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 antarctic December 1, 2009 03:00

Pressure Poisson Equation

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

 ztdep December 1, 2009 20:45

just use the "insultaion" boundary condition for pressure

 antarctic December 3, 2009 06:11

Can you please elaborate what you mean by insulation boundary condition?

 ztdep December 3, 2009 12:53

that means the gradient of p is zero

 kingjewel1 December 3, 2009 17:36

$\dfrac{\partial P}{\partial \overbar{n}}$ ?

 plg007 December 6, 2009 18:03

i really didn't get what you really want to know. please explain thoroughly what you exactly want.

 abcdef123 December 6, 2009 19:50

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.

 ztdep December 7, 2009 00:53

Quote:
 Originally Posted by abcdef123 (Post 238892) 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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