[faiazk]

Hello Everyone,

I am relatively new to Openfoam. I am trying to simulate wind flow having turbulent velocity with logarithmic velocity profile close to the ground. for that purpose I am using timevarryingmappedFixedvalue at the inlet boundary condition for U. I also have the necessary velocity folders for each time step inside the inlet folder under boundarydata folder inside Constant. I was able to run a case for a smaller empty domain for upto 5 seconds. But, when I increase the time step and run it for a longer period (say like 30s) the solver blows up. I am sharing the control dictionary and the error I am getting in this thread. Please help me on this. I am just curious whether there something wrong with the mesh or not. Please note that this is just an empty domain. I am trying to get the correct velocity profile and turbulence intensity.

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application pisoFoam;

startFrom startTime;

startTime 0;

stopAt endTime;

endTime 30;

deltaT 0.03;

writeControl timeStep;

writeInterval 5;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

functions
{
probes
{
type probes;
libs ("libsampling.so");
writeControl timeStep;
writeInterval 5;

fields

And I am also sharing the error I am receiving once I run pisoFoam after reaching time 5.07. My time step is 0.03 and it went well till 5.04.

Time = 5.04

Courant Number mean: 0.987221 max: 2.0711
smoothSolver: Solving for Ux, Initial residual = 0.0254167, Final residual = 6.02094e-06, No Iterations 9
smoothSolver: Solving for Uy, Initial residual = 0.0871783, Final residual = 5.66767e-06, No Iterations 11
smoothSolver: Solving for Uz, Initial residual = 0.0858853, Final residual = 8.63835e-06, No Iterations 10
GAMG: Solving for p, Initial residual = 0.145688, Final residual = 0.0127965, No Iterations 1
time step continuity errors : sum local = 5.17536e-05, global = -8.86575e-07, cumulative = -2.98201e-05
GAMG: Solving for p, Initial residual = 0.0311053, Final residual = 5.09854e-07, No Iterations 6
time step continuity errors : sum local = 2.06858e-09, global = -2.45448e-10, cumulative = -2.98203e-05
smoothSolver: Solving for k, Initial residual = 0.0797053, Final residual = 6.86189e+32, No Iterations 1000
bounding k, min: -8.15253e+41 max: 9.72954e+41 average: -6.62631e+35
ExecutionTime = 550.73 s ClockTime = 569 s

fieldAverage fieldAverage1 write:
Calculating averages

scalarTransport write:
smoothSolver: Solving for s, Initial residual = 0.129301, Final residual = 5.95047e-06, No Iterations 9

Time = 5.07

Courant Number mean: 0.988868 max: 2.08454
smoothSolver: Solving for Ux, Initial residual = 0.849795, Final residual = 0.00494518, No Iterations 1000
smoothSolver: Solving for Uy, Initial residual = 0.720148, Final residual = 0.000405804, No Iterations 1000
smoothSolver: Solving for Uz, Initial residual = 0.698049, Final residual = 0.00034483, No Iterations 1000
GAMG: Solving for p, Initial residual = 0.944956, Final residual = 0.0943667, No Iterations 8
time step continuity errors : sum local = 0.00432647, global = -0.000305037, cumulative = -0.000334857
GAMG: Solving for p, Initial residual = 6.08392e-12, Final residual = 6.08392e-12, No Iterations 0
time step continuity errors : sum local = 0.0311177, global = -0.000399824, cumulative = -0.000734681
smoothSolver: Solving for k, Initial residual = 0.999999, Final residual = 3.09126e-21, No Iterations 1
bounding k, min: -4.25568e+33 max: 9.2111e+36 average: 3.54553e+31
ExecutionTime = 577.16 s ClockTime = 596 s

fieldAverage fieldAverage1 write:
Calculating averages

scalarTransport write:
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::GaussSeidelSmoother::smooth(Foam::word const&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::Field<double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, unsigned char, int) at ??:?
#4 Foam::GaussSeidelSmoother::smooth(Foam::Field<doub le>&, Foam::Field<double> const&, unsigned char, int) const at ??:?
#5 Foam::smoothSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 Foam::fvMatrix<double>::solveSegregated(Foam::dict ionary const&) at ??:?
#7 Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
#8 Foam::functionObjects::scalarTransport::execute() at ??:?
#9 Foam::functionObjectList::execute() at ??:?

[vivek05]

Hi Faiaz Khaled,
Your error is due to k(turbulent kinetic energy) .if you the error message ,the residuals of k are going upto 10^32..this may be one of reason for code blow up. Change your boundary conditions ok k file. And another thing you can modify is solver used for k in fvSolution

Thanks,
Vivek

[Tobi]

Hi all,


as it was pointed out by Vivek, it seems that you have problems in your k-equation.

Originally Posted by vivek05

if you the error message ,the residuals of k are going upto 10^32.

Just a correction, it is not the residual value of k, it is the real cell values that are getting crazy.

• To get rid of the problem, you should first use an upwind scheme for k
• If you save the time steps, check out what your k field is doing and analyze why you get problems there. I expect to have such high values at bad cells or a mismatch of boundary conditions
• Other options, as Vivek mentioned, are modifying your fvSolution settings but this is probably not the primary source; linear solver should (at the end) give the same result.
• Another option is to use the field limiting object function to limit the values for k to reasonable quantities.

[faiazk]

Dear Mr. Vivek and Dr. Tobi,

Thank you very much. I will keep working on it and follow your suggestions.

I will get back to you people soon.

Thank you once again.

Regards,
Faiaz