Dr. Andrew Wells

Department of Physics, University of Oxford

The rapid solidification of a binary alloy leads to the formation of a chemically reactive porous medium, or mushy layer. Under certain growth conditions, convection of the interstitial liquid and local dissolution of the solid matrix lead to flow focusing in drainage channels devoid of solid: so-called chimneys. The dynamics of these convective chimneys evolve in space and time, with key implications in a range of solidification problems. For example, chimney formation leads to material inhomogeneities and defects in the casting of metal turbine blades. Meanwhile, in a geophysical context, chimneys form the primary conduits for salt fluxes from growing polar sea ice that provide buoyancy forcing for ocean circulation. I will describe a combination of theory, numerical modelling, and experiment that are used to explore the interplay between convection, phase change, and the resulting nonlinear dynamics of convection in mushy layers.