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April 17, 2014, 09:00 
wss validation

#1 
Senior Member
Ali reza
Join Date: Mar 2014
Posts: 103
Rep Power: 4 
hi
I am trying to find wall shear stress contours in a 3d pipe with openfoam .simulation information are laminar,unsteady,newtonian fluid.I am using icofoam solver . openfoam Y velocity quantities are almost the same as the right answers but wall shear stress quantities are completely wrong in the other word the right answers are given from 0.4 to 7 but mine are between [1.61669e06,1.61669e05] I used these codes please help me to find the solution. in 0 file ,wallShearStress folder Code:
dimensions [0 2 2 0 0 0 0]; internalField uniform (0 0 0); boundaryField { body { type calculated; value uniform (0 0 0); } inlet { type calculated; value uniform (0 0 0); } outlet { type calculated; value uniform (0 0 0); } } Code:
RASModel laminar; turbulence on; printCoeffs on; Code:
simulationType RASModel; 

April 17, 2014, 09:15 

#2 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 585
Rep Power: 20 
Ali,
CFD can be tricky for even seemingly trivial tasks. There are numerous settings and requirements that influence the answer since, after all you are modeling a real system with discretized equations and discrete time and space. With that said:
There are many possibilities for "why", but without more information this is as good as I can get. Have a look at http://www.cfdonline.com/Forums/ope...gethelp.html and people always love pictures. Good Luck! 

April 17, 2014, 10:12 

#3 
Senior Member
Ali reza
Join Date: Mar 2014
Posts: 103
Rep Power: 4 
thanks for your attention
I have attached the mesh . About transport properties I should mention that I put nu quantity equal to result of nu = mu/rho.This is checkMesh result: Code:
Create polyMesh for time = 0 Time = 0 Mesh stats points: 302592 faces: 885385 internal faces: 864251 cells: 291606 faces per cell: 6 boundary patches: 3 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 291606 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. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology body 19650 19700 ok (nonclosed singly connected) inlet 742 768 ok (nonclosed singly connected) outlet 742 768 ok (nonclosed singly connected) Checking geometry... Overall domain bounding box (14.2294 0 15.1572) (12.9588 47.2016 2.2) Mesh (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (3.50243e16 1.50181e16 6.31521e18) OK. Max cell openness = 3.22113e16 OK. Max aspect ratio = 9.66007 OK. Minimum face area = 0.000865714. Maximum face area = 0.0893054. Face area magnitudes OK. Min volume = 0.000258464. Max volume = 0.0187293. Total volume = 1091.82. Cell volumes OK. Mesh nonorthogonality Max: 24.5048 average: 5.06496 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.361871 OK. Coupled point location match (average 0) OK. Mesh OK. End Code:
application icoFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 4.8; deltaT 0.001; writeControl timeStep; writeInterval 20; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; libs ( "libOpenFOAM.so" "libgroovyBC.so" ) ; Code:
ddtSchemes { default Euler; } gradSchemes { default Gauss linear; grad(p) Gauss linear; } divSchemes { default none; div(phi,U) Gauss linear; } laplacianSchemes { default none; laplacian(nu,U) Gauss linear orthogonal; laplacian((1A(U)),p) Gauss linear orthogonal; } interpolationSchemes { default linear; interpolate(HbyA) linear; } snGradSchemes { default orthogonal; } fluxRequired { default no; p ; } Code:
solvers { p { solver PCG; preconditioner DIC; tolerance 1e06; relTol 0; } U { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } } PISO { nCorrectors 1; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; } 

April 17, 2014, 11:10 

#4 
Member
Eric Robertson
Join Date: Jul 2012
Posts: 95
Rep Power: 6 
Which data set are you comparing against?


April 17, 2014, 11:32 

#5 
Senior Member
Ali reza
Join Date: Mar 2014
Posts: 103
Rep Power: 4 
wall shear stress quantities


April 18, 2014, 10:32 

#6 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 585
Rep Power: 20 
Since i have no idea what your Re or Co number are I will start to make some more suggestions based on what you have given. Your mesh is not completely orthogonal (is this a Gambit mesh?) so you should change your Laplacian Schemes to
Code:
laplacianSchemes { default none; laplacian(nu,U) Gauss linear corrected; laplacian((1A(U)),p) Gauss linear corrected; } Code:
snGradSchemes { default corrected; } 

April 19, 2014, 16:09 

#7 
Senior Member
Ali reza
Join Date: Mar 2014
Posts: 103
Rep Power: 4 
thanks alot
I have changed what ever you mentioned but I found that I have not scaled the geometry and my dimensions are in meter but I need them to be in millimeter so I scaled them ,I have checked the solution in fluent with this scaled geometry with steady state boundary conditions it shows the right wall shear stress but as soon as I want to run it in openFoam with an unsteady boundary conditions it was diverged ,I post it here ,If it is possible take a look and help. PHP Code:
thank you 

April 21, 2014, 10:19 

#8 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 585
Rep Power: 20 
Run your case again and attach the text file of the output to this post if it is small. You can attach txt files....so use the command
Code:
icoFoam >log.icoFoam.txt 2>&1 Code:
what information is necessary to reproduce this issue? 

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