Difference of averaging and filtering in RANS and LES

Friendly · February 1, 2018, 18:03

Hi,

my problem is to understand the diffeference of averaging and filtering. I understand the concepts of RANS and LES, but not what excatly what the difference between a reynolds averaged and a filtered equation is.

I have red many of books and papers and the best answer so far for my understanding was:

The reynolds averaging is a total averaging. So a time averaged so that a physical quantity does not depend on the time itself.
In contrast to it the filtering is a lokal averaging so that is is dependent of the location.

But what is a total averaging and why is it not time dependent?
And why is the filterering dependet on the location? Because of the filter width?

I hope someone can enlighten me.

Best regards,
Friendly

FMDenaro · February 1, 2018, 18:43

This question has been discussed in the past, you can search in the main forum.
You can find some details in my notes here https://www.researchgate.net/publica..._Part_I_and_II

February 1, 2018, 18:03	Difference of averaging and filtering in RANS and LES	#1
Friendly Member Join Date: Jun 2017 Posts: 73 Rep Power: 9	Hi, my problem is to understand the diffeference of averaging and filtering. I understand the concepts of RANS and LES, but not what excatly what the difference between a reynolds averaged and a filtered equation is. I have red many of books and papers and the best answer so far for my understanding was: The reynolds averaging is a total averaging. So a time averaged so that a physical quantity does not depend on the time itself. In contrast to it the filtering is a lokal averaging so that is is dependent of the location. But what is a total averaging and why is it not time dependent? And why is the filterering dependet on the location? Because of the filter width? I hope someone can enlighten me. Best regards, Friendly

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February 1, 2018, 18:43		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,896 Rep Power: 73	This question has been discussed in the past, you can search in the main forum. You can find some details in my notes here https://www.researchgate.net/publica..._Part_I_and_II