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-   -   pressure outlet BC for Boussinesq with Fluent (http://www.cfd-online.com/Forums/main/14272-pressure-outlet-bc-boussinesq-fluent.html)

stephane October 19, 2007 09:38

pressure outlet BC for Boussinesq with Fluent
 
Hi,

I'm trying to solve a time dependent problem with Fluent using the boussinesq approximation. I have a velocity inlet and a pressure outlet (outflow is not good if the density is not constant). if I keep a constant gauge pressure at the outlet, after a certain time a gradient of pressure appears at the outlet creating a high velocity and there is divergence. I ve written an udf with a linear profile of pressure as well and used it at the outlet BC but it doesnt work either. So i'm wondering about the settings at the outlet.

thanks in advance, stéphane

momentum_waves October 20, 2007 07:09

Re: pressure outlet BC for Boussinesq with Fluent
 
Have you tried using no outlet b/c?

It may be better to set a pressure condition in your entering flow, as an initial condition.

I have found that setting the incorrect exit b/c in many simulations - especially pipe & duct flows - is seen by the flow field as a constraint. The unconstrained 'free exit' (do-nothing b/c) leaves the flow to decided what it wants to do.

Be careful of placing restraints where they may not be required. This can be one of the reasons for solver divergence via a so-called 'pressure blow-up'.

An exiting fluid will react differently in terms of pressure wave return sign, depending on the b/c used.

mw...

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