Approximate high-speed train undercarriage space flow field simulation method and device based on equal-ratio brake stand

Abstract

The application relates to a kind of approximate high-speed train undercarriage space flow field simulation method and device based on equal ratio brake bench.The method is simulated to the pre-constructed multi-car body fluid-solid coupling simulation model using fluid-solid coupling simulation method according to the running speed of high-speed train, the flow field distribution of high-speed train around and undercarriage space under different running speeds is obtained;According to the flow field distribution and the different undercarriage position of brake disc, the incoming flow velocity of brake disc at different undercarriage positions is obtained;According to the incoming flow velocity and different brake working condition setting import wind speed, the pre-constructed brake test bench fluid-solid-thermal simulation model is simulated using fluid-solid-thermal coupling simulation method, and the brake disc heat dissipation of brake bench test whole process is obtained.Compared with prior art, the application has the advantages of improving the accuracy of bench heat dissipation test and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of rail vehicle braking safety management, and in particular to a method and device for simulating the flow field of the space under a high-speed train based on a geometrically proportional braking test bench. Background Art

[0002] Brake discs play a vital role in the braking system of high-speed trains and are key components for ensuring train safety. In actual use scenarios, the temperature of the brake discs can rise sharply due to emergency braking. Because the brake discs are located on the bogies, the surrounding structure is relatively complex, including the vehicle floor, the tracks and ground, and the front and rear partitions of the bogies. Temperature changes in the brake discs can lead to temperature changes in the surrounding environment and components, which in turn affects the safety of the high-speed train's braking process. Therefore, studying the relationship between the air flow field in the bogie area of ​​high-speed trains and the temperature distribution and heat dissipation performance of the brake discs is crucial for improving the safety of high-speed trains during braking.

[0003] Bench testing is a widely used method for testing brake discs. The results obtained through this testing have practical application value and engineering reference value. However, the test standards currently used in bench testing differ significantly from actual operation on high-speed trains. Furthermore, previous bench testing has primarily focused on the temperature changes of the brake disc itself, without considering the complex structure of the actual bogie area and other factors that may affect heat dissipation. This also overlooks the impact of the brake disc on ambient temperature changes, which in turn reduces the accuracy of the test results. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method and device for simulating the flow field under the high-speed train based on a proportional brake test bench. The fluid-solid coupling simulation model of a multi-section car body containing multiple brake discs is subjected to fluid-solid coupling simulation to obtain the flow field distribution around the high-speed train and under the car. On this basis, considering the proportional brake test bench structure, an air intake scheme for the brake discs at different under-car positions is proposed, and the fluid-solid-thermal coupling simulation method is used for simulation to obtain the heat dissipation of the brake discs during the entire brake test bench test. As a result, researchers can compare the heat dissipation results of the brake discs obtained by different air intake schemes, derive the influence of different air intake schemes on the test bench heat dissipation results, and improve the accuracy of the test results.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to a first aspect of the present application, a simulation method for the flow field of the space under a high-speed train based on an isometric brake bench is provided, comprising the following steps: simulating a pre-constructed multi-car body fluid-solid coupling simulation model by using a fluid-solid coupling simulation method according to different running speeds of a high-speed train, to obtain the flow field distribution of the space around and under the high-speed train at different running speeds, wherein the running speeds of the high-speed train are pre-acquired, and the multi-car body fluid-solid coupling simulation model comprises a first simulation model and a fluid air domain model, the first simulation model is a combination of a pre-set brake disc model, a train model and a bogie model, and the fluid air domain model is established around the first simulation model; acquiring the incoming flow wind speed of the brake disc at different under-car positions according to the flow field distribution and different under-car positions of the brake disc, wherein the different under-car positions of the brake disc are pre-positioned; setting an import wind speed according to the incoming flow wind speed and different brake working conditions, simulating a pre-constructed brake test bench fluid-solid-thermal simulation model by using a fluid-solid-thermal coupling simulation method, to obtain the brake disc heat dissipation condition in the whole brake bench test process, wherein the brake working conditions are pre-acquired, and the brake test bench fluid-solid-thermal simulation model is established based on the brake disc model and a pre-set isometric brake bench test bench structure model.

[0007] As a preferred technical solution, the train model is established according to the body shape and under-car structure of an actual running train, the train model comprises a train head part and an intermediate car part, and the under-car closed form of the train model comprises an open type, a semi-closed type and a fully-closed type.

[0008] As a preferred technical solution, the brake disc model is constructed according to the shape and material of an axle-mounted brake disc or a wheel-mounted brake disc.

