# pressure ratio simpleFoam boundary case/0/p

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 June 2, 2009, 07:43 pressure ratio simpleFoam boundary case/0/p #1 New Member   Join Date: May 2009 Posts: 14 Rep Power: 16 Hi Folks! I'm trying to calculate the inlet pressure of a test element, which represents a stepped seal labyrinth of a turboengine.This actually looks quite similar to a pipe (one Volume, inlet, outlet, wall). I want to compare these pressure results with experimental data files. The solver I use is simpleFoam, the velocity at the inlet is 10.4546m/s, the outlet pressure is constant (1bar) my problem seems to be very simple, but I'm struggling real hard with the boundary conditions in 0/p.. Due to the dimensions (N/mē), I also set the internalField + outlet value 1e5, but in that case, no velocity profile was visualized and the pressure values were not realistic. It should be a pressure ratio (inlet- outlet) of 1.07 Paraview shows negative pressure values, if I use the following configuration: dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { outlet { type fixedValue; value uniform 0; } wand { type zeroGradient; } inlet { type zeroGradient; } } The 0/U looks like: dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { outlet { type zeroGradient; } wand { type fixedValue; value uniform (0 0 0); } inlet { type fixedValue; value uniform (10.4546 0 0); } } Can u help me with this? If you know any case where I can see how it's done please let me know. I couldn't find anything.. thank u, Mitch

 June 2, 2009, 08:12 #2 Senior Member     Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 20 Hello Mitch, Due to the fact that you're using an incompressible flow solver, the pressure dimension is not N/m2 but m2/s2 (the pressure is divided by the density). Moreover, the computed value of the pressure is a relative one (p_calculated = p-p_reference) so there is no unphysical behavior if you get negative pressures, it just means that the absolute pressure happens to be smaller than the reference pressure you wrote in the dictionary. I hope this is helpful, Dragos

 June 29, 2009, 18:43 #3 New Member   Join Date: May 2009 Posts: 14 Rep Power: 16 Thanks for the answer. You're right, I didn't consider that..

 Tags boundary condition, pipe, pressure ratio, simplefoam, velocity inlet