A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems

Abstract

The application discloses a high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems, comprising the following steps: S1, constructing a geometric model, wherein the geometric model comprises a high-speed train, a track and a virtual wind tunnel; S2, dividing a grid conforming to the flow field and heat dissipation characteristics of the high-speed train; S3, establishing a dynamic region and a static region, a fluid region and a solid region; S4, completing high-speed train emergency mechanical braking heat dissipation simulation by setting flow and heat dissipation boundary conditions; and S5, determining braking heat dissipation evaluation criteria, and analyzing the temperature change and the highest temperature of the brake disc surface and the space key measuring points in the emergency braking process. According to the application, the method has the advantages of low simulation cost and reasonable precision.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical brake heat dissipation simulation, and in particular to a high-speed train emergency brake heat dissipation simulation method based on a multi-reference coordinate system method. Background Art

[0002] In recent years, my country's high-speed trains have developed rapidly, with operating speeds reaching 350km / h. At present, the new generation of trains CR450 with a speed of 400 kilometers per hour is being developed. The increase in operating speed has brought convenience to people's daily travel, but it has also brought considerable challenges to the braking problems of high-speed trains. In particular, the operation of intercity EMUs has put forward more stringent requirements on braking safety and reliability. Problems in any aspect will have extremely serious consequences. High-speed train braking includes common braking, emergency mechanical braking, unconventional braking and auxiliary braking. The braking method of the train is constantly improving with the increase in train speed. At present, the train is equipped with a mechanical braking system and a power braking system. The vehicle braking process mainly converts the kinetic energy of the train into heat energy, but speed and braking are a contradiction. The higher the speed, the greater the heat energy converted during the braking process. During the braking process of the high-speed train brake disc, the huge braking heat load causes the brake disc to produce a large temperature gradient, but due to the structural constraints of the brake disc, thermal stress will be generated inside, posing a certain threat to the safe operation of the brake disc.

[0003] At present, if the "Fuxing" train in my country, which runs at a speed of 350 kilometers per hour, implements emergency mechanical braking at an initial speed of 350km / h, its braking distance is close to 5500m. If the CR450 train with a speed of 400 kilometers per hour, which is under development, implements emergency mechanical braking at an initial speed of 400km / h, its braking distance will definitely exceed 6500m. The traditional sliding grid-based high-speed train emergency mechanical braking method requires the creation of a 7000m long computational domain and the completion of the mutual movement between the train and the ground after each time step, which will result in a huge number of grids and calculation time, and cannot meet the requirements of rapid engineering updates and iterations. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-speed train emergency brake heat dissipation method with low cost and reasonable accuracy based on a multi-reference coordinate system. In order to achieve the above-mentioned purpose and other advantages according to the present invention, a high-speed train emergency brake heat dissipation simulation method based on a multi-reference coordinate system is provided, comprising:

[0005] S1. constructing a geometric model, wherein the geometric model includes a high-speed train, a track and a virtual wind tunnel;

[0006] S2, divide the grids that meet the flow field and heat dissipation characteristics of high-speed trains;

[0007] S3, establish dynamic domain and static domain, fluid domain and solid domain;

[0008] S4. Complete the heat dissipation simulation of emergency braking of high-speed train by setting flow and heat dissipation boundary conditions;

[0009] S5. Determine the evaluation standard for brake heat dissipation, and analyze the temperature changes and maximum temperatures of the brake disc surface and key spatial measurement points during emergency braking.

[0010] By creating a new coordinate system and setting its moving speed with physical time, the dynamic domain is applied to the coordinate system to form a static train-ground relative motion method based on multiple reference coordinate systems, which can avoid the huge computational domain and computational cost caused by the traditional sliding grid method.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1) When a high-speed train brakes urgently, the deceleration in different speed ranges is different. The traditional method needs to first calculate the maximum braking distance and create a huge calculation domain. The present invention does not need to create a huge calculation domain of several kilometers, but only needs to create a small calculation domain of L+40H (L is the length of the train, H is the height of the train), which is about 1 / 20 of the length of the traditional method.

[0013] 2) If the deceleration changes in the traditional method, the calculation domain needs to be recreated. This method only needs to give the deceleration of the coordinate system, which greatly increases the convenience of use and saves modeling costs.

