CFD Meshing for BMW car

OBJECTIVE:

The objective of this project is to do a basic geometric check and the do a Surface & Volumetric mesh using ANSA, on the given BMW M6 car model. Also to define the different targlent lengths on the respective PID's.

TOOLS Used:

• Checks:

Checks is basically used to checks the errors in the model.

Tools used under Checks:

Checks manager`rarr`Geometry checks`rarr`Execute.

By clicking checks command a new pop up will appear, in that by clicking checks manager we can get a pop up window with diiferent types of checks that can be performed. In that by clicking Geometry_Checks and from the obtained pop up we can select geometry and penatration command and then execute. Then ansa will do the geometry check and will give the results.

• Topo:

Faces:

Delete(to delete the unwanted faces). New (to create the required faces).Intersect(to intersect required cons with faces).

Curves:

Create (to create required curves). Delete(to delete unwanted curves or unwanted created curves)

Hot Points:

Insert (to insert hot points if needed) Intersect (to intersect created curves & faces).Delete(to delete unrequired Hot points). Project(to project an exisiting hot point on a con)

CONS:

Fill hole(to fill holes).Project(to project cons on faces)

Points:

New(To create new points), Relative(To create a relative point to a exisiting Nodes or points).

• PID Selection:

To define PID's specifically.

PID(from the lists from the top)→create New PID→ name the PID>→Apply(select the particular PID).

• Utilities:

Transform`rarr`Copy(copy the surface to be transformed)`rarr`Entities(select the entities to be copied)`rarr`Symmetry(to do symmetry of the entities)Mirror 3 points plane(select the points to symmetry the selected entities).

Measure`rarr`Nodes(to measure the nodes)or Cons(to measure the cons).

Compress(to compress the unwantedly created PID's).

Mesh Parameters(to define the required mesh parameters).

Quality Criteria(to define the quality of the required mesh).

• MESH:

In this we are going to use CFD mesh.

Perimetes`rarr`Spacing`rarr`Auto CFD`rarr`Perimeters(select the perimeters)`rarr`Macros(Select the macros).

Mesh generations`rarr`CFD`rarr`Visible(to mesh all the models that are visible) or Select(to mesh a particular PID).

Shell Mesh:

Recontruct(to reconstruct the created mesh to avoid off elements).Smooth(to smooth the PID's)

• Volume Mesh:

Volume→Define→Whole db.

Procedure:

Given Model,

The given model has very bad resolution, the parts of the model are not very fine, so we can change the perimeter length to get a fine model.

From the above image we can clearly see the difference after changing the perimeter length.

We can cut the model in half to performe geometry checks and the symmetry it since the other half is exactly the same except for the logo,

Lets do a geometry checks first,

from the above image we can see there are a lot of triple and single cons present in the model, to clear them we should do a geometry clean up.

After geometry clean up:

Geometry Check after geometry clean up:

We can see there are no penetration in geometry after clean up, only the single cons that are to be symmetried are present.

PID's:

Defining the PID's

Meshing:

• Mesh parameters and Quality criteria for 1mm target length models.

a higher max lenght can be given in quality criteria to get a fine mesh,

LOGO:

from the above image we can see there are some off elements after meshing we an try cleaning it up by doing reconstruction of the mesh and smoothing of the mesh.

we can see there are no off elements after recontruction of the mesh.

Grills:

We can do the same process on the grills and the mesh parameters and quality criteria need not to changed because the target length of the grills are also 1mm.

from the above image we can see that the grills are perfectly meshed withot any off elements.

• Mesh parameters and Quality criteria for 2mm target length models.

Optical rearview Mirror:

After meshing we can see there are a lot of off elements, we can rectify them by doing some geometry clean up and reconstructing the mesh.

from the above image we can see the off elements are rectified and a fine mesh is obtained by recontructing the mesh.

We should follow the same procedure for rest of the PID's.

Windows:

Windows meshed with no off elements.

Rims and tyres:

from the above image we can see the tyres and rims are meshed without any off elements.

• Mesh parameters and Quality criteria for 3mm target length models.

Silencer:

the silencer is also meshed without any off elements.

Before doing the body with 3mm target lenght, we should the remaining small PID the lights with 4mm target length, because the body is a very big PID it will have more off elements.

• Mesh parameters and Quality criteria for 4mm target length models.

Lights:

The lights are meshed without any off elements.

Body:

We can see the body contains a lot of off elements after meshing, body is tend to have some off elements at the point of interaction with other PID's with different target lengths, this kind of off elements are justfieble.

the off elements on the surface of the body are rectified, the off elements at the point of interaction are ignored.

Since the whole half of the car is meshed, we can just simply transform the model to create a whole car model.

To get the whole car model we are doing transform and then symmetry with respect to three point plane. And then doing a final geometry check.

Final car model:

Final geometry checks:

From the image we can see the final model is complete without any geometry or penetration issue.

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 'Reative option' in points of Topo Deck.

Creating a reference point at the bottom at a distance of 75mm:

Creating points at FRONT:

Creating a point at Rear:

Then similarly creating points at top and then sides:

Then we have to connect the points using curve option to create the walls.

The creating the base using the curves,

We can offset the bottom surface at the top to create the top suface and we can delete the unnessary points and deleting the created curves. Then with the top and bottom surface as reference we can create the side walls.

Defining the PID's for the wind tunnel:

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 compare to the top portion as it relatively at larger distance than botttom. 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 surfaces 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.

Meshing of the walls:

Fully meshed tunnel:

The final mesh:

Since performing volumetric mesh required 2-3 days so we did not perform it.

Learning Outcomes:

• Got familiar with more complicated and advance ANSA tools
• Learnt about volumetric meshing along with 2D meshing.
• Selection of volumes for volumetric meshing
• Different mesh length sizes tend to give errors at the contact regions of 2 different mesh length regions, therefore mesh ranges can be given to avoid erasing of mesh.
• Learnt how to create a wind tunnel and Using spacing option in surface meshing helps in having varying mesh lengths along the surfaces.
• Learnt how to clear any off elements created while meshing using reconstruct option.
• Got familiar which types of off elements are justifieble.
• Using the mesh modifying tools like move, split and smooth options.

Results:

Complete car model with wind tunnel ANSA file:

https://drive.google.com/file/d/1wGZrXF30waRMLWW94wbURc1_SkdB_ix-/view?usp=sharing

Conclusion:

• BMW car model is topo cleaned and surface meshed appropriately.
• Wind tunnel is created and suraface meshed with reference to the car model size.
• Different Volumes of the car model is created since the 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.