Week 4 Challenge : CFD Meshing for BMW car

AIM:

This project aims to do a geometric cleanup and create an enclosure around the BMW M6 car and do surface meshing on both.

OBJECTIVES:

• Cut the model in half as its symmetric in order to reduce our work and time required for cleanup and meshing.
• Check for the geometrical errors.
• Create and assign PIDs.
• Perform surface mesh with the given target lengths as per PIDs.
• Use the Mirror option to mirror the meshed half and get the whole car.
• Create an enclosure which will represent a wind tunnel.
• Perform surface mesh on the enclosure also.
• Element type to be used is “Triangular” for surface meshing.

PROCEDURE:

Step 1 -

The first step we need do is import the given geometry, cut it in half and do a geometry checkup on the remaining half to find out all the errors that are present in the geometry.

Imported Geometry -

As we can see we have many single cones, gaps/open faces and overlapping surfaces in the geometry, and 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'll select the one half to delete as shown below, but while selecting a half we'll deselect the logo as it's not symmetric.

Selecting one half to delete -

Remaining half/ Final model -

Now we can start with the geometry clean up. As the model has too many errors, we'll do the geometry clean up part by part.

First, we'll start the cleaning up the front lights, since we're only concerned about the flow over the car, we don’t need any element/surface present inside the car. Having such a surface or element will only increase the number of elements and as a result increase the mesh time.

Front Lights -

As we can see there are lots of elements/surface inside the lights, we'll need to clear all of them.

Cleaned Front light -

Now we'll move to Grills :-

Before cleanup -

After cleanup -

Rear View Mirror :-

Before Cleanup -

After cleanup -

Windows, Body and Back lights :-

Before cleanup -

After Cleanup -

A part on the body :-

Before cleanup -

After cleanup -

Logo :-

Before cleanup -

After cleanup -

Floor :-

Before cleanup -

As we can see the floor is uneven and since in are analysis, we're not focusing on the analysis beneath the floor hence we'll delete this point and create a new even floor till the back tyre part. After that we'll just keep it as same, we'll only delete the unnecessary parts and will cut short the surfaces which are penetrating into tyre.

After cleanup -

Tyres :-

Before cleanup -

After cleanup -

We have successfully cleaned up the whole geometry, we can also check that by running the geometry checkup as shown below.

Complete Geometry -

Geometry check -

As we can see there are no error and only two warnings for convex CONS, we can ignore that for now.

Step 2 -

In this next step we'll divide the single PID model into several different PID in order to mesh the model more accurately and easily.

To create a new PID we'll open the PID manager, we'll add new PID by clicking on the "NEW" option present at the bottom options and under "NEW" option we'll select "Shell parameters".

We'll create 8 PIDs (as shown below) and in order to assign each PID to a component all we need to do is click on the PID and then click on apply, after the select the required part, you want to assign to the selected PID and press the mouse middle button.

PID list -

Geometry as different PIDs -

Step 3 -

Now we move to mesh mode from topo mode in order to mesh the given model.

The first thing we need to do is open the mesh parameters from the top option list and input the target length for the selected PID.

The target length for different PIDs is listed below

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

We can mesh the given geometry by separating them by their target length.

Target length of 2mm –

The PIDs with target length of 2mm are:

• Rims and Tyres
• Optical Rear view mirror
• Windows

Quality Criteria for 2mm target length -

Above mentioned meshed elements –

Tyres -

Optical Rear-view mirror -

Windows -

Target length of 1mm –

The PIDs with target length of 1mm are:

• Grill
• Logo

Quality Criteria for 1mm target length -

Above mentioned meshed elements –

Grill -

Logo -

Target length of 4mm –

The PIDs with target length of 4mm are:

• Lights

Quality Criteria for 4mm target length -

Above mentioned meshed elements –

Lights -

Target length of 3mm –

The PIDs with target length of 3mm are:

• Body
• Silencer

Quality Criteria for 1mm target length -

As body PID is in contact with other PIDs whose minimum length is 0.4mm and hence we'll have to give the minimum length as 0.4mm.

Above mentioned meshed elements –

Body -

Silencer -

Full meshed geometry -

Now as we're done with everything, we can mirror this half in order to get the full car. We'll use the "Transform" option and copy this half as shown below.

Transform -

Complete car -

Now we'll have to create an enclosure around the car so that we can do the wind tunnel simulation. We'll create the enclosure by following the steps mentioned below.

1.) We'll first create three points as shown below with their dimensions.

2.) We'll offset these points in both the direction so that we can create a surface as sown below.

3 We'll create a surface using these points and then offest it to get the top surface also.

4.) We'll now close all the sides and our enclosure will be ready.

We'll now assign them PIDs also as shown below.

PID List -

PIDs -

Now we'll move on to mesh the enclosure with different specified target lengths.

Top surface target length - 100mm

Bottom surface target length - 20mm

and for the front, back and side surfaces well use the "spacing" option in order to get varying target length that starts from bottom surface with 20mm target length and will go till top surface with 100mm target length as shown below.

Generated Mesh -

Total number of elements of the whole geometry -

ANSA model link -

https://drive.google.com/file/d/1lZ0GDYbMt4vLShyB_7U4hoSEwjvuPv7D/view?usp=sharing