Week 4 Challenge : CFD Meshing for 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.

Given Target lengths for the different parts of a model are as follow:

1. Body - 3 mm
2. Lights - 4 mm
3. Grills - 1 mm
4. Rims and Tyres - 2 mm
5. Optical Rear view mirror - 2 mm
6. Window - 2 mm
7. Silencer - 3 mm
8. Logo - 1 mm

Procedure:

1. Importing the file:

• To import the given file to ANSA
• In ANSA, Go to File -> select Open
• Select and open the given file with .ansa extension
• The BMW model is opened in ANSA

2. Topo clean-up:

• After importing the ANSA file onto screen to perform topo cleanup
• 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, 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.

After fining Before fining

Symmetric model

a. Grills:

• Go to FACES -> CUT and enable the parametric cut and then cut the fins that are present on the grill
• Perform to all fins and remove the unwanted surface
• Goto FACES -> NEW -> COONS to join the deleted surfaces by using these options and the geometry clean up is completed
• Delete the half part of the car and perform the geometry clean up for the remaining parts
• To perform geometry clean up for bottom grill we have to isolate the part and lock it by using NOT mode and LOCK mode
• Go to CONS -> PROJECT and project the cons of the grills onto the surface and delete the unwanted surfaces
• Sometimes we can create a new surface by deleting the old surface according to our necessity
• Go to FACES -> NEW > COONS to join the deleted surfaces by using these options and the geometry clean up is completed
• Perform similar operations on the intake grill
• Remove the interior extruded surfaces by using the DELETE option

b) Windows, rear lights, roof region,logo, Rims and tyres:

• 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 as brfore 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.

Logo Windows

• 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.

3. Surface meshing:

• We need to mesh the components individually since the given mesh targets are different for each PID regions
• 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.
• Meshing the surface according to the given parameters

  Body - 3 mm

  Lights - 4 mm

  Grills - 1 mm

  Rims and Tyres - 2 mm

  Optical Rearview mirror - 2 mm

  Window - 2 mm

  Silencer - 3 mm

  Logo - 1 mm

Logo and grill surface mesh

Window and rims and tyres surface mesh

Silencer and Rear mirror Surface mesh

• After meshing, we can choose re-construct under shell mesh to reduce the off elements. And later the remaining off elements can be edited manually.

4. Symmetry on the 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 diselect the logo sice we dont need a copy of the logo.
• 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 performed 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 probem.

5. Creating wind tunnel:

• First, we need to create reference points to create wind tunnel surfaces
• Select relative under points in topo mode, create a point below the car taking one reference point and entering the correct values.
• And calculating the wind tunnel dimensions appropriately, we can create the wind tunnel accurately.
• The wind tunnel dimmensions are: ( standard distance of the tunnel wrt to car model)

  car model: 1300mm .................. (x)

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

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

  Top surface distance(from reference points): 4323mm .................. (3x)

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

• Create all the other wind tunnel surface using the new surface option.

• We need to apply surface meshing depending the mesh length near the car and regions far away from it.

• Therefore we need to apply different mesh lengths at the bottom and top wind tunnel surfaces.

• We need to use spacing option to have a mesh length varying from the small mesh length size to larger mesh length.Surface meshing can be achieved by doing this accordingly.

Conclusions:

• BMW car model is topo-cleaned and surface meshed appropriately

• Wind tunnel is created and surface meshed with reference to the car model size.

• Different volumes of the car model is created since th silencer and tyres are not connected to the car body.

• Single volume is created of the car body so that it can be avoided at one go when creating a volumetric mesh.

• Required physics tests can be performed on the wind tunnel volume model after volumetric meshing successfully.

solved model google drive link: https://drive.google.com/file/d/12p0QnhwsQUsTtHHuuME0m-JwfWuOydOt/view?usp=sharing