Biological lift force

Abstract

The profound impact of lift force on human travel is mirrored by its vital role in animal locomotion. In this talk, I will share two uses of lift force in biology in the context of flying and fast swimming.

I will first present flapping flight from the point of view of vortex formation. A recurring feature in animal locomotion is a roll-up of free shear layers into swirling vortical structures. During these roll-up processes, animals experience unsteady aerodynamic forces associated with the forming vortex, which can augment the force production. By considering vorticity flux and maximum circulation in the growing vortex, the dimensionless vortex formation time (inverse of Strouhal number) is generalized. The newly defined dimensionless vortex formation time associated with flight kinematics of wide set of biological flyers fell within a narrow range, pointing to a potentially a strong evolutionary selection pressure to maximize the leading edge vortex circulation.

The second part of the talk will be about the lift-based thrust of a whirligig beetle. The whirligig beetle is the fastest swimming insect, with forward swimming speeds reaching 100 body lengths per second. Previous studies have suggested that these beetles use a purely drag-based thrust to achieve their impressive swimming speed; however, our newly observed leg kinematics of the free-swimming beetle indicate drag-based thrust is used only in the early part of the power stroke and that lift-based thrust kicks in for the second half of the stroke. This observation is in-line with observed patterns in mammalian swimming, in which faster-swimming organisms rely on lift-based thrust generation to generate speeds not attainable through drag-based means alone.

About the speaker

Dr. Chris Roh received his B.S. in Biological Engineering from Cornell University in 2012 and his M.S. and Ph.D. in Aeronautics from the California Institute of Technology in 2013 and 2017, respectively. Chris has been fascinated by the diversity of insects and the different stories each tells. This deep-rooted passion, combined with a more newly found love for intricate fluid flows, led him to study the hydrodynamics of insects at Caltech under the guidance of Professor Morteza Gharib. He is now an Assistant Professor at Cornell University in the Biological and Environmental Engineering department. As the principal investigator of the in vivo Fluid Dynamics Lab, Chris continues to observe ‘life in moving fluids’ with engineering applications in mind. He is a recipient of the National Science Foundation Graduate Research Fellowship and the Richard B. Chapman Memorial Award.