October 2:  Stephen Childress, CIMS

Symmetry and Locomotion
  

  Natural locomotion in fluids, swimming, flying and hovering, involves a variety of mechanisms as the Reynolds number varies from small to large. Symmetry considerations play a significant role in the effectiveness of the body movements leading to locomotion. In this talk we review some of the basic principles of locomotion at low and high Reynolds numbers, and discuss some particular problems: (1) The swimming of the small shell-less mollusks spans an intermediate range of Reynolds numbers, to which these organisms have adapted using both cilia and a pair of wings. We discuss their transition to "flapping flight" as a bifurcation in a frequency Reynolds number. (2) Hovering flight is created in the laboratory using an oscillating air chamber. Experiments using asymmetrical bodies, both flexible and rigid, are described, and the production of lift by vortex shedding is discussed. (3) Locomotion by symmetry breaking in the mass distribution within the body will examined in in both inviscid and viscous fluids.