Pressure Poisson Equation

antarctic · December 1, 2009, 03:00

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

[latex]\dfrac{\partial P}{\partial \overbar{n}}[/latex] ?

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

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

December 1, 2009, 03:00	Pressure Poisson Equation	#1
antarctic New Member Arnie Join Date: Jul 2009 Posts: 6 Rep Power: 17	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

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December 1, 2009, 20:45		#2
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	just use the "insultaion" boundary condition for pressure

December 3, 2009, 06:11		#3
antarctic New Member Arnie Join Date: Jul 2009 Posts: 6 Rep Power: 17	Can you please elaborate what you mean by insulation boundary condition?

December 3, 2009, 12:53		#4
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	that means the gradient of p is zero

December 3, 2009, 17:36		#5
kingjewel1 Senior Member Join Date: Jul 2009 Posts: 260 Rep Power: 18	[latex]\dfrac{\partial P}{\partial \overbar{n}}[/latex] ?

December 6, 2009, 18:03		#6
plg007 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
abcdef123 New Member abcdef123 Join Date: Dec 2009 Posts: 17 Rep Power: 16	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.