monitoring Velocity fluctuation

ansari.nazanin · April 15, 2016, 05:26

Hi everyone, i am simulating a delta wing to validate some results for literature.
I have some questions about it.
-For validating turbulence intensity distributions, Urms, Vrms and Wrms is it ok to draw the Reynolds stresses in CFD-Post? Are they the same?(Using Reynolds stresses methods). If yes, why are my results quite different from the literature?Is there any explanation for it?

-How can i calculate and draw the amplitude spectra of fluctuating pressure coefficient in ANSYS CFX?(The photos from the literature and some values validation are to be seen in attached photos)

1.jpg

2.jpg

^3.png

4.jpg

5.jpg

ghorrocks · April 15, 2016, 07:59

Is your first question:
Can I compare Reynolds stresses to RMS fluctuations?

No, but they are related. Look at any turbulence modellign textbook for details.

OR

What is my simulation inaccurate?

FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

Second Question: Define a monitor point recording pressure at the location you wish to measure and do a transient simulation. This will give you the pressure versus time history. Then process the pressure history using whatever filtering approach you like to separate the mean from fluctuating components.

ansari.nazanin · April 15, 2016, 08:13

Dear Glenn,
thank you very much for your answer, i have checked it in the turbulent book by Pope, but does'nt seem to find it. Could you please tell me how these two are related?

ansari.nazanin · April 15, 2016, 08:15

i just know that the Reynolds stresses are the covariance of velocity fluctuations. Is that correct?

ghorrocks · April 16, 2016, 07:47

See https://en.wikipedia.org/wiki/Reynolds_stress

April 15, 2016, 05:26	monitoring Velocity fluctuation	#1
ansari.nazanin New Member Nazanin Ansari Join Date: Sep 2013 Posts: 12 Rep Power: 13	Hi everyone, i am simulating a delta wing to validate some results for literature. I have some questions about it. -For validating turbulence intensity distributions, Urms, Vrms and Wrms is it ok to draw the Reynolds stresses in CFD-Post? Are they the same?(Using Reynolds stresses methods). If yes, why are my results quite different from the literature?Is there any explanation for it? -How can i calculate and draw the amplitude spectra of fluctuating pressure coefficient in ANSYS CFX?(The photos from the literature and some values validation are to be seen in attached photos) 1.jpg 2.jpg ^3.png 4.jpg 5.jpg

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April 15, 2016, 07:59		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Is your first question: Can I compare Reynolds stresses to RMS fluctuations? No, but they are related. Look at any turbulence modellign textbook for details. OR What is my simulation inaccurate? FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F Second Question: Define a monitor point recording pressure at the location you wish to measure and do a transient simulation. This will give you the pressure versus time history. Then process the pressure history using whatever filtering approach you like to separate the mean from fluctuating components.

April 15, 2016, 08:13		#3
ansari.nazanin New Member Nazanin Ansari Join Date: Sep 2013 Posts: 12 Rep Power: 13	Dear Glenn, thank you very much for your answer, i have checked it in the turbulent book by Pope, but does'nt seem to find it. Could you please tell me how these two are related?

April 15, 2016, 08:15		#4
ansari.nazanin New Member Nazanin Ansari Join Date: Sep 2013 Posts: 12 Rep Power: 13	i just know that the Reynolds stresses are the covariance of velocity fluctuations. Is that correct?

April 16, 2016, 07:47		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	See https://en.wikipedia.org/wiki/Reynolds_stress