[281419]

Hi,

I am simulating an in the third dimension extuded airfoil (2.5d) with Openfoam/SimpleFoam with kwSST turbulence model. Mesh has O-type grid topology with BC symmetryPlane for the front and back disk for U, p, k, omega and nut. Simulation runs quite well, but at the junction of the symmetryPlane with the airfoil wall, I see quite strange behaviour of the velocity (see pictures). Although U velocity on the symmetryPlane looks ok, on the slices it seems that symmetryPlane behaves like a wall...
Any ideas what might be the reasons for this and how I can fix this problem?

Thanks for your support,
Chris
Slide1.JPG

Slide2.JPG

Slide3.JPG

[wyldckat]

Quick question: Which OpenFOAM version are you using? Because this feels like a problem related to the wall treatment using values from the neighbouring patch.

In addition, what does this command give you?

patchSummary -constant -expand

[281419]

Thank you Bruno for your reply on this topic. I am using OF versión 2.4.0. Please find below the output of patchSummary -constant -expand. The patch "Walls" stands for the airfoil surface.

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.4.0 |
| \\ / A nd | Web: http://www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 2.4.0-f0842aea0e77
Exec : patchSummary -constant -expand
Date : Nov 23 2015
Time : 11:55:26
Host : "cengfer-VirtualBox"
PID : 22726
Case : /home/cengfer/OpenFOAM/cengfer-2.4.0/run/VGs/AA_400_F1_LM_VG/kwSST/AoA_7_nowallfunction
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time
Create mesh for time = constant
Time = constant
Valid fields:
symmetryPlane : Back
wall : VG
symmetryPlane : front
patch : inlet
patch : outlet
wall : walls
Time = 0
Valid fields:
volScalarField nut
volVectorField U
volScalarField k
volScalarField p
volScalarField omega
symmetryPlane : Back
scalar nut symmetryPlane
scalar k symmetryPlane
scalar p symmetryPlane
scalar omega symmetryPlane
vector U symmetryPlane
wall : VG
scalar nut fixedValue
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U fixedValue
symmetryPlane : front
scalar nut symmetryPlane
scalar k symmetryPlane
scalar p symmetryPlane
scalar omega symmetryPlane
vector U symmetryPlane
patch : inlet
scalar nut calculated
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U freestream
patch : outlet
scalar nut calculated
scalar k inletOutlet
scalar p fixedValue
scalar omega inletOutlet
vector U freestream
wall : walls
scalar nut fixedValue
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U fixedValue
Time = 2500
Valid fields:
volScalarField nut
volVectorField U
volScalarField k
volScalarField p
volScalarField omega
symmetryPlane : Back
scalar nut symmetryPlane
scalar k symmetryPlane
scalar p symmetryPlane
scalar omega symmetryPlane
vector U symmetryPlane
wall : VG
scalar nut fixedValue
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U fixedValue
symmetryPlane : front
scalar nut symmetryPlane
scalar k symmetryPlane
scalar p symmetryPlane
scalar omega symmetryPlane
vector U symmetryPlane
patch : inlet
scalar nut calculated
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U freestream
patch : outlet
scalar nut calculated
scalar k inletOutlet
scalar p fixedValue
scalar omega inletOutlet
vector U freestream
wall : walls
scalar nut fixedValue
scalar k fixedValue
scalar p zeroGradient
scalar omega fixedValue
vector U fixedValue
End

[wyldckat]

Hi Chris,

OK, I believe I've spotted at least one possible problem:

wall : VG
  scalar nut fixedValue
  scalar k fixedValue
  scalar p zeroGradient
  scalar omega fixedValue
  vector U fixedValue
wall : walls
  scalar nut fixedValue
  scalar k fixedValue
  scalar p zeroGradient
  scalar omega fixedValue
  vector U fixedValue

You aren't using wall treatment functions for "nut", "k" and "omega". This may or may not be the problem...

The other thing I only noticed just now is a very strange detail that is visible in the image "Slide2.JPG" you attached in the first post... Why does it look like the symmetry plane seems to have been made with a mesh different from the one used for the mesh on the smaller plane?

edit: By the way, what does this command give you?

checkMesh -constant -allGeometry -allTopology

And what post-processing application are you using?

