Session A1: Physics of Fluids: Session I

The Dynamics of Greenland's Glacial Fjords and Their Role in Climate.

Rapid mass loss from the Greenland Ice Sheet has sparked interest in its glacial fjords for two main reasons: Increased submarine melting of glaciers terminating in fjords is a plausible trigger for glacier retreat, and the anomalous freshwater discharged from Greenland is transformed by fjord processes before being released into the large-scale ocean. Knowledge of the fjords' dynamics is thus key to understanding ice sheet variability and its impact on climate. Major gaps in understanding include the interaction of the buoyancy-driven circulation (forced by the glacier) and shelf-driven circulation, and the dynamics in the near-ice zone. These must be addressed before appropriate forcing conditions can be supplied to ice sheet and ocean/climate models. Idealized laboratory experiments have been conducted to investigate the leading order dynamics that control submarine melting and the meltwater export near a vertical ice/ocean interface as a function of ambient properties and stratification, subglacial discharge characteristics and fjord topography, in particular the presence and height of a sill.   

Bursting bubbles and the search for invisible droplets

When a bubble bursts at an interface, the capillary waves create an intriguing cusp, which is responsible for an upward jet that can break into droplets. This jet drop phenomena is relevant to a variety of topics including the transport of respiratory pathogens and cloud-forming marine aerosols. The first part of this talk addresses how gravity and viscosity can inhibit jet drop production. The dominant role of gravity appears to be its role in the setting the bubble shape. The second part of the talk explores the size of the smallest aerosols produced. Given that the size of these droplets may be smaller than the wavelength of visible light, we are indeed searching – both experimentally and numerically – for invisible droplets.   

Superhydrophobic Drag Reduction

Superhydrophobic surfaces combine hydrophobic surface chemistry with surface roughness at the micron scale. The result is free-surface contact angles in excess of 170 degrees and drag reduction of boundary layers next to these surfaces. Both the laminar and turbulent drag reduction mechanisms are discussed in this presentation. Direct numerical simulations of turbulent channel flow are used to investigate the turbulent drag reduction dynamics, slip velocities, wall shear stresses, and Reynolds stresses for a variety of superhydrophobic surface micro-features, and geometry configurations, at friction Reynolds numbers of 180, 395, and 590. It is shown that in the turbulent regime these surfaces can be modeled well as ``anti-rough'' surfaces.