Transport processes and multiphase flows: (I) Shear-induced diffusion and (II) Developments of biofilms during flow

Howard Stone, Princeton University
March 30th, 2011 at 4PM–5PM in 939 Evans Hall [Map]

Many processes contain suspended objects, which may be rigid particles, drops and bubbles, cells, etc. These objects can alter the flow since they can be distributed nonuniformly. In this talk, I describe two problems of this type. In the first example, we develop a microfluidic approach to study the transverse “diffusion” processes that occur when colloidal particles are sheared. We report the shear-induced diffusivity for nonspherical particles, which we show varies linearly with the number density of particles. We then apply this result to a theoretical calculation of the Taylor dispersion of colloids. Second, we study the development of biofilms on surfaces and identify conditions that lead to “bacterial streamers”. In particular, we report the formation of these filamentous structures suspended in the middle plane of curved microchannels under conditions of laminar flow. We use numerical simulations and analytical solutions of the three-dimensional flow in curved channels to highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Thus, we bring together experiments, simulations, and models to rationalize the spatial and temporal development of bacterial streamers.