Week 4 Challenge : CFD Meshing for BMW car
Aim :
To clean up and mesh a computational domain for an external flow analysis of a BMW Car.
Methodology :
A. Geometry cleanup :
- Firstly delete half of the BMW car model and perform topo cleanup to that half as they are symmetric.
- Secondly perform geometry check for single cons, double cons, overlapped surfaces and bad surfaces and rectify it by using the following tools as shown below.
- Delete: This was used to delete any entity which cause geometrical errors such as overlapping surfaces, Single and Triple cons.
- Extend: This is used to extend single cons to another face.
- Intersect: This is to intersect between two faces.
- New: This can create new faces between coons.
- Curve: To create a curve between two hot points.
- Project: To project a hot point from one edge to another.
- Fill hole: To fill a closed hot of a specified tolerance.
- Cut: To cut a face into parts
B. Creation of enclosure :
3. The outer domain was created with a width distance of L measured from the both extreme ends, Length of 6L measured from the rear and 3L measured from the front of the tesla truck and the Height of 4L measured from the top. Where L is the length of the cyber truck ~1.3m. It was created with the help of Relative points to define the points and the curves to join the created points and the New option in faces to generate the macros/surfaces.
C. Assigning PID's :
D. Creation of surface mesh :
4. 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
5. Mesh quality parameters such as minimum length, maximum Length & Skewness are maintained accordingly.
Logo :
Target Length - 1 mm
Minimum length - 0.4 mm
Maximum length - 2mm
Skewness - 0.5
Silencer :
Target Length - 3mm
Minimum length - 2mm
Maximum length - 4mm
Skewness - 0.5
Window :
Target Length - 2mm
Minimum length - 1mm
Maximum length - 3mm
Skewness - 0.5
Optical Rear view mirror :
Target Length - 2mm
Minimum length - 1mm
Maximum length - 3mm
Skewness - 0.5
Rims and Tyres :
Target Length - 2 mm
Minimum length - 1mm
Maximum length - 3mm
Skewness - 0.5
Grills :
Target Length - 1 mm
Minimum length - 0.3 mm
Maximum length - 2 mm
Skewness - 0.5
Lights :
Target Length - 4 mm
Minimum length - 2mm
Maximum length - 4mm
Skewness - 0.5
Body :
Target Length - 3mm
Minimum length - 1mm
Maximum length - 5mm
Skewness - 0.5
Total body after meshing :
Total number of elements = 10,65,796
6. The base wall is closer to the car surface so mesh should be kept finer near the base and comparetively kept coarse away from the base in order to reduce our computational time. So for this spacing option was choosen from the mesh tech with a growth rate of 1.1. Target length 20 mm was choosen for the base wall & 100 mm was choosen for the top surface of the enclosure.
7. Mesh quality parameters are shown below.
For top surface of enclosure :
Minimum length- 95 mm, Maximum Length-105 mm & Skewness - 0.5.
For base surface of enclosure :
Minimum length-15 mm, Maximum Length-25 mm & Skewness - 0.5.
Total number of elements = 3,82,046
8. In total there are 14,47,842 elements out of which 10,65,796 are tesla cyber truck surface mesh & 3,82,046 are enclosure surface mesh.
E. Volumetric mesh :
9. In volumetric mesh deck using the Auto-Detect feature check for the volumetric errors before proceeding it.
10. Under the list tap it will show the list of volumes. Since we are interested in external flow analysis keep the volume common to BMW car and the enclosure delete all the remaining volumes.
11. Then using the tetra CFD mesh perform the volumetric mesh since it is time consuming and requires reasonable computational power here we stopped with surface mesh itself.
Learning Outcomes :
- PID creation and PID assignment,
- Different selection techniques and visibility tools,
- Advanced Topology cleanup
- Advanced tools used in Surface mesh and in Volumetric mesh.
Conclusion :
Topo clean up and mesh a computational domain for an external flow analysis of a BMW car is successfully done.
Link : https://drive.google.com/file/d/1NgJvSnWCJBbnmpaI4Y1QcWG7g_BGdlfL/view?usp=sharing