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[GAMBIT] periodic boundary condition for a rectangular duct domain 

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April 5, 2013, 01:01 
periodic boundary condition for a rectangular duct domain

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Ayyappadas G
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Hi all,
I am new to CFD and i m doing a work on the film cooling on a flat plate, and i used gambit for modelling a 3D rectangular geometry as a domain. The bottom face of the rectangular duct is the taken as the test plate. I gave the following boundary conditions: 1. duct inlet > Velocity inlet 2. duct outlet> pressure outlet 3. test plate > wall 4. Top side> wall( opp face of test plate) 5. right side face> symmetry 6. left side face> Periodic After that i did export > mesh, but the file is not exporting successfully. It is showing some errors with the periodic boundary condition, warn: boundary entity periodic side shadow does not contain any valid entity and is not written. error: periodic boundary entities are not specified on the same boundary entity. please help... what is the error and how can I resolve it... thanks in advance 

April 5, 2013, 08:44 

#2 
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Maxime Perelli
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can you attach a sketch of your geometry with your BC.
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April 5, 2013, 12:47 

#3 
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thanks for showing interest to help me, sir
here i m attaching its sketch... i did this in gambit... for the left face of the duct i want to giv periodic boundary condition. how can I resolve it...sir 

April 5, 2013, 13:10 

#4 
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can show where is the periodic BC on the picture?
Periodicity has some rules to be well defined Anyway your splits around your cylinder are wrong, since it will generate skewed cells.
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April 7, 2013, 05:14 

#5 
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i gave periodic boundary condition for the flat side(opposite to the face having semicircle groove) of the rectangular domain.
sir, here i m supposed to model a film cooling over a falt plate. in actual experimental setup consist of a rectangular duct with a test plate at the base portion of the rectangle, where the test plate contains certain number of holes inclined at 35 deg to the streamwise direction. hot stream of air is fed through the inlet pace of the rectangle while coolant air is blown through inclined holes. for reducing the iteration, i took one half of the coolant hole for modelling... here i m attaching the top view of the test plate of actual experimental setup. that section shown by dotted line is taken in to consideration for the simulation. 

April 8, 2013, 01:48 

#6 
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ok
Then you shouldn't use the symetry, and you have to model the reflected zone. Thus, as I said, periodic BC has some rules: mesh from both periodic surfaces has to be linked, and you should give at least 2 surfaces (not coplanar) in the BC set check this tutorial: http://aerojet.engr.ucdavis.edu/flue.../tg/node26.htm
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April 9, 2013, 05:08 

#7 
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thank you...sir


May 23, 2013, 07:21 

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would you please take a look at my geometry. i don't know to use symmetry BC or periodic for the surfaces which i had labeled in the photo it is a 120 degree model of a wind turbine. 

May 23, 2013, 08:01 

#9 
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periodic: all surfaces which belongs to plane (yz) are supposed to be meshlinked with the surfaces which belongs to 120°rotated (yz)
That means that both sufacegroups have exactly same mesh, which allows you to use periodicity. Now I don't remember how to define the periodic BC: all surfaces as one BC, or each plane as a BC, etc... But I think, you only need one BC
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May 23, 2013, 08:30 

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you mean,after meshing all the volume,i must go to "link face meshes" panel and choose the faces which are going to be linked?? and i don't know to choose what for vertices which are needed in this panel??? 

May 23, 2013, 09:14 

#11 
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no before meshing the volume. Thus you will have to modify the surface mesh.
I confirm you need to set all your periodic surfaces as one periodic BC (in my case the 4 color surfaces) Sans titre.jpg
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May 23, 2013, 16:23 

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i had done it successfully but after using this mesh in fluent and starting itarating i recived this message: Error: divergence detected in AMG solver: pressure correction Error: divergence detected in AMG solver: xmomentum Error: divergence detected in AMG solver why is that? is that related to my mesh??? 

May 24, 2013, 01:13 

#13 
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could be many things
Check all your BC (set up). If you don't see anything, then you may try to set your periodic BC as wall, and iterate (just to see if it comes from periodicity). And off course a check mesh
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May 24, 2013, 04:34 

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because when i used symmetry instead of periodic.i did,t have this problem. but i don't know what i must change about this periodic bcs 

May 24, 2013, 04:52 

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how did you set it?
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May 24, 2013, 05:24 

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May 24, 2013, 05:31 

#17 
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I meant how did you set it in fluent?
http://aerojet.engr.ucdavis.edu/flue...4.htm#Periodic
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May 24, 2013, 05:43 

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May 24, 2013, 06:05 

#19 
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what gives your a check mesh?
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May 24, 2013, 06:18 

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Grid Check
Domain Extents: xcoordinate: min (m) = 1.194447e+005, max (m) = 1.000000e+002 ycoordinate: min (m) = 1.680000e+005, max (m) = 6.120000e+005 zcoordinate: min (m) = 1.200000e+005, max (m) = 6.000000e+004 Volume statistics: minimum volume (m3): 1.474610e+002 maximum volume (m3): 2.305678e+012 total volume (m3): 1.166610e+016 Face area statistics: minimum face area (m2): 5.263843e+000 maximum face area (m2): 3.819772e+008 Checking number of nodes per cell. Checking number of faces per cell. Checking thread pointers. Checking number of cells per face. Checking face cells. Checking bridge faces. Checking righthanded cells. Checking face handedness. Checking face node order. Checking element type consistency. Checking boundary types: Checking face pairs. Checking periodic boundaries. Zone 6: xtranslation: min (m) = 0.000000e+000, max (m) = 1.029000e+005 ytranslation: min (m) = 0.000000e+000, max (m) = 0.000000e+000 ztranslation: min (m) = 1.800000e+005, max (m) = 0.000000e+000 Zone 8: xtranslation: min (m) = 1.029000e+005, max (m) = 0.000000e+000 ytranslation: min (m) = 3.955078e002, max (m) = 3.878906e+000 ztranslation: min (m) = 0.000000e+000, max (m) = 1.800000e+005 Zone 10: xtranslation: min (m) = 1.029000e+005, max (m) = 0.000000e+000 ytranslation: min (m) = 0.000000e+000, max (m) = 0.000000e+000 ztranslation: min (m) = 0.000000e+000, max (m) = 1.800000e+005 Checking node count. Checking nosolve cell count. Checking nosolve face count. Checking face children. Checking cell children. Checking storage. Done. 

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