Hello All
Would like to know whether any one has Best practices/guidelines for setting up Embedded LES in Ansys Fluent.
I am confused how to define RANS in the global region and define LES in specific regions in the mesh. ie, two schemes in a single mesh.
In Fluent you chose the DES approach, see https://www.sharcnet.ca/Software/Fluent6/html/ug/node501.htm
Hi Filippo
DES - uses RANS in the near wall region and solves LES in the outer domain.
Embedded LES is reverse of DES. It creates a sub domain of interest inside global domain. This subdomain solves for LES and remaining global region is solved using RANS. This can be used if we are interested in using LES only for a specific region in a global domain.
I have attached a screenshot of Fluent where it can be done. Looking for best practices used for this approach.
In my opinion, DES, embedded LES or other nomenclature means nothing.
The key is in the fact that the simulation is a hybrid within (U)RANS and LES. From a computational point of view I understand the final goal of doing that. From a theoretical point of view, there is no one of these formulation that has a convincing basis. That's for sure that someone will argue my opinion but, at present, I never read a convincing paper.
Thanks for such an overview about these methods. DES, Embedded LES etc. fall under the broad category of hybrid LES. Depending on problems/requirements, we apply DES or Embedded LES etc. For eg: someone who cant afford the computation expense of a proper LES.
You need to define the interfaces between RANS and LES zones. Of course, an outflow for the RANS zone must be properly transformed in an inflow for the LES zone. Some proposals exist, you can see here
http://www.iawe.org/Proceedings/BBAA7/N.Jorgensen.pdf
http://www.tfd.chalmers.se/~lada/postscript_files/paper_embedded_LES.pdf
Fluent can allows ELES https://www.sharcnet.ca/Software/Ansys/16.2.3/en-us/help/cfx_ref/bp_turbu_s_9.html
Thank you for the Chalmers paper. I am following the other papers. Will update the findings.
Hi Joemon,
In my case, I normally prepare two separate volumes for RANS and LES regions. They have conformal mesh, and I meshed LES region using BOI (body of influence), and I just used Ansys meshing tool.
When they are translated into fluent, you can define the RANS and LES interfaces (if you want details, I can provide further)
Back to your question, you define RANS for the whole model. But in the Cell Zone Conditions, you choose your LES region (volume) and click on 'LES ZONE' that the tab of Embedded LES will become 'active', and you can define vortex method.
Hope this helps.
Daniel
Hi Daniel
How do we make grids for LES and RANS separately. LES region needs fine meshing as of kolmogrov scale and RANS doesnt need that. How the interface meshes will be is a doubt from my side.
Hi Joemon
As initial preperation step for Ansys meshing, I use spaceclaim to prepare the model. In spaceclaim, even if you have two volumes (LES inside RANS volume) you can define the topology option as 'merge'; then conformal mesh will be created later in Ansys meshing. However, ELES allows non-conformal mesh so it is not a big problem if the two volumes are not conformal, as long as the grid size difference is not beyond the allowing threshold. For the overlapping surfaces of the two volumes, you need to define them later as 'interior' in Fluent. Once they are defined as 'interior' you can define them as 'Les rans interface'. For non-conformal mesh, you need to use 'create/edit mesh interface dialogue box' to define the overlapping surfaces of LES and RANS volumes as interfaces.
How does the above sound to you?
Daniel
Hi Daniel
If ELES allows non conformal meshing, i think its not a problem.
Thanks for the detailed explanation.
Joemon
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