Simulation method and device for lower space flow field of approximate high-speed train based on equal-ratio brake bench

Abstract

The invention relates to a method and a device for simulating an under-train space flow field of an approximate high-speed train based on an equal-ratio braking rack. The method comprises the following steps: simulating a pre-constructed multi-section train body fluid-solid coupling simulation model by utilizing a fluid-solid coupling simulation method according to the running speed of a high-speed train to obtain the flow field distribution conditions of the space around and under the high-speed train at different running speeds; according to the flow field distribution condition and the different under-vehicle positions of the brake disc, the incoming flow wind speed of the brake disc at the different under-vehicle positions is obtained; the inlet wind speed is set according to the incoming flow wind speed and different brake working conditions, a pre-constructed brake test bench flow-solid-heat simulation model is simulated by using a flow-solid-heat coupling simulation method, and the heat dissipation condition of the brake disc in the whole process of the brake test bench test is obtained. Compared with the prior art, the method has the advantages of improving the accuracy of the 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 space flow field under a high-speed train based on a geometric brake bench. Background Art

[0002] Brake discs play a vital role in the braking system of high-speed trains and are key components to ensure train safety. In actual application scenarios, the temperature of the brake disc will rise sharply due to emergency braking. Since the brake disc is located on the bogie and the surrounding structure is relatively complex, including the bottom of the vehicle, the track and the ground, the front and rear end partitions of the bogie, etc., the temperature change of the brake disc will cause the temperature change of the surrounding environment and components, which will in turn affect the safety of the high-speed train braking process. Therefore, studying the relationship between the air flow field in the bogie area of ​​the high-speed train and the temperature distribution and heat dissipation performance of the brake disc is important for improving the safety of the high-speed train braking process.

[0003] Bench test is a widely used method for physical testing of brake discs. The results obtained through the experiment have practical application value and engineering reference value. However, the test standards used in the current bench test are quite different from the actual application under the high-speed train. In addition, the previous bench tests mainly studied the temperature changes of the brake disc itself, without considering the complex structure of the actual bogie area and other factors that may affect the heat dissipation performance. The influence of the brake disc on the temperature change of the surrounding environment was ignored, which reduced 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 to provide a method and device for simulating the flow field of the space under the high-speed train based on a proportional brake 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, the proportional brake bench structure is considered, and air intake schemes for brake discs at different under-car positions are proposed. The fluid-solid-heat coupling simulation method is used for simulation to obtain the heat dissipation of the brake disc during the entire brake bench test. As a result, researchers can compare the heat dissipation results of the brake disc obtained by different air intake schemes, derive the influence of different air intake schemes on the test results of the bench heat dissipation, 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 invention, there is provided a method for simulating the flow field of the space under a high-speed train based on a proportional brake test bench, comprising the following steps: 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 the high-speed train and the space under the car at different running speeds, wherein the high-speed train running speed is obtained in advance, and the multi-section car body fluid-solid coupling simulation model comprises a first simulation model and a fluid-air domain model, wherein 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 Establish around the first simulation model; 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, wherein the different under-vehicle positions of the brake disc are pre-positioned; 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 brake test bench flow-solid-thermal simulation model to obtain the heat dissipation of the brake disc during the entire 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 preset proportional brake bench test bench structure model.

[0007] As a preferred technical solution, 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.

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

[0009] As a preferred technical solution, before simulating a pre-constructed 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, and the brake disc and the axle part directly connected to the brake disc are retained.

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

[0011] As a preferred technical solution, the positioning of the brake disc at different under-car 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.

[0012] As a preferred technical solution, the braking conditions include emergency braking, normal braking, braking on long and steep slopes, and multiple continuous braking at different initial braking speeds and braking decelerations.

[0013] As a preferred technical solution, 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 condition of the train under varying deceleration is simulated by writing a user-defined function.

[0014] As a preferred technical solution, 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.

[0015] According to a second aspect of the present invention, there is provided a flow field test device for approximating the space under a high-speed train based on a geometric brake bench, comprising a flow field distribution acquisition module, an incoming wind speed acquisition module and a 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 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, wherein the high-speed train running speed is obtained in advance, and the multi-section car body fluid-solid coupling simulation model comprises a first simulation model and a fluid-air domain model, wherein the first simulation model is a combination of a preset brake disc model, a train model and a bogie model, and the fluid The 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, and 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 brake test bench flow-solid-thermal simulation model to obtain the heat dissipation of the brake disc during the entire brake bench test process. 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 preset proportional brake bench test bench structure model.