[0009] As a preferred technical solution, before simulating the pre-constructed multi-car body fluid-solid coupling simulation model by using the fluid-solid coupling simulation method, a fluid domain is extracted from the multi-car body fluid-solid coupling simulation model by using a Boolean operation, and the brake disc and the axle part directly connected with the brake disc are reserved.

[0010] As a preferred technical solution, the fluid air domain model is an incompressible ideal gas model with density changing with temperature.

[0011] As a preferred technical solution, the positioning of the different under-car positions of the brake disc comprises the difference between a train head car and an intermediate car, the difference between the intermediate cars at different numbers of sections from the train head car, and the difference between the brake axle discs and the brake wheel discs at different positions on the axle.

[0012] As a preferred technical solution, the brake working conditions comprise emergency braking, normal braking, long and large slope braking and multiple continuous braking with different brake initial speeds and brake decelerations.

[0013] As a preferred technical solution, when the pre-constructed brake test bench flow-solid-thermal simulation model is simulated by using the flow-solid-thermal coupling simulation method, the heat generated by friction is simulated by applying an equivalent heat flux, and the braking condition of the train under the changing deceleration is simulated by writing a user-defined function.

[0014] As a preferred technical solution, when the pre-constructed brake test bench flow-solid-thermal simulation model is simulated by using the flow-solid-thermal coupling simulation method, the simulation time is configured to be greater than the time of the braking condition.

[0015] According to the second aspect of the present application, an approximate high-speed train undercarriage space flow field test device based on an equal ratio brake bench is provided, comprising a flow field distribution acquisition module, an incoming flow wind speed acquisition module, and a heat dissipation condition acquisition module; the flow field distribution acquisition module is used to simulate a pre-constructed multi-car body flow-solid coupling simulation model by using a flow-solid coupling simulation method according to different high-speed train running speeds, to obtain the flow field distribution of the high-speed train surrounding and undercarriage space under different running speeds, wherein the high-speed train running speed is pre-acquired, the multi-car body flow-solid coupling simulation model comprises a first simulation model and a fluid air domain model, the first simulation model is a combination of a pre-set brake disc model, a train model and a bogie model, and the fluid air domain model is established around the first simulation model; the incoming flow wind speed acquisition module is used to acquire the incoming flow wind speed of the brake disc at different undercarriage positions according to the flow field distribution and different undercarriage positions of the brake disc, wherein the different undercarriage positions of the brake disc are pre-positioned; the heat dissipation condition acquisition module is used to set an inlet wind speed according to the incoming flow wind speed and different braking conditions, to simulate a pre-constructed brake test bench flow-solid-thermal simulation model by using a flow-solid-thermal coupling simulation method, to obtain the brake disc heat dissipation condition of the whole brake bench test process, wherein the braking condition is pre-acquired, and the brake test bench flow-solid-thermal simulation model is established based on the brake disc model and a pre-set equal ratio brake bench test bench structure model.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] 1. The present invention simulates a multi-section car body fluid-solid coupling simulation model including multiple brake discs to obtain the flow field distribution around and under the high-speed train at different operating speeds, and then calculates the flow field characteristics (including the incoming wind speed) of the brake disc at different under-car positions according to the flow field distribution and the different under-car positions of the brake disc obtained by positioning. The flow field characteristics obtained by simulation are then applied to the simulation of the bench test and the thermal field analysis of the bench test, so that the bench test can be used to perform flow field and thermal simulation for the under-car space of different sections of the vehicle. When performing the fluid-solid-thermal coupling simulation, the method sets the inlet wind speed according to the incoming wind speed obtained by the fluid-solid coupling simulation, and studies the thermal dissipation performance of the brake disc at different under-car positions under actual vehicle operation conditions on the bench test bench. This can not only reduce the strong binding of the ambient temperature test to the high-speed train actual vehicle test, but also solve the problem that it is difficult to carry out the observation of the ambient temperature change around the brake disc under the actual vehicle test conditions, thereby making it difficult to carry out experimental tests related to heat dissipation and the related research on heat dissipation unable to obtain experimental accuracy verification, thereby effectively improving the accuracy of the test results;

