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Challenge

Week 4 Challenge : CFD Meshing for BMW car

SSamuel Dsilva2 Aug 2022

AIM / Objective: - Perform topological cleaning of a BMW automobile, wind tunnel construction, and CFD meshing in ANSA.

Procedure: -

Step 1 - To Import CAD file in ANSA

For importing the CAD Geometry go to file and click open.
go to the directory where the cad file is present.
select the geometry file with the .ansa extension and click open.
After importing the geometry switch the Draw mode to PID.
Also, enable cross Hatches and labels.

Step 2 - Geometrical Quality Check

There may be more errors, single cons, holes, missing surfaces, overlapping surfaces, and so on in a geometry.
Before meshing up we have to fix these errors to obtain a good mesh and a water-tight geometry.
To perform checks, go to the checks option in the upper toolbar and select geometry in that.
A window pops up, select all the checks but exclude unmeshed macros because we haven't meshed the geometry yet.
also don't select the sharp edges to check.
After selecting the required checks click on execute.

We can see that the model has many errors such as single cons, triple cons, cracks, and so on.
We can also press ctrl + shift to view the geometry in wireframe mode.

we can see that the single cons and triple cons are present, we have to resolve these errors to move forward towards meshing.

Step 3 - Topological cleanup

in topo cleanup we will solve all the errors and make the geometry ready for meshing.
we will switch to ENT viewing mode.

some elements of geometry are out of shape i.e. They are irregular. We can fix them using the fine option from the auxiliaries section under the topo deck, but it will take a lot of time.
So instead, we will be using another method.
go to mesh deck and click on length under the perimeters section.
a window pops up, select the perimeter option, and select the whole geometry.
do a middle click to confirm the selection.
enter the length as 1 and click on OK.
return to topo deck, we can see that all elements of the geometry are back in shape and the irregularities are gone.

since geometry is symmetrical, we can delete half of it and only work on the other half.
After solving all the errors, we can again have the other half by using the copy option.
To delete the half portion, click on the delete option and select the half of the geometry but exclude the LOGO, as the logo is not symmetrical.

Do a middle click to confirm the selection and click on OK.
Now we have the half section of the car.

We will first perform the geometry clean-up of the LOGO.

we will delete the surfaces which create a volume for the logo, which can be understood by the triple cons present.
since we want to create a common volume for the whole body.

some surfaces are not connected so we can use the Topo option.
But here the topo option is not working so we will project the cons onto the surface

Now we can delete the surface very well.

We have single cons present we have to fix these errors.
There is a gap between the single cons we can fix it by deleting the outer ring surface and then creating a new one.

now we will create a new surface there using coons.

for now, we have done the topo cleanup of the LOGO.
We will perform topo clean-up of the optical rearview mirror.

We will begin by isolating the rearview mirror first using the !Not option and lock the view.

we will delete the duplicate surfaces and also keep only the outer surfaces so that there are no triple cons which means no additional volume is present.

a triple con is present here which we have to resolve by deleting the extra surfaces and merging the volume of rear-view mirror into the car body.

After doing that we have completed the first stage but there are still triple cons present in the mirror so we will resolve that by deleting the surfaces and resolving the triple cons.

we can see that there is no hidden volume or triple cons present, which concludes that we have successfully performed the topo clean-up of the optical rearview mirror.
Now we will perform topo clean-up of the windows.
If we turn off the double cons and switch to shadow mode, we will notice that there are triple cons present in the windows region.

which indicates that there is a different volume present, so we have to resolve these triple cons by deleting those additional surfaces which also include duplicate surfaces.

After resolving the triple cons, we have successfully completed the topo cleanup of the windows.
Now we will perform a topo cleanup of the Lights.

We can see that there are triple cons present in the lights region.
We have to resolve this by deleting the surfaces which cause the triple cons and creating a separate volume.

there is a single con present which is not getting resolved by topo option which means that there are two single cons present which are not merging with topo option.
so, we will manually merge them using the paste option from the cons section in the topo deck.

now we will perform the topo clean-up of the rear lights.

we can see that a triple con is present so we have to get rid of it and make it a double con.
triple cons means there are three surfaces present which are creating a separate volume.
we will delete these extra surfaces.

Below the rear light, we got a triple con which we have to fix.

we have to delete the extra surfaces which leads to the creation of the triple cons.

the errors in this geometries a solved for now.
in the side of the car, we got an entity where a lot of errors are present.

we can see that there are single cons, triple con and a missing surface present.
we need to fix these errors.
we will start by deleting the extra surfaces.

