[AmiN.D]

Hi Cfd-Online!


I'm a newbie in OpenFOAM world and happen to submit weekly projects since last month!


I' trying to simulate a very simple problem and geometry with kOmegaSST model in "simpleFoam" but the results are odd to me!
The geometry as you can see in attachment is a semi-orifice form and the fluid is water at 25ºC and gotta simulate it for Re=30 and Re=3000!
I dont use a fine mesh [Overall number of cells of each type :
hexahedra: 40000] .

With SST model i'm getting very small yPlus number for Re=3000 and Re=30
for example here are the results for Re=3000:

fixedWalls y+ : min: 0.000135994 max: 0.97708 average: 0.192186

and i assume it should be something between 5<y+<30
Both cases dont converge after 10000 interval which might be okay for Re=3000 but odd for Re=30, although after 8000 you dont see that much change in numbers.
what do you thing about y+ and also k,Omega, nut behavior ?



here are the conditions:


U:

internalField uniform (0 0 0);

boundaryField
{
inlet
{
type fixedValue;
value uniform (0 0 -0.03);
}
outlet
{
type zeroGradient;
}

fixedWalls
{
type fixedValue;
value uniform (0 0 0);
}
fandb
{
type empty;
}

}

P:

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

internalField uniform 0;

boundaryField
{
inlet
{
type zeroGradient;
}
outlet
{
type fixedValue;
value uniform 0;
}
fixedWalls
{
type zeroGradient;
}
fandb
{
type empty;
}
}

Omega:

internalField uniform 0.3086;

boundaryField
{
inlet
{
type fixedValue;
value uniform 0.3086;
}
outlet
{
type zeroGradient;
}
fixedWalls
{
type omegaWallFunction;
value uniform 0.3086;
}

fandb
{
type empty;
}
}

k:

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

internalField uniform 4.66e-06;

boundaryField
{
inlet
{
type fixedValue;
value uniform 4.66e-06;
}
outlet
{
type zeroGradient;
}
fixedWalls
{
type kqRWallFunction;
value uniform 4.66e-06;
}
fandb
{
type empty;
}


}

nut:

internalField uniform 0;

boundaryField
{
inlet
{
type calculated;
value uniform 0;
}
outlet
{
type calculated;
value uniform 0;
}

fixedWalls
{
type nutkWallFunction;
value uniform 0;
}
fandb
{
type empty;
}
}

fvSolution:

solvers
{
p
{
solver GAMG;
tolerance 1e-08;
relTol 0.01;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration on;
agglomerator faceAreaPair;
nCellsInCoarsestLevel 10;
mergeLevels 1;
}

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

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

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

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

SIMPLE
{
nNonOrthogonalCorrectors 0;

residualControl
{
p 1e-6;
U 1e-6;
}
}

potentialFlow
{
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
fields
{
p 0.3;
}
equations
{
U 0.7;
k 0.7;
epsilon 0.7;
omega 0.7;
}
}

cache
{
grad(U);
}

thanks in advance

[klausb]

Hi,

check this to better understand what you're trying to do:
https://www.brighthubengineering.com...urbulent-flow/

Calculate the turbulence properties using e.g.:
https://www.cfd-online.com/Tools/turbulence.php

Dig a bit deeper into y+ ranges and mesh densities/properties suitable for your cases i.e. internal flow at your cases Re numbers.

Calculate y+ wall distance using e.g.:
https://www.cfd-online.com/Tools/yplus.php
And create a mesh that meets the y+ wall distance requirement for your case

Re = 3000 should be a turbulent case and kOmegaSST should work

Re = 30 should be a laminar flow case so maybe switch off turbulence in the constant/turbulenceProperties file

simulationType RAS;

RAS
{
    // Tested with kEpsilon, realizableKE, kOmega, kOmegaSST, v2f,
    // ShihQuadraticKE, LienCubicKE.
    RASModel        kOmegaSST;

    turbulence      on; // change this to off for laminar flow

    printCoeffs     on;
}