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IDProjectCategoryView StatusDate SubmittedLast Update
0000179OpenFOAM[All Projects] Bugpublic2011-04-08 14:482014-02-10 13:16
Reporterromant 
Assigned Tohenry 
PrioritynormalSeveritymajorReproducibilityalways
StatusclosedResolutionno change required 
PlatformAMD64OSLinux UbuntuOS Version10.10
Product Version1.7.x 
Target VersionFixed in Version 
Summary0000179: k-omega sst model breaks down with high resolution grid
DescriptionThe k-omega model does break down and does not produce predictions at all if the grid resolution goes up.

Steps To Reproduceincrease the resolution for a k-omega low-Reynolds number simulation, but keep the cell closest to the wall the same. all other cells should not be smaller than the cell closest to the wall.
Additional Informationthe cases in the attached file only need to be run with buoyantBoussinesqSimpleFoam
TagsNo tags attached.
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-  Notes
(0000350)
romant (reporter)
2011-05-05 09:11
edited on: 2011-05-05 09:18

the case files for this can be found under http://www.reactor.sci.kth.se/files/breakdownKOmega.zip [^]

it is a simulation of a heated rod submersed in liquid metal. the crossectional results for k, omega, p_rgh and p can be found in the figures within the zip file. the velocity distribution and temperature distribution are found in radialUdist and radialTempDist within the cases respectively. they can be plotted with any plotting program that supports text file input. the first column is the radial position and the 4 column is the velocity.

case 36 is the original case with 36000 cells,
sens01 with 60000 cells and sens02 with 105000 cells.

when increasing the velocity one can see that the case will not break down. the velocity can be changed in the file, input values. for example setting 1.55 m/s the case will produce reasonable results can converges after about 24000 iterations

(0000351)
henry (manager)
2011-05-05 10:03

Note that the k-omega SST model we provide is in high-Re form and does not include the wall-damping terms often included in the k-omega model for near-wall and low-Re flow. However, you can still use the k-omega SST model for low-Re and near wall flow for a range of resolutions if you use a continuous wall-function (which in OpenFOAM-1.7.x is named nutSpalartAllmarasWallFunction for historical reasons) and this should be used as the wall BC in nut. The BC of k for the continuous wall-function should be kqRWallFunction.

If these changes do not help it may be worth investigating the viscosity averaging in omegaWallFunctionFvPatchScalarField:

        scalar omegaVis = 6.0*nuw[faceI]/(beta1_*sqr(y[faceI]));
        scalar omegaLog = sqrt(k[faceCellI])/(Cmu25*kappa_*y[faceI]);
        omega[faceCellI] = sqrt(sqr(omegaVis) + sqr(omegaLog));

we have found cases for which this causes a sudden change in the viscosity near the wall if the mesh is sufficiently fine and that just using the logarithmic part give more continuous behavior:

        omega[faceCellI] = omegaLog;

- Issue History
Date Modified Username Field Change
2011-04-08 14:48 romant New Issue
2011-05-05 09:11 romant Note Added: 0000350
2011-05-05 09:15 romant Note Edited: 0000350 View Revisions
2011-05-05 09:18 romant Note Edited: 0000350 View Revisions
2011-05-05 10:03 henry Note Added: 0000351
2011-05-23 09:46 andy Status new => closed
2011-05-23 09:46 andy Assigned To => henry
2011-05-23 09:46 andy Resolution open => no change required