# Pressure Poisson Equation

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 December 1, 2009, 03:00 Pressure Poisson Equation #1 New Member   Arnie Join Date: Jul 2009 Posts: 6 Rep Power: 9 hi friends, I am writing a program for solving NS equations. The scheme i have thought of is similar to SIMPLER. Using the expression for velocities (as a function of neighbor velocities, body forces and pressure gradient) in the continuity equation, I derived a discretised, elliptic equation for pressure (not pressure correction). however, I am confused as to how to apply boundary condition for outlet or nodes where pressure is given as a boundary condition. Because, derivation of the discretised pressure equation using continuity equation is not possible where pressure BC is given. Can anybody help me in this regard? Thanks

 December 1, 2009, 20:45 #2 Senior Member     p ding Join Date: Mar 2009 Posts: 315 Rep Power: 11 just use the "insultaion" boundary condition for pressure

 December 3, 2009, 06:11 #3 New Member   Arnie Join Date: Jul 2009 Posts: 6 Rep Power: 9 Can you please elaborate what you mean by insulation boundary condition?

 December 3, 2009, 12:53 #4 Senior Member     p ding Join Date: Mar 2009 Posts: 315 Rep Power: 11 that means the gradient of p is zero

 December 3, 2009, 17:36 #5 Senior Member   Join Date: Jul 2009 Posts: 246 Rep Power: 10 $\dfrac{\partial P}{\partial \overbar{n}}$ ?

 December 6, 2009, 18:03 #6 New Member   Dave Petric Join Date: Dec 2009 Posts: 1 Rep Power: 0 i really didn't get what you really want to know. please explain thoroughly what you exactly want.

 December 6, 2009, 19:50 #7 New Member   abcdef123 Join Date: Dec 2009 Posts: 17 Rep Power: 9 I agree with ztdep about using zero gradient for walls and outlet. But for an inlet wouldn't you need to specify the pressure there? I've always just used a p = 0 at the inlet. I would appreciate an opinion on this. Thanks.

December 7, 2009, 00:53
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p ding
Join Date: Mar 2009
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Quote:
 Originally Posted by abcdef123 I agree with ztdep about using zero gradient for walls and outlet. But for an inlet wouldn't you need to specify the pressure there? I've always just used a p = 0 at the inlet. I would appreciate an opinion on this. Thanks.
for incompressible flow, we only consider the pressure difference . for the inlet, generaly, the normal speed is known. so we have the u'=de*pc' = 0, then we have de = 0 then Ae= rho*de*Ae =Ae=0

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