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

#1 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
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 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
Anyone? Even a simple Yes or No will suffice.


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

#3 
Senior Member
Xiaofeng Liu
Join Date: Mar 2009
Location: State College, PA, USA
Posts: 118
Rep Power: 9 
For incompressible laminar flow, Yes
__________________
Xiaofeng Liu, Ph.D., P.E., Assistant Professor Department of Civil and Environmental Engineering Penn State University 223B Sackett Building University Park, PA 16802 Web: http://water.engr.psu.edu/liu/ 

September 19, 2008, 10:59 
Thanks Xiaofeng.

#4 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
Thanks Xiaofeng.


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

#5 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
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 
Senior Member
Niels Gjoel Jacobsen
Join Date: Mar 2009
Location: Deltares, Delft, The Netherlands
Posts: 1,693
Rep Power: 27 
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
__________________
Please note that I do not use the Friendfeature, so do not be offended, if I do not accept a request. 

October 1, 2008, 19:56 
Thanks very much for that resp

#7 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
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 
Member
Mahendra
Join Date: Mar 2009
Location: Pune, Maharashtra, India
Posts: 65
Rep Power: 9 
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]. }  

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Boundary condition question  cestrin  FLUENT  0  July 21, 2008 23:53 
Basic Boundary Conditions Question  vcoralic  OpenFOAM PreProcessing  0  June 26, 2006 07:56 
Question about Boundary condition..  Sam  CFX  0  May 9, 2005 21:53 
boundary condition question  tucker  FLUENT  1  May 4, 2005 12:42 