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Filtered navier stokes equation..LES::

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Old   March 14, 2007, 05:01
Default Filtered navier stokes equation..LES::
Palani Velladurai
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hI ! FOR Large eddy simulation´,,,I have seen that , we r usin filtered navier stokes equation..Is the same one like Avaraged Navier stokes....or ????

reply me
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Old   March 14, 2007, 05:21
Default Re: Filtered navier stokes equation..LES::
john deas
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Reynolds equations are time-averaged NS while LES are spatially filtered NS.
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Old   March 14, 2007, 07:03
Default Filtered navier stokes equation..LES::once again
Palani Velladurai
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hello !!!

In Rynolds averaged navier stokes equation.....

we are having variables for example ...(Velicoty)

v = V(Time averaged) + v'( Fluctutating term)

this V (time averaged) values are obtained by takin average of all the values over time....

Similarly for Filtered equations we are applying spatial filters.....

what s the mathtematical idea behind that one???

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Old   March 14, 2007, 08:16
Default Re: Filtered navier stokes equation..LES::once aga
john deas
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I guess you average the velocity on each computational cell and that leads you to introduce a new term. For Reynolds-averaged NS your new term will be Reynolds stress, and for LES it will be eddy viscosity. Then you will link this eddy viscosity to the averaged velocity components in some new equation. OK... as you can read I can not go much more beyond this basic description of LES, sorry.
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Old   December 1, 2010, 04:47
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I m also trying to understand same problem.. i guessed smthing like below
filtering on u = u(filtered)
but filtering on u*u != u(filtered)*u(filtered)

i dont know whether it is right or wrong.. comments please
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Old   September 15, 2011, 12:52
Default Reylnolds averaging
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Asya Skal
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I have solved NS equation in serial of six papers by spatial averaging enstead of velosity, as did Reynolds.
Read my first one in

Journal of Engineering and Technology Research; June 2011; 3(6) - Cached
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Asya S. Skal. Does a physically reasonable solution of the Navier Stokes equations. exist? [Abstract] [Full Text] [Full Article - PDF] pp. 168-170 ...
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Old   September 15, 2011, 18:07
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I must admit I have a hard time understanding why this paper was accepted... I have never heard of this journal as well.... Am I just being ignorant, or is this fishy?

I think digging up old threads to plug one's papers is not the most helpful approach either..
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Old   September 6, 2013, 02:51
Default Filtered navier stokes equation..LES and Stress
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After filtering out N-S equation, we get the filtered velocity (\tilde{U}) and filtered residual velocity (\tilde{u'}). Well, if we consider the filtered fluid motion; an instantaneous velocity (u) consists of filtered velocity (\tilde{U} + \tilde{u'}). In Reynolds averaging; if we take average of mean velocity \bar{U} and perturbation velocity(u') we get \bar{\bar{U}} = \bar{U} and \bar{u'} = 0. But if we take Reynolds averaging of (\bar{\tilde{U}}) we get (\bar{\tilde{U}}) \neq(\tilde{U}) also \bar{\tilde{u'}} \neq 0, that is filtered residual velocity is not equal to zero. Also, \bar{\tilde{U}} does not represent the mean motion, but rather the sum of the mean motion plus the large scales in the turbulence.
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