singularity?

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April 21, 2012, 20:25
singularity?
#1
Senior Member

Mihai Pruna
Join Date: Apr 2010
Location: Boston
Posts: 190
Blog Entries: 1
Rep Power: 7
I am trying to model a simple pipe with total pressure at inlet and fixed 0 pressure at outlet. Tried various things, last one being a filleting of the edges.
Please see images. Flat face facing you is inlet,curved faces are wall and there is symmetry on the Z=0 plane.
I pasted the BCs,o refer to this post:
internal flow BCs: pressure driven versus velocity driven
I am attaching screenshots. I already tried smaller relaxation factors. still got huge values.

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
location "0";
object nut;
}
dimensions [0 2 -1 0 0 0 0];
internalField uniform 0;
boundaryField
{
rightZmax
{
type freestream;
freestreamValue uniform 0;
}
leftZmin
{
type symmetryPlane;
}
inletXmin
{
type freestream;
freestreamValue uniform 0;
}
outletXmax
{
type calculated;
value uniform 0;
}
topYmax
{
type freestream;
freestreamValue uniform 0;
}
bottomYmin
{
type freestream;
freestreamValue uniform 0;
}
Sductface1
{
type nutkWallFunction;
value uniform 0;
}
Sductface2
{
type nutkWallFunction;
value uniform 0;
}
SDuctInlet
{
type calculated;
value uniform 0;
}
SDuctOutlet
{
type calculated;
value uniform 0;
}
Sductface5
{
type nutkWallFunction;
value uniform 0;
}
Sductface6
{
type nutkWallFunction;
value uniform 0;
}
Sductface7
{
type nutkWallFunction;
value uniform 0;
}
Sductface8
{
type nutkWallFunction;
value uniform 0;
}
}

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object k;
}
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0.240000;
boundaryField
{
outletXmax
{
type inletOutlet;
inletValue \$internalField;
value \$internalField;
}
inletXmin
{
type freestream;
freestreamValue uniform 0.240000;
}
bottomYmin
{
type freestream;
freestreamValue uniform 0.240000;
}
topYmax
{
type freestream;
freestreamValue uniform 0.240000;
}
leftZmin
{
type symmetryPlane;
}
rightZmax
{
type freestream;
freestreamValue uniform 0.240000;
}
Sductface1
{
type kqRWallFunction;
value \$internalField;
}
Sductface2
{
type kqRWallFunction;
value \$internalField;
}
SDuctInlet
{
type fixedValue;
value uniform 0.240000;
}
SDuctOutlet
{
}
Sductface5
{
type kqRWallFunction;
value \$internalField;
}
Sductface6
{
type kqRWallFunction;
value \$internalField;
}
Sductface7
{
type kqRWallFunction;
value \$internalField;
}
Sductface8
{
type kqRWallFunction;
value \$internalField;
}
}

FoamFile
{
version 2.0;
format ascii;
class volVectorField;
location "0";
object U;
}
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0.000000 0.000000 0.000000);
boundaryField
{
inletXmin
{
type freestream;
freestreamValue uniform (0.000000 0.000000 0.000000);
}
outletXmax
{
type inletOutlet;
inletValue \$internalField;
value \$internalField;
}
bottomYmin
{
type freestream;
freestreamValue uniform (0.000000 0.000000 0.000000);
}
topYmax
{
type freestream;
freestreamValue uniform (0.000000 0.000000 0.000000);
}
rightZmax
{
type freestream;
freestreamValue uniform (0.000000 0.000000 0.000000);
}
leftZmin
{
type symmetryPlane;
}
Sductface1
{
type fixedValue;
value uniform (0 0 0);
}
Sductface2
{
type fixedValue;
value uniform (0 0 0);
}
SDuctInlet
{
}
SDuctOutlet
{
}
Sductface5
{
type fixedValue;
value uniform (0 0 0);
}
Sductface6
{
type fixedValue;
value uniform (0 0 0);
}
Sductface7
{
type fixedValue;
value uniform (0 0 0);
}
Sductface8
{
type fixedValue;
value uniform (0 0 0);
}
}

