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Old   December 1, 2009, 03:00
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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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Old   December 1, 2009, 20:45
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just use the "insultaion" boundary condition for pressure
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Old   December 3, 2009, 06:11
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Can you please elaborate what you mean by insulation boundary condition?
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Old   December 3, 2009, 12:53
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that means the gradient of p is zero
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Old   December 3, 2009, 17:36
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[latex]\dfrac{\partial P}{\partial \overbar{n}}[/latex] ?
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Old   December 6, 2009, 18:03
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i really didn't get what you really want to know. please explain thoroughly what you exactly want.
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Old   December 6, 2009, 19:50
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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.
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Old   December 7, 2009, 00:53
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Quote:
Originally Posted by abcdef123 View Post
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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