[siw]

Can CFX perform Delayed Detached Eddy Simulations (DDES)? I cannot find any mention of it in the User Guides or in the CFX-Pre GUI. However, in the document Best Practice: Scale-Resolving Simulations in ANSYS CFD by F. R. Menter it recommends using DDES rather than DES. I known Fluent can be used both DES and DDES, so it's odd that it'd not be in CFX.

Also in the DES section of the CFX Modeling Guide (v14.5) sec 4.1.12.2.6 (see image) it says that the vorticity needs to be included in the output list for CFD-Post with a CCL. But there's can it be added to the variable output using the GUI (see image) without the CCL. The same goes for the averaging statistics?

[ghorrocks]

I am not familiar with DDES but as far as I know all the new turbulence options in Fluent are also in CFX. So I suspect it is in CFX as well, but I do not know exactly how it is implemented.

I do not understand your question about adding the vorticity to the results file.

[siw]

Thanks for the reply Glenn.

I've attached an image showing the turbulence models available and DES is there but not DDES, notice that many LES options are listed. So I thought that DDES is selected within the option of DES (just like Fluent) but there is not any such option (see second image which I've checked all boxes to see what's there). So as you say if it's in Fluent then it should be in CFX, but where?

All I was asking about with the vorticity was in reference to the comment in the CFX Modeling Guide (sec 4.1.12.2.6). There is says it's a good idea to output the vorticity and to do that CCL is needed. But I was asking if rather than use the CCL, as per the guide, then the GUI options (images previously attached) does the same job. Likewise, with the averaging statistics.

[ghorrocks]

It may well be an option inside the DES model. I suspect you might have to talk to ANSYS support to find out where.

Your GUI options to output vorticity look good to me. Sounds like there is no need for CCL to include it any more.

[siw]

Thanks Glenn.

Has anyone here ever successfully conducted a DES using CFX?

With RANS and URANS being inaccurate for many types of complex/industrial flows and LES still being too computational intensive I would have thought more people would be using SAS or DES as a middle option, but there's hardly ever any topics on DES.

[Far]

If you look at the DES model, it is based on SA model which is not available in CFX... and DDES is also proposed based on grid sensitivity of DES-SA model. While SST-DES does not suffer from theses limitations as written in theory guide...

The ANSYS CFX version of the DES model is based on the SST formulation. The advantage of this combination is that the accurate prediction of turbulent boundary layers up to separation and in mildly separated regions carries over from the SST model. In addition, the SST model supports the formulation of a zonal DES formulation [ 56 ], which is less sensitive to grid resolution restrictions than the standard DES formulation, as proposed by Strelets [ 58 ]. Refer to the ANSYS CFX technical report [ 55 ] for details.

[58] Strelets, M.,
“Detached Eddy Simulation of Massively Separated Flows”,
AIAA Paper 2001-0879, 39th Aerospace Sciences Meeting and Exhibit, Reno, NV, 2001.

Quote from one paper :

. The transfer function for the S-A one equation based DES model4 solely depends on the local grid spacing. In the two-equation based hybrid models5,8-10, the transfer from RANS to LES regions depends on both local grid spacing and turbulent flow properties.

What i see is that SA based DES or DDES models are more popular ...

Edit: Here I found the DDES-SST
http://dr.ntu.edu.sg/bitstream/handl...pdf?sequence=1

[Far]

Ok. We have DDES - SST available in CFX...

CFX theory guide...


some thing similar in fluent theory guide...


Also search this document on google >>>> 87333253-DES-Turbulence-030808.pdf

[Mazze[ITA]]

Originally Posted by Far

Ok. We have DDES - SST available in CFX...

Also search this document on google >>>> 87333253-DES-Turbulence-030808.pdf

Yes, also according to this (http://cfd.grs.de/downloads/best-pra...enter-2012.pdf) the DES model implemented in CFX is actually DDES.

Furthermore, I found the document you were mentioning: http://www.docshut.com/unzpu/des-turbulence-030808.html