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Palani Velladurai March 14, 2007 06:01

Filtered navier stokes equation..LES::
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

john deas March 14, 2007 06:21

Re: Filtered navier stokes equation..LES::
Reynolds equations are time-averaged NS while LES are spatially filtered NS.

Palani Velladurai March 14, 2007 08:03

Filtered navier stokes equation..LES::once again
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???

john deas March 14, 2007 09:16

Re: Filtered navier stokes equation..LES::once aga

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.

tushar December 1, 2010 05:47

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

asyaskal September 15, 2011 12:52

Reylnolds averaging
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
You +1'd this publicly. Undo
Asya S. Skal. Does a physically reasonable solution of the Navier Stokes equations. exist? [Abstract] [Full Text] [Full Article - PDF] pp. 168-170 ...

cfdnewbie September 15, 2011 18:07

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..

eurotel September 6, 2013 02:51

Filtered navier stokes equation..LES and Stress
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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