| JEBland |
June 9, 2022 18:34 |
Stabilizing simpleFoam for Pressure-Driven Flows
3 Attachment(s)
I'm attempting to get a square channel toy model working for pressure-driven laminar flow using simpleFoam, and the pressure is quite wild for the first few hundred iterations. The pressure is initialized to (approximately) the average pressure of the inlet & outlet. Is there an efficient way to limit the initial iterations to encourage stability in pressure-driven simulations?
I understand that there might be "shocks" in the flow when setting up pressure based BCs, but I would expect that for an initially still fluid with the interior pressure set to the average pressure of the boundaries, that the peak & min pressures should also be approximately bounded by inlet and outlet pressures - instead the peak min/max values of the pressure at orders of magnitude larger than the final resulting values, even with the relaxation factors set to 0.1 for p and U.
Explicit limitation of p doesn't seem to be respected by simpleFoam, either.
While the pressure-driven BCs are on the list of the -listScalarBCs and -listVectorBCs for potentialFoam, my attempts to initialize with potentialFoam were fruitless. Apparently this isn't new, but to my knowledge, pressure driven flow has not been incorportated into potentialFoam ( https://bugs.openfoam.org/view.php?id=1845).
I don't mind that it can take a while to converge in simpleFoam, but it's frustrating that even with the relaxation set to 0.1 that there are still domains moving through and not being smoothed by the solver.
A couple of shallow attempts to bound the solver settings in fvSchemes didn't seem to do much, either.
https://www.openfoam.com/documentati...erical-schemes
https://cfd.direct/openfoam/user-guide/v6-fvSchemes/
Attached are a couple sample images, which represent some of the unstable initial behavior where the inlet has a pressure of 7.3 m^2/S^2 and the outlet has a pressure of 0.52 m^2/s^2. I'm using the totalPressure boundary condition for the pressure and the pressureInletOutlet - from the guide, this combination should have "very good" stability.
p:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -2 0 0 0 0];
internalField uniform 3.9 ;
boundaryField
{
Leg1InOut // inlet
{
type totalPressure;
p0 uniform 7.3;
value 7.3;
}
Leg2InOut // outlet
{
type totalPressure;
p0 uniform 0.52;
value 0.52;
}
walls
{
type fixedFluxPressure;
value 0;
gradient 0;
}
}
U:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0 0 0);
boundaryField
{
Leg1InOut
{
type pressureInletUniformVelocity;
value uniform (0 0 0);
}
Leg2InOut
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
walls
{
type noSlip; // zeroGradient;
}
}
blockMeshDict:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
length 1.0;
width 0.1;
height 0.1;
xMin #calc "-0.5 * $length";
xMax #calc " 0.5 * $length";
yMin #calc "-0.5 * $height";
yMax #calc " 0.5 * $height";
zMin #calc "-0.5 * $width";
zMax #calc " 0.5 * $width";
vertices
(
//
// Leg1
// |
// |
// Leg2
//
//
( $xMin $yMin $zMin) // 0
( $xMax $yMin $zMin) // 1
( $xMax $yMax $zMin) // 2
( $xMin $yMax $zMin) // 3
( $xMin $yMin $zMax) // 4
( $xMax $yMin $zMax) // 5
( $xMax $yMax $zMax) // 6
( $xMin $yMax $zMax) // 7
//
);
blocks
(
//
hex (0 1 2 3 4 5 6 7) (100 10 10) simpleGrading (1 1 1) // Leg1 - Leg2
//
);
edges
(
);
boundary
(
Leg1InOut
{
type patch;
faces
(
(0 4 7 3) // nX
);
}
Leg2InOut
{
type patch;
faces
(
(2 6 5 1) // pX
);
}
walls
{
type wall;
faces
(
(2 3 6 7) // pY
(0 1 5 4) // nY bottom
(1 0 3 2) // nZ
(4 5 6 7) // pZ
);
}
);
// ************************************************************************* //
controlDict:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
application simpleFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 10000;
deltaT 1;
writeControl timeStep;
writeInterval 10;
purgeWrite 0;
writeFormat binary; // ascii;
writePrecision 6;
writeCompression off;
timeFormat general;
timePrecision 6;
runTimeModifiable true;
functions
{
#includeFunc flowRatePatchpatches
(
Leg1InOut
Leg2InOut
);
}
// ************************************************************************* //
fvSolution:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
solvers
{
p
{
solver GAMG;
tolerance 1e-7;
relTol 0.01;
smoother DICGaussSeidel;
}
U
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-05;
relTol 0;
}
"(p|U)Final"
{
relTol 0;
}
}
SIMPLE
{
momentumPredictor no;
nNonOrthogonalCorrectors 0;
consistent no;
residualControl
{
p 1e-4; // 4
U 1e-5; // 5
}
}
relaxationFactors
{
fields
{
p 0.1;
}
equations
{
U 0.1;
}
}
// ************************************************************************* //
fvSchemes:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
ddtSchemes
{
default steadyState;
}
gradSchemes
{
default Gauss linear;
}
divSchemes
{
default none;
div(phi,U) bounded Gauss upwind;
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default Gauss linear corrected;
// default Gauss linear limited corrected 0.4; // Doesn't do much?
}
interpolationSchemes
{
default linear;
}
snGradSchemes
{
default corrected;
}
// ************************************************************************* //
Any assistance would be appreciated. |