[0018] 2. In the multi-section car body fluid-solid coupling simulation model used in the present invention, the first simulation model is a combination of a preset brake disc model, a train model and a bogie model. The train model is established according to the car body shape and the undercarriage structure of the actual running train, and the brake disc model is constructed according to the shape and material of the axle-mounted brake disc or the wheel-mounted brake disc. Therefore, when the method is applied, modeling and analysis can be performed for different train models, and the positions of different brake discs can be accurately located. The characteristics of the flow in front of the brake disc can be extracted and analyzed respectively. The heat dissipation simulation of brake discs with different structures and materials, different car body shapes and different undercarriage spaces can be performed. Simulation can also be performed according to different braking conditions, and the method has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the simulation method according to an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the shaft disc and brake pad in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Existing research on brake disc thermal variations and their impact on the surrounding environment primarily involves real-vehicle testing and numerical simulation. Real-vehicle testing, however, is limited by factors such as the line environment, resulting in limited testing opportunities and extremely high costs. This makes it difficult to meet the research needs for high-speed train brake disc temperature variations. Furthermore, real-vehicle testing struggles to obtain real-time temperature variations and flow field information surrounding the brake disc. Numerical simulation can simulate the temperature variations of the brake disc under the high-speed train vehicle, as well as the temperature variations of the surrounding environment, throughout the braking process. However, to further verify the accuracy of this simulation, brake disc temperature variation testing is still required. Furthermore, current bench testing methods lack an experimental solution for approximating the flow field for brake discs at different undercarriage locations on high-speed trains. Previous bench testing has only studied the temperature variations of the brake disc itself, excluding the impact of inlet air velocity on the temperature variation of the brake disc itself, and the error in temperature variation is negligible. However, as the initial braking velocity of high-speed trains increases, the temperature of the brake disc itself reaches higher levels, necessitating further research into the impact of the brake disc on the temperature variation of the surrounding environment to ensure safety. However, if the old bench test air supply scheme is used, the temperature changes in the environment around the brake disc are closely related to the flow characteristics of the flow field, so different air supply methods will affect the test results. In addition, because high-speed trains generally have multiple carriages, the brake discs located at different locations under the car have different air supply conditions, which will also affect the temperature changes in the environment around the brake disc.

[0022] In view of the problems in the prior art, the present invention proposes a method for simulating the flow field under the high-speed train space based on a proportional brake test bench. The method first uses a fluid-solid coupling simulation method to simulate a pre-constructed multi-section car body fluid-solid coupling simulation model according to different high-speed train running speeds, and obtains the flow field distribution around and under the high-speed train at different running speeds. The high-speed train running speed is pre-acquired, and the multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model. The first simulation model is a combination of a preset brake disc model, a train model and a bogie model, and the fluid-air domain model is established around the first simulation model; secondly, according to the flow field distribution and different under-car positions of the brake disc, the incoming wind speed of the brake disc at different under-car positions is obtained, and the different under-car positions of the brake disc are pre-positioned; finally, according to the incoming wind speed and different braking conditions, the inlet wind speed is set, and the pre-constructed brake test bench fluid-solid-thermal simulation model is simulated using a fluid-solid-thermal coupling simulation method to obtain the brake disc heat dissipation during the entire brake bench test process. The braking conditions are pre-acquired, and the brake test bench fluid-solid-thermal simulation model is established based on the brake disc model and a preset proportional brake bench test bench structure model.

[0023] Traditional on-board and bench tests require significant human and material resources. In contrast, the simulation method proposed in this invention utilizes a computer for simulation analysis, clearly capturing temperature change and flow field velocity nephograms of the brake disc and its surroundings during the braking process. Compared to traditional numerical simulation methods, the simulation method proposed in this invention considers the impact of the high-speed train's undercarriage environment on the flow field distribution around the brake disc, as well as the effect of varying flow field distributions on the disc's heat dissipation. Combining this impact with bench testing, the simulation results can better guide testing methods for approximating the flow field under high-speed trains on a scaled brake bench.

[0024] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0025] Example

[0026] like Figure 1 As shown, this embodiment provides a method for simulating the flow field under a high-speed train based on a proportional brake test bench, comprising the following steps:

[0027] Step S1: According to different high-speed train running speeds, a pre-built multi-section car body fluid-solid coupling simulation model is simulated using a fluid-solid coupling simulation method to obtain the flow field distribution around and under the high-speed train at different running speeds.

[0028] In this step, different high-speed train operating speeds are pre-set in the computational fluid software. The multi-section carbody fluid-structure coupling simulation model includes a first simulation model (a combination of a preset brake disc model, train model, and bogie model) and a fluid-air domain model. The fluid-air domain model is built around the first simulation model.

[0029] Step 1.1) Brake disc models are divided into two types: a brake shaft disc model and a brake wheel disc model. These are three-dimensional models of brake discs with different structures and materials. Optionally, models can be constructed based on their shape and material properties, with appropriate simplifications. Key parameters of the brake disc material used in the modeling process include density, thermal conductivity, and specific heat capacity.

