How to set the turbulence length scale?

February 24, 2006, 02:46

I decided to simulate a case of flow around a circular cylinder at Re 20000. But I'm not sure how to set the value of turbulence length scale. Who can tell me how to set it?

Thanks a lot.

February 24, 2006, 05:19

use k-epsilon model along with segregated solver then there is no need of giving turbulence length scale

jyothsna k · February 24, 2006, 06:04

An approximate relationship for turbulent length scale is: l=0.07*L where l is the turbulent length scale and L is the geometric relevant dimension. For your problem in my opinion you should use as geometric relevant dimension the diameter of the cylinder. Hope this helps Regards Emanuele

February 24, 2006, 07:02

Thanks a lot.

February 25, 2006, 07:52

And how is it defined this "relevant lenght"? If we are talking about a flow around an helicopter (or whatever), this lenght would be the total lenght of the helicopter? why could not be the lenght of the rotor helices or any other lenght?

Thanks!

February 25, 2006, 12:47

use turbulence intensity and hydraulic diameter to specify turbulence. The following relation is mentioned by FLUENT T.I = 0.16 * Re ** (-1/8)

February 28, 2006, 18:28

The relavant lenght is Diameter of cylinder in this case.

Regards

February 24, 2006, 02:46	How to set the turbulence length scale?	#1
yflin Guest Posts: n/a	I decided to simulate a case of flow around a circular cylinder at Re 20000. But I'm not sure how to set the value of turbulence length scale. Who can tell me how to set it? Thanks a lot.

February 24, 2006, 05:19	Re: How to set the turbulence length scale?	#2
satish Guest Posts: n/a	use k-epsilon model along with segregated solver then there is no need of giving turbulence length scale

February 24, 2006, 06:04	Re: How to set the turbulence length scale?	#3
Emanuele Guest Posts: n/a	An approximate relationship for turbulent length scale is: l=0.07*L where l is the turbulent length scale and L is the geometric relevant dimension. For your problem in my opinion you should use as geometric relevant dimension the diameter of the cylinder. Hope this helps Regards Emanuele jyothsna k likes this.

February 24, 2006, 07:02	Re: How to set the turbulence length scale?	#4
yflin Guest Posts: n/a	Thanks a lot.

February 25, 2006, 07:52	Re: How to set the turbulence length scale?	#5
Freeman Guest Posts: n/a	And how is it defined this "relevant lenght"? If we are talking about a flow around an helicopter (or whatever), this lenght would be the total lenght of the helicopter? why could not be the lenght of the rotor helices or any other lenght? Thanks!

February 25, 2006, 12:47	Re: How to set the turbulence length scale?	#6
A Guest Posts: n/a	use turbulence intensity and hydraulic diameter to specify turbulence. The following relation is mentioned by FLUENT T.I = 0.16 * Re ** (-1/8)

February 28, 2006, 18:28	Re: How to set the turbulence length scale?	#7
fred Guest Posts: n/a	The relavant lenght is Diameter of cylinder in this case. Regards

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