Flow structures and dynamics in the wakes of sliding bubbles. (September 2016)

• Record Type: Journal Article
• Authors: O'Reilly Meehan, R.; Donnelly, B.; Nolan, K.; Persoons, T.; Murray, D.B.
• Is Part Of: International journal of multiphase flow. Volume 84(2016)
• Page Start: 145
• Page End: 154
• Publication Date: 2016-09
• Subjects: Sliding bubble -- Wake structures -- Particle image velocimetry; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2016.03.010
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Time-Resolved particle image velocimetry used to study the wakes of sliding bubbles. Hairpin vortex wake structure is observed, similar to that of a near-wall bluff body. Deformation of the bubble interface and path oscillations linked to vortex shedding. Abstract: An experimental investigation is reported for the flow structures in the wake of an air bubble sliding under an inclined surface in quiescent water. Time-resolved particle image velocimetry (PIV) is used to study the wakes of sliding bubbles for a range of measurement planes, bubble diameters and surface inclination angles. Additionally, key aspects of the bubble's motion are measured simultaneously using a novel method that accounts for the motion of the bubble's interface. Thus, vortex shedding may be linked to changes in the bubble shape and path. Analysis of the measured velocity and vorticity fields reveals a wake structure consisting of a near wake that moves in close proximity to the bubble, shedding vorticity at the inversion points of the bubble path. Downstream of the bubble in the far wake, these structures evolve into asymmetrical, oppositely-oriented hairpin vortices that are generated in the near wake. These hairpin vortices bear similarities to those observed behind freely rising bubbles and near-wall bluff bodies and are found to cause significant motion of the bulk fluid. This bulk fluid motion has the potential to offer significant convective cooling of adjacent heated surfaces, such as submerged electronics components.