Atmospheric boundary layer testing. Final project report

Low-speed wind-tunnel studies have been conducted that examined mean velocity profiles and longitudinal turbulence quantities including the energy spectra for a zero-pressure-gradient turbulent boundary layer flow over a rough-to-smooth change in surface roughness. The flow examined modeled the lower 30 to 50 m of the urban atmospheric boundary layer. The wind-tunnel flow was developed over a 12 m long flow conditioning section where roughness elements occupied the lower 10 to 13% of a 70 cm thick boundary layer with the freestream velocity of approximately 3.0 m/s. The present results provided unique information concerning the wind tunnel simulation of the urban atmospheric boundary layer in the following areas: (1) the presence and growth of an ''inner boundary layer'' downstream of a step transition in surface roughness; (2) the enhancement of boundary layer thickness ad turbulence characteristics using vortex generators or spires; and (3) determination of the appropriate modeling length scales. 56 figs., 4 tabs.