Collisional Interactions in a Viscous Fluid

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COLLISIONAL INTERACTIONS IN A VISCOUS FLUID M.L. Hunt and C.E. Brennen Abstract The proposed work investigates particulate flows in which both hydrodynamic effects and collisional interactions are important. This research lies between suspension flows and granular material flows and encompasses debris flows, slurry and sludge transport, milling and mining applications, sediment transport, abrasive machining, polishing and surface erosion technologies. These flows are characterized by having fluid and solid phases of comparable density, solid fractions approaching that of a packed bed, and particle Reynolds and Stokes numbers greater than unity. The proposed work emphasizes a fundamental understanding of the fluid and solid mechanics of collisional interactions, including the development of models and computational tools, and the education of students and scholar through research opportunities. The research focuses on the interactions of individual particles colliding with a surface. To date, we have done extensive measurements of normal particle collisions. These results demonstrated that below a critical Stokes number, about 10, all of the particles kinetic energy is lost during the compression of the lubrication film with no rebound of the particle. Above a second Stokes number, about 2000, the particle rebounds with negligible effect of the lubrication layer. The proposed work expands on these experiments by measuring oblique collisions in which the particle may roll or slide. Related experiments involve binary-particle collisions in a liquid, which differs from the particle-wall collisions because the target particle may move prior to the impact. Both of these experiments would be performed for Stokes number from 10 to 3000, and include different material properties and surface conditions. Measurements are also proposed of the surface deformation and erosion during impact using controlled collisions with a single particle in a viscous fluid. Both normal and oblique collisions will be examined for different Stokes numbers and material properties. An analytical study will accompany the measurements. The final subject involves exploratory measurements of the fluid motion resulting from a particle collision. As a particle approaches a wall, the fluid in the gap is forced radially outward, and then the fluid reverses direction as the particle rebounds. These flow reversals affect the wall shear stress in the single particle experiments and in dense particulate flows. An integral part of this research work is the education students and scholars. The PIs have included students in all aspects of their research, including the authoring of technical papers and presentations at appropriate scientific meetings. In prior and ongoing research, the PIs have placed a heavy emphasis on the inclusion of student from underrepresented groups and extensive involvement of undergraduate students. Some of these undergraduates have been recognized for their outstanding research, and approximately half have gone on to engineering graduate programs. The PIs have also presented their research to local schools through community and campus programs.