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-   -   LES Tutorial using fluent (http://www.cfd-online.com/Forums/fluent/32167-les-tutorial-using-fluent.html)

 anindya September 19, 2003 05:53

LES Tutorial using fluent

Is there any LES tutorial using FLUENT ?

Thanks

Anindya

 Chetan Kadakia September 25, 2003 05:05

Re: LES Tutorial using fluent

There is. Fluent has an acoustic model where LES is used with flow over a cylinder.

Why do you need a tutorial using Fluent? LES requires a fine mesh and small time step. Other than that, just select the LES and run it.

What are you trying to accomplish? How can I help you?

 anindya September 25, 2003 11:36

Re: LES Tutorial using fluent

I am trying to simulate an impinging jet flow using LES. I would like to see the jet coming out of the nozzle and then hitting the ground plane. I would also like to see how the wall jet then develop and the boundary layer profile at various r/D distances on the ground surface.

I am also trying to see how the ground pressures change if instead of having a stationary jet, the jet nozzle is moving at some velocity v relative to the ground plane.

How can I do that? Can you give me some insight to modeling these?

 raunakjung October 14, 2016 04:03

Are inlet conditions different for LES ?

 LuckyTran October 14, 2016 10:38

Quote:
 Originally Posted by raunakjung (Post 621480) Are inlet conditions different for LES ?

You need time-accurate inlet boundary conditions for LES. That is, you "cannot" just specify the time-averaged mean flow quantities, you need to specify the instantaneous quantities. You can use like the synthetic vortices like the spectral synthesizer if needed to generate the instantaneous quantities from time-averaged quantities. But philosophically, the need for time-accurate inlet conditions is what makes LES harder than RANS.

 raunakjung October 16, 2016 01:17

I see use of TUI COMMAND /solve/initialize/init-instantaneous-vel

to superimpose the synthesized turbulence on the mean flow. Is this practice appropriate to generate instantaneous velocity ?

 LuckyTran October 16, 2016 03:16

Quote:
 Originally Posted by raunakjung (Post 621644) I see use of TUI COMMAND /solve/initialize/init-instantaneous-vel to superimpose the synthesized turbulence on the mean flow. Is this practice appropriate to generate instantaneous velocity ?
That tool is for generating initial conditions for LES from RANS or mean-flow data. It is for perturbing the mean flow to give it some synthetic turbulence or else the LES will stay laminar. Its usable for generating instantaneous velocity for the initial conditions but you still need boundary conditions!

 Zbynek October 17, 2016 09:17

It is pretty much as LuckyTran said. If you have a system that does not contain any inlets and you have a converged RANS solution of the system available, you can switch to LES and let the flow field develop over time till it reaches a pseudo-steady state. The utility /solve/initialize/init-instantaneous-vel is useful in the sense that it introduces a perturbation to the RANS solution and so you should achieve the pseudo-steady state earlier. However, if an inlet is present in the system, you surely need a way how to perturb the inlet condition. Fluent gives you two options, I think - spectral syntesizer and vortex method.

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