[Joseph 27]

Hello,

Sorry for the long post, but I need help troubleshooting a CFD simulation.

I’m trying to simulate airflow in a classroom with students and tables. The classroom has:

3 inlets (vents on the roof),
3 outlets (also vents),
1 door, and
3 windows (considered as "walls" since they are closed).
The room dimensions are 3 x 5 x 8 meters. To avoid errors with ideasFoam, I modeled the humans as cylinders with a mouth. The cylinder bases are linked to the floor, and the tables are attached to the walls. When I created the mesh, the cylinder bases became part of the floor, and one face of each table was linked to the wall. This setup allowed ideasFoam to function without errors.

I refined the mesh multiple times, and checkMesh reports no issues.

Next, I used createBaffles to add face zones to the boundary file, as everything inside the box was initially added to the faceZones file, not boundary. Once the boundaries were correctly updated, I defined:

3 tables and 4 humans (excluding the mouth) as walls.
Inlets, outlets, and mouths as patches.
(This is a simplified test setup. Once it works, I plan to include all students and tables.)

After preparing everything, I ran simpleFoam with the setup. To ensure stability, I:

Reduced the time step (deltaT),
Adjusted relaxation factors, and
Tightened solver tolerances (resTol).
Unfortunately, the simulation crashed immediately.

When I changed the solver for p (pressure) to PCG, the simulation ran. It converged smoothly with a small time step (deltaT = 0.001) until 1.5 seconds. However, after this point, the bounding k starts to increase steadily, reaching unrealistic values (e.g., max: 9.38163e+07).

Do you have any insights into what I might be doing wrong?

Here are the files I used:

boundary
U
p
k
epsilon
nut
fvSolution
fvSchemes
controdict

Thank you in advance for your help!


/*--------------------------------*- C++ -*----------------------------------*\
| ========= |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Website: https://openfoam.org |
| \\ / A nd | Version: 12 |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -1 0 0 0 0];

internalField uniform 0;

boundaryField
{
floor
{
type nutkWallFunction;
value uniform 0;
}

walls
{
type nutkWallFunction;
value uniform 0;
}

ceiling
{
type nutkWallFunction;
value uniform 0;
}

inlet_door
{
type calculated;
value uniform 0;
}

windows
{
type zeroGradient;
}

inlets
{
type calculated;
value uniform 0;
}

outlets
{
type zeroGradient;
}

humans_master
{
type nutkWallFunction;
value uniform 0;
}

humans_slave
{
type nutkWallFunction;
value uniform 0;
}

mouths_master
{
type calculated;
value uniform 0;
}

mouths_slave
{
type calculated;
value uniform 0;
}

tables_master
{
type nutkWallFunction;
value uniform 0;
}

tables_slave
{
type nutkWallFunction;
value uniform 0;
}
}

// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
| ========= |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Website: https://openfoam.org |
| \\ / A nd | Version: 12 |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object epsilon;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -3 0 0 0 0];

internalField uniform 0.331;

boundaryField
{
floor
{
type epsilonWallFunction;
value uniform 0.0;
}

walls
{
type epsilonWallFunction;
value uniform 0.0;
}

ceiling
{
type epsilonWallFunction;
value uniform 0.0;
}

inlet_door
{
type zeroGradient;
}

windows
{
type zeroGradient;
}

inlets
{
type fixedValue;
value uniform 0.331;
}

outlets
{
type zeroGradient;
}

humans_master
{
type epsilonWallFunction;
value uniform 0.0;
}

humans_slave
{
type epsilonWallFunction;
value uniform 0.0;
}

mouths_master
{
type zeroGradient;
}

mouths_slave
{
type zeroGradient;
}

tables_master
{
type epsilonWallFunction;
value uniform 0.0;
}

tables_slave
{
type epsilonWallFunction;
value uniform 0.0;
}
}

// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 12
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
location "0";
object k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0.0258;

boundaryField
{
floor
{
type kqRWallFunction;
value uniform 0.0;
}

walls
{
type kqRWallFunction;
value uniform 0.0;
}

ceiling
{
type kqRWallFunction;
value uniform 0.0;
}

inlet_door
{
type zeroGradient;
}

windows
{
type zeroGradient;
}

inlets
{
type fixedValue;
value uniform 0.0258;
}

outlets
{
type zeroGradient;
}

humans_master
{
type kqRWallFunction;
value uniform 0.0;
}

humans_slave
{
type kqRWallFunction;
value uniform 0.0;
}

mouths_master
{
type zeroGradient;
}

mouths_slave
{
type zeroGradient;
}

tables_master
{
type kqRWallFunction;
value uniform 0.0;
}

tables_slave
{
type kqRWallFunction;
value uniform 0.0;
}
}

// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 12 |
| \ / A nd | Web: www.OpenFOAM.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
location "0";
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (0 0 0);

