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Old   April 24, 2013, 12:33
Default Natural convection
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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
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Old   April 25, 2013, 07:17
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Glenn Horrocks
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This looks like Fluent settings. Try the Fluent forum.
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Old   April 25, 2013, 08:56
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Erik
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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.
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Old   April 25, 2013, 09:42
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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.

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Old   October 13, 2013, 07:54
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Ashutosh
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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..
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Old   October 13, 2013, 17:09
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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.
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Old   October 14, 2013, 07:11
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Boussinesq's model prescribes the density as a function of thermal expansion coefficient \beta and the difference between local temperature T and operating temperature T_0, and density at operating temperature \rho .

\rho=\rho_0 (1- \beta (T-T_0))

The Boussinesq assumption is valid only when \beta (T-T_0) << 1

Otherwise you have fairly large temperature differences and you need to comprehensively model density as a function of temperature/pressure as Glenn mentioned

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