Week 4 Challenge : CFD Meshing for BMW car

CFD meshing on BMW car

Aim:

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.

Objective:

- Target lengths for the different parts of a model are as follows:

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

Model: BMW M6

Procedure:

• Upload the ANSA file to screen to perform geometry clean up

• Go to mesh and choose length and enter 1 mm under perimeters to smoothen the sharp curves of the car and give it a fine look.

• Since the car is symmetric from the middle to any end, we can delete one-side of the car and perform the necessary operations on the car and use symmetry option to produce the complete car.

• We can now start with the topo clean-up by removing the single and unnecessary triple cons. First click on topo and box select the entire to identify or joins any unjoined single cons or triple cons so that we can identify the required clean-up accordingly.
• Once the geometry is checked and has no errors, we can now assign names to different components using PID.
• After giving required PID’s we can further move to the surface mesh
• Give required length perimeters to different elements as given in data
• After meshing create a closure for computational analysis.

Geometry clean up

Here we are going to start with the grill part

• The grill is not projecting to the surface and there are so many intersectional error, single cons, some cracks

• Now to remove the single and triple cons and to maintain a single volume, to create a single volume we need to have double cons everywhere, to do this we need to performs few cuts and re-surfacing of parts to maintain a single volume.
• Use the faces>>new>> fitted or cons or planar option to create the surface on deleted or missing faces.
• Clear all the unwanted hot points

• After clearing the geometrical errors and intersectional errors in grill part check with the checks>>check geometry>>execute to see the results of grill

Next we are clearing the mirror, windows, logo, lights

• There are extra surfaces present under every element, just delete all extra surfaces.
• Delete the triple cons or extra surfaces to remove the triple cons, these double surfaces are not necessary since we need to have a single volume.

• Do the same for windows, rear lights and roof area where extra internal parts are present which is of no use to create surface or volumetric mesh.
• The logo of the car is under a single surface, therefore using project cons, create a separate surface and delete the extra surfaces to maintain a single volume.

• After clearing the geometrical errors and intersectional errors, check with the checks>>check geometry>>execute to see the results of geometry cleanup.

Next we are clearing design feature near to fender

• Identify the triple and single cons, and delete the extra unwanted surface to maintain a common volume.

• Use the intersect option to identify the triple cons at the intersection area and can delete the smaller surfaces individually.
• Extended the single cons on the adjacent surface to create triple cons and delete the unwanted surfaces by doing that.
• Delete and re-create surfaces accordingly to have a smooth and perfect shape at tight corners. Also uncut the lines which are necessary which might cause trouble during meshing.

Wheel,body and Base region:

• Isolate the wheels to perform geometry clean-up, to rectify the triple cons, hide the surface blocking the view and delete the overlapping surfaces causing triple cons.

• Create larger surfaces after deleting smaller surfaces which are parallel to each
• The base of the car is intersecting with the tyre, therefore we need to delete the excess surface and also delete the extra design surfaces which cause smaller edges, this causes problems while creating mesh.
• Therefore we need to clean the entire base and create new surfaces accordingly having smooth edges.

• Use cons2curve option to get the correct angle and measurement towards the edge this will be useful for creating surfaces easily.
• After creating the surface, we need to check if the base surfaces have no intersection with the Tyre region.

• After checking and performing topo-clean up for the entire half car model. We need to perform geometry checks to find small cracks are unchecked faces extra which is not good for the geometry, therefore we need to perform checks and clean the geometry accordingly.

Once the geometry is checked and has no errors, we can now assign names to different components using PID.

After assigning the names, we need to transform the entire half. Performing symmetry on the car model:

Perform symmetry under transform option to create a exact same opposite body of the car to create a full body car.

• Use the copy option and select the half body car and deselect the logo and silencer since we don’t need a copy of the logo and silencer.
• After choosing the model, middle click mouse, we get a window, choose symmetry and choose mirror 3 points plane and choose 3 points on the edge to be perform symmetry.
• After choosing 3 points, middle click twice and the symmetry is performed, click middle click again to confirm the geometry and complete the process.

• There will be few single cons present near the middle section, use paste or other tools to solve the problem.

Surface meshing:

We need to mesh the components individually since the given mesh targets are different for each PID region.

Assign the mesh parameters and quality parameters for each PID accordingly, assigning the correct min and max length will reduce mesh failure and off elements.

BODY 3mm

Grill logo 1mm

Tyre, ORVM, window 2mm

Silencer 3mm

Click on freeze option after creating the surface mesh so that other Pid’s could not get meshed

After meshing, we can see some off elements in meshed region choose re-shape under shell mesh to reduce the off elements. And later the remaining off elements can be edited manually by moving the shell and splitting the large mesh area etc...

Creating wind tunnel:

1. First, we need to create reference points to create wind tunnel surfaces.
2. Select relative under points in topo mode, create a point below the car taking one reference point and entering the correct values.

And by calculating the wind tunnel dimensions appropriately, we can create the wind tunnel accurately.

1. The wind tunnel dimensions are: (standard distance of car model)

car model: 1306mm (x)

Front surface distance (from reference points): 5875mm(4x)

Back surface distance (from reference points): 8480mm(6x)

Top surface distance (from reference points): 4500mm(3x)

1. After creating the bottom surface use the curves for having the reference of cons, we can delete all the hot points and curves.

2. Create all the other wind tunnel surfaces using the new surface option.

Surface meshing of wind tunnel:

1. We need to apply surface meshing depending on the mesh length near the car and regions far away from it.
2. Therefore, we need to apply different mesh lengths at the bottom and top wind tunnel surfaces.
3. We need to use spacing option to have a mesh length varying from the small mesh length size to larger mesh length.
4. Surface meshing can be achieved by doing this accordingly.

Learning outcomes:

• Performed various topo clean-ups using different tools.
• Understood the need of double cons and removing unnecessary triple and single cons.
• The use of symmetry helps in reducing the work time and helps in having accurate results with less work.
• Create surfaces using the reference hot points by using relative points.
• Surface meshing for different components and their varying mesh lengths.
• Using spacing option in surface meshing helps in having varying mesh lengths along the surfaces.
• Using re-construct option to reduce off elements to a level where we can edit it manually.
• Using mesh modifying tools like move, split and smooth options.

Conclusion

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 are 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.

FILE LINK-https://drive.google.com/file/d/19ZiWM5qcBngFf8rnjeya209sppEc8ICR/view?usp=sharing