Week 4 Challenge : CFD Meshing for BMW car
Aim:
To perform geometry clean-up of the BMW car and develop a wind tunnel while perform meshing with mesh sizes as suggested.
Link for downlading the model for reviewing: https://drive.google.com/file/d/1JPIft7bayyRXt60MGRJYVLNxavEIb4RZ/view?usp=sharing
Objectives:
1. To perform geometry cleanup using different options like from the Topo tab.
2. To assign the different PID's to different parts of the BMW car
3. To mesh with different mesh sizes and evaluate the mesh sizes.
4. Develop the wind tunnel model around the car and perform meshing using options like quality critieria, mesh sizes, length, macros, Spot mesh, spacing.
Procedure:
- Due to the symmetry of the car, only left part of the car was selected for cleaning up the geometry.
- Initial geometry check was performed for single cons and triple cons.
- Irrelevant surfaces that are inside the Car body is deleted to have a single volume.
- New surfaces were added to avoid the formation of single cons and triple cons.
- Common surfaces near the intersecting bodies were deleted to get a single close volume.
- PID’s were created for the different parts like tyres and rims, windows, mirror, grills, silencer, car body, lights and logo.
- Every PID region is meshed leaving Car body to the last.
- Measure option is used to check the length and macros to confirm whether mesh criteria will be attained.
- Mesh criteria is below:
1. Body -3mm
2. Lights - 4 mm
3. Grills - 1mm
4. Rims and Tyres - 2mm
5. Mirror-2mm
6. Window - 2mm
7. Silencer - 3mm
8. Logo - 1mm
· Meshing is performed and reconstruct option was used. So that the off elements are corrected.
· Mesh sizes are readjusted to the minimum length and maximum length sometimes near the grills PID.
· In case if the mesh is not solved, options like move, paste, macros-cut, smooth were utilised to remove the off-elements.
- This ensures that when car body is meshed, all other meshed bodies needs to be intact with the mesh and the mesh should not be deleted.
- For this to happen, the coons that are in common with the car body and other PIDs were deselected individually before meshing the car body. Later on the meshing was done for the car body.
- Transform option with symmetry is used after meshing half of the car.
- New single cons formed were rectified using paste option.
Development of the wind tunnel:
· The wind tunnel is developed using curves and points options.
· The dimensions of the wind tunnel are 75mm for the bottom surface, 4 times front the front bumper, 6 times from the rear bumper, 3 times from the top.
· Appropriate PID’s are created for the wind tunnel.
· New surfaces are created accordingly using fitted surfaces option.
· Bottom surface was meshed with 20mm, top surface is meshed with 100mm and while side,back and front surfaces are meshed using the spacing option in the mesh tab.
· The mesh is created using spot mesh tab and local sizes.
· Later for the volume meshing the body were defined.
Result:
- Geometry clean-up was performed on the half of the car body
- Meshing was performed as suggested.
- Transform option was used to develop the whole car.
- Wind tunnel is developed and meshing was performed as suggested.
Conclusion:
1. Geometry checks needs to done whether the symmetry option is used or not.
2. Geometry cleanup should be performed before meshing using checks.
3. Quality criteria should be decided before starting of the mesh which will reflect the mesh adapting to the actual body.
4. After transformation into full body, care should be taken to avoid the single and triple cons.
5. All the geometry should be ideally cleaned before proceeding to the meshing, including whether the cons have sizes suitable for meshing. After meshing macros option can be used to cut the cons so that the mesh qualifies the quality criteria.
6. Meshing should be available on all the PID’s.
7. Development of wind tunnel should be done according to the specifications and also needs to meshed diligently.
