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-   -   Recommeded boundary conditions for a DES (http://www.cfd-online.com/Forums/cfx/121615-recommeded-boundary-conditions-des.html)

siw August 1, 2013 08:31

Recommeded boundary conditions for a DES
 
Hi,

I'm setting up a DES of a flat plate in a domain similar to that in:

http://turbmodels.larc.nasa.gov/flatplate_val.html

but in my case there's also an obstacle on the plate. Also my domain size is larger and in 3D.

What would be the recommended DES boundary conditions where the image in the hyperlink shows symmetry and farfield Riemann BC? Symmetry should not be used in any DES (or LES).

Thanks.

flotus1 August 1, 2013 09:29

Dont mix up the recommendations for DES. Symmetry boundary conditions should not be used to exploit symmetries of the domain. For example, if you want to simulate the flow in a pipe, you should not model only half of the pipe and use a symmetry boundary at the cutting plane (the way you would do it with a RANS approach)
But the way the symmetry boundary condition is used here might be usable for a DES if there are no perturbations at the inlet.
For the farfield boundaray condition, a symmetry can also be used in a DES if the turbulent fluctuations decay far enough before reaching the boundary.

siw August 1, 2013 10:49

That is what I was asking about. In RANS (as shown the hyperlink) symmetry is okay upstream of the flat plate - but not okay for DES. Menter's ANSYS SRS Best Practice Guide I think mentions that. So what would be recommended for DES instead.

flotus1 August 1, 2013 11:15

Like I said, if you have no perturbations at the inlet, a symmetry boundary condition at this boundary might be justified even for DES.
Otherwise, you will have to mirror the whole geomety along the plane y=0 and simulate the entire domain.


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