High speed train
Introduction
High-speed trains travel in the subsonic compressible flow regime with Mach numbers in the range of 0.3 to 0.4. In CFD, the pressure-based solver of SIMPLE algorithm is often used for low-speed flows and the density-based solver for high-speed flows. This challenge aims to validate the stability of Baram's incompressible solver, buoyantSimpleNFoam, in the subsonic compressible flow regime.
We use a high-speed train model with simplified vehicle connections, bogies (wheels), and pantographs, and the train speed is 400 km/h.
With a mesh of about 2 million mesh, the convergence was achieved in about 300 iterations (about 20 minutes on an 8-core CPU). The convergence is much better compared to the results obtained using OpenFOAM's standard solvers buoyantSimpleFoam and rhoSimpleFoam.
Geometry
Use given stl file for train geometry.
Using [Hex6] for the computational domain and one hexahedron to create a dense mesh around the vehicle, set it up as shown in the following image.
Click the [Import] button at the bottom to select the train.stl file.
You will have a volume called Visualization_Toolkit_generated_SLA_File and a surface called Visualization_Toolkit_generated_SLA_File_surface.
In Geometry, select a face and right-click and select Edit/View. In the window that opens, change the name as train_surface로 변경한다.
Create hexahedron for computational domain
Click the [Add] button and select [Hex6] and set values as follows
- far : Use [Hex6] to define inlet, outlet, bottom, etc.
- Type : None
- Min./Max. : (-75 -40 0) / (260 0 40)
- Since it is symmetrical, we only create half of it in the y-axis.
In Geometry, select surfaces and right-click and select Edit/View. In the window that opens, change the name as follows
- far_xMin : inlet
- far_xMax : outlet
- far_yMin : side
- far_yMax : symmetry
- far_zMin : ground
- far_zMax : top
Create hexahedron for mesh refinement
Click the [Add] button and select [Hex] and set values as follows
- refine box : Use [Hex]
- Type : None
- Min./Max. : (-18 -5 0) / (100 5 7)
In Geometry, select Hex_1_surface and right-click and select Edit/View. In the window that opens, change the type to [None]
Click the [Next] button to move on to the next step.
Region
Click the (+) icon at the top to create a region. Move the mouse to the intersection of the lines that appear in light green color in the graphics window and position it inside the computation domain. Click the [Add] button to complete the setup.
Click the [Next] button to move on to the next step.
Base Grid
Select [Use Hex6] option and set the number of grids to 100, 20, and 20. Click the [Generate] button to generate the base grid.
Click the [Next] button to move on to the next step.
Castellation
Use default conditions for [Configuration] and [Advanced].
Define mesh refinement for the car.
Click the (+) icon under [Surface/Feature Refinement] and set the following settings for train_surface
- Surface Refinement
- Minimum Level : 5
- Maximum Level : 5
- Feature Edge refinement Level : 5
- Surfaces : train_surface
Click the (+) icon under [Volume Refinement] and set the following settings for Hex_1
- Volume Refinement Level : 4
- Volume : Hex_1
When you're done setting up, your screen should look like this
To enable parallelization, click [Parallel]-[Environment] in the menu and enter the desired value for [Number of Cores].
Click the [Refine] button and the castellation step starts.
Click the [Next] button to move on to the next step.
Snap
Use the default settings and click the [Snap] button to start snap.
Click the [Next] button to move on to the next step.
Boundary Layer
Create boundary layer at car body.
Click the (+) icon under [Configuration] to add a [Setting], and set it as follows
- Number of Layers : 5
- Thickness Model Specification : First and Expansion
- Size Specification) : Relative
- First Layer Thickness : 0.1
- Expansion Ratio : 1.2
- Min. Total Thickness : 0.3
- Boundary : train_surface
Use default settings for [Advanced Configuration].
Click [Apply] button to start boundary layer step.
The final mesh looks like this
Click the [Next] button to move on to the next step.
Export
Click [Export as BaramFlow project] to export the mesh to the desired location.