Abstract: Interactions through flows are thought to be a major reason that swimming and flying animals come together in schools and flocks. But unlike drafting or peloton effects among bicyclists or race cars, the hydro- or aero-dynamic interactions for flapping locomotion remain unknown. I’ll describe our research program aimed at understanding the fluid dynamics of collective locomotion through increasingly elaborate lab experiments, simulations, and math modeling. Our work focuses on “mock flocks” of self-propelling and hydrodynamically coupled robotic flappers that generate and interact through vortex flows. By allowing the flock to freely display whatever arrangements and dynamics might emerge from the interactions, we learn the rules of engagement and group-wide consequences. Many surprises turn up, including ordering up in few-member groups to form “crystals”, which however are upset for larger groups due to unusual traveling wave instabilities (“flonons”) that dislodge members from their positions and cause collisions. Our modeling suggests that these effects are general and therefore may impact animal groups.

Bio: Prof. Ristroph is an applied mathematician and experimental physicist at New York University's Courant Institute of Mathematical Sciences. He directs the Applied Math Lab and co-directs the Fluid Physics Lab, which specialize in fluid mechanics, flow-structure interactions, and especially the areas of biological and geophysical fluid dynamics. Ristroph was previously an NSF postdoc at NYU, received his PhD in Physics from Cornell, and his BS in Physics from UT Austin.