Mesh division method for simulating tunnel train movement based on overlapped grids

Abstract

According to the method, a geometric model is established according to the actual movement condition of a train in a tunnel, and the whole drainage basin condition is divided into a foreground area and a background area. The method mainly comprises the steps of geometric model establishment, background region and foreground region division, background region '0'-shaped segmentation, background region structured grid division, foreground region unstructured grid division and grid motion inspection. In the background area and foreground area grid division process, independent encryption of grids can be achieved, namely, different grid density setting can be conducted on different positions, for example, the influence of an inlet air domain on a result is small, a large grid size can be set, the number of the grids can be reduced, and the calculation efficiency is improved; and the boundary layer and the train surface can be encrypted. In the follow-up numerical simulation research process, if the vehicle model structure needs to be changed for research, only the step 5 needs to be carried out again to divide the component area grid, the grid of the whole fluid domain does not need to be divided again, and the grid division workload is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fluid machinery, in particular to a pre-processing method for dynamic numerical simulation of an unsteady flow field. Background Art

[0002] The progress of science and technology has promoted the great development of high-speed railways. With the continuous increase in the operating speed of high-speed trains, people's pursuit of higher-speed land transportation has intensified. As a result, high-speed maglev trains came into being. Ordinary high-speed wheel-rail trains have inevitable aerodynamic problems, so the aerodynamic problems of maglev trains running at ultra-high speeds will be more prominent. Therefore, it is necessary to study the aerodynamic problems encountered by high-speed maglev trains. In the absence of standards and measured data, the research on the above problems is mainly based on the Computational Fluid Dynamics (CFD) method. The CFD method refers to the use of computers to use numerical methods to discretize and solve fluid mechanics control equations, so as to achieve the purpose of predicting the characteristics of flow field laws.

[0003] When studying tunnel aerodynamics and other issues, the phenomenon of train movement in the flow field is involved. There are moving boundaries in the flow field, and the application of dynamic mesh technology in CFD calculations needs to be considered. In the CFD solver ANSYS FLUENT, the main dynamic mesh forms are: sliding mesh, dynamic mesh, overlapping mesh, etc. Overlapping mesh has the advantages of flexible model configuration changes and high solution quality, and can avoid problems such as mesh reconstruction failure that may occur in traditional dynamic mesh forms. In addition, fully structured meshes can be used in regular flow fields and unstructured meshes can be used in complex areas to further increase the accuracy of simulation calculations and reduce the time consumption of simulation calculations. The first step in CFD numerical calculations is pre-processing to generate high-quality flow field meshes. A set of high-quality meshes can not only improve the accuracy of simulation results, but also reduce the calculation time. The current mainstream meshing software at home and abroad includes Gambit, ICEM, Ansys Meshing, etc. Among them, Ansys Meshing has the advantages of strong versatility and high quality of generated meshes. Summary of the invention

[0004] In response to the above-mentioned prior art, the present invention provides a grid division method for simulating tunnel train motion based on overlapping grids. The method can divide structured grids in the background area and unstructured grids in the foreground area, thereby reducing the number of grids, improving the grid quality, and facilitating independent encryption of boundary layer grids and overlapping grid settings in subsequent numerical simulations.

[0005] In order to solve the above technical problems, the present invention proposes a grid division method for simulating tunnel train movement based on overlapping grids. According to the actual situation of the train moving in the tunnel, the geometric models of the tunnel and the train are respectively established; the topological structures of the flow basin in the tunnel and the flow basin near the train are respectively established, and the flow basin in the tunnel is used as the background area of ​​the overlapping grid, and the flow basin near the train is used as the foreground area of ​​the overlapping grid; the background area topological structure is divided into "O" shape; the background area is structured grid divided, and the boundary layer area grid located near the wall is encrypted; the foreground area is unstructured grid divided, and the boundary layer area grid located on the vehicle surface is encrypted; finally, the background area grid and foreground area grid processed as above are imported into Fluent for grid motion inspection.

[0006] Furthermore, the grid generation method for simulating tunnel train motion based on overlapping grids of the present invention adopts flow field pre-processing software such as SolidWorks, Ansys SCDM, Ansys Meshing, etc., and includes the following steps:

[0007] Step 1: Establishing the geometric model of the tunnel and the train: According to the actual situation of the train moving in the tunnel, the geometric model of the train is established in the SolidWorks software; the geometric model of the tunnel is established in the Ansys SCDM software. The geometric model of the tunnel includes the air domain, track, and air shaft at the entrance and exit of the tunnel.

[0008] Step 2: Division of background area and foreground area: Establish the topological structure of the watershed in the tunnel in the Ansys SCDM software, and use the watershed as the background area; establish the topological structure of the watershed near the train in the Ansys SCDM software, and use the watershed as the foreground area.

