[ABS_abbas]

Hi everyone,
I simulate a transient and in-compressible flow inside a PEM fuel cell and I don't know, how to enforce the " PRESSURE INLET " boundary condition?
my domain is a rectangular channel that fluid flows into the channel.
my domain is like a lid driven cavity. my inlet pressure is known but my velocity inlet (u_in) is unknown. other boundary is wall.
my domain have just one inlet boundary and 3 wall boundary. with no outlet boundary.


fluid(fuel) comes into channel and it is consumed(we have a sink inside channel that consume the fuel that comes to channel).there isn't any outlet.
I should set P_in=1 atm in inlet, but I heard that in SIMPLE we don't have absolute pressure.
what should I do?

[piu58]

Pressure driven flows are problematic. If you simply set a pressure difference this stay forever and drives the flow more and more until the system explodes. In reality, there is a balance between pressure difference and pressure resistance at a special flow.

I would start with velocity driven flow, set the pressure at the outflow to zero and change the inlet velocity until the measured / calculated pressure there is in the near of your known value.

[sheaker]

I think I succeed in pressure driven flow. Check this boundary condition.
For p:

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

internalField   uniform 101320;

boundaryField
{
    inlet
    {
        type            totalPressure;
        p0              uniform 101325;
        U               U;
        phi             phi;
        rho             none;
        psi             none;
        gamma           1;
        value           uniform 101325;
    }

    outlet
    {
        type            fixedValue;
        value           uniform 101320;
    }


    wall
    {
        type            zeroGradient;
    }

    defaultFaces
    {
    type        empty;
    }
}

For U:

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

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type            pressureInletVelocity;
        value           uniform (0 0 0);
    }

    outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }

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

Let me know if it works for You, please.
Have a nice day.
Sheaker

[ABS_abbas]

Originally Posted by piu58

Pressure driven flows are problematic. If you simply set a pressure difference this stay forever and drives the flow more and more until the system explodes. In reality, there is a balance between pressure difference and pressure resistance at a special flow.

I would start with velocity driven flow, set the pressure at the outflow to zero and change the inlet velocity until the measured / calculated pressure there is in the near of your known value.

thank you Mr. Pilz. but I think you didn't understand my problem.my case doesn't have outlet boundary. just one inlet and other boundaries are wall.
so I can't have an outlet boundary. I have to set pressure inlet in Inlet of domain.
information of my simulation:
transient, flow is in-compressible, using finite volume (SIMPLE algorithm), with Collocated grid.
I heard that in in-compressible flow, I have to set the pressure of a point to zero as a reference pressure point. is it correct?

[ttsurvase]

I am replying to your first query, inletOutlet Boundary condition is employed when user is not sure of flow direction. In inletOutlet BC, two boundary conditions are used. 1.zero Gradient, if flow is going out of domain. 2. fixedValue Bc, if flow is reversing. To accomodate both. I will explain the use using following example:
U: outlet { type inletOutlet; inletValue uniform (-2 0 0); value (0 0 0); }
So in the case, inletValue uniform (-2 0 0) is used for flow reversal phenomenon. While, if flow is going out, value 0 tells solver to use zeroGradient BC.

For more information, I will share the link of tutorial:
https://www.cfd.at/sites/default/fil...le%20Eight.pdf