Best regards,
Bruno

[281419]

Hi Bruno, thanks for your reply and your comments.
Ok, I will run a new simulation imposing WallFunctions for the turbulence parameters to see if this solves the problem. To properly simulate the effect of VGs I thought it might be better to work without wallFunctions (having a mesh with y+ of about 1)
I use Tecplot as a post-processor where you generate cut-planes at distinct x-positions. Thus this should be just a graphical issue. The mesh is ok in this zone. Please find below as well the output of the checkMesh command.
Thank you for your support and best regards

Build : 2.4.0-f0842aea0e77
Exec : checkMesh -constant -allGeometry -allTopology
Date : Nov 27 2015
Time : 10:17:35
Host : "cengfer-VirtualBox"
PID : 2817
Case : /home/cengfer/OpenFOAM/cengfer-2.4.0/run/VGs/AA_400_F1_LM_VG/kwSST/AoA_7_nowallfunction
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time
Create polyMesh for time = constant
Enabling all (cell, face, edge, point) topology checks.
Enabling all geometry checks.
Time = constant
Mesh stats
points: 5896527
faces: 17405780
internal faces: 17124100
cells: 5754980
faces per cell: 6
boundary patches: 6
point zones: 0
face zones: 0
cell zones: 0
Overall number of cells of each type:
hexahedra: 5754980
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 0
Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Topological cell zip-up check OK.
Face-face connectivity OK.
Number of regions: 1 (OK).
Checking patch topology for multiply connected surfaces...
Patch Faces Points Surface topology Bounding box
Back 97552 98280 ok (non-closed singly connected) (-24.6549 -24.9432 0) (25.5972 24.9996 0)
VG 700 717 ok (non-closed singly connected) (0.298476 0.186533 0.0117857) (0.321296 0.198511 0.0166014)
front 97552 98280 ok (non-closed singly connected) (-24.6549 -24.9432 0.0275) (25.5972 24.9996 0.0275)
inlet 24426 24900 ok (non-closed singly connected) (-24.6549 -24.9432 0) (0.53812 24.9996 0.0275)
outlet 18526 18900 ok (non-closed singly connected) (0.393772 -24.9432 0) (25.5972 24.9996 0.0275)
walls 42924 43667 ok (non-closed singly connected) (-7.25798e-17 -0.211739 0) (1 0.187696 0.0275)
Checking geometry...
Overall domain bounding box (-24.6549 -24.9432 0) (25.5972 24.9996 0.0275)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (3.75536e-19 2.70399e-19 -6.6596e-15) OK.
***High aspect ratio cells found, Max aspect ratio: 7341.95, number of cells 145620
<<Writing 145620 cells with high aspect ratio to set highAspectRatioCells
Minimum face area = 1.34541e-09. Maximum face area = 0.876489. Face area magnitudes OK.
Min volume = 3.13842e-13. Max volume = 0.000498503. Total volume = 54.2262. Cell volumes OK.
Mesh non-orthogonality Max: 82.2557 average: 3.22483
*Number of severely non-orthogonal (> 70 degrees) faces: 120.
Non-orthogonality check OK.
<<Writing 120 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 3.39478 OK.
Coupled point location match (average 0) OK.
Face tets OK.
*Edges too small, min/max edge length = 7.49328e-06 2.23598, number too small: 1016422
<<Writing 1016422 points on short edges to set shortEdges
All angles in faces OK.
Face flatness (1 = flat, 0 = butterfly) : min = 0.96569 average = 1
All face flatness OK.
Cell determinant (wellposedness) : minimum: 5.94959e-12 average: 0.453186
***Cells with small determinant (< 0.001) found, number of cells: 2206620
<<Writing 2206620 under-determined cells to set underdeterminedCells
Concave cell check OK.
Face interpolation weight : minimum: 0.0200078 average: 0.488228
***Faces with small interpolation weight (< 0.05) found, number of faces: 2014
<<Writing 2014 faces with low interpolation weights to set lowWeightFaces
Face volume ratio : minimum: 0.0202955 average: 0.94853
Face volume ratio check OK.
Failed 3 mesh checks.
End

[wyldckat]

Hi Chris,

Wow, this mesh is pushing the limits of the advisable mesh characteristics!
Highly skewed faces, very small volumes in comparison to the largest cells, non-orthogonality issues in some faces... I know that simulations with airfoils can work very well with these mesh characteristics, but I don't know what are the limitations on what OpenFOAM's solvers can handle with meshes.

Now I'm wondering if there is a problem with the rendering of the mesh in Tecplot, perhaps there is a problem in sampling the fields in those section cuts as well?
If it was in ParaView, this problem could easily occur if you didn't load both the internal mesh and the surface mesh fields, because the point data field (the values at the vertexes of the cells) for the internal field isn't always complete, namely near the boundaries.

Best regards,
Bruno