In this talk, I will discuss a few laboratory experiments where moving structures freely interact with the surrounding fluid. These moving structures, or boundaries, behave in asymmetric ways - either because of their anisotropic construction or by the spontaneous breaking of symmetry in their response to the fluid. When subjected to reciprocal forcing, their motion might be described as a ratcheting behavior. In one case, fluid is forced through a corrugated channel that is under shaking. In another, a solid body hovers stably in an oscillatory airflow, mimicking a hovering insect. Lastly, a symmetric wing leaps into a forward flight when flapped up and down, following a symmetry breaking bifurcation. These phenomena can be viewed as the starting points for understanding the effect of increasing biological realism.
Work webpage: http://physics.nyu.edu/jz11/