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Old   September 20, 2011, 21:59
Default icoFoam continuity error
  #1
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Debb
Join Date: Sep 2011
Location: Toronto, Canada
Posts: 19
Rep Power: 5
tellico is on a distinguished road
after many many attempts I got my blockMesh file to work and now I'm having trouble running icoFoam,

the application is a funny shaped tank with a large inlet tunnel on one side and and outlet sump in the base, I can get icoFoam to run without any issues if I specify inlet and outlet initial values of (0 0 0) but when I try to add in an actual inlet flow (-0.7 0 0) and outlet flow of (0 0 -0.1) I get an error message saying that:
"Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 1e-300
Specified mass inflow : 0
Specified mass outflow : 0.06
Adjustable mass outflow : 0"
I'm not sure if I've specifying the correct inlet and outlet vectors, and am I correct in specifying zerogradient p for the outlet since I know there will be a pressure at the outlet due to the water column?
any help would be much appreciated

blockMesh file is the following (note: a few lines were giving me trouble so I disabled them for now and will try to fix them later)
convertToMeters 1;

vertices
(
(2.5 0 0) // point 0
(2.5 1 0)
(2.5 2.5 0)
(2.5 4 0)
(2.5 5.5 0)
(4.5 4 0) // point 5
(5.5 2.5 0)
(6 1 0)
(6 0 0)
(5.5 -2.25 0)
(2.5 -2 0) // point 10
(2.5 -4 0)
(2.5 -5.5 0)
(1.5 -4 0)
(1.5 -2 0)
(0 -2 0) // point 15
(0 -4 0)
(-1.5 -4 0)
(-2.5 -5.5 0)
(-4.5 -4 0)
(-5.5 -2 0) // point 20
(-1.5 -2 0)
(2.5 0 3)
(2.5 1 3)
(2.5 2.5 3)
(2.5 4 3) // point 25
(2.5 5.5 3)
(4.5 4 3)
(5.5 2.5 3)
(6 1 3)
(6 0 3) // point 30
(5.5 -2.25 3)
(2.5 -2 3)
(2.5 -4 3)
(2.5 -5.5 3)
(1.5 -4 3) // point 35
(1.5 -2 3)
(0 -2 3)
(0 -4 3)
(-1.5 -4 3)
(-2.5 -5.5 3) // point 40
(-4.5 -4 3)
(-5.5 -2 3)
(-1.5 -2 3)


);

blocks
(
//hex (5 4 26 27 25 3 3 25) (1 1 1) simpleGrading (1 1 1) //block 0
hex (6 5 3 2 28 27 25 24) (10 10 10) simpleGrading (1 1 1)
hex (7 6 2 1 29 28 24 23) (10 10 10) simpleGrading (1 1 1)
hex (8 7 1 0 30 29 23 22) (10 10 10) simpleGrading (1 1 1)
hex (9 8 0 10 31 30 22 32) (10 10 10) simpleGrading (1 1 1) // block 5
hex (11 33 31 9 10 32 32 10) (10 10 10) simpleGrading (1 1 1)
hex (12 34 31 9 11 33 33 11) (10 10 10) simpleGrading (1 1 1)
hex (13 35 34 12 11 33 33 11) (10 10 10) simpleGrading (1 1 1)
hex (13 11 10 14 35 33 32 36) (10 10 10) simpleGrading (1 1 1)
hex (13 14 15 16 35 36 37 38) (10 10 10) simpleGrading (1 1 1)
hex (16 15 21 17 38 37 43 39) (10 10 10) simpleGrading (1 1 1)
hex (17 21 20 19 39 43 42 41) (10 10 10) simpleGrading (1 1 1)
//hex (17 19 41 39 18 40 40 18) (1 1 1) simpleGrading (1 1 1)
hex (12 13 17 18 34 35 39 40) (10 10 10) simpleGrading (1 1 1)
);

edges
(

);

patches
(
patch inlet
(
(9 8 30 31)
)


patch outlet

(
(17 13 12 18)
)


patch walls
(
(29 30 8 7)
(28 29 7 6)
(27 28 6 5)
//(26 27 5 4)
(5 3 25 27)
//(25 26 4 3)
(24 25 3 2)
(23 24 2 1)
(22 23 1 0)
(32 22 0 10)
(32 36 14 10)
(37 36 14 15)
(43 37 15 21)
(42 43 21 20)
(41 42 20 19)
//(40 41 19 18)
//(19 17 39 41)
(31 34 12 9)

)
);

mergePatchPairs
(
);

P file is:
dimensions [0 2 -2 0 0 0 0];

internalField uniform 1;

boundaryField
{
walls
{
type zeroGradient;
}

inlet
{
type zeroGradient;

}
outlet
{
type zeroGradient;
}
defaultFaces
{
type zeroGradient;
}
}

U file is:
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);


boundaryField
{
walls
{
type fixedValue;
value uniform (0 0 0);
}

inlet
{
type fixedValue;
value uniform (-0.7 0 0);

}

outlet
{
type fixedValue;
value uniform (0 0 -0.1);

}

defaultFaces
{
type zeroGradient;
}
}
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Old   September 21, 2011, 04:43
Default velocity boundary conditions
  #2
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supercommandodhruv
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Posts: 57
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Hey tellico,

Why don't you try to have a boundary condition which is having fixed value of velocity at the inlet and pressure at the outlet. You can assign zeroGradient boundary condition for U at the outlet and p at the inlet.
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