[0030] Step 1.2) The train model, also known as a finite element simulation model of the car body or a three-dimensional model of the multi-section car body, is established by analyzing the car body shape and undercarriage structure of different trains. The construction process is based on the actual operation of the train. The train model consists of a front section and an intermediate section. The number of intermediate sections is set according to the specific analysis requirements, and the enclosure state of the undercarriage space can be divided into open (i.e., non-enclosed), semi-enclosed, and fully enclosed types. For the bogie section, appropriate simplification is performed based on the focus of this method on thermal dissipation analysis.

[0031] Combining the brake disc model, train model, and bogie model yields a model encompassing the multi-section train, bogie, and brake discs—the first simulation model. Building a fluid-air domain model around the complex model encompassing the multi-section train, bogie, and brake discs yields a fluid-structure coupling simulation model of the multi-section train body with multiple brake discs.

[0032] Step 1.3) Further, when setting the fluid domain material parameters, traditional studies usually use fluid materials with constant properties, without considering the influence of the physical properties of air changing with temperature, that is, the temperature, viscosity and pressure of the air are regarded as fixed values. However, in the actual braking process, a large amount of heat is generated, causing the brake disc to experience a wide temperature range in the heat dissipation simulation. Therefore, this embodiment uses an incompressible ideal gas model whose density changes with temperature. In addition, in order to optimize computing resources, the required fluid calculation area is extracted from the complete train model (i.e., the multi-section car body fluid-solid coupling simulation model) through Boolean operations / Boolean subtraction operations, retaining only the brake disc and the axle part directly connected to it. If the wheel disc needs to be analyzed, the solid model of the wheel is also retained. This method can effectively reduce computing costs while ensuring simulation accuracy.

[0033] Step 1.4) Meshing is crucial for simulation calculations, as mesh quality directly impacts the convergence speed and accuracy of numerical calculations. In this example, an unstructured mesh was selected for meshing. Because the brake disc contains delicate structures such as heat sinks, these areas are meshed more finely to ensure thermal simulation accuracy. Meanwhile, considering computational cost, the mesh in other areas is relatively sparse. Based on the characteristics of flow field distribution in computational fluid dynamics, density boxes are used to locally refine the mesh around the brake disc and in the wake.

[0034] Step 1.5) Under actual operating conditions, the brake disc not only translates as the train moves forward but also rotates around the axle. During the simulation of the undercarriage space, the brake disc's translational motion is treated as an airflow in the air domain that is opposite to the train's forward direction and has the same velocity as the train. Therefore, the inlet of the computational domain is defined as a velocity inlet, with a uniform inflow condition, the airflow direction opposite to the high-speed train's direction of motion, and the velocity value equal to the train's operating speed. This setting allows for a more accurate simulation of the interaction between the brake disc and the surrounding air during actual braking. Using fluid-structure interaction simulation methods in ANSYS FLUENT, the flow field characteristics of the multi-section train body and its undercarriage brake disc are simulated at different operating speeds. The operating behavior of the multi-section train is simulated as the air intake action of the front air inlet in the flow field. A corresponding velocity is applied to the surrounding environment and track, which is equivalent to the operating speed of the high-speed train, to simulate the train's movement. Furthermore, the different train operating speeds are converted into different air inlet wind speeds and relative velocities. The rotating motion of the brake disc is simulated using a moving reference system. Rotating components such as the brake disc and wheelset are defined as rotating areas to simulate the rotation mode of the brake disc during braking.

[0035] Step S2, obtaining the incoming wind speed of the brake disc at different under-vehicle positions according to the flow field distribution and different under-vehicle positions of the brake disc, where the different under-vehicle positions of the brake disc are pre-positioned.

[0036] Specifically, this step first requires locating the brake discs at different undercarriage positions of the high-speed train, and then analyzing the distribution of the flow field around them. By combining the actual application scenarios with the flow conditions of the bench test, the flow field velocity (i.e., the incoming wind speed) of the incoming flow in front of the brake discs at different undercarriage positions is obtained as the train runs at different speeds.

[0037] Step 2.1) Using the fluid-structure interaction simulation results for the train and brake discs from step S1, the flow field characteristics around the brake discs are determined by positioning the brake discs at different undercarriage locations. The positioning of the brake discs at different undercarriage locations includes differences between the lead car and the middle car, the number of middle cars from the lead car, and the locations of the brake discs and wheel discs on the axle.