In the back of this geometry, there are a lot of unnecessary surfaces which we will delete to get rid of some errors.
we will first separate the surfaces using the intersect option from the faces section under topo deck.
after intersecting the surfaces we will delete the unwanted surfaces.

we can see that we have fixed some single cons and a triple con.
for better viewing and clean up of the geometry we will isolate the portion we are working on from the rest of the geometry using the !not OPTION.

Lock the view.
now we will try to patch the missing surface.
we will create cuts and then create a new surface.

we have created the cut now we will delete the surface which is not needed and patch it up using the coons option.

Now we have solved all the errors in this entity.
we will perform the topo clean up of the silencer.

since the silencer is a separate entity and is not connected to the the car body through the geometry it will have its own separate volume
before we perform any operations in the silencer we have to isolate it from the rest of the body using the !NOT option and lock the view.

we can see that there are no errors in the geometry but even though there are no triple cons we can't assume that it doesn't have extra surfaces which generate different volumes.
we will check for additional surfaces by hiding the outer surfaces using the not option.
after hiding the surfaces we have found that there are no errors in this geometry.
Now we will perform the topo clean up of the rims and tires.

we can see that there are some errors in that geometry.
first we will fix the errors in the front wheel and then we will fix the rear wheel.
now we will isolate the front wheel from the rest of the body using the !NOT option and lock the view.

we got some triple cons which we will fix by deleting the extra surfaces and making the geometry hollow to have its own volume.

after solving the triple con, we can see some single cons are generated.
we can fix this single cons by using paste option from the cons section in the topo deck.
or we can delete that surface and create a new one there using the coons option.

now we don't have any errors in this geometry.
we will fix the rear wheel now.

we will isolate the rear wheel using the !NOT option and Lock the view to work on it.

we can see that there is a triple con which is the same as the front wheel.
so we will follow the same procedure from rear wheel.

we have successfully performed the topo cleanup of the rims and wheels.
Now we will move forward to the topo cleanup of the grills.

we will start by fixing the bottom corner grill.
to work on it we will isolate it from the rest of the body using the !NOT option and lock the view.

we can see there are some triple cons present which we will fix by deleting the extra surfaces.

after getting rid of extra surfaces we have fixed the triple cons.
but if we see the back of this geometry there are some surfaces present which make separate volume for the fins.

so we will delete these surfaces.

we will also delete the surface which make a separate volume for the fins.

Now we can see that there are single cons so we will patch the holes and the single cons will be fixed.
but before we create a new surface we have to make some changes.

we have to delete some surface for that we will use the cut option to separate it from the existing surface.

we have cut the surface now we will delete the unwanted surface.

now we we will also delete the upper surfaces.

we can see that there are some small surfaces present which we have to solve before creating new surfaces.

we can solve this by cutting the plane and deleting the extra surfaces.

after solving this we can see that some surfaces are flat while some are curved.
so we will delete the extra surface from the curved surface and make it flat.
we will separate the extra surface using the cut option and then delete them.

we also have delete the upper surface and made it flat.

we can see that one surface is not flat so we will delete it and create a new one there.

now all our surfaces are flat and now we will go ahead and patch the surfaces.
we will use the fill hole command to create the surfaces.

we can see that all the errors are fixed and we have completed the topo cleanup of the bottom corner grill.
Now we will perform the topo cleap up of the bottom middle grill.

we can see that there are some single cons and triple cons present.
we will fix these errors but before we start we will isolate this grill and lock the view.

as we can see that in the wireframe mode, some triple cons and single cons are present also overlapped surfaces are there.
we will delete any overlapped surface and extra surfaces first to get rid of the triple cons.

we have fixed the triple cons.
now we will merge the grill with the car bdy so that it will create a single volume.
for this we have to delete some more surface and patch some too.

As we have solved all the errors and also merged them with the body, we have successfully performed the topo clean of the bottom middle grill.
Now we will perform topo cleanup of the top grill.

We will isolate the top grill and lock the view so that we can work on it more effectively.

We can see that there is lot of single cons, some triple cons present also there are overlapped surfaces and missing surfaces.
We will start by deleting the unwanted surfaces first.

still, a lot of single cons are present which we will solve also we have to patch some missing surfaces.

we will project these single cons onto the surfaces behind it.

we have projected it only on the top surface we will use the project cut option to cut it from the side.

