Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Difference between Outlet and Open Boundary condition for fluid flow

Posted Sep 29, 2014, 9:57 a.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.4 2 Replies

Victor Koppejan
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi everyone,

I was wondering if one of you could explain the difference between the outlet and open boundary condition for fluid flow (single phase k-e).

I've gone through the CFD manual but I can't visualize for which scenario's I would use one or the other.

Thank you for your help.

Victor
2 Replies Last Post Sep 29, 2014, 3:02 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Sep 29, 2014, 2:38 p.m. EDT
Hi
when you have a doubt like that, turn on the "equation settings and the equations view" (under "options", or top border icon of physics tree) and check the underlying equations of COMSOL, in both the Equation tab, and the equation view node.

An "open boundary" allow two-way flow with free pressure and velocity definition. The "outlet" requires an output pressure or velocity, with or no backflow suppression and/or normal flow conditions ... it's all written

--
Good luck,
Ivar
Hi when you have a doubt like that, turn on the "equation settings and the equations view" (under "options", or top border icon of physics tree) and check the underlying equations of COMSOL, in both the Equation tab, and the equation view node. An "open boundary" allow two-way flow with free pressure and velocity definition. The "outlet" requires an output pressure or velocity, with or no backflow suppression and/or normal flow conditions ... it's all written -- Good luck, Ivar
Victor Koppejan
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Sep 29, 2014, 3:02 p.m. EDT
Hi Ivar,

Thank you for replying so fast. I look at the equations but I have the follwing doubt.

Setting the pressure to zero in the outlet node should give the same results as the open boundary.

Its introduced in the comsol 4.4 intro as being more stable and improving mass conservation. So I'm hoping people who've used both could share their thoughts on why they used them.

Hope to hear more from you.

Hi Ivar, Thank you for replying so fast. I look at the equations but I have the follwing doubt. Setting the pressure to zero in the outlet node should give the same results as the open boundary. Its introduced in the comsol 4.4 intro as being more stable and improving mass conservation. So I'm hoping people who've used both could share their thoughts on why they used them. Hope to hear more from you.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content