[0009] Step 3: "O"-shaped segmentation of the background area: In the Ansys SCDM software, draw a rectangle on the end face of the tunnel with the center point of the end face as the midpoint. The length of the rectangle is 1 / 2 of the tunnel width, and the height of the rectangle is 1 / 3 of the tunnel height. The flow basin in the tunnel is cut along the axial path of the tunnel with the rectangle as the starting point; select several points on the boundary of the tunnel end face, connect the points with the rectangular frame, and cut the flow basin in the tunnel along the axial path of the tunnel with the connecting line as the starting point. The positions of the several points are based on the cross-sectional form of the tunnel. Specifically, for a circular tunnel, two trisection points of the arc part and two intersection points of the arc part and the bottom edge can be selected; for a rectangular tunnel, four vertices of the rectangular face can be selected; for a horseshoe tunnel, the slow round point and the slow round point of the horseshoe curve can be selected.

[0010] Step 4: Structured meshing of the background area: In the Ansys Meshing software, the topological structure of the background area obtained in step 3 is meshed, the boundary layer mesh size calculated using the y+ formula is used to set the line density of the edges in the topological structure of the background area; the mesh is generated and the mesh quality is checked. When the mesh quality meets the requirements, a mesh file is generated and saved, which is recorded as the background area mesh file.

[0011] Step 5: Unstructured meshing of the foreground area: In the Ansys Meshing software, mesh the topological structure of the foreground area obtained in step 2. Set the overall unit size of the foreground area mesh, encrypt the surface of the train geometry model; select the tetrahedron-dominated mesh generation method; generate the mesh and check the mesh quality. After the mesh quality meets the requirements, generate a mesh file and save it, which is recorded as the foreground area mesh file.

[0012] Step 6: Grid motion check: Use Ansys Fluent software to open the background area grid obtained in step 4, and add the foreground area grid obtained in step 5 to the Zone module; set the foreground grid motion related parameters, set the iteration steps and time step; activate Display Grid in Display Options, set the display frequency in Display Frequency; click the Preview button to start previewing. After confirming that the grid motion is correct, the grid file at this time can be used for subsequent numerical simulation calculations.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The method of the present invention is to establish a geometric model according to the actual situation of the train moving in the tunnel, and divide the entire flow basin into a foreground area and a background area. It mainly includes the establishment of a geometric model, the division of the background area and the foreground area, the "O"-shaped segmentation of the background area, the structured grid division of the background area, the unstructured grid division of the foreground area, and the grid motion test. In the process of grid division of the background area and the foreground area, the independent encryption of the grid can be achieved, that is, different grid densities can be set for different positions. For example, the inlet air domain has little effect on the results, and a large grid size can be set to reduce the number of grids and improve the calculation efficiency; the boundary layer and the train surface can also be encrypted. In the subsequent numerical simulation research process, if the vehicle structure is to be changed for research, it is only necessary to re-carry out step five to divide the component area grid, without re-dividing the grid of the entire fluid domain, thereby reducing the workload of grid division. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the division of background area and foreground area, where a) is the background area and b) is the foreground area

[0016] Figure 2 This is an illustration of the "O"-shaped division of the background area.

[0017] Figure 3 Schematic diagram of the grid result divided by the present invention

[0018] Specific implementation methods

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0020] The grid generation method for simulating tunnel train motion based on overlapping grids of the present invention comprises the following steps:

[0021] Step 1: Establishing the geometric model of the tunnel and the train: According to the actual situation of the train moving in the tunnel, the geometric model of the train is established in the SolidWorks software; the geometric model of the tunnel is established in the Ansys SCDM software. The geometric model of the tunnel includes the air domain and the track at the entrance and exit of the tunnel, and the geometric model of the train can be appropriately simplified.

[0022] Step 2: Division of background area and foreground area: Figure 1 As shown in a), the topological structure of the watershed in the tunnel is established in the Ansys SCDM software, and the watershed is used as the background area; Figure 1 As shown in b), the topological structure of the watershed near the train is established in the Ansys SCDM software, and the watershed is used as the foreground area. The nearby watershed is a rectangular watershed surrounding the train.

[0023] Step 3: Background area "O"-shaped segmentation: Figure 2 As shown, in the Ansys SCDM software, a rectangle is drawn on the tunnel end face with the end face center point as the midpoint, the rectangle length is 1 / 2 of the tunnel width, the rectangle height is 1 / 3 of the tunnel height, and the flow basin in the tunnel is cut along the axial path of the tunnel with the rectangle as the starting point; the slow round point and the slow round point of the horseshoe curve are selected on the boundary of the tunnel end face, the points are connected with the rectangular frame, and the flow basin in the tunnel is cut along the axial path of the tunnel with the connecting line as the starting point.

