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[GAMBIT] How to set up a wind tunnel with interior?

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Old   December 20, 2009, 15:11
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it comes from the lines wich are tangential (between base of hemisphere and brick's edge)
Post a picture of the plane (just to be sure that your big brick is meshed and exported)
In your case the hemisphere will just have a mesh control functionality. Indeed you may refine your mesh inside it (eg: around the small bricks), and coarse the mesh outside it.
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Old   December 20, 2009, 15:26
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okay, here the mesh. seen on the picture are the velocity vectors of the lorry (the two small bricks) the interior and the plane.
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Old   December 20, 2009, 15:43
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then it is ok, all the domains are exported.
To your first question, I believe fluent prefers displaying vectors on a plane.
Display pathlines from your inlet and yoou will see If you have any interior problem
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Old   December 20, 2009, 16:04
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yes, by showing the pathlines of the inlet to the outlet it looks pretty good:

but now i ask my self if the interior is necessary? ^^
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Old   December 21, 2009, 02:12
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As I said, in your case the hemisphere isn't necessary (your fluid domain es the big brick containing your hemisphere).
Per Default, Gambit exports and creates the fluid domain called something like "interior".
SO you don't need to specify the interior domain, except if you need to handle more than one fluid domain (porous, multiphase etc....)
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Old   December 21, 2009, 06:47
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okay, so, interior is good when i use more than one fluid domain. yes, this makes obviously sense for me.

its just that our teacher told us we should create an interior to mesh/iterate faster.
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Old   December 21, 2009, 07:45
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Indeed you can have more control on your mesh refinement inside your hemisphere. But it is not a must
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Old   December 21, 2009, 11:45
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but i still think that there is something wrong with my interior. in my opintion the flow IN the interior should be also filled with velocity vectors ect. like in the standard-interior created from gambit.

i will explain you very accurate what i did to create this hemispheric interior. maybe you can see an error in my steps and i could solve this problem then.

I create all the geometries in gambit. my wind tunnel is A, the lorry (two small bricks, with the red circle) is B, and the interior is C.


First step i have done: substract the lorry B from the wind tunnel A in one step. This is the same like in 2D. This gives me a new geometry, lets call it D.

But then i have a problem, the until now spheric interior has to be splitted from D.
So when i go to split volume, i chose volume 1 (D) and split the sphere (C) from it.

I just activate the option "connected" and NOT bidirectional and then just the hemispheric geometry stays.

Thats all, now just set up the boundary conditions and export the file as mesh for fluent.


Is this okay? Its the way i did it.
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Old   December 21, 2009, 12:57
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It's look like ok from my side.
How did you set your Interior in gambit?
in BC Panel as Interior or in Continuum Panel as Fluid?
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Old   December 21, 2009, 13:03
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i set it in "specify boundary types" as interior.
i didn't specified something in the "specify continuum types" windows.
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Old   December 21, 2009, 13:07
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That's the reason, the BC is just available for surfaces
Define your hemisphere as fluid in "specify continuum types", and export it.
You will be able to get what you want.
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Old   December 21, 2009, 19:03
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Okay, the thing is now the following. I changed the things you told me and now the mesh in gambit looks pretty well!

but now i cant iterate in fluent. i dont know why but the iteration goes to infinity after approx. 120 iterations. at the beginning the line looks steady, but then it goes up and down and up and down and this over values of 1000000000000000000 ^^
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Old   December 22, 2009, 01:32
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*check the set up of the new fluid domain in the bc-panel (eg: material).
*check the results to be sure that the fluid flows well

But as I previously said, defining the hemisphere as a separate fluid domain, won't bring you anything (except viewing it separately)
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Old   December 25, 2009, 19:10
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okay, this problem is now solved. thanks a lot for your help.

next problem

now i try to solve this with the k-epsilon model and the teacher told us y+ should be between 50 and 500. My y+ is over 40000... i try now since many hours different meshs but there is no change.

Adapting the y+ value is also no solution. Any tip for my about this problem?
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Old   January 4, 2010, 01:45
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http://geolab.larc.nasa.gov/APPS/YPlus/
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Old   January 5, 2010, 16:15
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yes, that was a big help

do you know/can you tell me which formula the first calculator uses?

kind regards
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Old   January 6, 2010, 02:24
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check turbulence theory , especially log-law for wall treatment
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Old   December 1, 2010, 14:03
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