Characteristic length in Rayleigh number

azizi0407 · August 21, 2016, 02:01

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!

azizi0407 · August 22, 2016, 00:27

Help pls..

Mohawk · August 22, 2016, 03:51

http://adf.ly/1dLnuNThis can help

azizi0407 · August 22, 2016, 04:43

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.

August 21, 2016, 02:01	Characteristic length in Rayleigh number	#1
azizi0407 New Member a0407 Join Date: Aug 2016 Posts: 10 Rep Power: 9	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 00:26.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[mesh manipulation] Mesh Refinement	Luiz Eduardo Bittencourt Sampaio (Sampaio)	OpenFOAM Meshing & Mesh Conversion	42	January 8, 2017 12:55
[snappyHexMesh] sHM layer process keeps getting killed	MBttR	OpenFOAM Meshing & Mesh Conversion	4	August 15, 2016 03:21
foam-extend_3.1 decompose and pyfoam warning	shipman	OpenFOAM	3	July 24, 2014 08:14
[Commercial meshers] Trimmed cell and embedded refinement mesh conversion issues	michele	OpenFOAM Meshing & Mesh Conversion	2	July 15, 2005 04:15
characteristic Length	CFD MAN	Main CFD Forum	3	September 11, 2002 07:26

August 22, 2016, 00:27		#2
azizi0407 New Member a0407 Join Date: Aug 2016 Posts: 10 Rep Power: 9	Help pls..

August 22, 2016, 03:51		#3
Mohawk Member Mustafa Join Date: May 2013 Posts: 54 Rep Power: 12	http://adf.ly/1dLnuNThis can help

August 22, 2016, 04:43		#4
azizi0407 New Member a0407 Join Date: Aug 2016 Posts: 10 Rep Power: 9	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.