## Fluids

#### How to switchon LES in Fluent 17.2?

• José Mantovani
Subscriber

So guys, I try to do a comparative study using RANS, DES, and LES turbulence models in the geometry image below.

The boundary conditions are inlet, outlet and the rest of edges I set as wall. I dont use symmetry. Where a dotted line I set up as a wall.

First for the RANS approach I just solve a transient flow with SST k-omega model.

For the DES approach, first I solve the initial flow with SST k-omega as steady state with some iterations, after I set the viscous model to DES and calculate the transient flow.

For the LES approach, in the same way as use in DES approach, I solve the initial flow with SST k-omega as steady state and after I set the viscous model to LES. But it do not work. I try to switchon using the code ( (repsetvar 'les-2d? #t) ) and dont work! So, I dont know what's the problem...

I know the LES model is suitable for 3D and can cause non-physical 2D results. Even because, even if the flow in which the mean velocity and pressure vary in only one or two spatial dimensions, turbulent fluctuations always have three-dimensional spatial characteristics.

What's can be the problem? The LES is not available to ANSYS Fluent 17.2 or need some other setup?

Somebody help me? Thanks guys!

• raul.raghav
Subscriber
I’ll apologize if this sounds silly in anyway .
The command is correct and there shouldn’t be any issues running LES on 2D cases. Did you try using the inverted apostrophe instead of the regular apostrophe in front the “les”? The inverted apostrophe would the symbol along with the approximate symbol on the left side of the keyboard.
• José Mantovani
Subscriber

I try just this code (repsetvar 'les-2d? #t) . You say the code like this: (repsetvar "les-2d? #t) ?

Another question is the extent to which I use a large time step size (like 0.2) so it is more difficult for the waste to fall below the tolerance when compared to using a small time step size (like 0.001). Is there any relationship between or was it just a coincidence? Because I realized this when doing with these two values, I used a larger one to reduce the calculation time but the residuals are under tolerance...

Very thanks my friend Rahul.

Mantovani.

• raul.raghav
Subscriber

Look at the attached screenshot of the keyboard for the symbol I'm mentioning.

To answer the question, please refer to the following document which also attached as a pdf in the post.

TFD-Chalmers: Ansys - Quick guide to setting up LES-type simulations

• José Mantovani
Subscriber

I will try input the code and see this pdf file!

Thanks a lot Rahul!

Mantovani.

• raul.raghav
Subscriber

Any update on this problem, Mantovani?

• José Mantovani
Subscriber

Hello Rahul!

Thanks for the attention! By the beginning I used the correct symbol ' " and no the symbol in the right of screenshot.. But I try input this code before to choose some turbulent model and it's work very well. I want post here the video of simulation, but I dont know how to send here... I think the format dont accept videos.

Thanks again Rahul!

Mantovani.