lift and drag on ship superstructures

vaina74 · June 8, 2010, 10:21

I'm going to study the aerodynamic aspect of ship superstructures. I started with a simple 2D model (see pic 1-2), a top view of a superstructure (abot 30x80 m). I used the simpleFoam solver (with wall functions) and I'd like to have some suggestions. I already studied airfoils and propeller blades in water (convergence before 1000 iterations and correct y+), but now I think I have a few problems about convergence and y+. Here are my boundary conditions:
p

Code:

#include        "initialConditions"

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

internalField   uniform $pressure;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    #include "frontBackPatches"

    outlet
    {
        type            fixedValue;
        value           $internalField;
    }

    main_body
    {
        type            kqRWallFunction;
        value           $internalField;
    }
}

U

Code:

#include        "initialConditions"

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

internalField   uniform $flowVelocity;

boundaryField
{
    #include "fixedInlet"

    #include "frontBackPatches"

    outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           $internalField;
    }

    main_body
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }
}

k

Code:

#include        "initialConditions"

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

internalField   uniform $turbulentK;

boundaryField
{
    #include "fixedInlet"

    #include "frontBackPatches"

    main_body
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    outlet
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }
}

omega

Code:

#include        "initialConditions"

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

internalField   uniform $turbulentOmega;

boundaryField
{
    #include "fixedInlet"

    #include "frontBackPatches"

    main_body
    {
        type            kqRWallFunction;
        value           $internalField;
    }

    outlet
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }
}

My system settings are:

Code:

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default steadyState;
}

gradSchemes
{
    default         Gauss linear;
    grad(p)         Gauss linear;
    grad(U)         Gauss linear;
//    grad(U)         cellLimited Gauss linear 1;
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss linearUpwindV Gauss linear;
    div(phi,k)      Gauss upwind;
    div(phi,omega)  Gauss upwind;
    div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
//    default         Gauss linear limited 0.5;
//    default         Gauss linear limited 0.333;
}

interpolationSchemes
{
    default         linear;
    interpolate(U)  linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p;
}

and

Code:

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.1;
        smoother         GaussSeidel;
        nPreSweeps       0;
        nPostSweeps      2;
        cacheAgglomeration on;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;
    };

    U
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    };

    k
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    };

    omega
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    };
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    convergenceCriterion 1e-5;
}

relaxationFactors
{
    p               0.3;
    U               0.7;
    k               0.7;
    omega           0.7;
}

Maybe the mesh is bad, but I tried to refine it and I obtain worse

,

and y+. Any suggestions about domain dimensions, fvSchemes, initial conditions ( $\kappa$ =0.015 and $\omega$ =80) and so on?

I thought about a different mesh (see pic3) but I'm in troubles with inlet and outlet boundary conditions for p and U. I'd like to set different apparent winds, so I believe I can't establish which patch is an inlet or outlet one beforehand. Are there any derived boundary conditions, similar to inletOutlet and outletInlet, to that aim?

Thanks for your help.

vaina74 · June 8, 2010, 10:22

Here is pic2

vaina74 · June 8, 2010, 10:23

Here is pic3

vaina74 · June 8, 2010, 13:30

I changed the outlet bc in the U file:

Code:

outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }

but I think the case is still not OK. After 2000 iterations (steady case), the aerodynamic coefficients are not so 'stable':

Code:

Time = 1990

smoothSolver:  Solving for Ux, Initial residual = 0.0194878, Final residual = 0.00140397, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00675477, Final residual = 0.000472691, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0338792, Final residual = 0.00292316, No Iterations 2
time step continuity errors : sum local = 6.87276e-06, global = 4.32326e-07, cumulative = 0.000196135
smoothSolver:  Solving for omega, Initial residual = 0.000500113, Final residual = 4.49831e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00747582, Final residual = 0.000625669, No Iterations 3
ExecutionTime = 737.82 s  ClockTime = 889 s

forces output:
    forces(pressure, viscous)((1373.57 6530.95 1.82693e-15) (14.9359 2.98526 -5.12444e-18))
    moment(pressure, viscous)((-3265.47 686.785 231467) (-1.49263 7.46796 93.4669))

forceCoeffs output:
    Cd = 1.10008
    Cl = 0.714475
    Cm = 0

Time = 1991

smoothSolver:  Solving for Ux, Initial residual = 0.0191039, Final residual = 0.001403, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00664963, Final residual = 0.000467334, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0339034, Final residual = 0.00296081, No Iterations 2
time step continuity errors : sum local = 6.91286e-06, global = 5.84111e-07, cumulative = 0.000196719
smoothSolver:  Solving for omega, Initial residual = 0.000495335, Final residual = 4.50325e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00712408, Final residual = 0.000611907, No Iterations 3
ExecutionTime = 738.23 s  ClockTime = 889 s

