FLUTE-Seminar-Estella Yu

The Fluids and Thermal Engineering Research Group warmly invites you
to attend their Virtual Thursday Seminar on 29^th October 2020 at 15.30pm

We study bubble motion in a vertical capillary tube under an external flow.  Bretherton (1961) showed that, without external flow, a bubble can spontaneously rise when the Bond number (Bo ≡ ρgR^2/γ) is above the critical value 0.842. It was then shown by Magnini et al. (2019) that the presence of an imposed liquid flow, in the same (upward) direction as buoyancy, accelerates the bubble and thickens the liquid film around it. In this work we carry out a systematic study of the bubble motion under a wide range of external flows, focusing on the inertialess regime with Bo above the critical value. We show that a rich variety of bubble dynamics occur when an external downward flow is applied, opposing the buoyancy-driven rise of the bubble. We reveal the existence of a critical capillary number of the external downward flow (Cal ≡ μU_l/γ) at which the bubble arrests and changes its translational direction. Depending on the relative direction of gravity and the external flow, the film thickness follows two distinct solution branches. The results from theory, experiments and numerical simulations confirm the existence of the two solution branches and reveal that the two branches overlap over a finite range of Cal, thus suggesting non-unique, history-dependent solutions for the steady-state film thickness under the same external flow conditions. Furthermore, inertialess symmetry-breaking shape profiles at steady state are found as the bubble transits near the tipping points of the solution branches, which are shown both in experiments and numerical simulations.

Estella is currently a postdoctoral fellow in the Department of Mechanical and Aerospace Engineering at Princeton University.  She received her PhD degree in the same department in the Complex Fluids Group, advised by Professor Howard A. Stone. Estella's research is built around multiphase flows, thin films and colloid science, where she develops an efficient and cost-effective particle separation technique by combining the results from analysis, experiments and simulations.

This seminar will be delivered through Teams, Office 365.  If you haven't received an invitation and would like to attend, please contact Research Administrator, Sarah Taylor.