Talk:Reynolds-averaged Navier–Stokes equations

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[edit] Osbourne Reynolds?

  • I believe that this article would benefit a lot if it had a reference to the scientific author of the theory: Osborne Reynolds --Mecanismo 09:15, 4 October 2005 (UTC)

[edit] Time average vs. Ensemble average

I think that speaking in terms of Time average when dealing with Reynolds equations is not correct in principle. As far as I know, for the Reynolds decomposition to make (theoretical) sense, average must be considered as an ensemble average.

Time average (or even volume average) and ensemble average concide only when the flow is statistically steady, which means that

\frac{\partial \overline{u}}{\partial t}=0

and that makes Reynolds equations time independent, which is not the case.

In practice, time average is performed in data analysis assuming that the averaging interval is much shorter than the typical scale of statistical unsteadiness. This allows to approximate the ensemble average with the time average (the same holds in space). This is related to the ergodic hypothesis.

However, because the author seems to be convinced of the contrary, I would like to discuss this fact to make someone convince me that I am wrong, before editing this (and related) articles.


Well, I agree with you. I started the article, and talked about time averaging and 'applicable to steady flows', because like you say thats how Ive used it in practice. I say go ahead, change what you need to and include relevant parts of your discussion in the article. Maybe "the author" is a bit of a misnomer on wikipedia, but yeah someone did add a bit about "Ensemble averaging is not the same as Reynolds averaging" which confused me. Dougalc 22:02, 7 May 2006 (UTC)