Natural convection

stopjumpshot · April 24, 2013, 12:33

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

resto
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

and operating temperature

, 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

April 24, 2013, 12:33	Natural convection	#1
stopjumpshot 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, 08:56		#3
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	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
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	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.

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April 25, 2013, 07:17		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	This looks like Fluent settings. Try the Fluent forum.

October 13, 2013, 07:54		#5
dreamz Member Ashutosh Join Date: Jul 2013 Posts: 98 Rep Power: 12	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
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	Boussinesq's model prescribes the density as a function of thermal expansion coefficient $\beta$ and the difference between local temperature and operating temperature , 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