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Near-wall dynamics of neutrally buoyant particles in a wall-normal flow

Li, Qing. Near-wall dynamics of neutrally buoyant particles in a wall-normal flow. PhD, Génie des Procédés et de l'Environnement, Institut National Polytechnique de Toulouse, 2019

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Abstract

Two-phase suspensions encountered in various engineering applications(like crude oil extraction, elaboration of food, concrete or cosmetics), can exhibit rich dynamics when submitted to flow in complex geometries. Predicting the response of such heterogeneous material under flow is an important issue in view of applications. To build these predictive models, basic understanding of the dif- ferent scales is required for configurations such as pipe flow through an elbow or T-shape section, mixing a solid-liquid dispersion by a rotating impeller, etc. Suspension flows normal to an obstacle have seen limited attention with the carrier fluid being liquid phase. In this context, we examined particle dynamics in the well-known Hiemenz boundary-layer flow, with the aid of numerical simu- lations. We focused essentially on one or two neutrally buoyant particles, which are of finite size compared to the boundary layer thickness (particles have a finite inertia near the wall because they are forced to stop at the wall), and which are located at the symmetry axis of the flow. We used direct numerical simulations in order to measure the particle slip with respect to the local flow, the hydrodynamic force experienced by the particle and the energy loss during solvent-mediated particle-wall interaction. All these quantities were determined as unique functions of the ratio between the particle size and the thickness of the viscous boundary layer. When the particle size is increased, the simulations highlighted a transition of the particle dynamics from viscous damping to rebound, occurring for particle size O(). We established a model for the hydrodynamic force experienced by the incident particle, and for the restitution coefficient in wall-normal flow. For two identical particles on the axis, certain separations lead to particle collision before the lower (closer to wall) particle hits the wall; the resulting momentum exchange leads to larger impact velocity than for one particle. The simulations reveal that dynamics of the colliding pair includes unexpected rebound without contact with the wall for the lower of two particles, due to sheltering by the upper particle from drag allowing the pressure force to dominate.

Item Type:PhD Thesis
Uncontrolled Keywords:
Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Laboratory name:
Research Director:
Morris, Jeffrey F. and Abbas, Micheline
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Deposited On:07 Apr 2020 14:41

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