[0024] Step 4: Structured meshing of background area: In the Ansys Meshing software, mesh the topological structure of the background area obtained in step 3, use the boundary layer mesh size calculated by the y+ formula to set the line density of the edges in the topological structure of the background area; generate a mesh and check the mesh quality. When the mesh quality meets the requirements, generate a mesh file and save it, such as Figure 3 Shown is a background area grid, recorded as a background area grid file.

[0025] Step 5: Unstructured meshing of the foreground area: In the Ansys Meshing software, mesh the topological structure of the foreground area obtained in step 2. Set the overall unit size of the foreground area mesh, encrypt the surface of the train geometry model; select the tetrahedron-dominated mesh generation method; generate the mesh and check the mesh quality. After the mesh quality meets the requirements, generate a mesh file and save it, which is recorded as the foreground area mesh file.

[0026] Step 6: Grid motion check: Use Ansys Fluent software to open the background area grid obtained in step 4, and add the foreground area grid obtained in step 5 to the Zone module; set the foreground grid motion related parameters, set the iteration steps and time step; activate Display Grid in Display Options, set the display frequency in Display Frequency; click the Preview button to start previewing. After confirming that the grid motion is correct, the grid file at this time can be used for subsequent numerical simulation calculations.

[0027] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the purpose of the present invention, all of which are within the protection of the present invention.

Claims

1. A grid generation method for simulating tunnel train motion based on overlapping grids, characterized in that: Establishing the geometric models of the tunnel and the train respectively; establishing the topological structures of the watershed in the tunnel and the watershed near the train respectively, taking the watershed in the tunnel as the background area of ​​the overlapping grid, and taking the watershed near the train as the foreground area of ​​the overlapping grid; Perform "O"-shaped division on the background area topology structure; The background area is structured and meshed, while the boundary layer area near the wall is encrypted. The foreground area is divided into unstructured grids; finally, the background area grids and foreground area grids processed as above are imported into Fluent for grid motion inspection.

2. The grid generation method for simulating tunnel train motion based on overlapping grids according to claim 1 is characterized in that: Use SolidWorks, Ansys SCDM, Ansys Meshing and other flow field pre-processing software, and include the following steps: Step 1: Establishing the geometric model of the tunnel and the train: According to the actual situation of the train moving in the tunnel, the geometric model of the train is established in the SolidWorks software; the geometric model of the tunnel is established in the Ansys SCDM software. The geometric model of the tunnel includes the air domain, track, and air shaft at the entrance and exit of the tunnel. Step 2: Division of background area and foreground area: Establish the topological structure of the watershed in the tunnel in the Ansys SCDM software, and use the watershed as the background area; establish the topological structure of the watershed near the train in the Ansys SCDM software, and use the watershed as the foreground area. Step 3: "O"-shaped segmentation of the background area: In the Ansys SCDM software, draw a rectangle on the end face of the tunnel with the center point of the end face as the midpoint. The length of the rectangle is 1 / 2 of the tunnel width, and the height of the rectangle is 1 / 3 of the tunnel height. The watershed in the tunnel is cut along the axial path of the tunnel with the rectangle as the starting point; select several points on the boundary of the tunnel end face, connect the points with the rectangular frame, and cut the watershed in the tunnel along the axial path of the tunnel with the connecting line as the starting point. The positions of the several points are based on the cross-sectional form of the tunnel. Specifically, for a circular tunnel, two trisection points of the arc part and two intersection points of the arc part and the bottom edge can be selected; for a rectangular tunnel, four vertices of the rectangular face can be selected; for a horseshoe tunnel, the slow round point and the slow round point of the horseshoe curve can be selected. Step 4: Structured meshing of the background area: In the Ansys Meshing software, the topological structure of the background area obtained in step 3 is meshed, the boundary layer mesh size calculated using the y+ formula is used to set the line density of the edges in the topological structure of the background area; the mesh is generated and the mesh quality is checked. When the mesh quality meets the requirements, a mesh file is generated and saved, which is recorded as the background area mesh file. Step 5: Unstructured meshing of the foreground area: In the Ansys Meshing software, mesh the topological structure of the foreground area obtained in step 2. Set the overall unit size of the foreground area mesh, encrypt the surface of the train geometry model; select the tetrahedron-dominated mesh generation method; generate the mesh and check the mesh quality. After the mesh quality meets the requirements, generate a mesh file and save it, which is recorded as the foreground area mesh file. Step 6: Grid motion check: Use Ansys Fluent software to open the background area grid obtained in step 4, and add the foreground area grid obtained in step 5 to the Zone module; set the foreground grid motion related parameters, set the iteration steps and time step; activate Display Grid in Display Options, set the display frequency in Display Frequency; click the Preview button to start previewing. After confirming that the grid motion is correct, the grid file at this time can be used for subsequent numerical simulation calculations.

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