[0038] Step 2.2) Since the flow conditions in actual application scenarios during simulation and actual bench testing are usually equivalent to the flow directly in front of the brake disc, the flow on the brake disc is concentrated in the area below the brake disc due to the undercar structure. The brake disc in this area is subjected to the strongest flow wind, and other flow field characteristics around the brake disc are formed under the action of this flow wind. Therefore, when analyzing the flow field around the brake disc at different undercarriage positions, focus on extracting the flow field velocity distribution characteristics in front of the lower part of the front part of the brake disc.

[0039] Analysis of the fluid-structure interaction simulation results in step 2.3 reveals that the incoming wind speed ahead of the brake disc varies at different undercarriage locations. A functional relationship between the incoming wind speed at these locations and the train's operating speed has been established, showing that the incoming wind speed at these locations exhibits different multiples of the train's operating speed. Therefore, in subsequent bench simulations and physical bench tests for brake discs at different undercarriage locations, the inlet air volume will be modified to achieve approximate simulations and tests of the undercarriage environment.

[0040] Step S3, setting the inlet wind speed according to the incoming wind speed and different braking conditions, and using the fluid-solid-thermal coupling simulation method to simulate the pre-constructed brake test bench flow-solid-thermal simulation model to obtain the brake disc heat dissipation during the entire brake bench test process. The braking conditions are obtained in advance, and the brake test bench flow-solid-thermal simulation model is established based on the brake disc model and the preset proportional brake bench test bench structure model.

[0041] In this step, the geometric brake test bench structure model is simulated according to the structure of the geometric brake test bench, that is, Figure 1 Based on the three-dimensional model of the brake bench in the figure, a fluid-solid-thermal simulation model of the brake test bench can be established based on Boolean operations, the brake disc model and the three-dimensional model of the brake bench. By using the fluid-solid-thermal coupling simulation method, combined with the simulation results of the brake disc inlet wind speed at different under-vehicle positions obtained in step S2, different inlet wind speeds are set according to different braking conditions. By writing user-defined functions, the heat dissipation of the brake disc during the entire brake bench test process can be reproduced.

[0042] In step 3.1), a fluid-solid-thermal simulation model of the brake test bench was constructed using computer modeling software, referencing the dimensions of an actual brake test bench. The brake discs were modeled using the same structure and materials as in step 1.1, including various brake disc types, such as the brake shaft disc and the brake wheel disc. Relevant components, such as the support frame and rotating shaft, were configured around the brake discs, based on the physical brake test bench configuration, to ensure that the simulated flow environment more closely resembled the actual operating environment.

[0043] Step 3.2) The core of this method is to explore the heat dissipation characteristics of the brake disc, and does not cover research directions such as friction contact and thermal stress. Therefore, a method based on the principle of friction work is adopted to simulate the friction heat generation process by calculating and applying the equivalent heat flux. This method can simulate the heat generated during the braking process without directly simulating the details of the friction contact. On the brake disc, the position of the brake pad friction area is set along the radius of the brake disc, and the heat flux input at different radii is also different. During the simulation, the heat flux input of each area is different. This differentiated heat flux input method can more accurately simulate the temperature distribution of the brake disc during the actual braking process, thereby providing more realistic input for studying the heat dissipation law of the brake disc. Figure 2 A simplified model of a disc and brake pad is shown, where the brake pad's friction surface is treated as a continuous sector with a central angle of θ. In this model, the heat flux density in the annular region of radius r on the brake disc is assumed to be uniform. The heat flux density in the sector of radius r and radial width dr on the brake pad and the corresponding annular region of radius r and radial width dr on the brake disc are calculated. The heat flux density in the narrow ring of radial width dr on the disc surface is:

[0044]

[0045] Where f is the friction coefficient between the brake pad and the wheel disc, N is the pressure exerted by the brake pad on the brake disc, S is the area of ​​the brake pad, ΔA ... 闸 is the area of ​​the narrow sector with radius r and radial width dr on the gate, v r is the linear velocity of the gate at a radius of r, ΔA 盘 is the area of ​​the narrow ring with radius r and radial width dr on the shaft disk surface, and η is the proportional coefficient of friction heat transmitted into the shaft disk surface, that is, the heat distribution coefficient.

[0046] Step 3.3) The heat generated by friction is transferred to the two contacting objects at a certain ratio. The heat distribution coefficient method sets the heat distribution coefficient between the two friction surfaces as a constant, ignoring the heat conduction due to the temperature difference between the two surfaces. By simplifying the formula by assuming that the temperature of the brake disc and the brake pad remains equal at all times, the heat distribution coefficient calculation formula for the brake disc is obtained:

[0047]

[0048] Where k d 、c d , ρ d and S d They represent the thermal conductivity, specific heat, density and friction area of ​​the brake disc, respectively. p 、c p , ρ pand S p They represent the thermal conductivity, specific heat, density and friction area of ​​the brake pad respectively.

