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monitoring Velocity fluctuation

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Old   April 15, 2016, 05:26
Default monitoring Velocity fluctuation
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Nazanin Ansari
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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)

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2.jpg

^3.png

4.jpg

5.jpg
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Old   April 15, 2016, 07:59
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Glenn Horrocks
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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.
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Old   April 15, 2016, 08:13
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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?
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Old   April 15, 2016, 08:15
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i just know that the Reynolds stresses are the covariance of velocity fluctuations. Is that correct?
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Old   April 16, 2016, 07:47
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See https://en.wikipedia.org/wiki/Reynolds_stress
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