# [GAMBIT] Boundary layer direction

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 November 7, 2012, 09:39 Boundary layer direction #1 New Member   Join Date: Oct 2012 Posts: 14 Rep Power: 5 Hello, I have a very frustrating problem and i read through so many posts but nothing works. I have substracted my cubic like geometry from a big cube for the computational domain and now want to create a boundary layer on the inner surface of course pointing to the fluid. But gambit always points it inside ?!?!! I have read about using the middle button of the mouse, double left klick and to use the list and add the same face until it points the right way. But it just doesn't work.. :-( Also i tried defining the space in between as fluid and the structure as solid.. I would appreciate any type of help a lot! Pleeease help me! Thanks! Last edited by Markus; November 7, 2012 at 09:58.

 November 8, 2012, 05:43 #2 Senior Member   Marion Join Date: Jul 2012 Location: France Posts: 122 Rep Power: 7 Hi Markus, Do you have volumes other than your fluid domain in Gambit? Can you add a picture, it would be easier to understand... Marion.

November 8, 2012, 07:54
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Hi Marion,

Thank you for answering. I think i only have the fluid volumes. (see pictures 3 and 4)

The geometry in the middle is the thing i want to put in the flow. then thought its good to make a close region for the boundary layer and a fine mesh and then i wanted to fill the rest of the computational domain (volume2) using a size function.

best,
Markus
Attached Images
 pic1.jpg (82.7 KB, 22 views) pic2.jpg (88.0 KB, 13 views) pic3.jpg (88.4 KB, 13 views) pic4.jpg (90.9 KB, 14 views)

 November 8, 2012, 09:32 #4 Member   Tamil Nadu Join Date: Oct 2012 Posts: 44 Rep Power: 5 Hi Markus, Mine is also similar problem, I feel. I want to model a building in GAMBIT 3D. Finally, aim of my project is to simulate the temperatures of the walls of building when water flows through pipes inserted in the ceiling (using Ansys Fluent). Is it possible to solve??

November 8, 2012, 11:12
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Quote:
 Originally Posted by Markus Hi Marion, Thank you for answering. I think i only have the fluid volumes. (see pictures 3 and 4) The geometry in the middle is the thing i want to put in the flow. then thought its good to make a close region for the boundary layer and a fine mesh and then i wanted to fill the rest of the computational domain (volume2) using a size function. best, Markus
Markus,

Try to split your volumes first, it will be easier to control the mesh.

Is it hollow in the middle? or do you still have a volume there?

If you want, you can attach your model and I'll have a try.

Marion.

November 8, 2012, 11:24
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i think it is hollow... :-)
That would be very nice of you, thanks!

Markus
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 satsat2zip.zip (51.3 KB, 3 views)

 November 9, 2012, 04:17 #7 Senior Member   Marion Join Date: Jul 2012 Location: France Posts: 122 Rep Power: 7 Hi, I've just had a look, and I got the same issue on your original model. But I confirm my advice: split your volume into smaller domains. I split it in 8, and I used BL on edges it worked very well As it is a simple geometry, you can even split it on each side of your small parallelepipeds. I hope this helps, Marion.

November 9, 2012, 04:18
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Quote:
 Originally Posted by Marion Hi, I've just had a look, and I got the same issue on your original model. But I confirm my advice: split your volume into smaller domains. I split it in 8, and I used BL on edges it worked very well As it is a simple geometry, you can even split it on each side of your small parallelepipeds. I hope this helps, Marion.

Here are some snapshots.
Attached Images
 Image1.jpg (36.5 KB, 11 views) Image2.jpg (30.1 KB, 8 views)

 November 9, 2012, 04:53 #9 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,285 Blog Entries: 6 Rep Power: 43 boudary layer is good option, but should be used where it is appliable. Dividing into small volume is the best approach for hexa mshing and mesh control in particular area. For example see this thread Boundary layer mesh & map mesh in rectangular ribbed channel and this video: http://www.youtube.com/watch?v=Gub1Kbcup2k&feature=plcp

 November 9, 2012, 05:38 #10 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,285 Blog Entries: 6 Rep Power: 43 How many cubes are there? do you want to mesh inside the small cube, where small sheets are present? Is it part of Fluid? Do you have access to ICEM?

 November 9, 2012, 12:14 #11 New Member   Join Date: Oct 2012 Posts: 14 Rep Power: 5 hi Thank you very much for all the advice, i will try it out. Markus

 November 9, 2012, 13:10 #12 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,285 Blog Entries: 6 Rep Power: 43 There are three cubes and some protrusion (six in total)? volume inside the small cube (cube) is hollow? and also volume inside six small box is also hollow?

November 9, 2012, 14:09
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The geometry which represents the solid is the big cube and the six cubes on the surfaces, they are not fluid.

Its a model of a cubesat with thrusters (6 small cubes ) for an underwater test.

I did try by splitting, but it also looks strange now
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November 9, 2012, 14:22
#14
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like this.....
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 room1.jpg (66.9 KB, 14 views) room2.gif (41.6 KB, 18 views)

November 12, 2012, 06:01
#15
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I hope this is helpful to you.
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