[0014] 3) The traditional method needs to change the physical position of the grid after each time step iteration. If the interface is not handled properly, it will not only affect the accuracy, but also easily lead to divergence and increase the calculation time. The present invention only changes the coordinate system, without changing the physical position of the grid. It is easy to achieve the correspondence between the dynamic domain and the static domain nodes, ensure accuracy and convergence, and reduce the update time. The simulation time of the train implementing emergency braking at an initial speed of 350km / h is only 1 / 50 of that of the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of a high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems according to the present invention;

[0016] Figure 2 A high-speed train braking heat dissipation simulation model diagram of a high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems according to the present invention;

[0017] Figure 3 A diagram showing the relationship between train speed and time of a high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems according to the present invention;

[0018] Figure 4It is a temperature variation curve diagram of the brake disc surface and the measuring points near the bearing according to the high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example 1

[0021] Reference Figure 1 , a high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems, comprising the following steps:

[0022] 1) Construct a geometric model. The constructed geometric model should include a high-speed train, track and virtual wind tunnel. Among them, the high-speed train includes a head car, a middle car and a tail car that are connected in sequence to form a car body, as well as a bogie and a pantograph arranged on the car body. The middle car is in the straight section of the high-speed train. The head car and the tail car respectively include a nose tip, a curved section and a straight section that transition in sequence. The geometric model contains key areas such as the head shape, bogie and pantograph. The track and roadbed are both standard tracks and standard roadbeds in my country. The virtual wind tunnel was created with reference to the standard TB / T 3503.4-2018.

[0023] 2) Divide the grid that meets the flow field and heat dissipation characteristics of high-speed trains. First, create a grid that can better simulate the surface boundary layer of the high-speed train, then divide smaller surface grids and volume grids in the areas with large flow separation such as the head and tail car curves and bogies, and finally the spatial volume grid should be gradually grown from the car body to the outside.

[0024] 3) Establish dynamic domain, static domain, fluid domain and solid domain. The body space close to the train is the dynamic domain, and the other body spaces are the static domain; the area where the brake disc and axle are located is the solid domain, and the other areas are the fluid domain, considering fluid-solid coupling heat dissipation.

[0025] 4) Use effective turbulence models and numerical formats. In order to obtain high-precision flow and heat dissipation simulation results, the transient simulation should use the kw SST turbulence model, and the time and space numerical formats should be at least second-order formats. An implicit format should be used with a small time step and a sufficient number of iterations.

[0026] 5) Set appropriate flow and heat dissipation boundary conditions. Create a new coordinate system and set its moving speed with physical time. Apply the dynamic domain to the coordinate system to form a static high-speed train and ground relative motion method based on multiple reference coordinate systems. The pressure on the sides and top of the virtual wind tunnel is 0Pa. The ground and train surfaces are non-slip walls in their respective coordinate systems. The heat flux density on the brake disc surface is given, and other components such as bearings are given a certain wall temperature.

[0027] 6) Determine appropriate brake heat dissipation evaluation criteria. Focus on the brake disc and other non-high temperature resistant surfaces, as well as the temperature gradient and maximum temperature of key measurement points in the flow field.

[0028] Example 2

[0029] like Figure 2 As shown, it is a high-speed train emergency brake heat dissipation simulation model in this embodiment, and the model includes a leading car 101, a middle car 102, a tail car 103, a trailer bogie 104, a power bogie 105, a pantograph 106 and a virtual wind tunnel 107. The leading car 101, the middle car 102 and the tail car 103 are sequentially connected to form the body of the high-speed train, the middle car 102 is in the straight section of the high-speed train, the leading car 101 and the tail car 103 respectively include a nose tip, a curved section and a straight section that transition in sequence, the leading car 101 and the tail car 103 are provided with a trailer bogie 104, the middle car 102 is provided with a power bogie 105, and the pantograph 106 is located in the middle car 102.

[0030] For a three-car high-speed train, first create a mesh that meets its flow and heat dissipation characteristics. Among them, the number of surface meshes of the head car 101, the middle car 102 and the tail car 103 are approximately 442,000, 428,000 and 442,000 respectively, the number of surface meshes of the trailer bogie 104 and the power bogie 105 are approximately 540,000 and 714,000 respectively, and the number of surface meshes of the pantograph 106 is approximately 266,000. The interface and other surfaces of the dynamic domain 108 are approximately 777,000 and 6,000 respectively, and the interface, ground and surroundings of the static domain 109 are approximately 731,000, 384,000 and 50,000 respectively. Create a mesh encryption area at the bottom of the train, where the volume mesh size of the first encryption area 201 is 100mm, and the volume mesh size of the second encryption area 202 is 50mm. The volume mesh size of solid domains such as brake discs is 50mm.

