[king lui]

Hello everybody,

I want to do a 3-dimensional analysis in Fluent and the most important part of my assembly is a cylinder.
The problem is in Gambit when I want to create a boundary layer around my cylinder, that Gambit creates it just inside the cylinder which is a solid body and for my problem of an external flow I need the boundary layer obviously on the outer surface of the body.

Maybe someone could help me and knows what can I do that my boundary layer is on the outer surface.

Thanks for your help...

[-mAx-]

Except if you need keeping the solid domain, you may delete it. Then your problem disappear, because only the fluid domain remains.
Else you can click on middle button of your mouse for switching BL-direction

[king lui]

Hey Max,

thanks for your help but i tried this already. I subtracted my cylinder from the rest of the domain and specified it as a wall the rest of the domain is a fluid but it still doesn´t work, my boundary layer ist still inside the cylinder and i can´t choose the direction.

[-mAx-]

If your cylinder has a thickness, and you substracted it, then your cylinder may have one adjacent domain: the fluid.
You can post a picture

[king lui]

Yes, and i thought then if there is just one adjacent domain, the boundary layer should be in the fluid domain. on the picture there are two cylinders, just consider the inner one (smaller) the other one is just an interior.

[-mAx-]

if your problem is symmetric, work with one quater of your domain.
if it is not symmetric, split your dommain into 4 domains.
The split planes will resolve your issue
Hope it helps

[king lui]

Unfortunately it isn´t a symmetric problem. And also to split the domain into 4 domains wasn´t successful...

Is there maybe an alternative to create the boundary layer manual?

[-mAx-]

Originally Posted by king lui

Unfortunately it isn´t a symmetric problem. And also to split the domain into 4 domains wasn´t successful...

Is there maybe an alternative to create the boundary layer manual?

Splitting along (xz) and (yz) works: I reproduced your geometry and tested it
If you still have problem you can provide me your geometry, I will described you how to proceed

[king lui]

This would be great...

I created my geometry in mm,

so the ellipse has a length of 10000mm (x) a height of 6000mm (y) and a depth of 12000mm (z). The cylinder which is used as a interior has a diameter of 600mm and a depth of 12000mm. The cylinder which is the wall has a diameter of 300mm and a depth of 9000mm, the cylinder is always moved into the middle of the domain (1500mm in z-direction)

thanks for your help

[-mAx-]

we are agree that the 300mm diameter-cylinder is considered as a hole and you want to attach the BL around its outter surfaces, right?

[king lui]

Yes exactly, thats right.

[-mAx-]

Ok as I said yesterday, you can create a plane (yz) (20000x20000) and a plane (xz) (20000x200000)
Split all the volumes with those planes --> your domain will be splitted into quarter.
Then you can create your BL.

[king lui]

I tried your method and it works finally. Thank you very much for your help, without that I would have much more trouble because of this problem.

Thank you

[king lui]

Now I have the next problem

The orientation of the boundary layer and anything works but when I mesh my volume around the boundary layer the following error occurs:

ERROR: Currently, 3D boundary layers are limited to flat face groups
with END conditions around the boundary. The problems occur in volume...
along the following edges: Edge...

You can turn the MESH.VOLUME. USE_3D_Boundary_Layers default off
and try again.

I tried already to turn the default off, but the error still occurs.
And as I saw from your picture you had not this problem.

Maybe you have an idea to solve also this problem?

Sorry for bothering you

[king lui]

Okay, I solved this problem now, but anyway thank you.

[samer]

hello every body
the problem consists of a cylindre and an interior sphere, i can't create the boundary layer at the exterior side of the sphere, it also created at the interio side.
I substract the 2 volumes and i make a split with a plane and also the same probleme

[-mAx-]

Do you need to keep the sphere (solid conduction?)?
If not delete the sphere, the outter surface should remain, and retry applying a BL.

[samer]

Thanks MAX
But the problem that the sphere and the cylinder are one volume(because i subtracted the shere from the cylinder)

Originally Posted by samer

hello every body
the problem consists of a cylindre and an interior sphere, i can't create the boundary layer at the exterior side of the sphere, it also created at the interio side.
I substract the 2 volumes and i make a split with a plane and also the same probleme

[-mAx-]

post a picture with your BL

[rohitjvbibin]

Originally Posted by king lui

Now I have the next problem

The orientation of the boundary layer and anything works but when I mesh my volume around the boundary layer the following error occurs:

ERROR: Currently, 3D boundary layers are limited to flat face groups
with END conditions around the boundary. The problems occur in volume...
along the following edges: Edge...

You can turn the MESH.VOLUME. USE_3D_Boundary_Layers default off
and try again.

I tried already to turn the default off, but the error still occurs.
And as I saw from your picture you had not this problem.

Maybe you have an idea to solve also this problem?

Sorry for bothering you

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Hey can you tell me how to turn it off default....Where can i find the option..I also tried to volume mesh my helical geometry but this 3d boundary layer problem persists....No matter what size i provide...