Particle resuspension in a turbulent boundary layer-observed and modeled

Particle resuspension from a surface solely by turbulent fluid forces has been examined experimentally by observing, in detail, the intermittent particle resuspension process. Experiments were conducted in an environmental wind tunnel, where sparse beds of monodisperse Lycopodium spores (Club moss) were placed flush with the floor of the wind tunnel, and exposed to a steady, well developed turbulent boundary layer flow. Particle bed concentration was monitored in situ throughout each experimental trial using an optical system designed to detect forward scattering from a He-Ne laser beam. Experimental trials were conducted at three free-stream velocities (6.0, 7.5 and 9.0 ms −1) for a duration of 35 min. Particle resuspension was observed to occur in discrete and intermittent events, with the fraction of particles resuspended as a function of time generally following an exponential decay. A Monte-Carlo particle resuspension model was developed and used to simulate the resuspension process, based on the hypothesis that particle resuspension is associated with coherent structures (bursts) which vary in magnitude. This model was found to successfully reproduce many of the features of particle resuspension observed experimentally.