficiency.In order to improve the related design,in the present ...Proton exchange membrane fuel cells(PEMFCs)are largely used in various applications because of their pollution-free products and high energy conversion efficiency.In order to improve the related design,in the present work a new spiral flow field with a bypass is proposed.The reaction gas enters the flow field in the central path and diffuses in two directions through the flow channel and the bypass.The bypasses are arranged incrementally.The number of bypasses and the cross-section size of the bypasses are varied parametrically while a single-cell model of the PEMFC is used.The influence of the concentration of liquid water and oxygen in the cell on the performance of different flow fields is determined by means of Computational fluid dynamics(COMSOL Multiphysics software).Results show that when the bypass number is 48 and its cross-sectional area is 0.5 mm^(2),the cell exhibits the best performances.展开更多
Transparent flow field visualization techniques play a critical role in engineering and scientific applications.They provide a clear and intuitive means to understand fluid dynamics and its complex phenomena,such as l...Transparent flow field visualization techniques play a critical role in engineering and scientific applications.They provide a clear and intuitive means to understand fluid dynamics and its complex phenomena,such as laminar flow,turbulence,and vortices.However,achieving fully two-dimensional quantitative visualization of transparent flow fields under non-invasive conditions remains a significant challenge.Here,we present an approach for achieving flow field visualization by harnessing the synergistic effects of a dielectric metasurface array endowed with photonic spindecoupled capability.This approach enables the simultaneous acquisition of light-field images containing flow field information in two orthogonal dimensions,which allows for the real-time and quantitative derivation of multiple physical parameters.As a proof-of-concept,we experimentally demonstrate the applicability of the proposed visualization technique to various scenarios,including temperature field mapping,gas leak detection,visualization of various fluid physical phenomena,and 3D morphological reconstruction of transparent phase objects.This technique not only establishes an exceptional platform for advancing research in fluid physics,but also exhibits significant potential for broad applications in industrial design and vision.展开更多
Hydrogen serves as an efficient energy vector with advantages such as high energy density,greenness,and cleanliness.Hydrogen generation from water electrolysis with renewable energy is an effective approach for achiev...Hydrogen serves as an efficient energy vector with advantages such as high energy density,greenness,and cleanliness.Hydrogen generation from water electrolysis with renewable energy is an effective approach for achieving renewable energy consumption and green hydrogen energy production.Polymer electrolyte membrane water electrolysis(PEMWE)is capable of presenting the merits of high current density,high productivity,superior gas purity,low energy consumption and high safety.The development of PEMWE is an important part of achieving the coupling of renewable energy,electric energy and hydrogen energy.As a crucial component of PEMWE,bipolar plates(BPs)constitute the mechanical support of the whole cell and provide a channel for electron transport and material supply.These channels determine the electrochemical and hydrodynamic response of a PEMWE.This work reviews the latest developments and applications of BPs,with a focus on the challenges of flow field structure and material fabrication.The specific content covers the BP matrix,types of surface layers,and effect of flow field design on mass transfer.Extended-term growth and feasibility studies of BPs,which can provide a reference and guidance for the configuration of high-behavior flow fields in PEMWEs in the long run,are envisioned.展开更多
Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aer...Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.展开更多
The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personn...The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.展开更多
Compared with Pidgeon process,the relative vacuum continuous magnesium smelting process reduces the ratio of material to magnesium by changing raw materials and the direct reduction after calcination of prefabricated ...Compared with Pidgeon process,the relative vacuum continuous magnesium smelting process reduces the ratio of material to magnesium by changing raw materials and the direct reduction after calcination of prefabricated pellets,so that the energy consumption per ton of magnesium produced is reduced by 30∼40%,and the carbon emission is reduced by 43∼52%,breaking through the vacuum conditions to achieve continuous production.However,in the process of industrialization,it was found that the magnesium yield in the condenser was low.Therefore,this paper constructs a condenser model of relative vacuum continuous magnesium refining process,and comprehensively analyzes the condensation mechanism of magnesium vapor through simulation and experiment.It is found that the dynamic characteristics of magnesium vapor condensation is an important index to measure its continuity.Under the condition offlowing argon as the protective gas,when the condensation plate spacing is 10 cm,the surface roughness amplitude variance is 2,and the carrier gasflow rate is 20×10^(-3) m/s,the magnesium vapor has a better condensation effect,and the condensation efficiency formula is derived.展开更多
