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How to Set Rayleigh Number In Fluent ?

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Old   February 14, 2018, 19:02
Default How to Set Rayleigh Number In Fluent ?
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Hi ,

I am doing my final year dissertation and I am struggling to set up my simulation correctly , and I am not being able to make any progress because of this issue ; I would greatly appreciate any help on this .

I want to achieve a Rayleigh number of 2x10^9 by using Boussinesq approximation . I have a rectangular cavity that must have an aspect ratio of 4.
I entered relevant air properties and Ive set a height of 1m ( therefore width is 0.25m to achieve aspect ratio of 4) . By using the Rayleigh number expression , based on the air properties and 1m cavity length length , I obtained a temperature difference of 20K that would correspond to a Rayleigh number of 2x10^9 . However , this is not giving me reasonable results . The solution is not even converging . Can someone please help me out by spotting this error in my approach or telling me how can I correctly achieve a Rayleigh number of 2x10^9 . I would greatly appreciate any help . I attached a copy of the excel sheet that shows how I carried out my calculations .
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File Type: xlsx CFD FORUM.xlsx (36.4 KB, 2 views)
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Old   February 15, 2018, 12:21
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Cees Haringa
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The rayleigh number depends on the physical properties of your fluid, it has nothing to do with turbulence. You can tune the parameters in the Rayleigh number definition such that you get the appropriate value. of course, be sure to check that you set the parameters such that other dimensionless numbers are also in the proper range!
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