Unsteady simple-based sovler and dual time stepping

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 May 17, 2011, 09:26 Unsteady simple-based sovler and dual time stepping #1 New Member   Join Date: Feb 2011 Posts: 20 Rep Power: 8 Hi Foamer! I've been interested in implementing in openFoam the simple algorithm for the simulation of unsteady flows with a dual time stepping method. Before I start coding any stupid thing, I was wondering if: adding a time derivative in the currant simpleFoam solver is enough to make it become unsteady you could refer to me articles that discuss the dts implementation in incompressible solvers It'll be interesting to see how an unsteady simple-based solver behave with respect to pisoFoam. Great thanks! L1011

 May 17, 2011, 09:40 #2 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 ...and pimpleFoam is not good enough because?

 May 17, 2011, 09:48 #3 Senior Member   Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,215 Blog Entries: 1 Rep Power: 17 i guess so, add fvm::ddt(U) to UEqn then compare the result of simpleFoam for cavity with pisoFoam

 May 18, 2011, 11:28 Hi! #4 New Member   Join Date: Feb 2011 Posts: 20 Rep Power: 8 Thanks for your responses! @Niklas: you're right pimpleFoam already provides the implementations I intended to do. But what about the dual time stepping? In fact what I'm trying to do is, for each physical iteration: move/deform a mesh execute sub-iterations until convergence is reached back to 1 and I'm wondering if the correction loops (nNonOrthogonalCorrectors, nOuterCorrectors, nCorrectors) can be considered as sub-iterations in the same meaning of the dual time step method? L1011

May 20, 2011, 11:17
#5
New Member

Join Date: Feb 2011
Posts: 20
Rep Power: 8
Any guesses?

I used pimpleFoam to simulate the flow around a NACA0012 airfoil and the following settings:

Code:
```/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \    /   O peration     | Version:  1.7.1                                 |
|   \  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
version     2.0;
format      ascii;
class       dictionary;
location    "system";
object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
ddtSchemes
{
default         backward;
}
gradSchemes
{
default         Gauss linear;
grad(p)         Gauss linear;
grad(U)         Gauss linear;
}
divSchemes
{
default         none;
div(phi,U)         Gauss limitedLinearV 1;
div(phi,k)         Gauss upwind;
div(phi,omega)         Gauss upwind;
div((nuEff*dev(grad(U).T())))         Gauss linear;
}
laplacianSchemes
{
default         none;
laplacian(nuEff,U)          Gauss linear corrected;
laplacian((1|A(U)),p)          Gauss linear corrected;
laplacian(DkEff,k)          Gauss linear corrected;
laplacian(DomegaEff,omega)          Gauss linear corrected;
}
interpolationSchemes
{
default         linear;
interpolate(U)           linear;
}
snGradSchemes
{
default         corrected;
}
fluxRequired
{
default         no;
p       ;
}

// ************************************************************************* //```
Code:
```/*--------------------------------*- C++ -*----------------------------------*\n| =========                 |                                                 |
| \      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \    /   O peration     | Version:  1.7.1                                 |
|   \  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
version     2.0;
format      ascii;
class       dictionary;
location    "system";
object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver          GAMG;
tolerance       1e-7;
relTol          0;
mergeLevels  1;
smoother  GaussSeidel;
agglomerator faceAreaPair ;
nCellsInCoarsestLevel  100;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration true;
}

pFinal
{
solver          GAMG;
tolerance       1e-7;
relTol          0;
mergeLevels  1;
smoother  GaussSeidel;
agglomerator faceAreaPair ;
nCellsInCoarsestLevel  100;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration true;
}

U
{
solver          smoothSolver;
tolerance       1e-7;
relTol          0;
nSweeps  2;
smoother  GaussSeidel;
}
UFinal
{
solver          smoothSolver;
tolerance       1e-7;
relTol          0;
nSweeps  2;
smoother  GaussSeidel;
}

k
{
solver          smoothSolver;
smoother GaussSeidel ;
nSweeps 1 ;
tolerance        1e-7;
relTol           0;
}

omega
{
solver          smoothSolver;
smoother GaussSeidel ;
nSweeps 1 ;
tolerance        1e-7;
relTol           0;
};

}
PIMPLE
{
nNonOrthogonalCorrectors 4;
pRefValue 1;
pRefCell 0;
nOuterCorrectors 10;
nCorrectors     2;
};
relaxationFactors
{
default                  1;
p                  0.5;
U                  0.5;
k                  0.5;
omega                  0.5;
};

}

// ************************************************************************* //```
However,I made two strange observations:

1) Even-tough the aerodynamic coefficients get in absolute close to zero, they change significantly from one iteration to the other (see attached file).

2) The velocity field converges from the first outer iteration while the pressure needs couple iteration to get physical.

Do anyone has already experienced something similar?

Thanks in advance!

L1011
Attached Images
 Screenshot-5.png (29.1 KB, 39 views)

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

All times are GMT -4. The time now is 14:43.

 Contact Us - CFD Online - Top