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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
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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)
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Posted: 10 years 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
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Posted: 10 years 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.

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