# Natural convection

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 April 24, 2013, 12:33 Natural convection #1 New Member   Join Date: Apr 2013 Posts: 2 Rep Power: 0 hi everyone ı am studying natural convection in a closed room. Room is heated below and cooled by window. But solition is not converged. Can you help me in this problem? steady-state turbulance model: Realizable k-epsilon model matterrial of fluid : air boussinesq Solution methods :Green-gausse node based, pressureresto the other parameters are second order upwind solition controls: momentum 0.7, others are default

 April 25, 2013, 07:17 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,815 Rep Power: 85 This looks like Fluent settings. Try the Fluent forum.

 April 25, 2013, 08:56 #3 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 486 Rep Power: 9 3D buoyant flows often have no steady state solution, hence will never converge using steady state solver. You can only converge your imbalances or wait until the variable you care about is steady. amin_gls likes this.

 April 25, 2013, 09:42 #4 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 11 Seems you are using Boussinesq's model for gravity in buoyant flow. You should be careful here since this model is valid only for small differences in the temperature throughout the domain, which allow the definition of density as a function of temperature and expansion coefficient. The definition will collapse in the presence of higher temperature gradients. OJ amin_gls and hwangpo like this.

 October 13, 2013, 07:54 #5 Member   Ashutosh Join Date: Jul 2013 Posts: 98 Rep Power: 4 Please can you be more specific as to what temperature range can we allow for buoyant flows? Also if my temperature range exceeds this one how should I model the flow..

 October 13, 2013, 17:09 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,815 Rep Power: 85 That depends on how accurate you want to be. The alternative is to use a more complete constitutive model such as ideal gas or real gas.

 October 14, 2013, 07:11 #7 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 11 Boussinesq's model prescribes the density as a function of thermal expansion coefficient and the difference between local temperature and operating temperature , and density at operating temperature . The Boussinesq assumption is valid only when Otherwise you have fairly large temperature differences and you need to comprehensively model density as a function of temperature/pressure as Glenn mentioned OJ

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