Now we will delete the upper portion of the grills.

We will also delete the backside surface of the grills since we have to make a single volume for the body of car.

Now we will delete the extra surface from the bottom for that we will first cut it.

we have cut the surface now we will delete it.

now we have to create new surfaces here

here we have to make some changes by deleting the surface which will cause a problem.

we will delete the upper surface.

now we have only one surface left to create after which the geometry will be complete.
we have to create that surface part by part for that we will project the hotpoint on the single cons using the multi project option.

now we can create the surface.

all the errors are fixed and we have completed the topo clean up of the grills.
now the only thing that is remaining is the body.
we will perform the topo clean up of the body.

we can see that there are some triple cons and overlapped/improper surfaces
we will solve this by deleting the unnecessary surface and creating new ones where required.

we will delete this unwanted surfaces.

after deleting that we got rid of the single cons and some triple cons.

there is a gap between the surfaces which causes single cons.
using fill hole option we will fix this surface.

the surface is fixed.

a triple cons is present here which means a extra surface is there.
we will delete this surface.

triple con is fixed.

If we look at the bottom surface of the body we can see that the bottom surface intersects through the wheel.
we will delete that unwanted surface and patch it up wherever needed.
we will first hide the wheel so we can work on it properly.

Now we will delete the unnecessary surfaces.

here at intersection con is not formed so we will use the intersect command to separate them so we can delete the unnecessary part.

we will use the cons2curvers option to create curves from the single cons, so that when we delete th surface we will have the refrence.

there is a triple con present here which we have to solve by deleting some surface and then creating new one.

we have fixed the front part to some extend.
now we will fix the rear part then come to the middle part.
using the cons2curves we will first create the curves for reference.

some surfaces also intersect through the rear wheel we will delete those.

we will hide the rear wheel too.

now we will delete all the unnecessary surfaces and create new surfaces.

we have fixed the rear portion too.
now we will fix the middle portion.

we have fixed the body.
now we will check the whole geometry if there are any single cons, triple cons or any errors present using the geometry check option.

we can see that the only errors are the single cons which will be solved when the other half geometry is completed.
with this we are done with topo clean up of the half geometry.
Now we will assign the PIDs to the parts.

Step 4 - Assigning PIDs

Before going to meshing we have to assign PID to each elements.
to assign PID,open the properties

we can see that there are already some PID assigned.
we will create new PIDs named as Body, Lights, Grills, Rims and Tyres, Optical Rear View Mirror, Window, Silencer, and Logo.
to create new PID right click in the windows, go to New and then PShell and click on PShell.

insert the Name as Body and click okay.

A new PID by the name Body is created.
In the same way, we will create all the other PIDs.

After creating the PIDs we will assign them to the respective entity.
we will assign the LOGO first.
Isolate the Logo entity using the !Not option.

In the property window right click on Logo and click on Apply
select the logo and do a middle click to confirm the selection.
now we have successfully applied the Logo PID.
In the same way, we will apply all other PIDs to their respective entities.

after apply the PIDs, we have to make sure that we have not left any elements.
we will select all the remaining PIDs and see whether we have any elements left.

Select all the remaining PIDs, right click and select show only.
press F9 button to fit the geometry to the screen.

we can see that there are no elements leftout.
we will delete this unnecessary PIDs now.
open the Compress option, A window will pop.

Click on Okay, it will compress/ delete all the remaining PIDs which are not needed.

we have successfully assigned the PIDs.
Now we will move to the meshing process.

Step 5 - Checking the quality criteria before meshing

Before we move to mesh we have to make sure that the geometry meets the quality criteria so that the mesh developed is good.
we will first deal with the Body PID.
Isolate the body PID using the OR command and PID selection method.

the target mesh length for the body PID is 3mm, the max length is 5mm and the min length is 1mm.
so we have to make sure that the distance between any two cons or nodes is greater than 1mm to have a good mesh also we can delete any unnecessary cons.
we will use measure tool to measure the distance.

we can see that here the distance is less than 1mm, sowe will delete one of this cons to get rid of this irregularities.

we have solved this errors now.

we can see here that the distance between this two cons is very less i.e less than 1mm.
we have to delete one of cons from this, but one con forms the edge so we can't delete that so we will delete the other one.
before deleting we have to make some modification to that so it forms a closed loop after deleting the con.

