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-   -   [GAMBIT] hexahedral mesh for cyclone (http://www.cfd-online.com/Forums/ansys-meshing/110253-hexahedral-mesh-cyclone.html)

nabaen December 6, 2012 06:45

hexahedral mesh for cyclone
 
Hi
I'm trying to mesh a cyclone that is consisted of three volumes (1-tangential inlet,2-upper cylinder(gas outlet) 3-cyclone body(frustum+cylinder) with hexahedral elements.all faces were meshed with hex element and pave type.I can not mesh volumes 2,3 with hexahedral elements and cooper type. Because i can't specify true source faces. would yu please help me to mesh this cyclone.
Thanks in advanced.
http://postimage.org/image/6afrf11ct/

-mAx- December 6, 2012 07:56

Because the red surrounded volume cannot be meshed directly as cooper
You need to do some splits.

nabaen December 25, 2012 02:42

Hi,
Thank you so much for your reply .I could finally mesh my cyclone with hexahedral type . I defined a virtual face to split two volumes. My fluent case dose not converge .I guess the cyclone meshes are not suitable.
1-Can virtual face interrupt the gas flow?(It is not defined as a zone or boundary. Is it necessary to deifine this face?Can I ignore this virtual face?
2-I have 4 separated volumes 3 of them are cooper type and inlet is map type.what is your idea about the quality of meshes.Do you think cyclone mesh can be reason of model convergence problem ?
Thanks in advanced

nabaen December 25, 2012 02:51

cyclone mesh
 
Hi,
Thank you so much for your reply .I could finally mesh my cyclone with hexahedral type . I defined a virtual face to split two volumes. My fluent case dose not converge .I guess the cyclone meshes are not suitable.
1-Can virtual face interrupt the gas flow?(It is not defined as a zone or boundary. Is it necessary to deifine this face?Can I ignore this virtual face?
2-I have 4 separated volumes 3 of them are cooper type and inlet is map type.what is your idea about the quality of meshes.Do you think cyclone mesh can be reason of model convergence problem ?
Thanks in advanced
http://axgig.com/images/54732507926098137654.jpg

-mAx- January 3, 2013 02:31

if your splits are well done, then split surfaces are defined as interior.
The question is why it is not converging?
Is your checkmesh successfull?
Do you have walls in fluent which are not predefined in gambit?

nabaen January 8, 2013 02:41

I made my geometry once more. This time I did not uninited the volumes.So it consists of 4 volumes. They are meshed by hexahedral type, so that these volumes can not be united. There are 3 faces (marked by red color in attached picture ) that make the problem.I have to define them as boundary ,otherwise it will be known as wall and will be an obstruction for fluid.I defined them as interior but Fluent didn’t accept this faces as interior. What boundary should I define for these faces?
http://upload.tehran98.com/img1/108gqx37aa9gw4mdlsm.jpg

By the way I have not predefined the walls in gambit.Because I think they will be known as wall by defult in gambit.
Thank you in advanced.

-mAx- January 8, 2013 08:57

Quote:

Originally Posted by nabaen (Post 400654)
I have to define them as boundary ,otherwise it will be known as wall and will be an obstruction for fluid.I defined them as interior but Fluent didn’t accept this faces as interior. What boundary should I define for these faces?
http://upload.tehran98.com/img1/108gqx37aa9gw4mdlsm.jpg

By the way I have not predefined the walls in gambit.Because I think they will be known as wall by defult in gambit.
Thank you in advanced.

Gambit creates wall instead of interior (or internal) because your volumes aren t connected (if you select suc a surface, you will see there are 2 superposed surfaces).
Go to face / connect, and connect all.
It should fix the problem.
And yes, all outer surfaces which are not defined as BC, will be automatically set as wall

nabaen January 9, 2013 00:32

Thank you so much for your kind reply.
I didn’t understand which faces should connect. :confused: I selected all faces and entered to connect but a warning resulted.:(
I united three of volumes.Now it is comprised of 2 volumes.Can I define the red face as “interface”?http://upload.tehran98.com/img1/hfymmj1mxn4fcptone.jpg
I was wondering if you could check my geometry?https://hotfile.com/dl/188146938/16c...metry.dbs.html
Thanks in advanced.:) and excuse me for repeated question.

-mAx- January 9, 2013 02:01

your volumes aren t conected and not splitted
-Split volume 4 with volume 3
If you check edges 18 & 22, you see that both edges are tangential at vertex 13. That will be generate skewness cells.
So you can sweep face 14 in y-direction with vector (0 0.001 0), and then merge both volumes.
Finally merge also faces which common edge is source of problem (edge 18)

nabaen January 10, 2013 03:19

Thank you so much.:)
I split volume 4 with volume 3 as your guide. But face 9 &19 are still my problem .They will be known as wall in fluent and will obstruct flow gas to exit. What should I do?
http://upload.tehran98.com/img1/a6pfqvp4tyzodvwiih1.jpg
https://hotfile.com/dl/188303408/c14...metry.dbs.html
I wish all the best to you.

-mAx- January 10, 2013 03:45

I saw you defined face 9 as interface.
Delete this BC
If you did the same with face 19, delete the BC

nabaen January 10, 2013 04:33

Quote:

Originally Posted by -mAx- (Post 401114)
I saw you defined face 9 as interface.
Delete this BC
If you did the same with face 19, delete the BC

Yes ,Interface is not true.But if these two faces put undefined will be known as wall(How can I solve this?)

-mAx- January 10, 2013 04:44

if volumes are well connected, then Gambit defined split surfaces as internal (but won't appear in the BC panel)

nabaen January 10, 2013 05:05

Quote:

Originally Posted by -mAx- (Post 401123)
if volumes are well connected, then Gambit defined split surfaces as internal (but won't appear in the BC panel)

I am so sorry. It made me frustrated .
Do you mean is splitting volume 4 with volume 3 enough ?So I have to define face 8 as wall.

-mAx- January 10, 2013 05:10

if your surface 8 has to be a wall, then define it as wall, else Gambit will define it as internal

nabaen January 10, 2013 05:30

Only one more question.:p
you advised me to sweep face 14 (preventing skewness cells).It was done but an error Occurred in last stage(merging faces with same edge(edge 18) http://upload.tehran98.com/img1/fmhk...1t92uvvdok.jpg

-mAx- January 10, 2013 05:40

1 Attachment(s)
both displayed surfaces have 90° angle....
Then it is not possible to merge them
I meant like that:
Attachment 18082


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