Calculation for Turbulent Length Scale

aqib · December 13, 2010, 07:07

Hello everyone,
I am using SST (Gamma-Theta) Model for the simulation of my Cascade T106A.
I have the problem regarding to set my Turbulent Length Scale value.
By Default it is 1. How should i select this value?
Any formula for that?
Does it effect on my results?
Give your opinion....
Regards:
Chishty

ghorrocks · December 13, 2010, 17:22

Set the incoming and/or initial turbulence levels to match the experiments you are reproducing. The default is just a guessed value to give it a default value.

If you do not have experimental turbulence levels then your experimental conditions are not fully defined.

aqib · December 14, 2010, 00:55

i am using FSTI=0.1 & 0.4
but can't specify the Turbulent Length Scale....
Any formula or theory for that, from where i can get that value....

ghorrocks · December 14, 2010, 05:50

As I now know you are using Fluent I can't tell you exactly which options to choose but I am sure Fluent has similar options to CFX. To get the equations to convert between turbulence intensity, energy, length scales etc get a decent turbulence textbook such as "Turbulence modelled for CFD" by Wilcox.

aqib · December 14, 2010, 06:24

ok i will read that book and come back to you soon....

December 13, 2010, 07:07	Calculation for Turbulent Length Scale	#1
aqib Member Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 16	Hello everyone, I am using SST (Gamma-Theta) Model for the simulation of my Cascade T106A. I have the problem regarding to set my Turbulent Length Scale value. By Default it is 1. How should i select this value? Any formula for that? Does it effect on my results? Give your opinion.... Regards: Chishty

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December 13, 2010, 17:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Set the incoming and/or initial turbulence levels to match the experiments you are reproducing. The default is just a guessed value to give it a default value. If you do not have experimental turbulence levels then your experimental conditions are not fully defined.

December 14, 2010, 00:55		#3
aqib Member Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 16	i am using FSTI=0.1 & 0.4 but can't specify the Turbulent Length Scale.... Any formula or theory for that, from where i can get that value....

December 14, 2010, 05:50		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	As I now know you are using Fluent I can't tell you exactly which options to choose but I am sure Fluent has similar options to CFX. To get the equations to convert between turbulence intensity, energy, length scales etc get a decent turbulence textbook such as "Turbulence modelled for CFD" by Wilcox.

December 14, 2010, 06:24		#5
aqib Member Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 16	ok i will read that book and come back to you soon....