Week 4 Challenge : CFD Meshing for BMW car

CFD Meshing for BMW car

For the given 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.

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

Initial Model :

cut the model into a half  becauce it is symmentry on other side. so, we can work on one side and ues symmetry option to slove the model.

PROCEDURE : 

1) Our Model have so many single cons so apply topo to entire model and topo will work, it will join the two or three cons together respectively. 

check in geomentry and find the errors in the model

2) As our model has uneven surfaces so to make the surfaces fine use fine option from auxiliaries. If we have to do cons resolution of entire model 

in one shot then go to mesh desk and apply perimeters and macros equal to 1mm so that it will improve cons resolutions of the entire model. It will 

ultimately reduces the distance between two cons which equal to 1mm in order to make surface finish. 

3) If two single cons are near to each other then we can join them by using paste option. 

4) Topo cleanup for grills is done by deleting unnecessary surfaces from grills to remove triple cons, deleting un-wanted hot points, and single cons are removing by patching the new surfaces using New-Cons/Fitted options. 

5) Topo cleanup Tyre's and side mirror and head and taillight, includes triple cons by deleting the unwanted surfaces. 

6) For a logo the overlapped surfaces were identified and separated by projecting the surfaces on hood and are deleted following by removing small edges which may cause error during meshing. 

7) Lower car body need to correct by removing unwanted overlapped parts and the lower body intersecting with Tyres need to be deleted to make Tyres as a free volume keeping track of different parts in the lower body 'con2curve' is used to have blueprint are deleted surfaces with the help of which new surfaces are created. 

8) Geometric checks are performed to have no single cons present in the model and possible triple cons are removed by deleting it using universal delete option. 

9) Before creating surface mesh, the cons and small edges that have length less than minimum mesh length are identified by measuring the distance between cons and solved using 'cut' option in order to avoid mesh failing the mesh criteria at this small surfaces. 

10) PIDs are assigned using the PID manager which is present top deck for all parts in the body. 

• Body

• Lights

• Grills

• Rims and Tyres

• Optical Rear view mirror

• Window

• Silencer

• Logo

Half body with PID's

SURFACE MESHING : 

• 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

First of all, wisely choose the Quality criteria parameters which are only required: - 

1) Individual elements are meshed with respective mesh length with minimum and maximum length. 

2) Grills are isolated and give a mesh length of 1mm with minimum and maximum length of 0.5mm and 2mm with triangular elements and for   Quality criteria provide appropriate mesh length. Here is quality criteria and mesh element size for all the components. 

3) The mesh is seen in Hidden Mode and ENT wise, which will show off elements which are violating the criteria. So, we need to remove off elements by using options such as MOVE, SPLIT, RECONSTRUCT, SMOOTH the grid respectively, from this we can improve our meshing. 

• 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

4) Once the off elements' number reduced to 0 then meshing is done successfully, and Similar method is used for other PID's. 

5) Symmetry needs to be performed on the other half of car in which the all the components with mesh are copied directly to the other side using Transform option from the top side option list. 

WIND TUNNEL: 

Data for wind tunnel are as follow: 

The wind tunnel dimensions are, if x is the lengths of car then 

Front of wind tunnel is 4X from the car. 

Rear of wind tunnel is 6X from the car. 

Top of wind tunnel is 3X from the car. 

Side walls of wind tunnel are at X from the side portion of the car 

Bottom of wind tunnel is in close proximity of wheels 

Points are created by using 'Relative option' in points of Topo Deck. 

Total length of the Car 1280mm

Topo Deck- points - relative - points - select points. After the points are created join these points from bottom plane by 'create curves' 

Once the curves are created for top and bottom then create a surface with help of 'New' option in 'faces' 

Topo - Faces- New -Fitted -will open PID manager window-create new PID -double click on it to create surface on it.

As the analysis of what happens over the surfaces of car is of importance so the bottom of wind tunnel should have good resolution as compared to the top portion as it relatively at larger distance than bottom. So, mesh length of 20 is taken at bottom and 100 for top portion. 

As the front and rear of car are connected with the top and bottom surfaces then the mesh length for this surface should vary from 20 to 100 from bottom to top portion. This gradual variation can be achieved using Spacing option from the perimeters section of Mesh deck. 

Perimeters- Spacing -Geometric -factor of 1.1 and d-min of 20 successful application of this will be indicated by upward pointing arrows. 

Mesh is generated by applying Spot mesh for individual surfaces. 

volumetric mesh :

After surface mesh we should do volumetric mesh on model

when we enter the volumetirc mesh first we sholud go to Define optine to select and find the correct volume for mesh and delete the unwanted volumes, in this model have 8 volumes and we find the correct volume is one and deleted the remaining volumes. After deleting the unwanted volumes do mesh on the selected one..

Learning Outcomes: 

1. Learnt the complete CFD meshing skills on skech.
2. Performed various topo clean-ups using different tools.
3. Understood the need of double cons and removing unnecessary triple and single cons.
4. The use of symmetry helps in reducing the work time and help in having accurate results with less work.
5. Create surfaces using references hot points by using relative points.
6. Surface meshing for different components and their varying mesh lengths.
7. Using spacing option in surface meshing helps in having varying mesh lengths along the surfaces.
8. Using re-construct option to reduce off elements to a level where we can edit it manually.
9. Using the mesh modifying tools like move, split and smooth options.

Conclusions: 

1. BMW car model is topo cleaned and surface meshed appropriately.
2. Wind tunnel is created, and surface meshed with reference to the car model size.
3. Different Volumes of the car model is created since the silencer and tyres are not connected to the car body.
4. Single volume is created of the car body so that it can be avoided at one go when creating a volumetric mesh.
5. Required physics tests can be performed on the wind tunnel volume model after volumetric meshing successfully

CFD Meshing for BMW car:

https://drive.google.com/file/d/1V915bkDs8DNQmpxy0H1FW6tYT-rLlayN/view?usp=sharing