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YPlus for SpalartAllmaras

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Old   November 24, 2008, 17:22
Default Hi all, I am running MRFSimpl
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Dnyanesh Digraskar
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Hi all,
I am running MRFSimpleFoam with SpalartAllmaras turbulence model. I want to calculate YPlus for walls. When I use checkYPlus utility, it returns me 0 values for yP.
Sample o/p of YPlus:
Selecting incompressible transport model Newtonian
Selecting turbulence model SpalartAllmaras
Patch 0 named wing y+ : min: 0 max: 0 average: 0

Patch 1 named cylinder_wall y+ : min: 0 max: 0 average: 0

Time = 0.112876
Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting turbulence model SpalartAllmaras
Patch 0 named wing y+ : min: 0 max: 0 average: 0

Patch 1 named cylinder_wall y+ : min: 0 max: 0 average: 0

Time = 0.113321
Reading field p

Reading field U

Can anyone help me. I think selecting the SpallartAlmaras model, sets something in YPlus equation to 0, but im not sure about what.
Thanks alot for help.
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Old   December 12, 2008, 15:29
Default Dnyanesh, First and foremos
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Nate See
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Dnyanesh,

First and foremost let it be known that I am not a current user of OpenFOAM. I actually just found out about it today and am currently cruising the message board to try and get a feel for the product. Therefore, I do not know how the incompressible transport model or SA turbulence model has been implemented. However, I will impart my knowledge of the SA turbulence model.

The SA turbulence model solves a transport equation for the eddy viscosity. However, to insure that the Dirichlet boundary condition is satisfied at the wall, it will set the eddy viscosity equal to zero. The part that I am not 100% sure of, and hopefully someone else can chime in, is how the eddy viscosity relates to the kinematic viscosity (what y+ is based off of).

What I would suggest is taking the value one cell off of the surface (as long as it is relatively close to the surface, e.g. the first layer of the boundary layer grid) and use that value. This is what NASA's Fun3D, full Navier-Stokes solver, does to display the y+ on the surfaces.

Hope this helps,
Nate
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