[0016] Compared with the prior art, the present invention 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 running speeds, and then calculates the flow field characteristics (including the incoming flow 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, and then applies the simulated flow field characteristics to the bench test simulation 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 flow 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 the actual vehicle operation conditions on the bench test bench, which 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 thermal dissipation, and the related research on thermal dissipation cannot be verified by the test accuracy, 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, and simulation can be performed according to different braking conditions, and it has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 It is a simplified schematic diagram of the shaft disc and the brake pad in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Existing research on the thermal changes of brake discs and their impact on the surrounding environment mainly includes real vehicle test methods and numerical simulation methods. Among them, the real vehicle test is limited by factors such as the line environment, and the test opportunities are few and the cost is extremely high. It is difficult to meet the research needs of the temperature change of the brake disc of a high-speed train. In addition, it is difficult to obtain the real-time temperature change of the environment around the brake disc and the reference of the flow field flow in the real vehicle test. Numerical simulation can simulate the temperature change of the brake disc in the space under the high-speed train during the whole braking process and the temperature change of the surrounding environment, but in order to further verify the accuracy of the simulation, the temperature change test of the brake disc is still required. At the same time, the current bench test does not have an experimental scheme for approximate simulation of the flow field for the brake disc at different undercarriage positions of the high-speed train. The previous bench test only studied the temperature change of the brake disc itself. The influence of the inlet wind speed on the temperature change of the brake disc itself was not within the scope of the study, and the error of the temperature change was approximately ignored. However, with the increase of the initial braking speed of the high-speed train, the temperature of the brake disc itself reaches a higher level, and the influence of the brake disc on the temperature change of the surrounding environment needs to be studied to ensure safety. However, if the old bench test air intake scheme is used, the temperature change of the environment around the brake disc is closely related to the flow characteristics of the flow field, so different air intake methods will affect the test results. In addition, since high-speed trains generally have multiple sections, the brake discs located at different positions under the car have different air intake conditions, which will also affect the temperature change of 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 of the space under a high-speed train based on a proportional brake test bench. The method firstly 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 the high-speed train and the space under the car at different running speeds. The high-speed train running speed is obtained in advance, 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 obtained by pre-positioning; 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 by a fluid-solid-thermal coupling simulation method, and the brake disc heat dissipation during the whole process of the brake bench test is obtained. The braking condition is obtained in advance, and the brake test bench fluid-solid-thermal simulation model is established based on the brake disc model and the preset proportional brake bench test bench structure model.

[0023] Traditional real vehicle tests and bench tests require a lot of manpower and material resources. Compared with this, the simulation method proposed in the present invention can use a computer for simulation analysis, and can clearly obtain the temperature change cloud map and flow field trajectory velocity cloud map of the brake disc and its surrounding environment during the brake disc braking process. Compared with the traditional numerical simulation method, the simulation method proposed in the present invention takes into account the influence of the undercarriage environment of the high-speed train on the flow field distribution around the brake disc, and the influence of different flow field distribution on the heat dissipation of the brake disc, and combines this influence with the bench test, so that the simulation results can better guide the test method of approximating the undercarriage space flow field of the high-speed train on the proportional brake bench.

[0024] The present invention is described in detail below in conjunction with 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 of the space 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-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 the high-speed train and the space under the car at different running speeds.

[0028] In this step, different high-speed train running speeds are pre-set in the computational fluid software. 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.

[0029] Step 1.1) The brake disc model is divided into two types: brake shaft disc model and brake wheel disc model, which are three-dimensional models of brake discs with different structures and materials. Optionally, the modeling is performed according to the respective shapes and material properties and appropriately simplified. In the modeling process, the key parameters involved in the brake disc material include density, thermal conductivity and specific heat capacity.

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

[0031] The brake disc model, train model and bogie model are combined to obtain a model including multi-section train, bogie and brake disc, which is also the first simulation model. A fluid-air domain model is established around the complex model including multi-section train, bogie and brake disc, and a multi-section car body fluid-solid coupling simulation model including multiple brake discs can be obtained.

[0032] Step 1.3) Further, when setting the material parameters of the fluid domain, traditional studies usually use fluid materials with constant properties, without considering the effect of changes in the physical properties of air 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, and only the brake disc and the axle part directly connected to it are retained. If the wheel disc needs to be analyzed, the solid model of the wheel is also retained. This method can effectively reduce the computing cost while ensuring the simulation accuracy.