Bipolar plate is one of the key components of Proton Exchange Membrane Fuel Cell(PEMFC)and a reasonable flow field design for bipolar plate will improve cell performance.Herein,we have reviewed conventional and bionic...Bipolar plate is one of the key components of Proton Exchange Membrane Fuel Cell(PEMFC)and a reasonable flow field design for bipolar plate will improve cell performance.Herein,we have reviewed conventional and bionic flow field designs in recent literature with a focus on bionic flow fields.In particular,the bionic flow fields are summarized into two types:plant-inspired and animal-inspired.The conventional methodology for flow field design takes more time to find the optimum since it is based on experience and trial-and-error methods.In recent years,machine learning has been used to optimize flow field structures of bipolar plates owing to the advantages of excellent prediction and optimization capability.Artificial Intelligence(AI)-assisted flow field design has been summarized into two categories in this review:single-objective optimization and multi-objective optimization.Furthermore,a Threats-Opportunities-Weaknesses-Strengths(TOWS)analysis has been conducted for AI-assisted flow field design.It has been envisioned that AI can afford a powerful tool to solve the complex problem of bionic flow field design and significantly enhance the performance of PEMFC with bionic flow fields.展开更多
This study uses numerical simulations of liquid cooling flow fields to investigate polymer exchange membrane fuel cell(PEMFC)thermal control.The research shows that the optimum cooling channel design significantly red...This study uses numerical simulations of liquid cooling flow fields to investigate polymer exchange membrane fuel cell(PEMFC)thermal control.The research shows that the optimum cooling channel design significantly reduces the fuel cell’s temperature differential,improving overall efficiency.Specifically,the simulations show a reduction in the maximum temperature by up to 15%compared to traditional designs.Additionally,according to analysis,the Nusselt number rises by 20%with the implementation of serpentine flow patterns,leading to enhanced heat transfer rates.The findings demonstrate that effective cooling strategies can lead to a 10% increase in fuel cell performance under varying operational conditions,including pressures of 2 bar and relative humidity levels of 30%,60%,and 80%.These results underscore the importance of cooling flow design in optimizing PEMFC performance.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos. 91937301, 41875074, and 41675060the Second Tibetan Plateau Comprehensive Scientific Expedition 2019QZKK0104+1 种基金the National Key Scientific and Technological Infrastructure Project “EarthLab”provided by NOAA/OAR under NOAA–OU Cooperative Agreement #NA16OAR4320072, U.S. Department of Commerce
文摘Three types of previously used numerical methods are revisited for computing the streamfunctionψand velocity potentialχfrom the horizontal velocity v in limited domains.The first type,called the SOR-based method,uses a classical successive over-relaxation(SOR)scheme to computeψ(orχ)first with an arbitrary boundary condition(BC)and thenχ(orψ)with the BC derived from v.The second type,called the spectral method,uses spectral formulations to construct the inner part of(ψ,χ)-the inversion of(vorticity,divergence)with a homogeneous BC,and then the remaining harmonic part of(ψ,χ)with BCs from v.The third type,called the integral method,uses integral formulas to compute the internally induced(ψ,χ)-the inversion of domain-internal(vorticity,divergence)using the free-space Greenꞌs function without BCs and then the remaining harmonicψ(orχ)with BCs from v minus the internally-induced part.Although these methods have previously been successfully applied to flows in large-scale and synoptic-scale domains,their accuracy is compromised when applied to complex flows over mesoscale domains,as shown in this paper.To resolve this problem,two hybrid approaches,the integral-SOR method and the integral-spectral method,are developed by combining the first step of the integral method with the second step adopted from the SOR-based and spectral methods,respectively.Upon testing these methods on real-case complex flows,the integral-SOR method is significantly more accurate than the integral-spectral method,noting that the latter is still generally more accurate than the three previously-used methods.The integral-SOR method is recommended for future applications and diagnostic studies of complex flows.
