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August 28, 2011, 06:39 
Natural convection in an infinite vertical cavity

#1 
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Sergei
Join Date: Dec 2009
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I need to simulate natural convection flow between two differentially heated, infinite vertical walls. The problem is twodimentional, Rayleigh number is 1.01E+5.
pic01.jpg The simulation file (created in CCM+ 4.04) can be downloaded from http://www.sendspace.com/file/bwkssb Analitical solution is stated in Benjamin Gebhart  BuoyancyInduced Flows And Transport. Look at temperature and velocity plots pic02.png Reference density is located on the left side in the middle between top and bottom sides. It's calculated according to ideal gas law. Attachment 8991 Physics I wonder if it's correct to model infinite walls applying outlet pressure boundary conditions on the top and bottom sides. Is in OK? The point is that I can't make in converged (the residuals are: residuals.png Last edited by Zeppo; August 28, 2011 at 07:34. 

August 29, 2011, 02:21 

#2 
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Ping
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buoyant flow is naturally quite unstable and you might never achieve a steady solution. You need to set some monitoring points and dump some scenes to see what is changing every few iterations. Then try the unsteady solver with a reasonable dt  start with .01s maybe.
Also depending on you density range, you probably don't need ideal gas  try gravity + Boussinesq 

September 2, 2011, 12:35 

#3  
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Sergei
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Quote:
Velocity vector scene pic05.png Velocity plot pic06.jpg Temperature plot pic08.jpg Values are distributed relative to the center axis symmetrically so that they correspond with analytical solution. Bringing Ra back to 1E+5 results in solution to diverge. Quote:
Why "Reference Altitude" don't seem to affect the results? pic07.png 

August 31, 2013, 02:29 

#4 
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B Aram
Join Date: Aug 2012
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there is a similar problem in fluent tutorial, about natural convection. there is something that i didn't understand. the amount of Rayleigh number is 5e05. then it is suggested that due to this Rayleigh number, put 6.94e05 for gravity.
hoe is it possible? 

Tags 
ccm+ 4, natural convection, rayleigh number, vertical cavity, vertical walls 
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