[0049] Step 3.4) The train braking conditions may include emergency braking with different initial braking velocities and braking decelerations, common braking, long slope braking, and multiple continuous braking conditions. In the modeling of the brake bench, with reference to the actual brake disc bench structure, there is a special air inlet for blowing air according to the inlet wind speed set in the test outline. When modeling the fluid-solid-thermal coupling simulation model of the brake test bench, the way of entering the field can be achieved by setting the air inlet surface in the simulation. There are two ways to set the air inlet: one is to set the air inlet at the top with reference to the inlet wind position of the proportional brake test bench, and the other is to set the air inlet at the front and bottom of the brake disc with reference to the actual wind conditions of the brake disc under the high-speed train. When setting the upper air inlet according to the proportional brake test bench, the inlet wind speed is set according to the brake bench test outline, so that this working condition is the benchmark working condition for comparison with the air inlet bench test simulation results considering the undercar environment set in this embodiment. When setting the lower air inlet based on actual wind conditions, the wind speed setting is based on the actual operation of the brake disc, which experiences both translational motion with the train's advance and rotational motion around the axle. This translational motion is equated to air flow with the same magnitude and opposite direction as the ambient air velocity. In ANSYS FLUENT, the inlet is set as a velocity inlet, using a uniform incoming flow direction, aligned with the negative direction of the train's movement and equal to the high-speed train's operating speed. The wall temperature is set equal to the ambient temperature. The computational domain outlet is set as a pressure outlet, with the track and ground acting as sliding surfaces, and the velocity magnitude and direction are the same as the incoming air velocity.

[0050] Step 3.5) Based on the different inlet wind speed ratios of the brake discs at different under-vehicle positions obtained by analysis in step 2.3), the size setting of the inlet wind speed of the simulation model is modified to simulate the heat dissipation of the brake discs at different under-vehicle positions during the braking process. As for the material parameter setting of the fluid domain, in previous studies on brake disc heat dissipation, steady-state fluid materials were often used, ignoring the changes in the physical parameters of the air with temperature, that is, assuming that the temperature, viscosity, and reference pressure of the air are constant. However, in fact, a large amount of heat is generated during the braking process. In the simulation of brake disc heat dissipation, the simulated temperature has a large span. Therefore, this embodiment selects an incompressible ideal gas whose density can change with temperature. Accordingly, a pressure-based solver suitable for incompressible fluids is selected in the FLUENT software, and the built-in coupled algorithm is used to solve the problem. The Realizable k-ε turbulence model is selected to describe turbulent flow. This model is suitable for the simulation of complex flows. To improve numerical accuracy, a second-order upwind discretization scheme was selected. This scheme effectively captures shock waves and contact discontinuities in the flow and is suitable for high-speed flows and computational domains with complex geometries. Unlike steady-state fluid materials, the density of the incompressible ideal gas material used in this example varies with temperature, so the direction of the gravitational acceleration also needs to be configured.

[0051] Step 3.6) ANSYS FLUENT software provides a variety of computational models for simulating the motion areas of objects. These models can be roughly divided into two categories: single motion reference frame (SRF) and multiple motion reference frames. In the multiple motion reference frame, it is further subdivided into multiple reference frames (MRF), mixed plane (MPM), sliding mesh (SMM) and dynamic mesh (DMM) models. Because the SRF, MRF and MPM models do not fully consider the interaction between different motion areas, they have certain limitations in simulation applications and are mainly suitable for the calculation of steady-state flows. In contrast, the sliding mesh model and the dynamic mesh model can consider the mutual influence between different motion areas, thereby more accurately simulating the changes in the boundaries of the computational domain under transient flow conditions. When simulating the rotational motion of the brake disc, the dynamic mesh method can be used, and the multiple reference frame model (MRF) can be used to define the complex air flow area affected by rotating components (such as the brake disc and wheelset), and set the corresponding rotational angular velocity:

[0052]

[0053] Where v is the real-time running speed of the train, R 轮 is the rotation radius of the train wheels.

[0054] Step 3.7) Considering that the brake disc is designed with a complex heat dissipation rib structure, this complex structure can easily cause the surrounding air to be affected as the brake disc rotates. Therefore, a cylindrical fluid domain is established outside the dense air area around the brake disc, and it is assumed that the air in this area is disturbed during the braking process and then rotates. At the junction of the turbulent air area and the external air domain, a boundary called "interface" is set. This "interface" boundary allows data exchange of regional cross-sections between calculation models in different regions even when the grid nodes cannot be accurately connected, thereby ensuring the smooth progress of the calculation process. In this way, the impact of the brake disc rotation on the surrounding air flow and the resulting heat exchange process can be more accurately simulated.

