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September 9, 2019, 09:19 
Boussinesq approximation

#1 
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Ahmed
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I am solving High Rayleigh natural convection problem ( air in square cavity whose vertical sides are heated and horizontal ones are adiabatic )
so do i consider gas an ideal gas or use Boussinesq approximation? when Boussinesq approximation is used? thank you 

September 9, 2019, 10:06 

#2 
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Carlo_P
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Hey Tahtawy.
In the Boussinesq approximation you consider the density function of the static temperature, also if normally it depends also on the pressure and the velocity. So, if in your simulation there are small variations in pressure and small velocity, you can use the Boussinesq approximation. Otherwise, no. Cheers, Carlo 

September 9, 2019, 12:32 

#3  
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Filippo Maria Denaro
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Quote:
This model can be applied for small temperature difference 

September 9, 2019, 14:52 

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Ahmed
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September 9, 2019, 14:53 

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Ahmed
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Quote:
will bousinessq here will aid in converging the residual ? 

September 9, 2019, 15:37 

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Filippo Maria Denaro
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September 10, 2019, 03:46 

#7 
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Carlo_P
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Uhm...I don't agree to much..CFX Tutorial use this approxiamtion with a 70 degree of difference..


September 10, 2019, 04:27 

#8  
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Filippo Maria Denaro
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Quote:
https://www.sciencedirect.com/scienc...1793101300820X 

September 10, 2019, 05:12 

#9 
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Carlo_P
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Hey FMDenaro, thanks to post that article!
Uhm..so maybe the CFX tutorials are not so trustable.. Thanks again, Cheers, Carlo 

September 11, 2019, 04:49 

#10  
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Quote:
Its only valid for the air, for other fluids, it depends on the expansion factor at constant pressure. For example the error is much bigger for the water. 

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