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-   -   Outlet pressure boundary condition (http://www.cfd-online.com/Forums/openfoam-solving/60243-outlet-pressure-boundary-condition.html)

adamsview April 20, 2006 08:58

Hi all, is it possible to set
 
Hi all, is it possible to set an outlet boundary condition like fixedValue (=0) for the pressure, but in a way that it can be considered as "average" instead of "in each cell"?. Thank u.

jros April 24, 2006 06:25

I'm not an expert in OpenFoam,
 
I'm not an expert in OpenFoam, just reading the list to get a deeper feeling of the posibiliteies of OpenFOAM.

Tha said, I'll try to give a answer to your question:

"
Hi all, is it possible to set an outlet boundary condition like
fixedValue (=0) for the pressure, but in a way that it can be
considered as "average" instead of "in each cell"?. Thank u.
"

But keep in mind I'm not an expert.

A priory the closest posibility to what you are looking for may be to use a dynamic presure boundary condition.

That way you impose the dynamic presure as a boundary condition, but to implement you have to define the presure (the one of the navier stokes velocity equation) boundary conditions, by adding or substracting the contributions from velocity and gravity (review euler energy conservarion equation for a fluid without energy losses) to the dynamic presure that you define (if you have it).

This condition can be problematic if there is a zone in the outlet boundary condition in which the flow enters the fluid domain, because you dont' know what velocity to use to define presure from dynamic presure (fluent alows the user to define properties when the fluid enters velocity being normal to the boundary, but this produces slow convergence and bigger residuals).

This condition is pretty good (in may opinion) if the above condition is fullfilled, and if there are not big energy losses in the fluid close to the boundary condition (viscous effects are small in energetic terms, with respect to potential energy variation of the fluid due velocity changes of heigh change -if there is gravity).

This condition, to my knowledge, is implemented (or was) in fluent.

I hope this helps.

Javier Ros

chegdan November 7, 2011 14:07

This thread is old, but it came up in my searches quite a bit. An appropriate addition to this discussion is in the thread http://www.cfd-online.com/Forums/ope...condition.html


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