LES
The methodology of LES is increasingly used in PBL research. It is formulated by specifying the large-scale environment and calculating the fluid dynamics on scales ranging from approximately the PBL thickness down to a grid scale D limited by the feasible size of the computation. LES explicitly captures large turbulent eddies, which contain most of the turbulent kinetic energy and carry most of turbulent transport, and approximates the effects of small turbulent eddies in its subgrid-scale model.
This technique was first developed at NCAR in the late 1960s by Jim Deardorff and Doug Lilly, and is now widely used as a major tool for investigations of turbulence in engineering and geophysical fields.
Contact at ISAC: Umberto Rizza (u.rizza@isac.cnr.it)
DNS
Direct numerical simulation (DNS) does not require any turbulence parameterization. The Navier-Stokes and energy conservation equations are solved resolving all the scales of motion. Turbulent eddies, from the smallest to the largest, are computed. For its extreme accuracy and level of description, DNS can be considered as a numerical experiment: in principle, the whole spatial and temporal evolution of the flow velocity and scalar fields can be recovered.
Due to their large numerical cost, DNSs of the PBL have only recently been feasible, but they are now widely used and represent one of the most promising approach to the study of stratified, horizontally inhomogeneous atmospheric flows.
Contact at ISAC: Luca Mortarini (l.mortarini@isac.cnr.it)