[0055] Step 3.8): During emergency braking, the heat dissipation of the brake disc is a transient phenomenon, which requires that many parameters in the simulation analysis must change dynamically over time. These parameters include the wind speed at the air inlet (equivalent to the train speed), the rotational speed of the brake disc, and the heat flux density at different locations on the brake disc. Since FLUENT's standard interface and functions may not meet the requirements of these dynamic parameter changes, simulation can be implemented by writing user-defined functions (UDFs), especially when it is necessary to simulate changing deceleration. These UDFs can be written in C language and saved with a ".c" extension. Typically, each source file contains one UDF, but multiple consecutive UDFs can also be included in the same source file. In FLUENT, these written UDF programs can be compiled and loaded in the corresponding locations. Once the UDF is compiled, the defined variables will appear in FLUENT's User Defined Window. The user can select these functions in the corresponding dialog box and link them to the solver.

[0056] Step 3.9) To further investigate the temperature variations of the brake disc and the surrounding air under natural convection conditions, this example extends the simulation timeframe beyond the actual train braking time. This means the simulation covers not only the entire braking phase from start to finish, but also the period of time after the train is stationary. This allows for a more comprehensive observation and analysis of the continuous temperature variations of the brake disc and the surrounding air due to natural convection after the braking operation, leading to a more accurate understanding of the heat dissipation process.

[0057] Optionally, continue the analysis based on the above steps, specifically including:

[0058] Step S4, simulating the heat transfer process of the brake disc during the braking process and in a stationary state after the braking test on the brake bench, analyzing the heat dissipation process of the brake disc from multiple perspectives such as forced convection and natural convection, and analyzing the incoming flow of the brake disc corresponding to different positions under the vehicle.

[0059] After obtaining the solution in step 4.1), post-processing software can be used to generate a time-varying cloud map of the brake disc temperature during braking, a time-varying cloud map of the ambient temperature around the brake disc, and a time-varying cloud map of the velocity of the flow field around the brake disc and the vehicle body. Furthermore, the time-varying temperature curve for each point on the brake disc or in the air environment can be output. By comparing simulation results for different undercarriage structures, different brake disc materials, different brake disc structures, and different brake disc positions, the heat dissipation patterns of the brake disc can be compared under different braking conditions and at different position settings.

[0060] Step 4.2) The proportional brake bench test procedure for approximating brake discs at different undercarriage locations differs from the standard brake test procedure primarily in the air intake method. By setting different air inlet velocity variations, the bench test can approximate the flow field environment of the brake disc at different undercarriage locations.

[0061] Step 4.3) The braking conditions in the proportional brake bench test outline for brake discs at approximately different under-vehicle positions include an additional post-braking stage compared to the commonly used brake test outline. During this stage, the ambient temperature around the brake disc will undergo a relatively drastic change. The cooling procedure is not performed during this stage. Instead, the cooling procedure is performed only after the brake disc has fully dissipated its heat naturally, and the test of the next condition is continued.

[0062] Furthermore, this embodiment also provides an approximate high-speed train undercarriage space flow field test device based on a proportional brake bench, including a flow field distribution acquisition module, an incoming wind speed acquisition module, and a heat dissipation condition acquisition module, wherein the flow field distribution acquisition module is used to simulate a pre-constructed multi-section car body fluid-solid coupling simulation model according to different high-speed train running speeds using a fluid-solid coupling simulation method to obtain the flow field distribution around the high-speed train and the space under the car at different running speeds. The high-speed train running speed is pre-acquired, and the multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model. The first simulation model is a preset brake disc model, a train model, and a bogie model. In this combination, a fluid-air domain model is established around the first simulation model; the incoming wind speed acquisition module is used to obtain the incoming wind speed of the brake disc at different under-vehicle positions according to the flow field distribution and the different under-vehicle positions of the brake disc. The different under-vehicle positions of the brake disc are pre-positioned; the heat dissipation condition acquisition module is used to set the inlet wind speed according to the incoming wind speed and different braking conditions, and use the fluid-solid-thermal coupling simulation method to simulate the pre-built fluid-solid-thermal simulation model of the brake test bench to obtain the heat dissipation of the brake disc during the entire brake bench test process. The braking conditions are pre-acquired, and the fluid-solid-thermal simulation model of the brake test bench is established based on the brake disc model and the preset proportional brake bench test bench structure model. The specific operation process of each module is basically the same as the execution steps of the aforementioned method, and will not be repeated here.

