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Maynard, Auston

Mechanical Engineering

2011

MS

A bounded vortex flow consists of an axisymmetric vortex that is confined top and bottom between two plates (the "confinement plate" and "impingement plate", respectively) and surrounded laterally by a swirling annular slot jet. The bottom of the vortex terminates on the boundary layer along the impingement plate and the top of the vortex is drawn into a suction port positioned at the center of the confinement plate. The circumferential flow within the annular jet is important for supplying circulation to the central wall-normal vortex. This flow field is proposed as a method for mitigation of dust build-up on a surface, where the vortex-jet combination supplements the more traditional vacuum port by enhancing the surface shear stress and related particle transport rate. This thesis reports on a computational study of the velocity field and particle transport by a bounded vortex flow.
Fluid flow computations are performed using a finite-volume approach for an incompressible fluid and particle transport is simulated using a discrete-element method. Different flow regimes are observed as a function of the ratio of the plate separation distance and the average radius of the jet inlet, as well as the ratio of flow nite withdrawn at the suction outlet and that injected by the jet. In addition to the wall-normal vortex, a toroidal vortex ring forms in many cases which further enhances the surface shear stress. Particles are observed to roll along the impingement surface in a direction determined by the fluid shear stress lines. Particles roll outward when they lie beyond a separatrix curve of the surface shear stress lines, where particles within this separatrix curve roll inward, piling up at the center of the flow field. The inward rolling particles intermittently lift up due to collision forces and burst away from the impingement surface, eventually to become entrained into the flow out the suction port or resettling back onto the impingement surface.