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-   -   icoFOAM don't calculate right (http://www.cfd-online.com/Forums/openfoam-solving/110372-icofoam-dont-calculate-right.html)

 whyingwang December 10, 2012 03:03

icoFOAM don't calculate right

Hello FOAM users,
Recently I use icoFOAM to claculate a channel flow,like the picture show,
I use ICEM to make a struct-mesh,see below.
http://h.hiphotos.baidu.com/album/s%...44ac34828a.jpg
Later,I use icoFOAM,one of the two pipes is inlet another is outlet.
But I failed.After 2000 steps,It shows that the velocity still stay at inlet,like the picture shows.The red only can be see at one pipe.
http://b.hiphotos.baidu.com/album/s%...f9d62aa08a.jpg
Please,Who can tell me why?
Thanks.

 vainilreb December 10, 2012 03:38

My first quick guess would be:

You set the channel walls to "wall" - which usually means the velocity at the boundary is "uniform (0 0 0)". Have you had a look at a cross-section through the channel? There might be high flow velocities in the middle of the channel. This is what you see at the inlet cross-section, too. ;)

 whyingwang December 10, 2012 04:06

Quote:
 Originally Posted by vainilreb (Post 396589) My first quick guess would be: You set the channel walls to "wall" - which usually means the velocity at the boundary is "uniform (0 0 0)". Have you had a look at a cross-section through the channel? There might be high flow velocities in the middle of the channel. This is what you see at the inlet cross-section, too. ;)
Thanks For your answer.But, actually It's velocity at the middle of the channel is nearly zero,see below . My inlet velocity is 1.9m/s.
http://b.hiphotos.baidu.com/album/s%...b1ca137074.jpg

 vainilreb December 10, 2012 04:33

Well, at least there IS a flow profile. Please post your BC files, especially p and U! ;)

 whyingwang December 10, 2012 08:34

Quote:
 Originally Posted by vainilreb (Post 396602) Well, at least there IS a flow profile. Please post your BC files, especially p and U! ;)
OK，Here is my 0 time files
----------------------------------------------------------------------------------------------------------------------------
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 0;

boundaryField
{
inletWall
{
}
outletWall
{
type fixedValue;
value uniform 101.630;
}
upWalls
{
}
inPipe
{
}
outPipe
{
}
downWalls
{
}
outerWalls
{
}
}
---------------------------------------------------------------------------------------------------------------------------
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform (0 0 0);

boundaryField
{
inletWall
{
type fixedValue;
value uniform (0 0 -1.9099);
}
outletWall
{
}
upWalls
{
type fixedValue;
value uniform (0 0 0);
}
inPipe
{
type fixedValue;
value uniform (0 0 0);
}
outPipe
{
type fixedValue;
value uniform (0 0 0);
}
downWalls
{
type fixedValue;
value uniform (0 0 0);
}
outerWalls
{
type fixedValue;
value uniform (0 0 0);
}
}

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

 vainilreb December 10, 2012 08:54

Okay, first thing I see is your inlet velocity.
(0 0 -1.9099) points in negative Z-direction which is, according to the coordinate system, orthogonal to your inlet patch - because Y is the vertical axis!
Try (0 -1.9099 0).

And why is your pressure at the outlet so much higher than in the internal field? Uniform 0 for internal field means you've got ambient pressure level in the internal. Uniform 101.630 at the outlet means you've got 101.63 N/mē overpressure at the outlet. This probably won't work if you want the fluid to leave your channel at this patch. I suggest you try uniform 0 there, too.

Hope this will fix your problem.

 whyingwang December 10, 2012 09:42

Quote:
 Originally Posted by vainilreb (Post 396649) Okay, first thing I see is your inlet velocity. (0 0 -1.9099) points in negative Z-direction which is, according to the coordinate system, orthogonal to your inlet patch - because Y is the vertical axis! Try (0 -1.9099 0). And why is your pressure at the outlet so much higher than in the internal field? Uniform 0 for internal field means you've got ambient pressure level in the internal. Uniform 101.630 at the outlet means you've got 101.63 N/mē overpressure at the outlet. This probably won't work if you want the fluid to leave your channel at this patch. I suggest you try uniform 0 there, too. Hope this will fix your problem.
yes,Thank you Very Much,vainilreb.
I get the reason now.

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