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object omega;
}
dimensions [0 0 -1 0 0 0 0];
internalField uniform 1.780000;
boundaryField
{
inletXmin
{
type freestream;
freestreamValue uniform 1.780000;
}
outletXmax
{
type inletOutlet;
inletValue \$internalField;
value \$internalField;
}
bottomYmin
{
type freestream;
freestreamValue uniform 1.780000;
}
topYmax
{
type freestream;
freestreamValue uniform 1.780000;
}
leftZmin
{
type symmetryPlane;
}
rightZmax
{
type freestream;
freestreamValue uniform 1.780000;
}
Sductface1
{
type omegaWallFunction;
value \$internalField;
}
Sductface2
{
type omegaWallFunction;
value \$internalField;
}
SDuctInlet
{
type fixedValue;
value uniform 1.780000;
}
SDuctOutlet
{
}
Sductface5
{
type omegaWallFunction;
value \$internalField;
}
Sductface6
{
type omegaWallFunction;
value \$internalField;
}
Sductface7
{
type omegaWallFunction;
value \$internalField;
}
Sductface8
{
type omegaWallFunction;
value \$internalField;
}
}

FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0.000000;
boundaryField
{
inletXmin
{
type freestreamPressure;
freestreamValue 0.000000;
}
outletXmax
{
type fixedValue;
value \$internalField;
}
bottomYmin
{
type freestreamPressure;
freestreamValue 0.000000;
}
topYmax
{
type freestreamPressure;
freestreamValue 0.000000;
}
leftZmin
{
type symmetryPlane;
}
rightZmax
{
type freestreamPressure;
freestreamValue 0.000000;
}
Sductface1
{
}
Sductface2
{
}
SDuctInlet
{
type totalPressure;
gamma 1.4;
p0 uniform 100000.000000;
}
SDuctOutlet
{
type fixedValue;
value uniform 0.000000;
}
Sductface5
{
}
Sductface6
{
}
Sductface7
{
}
Sductface8
{
}
}

FoamFile
{
version 2.0;
format ascii;
class dictionary;
object fvSolution;
}
solvers
{
p
{
solver GAMG;
tolerance 1e-7;
relTol 0.1;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
}
U
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}
k
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}
omega
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}
}
SIMPLE
{
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;
residualControl
{
p 1e-5;
U 1e-5;
k 1e-5;
omega 1e-5;
}
}
potentialFlow
{
nNonOrthogonalCorrectors 10;
pRefCell 0;
pRefValue 0;
}
relaxationFactors
{
p 0.3;
U 0.7;
k 0.7;
omega 0.7;
}
cache
{
}
Attached Images
 sductissue.png (37.0 KB, 18 views) sductissuedgese.png (46.9 KB, 19 views)
__________________
Mihai Pruna's Bio

 April 22, 2012, 02:34 #2 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,895 Rep Power: 26 At a first sight, there could be something wrong in a group of cells (the red area). What discretization schemes are you using? If you have problematic cells, turn limiters on to see if the situation improves. __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

 April 23, 2012, 14:17 #3 Senior Member   Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 190 Blog Entries: 1 Rep Power: 7 well, this is what i have in my fv schemes, copied from the motorbike tutorial. will this work for internal flows as well? My solution seems to blow up only when I try to specify inlet pressure. FoamFile { version 2.0; format ascii; class dictionary; object fvSchemes; } ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) Gauss linearUpwindV grad(U); div(phi,k) Gauss upwind; div(phi,omega) Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; } __________________ Mihai Pruna's Bio

 April 23, 2012, 15:49 #4 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,895 Rep Power: 26 Yes, but it might help to put a limiter on the gradients too: Code: ```gradSchemes { default cellLimited Gauss linear 1; }``` Also, check your mesh to see if there are very skewed cells (checkMesh will tell you). __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as live DVD/USB, hard drive image and virtual image. OpenQBMM - An open-source implementation of quadrature-based moment methods

 April 23, 2012, 16:36 #5 Senior Member   Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 190 Blog Entries: 1 Rep Power: 7 Thanks for the suggestions. checkmesh returned all clear. hmm, my numbers are too big too....been focused on the numerics didn't bother to check Bernoulli. 100000 deltap/rho gives supersonic velocity...and I was using simpleFoam....gonna try with 10000 instead. __________________ Mihai Pruna's Bio

 April 24, 2012, 17:18 #6 Senior Member   Mihai Pruna Join Date: Apr 2010 Location: Boston Posts: 190 Blog Entries: 1 Rep Power: 7 thanks Alberto, the cell limiter helped prevent the values from attaining huge values. However, I discovered another issue with my patches, which I fixed and I am hoping the simulation will run properly without limiters. __________________ Mihai Pruna's Bio

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