Motorbike

¶ Motorbike

Pre-Processing

Mesh generation is the first step in the CFD simulation flow. Therefore, in this case there are no other sections such as 2. Settings and 4. Post-processing.

The case of Motorbike is handled as a steady-state, turbulent and incompressible flow, and the simular case (Wind around buildings) is shown here.

1. 3D geometry file

For this case, a OBJ (or .obj) of motorbike with a rider is used as the inner boundary (wall) in the volume field (or internal field).

The figures above show the size of the object (motorbike with a rider).
The relative placement of the motorbike in the volume field (internal field).

2. Surface feature extraction

Work on Linux
Item Value/Name
Command surfaceFeatureExtract (without any options) (in the parent directory)
Dictionary surfaceFeatureExtractDict (in the child directory, /system, under the parent directory)

(parent directory)$ cd system
(parant directory)/system$ ls
surfaceFeatureExtractDict
(parent directory)/system$ cd ..
(parent directory)$ surfaceFeatureExtract

At this step, the surface feature of the motorbike (and a rider) is extracted for the later-described hexahedral mesh generation.

3. Block mesh generation

Work on Linux
Item Value/Name
Command blockMesh (without any options) (in the parent directory)
Dictionary blockMeshDict (in the child directory, /constant/polyMesh, under the parent dictionary)

(parent directory)$ cd /constant/polyMesh
(parent directory)/constant/polyMesh$ ls
blockMeshDict
(parent directory)/constant/polyMesh$ cd ../..
(parent directory)$ blockMesh

After generating the block mesh, the volume field (internal field) is divided into block-shaped cells. The figure shows the patches of upper, front-end, back-end, inlet and outlet.

4. Decompose for parallel-processing

Usually, decomposition of the volume field is executed in prior to simulation for parallel processing of calculation. The decomposition, however, is applicable for parallel-processed hexahedral mesh generation for this case.

Hereafter and therefore, hexahedral mesh generation of one part of divided volume field is shown.

5. Hexahedral mesh generation

Work on Linux
Item Value/Name
Command snappyHexMesh (with option, "-overwrite") (in the parent directory)
The option means that "overwrite existing mesh/results files". In this case, block mesh.
Dictionary snappyHexMeshDict (in the child directory, /system, under the parent dictionary)

(parent directory)$ cd system
(parent directory)/system$ ls
snappyHexMeshDict
(parent directory)/system$ cd ..
(parent directory)$ snappyHexMesh -overwrite

After generating the hexahedral mesh. Partial hexahedral mesh (shown by patch) for the motorbike.
After generating the hexahedral mesh. Partial hexahedral mesh (shown by patch) for the lower wall.
After generating the hexahedral mesh. Hexahedral mesh (shown by patch) for the division's boundary.
After generating the hexahedral mesh. Hexahedral mesh (shown by patches) for the division (except the partial fron-end patch).

6. Entire mesh (After reconstruction)