CFD Analysis of Spiral Flow Fields in Proton Exchange Membrane Fuel Cells

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.

A RHEOLOGICAL MODEL FOR POLYMER MELTS WITH INTERNAL STRUCTURE IN FLOW FIELDS

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.

Hybrid Methods for Computing the Streamfunction and Velocity Potential for Complex Flow Fields over Mesoscale Domains

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.

AN EFFICIENT FINITE-DIFFERENCE ALGORITHM FOR COMPUTING AXISYMMETRIC TRANSONIC NACELLE FLOW FIELDS

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.

Simulation and Analysis on the Two-Phase Flow Fields in a Rotating-Stream-Tray Absorber by Using Computational Fluid Dynamics

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.

Numerical simulation of electro-magnetic and flow fields of TiAl melt under electric field

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.

Influence of slug flow on flow fields in a gas–liquid cylindrical cyclone separator:A simulation study

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.

Effects of harmonic electric field frequency on electromagnetic and flow fields of Ti-Al melt in a rectangular mold based on numerical simulation

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.

Comparative study on the flow fields of three atomization nozzles

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.

Numerical simulation of the dynamic characteristics of flow fields under ice

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.

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

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.

Flow and sound fields of scaled high-speed trains with different coach numbers running in long tunnel

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.

Flow field, sedimentation, and erosion characteristics around folded linear HDPE sheet sand fence: Numerical simulation study

Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.

Numerical simulation of flow field deposition and erosion characteristics around bridge-road transition section

Wind-sand flow generates erosion and deposition around obstacles such as bridges and roadbeds, resulting in sand damage and endangering railway systems in sandy regions. Previous studies have mainly focused on the flow field around roadbeds, overlooking detailed examinations of sand particle erosion and deposition patterns near bridges and roadbeds. This study employs numerical simulations to analyze the influence of varying heights and wind speeds on sand deposition and erosion characteristics at different locations: the bridge-road transition section(side piers), middle piers, and roadbeds. The results show that the side piers, experience greater accumulation than the middle piers. Similarly, the leeward side of the roadbed witnesses more deposition compared to the windward side. Another finding reveals a reduced sand deposition length as the vertical profile, in alignment with the wind direction, moves further from the bridge abutments at the same clearance height. As wind speeds rise, there’s a decline in sand deposition and a marked increase in erosion around the side piers, middle piers and roadbeds. In conclusion, a bridge clearance that’s too low can cause intense sand damage near the side piers, while an extremely high roadbed may lead to extensive surface sand deposition. Hence, railway bridges in areas prone to sandy winds should strike a balance in clearance height. This research provides valuable guidelines for determining the most suitable bridge and roadbed heights in regions affected by wind and sand.

Numerical simulation of melt flow and temperature field during DC casting 2024 aluminium alloy under different casting conditions

Casting speed,casting temperature and secondary cooling water flow rate are the main process parameters affecting the DC casting process.These parameters significantly influence the flow and temperature fields during casting,which are crucial for the quality of the ingot and can determine the success or failure of the casting operation.Numerical simulation,with the advantages of low cost,rapid execution,and visualized results,is an important method to study and optimize the DC casting process.In the present work,a simulation model of DC casting 2024 aluminum alloy was established,and the reliability of the model was verified.Then,the influence of casting parameters on flow field and temperature field was studied in detail by numerical simulation method.Results show that with the increase of casting speed,the melt flow becomes faster,the depths of slurry zone and mushy zone increase,and the variation of slurry zone depth is greater than that of mushy zone.With an increase in casting temperature,the melt flow rate increases,the depth of the slurry zone becomes shallower,and the depth of the mushy zone experiences only minor changes.The simulation results further indicate that the increase of the flow rate of the secondary cooling water slightly reduces the depths of both slurry and mushy zone.

