Negative pressure

Greetings fellow members,

I’m implementing a DG scheme for a Poiseuille flow in Freefem. While I get very satisfying results on the velocity, I’m surprised with negative values for the pressure. Anyone had a similar issue ?

Best regards.

Expected pressure :
Expected Pressure

My result :

Because generally the pressure is defined through a constant, so the solve this problem we impose the nulle mean value of the pressure .

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Thank you sir for the reply, it makes perfect sense.

Any idea how to retrieve the ‘physically acceptable’ values ? I tried adding a penalization term of the form intalledges of alpha*jump(p)*jump(q), but no success…

Best regards !

Is your problem an incompressible NS equation? then the pressure is the hydrodynamic pressure and it could be negative (it is only the relative pressure to a constant), and I think you could just add any constant to make sense

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I see now.

I just wanted for it to make more sense on its own, without forcing a constant to add or by stabilizing the scheme with a term…

Thank you sir !