[Andrea23]

Hi,

I have problem with a simulation and I hope you can help me.

I have run a simulation in indoor environment (a room) with inlet condition from 8 diffussers and outlet condition at extraction grilles. I have used simpleFoam with RNG k-epsilon for turbulence model.

The residual are stable, even if a little oscillating, residual for P is order of magnitued of 2*10^-2 and residual for U is 3*10^-3 (Image attached)

I have monitored velocity in 8 points, using probes, the velocity is not constant but it is bounded and oscillating between 2 values, like a periodic phenomena (images attached).

y+ values are: min 1e-2; max 7.6e+1; average 6e+0;

I need to create a finer mesh near walls?

log Check mesh, fvSchemes, fvSolution and Boundary conditions i have used are listed here:
I have even tried the options after "//"

MESH

Mesh stats
    points:           3859442
    faces:            10134517
    internal faces:   9480040
    cells:            3149724
    faces per cell:   6.22739
    boundary patches: 10
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     2824568
    prisms:        27670
    wedges:        0
    pyramids:      0
    tet wedges:    940
    tetrahedra:    0
    polyhedra:     296546
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   1
            5   2035
            6   67942
            7   10887
            8   179
            9   188981
           10   4
           12   23678
           15   2180
           18   659

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).
Checking geometry...
    Overall domain bounding box (-0.000251502 0 -0.00653899) (8.7855 7.23 2.88)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-4.84732e-15 6.82987e-16 -4.54469e-15) OK.
    Max cell openness = 3.74184e-16 OK.
    Max aspect ratio = 6.44698 OK.
    Minimum face area = 4.70551e-06. Maximum face area = 0.00337339.  Face area magnitudes OK.
    Min volume = 4.622e-08. Max volume = 0.000185767.  Total volume = 165.965.  Cell volumes OK.
    Mesh non-orthogonality Max: 50 average: 8.5995
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 2.632 OK.
    Coupled point location match (average 0) OK.

FVSOLVERS

solvers
{
    p
    {
        solver GAMG;
        tolerance 1e-07;
        relTol 0;
        smoother GaussSeidel;
       nPreSweeps 0;   //3
       nPostSweeps 2;   //3
       cacheAgglomeration on;
       agglomerator faceAreaPair;
       nCellsInCoarsestLevel 1000; //10; 20; 30;
       mergeLevels 1;

    }

    U
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-06;
        relTol          0;
    }
k
        {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-06;
        relTol          0.001;
    }
    epsilon
        {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-06;
        relTol          0.001;
    }

}

SIMPLE
{
   consistent          yes; //no;
   
    residualControl
    {
        p               1e-4;
        U               1e-5;
        "(k|omega|epsilon)" 1e-5;
    }
    nNonOrthogonalCorrectors 1;
   pRefCell        0;  
   pRefValue       0;

}

relaxationFactors
{
    fields
    {
        p            1; //0.3
    }
    equations
    {
        U               0.7;
        "(k|omega|epsilon).*" 0.7;
    }
}

FVSCHEMES

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default       cellMDLimited Gauss linear 0; //cellLimited leastSquares 1;//Gauss linear; 
   //grad (p)   Gauss linear 0.333;
     grad (U)    cellMDLimited Gauss linear 0.333;//cellLimited leastSquares 1;
	 
    limited       cellLimited Gauss linear 1; // cellLimited leastSquares 1;
    grad(k)         $limited;
    grad(epsilon)     $limited;  //sto rifacendo che per sbaglio avevo messo il cellLimited per grad(U)
}

divSchemes
{

    default         none;

    div(phi,U)      Gauss linearUpwind grad(U) ; //bounded Gauss linearUpwind limited;

    turbulence      bounded Gauss upwind;
    div(phi,k)      $turbulence;
    div(phi,epsilon) $turbulence;

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

laplacianSchemes
{
    default         Gauss linear limited 1;//corrected;//orthogonal;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default       limited 1; //corrected; //orthogonal;//  
}

U

This is before i have initialized the field with potentialFoam

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

internalField   uniform (0 0 0);

boundaryField
{
    diff1
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.044;
        rpm             82.8;
        value uniform   (0 0 0);
    }
    diff2
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.034;
        rpm             103.89;
        value uniform   (0 0 0);
    }
    diff3
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.043;
        rpm             26.32;
        value uniform   (0 0 0);
    }
    diff4
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.045;
        rpm             36.36;
        value uniform   (0 0 0);
    }
    diff5
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.045;
        rpm             79.05;
        value uniform   (0 0 0);
    }
    diff6
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.044;
        rpm             85.30;
        value uniform   (0 0 0);
    }
    diff7
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.039;
        rpm             105.35;
        value uniform   (0 0 0);
    }
    diff8
    {
        type            swirlFlowRateInletVelocity;
        flowRate        0.048;
        rpm             29.88;
        value uniform   (0 0 0);
    }
    outlet
    {
        type            zeroGradient;      //   type            pressureInletOutletVelocity;
      //  value           uniform (0 0 0);
    }
    walls
    {
        type            noSlip;
    }

EPSILON

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

internalField   uniform 0.013;

boundaryField
{
    walls
    {
        type            epsilonWallFunction;
        value           uniform 0.013;
    }
    diff1....diff8
    {
        type            turbulentMixingLengthDissipationRateInlet;
        mixingLength    0.0014;
        value           uniform 0.013;
    }
 
    outlet
    {
        type            inletOutlet;  //zeroGradient;
        inletValue      $internalField;
    }
}

K

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

internalField   uniform 0.0024;

boundaryField
{
    walls
    {
        type            kqRWallFunction; //kLowReWallFunction; //
        value           uniform 0.0024;
    }
    diff1...diff8
    {
        type            turbulentIntensityKineticEnergyInlet;
        intensity       0.05;
        value           uniform 0.0024;
    }

    outlet
    {
        type            inletOutlet; //zeroGradient;
        inletValue      $internalField;
    }
}

NUT

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

internalField   uniform 0;

boundaryField
{
    walls
    {
        type            nutUWallFunction;
        value           uniform 0;
    }
    diff1...diff8
    {
        type            calculated;
        value           uniform 0;
}
    outlet
    {
        type            calculated;
        value           uniform 0;
    }
}

P

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

internalField   uniform 0;

boundaryField
{
    walls
    {
        type            zeroGradient;
    }
    diff1...diff8
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 0;
    }
   
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
}

My questions are:

1)Do you know what I could modify to have a convergence?

2)Calculating a mean value for the velocity field is a good idea or it is not accurate? I know RANS calculate mean values so it is a mean of a mean.

Thanks for the help