we have solved the Body PID.
now we will make the Lights visible and see whether they have any conflicts.

the target length is 4mm, the max length is 5, and the min length is 3.
so we have to see whether there is any distance less than 3
as we can see there are not many surfaces in the lights so there are no distance which is less than 3.
Now we will make the grills visible and check them for the quality criteria.

the target length is 1mm, the max length is 2, and the min length is 0.3.

we can see that we have cons here that are not required now so we can delete them.
After solving this we are done with the grills.
now we will move to checking the Rims and Tyres.

the target length is 2mm, the max length is 3mm and the min length is 1mm.

we can see here that the distance is very less so we will modify this con.

In the same way, we will do it for the remaining geometries and the rear typres.

now we will check the Optical rear view mirror.

the target length is 2mm, the max length is 3mm and the min length is 1mm

here we cansee that the distance is less than 1, so we will delete one of the cons.

now we are done with the optical rear view mirror.
we will check the windows now.

the target length is 2mm, the max length is 3mm and the min length is 1.
we can see that there is no distance less than 1 so we can move forward with this.
we will check the silencer now.

the target length is 3mm, the max length is 5mm and the min length is 1mm.

We can see that the distance is less here so we will delete the cons and modify it a little.

we are done with the silencer now.
we will look at the logo now.

the target length is 1mm, the max length is 2mm and the min length is 0.4mm.

here as the cons get closer the distance is reduced so we will delete these surfaces and create a new one there.

we have solved this error.

we can see here that the distance is less than 0.4mm.
we will delete the surface and create a new one there to solve this problem.

we are done with the logo, now we will move forward to meshing.

Step 6 - 2D surface meshing

for meshing we will switch to mesh deck and change the decks to openfoam.

also change the view to PID.

open the quality criteria parameters and set the parameters as below.

we will turn off the shadow mode and enable the hidden mode.
in the hidden mode we can see the color codes of the quality criteria on the screen as weel when we are done meshing, so we can fix any errors or the elements which don't come in the quality criteria.

now we will start the meshing of the Logo.
isolate the logo PID.

set the minimum length as 0.4mm and max length as 2mm in the quality criteria parameters.

in the mesh parameter select Tria elements of 1st order and set the target length as 1mm, minimum length as 0.4 and max length as 2.

now click on length option from the perimeter section under the topo deck.
a windows pops up,

select the perimeter option and select the whole logo geometry using box select and do middle click to confirm the selection.

enter the length as 1 and click on okay.
Now select the macros option and select the whole logo geometry, do a middle click to confirm the selection.

enter the length as 1 and click on okay.
click on spot mesh from the mesh generation section under the mesh deck.
select the whole geometry and do a middle click to generate the mesh.

we can see that there are about 42 elements which dont pass the quality criteria.

to solve this we will use the reconstruct option.
click on reconstruct option from the shell mesh section under the mesh deck
select the visible option so that all the elements on the screen are selected i.e the logo geometry.

we can see that all the off elements are solved with this the meshing of the logo is complete.
we will mesh the grills.
isolate the grills PID.
since the target length is same as that of the logo we won't have to change the quality and mesh parameters
but the minimum length for the grills is 0.3 so we will change that in the quality criteria and mesh parameters.

now click on length option under the perimeters section in topo deck.
a window pops,

select perimeters option, select the whole geometry and do a middle click to confirm.

enter the length as 1 and click on okay.
select the macros option and select the whole geometry, do a middle click to confirm it.

enter the length as 1 and click on okay.
now click on spot mesh and click on visible from the drop down option to mesh the geometry.

we can see that there are about 152 off elements.
we can use the reconstruct option here.
click on reconstruct option under the shell mesh section in mesh deck.
and select the visible option from the drop down options to reconstruct the mesh.

we can see that most of the off elements are solves and the number of off elements is come down to 5.
we will manually go to these elements and fix it.

