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Old   December 1, 2010, 10:29
Question Pressure inlet BC
  #1
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Hi,
I'm a new openfoam user. I think my problem has already been discussed, but I didn't know why my calculation doesn't work...
I simulate a laminar flow between two "wavy" surfaces and I want apply a pressure BC at inlet and outlet.

So I use the following options :
for U:
boundaryField
{
inlet
{
type pressureInletVelocity;
value uniform (0 0 0);
}

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

outlet
{
type zeroGradient;
}
}

and for p:
boundaryField
{
inlet
{
type fixedValue;
value uniform 10;
}

wall
{
type zeroGradient;
}

outlet
{
type fixedValue;
value uniform 0;
}
}

Whatever the time step, calculations don't converge (the courant number increases after several iterations). I use the icoFoam solver.
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Old   December 2, 2010, 03:24
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  #2
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Masashi Ohbuchi
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Hi,
I've also tested for tutorial "icoFoam/elbow" with modifying boundary condition as follows.

0/U file
velocity-inlet-5
{
type pressureInletVelocity;
value uniform (1 0 0);
}

0/p file
velocity-inlet-5
{
type fixedValue;
value uniform 10;
}

And the simulation was completed and no error.
I suppose the problem might be elsewhere, such as fvSolution.
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Old   December 2, 2010, 07:36
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Nakul
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Hi,
I think that maybe your flux value should not be zero at inlet. Some finite velocity might be required at inlet.

If this is not the case then you may post your case here in order to get proper advice.
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Old   December 2, 2010, 08:11
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Masashi Ohbuchi
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I've tried again with following settings,

0/U

velocity-inlet-5
{
type pressureInletVelocity;
value uniform (0 0 0);
}

But, no error was occurred.
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Old   December 2, 2010, 08:17
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Cedric Van Holsbeke
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You have fixed static pressures at inlet and outlet. This is physically impossible.

At the inlet, you need a apply a total pressure (totalPressure boundary condition) and at the outlet a static pressure (fixedValue).
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Old   December 2, 2010, 12:39
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thanks for your replies.

Cedric, I don't see why a static pressure is not physical. If we consider an infinite pressurized vessels at inlet ?

If I apply a totalPressure at inlet, calculations converge but I don't have a constant static pressure. Moreover, results are little bit strange. I have a negative pressure p at inlet...

I'd like to have a constant pressure at inlet and at outlet to identify a darcy like law : q=k*(p_inlet - p_outlet), q being the mass flow rate and k a constant.

I don't really understand how the totalPressure BC work. Can you give me the meaning of all the parameters :

{
type totalPressure;
p0 uniform 1e3;
U U;
rho none;
psi none;
gamma 1;
value uniform 1e3;
}

thanks
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