[preichl]

Hi All,

I am new to OpenFoam and I am having a few issues getting a converged solution for laminar flow through a circular pipe (simplest problem I could think of to start with). I am using simpleFoam with (simulationType set to laminar in constant/turbulenceProperties and transportModel set to Newtonian in constant/transportProperties). My Reynolds number is about 20.

Essentially everything runs without a problem except that the Initial residual for the two non axial components of the velocity do not converge. The axial component and the pressure converge nicely (and all of the final residual values look good along the way) but the initial residual of the two non axial components bounce around and don't settle down.

I have tried altering the relaxation parameters but with little success. I have set the pressures at the ends of the pipe and have zeroGradient BCs for U. Mesh is a Hex mesh from gambit.

When I look at the results in paraFoam it indicates that the axial velocity is approx 1.8 m/s while the non axial components (U_x and U_y) are of the order of 1.0e-6 in a couple of regions (so the axial components are very small).

Does anyone have an idea as to what i need to to get the Initial Residual of the non axial components to converge?.

For what it is worth this problem does not seem to show up if I look at flows that have non negligible non axial components).

My contents of fvSolution file and my 0/p and 0/U files are listed below.

Thanks in advance and Kind Regards,

Paul.

solvers
{
p
{
solver GAMG;
tolerance 1e-08;
relTol 0;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration true;
nCellsInCoarsestLevel 20;
agglomerator faceAreaPair;
mergeLevels 1;
}

U
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-08;
relTol 0;
}

nuTilda
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-08;
relTol 0.1;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;
}

relaxationFactors
{
default 0;
p 0.3;
U 0.7;
nuTilda 1.0;
}

0/p File

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
wall
{
type zeroGradient;
}

inlet
{
type fixedValue;
value uniform 24;
}

outlet
{
type fixedValue;
value uniform 0;
}

}

0/U file

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
wall
{
type fixedValue;
value uniform (0 0 0);
}

inlet
{
type zeroGradient;

}

outlet
{
type zeroGradient;
}
}