Meshing of BMW M6 with creation of Wind Tunnel set up using ANSA

Objective: To mesh BMW M6 Model and create an wind tunnel for it Using Advanced Cfd by ANSA.

Procedure:

• Importing and setting up CAD model
• Identifying and Rectifying the Topological Errors
• Setting up the PIDS and defining the element length
• Rectifying the geometrical check up error
• Setting the mesh parameters and creating surface mesh
• Rectifying the surface mesh error check up
• Creating the Mirror model using Symmetry option.
• Modelling the wind tunnel for external CFD flow analysis

Importing and setting up CAD model

• Import CAD model and set the drawing style to PID mode.
• Go to quality criteria>presentation parameters>tick on Draw CONS option and adjust visibility of CONS.

Identifying and Rectifying the topological errors

Above is the PID view of Model

Above is the ENT view of Model to check topological errors in it

• As we can see in our model that there are alot of single cons, triple cons, ,missing faces are present but for CFD analysis and meshing of our model only double cons are required.
• There is an error in design style which becomes visible when Macros are disabled we have to delete this line by universal delete option.
• In order to make our work easy a new approach is taken in which half of the model is deleted and so only the errors present in side is to be made error free so we can mirror it by symmetry option present in Transform.
• As we know that flow is going to happen only at outside and external part of our model, so the faces present inside are extra and needs to be deleted . We have to make sure that it is double con.

Image of model with Removal of errors present in mirrors, side windows.

Cleaned up Image of inner side of model

In order to make this geometry free various tools are performed such as:

1. COONS: Coons are used to create new face. It is similar to FITTED.
2. DELETE: Universal delete is used to delete face. It is done left clicking on cross hatches of face.
3. HOT POINTS: These are points created on edges of face to make new face by COONS , FITTED on uneven face.
4. PROJECT: To get projection of desired cons on desired face so that we can remove that selected face only which is present in between desired cons.
5. CUT: It is used to make a cut between two hot points to remove the face in between them.
6. INTERSECT: when after projection of cons if it doesnot work then the the con which is not intersecting with other face, it intersects by extending that con on other face.It is basically extention of one selected con on other con.
7. GUIDE: This is use to form new face which is very small by the help of guide cons. This tools is use in intake grill geometry.

Error free image of Bottom and Side Grill

Error free image of Intake Grill

• Similarly in the same way errors present in Headlights of front and back are also made error free by making it double con. Inside face is deleted as flow is going to happen externally.
• After taking care of Errors present in body, windows, orvm, headlights, we can make this correction in error easily by assigning different parts in MODEL BROWSER. When we open model browser only single file or folder is there which makes correction difficult, so different parts are assigned in model browser to work easily by creting new file and whatever part we want in it can easily be move in it.

Error file image of Underneath part of model

• In order to make silencer error free seperate volume is created for silencer so that is does not collide with body

For Silencer we used to new tools such as:

1. EXTEND: It is used to extend the surface present by giving a value to it.
2. GLIDE: It is used when we have to extend a curve surface to some distance. This is the best option for extending for curvy surface.\'

Setting up the PIDS and defining the element length

Different PIDS of Different parts are allocated and the rest of it remove by the compress tool.

Rectifying the geometrical check up error

During the checking of geometrical error, we have to make sure that only single con which are present at boundary of our half model is there. If other errors are there make sure to correct them before moving to mesh.

Errors present in wheels are between rim and tire. There is an triple con present which is deleted by project. and topo is used to make it double con.

In order to make stripes identical on tire, translate is perform which is present in transform by deleting stripes on tire where we want. Now we have to copy stripes of tire by help of translate selecting points 1 and 2.

Setting the mesh parameters and creating surface mesh

With the help of model browser of different parts, we can easily mesh different parts with different element size. They are as follows:

1. Body- 3mm
2. Silencer-3mm
3. Lights-4mm
4. orvm,windows-2mm
5. tires and rims-2mm
6. grills and logos-1mm

Element- Tria

Setting mesh parameters for model:

1. Change from cfd mesh to general.
2. Target length- local
3. min length-0.9
4. max length-5.

Free Mesh is performed for this model.

Rectifying the surface mesh error check up

Image after correcting every surface mesh error check up

• Errors related to sharp edges can be fixed by split, cut, mv surf or by manupulating angles.
• Errors related to proximities can be fixed by changing factor and angle value.
• If errors are not fixed, we can try auto fix by which errors are fixed automatically by ANSA itself.
• Errors related to mesh quality are generally seen in hidden mode of model in ENT drawing mode, where the factors we need are given and we can turn it on and off according to requirements, In our case we need skeness, angle, min angle and max angle rest of it can be turned off. OFF represents the error we have to have work on so that this OFF is not visible.

In Quality criteria, select only that factors which are needed for our checking of mesh errors.

Errors in hidden mode can be corrected by use of RECONSTRUCT, SWAP, SPLIT, MV SURF, CUT IN MESH MODE

• Errors related to skeness are corrected by RECONSTRUCT, SWAP, SPLIT, MV SURF, CUT IN MESH MODE, PASTE
• Errors related to min length can be corrected by reconstruct by selecting MACROS AREA and changing local to average, minimizing the min length values and making sure remesh macros are ON .MV SURF can also be use by moving mesh so that error can be corrected.
• Errors related to max length are corrected by CUT, MV SURF, SWAP, SPLIT, PASTE
• CUT: It is done in mesh mode one is right click cut and other is by selecting two nodes to cut.
• SWAP: It basically swaps the edge
• SPLIT: It split the mesh.
• MV SURF: It helps in moving the mesh to correct the error.

Creating the Mirror model using Symmetry option

• We decided that we would make one half of our model and mirror it by suing symmetry.
• In order to perform mirror, go to transform >copy>select entities the vehicle without wheels>symmetry> 3 points plane>select three points on three different line to create plane>middle click>middle click again>finish>ok.
• similarly apply for the wheels by selecting 3 points on three different lines.

IF Single cons are there, use TOPO to make it double cons.

Modelling the wind tunnel for external CFD flow analysis

To perform CFD/External flow analysis a Virtual wind tunnel has to be created around the car.It is created in TOPO model as an Rectangular box.

Dimensions of wind tunnel are as follows:

1. 4X Front of the car
2. 6X Rear of the car
3. 3X top of the car
4. bottom close proximity with tires
5. 1X centre plane for left and right sides.

Inorder to create wind tunnel, RELATIVE points , PLANE, COPY is used.

• first create relative point and then create two points in other direction to it so that a plane can be created.
• create plane use tranform >copy>translate>give value>middle click>finish>ok.
• Spacing is selected in mesh for meshing to go from bottom to top 20-100 with factor 1.1

Learning Outcomes:

• Performing Mirror of model using symmetry option in transform
• performing and correcting different geomtrical errors like proximities, sharp edges, mesh quality, intersection.
• knowledge of rotation, translate, scaling, symmetry perform in translate option.
• new tools such as MV SURF, RECONSTRUCT, CUT, GUIDE, GLIDE, EXTEND, SPLIT, SWAP, RELATIVE POINTS, PLANE, ETC.
• Eliminating errors such as min angle, max angle, skeness, proximity, sharp edges, etc.
• How to create set up for wind tunnel model

Conclusion:

• Worked on topological errors of BMW M6 model
• Eliminating different geometrical check up errors
• Performing symmetry of model
• Worked on Mesh errors
• Create set up for wind tunnel

https://drive.google.com/open?id=1WYlJlyuMDRGC9EvL2SZ5YXZdGXCF0tnm