[0031] Ideal gas and k-ωSST turbulence models are used for transient flow and heat dissipation calculations. The thermal conductivity, dynamic viscosity and specific heat of air in the fluid domain change with temperature, while the density, specific heat and thermal conductivity of the solid domain do not change with temperature. The virtual wind tunnel is surrounded by a pressure boundary with a relative pressure of 0Pa. The virtual wind tunnel floor, track and train surface are all no-slip walls. The heat flux density is given on the brake disc surface, as shown in Equation 1. The bearing surface is given a wall temperature of 70°C. The wheels and axles are given rotating wall conditions. The dynamic domain uses a multi-reference coordinate system and a given moving speed. The relationship between the moving speed and time is as follows: Figure 3 The braking start speed is 400km / h and the ambient temperature is 37℃.

[0032] q(t)=0.8ma(v+at) / nA (1)

[0033] Among them, m is the train axle weight, v is the initial velocity, a is the deceleration, n is the number of brake discs installed on each axle, and A is the area of ​​the friction ring on the brake disc.

[0034] The time and space numerical formats of transient simulation are both in second-order format. The time step and number of iterations of each deceleration segment are as follows:

[0035] ● The vehicle speed was decelerated from 400 km / h to 361 km / h, with a time step of 0.002 s, 6 iterations per time step, and a total of 8775 time steps;

[0036] ● The vehicle speed was decelerated from 360 km / h to 316 km / h, with a time step of 0.002 s, 6 iterations per time step, and a total of 7765 time steps;

[0037] ● The vehicle speed was decelerated from 315 km / h to 251 km / h, with a time step of 0.003 s, 8 iterations per time step, and a total of 5877 time steps;

[0038] ● The vehicle speed was decelerated from 250 km / h to 121 km / h, with a time step of 0.006 s, 8 iterations per time step, and a total of 5625 time steps;

[0039] ●The vehicle speed decelerated from 120km / h to 0km / h, the time step was 0.012s, the number of iterations per time step was 12 times, and the total number of time steps was 2137.

[0040] In order to verify the simulation method of the present invention, the temperature change curves and the maximum temperature of the brake disc surface and the measuring points near the bearing are given respectively. Figure 4It can be seen that the surface temperature of the brake disc increases rapidly first and then decreases slowly with the braking time. In the early stage of braking, the temperature rises rapidly due to the high speed and high heat generation. In the later stage of braking, the temperature drops due to the low speed and low heat generation and the enhanced heat dissipation capacity. The highest surface temperatures of the brake discs at the 2nd end of the leading and middle cars and the 1st end of the tail car are 547, 645 and 555℃ respectively, and the temperatures of the measuring points near the corresponding bearings are 77, 92 and 78℃ respectively.

[0041] The number of devices and processing scales described here are used to simplify the description of the present invention, and the application, modification and variation of the present invention will be obvious to those skilled in the art.

[0042] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems, characterized in that: include: S1. constructing a geometric model, wherein the geometric model includes a high-speed train, a track and a virtual wind tunnel; S2, divide the grids that meet the flow field and heat dissipation characteristics of high-speed trains; S3, establish dynamic domain and static domain, fluid domain and solid domain; S4. Complete the heat dissipation simulation of emergency braking of high-speed train by setting flow and heat dissipation boundary conditions; S5. Determine the evaluation standard for brake heat dissipation, and analyze the temperature changes and maximum temperatures of the brake disc surface and key spatial measurement points during emergency braking.

2. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems as claimed in claim 1, characterized in that: In step S1, the high-speed train includes a leading car, a middle car and a tail car which are sequentially connected to form a car body, and a bogie and a pantograph arranged on the car body. The middle car is in a straight section of the high-speed train, and the leading car and the tail car respectively include a nose tip, a curved section and a straight section which transition sequentially.

3. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems as claimed in claim 2, characterized in that: In step S2, surface meshes of the high-speed train, the ground, the track and the virtual wind tunnel are created, and boundary layer meshes are created on the surface of the high-speed train and the ground; mesh densification areas are created in areas with large flow separation; and spatial body meshes are created by gradually growing the vehicle body outward.

4. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems as claimed in claim 3, characterized in that: The large flow separation area includes the curved section of the leading car, the curved section of the trailing car and the bogie, and the spatial body grid includes the body grid of the track and the body grid of the virtual wind tunnel.

5. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems as claimed in claim 4, characterized in that: In step S3, the body space close to the train is a dynamic domain, and the other body spaces are static domains; the area where the brake disc and the axle are located is a solid domain, and the other areas are fluid domains.

6. A high-speed train emergency braking heat dissipation simulation method based on multiple reference coordinate systems as claimed in claim 1, characterized in that: Step S4 specifically includes a turbulence model for transient simulation and time and space numerical formats, and the turbulence model for transient simulation is k-ωSST, and the time and space numerical formats are at least second-order formats.

Images