Simulation method for coupled transport and phase transition of snow and water in train bogie region

Abstract

The application provides a train bogie area wind-snow-water-ice coupling transport and phase state conversion simulation method, comprising the following steps: constructing a three-dimensional model of a train bogie and a train body, and performing mesh division on the model; constructing a train bogie area wind-snow-water-ice multi-phase coupling transport and phase state conversion numerical simulation model; setting initial conditions and boundary conditions; based on the constructed model, performing numerical simulation on the phase change and accumulation deformation process of the train bogie area in the ice and snow accumulation process; post-processing the numerical simulation calculation results, and analyzing the snow-water-ice complex conversion mechanism of the train bogie area and the phase change and deformation in the ice and snow accumulation process. The application can better simulate and analyze the snow-water-ice complex conversion mechanism of the train bogie area and the phase change and deformation in the ice and snow accumulation process, and accurately capture the multi-physical field coupling and multi-phase state conversion law in the snow accumulation and icing process of the train bogie area.

Description

Technical Field

[0001] This invention relates to the field of snow and ice accumulation analysis technology for railway bogies, and particularly to a simulation method for coupled wind, snow, water and ice transport and phase transition in the bogie region. Background Technology

[0002] Snow and ice accumulation in the bogie area is critical to the safe operation of rail trains. When rail trains operate for extended periods in windy and snowy environments, ambient winds carry snowflakes into the bogies. When numerous vortices exist during the travel of the train, the snowflakes attract each other within these vortices and subsequently adhere to and accumulate on nearby structural surfaces. The flow field in the bogie area is disturbed by the snow accumulation, altering the flow field structure and exacerbating snow formation. Furthermore, the braking system generates significant heat during braking, causing the snow on the bogies to melt, and the melted water quickly reverts to ice. Elastic components in the bogie area, such as air springs and axle box springs, also generate heat during train movement, causing surrounding snow to melt and turn into ice. This ice deposited on the bogies increases sprung mass, deteriorates the spring constant, affects the dynamic performance of the rail train, and threatens operational safety. When rail trains operate in extremely cold conditions, large-scale snow accumulation in the bogie area can occur, thus affecting the operational stability of the rail train.

[0003] In existing technologies, numerical simulation methods for analyzing snow icing in the bogie area of ​​railway trains mostly employ a two-phase flow method combining snow particle motion and airflow turbulence. The mechanistic analysis of snow icing in the bogie area remains at the stage of analyzing airflow trends and snow particle motion characteristics, without in-depth analysis of the phase transition and accumulation deformation processes of snow icing. Furthermore, anti-icing technologies are only applicable to optimizing the snow and wind trajectory in the bogie area and cannot effectively control the propulsion path of the liquid film on the surface of heating components and the trajectory of water droplets in space. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a numerical simulation method that can simulate the multiphase coupled transport of wind, snow, water, and ice in the bogie region, the process of snow melting, water film propulsion, solidification and icing on the surface of heating components in the bogie region, and the collision and icing of water droplets on the surface of insulation components, thereby obtaining the spatiotemporal evolution characteristics of multiphase coupled transport of wind, snow, water, and ice in the bogie region of railway vehicles.

[0005] To achieve the above objectives, this invention provides a simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region, comprising the following steps:

[0006] S1. Construct a 3D model of the rail train bogie and car body, and mesh the model.

[0007] S2. A numerical simulation model of multiphase coupled transport and phase transition of wind, snow, water, and ice in the bogie region of a rail vehicle is constructed. The constructed model includes: a coupled transport model that treats the air phase as a continuous phase and snow particles / stripping droplets as discrete phases to simulate the complex flow field structure in the bogie region; a snow particle-wall interaction behavior discrimination model to determine the splashing, rebounding, sliding, and adhesion states of snow particles on the liquid film surface; a melting-solidification model to simulate the snow particle melting and freezing phase transition process; a condensation and icing model to simulate the icing deformation process on the bogie surface; and a liquid film propulsion model to simulate the droplet stripping evolution process.

[0008] S3, set initial and boundary conditions;

[0009] S4, based on the model constructed in S2, numerically simulates the snow and ice accumulation in the bogie area of ​​a railcar;

[0010] S5 performs post-processing on the numerical simulation results to analyze the complex phase transition mechanism of snow-water-ice in the bogie region, as well as the phase change and accumulation deformation during the snow and ice accumulation process.

[0011] Furthermore, S1 includes the following sub-steps:

[0012] S11, construct a three-dimensional model of the rail train bogie, car body and computational domain;

[0013] S12, perform volume mesh generation on the computational domain and establish a volume mesh model of the computational domain;

[0014] S13. Considering the snow-water-ice phase transformation evolution of all important structural surfaces of the bogie of the railcar, a surface mesh model of the car body and bogie is established to accurately simulate the multiphase coupled transport and phase transition mechanism of wind-snow-water-ice in the bogie region.

[0015] Furthermore, in S12, the mesh density is planned according to the flow characteristics and analysis requirements. The volume mesh around the car body is densified to accurately simulate the gas phase flow around the car body; the volume mesh in the bogie area is further densified to accurately simulate the micro vortex structure in the bogie area and accurately capture the movement trajectory of snow particles.

