Reynolds stress models and traditional large-eddy simulations are reex
amined with a view toward developing a combined methodology for the co
mputation of complex turbulent flows. More specifically, an entirely n
ew approach to time-dependent Reynolds-averaged Navier-Stokes (RANS) c
omputations and very large-eddy simulations (VLES) is presented in whi
ch subgrid scale models are proposed that allow a direct numerical sim
ulation (DNS) to go continuously to a RANS computation in the coarse m
esh/infinite Reynolds number limit, In between these two limits, we ha
ve a large eddy simulation (LES) or VLES, depending on the level of re
solution. The Reynolds stress model that is ultimately recovered in th
e coarse mesh/infinite Reynolds number limit has built in nonequilibri
um features that make it suitable for time-dependent RANS. The fundame
ntal technical issues associated with this new approach, which has the
capability of bridging the gap between DNS, LES and RANS, are discuss
ed in detail. Illustrative calculations are presented along with a dis
cussion of the future implications of these results for the simulation
of the turbulent flows of technological importance.