| nikosb |
June 15, 2022 13:19 |
DNS of sphere at Re=3700 blows up
I am trying to run DNS of a sphere at Re=3700. I will be comparing the results of OpenFOAM against other codes and results in the literature.
I created an O grid for the mesh around a sphere in a cylindrical domain. The inlet is 5D from the sphere, the outlet is 20D and the radius of the cylindrical domain is 10D. Here are some photos of the mesh near the sphere. Around the sphere the grid is slightly stretched in the radial direction to cluster points near the surface of the sphere. The resolution is kept fine in a region behind the sphere up to 5D to resolve the near wake.
This photo showing a cross section cut showing the grid around the sphere and the wake
https://i.ibb.co/FVG3st2/mesh-side-view.png
Another photo showing a cross section cut in the wake with crinkle clip
https://i.ibb.co/Wz6zK3f/mesh-rear-view.png
The simulation blows up after 20 iterations. I ran the simulation with both pisoFOAM and simpleFOAM without any success. Simulationtype is laminar. Here is the output of the pisoFOAM run.
Code:
Time = 0.036
Courant Number mean: 0.0422403 max: 1.36537
smoothSolver: Solving for Ux, Initial residual = 0.0587041, Final residual = 8.42802e-06, No Iterations 5
smoothSolver: Solving for Uy, Initial residual = 0.0587602, Final residual = 7.79945e-06, No Iterations 5
smoothSolver: Solving for Uz, Initial residual = 0.00212533, Final residual = 2.55993e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.99465, Final residual = 0.0430159, No Iterations 2
time step continuity errors : sum local = 1.02157e-06, global = -6.00863e-12, cumulative = -3.02265e-08
GAMG: Solving for p, Initial residual = 0.979142, Final residual = 8.77358e-07, No Iterations 21
time step continuity errors : sum local = 2.42567e-11, global = -3.09213e-12, cumulative = -3.02296e-08
ExecutionTime = 401.43 s ClockTime = 403 s
forceCoeffs forces write:
Cm = -0.0331513
Cd = 0.697653
Cl = 0.0638549
Cl(f) = -0.00122385
Cl(r) = 0.0650787
Time = 0.038
Courant Number mean: 0.0422442 max: 2.85164
smoothSolver: Solving for Ux, Initial residual = 0.0998439, Final residual = 8.97566e+216, No Iterations 1000
smoothSolver: Solving for Uy, Initial residual = 0.100005, Final residual = 2.91442e+216, No Iterations 1000
smoothSolver: Solving for Uz, Initial residual = 0.00432983, Final residual = 2.49464e+215, No Iterations 1000
The simulation blows up suddenly from one time step to the next. The time step is 2e-3. I ran with smaller time step of 2e-4 and I still get the same problem.
Here is the fvScheme file
Code:
ddtSchemes
{
default backward;
}
gradSchemes
{
default Gauss linear;
}
divSchemes
{
default none;
div(phi,U) Gauss linear;
div(phi,k) Gauss limitedLinear 1;
div(phi,s) bounded Gauss limitedLinear 1;
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default Gauss linear corrected;
}
interpolationSchemes
{
default linear;
}
snGradSchemes
{
default corrected;
}
and the fvSolutions
Code:
solvers
{
p
{
solver GAMG;
tolerance 1e-06;
relTol 0.1;
smoother GaussSeidel;
}
pFinal
{
$p;
smoother DICGaussSeidel;
tolerance 1e-06;
relTol 0;
}
"(U|k|B|nuTilda|s)"
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-05;
relTol 0;
}
}
PISO
{
nCorrectors 2;
nNonOrthogonalCorrectors 0;
}
and the controDict
Code:
application pisoFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 300;
deltaT 2e-03;
adjustTimeStep yes;
maxCo 1.0;
writeControl adjustableRunTime;
writeInterval 10;
purgeWrite 0;
writeFormat binary;
writePrecision 6;
writeCompression off;
timeFormat general;
timePrecision 6;
runTimeModifiable true;
Any help with why it is blowing up and what to try next? |