基金This project is supported by the National Natural Science Foundation of China
文摘Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymer chain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense in continuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to as envelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, a phenomenological viscoelastic model is derived. The model is tested in simple shear flow, simple elongational flow, oscillatory shear flow, and relaxation process after flow suddenly stopped. The results show that the model works well to predict the change of internal structure and viscoelastic performance of polymer melts in flow fields.
文摘A finite difference method for computing the axisymmetric, transonic flows over a nacelle is presented in this paper. By use of the conservative full-potential equation, body-fitted grid, and the exact boundary conditions, a new AF scheme is constructed according to the criterion of optimum convergence. The proposed scheme has been applied to transonic nacelle flow problems. Computation for several nacelles shows the rapid convergence of this scheme and excellent agreement with the experimental results.
基金Supported by the National 863 Project (2001AA642030-1) and Zhejiang Provincial Key Research Project (010007037).
文摘The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The sismulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, and a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall; the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.
基金supported by the Program for New Century Excellent Talents in Universities of the Ministry of Education of China under Grant No.NCET-08-0164the Foundation of National Key Laboratory for Precision Heat Processing of Metals
文摘This article aims at building an electromagnetic and fluid model, based on the Maxwell equations and Navier-Stokes equations, in TiAl melt under two electric fields.FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed to perform the simulation, model setup, loading and problem solving.The melt in molds of same cross section area with different flakiness ratio (i.e.width/depth) under the load of sinusoidal current or pulse current was analyzed to obtain the distribution of electromagnetic field and flow field.The results show that the induced magnetic field occupies sufficiently the domain of the melt in the mold with a flakiness ratio of 5:1.The melt is driven bipolarly from the center in each electric field.It is also found that the pulse electric field actuates the TiAl melt to flow stronger than what the sinusoidal electric field does.
基金financially supported by the National Science Foundation of China(Nos.51274233,51574273)the Province Natural Science Foundation(Grant No.ZR2014EEM045)。
文摘A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS?Fluent via a user-defined function(UDF)and applied to the dissipation of liquid slugs in the inlet pipe of a gas–liquid cylindrical cyclone(GLCC)separator while varying the expanding diameter ratio and angle of inclination.The dissipation of liquid slug in inlet pipe is analyzed under different expanding diameter ratios and inclination angles.In the inlet pipe,it is found that increasing expanding diameter ratio and inclination angle can reduce the liquid slug stability and enhancing the effect of gravity,which is beneficial to slug flow dissipation.In the cylinder,increasing the expanding diameter ratio can significantly reduce the liquid carrying depth of the gas phase but result in a slightly increase of the gas content in the liquid phase space.Moreover,increasing the inclination angle results in a decrease in the carrying depth of liquid in the vapor phase,but enhances gas–liquid mixing and increases the gas-carrying depth in the liquid phase.Taking into consideration the dual effects of slug dissipation in the inlet pipe and carrying capacity of gas/liquid spaces in the cylinder,the optimal expanding diameter ratio and inclination angle values can be determined.
基金co-supported by the Joint Funds of the Natural Science Foundation of China and Guangdong Province(No.U1601201)the Natural Science Foundation of Jiangsu Province(No.BK20192007)the National Natural Science Foundation of China for Creative Research Groups(No.51921003)。
文摘A metallic interconnect plate with a flow channel array is one of the most important elements in a solid oxide fuel cell(SOFC). Electrochemical machining(ECM) is considered to be an adoptable technology for fabricating flow channels in an interconnect plate on account of its efficiency and low cost. With respect to the traditional electrolyte flow mode in ECM cross-channel array, the electrolyte usually flows from one side to the opposite side of the rectangular processing area. However, obvious flow marks are typically formed at the bottom of channels perpendicular to the flow. According to multiphysical simulation analysis, the low electrolyte velocity in the channels perpendicular to the flow leads to uneven distribution of electrolyte products. To improve the uniformity of the flow field, two new electrolyte flow modes, “two-in and two-out” and “three-in and one-out”, are proposed. By adding one or two additional electrolyte inlets to the sides of the traditional flow field, the electrolyte flow velocity in the channels perpendicular to the traditional flow will be increased. Corresponding simulations and experiments were performed and the results showed that the “three-in and one-out” flow mode can produce a flatter bottom surface for the cross-channel array. Parameter optimization experiments for the preferred flow mode were undertaken and the optimal flow field parameters were determined.
