CFD Online Discussion Forums - Total pressure boundary condition

Hi everybody,

I'm looking for a way to impose the total pressure as inlet boundary condition, instead than a velocity.

My first try was to set the inlet with a fixedValue in both pressure and velocity, but this way the simulation gives bad results: even if i'm working with an incompressible flow, the flow rate decrease during the simulation. This should be obviously impossible in incompressible flow, but it happens.

After some research I found a pressure boundary condition called, indeed, totalPressure.
http://www.openfoam.org/docs/cpp/

Code:

    myPatch

 {

 type            totalPressure;

 U               U;

 phi             phi;

 rho             none;

 psi             none;

 gamma           1.4;

 p0              uniform 1e5;

 }

The problem is that I don't know what to write in the 0/U myPatch subDict. Should i set a fixedValue? Shouldn't it be free to vary (increasing when p decrease and vice versa) ?

What kind of BC do I have to set in the U file?
Do you have other advices about this topic?

Thank you very much,
Luca