[0063] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for simulating the flow field under a high-speed train based on a proportional brake test bench, characterized in that: The following steps are involved: According to different high-speed train running speeds, a pre-constructed multi-section car body fluid-solid coupling simulation model is simulated using a fluid-solid coupling simulation method to obtain the flow field distribution around and under the high-speed train at different running speeds. The high-speed train running speed is pre-acquired. The multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model. The first simulation model is a combination of a preset brake disc model, a train model, and a bogie model. The fluid-air domain model is established around the first simulation model. According to the flow field distribution and different under-vehicle positions of the brake disc, the wind speed of the incoming flow to the brake disc at different under-vehicle positions is obtained, wherein the different under-vehicle positions of the brake disc are pre-positioned; The inlet wind speed is set according to the incoming wind speed and different braking conditions, and the pre-constructed flow-solid-thermal simulation model of the brake test bench is simulated using the fluid-solid-thermal coupling simulation method to obtain the heat dissipation of the brake disc during the entire brake bench test process. The braking conditions are obtained in advance, and the brake test bench flow-solid-thermal simulation model is established based on the brake disc model and the preset proportional brake bench test bench structure model.

2. The method for simulating the flow field under the high-speed train space based on a proportional braking test bench according to claim 1 is characterized in that: The train model is established based on the body shape and undercarriage structure of an actual running train. The train model includes a front part and a middle car part. The undercarriage enclosure forms of the train model include unenclosed, semi-enclosed and fully enclosed types.

3. The method for simulating the flow field under the high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: The brake disc model is constructed according to the shape and material of the axle-mounted brake disc or the wheel-mounted brake disc.

4. The method for simulating the flow field under a high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: Before simulating a pre-built multi-section vehicle body fluid-solid coupling simulation model using a fluid-solid coupling simulation method, a fluid domain is extracted from the multi-section vehicle body fluid-solid coupling simulation model using Boolean operations, retaining the brake disc and the axle portion directly connected to the brake disc.

5. The method for simulating the flow field under the high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: The fluid air domain model is an incompressible ideal gas model whose density varies with temperature.

6. The method for simulating the flow field under a high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: The positioning of the brake disc at different undercarriage positions includes the difference between the lead car and the middle car, the difference between the middle cars with different numbers of sections from the lead car, and the difference between the different positions of the brake shaft disc and the brake wheel disc on the axle.

7. The method for simulating the flow field under a high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: The braking conditions include emergency braking, normal braking, braking on a long slope, and multiple continuous braking at different initial braking speeds and braking decelerations.

8. The method for simulating the flow field under a high-speed train based on a proportional braking test bench according to claim 1 is characterized in that: When simulating the pre-built fluid-solid-thermal simulation model of the brake test bench using the fluid-solid-thermal coupling simulation method, the heat generated by friction is simulated by applying an equivalent heat flux density, and the braking conditions of the train under varying deceleration are simulated by writing a user-defined function.

9. The method for simulating the flow field under a high-speed train based on a proportional braking test bench according to claim 8 is characterized in that: When simulating a pre-built fluid-solid-thermal simulation model of a brake test bench using a fluid-solid-thermal coupling simulation method, the simulation time is configured to be greater than the time of the braking condition.

10. A test device for the flow field under a high-speed train based on a proportional braking test bench, characterized in that: It includes flow field distribution acquisition module, incoming wind speed acquisition module and heat dissipation acquisition module; The flow field distribution acquisition module is used to simulate a pre-constructed multi-section car body fluid-solid coupling simulation model using a fluid-solid coupling simulation method according to different high-speed train running speeds to obtain the flow field distribution around and under the high-speed train at different running speeds. The high-speed train running speed is pre-acquired. The multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model. The first simulation model is a combination of a preset brake disc model, a train model, and a bogie model. The fluid-air domain model is established around the first simulation model. The incoming wind speed acquisition module is used to acquire the incoming wind speed of the brake disc at different under-vehicle positions according to the flow field distribution and different under-vehicle positions of the brake disc, wherein the different under-vehicle positions of the brake disc are pre-positioned; The heat dissipation condition acquisition module is used to set the inlet wind speed according to the incoming wind speed and different braking conditions, and use the fluid-solid-thermal coupling simulation method to simulate the pre-constructed fluid-solid-thermal simulation model of the brake test bench to obtain the heat dissipation condition of the brake disc during the entire brake bench test process. The braking conditions are obtained in advance, and the brake test bench fluid-solid-thermal simulation model is established based on the brake disc model and a preset proportional brake bench test bench structure model.

Images