forces output:
    forces(pressure, viscous)((1270.77 6686.6 1.88893e-15) (14.8198 3.08212 -4.86763e-18))
    moment(pressure, viscous)((-3343.3 635.386 237418) (-1.54106 7.40989 98.9058))

forceCoeffs output:
    Cd = 1.10742
    Cl = 0.750391
    Cm = 0

Time = 1992

smoothSolver:  Solving for Ux, Initial residual = 0.0186364, Final residual = 0.00139815, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00654604, Final residual = 0.000462334, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0342788, Final residual = 0.00299029, No Iterations 2
time step continuity errors : sum local = 6.93894e-06, global = 6.87427e-07, cumulative = 0.000197406
smoothSolver:  Solving for omega, Initial residual = 0.000490721, Final residual = 4.50313e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00676195, Final residual = 0.000597454, No Iterations 3
ExecutionTime = 738.63 s  ClockTime = 889 s

forces output:
    forces(pressure, viscous)((1167.46 6845.19 1.95158e-15) (14.7014 3.17815 -4.62007e-18))
    moment(pressure, viscous)((-3422.6 583.732 243468) (-1.58908 7.35069 104.192))

forceCoeffs output:
    Cd = 1.11509
    Cl = 0.786788
    Cm = 0

Time = 1993

smoothSolver:  Solving for Ux, Initial residual = 0.0181001, Final residual = 0.00138872, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00644689, Final residual = 0.000457899, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0347106, Final residual = 0.00300199, No Iterations 2
time step continuity errors : sum local = 6.93254e-06, global = 7.49189e-07, cumulative = 0.000198155
smoothSolver:  Solving for omega, Initial residual = 0.000486142, Final residual = 4.50867e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.0064024, Final residual = 0.000582749, No Iterations 3
ExecutionTime = 738.98 s  ClockTime = 890 s

forces output:
    forces(pressure, viscous)((1062.53 7008.45 2.01487e-15) (14.5802 3.2732 -4.46006e-18))
    moment(pressure, viscous)((-3504.23 531.263 249696) (-1.6366 7.29011 109.348))

forceCoeffs output:
    Cd = 1.12318
    Cl = 0.824058
    Cm = 0

Time = 1994

smoothSolver:  Solving for Ux, Initial residual = 0.0175231, Final residual = 0.00137507, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00635044, Final residual = 0.000453938, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0347473, Final residual = 0.00297488, No Iterations 2
time step continuity errors : sum local = 6.85089e-06, global = 7.57133e-07, cumulative = 0.000198913
smoothSolver:  Solving for omega, Initial residual = 0.000481471, Final residual = 4.5085e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00605224, Final residual = 0.000567726, No Iterations 3
ExecutionTime = 739.26 s  ClockTime = 890 s

forces output:
    forces(pressure, viscous)((955.289 7176.48 2.07895e-15) (14.4579 3.36829 -4.57355e-18))
    moment(pressure, viscous)((-3588.24 477.645 256113) (-1.68415 7.22897 114.367))

forceCoeffs output:
    Cd = 1.13162
    Cl = 0.86231
    Cm = 0

Time = 1995

smoothSolver:  Solving for Ux, Initial residual = 0.016937, Final residual = 0.00135761, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00625675, Final residual = 0.000450832, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0342087, Final residual = 0.0029106, No Iterations 2
time step continuity errors : sum local = 6.70063e-06, global = 7.01239e-07, cumulative = 0.000199614
smoothSolver:  Solving for omega, Initial residual = 0.000477093, Final residual = 4.51017e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00571846, Final residual = 0.000553258, No Iterations 3
ExecutionTime = 739.57 s  ClockTime = 891 s

forces output:
    forces(pressure, viscous)((846.582 7347.19 2.14345e-15) (14.3335 3.46361 -4.82403e-18))
    moment(pressure, viscous)((-3673.59 423.291 262636) (-1.73181 7.16675 119.279))

forceCoeffs output:
    Cd = 1.14023
    Cl = 0.90114
    Cm = 0

Time = 1996

smoothSolver:  Solving for Ux, Initial residual = 0.0163787, Final residual = 0.00133729, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00615668, Final residual = 0.000448527, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0330994, Final residual = 0.00282895, No Iterations 2
time step continuity errors : sum local = 6.52723e-06, global = 5.932e-07, cumulative = 0.000200207
smoothSolver:  Solving for omega, Initial residual = 0.000472781, Final residual = 4.51361e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00540995, Final residual = 0.000539806, No Iterations 3
ExecutionTime = 739.9 s  ClockTime = 891 s

