Turbulence intensity from experimental data

ArathoN · November 20, 2014, 17:56

I'm having a last minute doubt how do you compute the turbulence intensity from experimental data?
I have the turbulence perturbation (u') along the normal direction (to the walls) of a channel and I wanted to estimate from them the turbulence intensity.

As an estimate I calculated with the trapezoid method the "mean" (or bulk) uprime (u') of the profile from which I calculated the turbulence intensity. Is this a good method?

I'm studying the backward facing step and the turbulence intensity values are all around 10% with which I obtained good values of the reachtment length. However if I consider I=5% the value will worsen and be nonsense eg the sst k omega model will underpredict contrary to any paper found until now.

ArathoN · November 21, 2014, 13:24

No one has an idea on how to estimate it?

ArathoN · November 22, 2014, 06:07

At the end I used the formula present in the fluent user guide:
Tu=0,16*Re^-1/8
Because this estimate the turbulence intensity at the core of the flow for fully enveloped channels, moreover I found out that the turbulence variables should be compute with respect to the bulk (or average) velocity.

I'm having good results on the BFS except for some configuration (I'm varying the angle of the step wall) where the reattachment length is underpredicted.

November 20, 2014, 17:56	Turbulence intensity from experimental data	#1
ArathoN Senior Member ArathoN Join Date: Jul 2011 Posts: 137 Rep Power: 15	I'm having a last minute doubt how do you compute the turbulence intensity from experimental data? I have the turbulence perturbation (u') along the normal direction (to the walls) of a channel and I wanted to estimate from them the turbulence intensity. As an estimate I calculated with the trapezoid method the "mean" (or bulk) uprime (u') of the profile from which I calculated the turbulence intensity. Is this a good method? I'm studying the backward facing step and the turbulence intensity values are all around 10% with which I obtained good values of the reachtment length. However if I consider I=5% the value will worsen and be nonsense eg the sst k omega model will underpredict contrary to any paper found until now.

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November 21, 2014, 13:24		#2
ArathoN Senior Member ArathoN Join Date: Jul 2011 Posts: 137 Rep Power: 15	No one has an idea on how to estimate it?

November 22, 2014, 06:07		#3
ArathoN Senior Member ArathoN Join Date: Jul 2011 Posts: 137 Rep Power: 15	At the end I used the formula present in the fluent user guide: Tu=0,16*Re^-1/8 Because this estimate the turbulence intensity at the core of the flow for fully enveloped channels, moreover I found out that the turbulence variables should be compute with respect to the bulk (or average) velocity. I'm having good results on the BFS except for some configuration (I'm varying the angle of the step wall) where the reattachment length is underpredicted.