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-   -   Natural Convection of air (https://www.cfd-online.com/Forums/fluent/85590-natural-convection-air.html)

Merida777 March 2, 2011 03:52
Natural Convection of air
 
Hi there I hope someone can help me. I am modeling natural convection of air in a large rectangular cavity and the results from my previous simulations are not accurate enough. I have simulated the problem using boussinesq, I have used turbulence models (Standard K-Epsilon and RNG), now I would like to use varying properties of air. I want to vary the properties of air according to a polynomial function, but as soon as the density is changed to a polynomial f(T) then the simulation will not converge.

Any help or suggestions will be much appreciated.
Thanks

chlp March 3, 2011 04:02
Quote:
Originally Posted by Merida777 (Post 297602)
the results from my previous simulations are not accurate enough
with which to compare the results? what is meant by "previous results"
Quote:
Originally Posted by Merida777 (Post 297602)
I have simulated the problem using boussinesq
boussinesq used in closed domain (no mass transfer, only energy - wall boundary) and with small difference of temperature
Quote:
Originally Posted by Merida777 (Post 297602)
I want to vary the properties of air according to a polynomial function
what equation of state are you use?

Merida777 March 3, 2011 04:28
Natural convection of air
 
What I am basically doing is testing different models in Fluent to try and get the most accurate results. The results from Fluent I then compare to experimental results. My previous results are previous models I have developed and what I am acctually saying is that with the varying properties of air I am unable to find any convergence. I have used the boussinesq approximation but my temperture differences are quite high so another test would to model the air as an ideal gas, but also as some f(T). That is why I want to try and model the air with varying properties. All the properties of air is defiened as a 2nd order polynomial function that is dependant on the temperture.

chlp March 3, 2011 04:44
Quote:
Originally Posted by Merida777 (Post 297751)
What I am basically doing is testing different models in Fluent to try and get the most accurate results.
I'm doing the same! at the present time i model the free-convection on horizontal cylinder and compare the results with correlations
Quote:
Originally Posted by Merida777 (Post 297751)
The results from Fluent I then compare to experimental results.
it would be nice to compare with the results in other CAE, e.g. FloWorks, CFX.
Quote:
Originally Posted by Merida777 (Post 297751)
All the properties of air is defiened as a 2nd order polynomial function that is dependant on the temperture.
For air in n.c density dependendsy from temperature (ideal gas law):
ro=353/T

Merida777 March 3, 2011 04:57
Natural convection of air
 
Thanks for the reply, I will be modelling air as an ideal gas and see what effect that has on the results.

chlp March 3, 2011 05:06
Quote:
Originally Posted by Merida777 (Post 297759)
Thanks for the reply, I will be modelling air as an ideal gas and see what effect that has on the results.
Still try to Soave-Redlih-Kwong model and compare results

Merida777 March 3, 2011 05:09
Natural convection of air
 
Thanks I will try that as well.


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