subgrid models
Hi Dear Friends,
Is the KEpsilon model a subgrid model? Thanks. 
Re: subgrid models
Hi,
I think the turbulent viscosity computed using the keps model cannot be considered as a subgrid viscosity because it doesn't vanish even if all the turbulent scales are resolved . best regards 
Re: subgrid models
The standard keps model was developed for timeaveraged equations. The term subgrid models is normally used in the context of spacefiltered simulations or Large eddy simulations.
Now, people have used subgrid keps models too. Where they solve additional equations for the subgrid 'k' and subgrid 'eps'. This is useful for some reasons like 'control of backscatter of energy' maybe. chidu... 
subgrid models for 2D ?
Hi,
there are subgrid scale models proper for 2D simulations (2DLES)?? 
Re: subgrid models for 2D ?
The 2D Les concept has been used as a cheap and dirty alternative to doing a full 3D simulation. I don't know what it means in a flow situation that actually involves threedimensional turbulence. I think in such cases (mostly in the industry) people just use the same subgrid scale models as they have for their 3D simulation. The best way to look at literature.
Of course, in principle, the LES concept can be applied to a problem in any number of dimensions. chidu... 
Re: subgrid models for 2D ?
subgrid model concepts has been developed in LES that is essentially spatial filtering of turbulent flowfield. LES does not removed the 3d fluctuation of turbulent. Thus performing LES (using 2D subgrid model) would be pointless as the simulation is definitely innaccurate. (See study by Michael Brauer, e.g. his paper in ECCOMAS 2000)
Currently there is some attempt to make LES cheap by combining it with RANS concept, e.g. Detached Eddy Simulation of Spallart. Within this framework, "2D subgrid scale" has been developed. More information on this can be found in onera and cerfacs website. Cheers 
Re: subgrid models
Backscatter is possible in the context of eddy viscosity models (like the Ke model) only is the eddy viscosity coefficient C_mu is negative (since K and e are by definition positive). Therefore, with fixed positive C_mu, there can not be any backscatter (in 2 or 3 dimensions).

Re: subgrid models
Yeah, but is there a contradiction here? If you fix C_mu to be positive then of course there will be no backscatter. I never said that one has to fix C_mu to be positive. In the case that you allow it go negative, using a subgrid keps model allows some flexibility!
In many cases anyways the fact that C_mu goes negative is a wierdness of the model rather than physical backscatter. Personally I don't believe LES models capture backscatter well. I was just making a point. Rereading your email, are you talking about RANS models? I was talking about LES!! chidu... 
Re: subgrid models
I was referring to LES models as well.
And of course, I agree with your opinion that physical backscatter, despite what many LES researchers (some well regarded) say, has nothing to do with C_mu going negative. I can state the reasons behind my belief if some one wants to refute them. Perhaps you could do the same if any one shows interest. 
Re: subgrid models for 2D ?
more references please

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