[0016] Furthermore, S2 includes the following sub-steps:

[0017] S21, Construct a coupled transport model that treats the air phase as a continuous phase and the snow / stripping droplets as a discrete phase: Construct a turbulence model to simulate the air flow field; Simulate the mechanical interaction between the snow / stripping droplets and the air flow field through drag effect function and lift effect function;

[0018] S22, construct a snow particle-wall interaction behavior discrimination model: if the snow particle's movement speed is less than the threshold capture speed, the snow particle's movement state after interacting with the wall is splashing or bouncing; then determine the relationship between the snow particle diameter and the minimum splash diameter. If the snow particle diameter is greater than or equal to the minimum splash diameter, the snow particle's movement state is splashing; if the snow particle diameter is greater than or equal to the minimum splash diameter, the snow particle's movement state is bouncing.

[0019] If the speed of the snow particles is greater than or equal to the threshold capture speed, the snow particles are either sliding or adhering. Then, determine the relationship between the wall friction speed and the threshold friction speed. If the wall friction speed is greater than or equal to the threshold friction speed, the snow particles slide after interacting with the wall. If the wall friction speed is less than the threshold friction speed, the snow particles are adhering after interacting with the wall.

[0020] S23, Constructing a melting-solidification model: The Lagrange collision model is used to simulate the collision effect of snow particles on the liquid film; the enthalpy formula is used to realize the phase composition characteristics of the bogie surface;

[0021] S24, Construct a condensation icing model to simulate the icing deformation process on the surface of a rail train bogie. Use icing mass removal and mesh deformation reconstruction techniques to simulate the evolution of the icing profile on the surface of the rail train bogie.

[0022] S25, Construct a liquid film propulsion model to simulate the droplet peeling evolution process, and use the peeling model to simulate the phenomenon of melted droplets peeling off the bogie surface.

[0023] Furthermore, the airflow field simulation in S21 can be carried out using the separated eddy (DES) or unsteady Reynolds-averaged flow (URANS) method based on the SST k-ω or Realizable k-ε turbulence model, with the near-wall surface treated as a full y+wall surface.

[0024] For the drag effect function and the lift effect function, assuming the snow particles / stripping droplets are spherical particles with smooth surfaces, their basic equation of motion is given by the following basic momentum conservation equation:

[0025]

[0026] Where v p F represents the instantaneous particle velocity. s It is the resultant force of the forces acting on the particle surface, F. b It is the resultant force of volume forces;

[0027] These forces can be decomposed into:

[0028] F s =F d +F p +F vm

[0029] F b =F g +F MRF +F u +F c +F Co

[0030] Where F d For drag force, F p For pressure gradient force, F vm For virtual mass force, F g For gravity, F u For a custom volume force, F c For contact force, F Co Coulomb force;

[0031] The drag force experienced by snow particles / exfoliated droplets in the air phase is given by the following drag force function:

[0032]

[0033] Among them, C d Let ρ be the drag coefficient of the particles, ρ be the density of the air phase, and v be the drag coefficient of the particles. s =vv p Let v be the particle slip velocity, v be the instantaneous velocity of the air phase, and A be the particle slip velocity. p This represents the projected area of ​​the particle.

[0034] The drag coefficient in the drag function is given by the Schiller-Naumann drag model:

[0035]

[0036] Among them, Re p It is the Reynolds number of the particle, and its function is defined as follows:

[0037]

[0038] Among them, D p is the particle diameter, μ is the dynamic viscosity;

[0039] The pressure gradient force experienced by snow particles / exfoliated droplets in the air phase is given by the following definition:

[0040]

[0041] Among them, V p It is the volume of the particle. It is the gradient of static pressure in the air phase;

[0042] The virtual mass force experienced by snow particles / exfoliated droplets in the air phase is given by the following function:

[0043]

[0044] Among them, C vm It is a virtual mass coefficient, which can be taken as 0.5, assuming that the particles are in a uniform, non-viscous, incompressible flow.

[0045] Furthermore, the threshold capture speed in S22 Threshold friction speed Minimum splash diameter Given the setting, the speed u of the snow particles p and snow grain diameter d p The snow particle diameter and wall friction velocity u were obtained through simulation. * The calculation methods include the following two:

[0046] Calculated using the formula:

[0047] u * =(τ / ρ) 1 / 2

[0048] Where τ is the shear force generated by the snow surface, and ρ is the air density;

[0049] Calculations can be made using the logarithmic law of wind speed profiles:

[0050]

[0051] Where k is the von Kármán coefficient, taken as 0.4, z0 is the ground roughness height, and z is the effective height.

[0052] Furthermore, the enthalpy formula in S23 is:

[0053] h ls * =h ls +(1-Y s * )h fusion

[0054] Among them, h ls For enthalpy, relative mass fraction Y s * Defined as the mass fraction of the water film - ice film occupied by ice cubes, relative to the mass fraction of ice cubes, Y. s * A function of temperature:

[0055]

[0056] Among them, T * Standardized temperature as defined:

[0057]

[0058] Among them, the function f(T) * This is called the fractional solid-phase curve, for Y s * and T * The linear dependence between them is defined by the solidification path as:

[0059] f(T * ) = 1 - T * .

