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[GAMBIT] Periodic BC

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Old   May 31, 2011, 03:30
Default Periodic BC
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Hello,

I have a problem which might be easily fixed with your help. I have created a 3d mesh for an airfoil, which is basically 2d with translation by .2m along z-axis, i.e. it has two identical x-y meshes one at z=0 and another at z=.2 that are periodically linked along z-direction (see figure). I have set boundary types as necessary in Gambit with no errors, but when I check the mesh in fluent I get the following message:

Periodic zone 3: x-translation: min (m) = -1.112668e+000, max (m) = 1.200599e+000
y-translation: min (m) = -1.276517e+000, max (m) = 1.132584e+000
z-translation: min (m) = 2.000000e-001, max (m) = 2.000000e-001
Done.

WARNING: Mesh check failed.

So there appear some strange translations in x and y-directions, which should be zero. When I ignore this warning and start solution in fluent I get meaningless result.

I will be grateful if someone could help me. I feel that it is something elementary.

Truffaldino
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Old   May 31, 2011, 07:17
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In gambit, define your 2 periodic surfaces as wall.
Re-export, and load your mesh in Fluent.
If the check Mesh is succesfull, then you problem lies on periodic surfaces
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Old   May 31, 2011, 18:50
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Quote:
Originally Posted by -mAx- View Post
In gambit, define your 2 periodic surfaces as wall.
Re-export, and load your mesh in Fluent.
If the check Mesh is succesfull, then you problem lies on periodic surfaces
Thanks mAx,

I did as you said and check is successfull with walls. Now I am trying to find what is wrong on periodic surfaces, but everything seems to be fine.

During the check wth periodic BC fluent also gives the following message

Reading "C:\Fluent12\wing.msh"...
194095 nodes.
15289 mixed shadow faces, zone 2.
15289 mixed periodic faces, zone 3.
15289 shadow face pairs.
17178 triangular shadow faces, zone 4.
17178 triangular periodic faces, zone 5.
17178 shadow face pairs.
2350 quadrilateral wall faces, zone 6.
1110 quadrilateral velocity-inlet faces, zone 7.
250 quadrilateral pressure-outlet faces, zone 8.
789613 mixed interior faces, zone 10.
324670 mixed cells, zone 1.

which shows some "shadow faces". What are those?

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Old   June 1, 2011, 00:50
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you can select them and display them in Fluent.
You will see where they are
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Old   June 5, 2011, 06:39
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Thanks mAx,

Unfortunately fluent does not show those side faces.

I have decided to try to try with much simpler mesh, simple periodic cube: Check mesh failed in fluent even for this primitive example. There is no single error or warning in gambit, but in fluent it shows non-existent translations in x,y-directions.

I will be grateful if someone could point me on my error.

Below I write down simple journal code for this test cube meshing (see image attached):

/---------------------------------/

reset

$version="FLUENT 5/6"

$mesh_output_file="C:\\Fluent12\\periodic.msh"


$L=1

$H=1

$z=1

$q_bl=1.2

$n_bl=5

$n=10

$n1=5

$nh=11

$nz=3

$dh_bl=.01


/************************************************** **************************************************/

solver select $version

/create side (x,y)-face "P"

vertex create "A" coordinates 0 0 0
vertex create "B" coordinates $L 0 0
vertex create "A1" coordinates 0 $H 0
vertex create "B1" coordinates $L $H 0

edge create "A_A1" straight "A" "A1"
edge create "B_B1" straight "B" "B1"
edge create "A_B" straight "A" "B"
edge create "A1_B1" straight "A1" "B1"

face create "P" wireframe "A_A1" "B_B1" "A_B" "A1_B1"

/--- Meshing this side (future periodic) face

edge mesh "A_B" successive ratio1 1 intervals $n
edge mesh "A1_B1" successive ratio1 1 intervals $n1

blayer create "bl" first $dh_bl growth $q_bl rows $n_bl wedge uniform
blayer attach "bl" face "P" edge "A_B"

edge mesh "A_A1" "B_B1" successive ratio1 1 intervals $nh

face mesh "P" triangle

/--- Creating volume by translating side (x,y)-face in z-directiobn

volume create "V" translate "P" vector 0 0 $z

/--- Wall (bottom) face

face modify "face.2" label "W"

/--- Inlet faces

face modify "face.3" label "Il"
face modify "face.5" label "It"

/--- Outlet face

face modify "face.4" label "O"

/-- Second periodic face

face modify "face.6" label "Pz"

/edges and vertex for periodic linking

vertex modify "vertex.5" label "Az"

edge modify "edge.5" label "A Az"

edge modify "edge.9" label "Az_Bz"
edge modify "edge.10" label "Az_A1z"

/--- Linking periodic faces

face link "P" "Pz" edges "A_A1" "Az_Bz" vertices "A" "Az" reverse periodic

/--- Meshing one edge in z-direction

edge mesh "A Az" successive ratio1 1 intervals $nz


/--- Creating groups and BC

group create "Periodic" face "P" "Pz"

group create "Wall" face "W"

group create "Inlet" face "Il" "It"

group create "Outlet" face "O"

physics create "periodic" btype "PERIODIC" group "Periodic"

physics create "wall" btype "WALL" group "Wall"

physics create "inlet" btype "VELOCITY_INLET" group "Inlet"

physics create "outlet" btype "PRESSURE_OUTLET" group "Outlet"

/--- Final meshing

volume mesh "V" cooper

/--- Saving mesh into file

export uns $mesh_output_file
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