[0033] Step 1.4) Grid division is very critical for simulation calculations, and the quality of the grid directly affects the convergence speed and accuracy of numerical calculations. In this embodiment, unstructured grids are selected for grid division. Since the brake disc contains fine structures such as heat sinks, in order to ensure the accuracy of thermal simulation, the grid division of these parts is more detailed; at the same time, considering the computational cost, the grids in other areas are relatively sparse. According to the characteristics of flow field distribution in computational fluid dynamics, the local grid encryption is performed around the brake disc and the wake area by setting a density box.

[0034] Step 1.5) Under actual operating conditions, the brake disc will not only move horizontally as the train moves forward, but also rotate around the axle. In the simulation of the space under the train, the translation of the brake disc is regarded as an airflow in the air domain that is opposite to the direction of the train's advance and has the same speed. Therefore, the inlet of the calculation domain is defined as the velocity inlet, and a uniform incoming flow condition is adopted. The airflow direction is opposite to the direction of movement of the high-speed train, and the speed value is equal to the running speed of the train. Such a setting allows a more accurate simulation of the interaction between the brake disc and the surrounding air during the actual braking process. In ANSYS FLUENT, the fluid-solid coupling simulation method is used to simulate and analyze the flow field characteristics of the multi-section car body fluid-solid coupling simulation model and its undercarriage brake disc at different running speeds. The running behavior of the multi-section train is simulated as the air intake action of the front air inlet in the flow field domain, and the corresponding speed is applied to the surrounding environment and the track, which is equal to the running speed of the high-speed train, to simulate the movement of the train. At the same time, the different running speeds of the train are converted into different air inlet wind speeds and converted into different relative speeds. The rotating motion of the brake disc is simulated by using a moving reference system. Rotating parts 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 positions under the vehicle according to the flow field distribution and different positions under the vehicle of the brake disc, where the different positions under the vehicle of the brake disc are pre-positioned.

[0036] Specifically, this step first requires positioning the brake discs at different undercarriage locations 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 flow wind speed) of the incoming flow in front of the brake discs at different undercarriage locations is obtained as the train running speed changes.

[0037] Step 2.1) Using the simulation results of the train and the brake disc using the fluid-solid coupling simulation method in step S1, the characteristics of the flow field around the different brake discs are obtained by positioning the brake discs at different undercarriage positions. The positioning of the brake discs at different undercarriage positions includes the difference between the lead car and the middle car, the difference in the number of middle cars from the lead car, and the difference in the different positions of the brake shaft disc and the brake wheel disc on the axle.

[0038] Step 2.2) Since the flow conditions in the actual application scenarios during the simulation process and the actual bench test are usually equivalent to the flow directly in front of the brake disc, according to the under-vehicle structure, the flow received by the brake disc is concentrated in the area below the brake disc. The brake disc in this area is subject 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 under-vehicle positions, focus on extracting the flow field velocity distribution characteristics in front of the front part of the brake disc.

[0039] Step 2.3) Analysis of the fluid-solid coupling simulation results shows that the wind speed in front of the brake disc at different undercarriage positions is different, and a functional relationship between the wind speed in front of the brake disc at different undercarriage positions and the train running speed is established. The wind speed in front of the brake disc at different undercarriage positions and the train running speed have different multiple relationships. Therefore, in the subsequent bench simulation experiments and physical bench tests corresponding to the brake disc at different undercarriage positions, the size of the inlet wind is modified to achieve approximate simulation and testing 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 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 obtained in advance, and the brake test bench fluid-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 bench test bench structure model is simulated and modeled according to the structure of the geometric brake bench test bench, that is, Figure 1 The three-dimensional model of the brake bench in the figure can be used to establish a fluid-solid-thermal simulation model of the brake test bench 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 in the entire process of the brake bench test can be reproduced.