[0060] Furthermore, S25 includes: modeling the breakup process of the liquid film on an acute-angled edge using an edge-peeling model; and modeling the breakup process of the liquid film surface using a wave-peeling model.

[0061] Edge spalling models for modeling the breakup process of liquid films on acute-angled edges include: edge spalling model for co-directional fluids and edge spalling model for anti-directional fluids;

[0062] For edge stripping of fluids in the same direction, the ratio FR of liquid film momentum flux to surface tension and gravity is calculated by the following formula:

[0063]

[0064] Among them, We f For the liquid film Weber number, Bo f For Bond number, L b h is the breaking length. f The liquid film thickness is given; the liquid film Weber number is as follows:

[0065]

[0066] Where, ρ f v is the density of the liquid film. f h is the velocity of the liquid film whose projection direction is orthogonal to the peeling edge. f Let σ be the liquid film thickness and σ be the surface tension; the Bond number for the thin film is as follows:

[0067]

[0068] Among them, g θ The acceleration component is perpendicular to the downstream wall; the breaking length is defined by the following formula:

[0069] L b =0.0388h f 0.5 Re f 0.6 We rel -0.5

[0070] Among them, Re f For the liquid film Reynolds number, Werel The relative Weber number is: The liquid film Reynolds number is:

[0071]

[0072] Where, μ f The viscosity is dynamic; the relative Weber number is as follows:

[0073]

[0074] Where ρ is the gas density, v g The gas velocity component perpendicular to the stripping edge;

[0075] If FR>FR c This can be considered as a breakage process, resulting in droplet peeling; in the fluid that has passed through the peeled edge, only a small portion of x remains. s Separated from the liquid film, this fraction can be approximated using the following formula:

[0076]

[0077] For edge stripping of anisotropic fluids, if the fluids move from both sides towards one side, they will merge into a series of Lagrange droplets that obey the laws of conservation of mass, momentum, composition, and energy; for anisotropic fluids, the stripping fraction x on both sides... s When set to 1, the droplet diameter is calculated based on the film properties on the side with the highest flux.

[0078] When modeling the breakup process of a liquid film surface using the wave stripping model, the liquid film stripping model is divided into three stages: after the wave develops at the liquid-gas interface, the liquid film surface becomes unstable → the ejected fluid volume forms a cylinder → the cylinder decomposes into droplets. The most unstable wavelength is the wavelength most likely to break up on the surface, and this wavelength is calculated as the resonant wavelength using the dissipation equation.

[0079]

[0080] in, It is the square of the relative velocity between the liquid film and the surrounding fluid (v) f -v)·(v f -v), σ is surface tension, f b It is the volume force (including inertial force) acting on the liquid film;

[0081] The minimum liquid film height required for droplet ejection is:

[0082]

[0083] The height of the liquid film to be peeled off is:

[0084]

[0085] The diameter of the generated droplets is:

[0086]

[0087] Among them, c D The value is set to 3.78;

[0088] All droplets initially have the same velocity as the liquid film and are placed at a point between the center of the grid cell and the center of the boundary surface.

[0089] Furthermore, in S5, post-processing yields the distribution characteristics of strong shear flow in the bogie region, the trajectory and concentration distribution of snow particles, the initial position of the liquid film formed after the snow adhering to the surface of the heating component melts after heat absorption, the propulsion and development trend of the liquid film on the surface of the heating component, the distribution and contour deformation evolution of ice on the surface of important components, and the phase evolution process of peeling droplets from the heating component to the surface of the insulating component through peeling-impact-icing, and these processes are analyzed.

[0090] The above-described solution of the present invention has the following beneficial effects:

[0091] The present invention provides a simulation method for coupled transport and phase transition of wind, snow, water, and ice in the bogie region. This method simulates the complex flow field structure in the bogie region by constructing a coupled transport model that treats air as a continuous phase and snow / snowdroplets as discrete phases; constructing a snow-wall interaction behavior discrimination model to determine the splashing, rebounding, sliding, and adhesion states of snow particles on the liquid film surface; constructing a melting-solidification model to simulate the snow melting and freezing phase transition process; constructing a condensation and icing model to simulate the icing deformation process on the bogie surface; and constructing a liquid film propulsion model to simulate the droplet stripping evolution process. Ultimately, the method yields the distribution characteristics of strong shear flow in the bogie region. The analysis of snow particle trajectory and concentration distribution, the initial position of the liquid film formed after the snow adhering to the surface of the heating component melts after heat absorption, the advancement and development trend of the liquid film on the surface of the heating component, the ice distribution and contour deformation evolution process on the surface of important components, and the phase evolution process of peeling droplets from the heating component to the surface of the insulation component through peeling-impact-icing, etc., can better analyze the complex snow-water-ice conversion mechanism and ice and snow accumulation in the bogie area of ​​railway trains. Compared with the wind and snow two-phase flow analysis in the existing technology, it is more reasonable and accurate, and can provide better guidance for snow prevention / removal measures in the bogie area of ​​railway trains.

