Week 4 Challenge : CFD Meshing for BMW car

AIM:

To mesh a BMW car model.

OBJECTIVE:

The aim of this challenge is to perform geometry clean up on a BMW car

perform surface meshing with the following 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

and create a wind tunnel for CFD analysis using ANSA software

PROCEDURE:

1) GEOMETRY CLEAN UP

2) ASSIGNING RELEVANT PID's

3) SURFACE MESHING

4) PERFORM SYMMETRY

5) CREATION OF WIND TUNNEL

GEOMETRY CLEAN UP:

First we have open the given BMW car model in ANSA software.

we enable all the cons and crosshatches to perform geometry clean up and also goto MESH > PARAMETERS > LENGTH and keep the length as 1mm to have smooth curves.

We can see that the geometry of the car is symmetric hence we edit one-half of the model and mirror it to get a full model. The right side of the model has more errors than the left side hence we delete the right side of the model.

GEOMETRY CLEAN UP OF GRILLS:

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 option.

Primarily we have to delete the unwanted surfaces by using DELETE option and make sure it is in ENT mode.

Goto 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.

Goto FACES > NEW > COONS /FITTED 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

GEOMETRY CLEAN UP FOR TYRES:

First, isolate the tires by using NOT and LOCK Mode

Then remove one of the tires because it has more errors and we cannot rectify and we can replicate the part by using the SYMMETRY option

Goto CONS > PROJECT and project the cons of circles of tires onto rims

Then DELETE the common surfaces present in between tires and rims

Thus geometry clean up of tires is completed.

GEOMETRY CLEAN UP FOR BOTTOM SURFACE:

First we remove the unwanted surfaces on the bottom part of the car model and also not associated with wheels.

Then we have created the surfaces on that particular bottom car using NEW>COONS/FITTED option.

geometry clean up of BOTTOM SURFACE is completed.

Performing symmetry on the car model:

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

b. Use the copy option and select the half body car and diselect the logo sice we dont need a copy of the logo.

c. 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.

d. After choosing 3 points, middle click twice and the symmetry is performed, click middle click again to confirm the geometry and complete the process.

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

ASSIGNING PID's:

To assign PID's for the given figure, goto PID MANAGER tool.

It shows all the PID's assigned to the figure.

First, isolate the body and lock the figure. Then goto > PROPERTIES it shows the PID's assigned to the body so we have to rename as BODY by creating a new PID.

Repeat the same process and assign PID's to all parts of the car.

Body:

LIGHTS:

GRILLS:

RIMS AND TYRES:

Optical Rear view mirror

Window

Silencer :

LOGO:

SURFACE MESHING:

Goto MESH > PERIMETERS > LENGTH and mesh the surface

Use TRIA elements and the mode of mesh is a spot mesh.

1. 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

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.

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

4. The wind tunnel dimmensions are:

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): 4323mm .................. (3x)

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

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

Surafce meshing of wind tunnel:

1. We need to apply surface meshing depending 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.

• Results:

ANSA FILE LINK:

https://drive.google.com/file/d/1fiVXODF8D4VTGhf25kVEo6dvPlvsIZOz/view?usp=sharing

Conclusions:

1) Finally 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.