[ehsanshams]

hi,
I am trying to solve flow in a horizontal duct with inflow/outflow and constant temperature walls (top and bottom). I tried to solve it using buoyantPimpleFoam. I am not sure what I am doing wrong in my boundary conditions that give me unreasonable results.

I will appreciate any helpful comments.

my inlet BCs:

U:
inlet
{
type surfaceNormalFixedValue;
refValue uniform -0.01;
}

T:
inlet
{
type zeroGradient;
}

p:
inlet
{
type calculated;
value $internalField;
}

p_rgh:
inlet
{
type fixedValue;
value uniform 1e5;
}

[romant]

Originally Posted by ehsanshams

hi,
I am trying to solve flow in a horizontal duct with inflow/outflow and constant temperature walls (top and bottom). I tried to solve it using buoyantPimpleFoam. I am not sure what I am doing wrong in my boundary conditions that give me unreasonable results.

I will appreciate any helpful comments.

my inlet BCs:

U:
inlet
{
type surfaceNormalFixedValue;
refValue uniform -0.01;
}

T:
inlet
{
type zeroGradient;
}

p:
inlet
{
type calculated;
value $internalField;
}

p_rgh:
inlet
{
type fixedValue;
value uniform 1e5;
}

For you temperature you should define an inlet temperature, you do have an temperature of the flow that comes in, don't you?

so for T inlet BC, I would suggest

inlet
{
type fixedValue;
value uniform 293; // in case it is room temperature, 
}

[ehsanshams]

Roman,
Thank you for reply.
I had already tested it with defined temperature and it would not help. The problem is I get reverse flow at inlet and also very large pressure inside the domain.
Now, I define p_rgh, T, and U as a constant value (at inlet), and still get a wrong answer.

Does anyone know what excatly the surfaceNormalFixedValue does at the inlet?
How can I learn the way openfoam handles boundary conditions?

Thank you,

[romant]

Inlet conditions

U:
inlet
{
type fixedValue;
value uniform (1 0 0);
}

p_rgh:
inlet
{
type buoyantPressure;
rho rhok;
value uniform 1e5;
}
T:
inlet
{
type fixedValue;
value uniform 293;
}

outlet conditions

U:
outlet
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}

p_rgh:
{
type fixedValue;
rho rhok;
value uniform 1e5;
}

T:
outlet
{
type zeroGradient;
}

[ehsanshams]

thanks Roman,
I tried this and worked well:

p_rgh:
-----------
inlet
{
type zeroGradient;
}

outlet
{
type fixedValue;
value uniform 1e5;
}

U:
--------
inlet
{
type surfaceNormalFixedValue;
refValue uniform -0.01;
}

outlet
{
type zeroGradient;
}

what does rho rhok; mean?

does it matter if use fixedValue instead of buoyantPressure for p_rgh at outlet?

thank you

[romant]

Originally Posted by ehsanshams

thanks Roman,
what does rho rhok; mean?

does it matter if use fixedValue instead of buoyantPressure for p_rgh at outlet?

buoyantPressure for p_rgh is also a zeroGradient boundary condition, but especially designed for buoyantFlows.

The description from OF for buoyantPressure is

Description
    Set the pressure gradient boundary condition appropriately for buoyant flow.

    If the variable name is "pd" assume it is p - rho*g.h and set the gradient
    appropriately.  Otherwise assume the variable is the static pressure.