CFD Online Discussion Forums - Water drop falling too slow

I wanted to sim the falling of a drop into water. Nothing complicated (!), I just followed the dam tutorial.

The problem is that the drop is falling too slow (from steady: 50mm in 1.2s) and the velocity is not increasing.

Please see enclosed pictures about alpha and U.

Here is checkmesh result:

Code:

Mesh stats

    points:           1520469

    faces:            4461972

    internal faces:   4430208

    cells:            1470988

    boundary patches: 3

    point zones:      0

    face zones:       0

    cell zones:       0

Overall number of cells of each type:

    hexahedra:     1448660

    prisms:        0

    wedges:        0

    pyramids:      0

    tet wedges:    0

    tetrahedra:    0

    polyhedra:     22328

Checking topology...

    Boundary definition OK.

 ***Total number of faces on empty patches is not divisible by the number of cells in the mesh. Hence this mesh is not 1D or 2D.

    Cell to face addressing OK.

    Point usage OK.

    Upper triangular ordering OK.

    Face vertices OK.

    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...

    Patch               Faces    Points   Surface topology                  

    defaultFaces        15876    16169    ok (non-closed singly connected)  

    atmos               0        0        ok (empty)                        

    wall                15888    16181    ok (non-closed singly connected)  

Checking geometry...

    Overall domain bounding box (0 0 0) (0.2 0.2 0.2)

    Mesh (non-empty, non-wedge) directions (0 0 0)

    Mesh (non-empty) directions (0 0 0)

    All edges aligned with or perpendicular to non-empty directions.

    Boundary openness (2.34348e-015 2.34348e-015 -2.43385e-014) OK.

    Max cell openness = 1.71543e-016 OK.

    Max aspect ratio = 0 OK.

    Minumum face area = 6.93889e-007. Maximum face area = 1.11156e-005.  Face area magnitudes OK.

    Min volume = 5.7801e-010. Max volume = 3.70593e-008.  Total volume = 0.008.  Cell volumes OK.

    Mesh non-orthogonality Max: 25.2571 average: 3.5358

    Non-orthogonality check OK.

    Face pyramids OK.

    Max skewness = 0.333721 OK.

    Coupled point location match (average 0) OK.

Mesh OK.

This are my BC:

U

Code:

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField

{

    atmos

    {

        type            pressureInletOutletVelocity;

        value           uniform (0 0 0);

    }

 

    wall

    {

        type            fixedValue;

        value           uniform (0 0 0);

    }

 

    defaultFaces

    {

        type            fixedValue;

        value           uniform (0 0 0);

    }

}

p_rgh

Code:

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 0;

boundaryField

{

    atmos

    {

        type            totalPressure;

        p0              uniform 0;

        U               U;

        phi             phi;

        rho             rho;

        psi             none;

        gamma           1;

        value           uniform 0;

    }

 

    wall

    {

        type            buoyantPressure;

        value           uniform 0;

    }

 

    defaultFaces

    {

        type            buoyantPressure;

        value           uniform 0;

    }

}

alpha (to be modified with setfields):

Code:

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField

{

    wall

    {

        type            zeroGradient;

    }

    atmos

    {

        type            inletOutlet;

        inletValue      uniform 0;

        value           uniform 0;

    }

    defaultFaces

    {

        type            empty;

    }

}

The box domain is 0.2x0.2x0.2m.
The water is a sphere with radius=8mm.

Flow is laminar.

g is defined as:

Code:

 

dimensions      [0 1 -2 0 0 0 0];

value           ( 0 0 -9.81 );

transportProperties is the tutorial one:

Code:

phase1

{

    transportModel  Newtonian;

    nu              nu [ 0 2 -1 0 0 0 0 ] 1e-06;

    rho             rho [ 1 -3 0 0 0 0 0 ] 1000;

    CrossPowerLawCoeffs

    {

        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;

        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;

        m               m [ 0 0 1 0 0 0 0 ] 1;

        n               n [ 0 0 0 0 0 0 0 ] 0;

    }

    BirdCarreauCoeffs

    {

        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515;

        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;

        k               k [ 0 0 1 0 0 0 0 ] 99.6;

        n               n [ 0 0 0 0 0 0 0 ] 0.1003;

    }

}

phase2

{

    transportModel  Newtonian;

    nu              nu [ 0 2 -1 0 0 0 0 ] 1.48e-05;

    rho             rho [ 1 -3 0 0 0 0 0 ] 1;

    CrossPowerLawCoeffs

    {

        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 1e-06;

        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;

        m               m [ 0 0 1 0 0 0 0 ] 1;

        n               n [ 0 0 0 0 0 0 0 ] 0;

    }

    BirdCarreauCoeffs

    {

        nu0             nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515;

        nuInf           nuInf [ 0 2 -1 0 0 0 0 ] 1e-06;

        k               k [ 0 0 1 0 0 0 0 ] 99.6;

        n               n [ 0 0 0 0 0 0 0 ] 0.1003;

    }

}

sigma           sigma [ 1 0 -2 0 0 0 0 ] 0.07;

The sim is running without any problem. Courant Number is well respected and residuals are ok.

It seems phase2 is too viscous...

I'm sure it's a silly mistake of mine but where ? Please be kind if you know it :o

Thanks.