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stopjumpshot April 24, 2013 12:33

Natural convection
 
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, pressure:presto
the other parameters are second order upwind
solition controls: momentum 0.7, others are default

ghorrocks April 25, 2013 07:17

This looks like Fluent settings. Try the Fluent forum.

evcelica April 25, 2013 08:56

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.

oj.bulmer April 25, 2013 09:42

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

dreamz October 13, 2013 07:54

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..

ghorrocks October 13, 2013 17:09

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.

oj.bulmer October 14, 2013 07:11

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

OJ


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