# potentialFOAM with non-zero pressure @outlet

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 November 13, 2009, 09:23 potentialFOAM with non-zero pressure @outlet #1 New Member   anonymous Join Date: Nov 2009 Location: Switzerland Posts: 8 Rep Power: 10 Hi everyone, recently i tried to use potentialfoam for getting a better initial-velocity field for further simulations. But i made the a strange, totally unphysical (or at least i think so) observation. Setting the value of the pressure at the outlet to let's say 100000 m^2/s^2 (so 100kPa for a fluid with 1 kg/m^3) leads to a incredibly high max. velocity. I only get good results with p=0 @outlet. First i thought that sth is wrong with my settings. But then i observed the same effect in the tutorial case pitzDaily. So with: outlet { type fixedValue; value uniform 0; } i obtain a max. velocity of about 27m/s . But with: outlet { type fixedValue; value uniform 100000; } the max velocity is 1e6 m/s . As far as i know the velocity in a potential flow shouldn't be affected by the reference value of the pressure. Has sb an idea what's wrong? Is it eventually a bug in potentialFoam (i briefly looked in the code, but everything look nice to me) ? If sb experienced the same effect, is there a better work around than just shifting the pressure to zero (and back..)? thanks for your answers

 September 8, 2010, 00:27 #2 New Member     Darío Montes Join Date: Aug 2009 Location: Córdoba, Argentina Posts: 12 Rep Power: 10 Hello. I've tried something similar but I was looking for the U field. Have you used into an airfoil too? Regards

 September 12, 2010, 23:34 #3 New Member   Join Date: Aug 2010 Posts: 11 Rep Power: 9 What are your inlet boundary conditions? From the tutorials I think they're zeroGradient with an outlet boundary condition of 0. If I understand the problem, it's trying to have an initial pressure of 1e6 Pa at one end and 0 Pa at the other (the whole pressure is uniform 0 at t=0), which is understandably hard to solve. Do you know your inlet/outlet boundary conditions well? Can you try putting in those pressures and seeing how that works out? How about trying to have the whole pressure at something closer to 1e6?

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