LES w/ no SGS

amanbearpig · June 20, 2013, 08:54

Is there an easy way to implement LES with no subgrid-scale model in Fluent? I have looked through the GUI and TUI and cannot seem to find a way to do this.

oj.bulmer · June 20, 2013, 09:03

If you do not want to use SGS models, how will you model the non-energy containing small eddies?

OJ

sbaffini · June 21, 2013, 05:49

Of course there is, it is just the laminar model under viscous model. Also, you can use a static Smagorinsky model and set the constant Cs to 0.

I would prefer the first one (much less costy); in this caase, however, in order to activate the second order central scheme you need to use the TUI:

solve->set->expert

and activate all the available schemes.

Whether or not the model is useful or necessary depends on a lot of factors, including, of course, which model and which numerical schemes you are using. More often than not it is almost useless in Fluent (even with a pure, unbounded, central scheme). This is mostly because of the eddy viscosity models and the Fluent features, but it is somehow difficult to explain briefly here.

For a complex application i would rather just select the bounded central scheme and no model at all (An approach also known as ILES).

Of course if you're in model development, you can actually work on specific issues and let the model do what those in Fluent can't.

Check this reference for a sensitivity on SGS model and numerical scheme in Fluent:

http://www.lamc.ing.unibo.it/aimeta2.../MEM-273-0.pdf

June 20, 2013, 08:54	LES w/ no SGS	#1
amanbearpig Member Join Date: Apr 2011 Posts: 57 Rep Power: 14	Is there an easy way to implement LES with no subgrid-scale model in Fluent? I have looked through the GUI and TUI and cannot seem to find a way to do this.

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June 20, 2013, 09:03		#2
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	If you do not want to use SGS models, how will you model the non-energy containing small eddies? OJ

June 21, 2013, 05:49		#3
sbaffini Senior Member Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,152 Blog Entries: 29 Rep Power: 39	Of course there is, it is just the laminar model under viscous model. Also, you can use a static Smagorinsky model and set the constant Cs to 0. I would prefer the first one (much less costy); in this caase, however, in order to activate the second order central scheme you need to use the TUI: solve->set->expert and activate all the available schemes. Whether or not the model is useful or necessary depends on a lot of factors, including, of course, which model and which numerical schemes you are using. More often than not it is almost useless in Fluent (even with a pure, unbounded, central scheme). This is mostly because of the eddy viscosity models and the Fluent features, but it is somehow difficult to explain briefly here. For a complex application i would rather just select the bounded central scheme and no model at all (An approach also known as ILES). Of course if you're in model development, you can actually work on specific issues and let the model do what those in Fluent can't. Check this reference for a sensitivity on SGS model and numerical scheme in Fluent: http://www.lamc.ing.unibo.it/aimeta2.../MEM-273-0.pdf