chtMultiRegionFoam- too slow

sandymech1 · November 19, 2017, 06:57

Hi to All,

I am trying to solve natural convection with conjugate heat transfer using chtMultiRegionFoam. Mesh inside domain is 160K only. I am using 0.001 time step size for solving. However with this set up, it is taking lot of time for solving. Case file is attached herewith for quick reference. Solver schemes of fluid region ,details of controldict and log output is given below. Certain lines of log output is also highlighted, where it seems problem.

I am not sure,where I am going wrong. It is kind request to you all, please help me in this regard .

Thanks

fvSchemes for Fluid region

Code:

ddtSchemes
{
    default Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;

    div(phi,U)      Gauss upwind;
    div(phi,K)      Gauss linear;
    div(phi,h)      Gauss upwind;
    div(phi,k)      Gauss upwind;
    div(phi,epsilon) Gauss upwind;
    div(phi,R)      Gauss upwind;
    div(R)          Gauss linear;
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default        Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

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

Name of solvers for fluid region

Code:

solvers
{
    rho
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-7;
        relTol          0.1;
    }

    rhoFinal
    {
        $rho;
        tolerance       1e-7;
        relTol          0;
    }

    p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;

        smoother         GaussSeidel;

    }

    p_rghFinal
    {
        $p_rgh;
        tolerance        1e-7;
        relTol           0;
    }

    "(U|h|k|epsilon|R)"
    {
        solver           PBiCGStab;
        preconditioner   DILU;
        tolerance        1e-7;
        relTol           0.1;
    }

    "(U|h|k|epsilon|R)Final"
    {
        $U;
        tolerance        1e-7;
        relTol           0;
    }
}

PIMPLE
{
    momentumPredictor   yes;
    nCorrectors         2;
    nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
    equations
    {
        "h.*"           1;
        "U.*"           1;
    }
}

//

Controldict file for solution

Code:

application     chtMultiRegionFoam;

startFrom       latestTime;

startTime       0.0001;

stopAt          endTime;

endTime         5;

deltaT          0.0001;

writeControl    adjustableRunTime;

writeInterval   0.001;

purgeWrite      0;

writeFormat     ascii;

writePrecision  8;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable yes;

maxCo           0.6;

// Maximum diffusion number
maxDi           10.0;

adjustTimeStep  yes;

//

Some of log output

Code:

Pimple iteration 0

Solving for fluid region fluidaround
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
Min/max T:299.9994 300.00149
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
Min/max T:299.9994 300.00149
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
Min/max T:299.9994 300.00149
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
GAMG:  Solving for p_rgh, Initial residual = 0.4402544, Final residual = 1.6539243e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.1458128e-09, global = -3.6487898e-11, cumulative = 1.7577776e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.9992465, Final residual = 5.1842275e-08, No Iterations 5
Min/max T:300.00141 300.00149
ExecutionTime = 3769.68 s  ClockTime = 3822 s

Region: fluidaround Courant Number mean: 5.0938106e-05 max: 0.10005987
Region: solidheater Diffusion Number mean: 0.62251892 max: 2.5951577
deltaT = 0.0005
Time = 0.011

Pimple iteration 0

Solving for fluid region fluidaround
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
Min/max T:299.9994 300.00149
GAMG:  Solving for p_rgh, Initial residual = 0.4402544, Final residual = 1.6539243e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.1458128e-09, global = -3.6487898e-11, cumulative = 1.7577776e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.9992465, Final residual = 5.1842275e-08, No Iterations 5
Min/max T:300.00141 300.00149
ExecutionTime = 3783.52 s  ClockTime = 3830 s

Region: fluidaround Courant Number mean: 5.0938106e-05 max: 0.10005987
Region: solidheater Diffusion Number mean: 0.62251892 max: 2.5951577
deltaT = 0.0005
Time = 0.011

