RMS root mean square velocity Fluent

C.C · July 31, 2013, 10:54

Hi all,

I want compare the root mean square velocity from my simulations with results from literature. I'm simulating a turbulent pipe flow with a low Reynolds k-e turbulence model in a steady state. From what i read i can obtain it in fluent if the problem is time dependent. As I'm simulating a steady state flow, can I obtain the RMS directly from Fluent?
Regards

flotus1 · July 31, 2013, 12:07

With the k-epsilon model, the turbulent kinetic energy $k=\frac{1}{2}\left[ \overline{u'u'} + \overline{v'v'} + \overline{w'w'}\right]$ is the only estimator you have for the actual Reynolds stresses in the turbulent flow.

To obtain the individual components of the Reynolds stresses, You have to perform a simulation with a reynolds stress turbulence model or a LES.
Among the transient statistics in fluent for a LES, you have the RMS-values of the fluctuating parts of the velocity components.

Far · July 31, 2013, 19:16

Yes, you can get root mean square velocity (also mean/average) in Fluent unsteady simulation. But you cannot get the different components of Reynolds stresses in RANS simulation.

CFDger · August 29, 2022, 12:14

Quote:

Originally Posted by Far

Yes, you can get root mean square velocity (also mean/average) in Fluent unsteady simulation. But you cannot get the different components of Reynolds stresses in RANS simulation.

Hello Far,

what would be the best way to calculate the rms of the velocity when I got my transient simulation in Fluent?

Thanks!

LuckyTran · August 29, 2022, 21:10

Enable the data sampling for time statistics, just click the box.

July 31, 2013, 10:54	RMS root mean square velocity Fluent	#1
C.C Member CC Join Date: Jun 2011 Posts: 73 Rep Power: 14	Hi all, I want compare the root mean square velocity from my simulations with results from literature. I'm simulating a turbulent pipe flow with a low Reynolds k-e turbulence model in a steady state. From what i read i can obtain it in fluent if the problem is time dependent. As I'm simulating a steady state flow, can I obtain the RMS directly from Fluent? Regards

July 31, 2013, 12:07		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,398 Rep Power: 46	With the k-epsilon model, the turbulent kinetic energy $k=\frac{1}{2}\left[ \overline{u'u'} + \overline{v'v'} + \overline{w'w'}\right]$ is the only estimator you have for the actual Reynolds stresses in the turbulent flow. To obtain the individual components of the Reynolds stresses, You have to perform a simulation with a reynolds stress turbulence model or a LES. Among the transient statistics in fluent for a LES, you have the RMS-values of the fluctuating parts of the velocity components. jzc likes this.

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July 31, 2013, 19:16		#3
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	Yes, you can get root mean square velocity (also mean/average) in Fluent unsteady simulation. But you cannot get the different components of Reynolds stresses in RANS simulation.

August 29, 2022, 21:10		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65	Enable the data sampling for time statistics, just click the box.