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November 10, 2015, 06:10 
Issue symmetryPlane 2.5d extruded airfoil simulation

#1 
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Oktanwurst
Join Date: Jan 2015
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Hi,
I am simulating an in the third dimension extuded airfoil (2.5d) with Openfoam/SimpleFoam with kwSST turbulence model. Mesh has Otype 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 

November 22, 2015, 08:04 

#2 
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Bruno Santos
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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? Code:
patchSummary constant expand
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November 23, 2015, 07:02 

#3 
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Oktanwurst
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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.
Code:
/**\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 2.4.0   \\ / A nd  Web: http://www.OpenFOAM.org   \\/ M anipulation   \**/ Build : 2.4.0f0842aea0e77 Exec : patchSummary constant expand Date : Nov 23 2015 Time : 11:55:26 Host : "cengferVirtualBox" PID : 22726 Case : /home/cengfer/OpenFOAM/cengfer2.4.0/run/VGs/AA_400_F1_LM_VG/kwSST/AoA_7_nowallfunction nProcs : 1 sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring runtime modified files using timeStampMaster allowSystemOperations : Allowing usersupplied 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 Last edited by wyldckat; November 23, 2015 at 16:57. Reason: Added [CODE][/CODE] markers 

November 23, 2015, 17:08 

#4 
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Bruno Santos
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Hi Chris,
OK, I believe I've spotted at least one possible problem: Code:
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 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? Code:
checkMesh constant allGeometry allTopology Best regards, Bruno Last edited by wyldckat; November 23, 2015 at 17:10. Reason: see "edit:" 

November 27, 2015, 05:56 

#5 
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Oktanwurst
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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 postprocessor where you generate cutplanes at distinct xpositions. 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 Code:
Build : 2.4.0f0842aea0e77 Exec : checkMesh constant allGeometry allTopology Date : Nov 27 2015 Time : 10:17:35 Host : "cengferVirtualBox" PID : 2817 Case : /home/cengfer/OpenFOAM/cengfer2.4.0/run/VGs/AA_400_F1_LM_VG/kwSST/AoA_7_nowallfunction nProcs : 1 sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring runtime modified files using timeStampMaster allowSystemOperations : Allowing usersupplied 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 zipup check OK. Faceface 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 (nonclosed singly connected) (24.6549 24.9432 0) (25.5972 24.9996 0) VG 700 717 ok (nonclosed singly connected) (0.298476 0.186533 0.0117857) (0.321296 0.198511 0.0166014) front 97552 98280 ok (nonclosed singly connected) (24.6549 24.9432 0.0275) (25.5972 24.9996 0.0275) inlet 24426 24900 ok (nonclosed singly connected) (24.6549 24.9432 0) (0.53812 24.9996 0.0275) outlet 18526 18900 ok (nonclosed singly connected) (0.393772 24.9432 0) (25.5972 24.9996 0.0275) walls 42924 43667 ok (nonclosed singly connected) (7.25798e17 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 (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (3.75536e19 2.70399e19 6.6596e15) 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 = 1.34541e09. Maximum face area = 0.876489. Face area magnitudes OK. Min volume = 3.13842e13. Max volume = 0.000498503. Total volume = 54.2262. Cell volumes OK. Mesh nonorthogonality Max: 82.2557 average: 3.22483 *Number of severely nonorthogonal (> 70 degrees) faces: 120. Nonorthogonality check OK. <<Writing 120 nonorthogonal 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 = 7.49328e06 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: 5.94959e12 average: 0.453186 ***Cells with small determinant (< 0.001) found, number of cells: 2206620 <<Writing 2206620 underdetermined 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 Last edited by wyldckat; November 28, 2015 at 13:59. Reason: Added [CODE][/CODE] markers 

November 28, 2015, 14:09 

#6 
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Bruno Santos
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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, nonorthogonality 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 

Tags 
airfoil 3d, simplefoam, symmetryplane, wall boundary condition 
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