Turbulence Reynolds Number (Re_y)

pmccourt · August 17, 2016, 07:19

Hi,

Would anyone be able to explain to me the difference between the turbulence Reynolds Number Re_y available as a result in fluent, and the standard Reynolds Number.

I am trying to determine if the outlet of a jet flow will be turbulent or laminar. As turbulence must be specified beforehand I was wondering would this result be useful in deciding 'how' turbulent the flow is at least?

Thanks for anyone help in advance

Andrea1984 · August 18, 2016, 05:55

I reckon you can find an explanation in any good Turbulence book.

A turbulent flow is characterised by a wide range of scales and you can define a Reynolds number at whichever scale you want, and each Reynolds number will be representative of a given scale within the turbulence spectrum.

I guess the "standard" Reynolds number you are referring to is the one defined at the characteristic scales of your domain.

The turbulent Reynolds number is usually defined at the energy containing scale, i.e. l_t=k^(3/2)/epsilon. The velocity scale in this case is k^(1/2) and therefore the turbulent Reynods number is equal to

Re_t = rho*u_t*l_t/nu = rho*k^(1/2)*l_t/nu

You can define other Reynolds numbers at different significant scales, e.g. the Taylor microscale or the Kolmogorov scale. For example, the Reynolds number associated with the Kolmogorov scale is equal to unity, since those scales are dominated by viscosity.

August 17, 2016, 07:19	Turbulence Reynolds Number (Re_y)	#1
pmccourt New Member Peter Join Date: Jun 2016 Posts: 10 Rep Power: 9	Hi, Would anyone be able to explain to me the difference between the turbulence Reynolds Number Re_y available as a result in fluent, and the standard Reynolds Number. I am trying to determine if the outlet of a jet flow will be turbulent or laminar. As turbulence must be specified beforehand I was wondering would this result be useful in deciding 'how' turbulent the flow is at least? Thanks for anyone help in advance

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[snappyHexMesh] snappyHexMesh sticking point	natty_king	OpenFOAM Meshing & Mesh Conversion	11	February 20, 2024 09:12
decomposePar no field transfert	Jeanp	OpenFOAM Pre-Processing	3	June 18, 2022 12:01
About the Reynolds Number and Y-plus in external flow	Mason liu	CFX	18	November 10, 2014 18:37
Cluster ID's not contiguous in compute-nodes domain. ???	Shogan	FLUENT	1	May 28, 2014 15:03
Turbulence Model for low Reynolds Number	Muhammad Shakaib	Main CFD Forum	2	July 3, 2006 15:42

August 18, 2016, 05:55		#2
Andrea1984 Senior Member Andrea Join Date: Feb 2012 Location: Leeds, UK Posts: 179 Rep Power: 16	I reckon you can find an explanation in any good Turbulence book. A turbulent flow is characterised by a wide range of scales and you can define a Reynolds number at whichever scale you want, and each Reynolds number will be representative of a given scale within the turbulence spectrum. I guess the "standard" Reynolds number you are referring to is the one defined at the characteristic scales of your domain. The turbulent Reynolds number is usually defined at the energy containing scale, i.e. l_t=k^(3/2)/epsilon. The velocity scale in this case is k^(1/2) and therefore the turbulent Reynods number is equal to Re_t = rhou_tl_t/nu = rhok^(1/2)l_t/nu You can define other Reynolds numbers at different significant scales, e.g. the Taylor microscale or the Kolmogorov scale. For example, the Reynolds number associated with the Kolmogorov scale is equal to unity, since those scales are dominated by viscosity.