use of common RANS B.C.'s in LES?

Sanjin Saric

I'm working on the RANS non-commercial code (standard k-eps turbulence model, SIMPLE algorithm, collocated grid, a second order space discretization method, the time integration is of second order using a fully implicit method with three time levels). The case to be simulated (modifying the existing code to perform LES with Smagorinsky model) is a low Re turbulent flow over backward-facing step. However, the proper B.C's for LES, periodic (in a spanwise direction) and convectiove outflow (outlet), are not available in the code. I wonder if anyone has an expirience in using the existing (although not physically correct?) symmetry (spanwise, 4h) and zero gradient (outlet, at x=35h) B.C.'s instead (typical for RANS) in LES simulation? Any suggestion or comment will be appreciated

thanx a lot in advance

Sanjin