[sliderhuang]

Hi guys, I am a new OpenFoam user, I am trying to use interFoam to simulate a binary droplet head-on collision in an axisymmetry scheme. The results showed that when I used denser mesh, droplets may deform more severely than the looser case before the collision. The images is attached as examples. And in my experimental experiences, droplets (without oscillation) may not deform before they touched each others, so I wonder what setting mistakes I've done in the setting process. Looking forward for someone's help !! The input is as below:

drop radius:0.118 mm
start position: (0,0,0.6)mm
velocity: (0,0,-1.25 )m/s

liquid: sigma-0.026(kg/s^2), density-758(kg/m^3), nu-2.81e-6(m^2/s)
air:density-1(kg/m^3), nu-1.48e-5(m^2/s)
gravity:0 (m/s^2)

boundary face(except symmtry axis face):
P: total pressure, uniform=101325
U: pressureInletOutletVelocity, uniform=(0 0 0)

domain 1
r-direction: 0.5 mm/200 cells
z-direction: 1.8 mm/720 cells

domain 2
r-direction: 0.5 mm/800 cells
z-direction: 1.8 mm/2880 cells

one of the setting file:

blockMeshDict

\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 0.001;

vertices
(
(0 0 0)
(0.4995 0.0218 0)
(0.4995 0.0218 1.8)
(0 0 1.8)
(0.4995 -0.0218 0)
(0.4995 -0.0218 1.8)
);

blocks
(
hex (0 4 1 0 3 5 2 3) (200 1 720) simpleGrading (1 1 1)
);


boundary
(
front
{
type wedge;
faces
(
(0 1 2 3)
);
}
back
{
type wedge;
faces
(
(0 3 5 4)
);
}
atmosphere
{
type patch;
faces
(
(1 2 5 4)
(3 5 2 3)
(0 4 1 0)
);
}

axis
{
type symmetryPlane;
faces
(
(0 3 3 0)
);
}
);
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


setFieldsDict

\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object setFieldsDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



regions
(
sphereToCell
{
centre (0.00 0.00 0.0006);
radius 0.000118;
fieldValues
(
volScalarFieldValue alpha.water 1
volVectorFieldValue U (0 0 1.25)
);
}

sphereToCell
{
centre (0.00 0.00 0.0012);
radius 0.000118;
fieldValues
(
volScalarFieldValue alpha.water 1
volVectorFieldValue U (0 0 -1.25)
);
}
);

defaultFieldValues
(
volScalarFieldValue alpha.water 0
);

fvScheme

\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
}

divSchemes
{
div(rhoPhi,U) Gauss linearUpwind grad(U);
div(phi,alpha) Gauss vanLeer;
div(phirb,alpha) Gauss linear;
div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

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

fvSolution

\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
"alpha.water.*"
{
nAlphaCorr 2;
nAlphaSubCycles 1;
cAlpha 1;

MULESCorr yes;
nLimiterIter 3;

solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-8;
relTol 0;
}

pcorr
{
solver PCG;
preconditioner DIC;
tolerance 1e-5;
relTol 0;
}

p_rgh
{
solver PCG;
preconditioner DIC;
tolerance 1e-07;
relTol 0.05;
}

p_rghFinal
{
$p_rgh;
relTol 0;
}

U
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-06;
relTol 0;
}
}

PIMPLE
{
momentumPredictor no;
nOuterCorrectors 1;
nCorrectors 3;
nNonOrthogonalCorrectors 0;
}

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

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

alpha.water
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object alpha.water;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 0 0 0 0 0 0];

internalField uniform 0;

boundaryField
{
front
{
type wedge;
}
back
{
type wedge;
}

axis
{
type symmetryPlane;
}
atmosphere
{
type inletOutlet;
inletValue uniform 0;
value uniform 0;
}

}

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

U
\*---------------------------------------------------------------------------*/
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
{
front
{
type wedge;
}
back
{
type wedge;
}


axis
{
type symmetryPlane;
}
atmosphere
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}

}


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

p_rgh
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
front
{
type wedge;
}
back
{
type wedge;
}
atmosphere
{
type totalPressure;
p0 uniform 101325;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 101325;
}

axis
{
type symmetryPlane;
}
}


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

Thx everyone again !!