The motion of 70 μm-diameter stainless steel microspheres, after their detachment from rough, flat surfaces due to turbulent air flow is considered. The microspheres are embedded fully in the viscous sublayer and initially are in static-contact equilibrium. Then, the microspheres are subjected to a slowly accelerating flow. Microvideographic observations of individual microsphere motion after detachment show that these relatively heavy microspheres move along the surface before any possible lift-off. A strobed laser-light sheet technique is used to obtain the microsphere velocities along the surface right after their detachment. The equations of motion of the microspheres are presented, including surface-roughness effects and dissipative forces and moments. The equations are solved numerically for detachment with and without consideration of a burst-sweep event initiating detachment. The measured microsphere velocities are compared to the numerical solutions. Results reveal that the microspheres undergo pure rolling along the surface before possible entrainment, that the sweep part of the event plays a role in the detachment process and that the dissipative contact forces and moments are negligible compared to the Hertzian and adhesion forces and moments.
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