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Characteristic length in Rayleigh number

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Old   August 21, 2016, 03:01
Default Characteristic length in Rayleigh number
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a0407
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Hi, I'm new in Fluent and Heat transfer. I'm trying to simulate a 2D natural convection from a horizontal cylinder in an enclosed vertical rectangle cavity. The cylinder's diameter is 40mm and the cavity's dimensions is 760mm in height and 260mm in width. My questions are
  • How do I set and calculate the Rayleigh number? What is the characteristic length? Will it be the diameter of cylinder or the length or height of the cavity? If I want to increased or decreased the Ra number, what value can I play around with?
  • How do we calculate the bulk temperature, to be input in reference value? I have tried to use mass-weighted average temperature of the fluid as the input, but the Nusselt number is lower than the value that i found in literature. Someone suggested to find the bulk temperature outside the the boundary layer, but I'm not sure how to do that.

Please help me in this matter. I never use CFD software before. Thank you!

Last edited by azizi0407; August 22, 2016 at 01:26.
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Old   August 22, 2016, 01:27
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Help pls..
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Old   August 22, 2016, 04:51
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http://adf.ly/1dLnuNThis can help
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Old   August 22, 2016, 05:43
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Hi Mohawk, thank you for your reply. I been to that page before. But it doesn't mention what to use for the characteristic length etc. plus the geometry file cant be open.
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fluent, natural convection, rayleigh number


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