[yang.l]

hi guys,

i was trying to simulate the settling process in a cylinder with driftfluxfoam, but now i have problem, the bottom is set to be a wall, during the process, the alpha.sludge in the bottom should increse with time. In the initial process, it did incresed, but then slowly decresed, it seems that, there is no wall in the bottom, and the sludge didnt concentrated at the bottom, but continues to sink.
There is another probelm, the alpha.sludge at the top should be 0 over 30 min, but it changes small in this entire process.
I guess ,there is something wrong with the set-up of boundary conditions, but i cant figure it out.
here is my boundary conditions:
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object alpha.sludge;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 0 0 0 0 0 0];

internalField uniform 0.00134;

boundaryField
{
cylinder
{
type zeroGradient;
}

bottom
{
type zeroGradient;
}

top
{
type zeroGradient;
}
}

FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (0 0 0);

boundaryField
{
cylinder
{
type noSlip;
}
bottom
{
type fixedValue;
value uniform (0 0 0);
}

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

}

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

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

internalField uniform 0;

boundaryField
{
cylinder
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;
}

bottom
{
type fixedFluxPressure;
value uniform 0;
}

top
{
type fixedValue;
value uniform 0;
}

}

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

The result is shown in the image.

[yang.l]

here is my BlockMesh,
convertToMeters 1;

vertices
(
(0 0 0) // 0

(0.02048 0 0) // 1
(0.01617 0.01617 0) // 2
(0 0.02048 0) // 3
(-0.01617 0.01617 0) // 4
(-0.02048 0 0) // 5
(-0.01617 -0.01617 0) // 6
(0 -0.02048 0) // 7
(0.01617 -0.01617 0) // 8

(0.03 0 0) // 9
(0.02121 0.02121 0) // 10
(0 0.03 0) // 11
(-0.02121 0.02121 0) // 12
(-0.03 0 0) // 13
(-0.02121 -0.02121 0) // 14
(0 -0.03 0) // 15
(0.02121 -0.02121 0) // 16

(0.02048 0 0.35368) // 17
(0.01617 0.01617 0.35368) // 18
(0 0.02048 0.35368) // 29
(-0.01617 0.01617 0.35368) // 20
(-0.02048 0 0.35368) // 21
(-0.01617 -0.01617 0.35368) // 22
(0 -0.02048 0.35368) // 23
(0.01617 -0.01617 0.35368) // 24

(0.03 0 0.35368) // 25
(0.02121 0.02121 0.35368) // 26
(0 0.03 0.35368) // 27
(-0.02121 0.02121 0.35368) // 28
(-0.03 0 0.35368) // 29
(-0.02121 -0.02121 0.35368) // 30
(0 -0.03 0.35368) // 31
(0.02121 -0.02121 0.35368) // 32

(0 0 0.35368) // 33
);

blocks
(
hex (0 1 2 3 33 17 18 19) (10 10 175) simpleGrading (1 1 1)
hex (0 3 4 5 33 19 20 21) (10 10 175) simpleGrading (1 1 1)
hex (0 5 6 7 33 21 22 23) (10 10 175) simpleGrading (1 1 1)
hex (0 7 8 1 33 23 24 17) (10 10 175) simpleGrading (1 1 1)

hex (2 1 9 10 18 17 25 26) (10 5 175) simpleGrading (1 1 1)
hex (3 2 10 11 19 18 26 27) (10 5 175) simpleGrading (1 1 1)

hex (4 3 11 12 20 19 27 28) (10 5 175) simpleGrading (1 1 1)
hex (5 4 12 13 21 20 28 29) (10 5 175) simpleGrading (1 1 1)

hex (6 5 13 14 22 21 29 30) (10 5 175) simpleGrading (1 1 1)
hex (7 6 14 15 23 22 30 31) (10 5 175) simpleGrading (1 1 1)

hex (8 7 15 16 24 23 31 32) (10 5 175) simpleGrading (1 1 1)
hex (1 8 16 9 17 24 32 25) (10 5 175) simpleGrading (1 1 1)
);

edges
(
arc 9 10 (0.02598 0.015 0)
arc 10 11 (0.015 0.02598 0)
arc 11 12 (-0.015 0.02598 0)
arc 12 13 (-0.02598 0.015 0)
arc 13 14 (-0.02598 -0.015 0)
arc 14 15 (-0.015 -0.02598 0)
arc 15 16 (0.015 -0.02598 0)
arc 16 9 (0.02598 -0.015 0)

arc 25 26 (0.02598 0.015 0.35368)
arc 26 27 (0.015 0.02598 0.35368)
arc 27 28 (-0.015 0.02598 0.35368)
arc 28 29 (-0.02598 0.015 0.35368)
arc 29 30 (-0.02598 -0.015 0.35368)
arc 30 31 (-0.015 -0.02598 0.35368)
arc 31 32 (0.015 -0.02598 0.35368)
arc 32 25 (0.02598 -0.015 0.35368)
);

boundary
(
bottom
{
type wall;
faces
(
(0 3 2 1)
(0 5 4 3)
(0 7 6 5)
(0 1 8 7)

(1 2 10 9)
(2 3 11 10)
(3 4 12 11)
(4 5 13 12)
(5 6 14 13)
(6 7 15 14)
(7 8 16 15)
(8 1 9 16)
);
}

top
{
type patch;
faces
(
(33 17 18 19)
(33 19 20 21)
(33 21 22 23)
(33 23 24 17)

(18 17 25 26)
(19 18 26 27)
(20 19 27 28)
(21 20 28 29)
(22 21 29 30)
(23 22 30 31)
(24 23 31 32)
(17 24 32 25)
);
}

cylinder
{
type wall;
faces
(
(9 10 25 26)
(10 11 26 27)
(11 12 27 28)
(12 13 28 29)
(13 14 29 30)
(14 15 30 31)
(15 16 31 32)
(16 9 32 25)

);
}
);

mergePatchPairs
(
);

[decah]

Hi Yang,

I think issue is with your velocity boundary conditions. Rather than fixing the value at 0 at the top, try the following:

top
    {

	type            pressureInletOutletVelocity;
	value		uniform (0 0 0);
    }

    bottom
    {
        type            noSlip;
    }
    
    cylinder
    {
        type            noSlip;
    }

Hope this helps.