SpalartAllarmasIDDES LES model

mmmn036 · April 23, 2014, 20:24

Hello,

Hope you all are doing good.

I was trying to run a simulation for inertial flow using LES turbulence model. To capture the near wall physics and as a requirement of LES, I had to chose the mesh such that y+1 ~1. But for my case, it becomes too expensive in computational time to be feasible.

I was looking other approaches and found DES might work well for my case. I could not get thorough idea how to use SpalartAllarmasIDDES LES model, I mean what i need to change from LES setup. What I understand is:

1. I need to put RASproperties and LESporperties in constant folder
2. need to put LESModel as SpalartAllmarasIDDES for LES and SpalartAllmaras for RANS.
3. need to put SpalartAllmarasIDDES coefficents.

What about the boundary conditions? How could I use two type of boundary condition for RANS and LES at the same time?
Is there any y+ restrictions?

Can anyone tell me the steps I should follow for using SpalartAllmarasIDDES turbulence model? I would appreciate that.

Thanks
MMMN

msuaeronautics · April 23, 2014, 21:01

This only requires the initialization of the turbulent viscosity (nuSgs) and the Spalart-Allmaras variable (nuTilda), as is the case with DDES and the RANS SA model.

You should pick nuSgs based on your desired turbulent viscosity ratio, while I believe nuTilda should probably be about 3 or 5 times nuSgs.

April 23, 2014, 20:24	SpalartAllarmasIDDES LES model	#1
mmmn036 Member Manjura Maula Md. Nayamatullah Join Date: May 2013 Location: San Antonio, Texas, USA Posts: 42 Rep Power: 13	Hello, Hope you all are doing good. I was trying to run a simulation for inertial flow using LES turbulence model. To capture the near wall physics and as a requirement of LES, I had to chose the mesh such that y+1 ~1. But for my case, it becomes too expensive in computational time to be feasible. I was looking other approaches and found DES might work well for my case. I could not get thorough idea how to use SpalartAllarmasIDDES LES model, I mean what i need to change from LES setup. What I understand is: 1. I need to put RASproperties and LESporperties in constant folder 2. need to put LESModel as SpalartAllmarasIDDES for LES and SpalartAllmaras for RANS. 3. need to put SpalartAllmarasIDDES coefficents. What about the boundary conditions? How could I use two type of boundary condition for RANS and LES at the same time? Is there any y+ restrictions? Can anyone tell me the steps I should follow for using SpalartAllmarasIDDES turbulence model? I would appreciate that. Thanks MMMN

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April 23, 2014, 21:01		#2
msuaeronautics Member Eric Robertson Join Date: Jul 2012 Posts: 95 Rep Power: 15	This only requires the initialization of the turbulent viscosity (nuSgs) and the Spalart-Allmaras variable (nuTilda), as is the case with DDES and the RANS SA model. You should pick nuSgs based on your desired turbulent viscosity ratio, while I believe nuTilda should probably be about 3 or 5 times nuSgs.