基金supported by the Program for New Century Excellent Talents in Universities (GrantNo. NCET-08-0164) of China’s Ministry of Educationthe Foundation of National Key Laboratory for Precision Hot Processing of Metals, China
文摘A model was established based on Maxwell's equations and Navier-Stokes' equations to numerically simulate the electromagnetic field and flow field in a rectangular mold with sectional aspect ratio of 5:1. The FEM (Finite Element Method) and APDL (ANSYS Parametric Design Language) were employed for the model to execute the modeling, meshing, load applying and solving. The Ti-Al alloy melt was selected to illustrate and validate the effects of the harmonic field frequency on the distribution of the physical fields in the mold. The simulated results demonstrate that with an increasing frequency the electric current forms an ellipsoid cavity where it becomes much weaker, and that the melt flows more intensely with low frequency (less than 5 kHz) than with high frequency (more than 5 kHz). The melt is pinched from the central part in the mold to bipolar parts in which it forms two vortexes in each side. The maximum value of fluid velocity exists near the bipolar zone.
基金This work was supported by the National Natural Science Foundation of China(51975245 and 52075214)Jilin Provincial Science&Technology Department(20200201058JC and 20190303039SF)+3 种基金Key Science and Technology R&D Projects of Jilin Province(2020C023-3)Program of Jilin University Science and Technology Innovative Research Team(2020TD-03)Youth Development Program of Jilin University(2020-JCXK-22)the Fundamental Research Funds for the Central Universities.
文摘Designing bio-inspired flow fields holds great potential in improving the performance of Proton Exchange Membrane Fuel Cell(PEMFC).Two kinds of biological prototypes are widely used:plant prototype and animal prototype.It remains a question which one of these prototypes is more appropriate for the scenario of PEMFC.Here,a comparative study was conducted to compare bionic flow fields based on animal and plant prototypes.First,a Corn Leaf Vein Mathematical Model(CLMM)was established by extracting structural parameters from corn leaves of two growth stages.Then the obtained CLMM and well-known Murray’s law were employed to design bionic flow fields corresponding to the plant and animal prototypes,respectively,which have been subsequently compared by numerical investigations.The results demonstrate that the flow field guided by Murray’s law outperforms the counterpart based on the structural parameters of CLMM in terms of PEMFC net output power,mass transport,water management and pressure drop,suggesting that animal circulation system is more suitable to the bionic flow field design of PEMFC than plant leaf veins.The work may also offer valuable insights into the design of other flow fields related to electrochemical energy conversion.
文摘In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.
基金Supported by the Ministry of Higher Education Malaysia and Universiti Teknologi Malaysia(Research University Grant Tier-1,Grant No.06H29)Ministry of Science,Technology and Innovation(MOSTI)Malaysia(Grant No.03-01-06-KHAS01)
文摘The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.
基金supported by the National Natural Science Foundation of China(Grant nos.41276191 and 40930848)
文摘Atmospheric and oceanic drag are the main environmental forces controlling sea ice drift. Oceanic drag includes the form drag generated by water pressure gradients on the side of ice floes or on ice ridges, and the skin friction generated by viscous flow on the bottom of ice floes. In this study, we carried out a two-dimensional numerical simulation using FLUENT software to investigate the characteristics of dynamic flow under ice with a smooth undersurface. We studied water drag and flow field distribution below the ice under different conditions of ice draft and flow velocity, and the results agreed well with data from laboratory-based physical modeling tests, demonstrating the ability of the numerical model to reproduce the dynamic interactions between sea ice and the flow field. The degree of distortion in the flow field caused by ice increased as the ice draft increased. Vortexes occurred in the wake field of the floe, and the centers of the vortexes moved away from the ice with increasing ice draft. The simulated drag of water on ice showed a clear linear relationship with the square of the flow velocity.
