Abstract

Hybrid, non-zonal closure models can be described as interpolations between RANS and LES formulas.  Hybrid simulations resolve large-scale turbulent eddies, so the reference to RANS is only to formulas, not to a Reynolds averaged description.   The aim of the hybrid approach is to make eddy resolving more attractive for applications.  Laminar to turbulent transition arises in some such applications.  Thus, a basic question is, can a hybrid turbulence model plausibly capture  laminar-to-turbulent transition? The answer is far from obvious. Indeed, for many hybrid models, the answer is no. However, solution adaptive models do have the potential to capture transition. Exactly how is a matter of empiricism, which will be discussed.  The initial stage is obvious:  precursors—-instability waves, or Klebanoff streaks—-are resolved.  But only the very earliest stage of breakdown is simulated.  After that the subgrid model replaces small scales, and, in the RANS zone, it replaces resolved stress by modeled stress.   The nature of hybrid transition will be discussed for the case of the ell^2-omega model.