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Presenter: Dr. Asghar Esmaeeli - Department of Mechanical Engineering, University of Michigan
Supervisor:

Date: Tue, February 20, 2001
Time: 11:00:00 - 00:00:00
Place: EOW 430

ABSTRACT

Abstract:

Direct numerical simulations of the motion of two- and three-dimensional buoyant bubbles in periodic domains are presented. The full Navier-Stokes equations are solved by a finite difference/front tracking method that allows a fully deformable interface between the bubbles and the ambient fluid and the inclusion of surface tension. Dynamics of a "regular" array of bubbles is compared with the corresponding "freely evolving" one at low and moderate Reynolds numbers.

The simulations show that a regular array is an unstable configuration and the break up, and the subsequent bubble-bubble interactions take place by "drafting, kissing, and tumbling." While a freely evolving array of bubbles rises faster than a regular one at low Reynolds number, the opposite is true for moderate Reynolds number flows due to larger viscous dissipation. The effect of the number of bubbles in each period is examined for the two-dimensional systems and it is found that although the rise Reynolds number is nearly independent of the number of bubbles, the velocity fluctuations in the liquid (the Reynolds stresses) increase with the size of the system.

The structure of the bubble distribution is examined and it is found that the three-dimensional bubbles show a tendency to line up horizontally, while the two-dimensional bubbles are nearly completely randomly distributed. A few examples of research work on more complex multiphase flow systems such as thermocapillary migration of bubbles, film boiling, and solidification will also be presented.