Pimple iteration 0

Solving for fluid region fluidaround
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
Min/max T:299.9994 300.00149
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
GAMG:  Solving for p_rgh, Initial residual = 0.4402544, Final residual = 1.6539243e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.1458128e-09, global = -3.6487898e-11, cumulative = 1.7577776e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.9992465, Final residual = 5.1842275e-08, No Iterations 5
Min/max T:300.00141 300.00149
ExecutionTime = 3802.89 s  ClockTime = 3840 s

Region: fluidaround Courant Number mean: 5.0938106e-05 max: 0.10005987
Region: solidheater Diffusion Number mean: 0.62251892 max: 2.5951577
deltaT = 0.0005
Time = 0.011

Pimple iteration 0

Solving for fluid region fluidaround
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.048237251, Final residual = 1.088459e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uy, Initial residual = 0.016310354, Final residual = 1.9615561e-08, No Iterations 3
DILUPBiCGStab:  Solving for Uz, Initial residual = 0.041151586, Final residual = 2.2887839e-08, No Iterations 3
DILUPBiCGStab:  Solving for h, Initial residual = 0.01527495, Final residual = 4.3386867e-08, No Iterations 2
Min/max T:299.9994 300.00149
GAMG:  Solving for p_rgh, Initial residual = 0.8569772, Final residual = 0.0058071545, No Iterations 9
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 1.4837011e-08, global = -1.8644987e-10, cumulative = 1.7575912e-06
GAMG:  Solving for p_rgh, Initial residual = 0.41170003, Final residual = 2.2614473e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 6.971801e-10, global = 1.7244533e-11, cumulative = 1.7576084e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.99927812, Final residual = 5.1847013e-08, No Iterations 5
Min/max T:300.00149 300.00156
GAMG:  Solving for p_rgh, Initial residual = 0.45318628, Final residual = 7.8711514e-07, No Iterations 1000
GAMG:  Solving for p_rgh, Initial residual = 0.44200316, Final residual = 1.096905e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 3.4963335e-09, global = 1.0997615e-10, cumulative = 1.7580701e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.9994912, Final residual = 4.152597e-07, No Iterations 6
Min/max T:300.00113 300.00127
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 2.5994397e-09, global = -8.2721193e-11, cumulative = 1.7555659e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.99936716, Final residual = 4.1521529e-07, No Iterations 6
Min/max T:300.00099 300.00113
GAMG:  Solving for p_rgh, Initial residual = 0.41170003, Final residual = 2.2614473e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 6.971801e-10, global = 1.7244533e-11, cumulative = 1.7576084e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.99927812, Final residual = 5.1847013e-08, No Iterations 5
Min/max T:300.00149 300.00156
ExecutionTime = 4073.65 s  ClockTime = 4080 s

Region: fluidaround Courant Number mean: 5.3334931e-05 max: 0.10426789
Region: solidheater Diffusion Number mean: 0.62251892 max: 2.5951577
deltaT = 0.0005
Time = 0.0115

Pimple iteration 0

Solving for fluid region fluidaround
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
GAMG:  Solving for p_rgh, Initial residual = 0.44200316, Final residual = 1.096905e-06, No Iterations 1000
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (fluidaround): sum local = 2.5994397e-09, global = -8.2721193e-11, cumulative = 1.7555659e-06

Solving for solid region solidheater
DICPCG:  Solving for h, Initial residual = 0.99936716, Final residual = 4.1521529e-07, No Iterations 6
Min/max T:300.00099 300.00113
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.028125658, Final residual = 4.8504238e-08, No Iterations 3

piu58 · November 20, 2017, 05:29

> fluidaround Courant Number mean: 5.3334931e-05 max: 0.10426789

It is not necessary to accept such a low Co number. Even in complicated cases 0.1 ... 0.01 is sufficient.

sandymech1 · November 20, 2017, 07:04

Hi Uwe,

Thanks for your reply and suggestion. I tried to increase time steps to 0.01s but it blows up solution after some time. Hence I tried to keep it too low. Any advice from your side? Boundary condition for fluidaround is given below. Fluidaround is cylinder, where top and bottom are flat portion and lateral is curved face of cylinder.

