r.m.s velocities calculation after sampled LES

Aero_Tn · April 1, 2020, 10:43

Hello everyone
I've run LES case, I did data sampling, but I cannot find how to display or calculate axial r.m.s velocity u', only RMSE values are available.
Does anyone know what formula should I use to find rms velocities values
Thank you

LuckyTran · April 2, 2020, 00:11

The RMSE of u is equivalent to the RMS of u' because the mean of u' is 0.

Aero_Tn · April 3, 2020, 01:58

Thank you LuckyTran for your reply, and I appreciate if you guide me to any reference telling this in fluent theory guide or elsewhere

LuckyTran · April 3, 2020, 13:56

It is verrry trivial. Just read up on RMS and RMSE

Note that the fluctuation velocity u' is the velocity u(t) with the mean subtracted out. People often mistakenly call u' the RMS velocity, which can add to the confusion.

The hint is that the RMSE of u' and the RMS of u' are the same. The mean of u' is 0. The RMS of the mean of a quantity is the same as the mean.

Aero_Tn · April 5, 2020, 13:23

Yes that's true, just got confused from some posts saying random things

.. anyway, thanks again

April 1, 2020, 10:43	r.m.s velocities calculation after sampled LES	#1
Aero_Tn New Member Akram Join Date: Oct 2016 Posts: 22 Rep Power: 9	Hello everyone I've run LES case, I did data sampling, but I cannot find how to display or calculate axial r.m.s velocity u', only RMSE values are available. Does anyone know what formula should I use to find rms velocities values Thank you

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April 2, 2020, 00:11		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,676 Rep Power: 66	The RMSE of u is equivalent to the RMS of u' because the mean of u' is 0.

April 3, 2020, 01:58		#3
Aero_Tn New Member Akram Join Date: Oct 2016 Posts: 22 Rep Power: 9	Thank you LuckyTran for your reply, and I appreciate if you guide me to any reference telling this in fluent theory guide or elsewhere

April 3, 2020, 13:56		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,676 Rep Power: 66	It is verrry trivial. Just read up on RMS and RMSE Note that the fluctuation velocity u' is the velocity u(t) with the mean subtracted out. People often mistakenly call u' the RMS velocity, which can add to the confusion. The hint is that the RMSE of u' and the RMS of u' are the same. The mean of u' is 0. The RMS of the mean of a quantity is the same as the mean.

April 5, 2020, 13:23		#5
Aero_Tn New Member Akram Join Date: Oct 2016 Posts: 22 Rep Power: 9	Yes that's true, just got confused from some posts saying random things .. anyway, thanks again