[0092] Other beneficial effects of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0093] Figure 1 This is a flowchart of the steps of the present invention;

[0094] Figure 2 This is a diagram illustrating the snow particle-wall interaction behavior discrimination process of the present invention;

[0095] Figure 3 This is a schematic diagram of the edge stripping model of the same-direction fluid of the present invention;

[0096] Figure 4 This is a schematic diagram of the edge peeling model of the anisotropic fluid of the present invention;

[0097] Figure 5 This is a schematic diagram of the three-stage process of the liquid film peeling model of the present invention;

[0098] In the figure, 1 represents the bogie wall, 2 represents the liquid film on the bogie surface, 3 represents the edge peeling droplets, 4 represents the sprayed liquid, and 5 represents the detached droplets. Detailed Implementation

[0099] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0100] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0101] It should also be noted that the illustrations provided in the following embodiments are merely schematic representations of the basic concept of this disclosure. The illustrations only show components relevant to this disclosure and are not drawn according to the actual number, shape, and size of components in implementation. In actual implementation, the type, quantity, and proportion of each component can be arbitrarily changed, and the component layout may be more complex. Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0102] like Figure 1 As shown, an embodiment of the present invention provides a simulation method for coupled wind, snow, water, and ice transport and phase transition in the bogie region of a train, specifically including the following steps:

[0103] S1. Construct a 3D model of the train bogie and car body, and mesh the model. This step specifically includes the following sub-steps:

[0104] S11, construct a three-dimensional model of the rail train bogie, car body, and computational domain.

[0105] It should be noted that this method is primarily used to investigate the multiphase coupled transport and phase transition mechanism of wind, snow, water, and ice in the bogie region of railway vehicles. The influence of the pantograph and air conditioning structure on the roof surface on the multiphase coupled transport and phase transition of wind, snow, water, and ice in the bogie region of railway vehicles can be ignored. Furthermore, the fine structures on the roof surface will reduce the simulation efficiency and significantly increase the simulation cost. Therefore, when using this method, the pantograph, air conditioning, and other fine structures on the top of the car body can be ignored. Understandably, the 3D model must fully preserve all important components and fine structures of the bogie, such as air springs, frames, traction motors, gearboxes, brake calipers, motor mounts, traction rods, and axle boxes.

[0106] S12, perform volume mesh generation on the computational domain and establish a volume mesh model of the computational domain to accurately simulate the gas phase flow characteristics in the computational domain and precisely capture the trajectory of snow particles.

[0107] It should be noted that the mesh density can be planned according to the flow characteristics and analysis requirements. The volume mesh around the car body can be densified to accurately simulate the gas flow around the car body, and the volume mesh in the bogie area can be further densified to accurately simulate the micro vortex structure in the bogie area and accurately capture the movement trajectory of snow particles.

[0108] S13. Establish surface mesh models of the car body and bogies to accurately simulate the multiphase coupled transport and phase transition mechanism of wind, snow, water, and ice in the bogie region of the railway train. This requires considering the snow phase transformation evolution on all important structural surfaces of the bogie, and surface meshes are set on the car body and bogie surfaces. When setting the surface mesh model, specific considerations can be made based on the size of the 3D model structure, while ensuring no distortion. Furthermore, to ensure a smooth transition between the surface mesh and the volume mesh, in this specific case, a multi-layered prism layer with a specific growth rate in the normal dimension is set between them.

[0109] S2. Construct a numerical simulation model of multiphase coupled transport and phase transition of wind, snow, water and ice in the bogie area of ​​rail vehicles.

[0110] The constructed models include: a coupled transport model that treats the air phase as a continuous phase and the snow / stripping droplets as discrete phases to simulate the complex flow field structure in the bogie region; a snow-wall interaction behavior discrimination model to determine the splashing, rebounding, sliding, and adhesion states of snow particles on the liquid film surface; a melting-solidification model to simulate the snow melting and freezing phase transition process; a condensation and icing model to simulate the icing deformation process on the bogie surface; and a liquid film propulsion model to simulate the droplet stripping evolution process.

[0111] This step specifically includes:

[0112] S21, Construct a coupled transport model that treats the air phase as a continuous phase and the snow particles / stripping droplets as discrete phases, specifically including:

[0113] To simulate the airflow field, a turbulence model is constructed. In specific cases, the separated eddy (DES) method or the unsteady Reynolds time-averaged (URANS) method based on the SST k-ω or Realizable k-ε turbulence model can be used. The near-wall surface is treated as a full y+wall surface.

[0114] The mechanical interaction between snow / stripping droplets and the airflow field is simulated using drag and lift effect functions. Assuming the snow / stripping droplets are spherical particles with smooth surfaces, their fundamental equation of motion is given by the following basic momentum conservation equation:

[0115]

[0116] Where v p F represents the instantaneous particle velocity. s It is the resultant force of the forces acting on the particle surface, F. b It is the resultant force of volume forces.

[0117] These forces can be decomposed into:

[0118] F s =F d +Fp +F vm

[0119] F b =F g +F MRF +F u +F c +F Co

[0120] Where F d For drag force, F p For pressure gradient force, F vm For virtual mass force, F g For gravity, F u For a custom volume force, F c For contact force, F Co It is the Coulomb force.