Code:

U
{
    internalField   uniform (0 0 0);

    boundaryField
    {
        ".*"
        {
            type            fixedValue;
            value           uniform (0 0 0);
        }
        lateral
	{
	    type	fixedValue;
	    value       uniform (0 0 0);
	}
	top
        {
            type            fixedValue;
            value           uniform (0 0 0);
        }
        bottom
        {
            type            inletOutlet;
            inletValue      uniform (0 0 0);
            value           uniform (0 0 0);
        }
    }
}

T
{
    internalField   uniform 300;

    boundaryField
    {
        ".*"
        {
            type            zeroGradient;
        }

        top
        {
            type            fixedValue;
            value           uniform 300;
        }
        bottom
        {
            type            inletOutlet;
            inletValue      uniform 300;
            value           uniform 300;
        }
	lateral
	{
	    type            fixedValue;
            value           uniform 300;

	}

        "fluidaround_to_.*"
        {
            	type            compressible::turbulentTemperatureCoupledBaffleMixed;
	          Tnbr            T;
        	  kappaMethod     fluidThermo;
    	      	value           uniform 300;
        }
    }
}

epsilon
{
    internalField   uniform 0.01;

    boundaryField
    {
        ".*"
        {
            type            epsilonWallFunction;
            value           uniform 0.01;
        }

        top
        {
            type            fixedValue;
            value           uniform 0.01;
        }

        lateral
        {
            type            fixedValue;
            value           uniform 0.01;
        }

        bottom
        {
            type            inletOutlet;
            inletValue      uniform 0.01;
            value           uniform 0.01;
        }
    }
}

k
{
    internalField   uniform 0.1;

    boundaryField
    {
        ".*"
        {
            type            kqRWallFunction;
            value           uniform 0.1;
        }

        top
        {
            type            fixedValue;
            value           uniform 0.1;
        }
	lateral
        {
            type            fixedValue;
            value           uniform 0.1;
        }

	
        bottom
        {
            type            inletOutlet;
            inletValue      uniform 0.1;
            value           uniform 0.1;
        }
    }
}

p_rgh
{
    internalField   uniform 1e5;

    boundaryField
    {
        ".*"
        {
            type            fixedFluxPressure;
            value           uniform 1e5;
        }

        bottom
        {
            type            fixedValue;
            value           uniform 1e5;
        }
    }
}

p
{
    internalField   uniform 1e5;

    boundaryField
    {
        ".*"
        {
            type            calculated;
            value           uniform 1e5;
        }

        bottom
        {
            type            calculated;
            value           uniform 1e5;
        }
    }
}

piu58 · November 20, 2017, 08:53

I usual set maxCo in controlDict and lte the solver choose delta t.

Code:

adjustTimeStep  yes;

maxCo           1;

Your write interval is 10x delta t. Do you need that? It may bet that the solver writes too much which is time consuming.

sandymech1 · November 20, 2017, 19:51

Hi Uwe Pilz,

Thanks for the information. It works.

Regards
Sandeep

November 20, 2017, 05:29		#2
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	> fluidaround Courant Number mean: 5.3334931e-05 max: 0.10426789 It is not necessary to accept such a low Co number. Even in complicated cases 0.1 ... 0.01 is sufficient. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

November 20, 2017, 08:53		#4
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	I usual set maxCo in controlDict and lte the solver choose delta t. Code: adjustTimeStep yes; maxCo 1; Your write interval is 10x delta t. Do you need that? It may bet that the solver writes too much which is time consuming. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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November 20, 2017, 19:51		#5
sandymech1 New Member Sandy Join Date: Aug 2017 Posts: 8 Rep Power: 9	Hi Uwe Pilz, Thanks for the information. It works. Regards Sandeep