After doing some topo clean up and meshing it again, we have fixed all the off elements.
We will mesh the windows now.
isolate the window PID.

open the quality criteria and set the minimum length as 1mm and max length as 3mm

in the mesh parameters select the trial elements of 1st order, set the target length as 2mm, min length as 1 and max length as 3.

click on the length option under the perimeters section in mesh deck.
a window pops up,

chose the perimeters option and select the whole geometry, do a middle click to confirm the selection.

enter the length as 2mm and click on okay.
now choose the macros option and select the whole geometry, do a middle click to confirm the selection.

enter the length as 2mm and click on okay.
click on spot mesh option under the mesh generation section in the mesh deck.
select the visible option to mesh the geometry.

we can see that there are about 57 off elements.
we can fix this by using the reconstruct option.
click on the reconstruct option under the shell mesh and select the visible option to reconstruct the mesh.

all the off elements are fixed now.
we will mesh the Rims and tyres.
isolate the rims and tyres PID.

since the target length, minimum and maximum length is same as that of the window PID we won't have to change that.
click on length option under the perimeters section in the Mesh Deck.
A windows pops up.

choose Perimeters and select the whole geometry, do a middle click to confirm the selection.
enter the lengths as 2 and click okay.

now choose Macros and select the whole geometry, do a middle click to confirm the selection.
enter the length as 2 and click on okay.

click on spot mesh option under the mesh generation section in the mesh deck.
select the visible option to mesh the geometry.

we can see that there are a lot of off elements.
we will fix these by using the reconstruct option.
click on reconstruct option in the shell mesh section in the mesh deck.
select the visible option to reconstruct the mesh.

the number of elements are reduced to 16 now.
we have to manually fix these elements now.

we have fixed the off elements.
We will mesh the optical rear view mirror.
isolate the optical rear view mirror PID.

the quality criteria is same as that of rims and Tyres, so we won't change that.
click on length option under the perimeters section in the mesh deck.
a window pops up,

choose perimeters and select the whole geometry, do a middle click to confirm the selection.
enter the length as 2mm and click on okay.

choose the macros option and select the whole geometry, do middle click to confirm the selection.
enter the length as 2mm and click on okay.

click on the spot mesh option in the mesh generation section under the mesh deck.
select the visible option to mesh the geometry.

we can see that there are some off elements.
we will fix this by using reconstruct option.
click on reconstruct option in the shell mesh section under the mesh deck.
select the visible option to reconstruct the mesh.

all the off elements are solved.
we will mesh the Lights now.
isolate the lights PID.

in the quality criteria set the minimum length as 3 and the max length as 5.

in the mesh parameters select the Tria elements of 1st order, set the target length as 4mm, minimum length as 3mm and maximum length as 5mm.

click on length option under the perimeters section in the mesh deck.
a window pops up,

choose the perimeters option and select the whole geometry, do a middle click.

enter the length as 4mm and click on okay.
choose the macros option and select the whole geometry, do a middle click.

enter the length as 4mm and click on okay.
now click on spot mesh option under the mesh generation in the mesh deck.
select the visible option to generate the mesh.

we can see that there are some off elements present.
we will use the reconstruct option to solve this off elemenst.
click on reconstruct option under the shell mesh section under the mesh deck.
select the visible option to reconstruct the mesh.

we have reduced the off elements to 9, we will fix these elements manually.

we have fixed the elements.
now we will mesh the silencer.
isolate the silencer PID.

open the quality criteria and set the mimum length as 1mm and max length as 5mm.

now open the mesh parameters.
select the trial elements of 1st order, set the target length to 3mm, the minimum length as 1mm and max length to 3mm

click on the length option under the perimeters section in the mesh deck.
a window pops up,

choose the perimeters option and select the whole geometry and do a middle click to confirm the selection.

insert the length as 3 and click on okay.
now select the macros and select the whole geometry, do a middle click to confirm the selection.

insert the length as 3 and click on okay.
click on the spot mesh option under the mesh generation section in mesh deck.
select the visible option to mesh the geometry.

we can see that we have about 77 off elements.
we will use the reconstruct option to solve this off elements.
click on the reconstruct option under the shell mesh section in the mesh deck.
and select the visible option to reconstruct the mesh.

all the off emensts are solved.
we will mesh the Body now.
isolate the body PID.

the quality parameter are same as that of the silencer, so we don't have to change that.
click on the length option under the mesh generation section of the mesh deck.
a window pops up,

choose the perimeter option and select the whole geometry but exclude the cons which are shared by other PIDs
make all other PIDs visible by clicking on ALL option, do a middle click to confirm the selection.

enter the length as 3mm and click on okay.

click on the spot mesh option under the mesh generation section in the mesh deck.
select the visible option to mesh the body.

we can see that there are a lot of off elements.
we will change the min length to 0.3 to get rid of some off elements.

we have 3 off elements now.
We will fix it by using the reconstruct option.
click on reconstruct option under the shell mesh section under the mesh deck and isolate the body PID after the process is completed.

we have only 1 off element now; we will fix it manually.