[0121] The drag force experienced by snow particles / exfoliated droplets in the air phase is given by the following drag force function:

[0122]

[0123] Among them, C d Let ρ be the drag coefficient of the particles, ρ be the density of the air phase, and v be the drag coefficient of the particles. s =vv p Let v be the particle slip velocity, v be the instantaneous velocity of the air phase, and A be the particle slip velocity. p This represents the projected area of ​​the particle.

[0124] The drag coefficient in the drag function is given by the Schiller-Naumann drag model:

[0125]

[0126] Among them, Re p It is the Reynolds number of the particle, and its function is defined as follows:

[0127]

[0128] Among them, D p is the particle diameter, and μ is the dynamic viscosity.

[0129] The pressure gradient force experienced by snow particles / exfoliated droplets in the air phase is given by the following definition:

[0130]

[0131] Among them, V p It is the volume of the particle. It is the gradient of static pressure in the air phase.

[0132] The virtual mass force experienced by snow particles / water droplets in the air phase is given by the following function:

[0133]

[0134] Among them, C vm It is a virtual mass coefficient, which can be taken as 0.5, assuming that the particles are in a uniform, non-viscous, incompressible flow.

[0135] S22, Construct a snow particle-wall interaction behavior discrimination model;

[0136] The snow particle-wall interaction behavior discrimination model can determine the relationship between the snow particle's velocity and the threshold capture velocity. If the snow particle's velocity is less than the threshold capture velocity, the snow particle's motion after interacting with the wall is either splashing or bouncing. It further determines the relationship between the snow particle's diameter and the minimum splash diameter. If the snow particle's diameter is greater than or equal to the minimum splash diameter, the snow particle's motion is splashing; otherwise, it is bouncing. If the snow particle's velocity is greater than or equal to the threshold capture velocity, the snow particle's motion is either sliding or adhering. Finally, it determines the relationship between the wall friction velocity and the threshold friction velocity. If the wall friction velocity is greater than or equal to the threshold friction velocity, the snow particle slides after interacting with the wall; otherwise, it adheres to the wall.

[0137] The specific judgment process is as follows: Figure 2 As shown, the threshold capture speed Threshold friction speed Minimum splash diameter Snow grain diameter d p The velocity u of the snow particles is given by the user. p The snow particle diameter and wall friction velocity u were obtained through simulation. * There are two main methods for calculating it:

[0138] Calculated using the formula:

[0139] u * =(τ / ρ) 1 / 2

[0140] Where τ is the shear force generated by the snow surface, and ρ is the air density.

[0141] Calculations can be made using the logarithmic law of wind speed profiles:

[0142]

[0143] Where k is the von Kármán coefficient, taken as 0.4, z0 is the ground roughness height, and z is the effective height.

[0144] S23, Construct a melting-solidification model, specifically including: using the Lagrange collision model to simulate the collision effect of snow particles on the liquid film; and using the enthalpy formula to realize the phase composition characteristics of the bogie surface.

[0145] The enthalpy formula is used to determine the distribution of the melted water film and condensed ice:

[0146] h ls * =h ls +(1-Y s * )h fusion

[0147] Among them, h ls For enthalpy, relative mass fraction Y s * h is defined as the mass fraction of the water film - ice film occupied by the ice cube. fusion To integrate latent heat, h ls * Let Y be the enthalpy of the melting water film and the condensation ice film. In this enthalpy model, the relative ice mass fraction Y is... s * A function of temperature:

[0148]

[0149] Among them, T * Standardized temperature as defined:

[0150]

[0151] Among them, T solidus T is the solid-state temperature. liquidus Let T be the liquid phase temperature. The function f(T) * This is called the fractional solid-phase curve, for Y s * and T * The linear dependence between them is defined by the solidification path as:

[0152] f(T * ) = 1 - T *

[0153] S24, Construct a condensation icing model to simulate the icing deformation process on the bogie surface, and use icing mass removal and mesh deformation reconstruction techniques to simulate the evolution of the icing profile on the surface of the rail train bogie;

[0154] In this embodiment, when removing the solidified mass using both icing mass removal and deformation model removal, a mesh deformation reconstruction technique is used to adjust the surface of the solidified volume, thereby simulating the evolution of the icing profile on the bogie surface. During each time step of the numerical simulation, the solid film thickness increment Δh is calculated.s And it is updated during each internal iteration of the separation process. Wherein, Δh s This indicates the increase in cured thickness during the time step.

[0155] S25, Construct a liquid film propulsion model to simulate the droplet peeling evolution process. The peeling model is used to simulate the phenomenon of melting droplet peeling on the bogie surface, including: using an edge peeling model to model the breakup process of the liquid film on the acute edge; and using a wave peeling model to model the breakup process of the liquid film surface.

[0156] Among them, the edge peeling model for modeling the breakup process of liquid film on acute-angled edges includes: edge peeling model for co-directional fluids and edge peeling model for anti-directional fluids.

