Self-preservation of a wake

lucamirtanini · January 25, 2019, 05:11

Hi all,

I have a doubt on the use of the word "self-preservation" in the case of the wake.

With the word self preservation, does the author mean (of the attached page of the book) that the behavior of the velocity defect and Reynolds stresses does not change in x (so it is preserved)?

Thank you in advance

LuckyTran · January 25, 2019, 10:22

Yes... the definition is given right there. You really should grow out of these semantic confusions.

LuckyTran · January 25, 2019, 10:24

It means if you write the velocity defect and Reynolds stresses in local velocity and length scales, they are invariant in x. And they call this the self-preservation hypothesis.

sbaffini · January 25, 2019, 11:08

Note that self preserving doesn't mean invariant... you'll get there at the end of the next page. I would prefer self-similar as a more intuitive description.

lucamirtanini · January 25, 2019, 11:35

Quote:

Originally Posted by LuckyTran

Yes... the definition is given right there. You really should grow out of these semantic confusions.

You are right.

But unfortunately it is not easy if you read a book on the turbulence for the first time, and if you are trying to self-learn.

Furthermore if you are not an english mother-tongue, I think it is natural to search for the weight of the word in order to be sure if you have really understood everything.

I am really thankful for your answers

FMDenaro · January 25, 2019, 11:36

I think that one could understand this issue by a reminding to the classical similar solution theory in the BL ...

lucamirtanini · January 25, 2019, 11:39

Quote:

Originally Posted by sbaffini

Note that self preserving doesn't mean invariant... you'll get there at the end of the next page. I would prefer self-similar as a more intuitive description.

I agree, self-similar is more intuitive

January 25, 2019, 10:22		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	Yes... the definition is given right there. You really should grow out of these semantic confusions. lucamirtanini likes this.

January 25, 2019, 10:24		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	It means if you write the velocity defect and Reynolds stresses in local velocity and length scales, they are invariant in x. And they call this the self-preservation hypothesis. lucamirtanini likes this.

January 25, 2019, 11:08		#4
sbaffini Senior Member Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,151 Blog Entries: 29 Rep Power: 39	Note that self preserving doesn't mean invariant... you'll get there at the end of the next page. I would prefer self-similar as a more intuitive description. lucamirtanini likes this.

January 25, 2019, 11:36		#6
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	I think that one could understand this issue by a reminding to the classical similar solution theory in the BL ... lucamirtanini likes this.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
wind turbine wake issue	vagge	OpenFOAM Running, Solving & CFD	6	October 11, 2016 07:45
Wake length behind a circular cylinder	Corleone84	STAR-CCM+	6	December 31, 2015 01:10
having problems with implementing the wake rollup for a panel method	smilesgiles89	Main CFD Forum	0	August 6, 2015 20:09
Wake behind a two crossing cylinders	Heini	FLUENT	0	May 8, 2013 16:54
Cylinder Wake calculation	Adam Chapman	Main CFD Forum	1	January 30, 2007 12:54