[0042] Step 3.1) By referring to the dimensions of the brake test bench in actual use, a fluid-solid-thermal simulation model of the brake test bench is established using computer modeling software. The brake disc is modeled using the same brake disc model as in step 1.1) with reference to the structure and material of the brake disc in actual use, including a variety of brake discs such as a brake shaft disc and a brake wheel disc. Around the brake disc, related components such as a support frame and a rotating shaft are configured according to the physical brake test bench, so that the simulated flow field environment is more similar to the actual application 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 used 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 a more realistic input for studying the heat dissipation law of the brake disc. Figure 2 A simplified model of the shaft disc and brake pad is shown, in which the friction surface of the brake pad is equivalent to a continuous sector with a central angle of θ. In this model, the heat flux density of the annular area with a radius of r on the brake disc is considered to be uniform. The heat flux density of the sector area with a radius of r and a radial width of dr on the brake pad and the corresponding annular area with a radius of r and a radial width of dr on the brake disc are calculated. The heat flux density on the narrow ring with a radial width of dr on the shaft 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 at the radius r on the gate, 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 to the shaft disk surface, that is, the heat distribution coefficient.

[0046] Step 3.3) The heat generated by friction will be transferred to the two objects in contact at a certain ratio. The heat distribution on the two friction surfaces. The heat distribution coefficient method sets the heat distribution coefficient between the two friction surfaces as a constant, ignoring the heat conduction between the two surfaces due to different temperatures. The formula is simplified by assuming that the temperature of the brake disc and the brake pad is always equal, and the heat distribution coefficient calculation formula for the brake disc is obtained:

[0047]

[0048] In the formula, k d 、c d , d and S d They represent the thermal conductivity, specific heat, density and friction area of ​​the brake disc, respectively. p 、c p , 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, common braking, long ramp braking, and multiple continuous braking conditions with different initial braking speeds and braking decelerations. In the modeling of the brake bench, the actual brake disc bench structure is referred to, and a special air inlet is used to blow 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 realized in the simulation by setting the air inlet surface. The setting of the air inlet is divided into two types: 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 side of the brake disc below the actual wind condition of the brake disc under the high-speed train. When setting the upper air inlet according to the proportional brake test bench, the air inlet wind speed is set according to the brake bench test outline, so that the working condition is the benchmark working condition for comparison of the air inlet bench test simulation results considering the undercarriage environment set in this embodiment. When setting the lower air inlet according to the actual wind conditions, the wind speed setting refers to the operation of the brake disc in actual working conditions, which has both translational movement with the train and rotational movement around the axle. The translational movement of the brake disc is equivalent to the air flow with the same speed and opposite direction as the air domain environment. In ANSYS FLUENT, the inlet is set as the velocity inlet, and a uniform incoming flow is used. Its flow direction is along the negative direction of the train operation, and the magnitude is equal to the running speed of the high-speed train. The wall temperature is set equal to the ambient temperature; the calculation domain outlet is set as the pressure outlet, and the track and the ground are the slip surface. The speed magnitude and direction are the same as the air flow speed.

[0050] Step 3.5) According to the different inlet wind speed ratios of the brake discs at different under-vehicle positions obtained by the 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. For the material parameter setting of the fluid domain, in previous studies on the heat dissipation of brake discs, steady-state fluid materials are often used, and the changes in the physical parameters of air with temperature are ignored, that is, the temperature, viscosity, and reference pressure of the air are assumed to be constant, but in fact a large amount of heat is generated during the braking process. In the simulation of the heat dissipation of the brake disc, the simulated temperature has a large span, so 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 (coupled algorithm) is used to solve the problem. The Realizable k-ε turbulence model is selected to describe turbulent flow, which is suitable for the simulation of complex flow. In order to improve the accuracy of numerical calculation, the discretization format selects the second-order upwind format, which can effectively capture shock waves and contact discontinuities in the flow and is suitable for high-speed flow and computational domains with complex geometric shapes. Unlike steady-state fluid materials, the density of the incompressible ideal gas material selected for simulation in this embodiment will change with temperature, so it is also necessary to add the setting of the gravitational acceleration direction.

[0051] Step 3.6) ANSYS FLUENT software provides a variety of computational models for simulating the motion area of ​​an object. 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 planes (MPM), sliding meshes (SMM) and dynamic meshes (DMM) and other models. Since 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 brake discs and wheelsets), and the corresponding rotation angular velocity is set:

[0052]

[0053] In the formula, 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 rotates accordingly. At the junction of the turbulent air area and the external air domain, a boundary named "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 docked, thereby ensuring the smooth progress of the calculation process. In this way, the impact of the rotation of the brake disc 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 process of the brake disc is a transient phenomenon, which requires that many parameters must change dynamically over time in the simulation analysis. These parameters include the wind speed at the air inlet (equivalent to the train speed), the rotation speed of the brake disc, and the heat flux density at different locations on the brake disc. Since the standard interface and functions of FLUENT may not meet the needs of these dynamic parameter changes, simulation can be achieved by writing user-defined functions (User Defined Function, referred to as UDF), especially when it is necessary to simulate the changing deceleration. These UDFs can be written in C language and the files are saved with a ".c" extension. Usually, 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 at the corresponding location. Once the UDF is compiled, the defined variables will appear in the user-defined window of FLUENT, and the user can select these functions in the corresponding dialog box and link them to the solver.