基金Thanks to Major Scientific and Technological Innovation Projects in Shandong Province(2018-CXGC0803)for the financial support of this article.
文摘Proton exchange membrane fuel cells(PEMFCs)are largely used in various applications because of their pollution-free products and high energy conversion efficiency.In order to improve the related design,in the present work a new spiral flow field with a bypass is proposed.The reaction gas enters the flow field in the central path and diffuses in two directions through the flow channel and the bypass.The bypasses are arranged incrementally.The number of bypasses and the cross-section size of the bypasses are varied parametrically while a single-cell model of the PEMFC is used.The influence of the concentration of liquid water and oxygen in the cell on the performance of different flow fields is determined by means of Computational fluid dynamics(COMSOL Multiphysics software).Results show that when the bypass number is 48 and its cross-sectional area is 0.5 mm^(2),the cell exhibits the best performances.
基金support from the Key Research and Development Program of the Ministry of Science and Technology of China(2022YFA1205000)the National Natural Science Foundation of China(12274217,12104225)+2 种基金the Natural Science Foundation of Jiangsu Province(BK20220068)Fundamental Research Funds for the Central UniversitiesThe authors acknowledge the technique support from the microfabrication center of the National Laboratory of Solid-State Microstructures.
文摘Transparent flow field visualization techniques play a critical role in engineering and scientific applications.They provide a clear and intuitive means to understand fluid dynamics and its complex phenomena,such as laminar flow,turbulence,and vortices.However,achieving fully two-dimensional quantitative visualization of transparent flow fields under non-invasive conditions remains a significant challenge.Here,we present an approach for achieving flow field visualization by harnessing the synergistic effects of a dielectric metasurface array endowed with photonic spindecoupled capability.This approach enables the simultaneous acquisition of light-field images containing flow field information in two orthogonal dimensions,which allows for the real-time and quantitative derivation of multiple physical parameters.As a proof-of-concept,we experimentally demonstrate the applicability of the proposed visualization technique to various scenarios,including temperature field mapping,gas leak detection,visualization of various fluid physical phenomena,and 3D morphological reconstruction of transparent phase objects.This technique not only establishes an exceptional platform for advancing research in fluid physics,but also exhibits significant potential for broad applications in industrial design and vision.
基金support from the Tianjin Natural Science Foundation for Outstanding Young Scholar(No.23JCJQJC00290)the Scientific Research Plan Project of Tianjin Education Commission(No.2023KJ207)+1 种基金Basic Research Collaborative Project of Beijing–Tianjin–Hebei(NO.E2024202285)Project of State Key Laboratory of Intelligent Green Vehicle and Mobility(No.KFY2403).
文摘Hydrogen serves as an efficient energy vector with advantages such as high energy density,greenness,and cleanliness.Hydrogen generation from water electrolysis with renewable energy is an effective approach for achieving renewable energy consumption and green hydrogen energy production.Polymer electrolyte membrane water electrolysis(PEMWE)is capable of presenting the merits of high current density,high productivity,superior gas purity,low energy consumption and high safety.The development of PEMWE is an important part of achieving the coupling of renewable energy,electric energy and hydrogen energy.As a crucial component of PEMWE,bipolar plates(BPs)constitute the mechanical support of the whole cell and provide a channel for electron transport and material supply.These channels determine the electrochemical and hydrodynamic response of a PEMWE.This work reviews the latest developments and applications of BPs,with a focus on the challenges of flow field structure and material fabrication.The specific content covers the BP matrix,types of surface layers,and effect of flow field design on mass transfer.Extended-term growth and feasibility studies of BPs,which can provide a reference and guidance for the configuration of high-behavior flow fields in PEMWEs in the long run,are envisioned.