[0157] For edge stripping of fluids flowing in the same direction, the schematic diagram is as follows: Figure 3 As shown, where θ is the included angle of the bogie surface, g θ The acceleration component is perpendicular to the downstream wall. The ratio FR of the liquid film momentum flux to surface tension and gravity is calculated by the following formula:

[0158]

[0159] Among them, We f For the liquid film Weber number, Bo f For Bond number, L b h is the breaking length. f Let be the liquid film thickness. The liquid film Weber number is as follows:

[0160]

[0161] Where, ρ f v is the density of the liquid film. f h is the velocity of the liquid film whose projection direction is orthogonal to the peeling edge. f Let be the liquid film thickness, and σ be the surface tension. The Bond number for thin films is as follows:

[0162]

[0163] Among them, g θ This represents the acceleration component perpendicular to the downstream wall. The breakage length is defined by the following formula:

[0164] L b =0.0388h f 0.5 Re f 0.6 We rel -0.5

[0165] Among them, Re fFor the liquid film Reynolds number, We rel This is the relative Weber number. The liquid film Reynolds number is:

[0166]

[0167] Where, μ f This refers to the dynamic viscosity. The relative Weber number is as follows:

[0168]

[0169] Where ρ is the gas density, v g The gas velocity component is perpendicular to the stripping edge.

[0170] If FR > FR c , of which FR c Setting it to the default value of 1 can be considered as a breakage process, resulting in droplet peeling. In the fluid that has passed the peeled edge, only a small portion of x... s Separated from the liquid film, this fraction can be approximated using the following formula:

[0171]

[0172] For edge spalling of anisotropic fluids, the schematic diagram is as follows: Figure 4 As shown, if fluids move from both sides towards one side, they will merge into a series of Lagrangian droplets that obey the laws of conservation of mass, momentum, composition, and energy. For example, if the two fluids have different temperatures, the droplet temperature is set to a value between the two. For countercurrent fluids, the separation fraction x on both sides... s Set to 1 (indicating complete stripping), the droplet diameter is calculated based on the film properties on the side with the highest flux.

[0173] When modeling the breakup process of a liquid film surface using a wave stripping model, instability occurs on the liquid film surface due to adjacent fluid flows and volume forces (such as gravity and liquid film acceleration), causing droplets to detach. This liquid film stripping model is divided into three stages, as follows: Figure 5 As shown: Waves develop at the liquid-gas interface, the liquid film surface is unstable (a) → the ejected fluid volume forms a cylinder (b) → the cylinder decomposes into droplets (c), where h f Let be the height of the liquid film on the bogie surface, and u be the velocity of the detached droplets. The most unstable wavelength is the wavelength most likely to experience surface breakage; this wavelength is calculated as the resonant wavelength using the dissipation equation:

[0174]

[0175] in, It is the square of the relative velocity between the liquid film and the surrounding fluid (v) f -v)·(vf -v), σ is surface tension, f b It is the volume force (including inertial force) acting on the liquid film.

[0176] The minimum liquid film height required for droplet ejection is:

[0177]

[0178] The height of the liquid film to be peeled off (i.e., the surface wave amplitude value) is:

[0179]

[0180] The diameter of the generated droplets is:

[0181]

[0182] Among them, c D The value is set to 3.78, which means that the diameter of each droplet generated from the cylinder is 3.78 times the diameter of the cylinder. All droplets initially have the same velocity as the liquid film and are placed at a point between the center of the grid cell and the center of the boundary surface, depending on the radius of the ejected droplet.

[0183] S3 sets the initial and boundary conditions.

[0184] Specifically, in this embodiment, the initial conditions to be set include setting the operating status of the rail train and the Lagrange parameters of the snow particles: setting the operating status of the rail train includes setting the speed level, ambient temperature, snowfall concentration, and air humidity. The ambient snowfall concentration can be obtained experimentally, and the snowfall concentration is set by controlling the input amount of snow particles through the particle flow rate in the injector; setting the Lagrange parameters of the snow particles includes the size diameter, humidity, viscosity, etc. The physical parameters of the snow particles can be obtained from field experiments, and the snow particle diameter and the spatiotemporal spraying can be randomized according to a custom function.

[0185] Boundary conditions are set for the car body surface and the bogie surface. Considering that snow particles will collide and bounce when they encounter the car body surface, more snow particles will randomly enter the bogie area and undergo phase change evolution on the bogie surface, resulting in ice accumulation. Therefore, the car body surface is set as the bounce boundary, and the bogie surface is set as a liquid film boundary with an initial thickness of 0, in order to consider the complex phase evolution of snow melting, liquid film propulsion, and condensation icing on the surface of the heating components in the bogie area, as well as the analysis of water droplet collision and icing on the surface of the insulating components.

[0186] S4, based on the model constructed in S2, numerically simulates the evolution of the icing profile on the surface of the railway train bogie. As a preferred implementation, the mesh structure and scale of the icing bogie surface are adjusted in real time using a mesh adaptive dynamic deformation algorithm.

[0187] S5 performs post-processing on the numerical simulation results to analyze the complex snow-water-ice conversion mechanism and ice and snow accumulation in the bogie area.