We have fixed all the Off elements.
With these, we have finished with the 2d meshing of the geometry.

Step 7 - completing the geometry.

we have only the half geometry of the car, so we have to create the other half of the car to complete the geometry.
switch to top view.

since the car is symmetric that why we we deleted the other half of the geometry and worked on the half geometry only.
now we will copy this half geometry and paste it.
click on the drop down arrow on the transform option.
choose copy,
select the whole geometry but exclude the logo, since it is not symmetrical.

do a middle click to confirm the selection.
a windows pops up.

go to symmetry, in the use section select mirror 3-point plane.
in this, we have to select 3 points to define the plane.

after selecting the 3 points do a middle click to confirm the selection.
a new window pops up.

in the PID section choose the No offset option, since we dont want any offset between the geometry.
also in the part section keep it as same part, so that it will have the same PIDs.
click on okay to copy the geomerty.

the geometry is completed.
we can see that after copying there are some single cons present.
we will switch to Ent mode
we can use topo to solve this single cons.

Now we will create the wind tunnel.

Step 8 - Creating a wind tunnel.

for aerodynamic analysis we need a wind tunnel.
so we will create a virtual wind tunnel in the software.
to create the wind tunnel we will switch to topo deck.
first, we need to measure the length of the car, we will measure the length of the car using the measure tool.

we can see that the length of the car is 1307.875 which we can round off to 1310.
before we start creating surface we have to define/ create some points, which will later act as nodes for creating cons and then surface
we will create a point at the middle of the bottom surface.
to create the point click on relative option under the points section in the topo deck.

a window pops in that select Points, and place the point in the geometry.

do a middle click to confirm the point location. a window will pop.

we want to place the point below the geometry such that the wheels won't touch the surface of the wind tunnel.
since our area of interest lies above the geometry we will live less gap between the bottom surface and the geometry.
to place the point below the geometry we will insert the value in the y- axis coordinate.
in the dy insert the value as -75. here minus sign indicates that we have to place the point below the geometry.

now the next point will be in front of the car.
the distance from the car to the point is expected to be 4 times the length of the car.
for that we have to measure the length from the center to the front of the car then add it.

the center to front of the car is 653.697 which can be rounded off to 655.
so the total will be 655 + (4 x 1310) = 5895
using the same method we will place a point at a distance of 5895 from the previous point.
only this time the value will be inserted in the dz and it will be positive.

now we have to place a point in the rear of the car.
the distance from the rear of the car to the rear point will be 6 times the length of the car.
but we also have to add the distance from the center of the car to the rear of the car.
we will measure this using the measure tool.

the distance from the center of the car to the rear of the car is 661.89 which can be rounded to 662.
so the total will be 662 + (6 x 1310) = 8522
we will use the same method to place the rear point at a distance of 8522 from the previous point.
this time we will enter the value in dz and the value will be negative.

now we have to create points on the side of the geometry.
the side distance is equal to the length of the car.

now we will create the bottom surface, but for that, we must create curves first.
we will use the create option in the curves section to create curves.

now that we have created the curves we will use the coons option to create the surface.
while creating the surface it asks for the PID.
since we have not created the PID for the wind tunnel we have to create a new one.
we will create a new PID with the name as BaseSurface Tunnel.

we will assign it to the newly created surface.

now we will offset the bottom surface to the top to create the top surface.
for that we will measure the distance from the bottom surface to the roof of the car first.

we can see that the distance from the bottom surface to the roof is 373.60 which can be rounded off to 375.
so the topo surface will be at 3 times the length of the car from the roof of the car.
that is 375 + (3 x 1310) = 4305
to offset the surface, click on offset in the faces section under the topo deck.
select the surface and do a middle click to comfirm the selection.
a window pops up, enter the offset distance as 4305 and click on okay.

now that we have create the top surface, we won't need the the points and the cons so we will delete those.

now we will create the side surfaces using the coons option.

in the same way we will create the front and rear surface.

Now we have to assign PID to the wind tunnel surfaces.
we will create a total of 4 new PIDs named as FrontFace Tunnel, RearFace Tunnel, SideFace Tunnel, and TopFace Tunnel.

now we will apply it to the respective surfaces.

