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-   -   trouble with the boundary conditions(natural convection) (http://www.cfd-online.com/Forums/openfoam/107513-trouble-boundary-conditions-natural-convection.html)

Ank September 29, 2012 06:01

trouble with the boundary conditions(natural convection)
 
1 Attachment(s)
Hey guys,

I am using Openfoam 2.0, I am simulating a cylinder with some tubes inside it carrying steam. My cylinder is open from bottom and top so that air enters from bottom and goes out from the top by getting heated up by the steam. I am using buoyantBoussinesqPimpleFoam solver. I am pasting my boundary conditions here,

0/U:

internalField uniform (0 0 0);

boundaryField
{

inlet
{
type zeroGradient;


}

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

outlet
{
type zeroGradient;

}

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

symmetry
{
type symmetryPlane;
}

}


0/p_rgh:

internalField uniform 0;

boundaryField
{
inlet
{
type zeroGradient;

}
pipe
{
type buoyantPressure;
rho rhok;
value uniform 0;
}

outlet
{
type buoyantPressure;
rho rhok;
value uniform 0;

}

wall
{
type buoyantPressure;
rho rhok;
value uniform 0;
}

symmetry
{
type symmetryPlane;
}
}


0/p:

boundaryField
{

inlet
{
type calculated;
value $internalField;

}
pipe
{
type calculated;
value $internalField;
}

outlet
{
type calculated;
value $internalField;
}

wall
{
type calculated;
value $internalField;
}

symmetry
{
type symmetryPlane;
}

}

0/T:

internalField uniform 300;

boundaryField
{

inlet
{
type zeroGradient;
}
pipe
{
type fixedValue;
value uniform 413;
}
outlet
{
type zeroGradient;
}
wall
{
type zeroGradient;
}

symmetry
{
type symmetryPlane;
}
}

all other parameters are zeroGradient at inlet and outlet, and fixed value at the walls.
I am getting a good flow patters and velocity vectors are in right direction but I am getting a problem with the temperature and it is going below 298 K for air, which is non physical for this case.

Can you please help me in choosing the right boundary conditions. I am attaching some snapshots with this thread.

Thank You

tian September 30, 2012 14:04

2 Attachment(s)
Hi,

I think you should set the temperatur field for the inlet condition also.

I test it with a similar case and it was working...

Bye
Thomas

Ank October 1, 2012 03:47

Hey thanks for your reply,
can you please tell me what other boundary conditions you used for the pressure velocity, k , epsilon etc..I cant see your attachment properly.

Ankur

tian October 1, 2012 07:04

Hi Ankur,

i used the HVAC Tool to build a similar case quickly (file ending *.hvac). I take your BC. I only changed the inlet BC as fixedValue for temperature.

Bye
Thomas

Ank October 1, 2012 07:28

hey thanks alot again..
I used pressureInletOutletVelocity also along with the fixed temperature bc..is it right to use it here? Now my temperature is coming in the right range..

Thanks
Ankur

tunkers October 2, 2012 12:46

Hello Ankur, You might find this thread helpful:

http://www.cfd-online.com/Forums/ope...condition.html

Ank October 3, 2012 03:50

hey Thanks Eric, I will run a test case with this BC also, I have not given total pressure ever as my BC. I am running with atmospheric on inlet and zeroGradient on outlet. For k and epsilon i have given zeroGradient on inlet and outlet.


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