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September 17, 2008, 15:04 
Hi all,
Given that the outw

#1 
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Srinath Madhavan (a.k.a pUl)
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Location: Edmonton, AB, Canada
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Hi all,
Given that the outward drawn unit normal to inlet and outlet boundaries point parallel to the xdirection, are the following the only conditions that need to be satisfied at these boundaries? For a fixed velocity inlet, u = fixed value v = fixed value (dp/dx) = 0.0 For a fixed pressure outlet, p = fixed value du/dx = 0.0 dv/dx = 0.0 Where: In 2D: U = [u,v] (u and v are the two components of velocity vector U) and assume that 'd' represents the partial derivative symbol. I would appreciate if someone can point out if I am incorrect or missing anything here. Thanks for your help. 

September 18, 2008, 13:02 
Anyone? Even a simple Yes or N

#2 
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Srinath Madhavan (a.k.a pUl)
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Anyone? Even a simple Yes or No will suffice.


September 18, 2008, 13:15 
For incompressible laminar flo

#3 
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Xiaofeng Liu
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For incompressible laminar flow, Yes
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September 19, 2008, 10:59 
Thanks Xiaofeng.

#4 
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Srinath Madhavan (a.k.a pUl)
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Thanks Xiaofeng.


October 1, 2008, 17:05 
For a plain channel or pipe fl

#5 
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Srinath Madhavan (a.k.a pUl)
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For a plain channel or pipe flow, dp/dx = 0 at the inlet boundary does not seem to make sense. The pressure should be allowed to change in the Xdirection. Can anyone comment on that?


October 1, 2008, 17:55 
Hi Srinath
Yes, I would lik

#6 
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Niels Gjoel Jacobsen
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Hi Srinath
Yes, I would like to give my two cents: Ideally you would say, that the only thing you know for sure is the pressure at the inlet and at the outlet, i.e. the energy gradient. Thus the intuitive way to set the boundary conditions would be to apply the pressure at both ends, which is equivalent of applying a body force. This solution converges asymptotically, thus far to slow to be interesting if you start with initial field 0 (unfortunately I cannot recall the reference on the asymptotic part). This would give a correct pressure gradient, i.e. constant, along your uniform channel. Another method is to apply the velocity at the inlet and a nonzero pressure gradient, but that implies that you _know_ the solution to the pressure field in advance, thus people have settled with the zero pressure gradient. I have read another article (again, cannot recall the exact reference), which did compare the results between a zeroGradient and the correct gradient solution, and the differences was small, at least from an engineerpointofview. Best regards, Niels
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October 1, 2008, 19:56 
Thanks very much for that resp

#7 
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Srinath Madhavan (a.k.a pUl)
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Thanks very much for that response Niels. You've brought some interesting facts to my attention. I'll try and dig up more information on this.


October 14, 2008, 00:25 
Hello People,
I am have a s

#8 
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Mahendra
Join Date: Mar 2009
Location: Pune, Maharashtra, India
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Hello People,
I am have a small doubt regarding pressure boundary condition. In Fluent i have specified 1500 Pa gauge (negative) boundary condition at outlet. In OpenFOAM what boundary condition should i give. like this or something different? outlet { type fixedValue; value 1225; // (1500/1.225) pressure/density since units of pressure are [0 2 2 0 0 0 0]. }  

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