Step 9 - Meshing the wind tunnel.

we will switch to mesh deck to mesh the geometry.
we will need finer mesh near the car whereas we can have a coarse mesh away from the car.
for now we will disable the min length and max length in the quality criteria.

click on length option under the perimeters section in the mesh deck.
in the window choose perimeter and select the top face.

do a middle click to comfirm.

enter the length as 100 and click on okay.
do the same for the macros as well.
now choose the perimeter option and select the bottom face.

do a middle click to confirm the selection.

enter the length as 20 and click on okay.
do the same with macros option.
we have to give varying mesh length.
for that click on spacing option under the perimeters section in the mesh deck.

in the windows, select the biasing as geometric, factor as 1.1, the dmin as 20 and dlimit as 100.

select the cons such that the arrow is pointed towards the top surface.
click on okay to confirm the selection.

now we can go forward and create the mesh.
we will isolate the base surface.

in the quality, criteria give the min length as 15 and max length as 25.

in the mesh parameters, give the target length as 20, min length as 15 and max length as 25

now click on spot mesh in the mesh generation section under the mesh deck.
click on visible to mesh the base surface.

now we will isolate the top surface.

in the quality criteria insert the min length as 80 and max length as 120.

in the mesh parameters insert the target length as 100, min length as 80 and max length as 120.

now using the spot mesh option mesh the top surface.

now make the wind tunnel visible.

in the mesh parameters change the target length to local.

now we will mesh the remaining surfaces one by one.
first we will mesh the rear face surface by using the spot mesh.

now we will do the same to the front face surface.

we will mesh the side faces now.

now we are done with the surface meshing.

Step 10 - Volumetric meshing.

To perform volumetric mesh, we will switch to the Volume mesh deck.
First we have to define all the volume.
to do so click on Define option under volume section in the volume mesh deck and select Auto Detect.
a window pops,

set the work on to whole db, and click on ok.

in a new window, it will show all the volumes detected.
we got 8 volumes here.

we will only keep the volume that is between the wind tunnel and the car and delete the rest.
so we will delete all the remaining volumes that are from 2 to 8 and keep only the volume 1.

now we can perform the volumetric meshing on this volume.
to perform the volumetric mesh we have to right click on the volume and click on remesh option.

(I have not gone ahead with the remesh option because my System is not that powerful and volumetric mesh takes around 2 days).

we have successfully completed the CFD meshing of the wind tunnel for the BMW car.

Learning Outcome: -

I was able to successfully carry out the CFD meshing of the Wind tunnel for a BMW car.
I learned and Performed the volumetric meshing of the wind tunnel.
I practiced the volume extraction that is to define volume.
I learned to give variable mesh length using the spacing option.
I practiced and performed the topo clean up of different geometries, assigning PIDs, copying the geometry to make it symmetrical.
learned creating geometries from the reference points and creating the reference curves/points.
I learned to check the quality criteria of the mesh elements and also to repair/fix them.
learned different mesh modifying tools.
Overall, now I can carry out similar procedures/ task on different geometries.

Result: -

The total number of Tria elements in the Body is 426216

The total number of Tria elements in the lights is 3132

The total number of Tria elements in the Grills is 195130

The total number of Tria elements in the Rims and Tyres is 293712

The total number of Tria elements in the Optical rear-view mirror is 9048

The total number of Tria elements in the window is 122668

The total number of Tria elements in the Silencer is 16824

The total number of Tria elements in the Logo is 451

The total number of Tria elements in the wind tunnel is 371602

The total number of elements in the whole geometry is 1442838

(Since the volumetric mesh is not completed due to lack of system capabilities, the elements i the volume mesh are not mentioned.)

Conclusion: -

Topo clean is done to get rid of the single cons, and triple cons and to fix any errors in the geometry such as missing surfaces.
target length is selected based on the minimum distance between two cons or nodes in that geometry so that the geometry is captured perfectly while meshing.
Additional volumes are formed because the silencer and the types are not connected to the car body.
quality errors are fixed using the reconstruct mesh option and i that does not work, the mesh elements are fixed manually using the fix, move, split option.
to reduce the work required for topo clean up half of the geometry is considered since it is symmetrical, and after the meshing it is copied and the whole geometry is completed.
Overall, the CFD meshing of the BMW car was completed successfully

https://drive.google.com/file/d/1fFNC4QvZgcxyn4lFY6rpPTQWCVkiTjrA/view?usp=sharing

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