boundaryField
{
floor
{
type noSlip;
}

walls
{
type noSlip;
}

ceiling
{
type noSlip;
}

inlet_door
{
type zeroGradient;
}

windows
{
type zeroGradient;
}

inlets
{
type fixedValue;
value uniform (0 0 0.35);
}

outlets
{
type fixedValue;
value uniform (0 0 -0.35);
}

humans_master
{
type noSlip;
}

humans_slave
{
type noSlip;
}

mouths_master
{
type zeroGradient;
}

mouths_slave
{
type zeroGradient;
}

tables_master
{
type noSlip;
}

tables_slave
{
type noSlip;
}
}

// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 12
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
floor
{
type zeroGradient;
}

walls
{
type zeroGradient;
}

ceiling
{
type zeroGradient;
}

inlet_door
{
type fixedValue; // Pressure reference point
value uniform 0;
}

windows
{
type zeroGradient;
}

inlets
{
type zeroGradient;
}

outlets
{
type zeroGradient;
}

humans_master
{
type zeroGradient;
}

humans_slave
{
type zeroGradient;
}

mouths_master
{
type zeroGradient;
}

mouths_slave
{
type zeroGradient;
}

tables_master
{
type zeroGradient;
}

tables_slave
{
type zeroGradient;
}
}

// ************************************************** *********************** //
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 12
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-5;
relTol 0.01;

}

pFinal
{
$p;
relTol 0;
}

"(U|k|epsilon)"
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-5;
relTol 0.01;
}

"(U|k|epsilon)Final"
{
$U;
relTol 0;
}
}

relaxationFactors
{
fields
{
p 0.2;
}
equations
{
U 0.3;
k 0.2;
epsilon 0.2;
}
}

PIMPLE
{
nNonOrthogonalCorrectors 2;
nCorrectors 2;

residualControl
{
p 1e-4;
U 1e-5;
"(k|epsilon)" 1e-5;
}
}


// ************************************************** *********************** //
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 12
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
default none;

div(phi,U) bounded Gauss upwind;
div(phi,k) bounded Gauss upwind;
div(phi,epsilon) bounded Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;

div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}


// ************************************************** *********************** //

/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 12
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

solver incompressibleFluid;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 3;

deltaT 0.0005;

writeControl adjustableRunTime;

writeInterval 0.1;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable yes;

adjustTimeStep yes;

maxCo 5;

debug 1;

// ************************************************** *********************** //

Example of the solution after 3s :

Time = 3s

smoothSolver: Solving for Ux, Initial residual = 0.00371234, Final residual = 6.68207e-06, No Iterations 2
smoothSolver: Solving for Uy, Initial residual = 0.00396574, Final residual = 1.20463e-05, No Iterations 2
smoothSolver: Solving for Uz, Initial residual = 0.00397317, Final residual = 1.27557e-05, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.000101223, Final residual = 9.75821e-06, No Iterations 35
DICPCG: Solving for p, Initial residual = 3.88401e-05, Final residual = 9.83166e-06, No Iterations 21
DICPCG: Solving for p, Initial residual = 1.7923e-05, Final residual = 9.83142e-06, No Iterations 17
time step continuity errors : sum local = 3.33501e-05, global = 2.51784e-05
DICPCG: Solving for p, Initial residual = 8.00657e-05, Final residual = 9.98959e-06, No Iterations 35
DICPCG: Solving for p, Initial residual = 3.17717e-05, Final residual = 9.49924e-06, No Iterations 21
DICPCG: Solving for p, Initial residual = 1.54928e-05, Final residual = 9.994e-06, No Iterations 1
time step continuity errors : sum local = 3.37548e-05, global = 2.51818e-05, cumulative = 0.00310968
smoothSolver: Solving for epsilon, Initial residual = 0.00443172, Final residual = 8.7404e-07, No Iterations 2
smoothSolver: Solving for k, Initial residual = 0.00427727, Final residual = 2.12083e-06, No Iterations 2
bounding k, min: 1.82005e-16 max: 9.38163e+07 average: 62990.6
ExecutionTime = 8353.48 s ClockTime = 8355 s