CFD Meshing for BMW car

Objective:

For the given car model, check and solve all geometrical errors on half portion and assign appropriate PIDs. Perform meshing with the given Target length and element Quality criteria. After meshing the half model, Do symmetry to the other side.

Target lengths for the different parts of a model are as follow:
Body - 3 mm
Lights - 4 mm
Grills - 1 mm
Rims and Tyres - 2 mm
Optical Rear view mirror - 2 mm
Window - 2 mm
Silencer - 3 mm
Logo - 1 mm

Car model:

In this project, we will prepare CFD mesh for a BMW M6 car inside a wind tunnel.

Procedure:

Topological cleanups

1. Edge refinements
   
   1. Upload the model file to ANSA
   2. Go into the 'mesh' section and set the length & macros in parameters to 1mm. To execute this command, ANSA will smoothen out all the edges so that they can be meshed by cells of length 1mm.
2. Splitting the model
   1. Since the car is symmetric about the vertical longitudinal plane it can be split in half for ease in meshing. Later, a completely meshed car model can be reproduced by applying the symmetry option on the meshed half-body.
   2. Select the half-car model except for the asymmetric logo.
   3. Delete this half to get a half-body model with single CONS.
3. Topo cleanup: headlamps
   1. For external flow CFD analysis, only the outer features of the car are necessary.
4. Topo cleanup: front grill
   1. The inner surfaces of the front grill are not needed and hence are deleted.
   2. Side grill before & after topo clean up.
5. Topo cleanup: Logo
6. Topo clean up: Windshield
7. Topo cleanup: Windows
8. Topo cleanup: back window
9. Topo cleanup: top front grill
   1. Before cleanup
   2. After cleanup
10. Topo cleanup: tuning indicator
    1. Before cleanup
    2. After cleanup
11. Topo cleanup: Tire
12. Topo cleanup: rear section
13. Topo cleanup: bottom cover
14. Geometry checks
15. Setting PIDs
16. Topo cleanup for meshing: exhaust
    • The minimum distance between two hot points or CONS must be greater than 1mm.
17. Topo cleanup for meshing: Logo
    • The minimum distance between two hot points or CONS must be greater than 1mm.
    • Sharp & small surfaces need to be removed.

Meshing

1. Logo
   • Target length: 1 mm
   • Min length: 0.5 mm
   • Max length: 2 mm
2. Silencer
   • Target length: 3 mm
   • Min length: 2 mm
   • Max length: 3 mm
3. Lights
   • Target length: 4 mm
   • Min length: 3 mm
   • Max length: 5 mm
4. Windows
   • Target length: 2 mm
   • Min length: 1 mm
   • Max length: 3 mm
5. Rearview mirror
   • Target length: 2 mm
   • Min length: 1 mm
   • Max length: 3 mm
6. Rim and tires
   • Target length: 2 mm
   • Min length: 1 mm
   • Max length: 3 mm
7. Grills
   • Target length: 1 mm
   • Min length: 0.5 mm
   • Max length: 2 mm
8. Body
   • Target length: 3 mm
   • Min length: 1 mm
   • Max length: 5 mm
9. Complete car surface mesh
   
   • The surface mesh for the entire car is generated using reflection about the plane of symmetry.
10. Adding wind Tunnel
    • The wind tunnel geometry is a box enclosing the car body.
    • The Front face lies `4*L` (length of car) from front grill, rear face `6*L` from bumper and top face `3*L` from roof
    • The base surface is 75 mm offset downwards from sill of the car.
11. Meshing Wind Tunnel
    • Top surface is meshed with 100 mm length
    • Base surface is meshed finer with 20 mm mesh length
    • To improve simulation times the mesh on side, rear and front surfaces is varied from 20 mm near base surface to 100 mm near top surface. The mesh length increases with a geometric factor of 1.1 from base to top surface.
12. Volume meshing
    
    • Only the relevant volume for CFD analysis is kept as shown below. This is the volume between car and wind tunnel
    • Remaing six volumes correspond to four tyres and two exhausts