On Modeling of Atmospheric Surface Layers by the Counter-Jet Technique

A new technique for tailoring mean profiles, thickness, and turbulent structure by spanwise-discrete upstream oriented wall jets with rapidly controllable velocities £/,and angle 0 to the ground is explored in the IIT Environmental Wind Tunnel. The boundary layers can be changed rapidly and reproducibly from outside the tunnel while experiments are in progress. Flexibility of the technique makes it attractive for the hitherto neglected study of sensitivity of measured effects (e.g., wind loads, pollutant dispersion) to changes in atmospheric layer. Separate and combined effects of Uj, 0, and wall roughness on longitudinal mean profiles and velocity fluctuations are illustrated.