Week 4 Challenge : CFD Meshing for BMW car

CFD Meshing for BMW car

Aim: CFD meshing for BMW car using ANSA

Objectives:

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

Procedure:

Topological clean up:

Import the ANSA file, The resolution of the model is too low.

To fix this go into mesh and select entire model, give 1mm length for both macros and perimeters.

Again go back to TOPO, now the low resolution is fixed, and all the parts of the model are rendered clearly.

Since the model is symmetric, we delete the half model and mesh other half, After clean up and meshing we project the half model to other side by symmetry option

 

Now we will delete unnecessary inside and outside parts, so that we will have only 6 volumes.

1. 4 tire volumes
2. 1 car volume
3. 1 volume between car and wind tunnel

Check for geometry and intersection errors.

Delete inside surfaces which we do not require.

Now we have two single cons present here,

We can fix this by connecting them using paste option.

Delete this unwanted surface.

Now fix the headlights, delete unwanted internal surfaces.

Hide all other PIDs and only keep the PID we working with.

Now delete this unnecessary surface.

Delete these extra surfaces present here which form triple cons

Project the coons on to the surface and fix the resolution.

Since the CON is not completely attached make a cut.

Fix the resolution of the perimeter.

 

Delete the surface, and create a new one.

Project these CONs on the surface and delete the extra surface.

Similarly do it for all the ribs.

Now fix this.

Delete the face.

Create new face.

Now grill is fixed.

Now we will fix this 3^rd part.

First delete the overlapped surfaces.

Now we have ribs, these create volumes to fix ribs needs to be opened from the inside.

Delete unwanted inside surfaces.

Make a cut here.

After creating the cut, delete the surface.

Similarly create cut in the upper surfaces and ribs, and delete the surfaces.

After deleting the surface, create new surface and fill the hole.

Similarly do it for all the ribs and upper surfaces and fill the hole.

Delete these curved surfaces.

Fill the holes.

LOGO:

Isolate the logo

Delete the surface to create a common volume.

 

Windshield:

Delete the extra surface, this will remove triple cons.

 

 

Side windows:

Delete the extra surfaces.

Now fix this model.

Delete the extra surfaces.

We have intersection errors at this region.

Delete the surfaces creating intersection error.

We have cleared intersection errors, now close the geometry and delete inside surfaces that create volumes.

Make a cut.

Delete the surface.

Similarly do it for all other ribs.

Now delete the Top surfaces.

To delete them create a plane cut.

Select three hot points and make a plane cut.

Now delete the top parts.

Delete these surfaces so that they don’t create separate volume.

Create surfaces to close the volumes.

Similarly close all the single CONS by creating the surfaces.

 

Now fix the side mirror.

Delete the surfaces causing triple CONS, and delete the overlapping surfaces.

We have fixed the triple CONS but the mirror will create separate volume, so open the side mirror from the inside so It creates common volume with the car.

Delete the surfaces covering the side mirror.

Now the side mirror shares common volume with the car.

Now fix the side door handle.

Delete the extra surfaces.

Use extend option to extend the inclined surfaces.

Make a cut and delete the extra surfaces.

Now delete this extra surface.

To delete it use Project cut option to create a cut.

Now delete the extended surface.

Since there is no CONS present between the surfaces, intersect the two.

Now Project cut and delete the extra surface.

Now delete the bottom surface, by creating a cut.

Make a cut and delete this extra surface.

Delete these surfaces.

Create a new surface.

Create surfaces and fix the single CONS.

 

Now fix the Base.

Create curves at the edge, by using Cons2Curve option.

Delete all the intersecting surfaces and create new one.

Now all the geometry errors are fixed check again for intersection and geometry errors.

All the errors are fixed.

Now assign PIDS.

 

Setting quality criteria.

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

Mesh Grills and Logo together since they have both same target length.

Mesh Windows, optical rear view mirror and Tyres together as they have target length of 2mm

 

 

Mesh silencer and Body together as they have target length of 3mm

 

Mesh the lights.

Complete meshing.

Mirror the half car by using transform tool > copy > symmetry > 3point plane.

Before copying hide the logo.

Fix the single CONS by pasting them together.

Check again for geometrical and intersection errors

Since there are no errors present, we proceed to wind tunnel creation.

Measure the distance between two extreme points on the bmw car model.

Let us approximately take car length as 1300 mm.

Select any point on the bottom surface of a model and create a point below it.

Now create point at a 4 times the length of the car from front extreme point.

To create this measure the distance from the bottom point we used to create point to the front extreme point.

That will be 650 + 1300*4 = 5850 mm

For the back face use the same length.

For the side faces, measure the extreme side point from centre and add car length to it.

That will be = 370 + 1300 = 1670mm

 

Create curves to create bottom surface.

To create top surface, set the offset of bottom face.

Create side faces, and assign the PIDs.

For bottom face use target length as 250mm

And for top face use target length as 400mm

For side faces use growing mess.

 

 

Total meshing is complete.

Number of elements = 1891510

Conclusion:

• We have successfully created CFD meshing of a BMW model.
• Number of elements we got is 1891510.

Reason for not making volumetric meshing:

• Since volumetric meshing is lot computationally demanding and requires lot of computer power, since our laptops aren’t capable of handling large amount of volumetric meshing we CFD meshing.

ANSA file : ANSA model file for BMW meshing