[0188] The post-processing process yields the distribution characteristics of strong shear flow in the bogie region, the trajectory and concentration distribution of snow particles, the initial position of the liquid film formed after the snow adhering to the surface of the heating component melts, the propulsion and development trend of the liquid film on the surface of the heating component, the distribution and contour deformation evolution of ice on the surface of important components, and the phase evolution process of peeling droplets from the heating component to the surface of the insulating component through peeling-impact-icing. By analyzing these processes, the complex snow-water-ice conversion mechanism and snow and ice accumulation in the bogie region can be analyzed. Compared with the two-phase flow analysis of wind and snow, this method is more reasonable and accurate, and can provide better guidance for snow prevention / removal measures in the bogie region of railway trains.

[0189] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0190] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A simulation method for coupled wind, snow, water, and ice transport and phase transition in the bogie region of a train, characterized in that, Includes the following steps: S1. Construct a 3D model of the train bogie and car body, and mesh the model. S2, construct a numerical simulation model of multiphase coupled transport and phase transition of wind-snow-water-ice in the train bogie region; The constructed models include: a coupled transport model that treats the air phase as a continuous phase and the snow / stripping droplets as discrete phases to simulate the complex flow field structure in the bogie region; a snow-wall interaction behavior discrimination model to determine the splashing, rebounding, sliding, and adhesion states of snow particles on the liquid film surface; a melting-solidification model to simulate the snow melting and freezing phase transition process; a condensation and icing model to simulate the icing deformation process on the bogie surface; and a liquid film propulsion model to simulate the droplet stripping evolution process. S2 includes the following sub-steps: S21, Construct a coupled transport model that treats the air phase as a continuous phase and the snow / stripping droplets as a discrete phase: Construct a turbulence model to simulate the air flow field; Simulate the mechanical interaction between the snow / stripping droplets and the air flow field through drag effect function and lift effect function; S22, construct a snow particle-wall interaction behavior discrimination model: if the snow particle's movement speed is less than the threshold capture speed, the snow particle's movement state after interacting with the wall is splashing or bouncing; then determine the relationship between the snow particle diameter and the minimum splash diameter. If the snow particle diameter is greater than or equal to the minimum splash diameter, the snow particle's movement state is splashing; if the snow particle diameter is greater than or equal to the minimum splash diameter, the snow particle's movement state is bouncing. If the speed of the snow particles is greater than or equal to the threshold capture speed, the snow particles are either sliding or adhering. Then, determine the relationship between the wall friction speed and the threshold friction speed. If the wall friction speed is greater than or equal to the threshold friction speed, the snow particles slide after interacting with the wall. If the wall friction speed is less than the threshold friction speed, the snow particles are adhering after interacting with the wall. S23, Constructing a melting-solidification model: The Lagrange collision model is used to simulate the collision effect of snow particles on the liquid film; the enthalpy formula is used to realize the phase composition characteristics of the bogie surface; S24, Construct a condensation icing model to simulate the icing deformation process on the surface of a rail train bogie. Use icing mass removal and mesh deformation reconstruction techniques to simulate the evolution of the icing profile on the surface of the rail train bogie. S25, Construct a liquid film propulsion model to simulate the droplet peeling evolution process, and use the peeling model to simulate the phenomenon of melted droplets peeling off the bogie surface; S3, set initial and boundary conditions; S4, based on the model constructed in S2, numerically simulates the snow and ice accumulation in the bogie area of ​​a railcar; S5 performs post-processing on the numerical simulation results to analyze the complex phase transition mechanism of snow-water-ice in the bogie region, as well as the phase change and accumulation deformation during the snow and ice accumulation process.

2. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 1, characterized in that, S1 includes the following sub-steps: S11, construct a three-dimensional model of the rail train bogie, car body and computational domain; S12, perform volume mesh generation on the computational domain and establish a volume mesh model of the computational domain; S13. Considering the snow-water-ice phase transformation evolution of all important structural surfaces of the bogie of the railcar, a surface mesh model of the car body and bogie is established to accurately simulate the multiphase coupled transport and phase transition mechanism of wind-snow-water-ice in the bogie region.

3. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 2, characterized in that, In S12, the mesh density is planned according to the flow characteristics and analysis requirements. The volume mesh around the car body is densified to accurately simulate the gas phase flow around the car body. The volume mesh in the bogie area is further densified to accurately simulate the micro vortex structure in the bogie area and accurately capture the movement trajectory of snow particles.

4. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 1, characterized in that, The airflow field simulation in S21 can be carried out using the separated vortex or unsteady Reynolds time-averaged method based on the SST k-ω or Realizable k-ε turbulence model, with the near-wall surface treated as a full y+wall surface. For the drag effect function and the lift effect function, assuming the snow particles / stripping droplets are spherical particles with smooth surfaces, their basic equation of motion is given by the following basic momentum conservation equation: Where v p F represents the instantaneous particle velocity. s It is the resultant force of the forces acting on the particle surface, F. b It is the resultant force of volume forces; These forces can be decomposed into: F s =F d +F p +F vm F b =F g +F MRF +F u +F c +F Co Where F d For drag force, F p For pressure gradient force, F vm For virtual mass force, F g For gravity, F u For a custom volume force, F c For contact force, F Co Coulomb force; The drag force experienced by snow particles / exfoliated droplets in the air phase is given by the following drag force function: Among them, C d Let ρ be the drag coefficient of the particles, ρ be the density of the air phase, and v be the drag coefficient of the particles. s =vv p Let v be the particle slip velocity, v be the instantaneous velocity of the air phase, and A be the particle slip velocity. p The projected area of ​​the particle; The drag coefficient in the drag function is given by the Schiller-Naumann drag model: Among them, Re p It is the Reynolds number of the particle, and its function is defined as follows: Among them, D p is the particle diameter, μ is the dynamic viscosity; The pressure gradient force experienced by snow particles / exfoliated droplets in the air phase is given by the following definition: Among them, V p It is the volume of the particle. It is the gradient of static pressure in the air phase; The virtual mass force experienced by snow particles / exfoliated droplets in the air phase is given by the following function: Among them, C vm It is a virtual mass coefficient, which can be taken as 0.5, assuming that the particles are in a uniform, non-viscous, incompressible flow.

5. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 1, characterized in that, Threshold capture speed in S22 Threshold friction speed Minimum splash diameter Snow grain diameter d p The velocity u of the snow particles is given by the user. p The snow particle diameter and wall friction velocity u were obtained through simulation. * The calculation methods include the following two: Calculated using the formula: you * =(t / r) 1 / 2 Where τ is the shear force generated by the snow surface, and ρ is the air density; Calculations can be made using the logarithmic law of wind speed profiles: Where k is the von Kármán coefficient, taken as 0.4, z0 is the ground roughness height, and z is the effective height.

6. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 1, characterized in that, The enthalpy formula in S23 is: h ls * =h ls +(1-Y s * )h fusion Among them, h ls For enthalpy, relative mass fraction Y s * Defined as the mass fraction of the water film - ice film occupied by ice cubes, relative to the mass fraction of ice cubes, Y. s * A function of temperature: Among them, T * Standardized temperature as defined: Among them, the function f(T) * This is called the fractional solid-phase curve, for Y s * and T * The linear dependence between them is defined by the solidification path as: f(T * )=1-T * 。 7. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to claim 1, characterized in that, S25 includes: modeling the breakup process of the liquid film on an acute-angled edge using an edge-peeling model; and modeling the breakup process of the liquid film surface using a wave-peeling model. Edge spalling models for modeling the breakup process of liquid films on acute-angled edges include: edge spalling model for co-directional fluids and edge spalling model for anti-directional fluids; For edge stripping of fluids in the same direction, the ratio FR of liquid film momentum flux to surface tension and gravity is calculated by the following formula: Among them, We f For the liquid film Weber number, Bo f For Bond number, L b h is the breaking length. f The liquid film thickness is given; the liquid film Weber number is as follows: Where, ρ f v is the density of the liquid film. f h is the velocity of the liquid film whose projection direction is orthogonal to the peeling edge. f Let σ be the liquid film thickness and σ be the surface tension; the Bond number for the thin film is as follows: Among them, g θ The acceleration component is perpendicular to the downstream wall; the breaking length is defined by the following formula: L b =0.0388h f 0.5 Re f 0.6 We rel -0.5 Among them, Re f For the liquid film Reynolds number, We rel The relative Weber number is: The liquid film Reynolds number is: Where, μ f The viscosity is dynamic; the relative Weber number is as follows: Where ρ is the gas density, v g The gas velocity component perpendicular to the stripping edge; If FR>FR c This can be considered as a breakage process, resulting in droplet peeling; in the fluid that has passed through the peeled edge, only a small portion of x remains. s Separated from the liquid film, this fraction can be approximated using the following formula: For edge stripping of anisotropic fluids, if the fluids move from both sides to one side, they will merge into a series of Lagrange droplets that obey the laws of conservation of mass, momentum, composition, and energy; for anisotropic fluids, the stripping fraction x on both sides... s When set to 1, the droplet diameter is calculated based on the film properties on the side with the highest flux. When modeling the breakup process of a liquid film surface using the wave stripping model, the liquid film stripping model is divided into three stages: after the wave develops at the liquid-gas interface, the liquid film surface becomes unstable → the ejected fluid volume forms a cylinder → the cylinder decomposes into droplets. The most unstable wavelength is the wavelength most likely to break up on the surface, and this wavelength is calculated as the resonant wavelength using the dissipation equation. in, It is the square of the relative velocity between the liquid film and the surrounding fluid (v) f -v)·(v f -v), σ is surface tension, f b It is the volume force acting on the liquid film; The minimum liquid film height required for droplet ejection is: The height of the liquid film to be peeled off is: The diameter of the generated droplets is: Among them, c D The value is set to 3.78; All droplets initially have the same velocity as the liquid film and are placed at a point between the center of the grid cell and the center of the boundary surface.

8. The simulation method for coupled wind, snow, water, and ice transport and phase transition in the train bogie region according to any one of claims 1-7, characterized in that, In S5, post-processing yields the distribution characteristics of strong shear flow in the bogie region, the trajectory and concentration distribution of snow particles, the initial position of the liquid film formed after the snow adhering to the surface of the heating component melts after heat absorption, the propulsion and development trend of the liquid film on the surface of the heating component, the distribution and contour deformation evolution of ice on the surface of important components, and the phase evolution process of peeling droplets from the heating component to the surface of the insulating component through peeling-impact-icing. These processes are then analyzed.

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