[0056] Step 3.9) In order to further study the temperature variation characteristics of the brake disc and the surrounding air domain under natural convection conditions, this embodiment extends the time range of the simulation beyond the actual time of train braking. This means that the simulation not only covers the entire stage from the beginning to the end of braking, but also includes the period of time when the train is stationary after the braking is completed. In this way, the continuous changes in the temperature of the brake disc and the air domain caused by natural convection after the braking action is completed can be more comprehensively observed and analyzed, so as to more accurately understand 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 of the brake bench test and in a stationary state after the braking, analyzing the heat dissipation process of the brake disc from multiple angles of forced convection and natural convection, and analyzing the incoming flow of the brake disc corresponding to different positions under the vehicle.

[0059] After the solution is obtained in step 4.1), the post-processing software can be used to obtain the temperature change cloud map of the brake disc during the braking process, the temperature change cloud map of the environment around the brake disc, the speed cloud map of the flow field trace around the brake disc and the vehicle body, and the temperature change of the point on the brake disc or in the air environment. By comparing the simulation results of different undercarriage structures, different brake disc materials, different brake disc structures, and brake discs in different positions, the heat dissipation law of the brake disc under different braking conditions and different position settings can be compared.

[0060] Step 4.2) The difference between the proportional brake bench test outline of the brake disc at different under-vehicle positions and the normal brake test outline is mainly concentrated in the difference in the air intake method. By setting different air inlet wind speed changes, the flow field environment of the brake disc at different under-vehicle positions can be approximately tested on the bench.

[0061] Step 4.3) The setting of the braking condition in the proportional brake bench test outline for brake discs approximately located at different positions under the vehicle will have an additional stage after the braking is completed 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 will not be executed during this stage. Instead, the cooling procedure will be executed after the brake disc has fully dissipated the heat naturally, and the test of the next condition will be continued.

[0062] Furthermore, the present embodiment also provides an approximate high-speed train undercarriage space flow field test device based on a proportional brake bench, comprising 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. Combination, the 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, and the different under-vehicle positions of the brake disc are obtained by pre-positioning; 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 brake test bench fluid-solid-thermal simulation model to obtain the brake disc heat dissipation of the entire brake bench test process. The braking condition is obtained in advance, and the brake test bench fluid-solid-thermal simulation model 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, which will not be repeated here.

[0063] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for simulating the flow field under the space of 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-built multi-section car body fluid-solid coupling simulation model is simulated by 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, wherein the high-speed train running speed is obtained in advance, and the multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model, wherein 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; According to the flow field distribution and different under-vehicle positions of the brake disc, the wind speed of the incoming flow of the brake disc at different under-vehicle positions is obtained, wherein the different under-vehicle positions of the brake disc are obtained by pre-positioning; The inlet wind speed is set according to the incoming wind speed and different braking conditions, and the pre-constructed fluid-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 acquired 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.

2. The method for simulating the flow field under the space of a high-speed train based on a proportional brake test bench according to claim 1 is characterized in that: The train model is established according to 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 an unenclosed type, a semi-enclosed type and a fully enclosed type.

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

5. The method for simulating the flow field under the space of a high-speed train based on a proportional brake 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 the space of a high-speed train based on a proportional brake 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 axle disc and the brake wheel disc on the axle.

7. The method for simulating the flow field under the space of a high-speed train based on a proportional brake 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 the space of a high-speed train based on a proportional brake 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 condition of the train under varying deceleration is simulated by writing a user-defined function.

9. The method for simulating the flow field under the space of a high-speed train based on a proportional brake 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 approximating the flow field under a high-speed train based on a proportional brake bench, characterized in that: It includes a flow field distribution acquisition module, an incoming wind speed acquisition module, and a heat dissipation acquisition module; The flow field distribution acquisition module is used to simulate the 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, wherein the high-speed train running speed is obtained in advance, and the multi-section car body fluid-solid coupling simulation model includes a first simulation model and a fluid-air domain model, wherein 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; 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 acquired 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.

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