In large eddy simulations (LES), a flat ground model and rough wedge ground models with different wedge heights were adopted to investigate near-surface wind field characteristics under condition of time-varying upstream inflows. In both flat ground model and rough wedge ground models, simulated results show that there is downdraft in peak period of gusty wind and updraft in valley period, respectively. Intensity of downdraft/updraft flows are related to ground roughness in upwind areas and amplitude of inflows. It follows that wind velocity and direction in atmospheric boundary layer always change over time in time-varying upstream inflows, which enhances transportation of mass and energy in actual atmospheric boundary layer.

In the Sagaut mixed-scale model,an improved subgrid-scale(SGS) characteristic length,representing the scale of local energy-containing SGS motions,is proposed.Large-eddy simulations(LES) at temporal mixing layer and neutral atmospheric boundary layer indicate that by the improved SGS characteristic length,satisfactory spatial distribution of the SGS motions can be obtained and are closer to the results of direction numerical simulations(DNS).Compared with the basic model,the modified model with the improved SGS characteristic length produces more accurate mean quantities and turbulent statistics.The results demonstrate its valuable and wide application to LES.