[t.oliveira]

Dear all,

I would like to impose the following boundary conditions for the incompressible flow in a channel.

The pressures are known at the inlet and at the outlet.
The velocity boundary field in the inlet is equal to the velocity boundary field at the outlet. They can be non-uniform.

For the pressure I am using ./0/p:

inlet
{
type fixedValue;
value uniform 1;
}
outlet
{
type fixedValue;
value uniform 0;
}

For the velocity, I can't find the appropriate boundary condition. Could you please advise me on that?

Best wishes,

Thomas

[jherb]

If you specify velocities (fixedValue) at both inlet and outlet as well as pressure on both, you will (very likely) run into numerical instabilities.

Normal advice is to use fixedValue for pressure at the outlet and zeroGradient at the inlet. For the velocity it is the other way around: fixedValue at inlet and zeroGradient (or inletOutlet) at the outlet.

[t.oliveira]

Dear jherb,

I don't want to specify fixedValue for velocities, but to impose that the velocity boundary field in the inlet be equal to the velocity boundary field at the outlet.

Best wishes,
Thomas

[jherb]

Do you mean cyclic boundary conditions?

[t.oliveira]

Yes, but just for the field U, not for every field.

[jherb]

Have you seen these threads:
http://www.cfd-online.com/Forums/ope...et-outlet.html
http://www.cfd-online.com/Forums/ope...tml#post440282
http://www.cfd-online.com/Forums/ope...sure-drop.html