12Different Reynolds number turbulent flows Small Re flows: laboratory (tea cup) turbulence; largest eddies ~ O(m); RAN or DNSMedium Re flows: engineering flows;largest eddies ~ O(10 m); RAN or DNS or LESLarge Re flows: geophysical turbulence;largest eddies > km; RAN or LES
13Geophysical turbulence PBL (pollution layer)boundary layer in the oceanturbulence inside forestdeep convectionconvection in the Sun…..
14LES of PBL inertial range, km m mm resolved eddies SFS eddies L energy inputdissipation
15Major difference between engineer and geophysical flows: near the wall Engineering flow: viscous layerGeophysical flow: inertial-subrange layer; need to use surface-layer theory
16The premise of LESLarge eddies, most energy and fluxes, explicitly calculatedSmall eddies, little energy and fluxes, parameterized, SFS model
17The premise of LESLarge eddies, most energy and fluxes, explicitly calculatedSmall eddies, little energy and fluxes, parameterized, SFS modelLES solution is supposed to be insensitive to SFS model
18Caution near walls, eddies small, unresolved very stable region, eddies intermittentcloud physics, chemical reaction…more uncertainties
19A typical setup of PBL-LES 100 x 100 x 100 pointsgrid sizes < tens of meterstime step < secondshigher-order schemes, not too diffusivespin-up time ~ 30 min, no usesimulation time ~ hoursmassive parallel computers