effect of turbulent intensity in RANS in Fluent

Shamoon Jamshed · December 22, 2020, 10:19

Dear Fellas,

I was curious that since T.I is u'/U where u' is fluctuating and U is the mean velocity, how come it comes into play in RANS where u' is zero. I mean in a mean flow how turbulent intensity is computed and what is its role/effect?

Shamoon Jamshed · December 29, 2020, 13:52

Anyone please?

LoGaL · December 29, 2020, 16:38

To my understanding, RANS models are plain wrong when turbulence is low --> U' is very low. RANS model always presume the existence of a reasonable amount of turbulence.

Also, keep in mind, RANS models model (forgive th poor choice of words) the fluctuations, they do not solve them. You can have a quick look, say, for example, at k-espilon model. U' is appears in none of the turbulence equations used by the solver.

https://www.cfd-online.com/Wiki/Stan...-epsilon_model

Shamoon Jamshed · December 30, 2020, 04:26

That's my question that when we do not have u' how come TI is computed? RANS do compute fluctuations but rather product of fluctuations u'v' called as Reynolds Stress. Individual fluctuations are not computed and neither modeled.

December 22, 2020, 10:19	effect of turbulent intensity in RANS in Fluent	#1
Shamoon Jamshed Senior Member Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 377 Rep Power: 18	Dear Fellas, I was curious that since T.I is u'/U where u' is fluctuating and U is the mean velocity, how come it comes into play in RANS where u' is zero. I mean in a mean flow how turbulent intensity is computed and what is its role/effect?

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December 29, 2020, 13:52		#2
Shamoon Jamshed Senior Member Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 377 Rep Power: 18	Anyone please?

December 29, 2020, 16:38		#3
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 373 Rep Power: 12	To my understanding, RANS models are plain wrong when turbulence is low --> U' is very low. RANS model always presume the existence of a reasonable amount of turbulence. Also, keep in mind, RANS models model (forgive th poor choice of words) the fluctuations, they do not solve them. You can have a quick look, say, for example, at k-espilon model. U' is appears in none of the turbulence equations used by the solver. https://www.cfd-online.com/Wiki/Stan...-epsilon_model

December 30, 2020, 04:26		#4
Shamoon Jamshed Senior Member Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 377 Rep Power: 18	That's my question that when we do not have u' how come TI is computed? RANS do compute fluctuations but rather product of fluctuations u'v' called as Reynolds Stress. Individual fluctuations are not computed and neither modeled.