Moving boundaries in fluid flows: Mudballs, meteorites, lollipops, and bubbles
Leif Ristroph, CIMS

Classical fluid mechanics considers flows that must conform to immovable solids, but in the real world all boundaries are compliant over some time scale. A flag flaps and flutters in a stiff breeze, while a mountain is gradually carved by wind and water erosion. In all such problems, shapeable boundaries conspire with fluid flows to give physically and mathematically interesting morphologies and shape dynamics. I will discuss some of the cases we’ve studied recently in Courant’s Applied Math Lab through experiments combined with models and simulations. We’ll explore the “sculptures” formed by fluidic erosion, ablation and dissolution, which are the persistent processes that carve stone and clay into landforms. A more delicate example is that of a soap film that deforms when blown with an external flow, eventually birthing a bubble.