基金supported by the National Natural Science Foundation of China (Grant No. 52072267)Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems (Grant No. 23DZ2229029)
文摘Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.
基金supported by the National Natural Science Foundation of China(Grant No.U2341269)。
文摘The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.
基金the National Natural Science Foundation of China(U1908225,U1702253)the Special Funds for Ba-sic Research Operations of Central Universities(N182515007,N170908001,N2025004).
文摘Compared with Pidgeon process,the relative vacuum continuous magnesium smelting process reduces the ratio of material to magnesium by changing raw materials and the direct reduction after calcination of prefabricated pellets,so that the energy consumption per ton of magnesium produced is reduced by 30∼40%,and the carbon emission is reduced by 43∼52%,breaking through the vacuum conditions to achieve continuous production.However,in the process of industrialization,it was found that the magnesium yield in the condenser was low.Therefore,this paper constructs a condenser model of relative vacuum continuous magnesium refining process,and comprehensively analyzes the condensation mechanism of magnesium vapor through simulation and experiment.It is found that the dynamic characteristics of magnesium vapor condensation is an important index to measure its continuity.Under the condition offlowing argon as the protective gas,when the condensation plate spacing is 10 cm,the surface roughness amplitude variance is 2,and the carrier gasflow rate is 20×10^(-3) m/s,the magnesium vapor has a better condensation effect,and the condensation efficiency formula is derived.
基金supported by the National Natural Science Foundation of China(52075214and 51975245)the National Key R&D Program of China(No.2022YFE0138500)+3 种基金Jilin Provincial Science&Technology Department(20220201115GX)Key Science and Technology R&D Projects of Jilin Province(2020C023-3)Program of Jilin University Science and Technology Innovative Research Team(2020TD-03)the Fundamental Research Funds for the Central Universities.
文摘Bipolar plate is one of the key components of Proton Exchange Membrane Fuel Cell(PEMFC)and a reasonable flow field design for bipolar plate will improve cell performance.Herein,we have reviewed conventional and bionic flow field designs in recent literature with a focus on bionic flow fields.In particular,the bionic flow fields are summarized into two types:plant-inspired and animal-inspired.The conventional methodology for flow field design takes more time to find the optimum since it is based on experience and trial-and-error methods.In recent years,machine learning has been used to optimize flow field structures of bipolar plates owing to the advantages of excellent prediction and optimization capability.Artificial Intelligence(AI)-assisted flow field design has been summarized into two categories in this review:single-objective optimization and multi-objective optimization.Furthermore,a Threats-Opportunities-Weaknesses-Strengths(TOWS)analysis has been conducted for AI-assisted flow field design.It has been envisioned that AI can afford a powerful tool to solve the complex problem of bionic flow field design and significantly enhance the performance of PEMFC with bionic flow fields.
基金supported by Zhejiang Province Spearhead and Leading Goose Research and Development Key Program(2023C01239)2023 Zhejiang Province“Jianbing”“Lingyan”R&D Research and Development Plan Project-Ultra-Long Endurance Hydrogen-Electric Hybrid Unmanned Aerial Vehicle 2023C01239.
文摘This study uses numerical simulations of liquid cooling flow fields to investigate polymer exchange membrane fuel cell(PEMFC)thermal control.The research shows that the optimum cooling channel design significantly reduces the fuel cell’s temperature differential,improving overall efficiency.Specifically,the simulations show a reduction in the maximum temperature by up to 15%compared to traditional designs.Additionally,according to analysis,the Nusselt number rises by 20%with the implementation of serpentine flow patterns,leading to enhanced heat transfer rates.The findings demonstrate that effective cooling strategies can lead to a 10% increase in fuel cell performance under varying operational conditions,including pressures of 2 bar and relative humidity levels of 30%,60%,and 80%.These results underscore the importance of cooling flow design in optimizing PEMFC performance.
