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Fluid Seminar: Detailed Simulations of Near-Wall Bubble-Cluster Dynamics

Event Type
fluid mechanics
Mechanical Science and Engineeering
143 Mechanical Engineering Building
Oct 18, 2013   12:00 pm  
Mr. Arpit Tiwari, University of Illinois
Originating Calendar
MechSE Seminars


The collapse of bubble-clusters adjacent to material surfaces is an important damage mechanism in both engineering and biomedical applications. Because of their complexity, bubble-cloud dynamics have largely been represented in the past theoretical studies using simplified homogeneous (volume or ensemble-averaged) bubbly-flow models that neglect the details of bubble-scale dynamics. However, the details of the bubble-scale dynamics are potentially important near a wall.  For example, damage is expected to depend upon local peak pressures rather than an average pressure as might be computed with a homogeneous model.  Here, we simulate the expansion and subsequent collapse of a hemispherical cluster of 50 bubbles adjacent to a planar rigid wall using a computationally efficient diffuse-interface based numerical scheme we developed for compressible multiphase flows that represents in detail the coupled-asymmetric dynamics of each bubble within the cluster. Simulations show that collapse propagates inward, and a geometrical pressure-focusing occurs, with gross features as can be anticipated by a homogenized model, but the peak pressures for example depend strongly on the arrangement of the bubbles. In particular, we show strong dependence of peak pressure on the dynamics of the bubbles near the focus region. The dynamics of bubbles depend on their spatial location within the cluster, and the dynamics of the outer bubbles are significantly different compared to the central bubbles. The inward propagating collapse phase is associated with re-entrant jetting of bubbles toward the cluster center. As a result, the bubbles follow highly non-spherical dynamics, which are even accompanied with topological changes. The initial acceleration of bubbles that drives the expansion phase is identified as an important parameter governing the bubble interactions, and hence the pressure focusing.

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