forces output:
    forces(pressure, viscous)((737.789 7516.79 2.20766e-15) (14.2067 3.55839 -5.0285e-18))
    moment(pressure, viscous)((-3758.39 368.895 269100) (-1.7792 7.10333 124.06))

forceCoeffs output:
    Cd = 1.14867
    Cl = 0.939827
    Cm = 0

Time = 1997

smoothSolver:  Solving for Ux, Initial residual = 0.0158759, Final residual = 0.00131455, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00605029, Final residual = 0.000446912, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0316095, Final residual = 0.00272361, No Iterations 2
time step continuity errors : sum local = 6.31621e-06, global = 4.49215e-07, cumulative = 0.000200656
smoothSolver:  Solving for omega, Initial residual = 0.00046907, Final residual = 4.51689e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00512825, Final residual = 0.000303408, No Iterations 4
ExecutionTime = 740.26 s  ClockTime = 891 s

forces output:
    forces(pressure, viscous)((628.927 7684.96 2.27177e-15) (14.0771 3.65174 -5.07449e-18))
    moment(pressure, viscous)((-3842.48 314.464 275471) (-1.82587 7.03855 128.654))

forceCoeffs output:
    Cd = 1.1569
    Cl = 0.978326
    Cm = 0

Time = 1998

smoothSolver:  Solving for Ux, Initial residual = 0.0154559, Final residual = 0.00129072, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00593228, Final residual = 0.000445859, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0298766, Final residual = 0.00256894, No Iterations 2
time step continuity errors : sum local = 6.00456e-06, global = 3.05541e-07, cumulative = 0.000200962
smoothSolver:  Solving for omega, Initial residual = 0.000465651, Final residual = 4.52165e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00486797, Final residual = 0.000301362, No Iterations 4
ExecutionTime = 740.64 s  ClockTime = 892 s

forces output:
    forces(pressure, viscous)((520.223 7851.81 2.336e-15) (13.9439 3.74411 -5.15829e-18))
    moment(pressure, viscous)((-3925.91 260.111 281738) (-1.87205 6.97195 133.108))

forceCoeffs output:
    Cd = 1.16496
    Cl = 1.01662
    Cm = 0

Time = 1999

smoothSolver:  Solving for Ux, Initial residual = 0.0151284, Final residual = 0.00126767, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00580735, Final residual = 0.000445745, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0279414, Final residual = 0.00237774, No Iterations 2
time step continuity errors : sum local = 5.61149e-06, global = 1.95978e-07, cumulative = 0.000201158
smoothSolver:  Solving for omega, Initial residual = 0.000462446, Final residual = 4.52691e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00465002, Final residual = 0.000301046, No Iterations 4
ExecutionTime = 740.99 s  ClockTime = 892 s

forces output:
    forces(pressure, viscous)((413.176 8014.36 2.40016e-15) (13.8087 3.83569 -5.36615e-18))
    moment(pressure, viscous)((-4007.18 206.588 287786) (-1.91784 6.90434 137.402))

forceCoeffs output:
    Cd = 1.17267
    Cl = 1.05409
    Cm = 0

Time = 2000

smoothSolver:  Solving for Ux, Initial residual = 0.0148846, Final residual = 0.00124765, No Iterations 4
smoothSolver:  Solving for Uy, Initial residual = 0.00568015, Final residual = 0.000446866, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.0257257, Final residual = 0.0021881, No Iterations 2
time step continuity errors : sum local = 5.21265e-06, global = 8.4432e-08, cumulative = 0.000201242
smoothSolver:  Solving for omega, Initial residual = 0.00045956, Final residual = 4.53259e-05, No Iterations 4
smoothSolver:  Solving for k, Initial residual = 0.00447416, Final residual = 0.000302495, No Iterations 4
ExecutionTime = 741.69 s  ClockTime = 893 s

forces output:
    forces(pressure, viscous)((308.845 8170.8 2.46409e-15) (13.6723 3.9266 -5.67718e-18))
    moment(pressure, viscous)((-4085.4 154.422 293552) (-1.9633 6.83616 141.523))

forceCoeffs output:
    Cd = 1.17989
    Cl = 1.09033
    Cm = 0

End

Finalising parallel run

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