Research on simulation of gun muzzle flow field empowered by artificial intelligence

Artificial intelligence technology is introduced into the simulation of muzzle flow field to improve its simulation efficiency in this paper.A data-physical fusion driven framework is proposed.First,the known flow field data is used to initialize the model parameters,so that the parameters to be trained are close to the optimal value.Then physical prior knowledge is introduced into the training process so that the prediction results not only meet the known flow field information but also meet the physical conservation laws.Through two examples,it is proved that the model under the fusion driven framework can solve the strongly nonlinear flow field problems,and has stronger generalization and expansion.The proposed model is used to solve a muzzle flow field,and the safety clearance behind the barrel side is divided.It is pointed out that the shape of the safety clearance under different launch speeds is roughly the same,and the pressure disturbance in the area within 9.2 m behind the muzzle section exceeds the safety threshold,which is a dangerous area.Comparison with the CFD results shows that the calculation efficiency of the proposed model is greatly improved under the condition of the same calculation accuracy.The proposed model can quickly and accurately simulate the muzzle flow field under various launch conditions.

Flow Field Characteristics of Multi-Trophic Artificial Reef Based on Computation Fluid Dynamics

On the basis of computational fluid dynamics,the flow field characteristics of multi-trophic artificial reefs,including the flow field distribution features of a single reef under three different velocities and the effect of spacing between reefs on flow scale and the flow state,were analyzed.Results indicate upwelling,slow flow,and eddy around a single reef.Maximum velocity,height,and volume of upwelling in front of a single reef were positively correlated with inflow velocity.The length and volume of slow flow increased with the increase in inflow velocity.Eddies were present both inside and backward,and vorticity was positively correlated with inflow velocity.Space between reefs had a minor influence on the maximum velocity and height of upwelling.With the increase in space from 0.5 L to 1.5 L(L is the reef lehgth),the length of slow flow in the front and back of the combined reefs increased slightly.When the space was 2.0 L,the length of the slow flow decreased.In four different spaces,eddies were present inside and at the back of each reef.The maximum vorticity was negatively correlated with space from 0.5 L to 1.5 L,but under 2.0 L space,the maximum vorticity was close to the vorticity of a single reef under the same inflow velocity.

Analysis of the Flow Field and Impact Force in High-Pressure Water Descaling

This study aims to improve the performances of the high-pressure water descaling technology used in steel hot rolling processes.In particular,a 2050 mm hot rolling line is considered,and the problem is investigated by means of a fluid–structure interaction(FSI)method by which the descaling effect produced by rolling coils with different section sizes is examined.Assuming a flat fan-shaped nozzle at the entrance of the R1R2 roughing mill,the outflow field characteristics and the velocity distribution curve on the strike line(at a target distance of 30–120 mm)are determined.It is found that the velocity in the center region of the water jet with different target distances is higher than that in the boundary region.As the target distance increases,the velocity of the water jet in the central region decreases.Through comparison with experimental results,it is shown that the simulation model can accurately predict the impact position of the high-pressure water on the impact plate,thereby providing a computational scheme that can be used to optimize the nozzle space layout and improve the slabs’descent effect for different rolling specifications.

AN EXPERIMENTAL STUDY ON THE FLOW FIELDS OF THE WEST LAKE BY ELECTRO-HYDRODYNAMIC ANALOGUE METHOD

Electro hydrodynamic analogue (EHA) method is applied to study the flow fields in the West Lake. It gives out a satisfactory result on water velocities and discharges of the bridge openings.

Numerical Investigation of the Multiphase Flow Originating from the Muzzle of Submerged Parallel Guns

A two-dimensional model,employing a dynamic mesh technology,is used to simulate numerically the transient multiphaseflowfield produced by two submerged parallel guns.After a grid refinement study ensuring grid inde-pendence,five different conditions are considered to assess the evolution of cavitation occurring in proximity to the gun muzzle.The simulation results show thatflow interference is enabled when the distance between the par-allel barrels is relatively small;accordingly,the generation and evolution of the vapor cavity becomes more com-plex.By means of the Q criterion for vorticity detection,it is shown that cavitation causes the generation of vorticity and the evolution of the vapor cavity can result in an asymmetric distribution of vorticity for a certain distance of the barrels.In particular,the evolution of the vapor cavity can hinder the expansion of the gas and force it toflow outward,while an asymmetric distribution of vorticity can lead to a gas jetflowing outward and rotating simultaneously.