Chris Roh, Cornell
Friday, October 1, 2021
Honeybees display a unique bio-locomotion strategy at the air-water interface. When water’s adhesive force traps them on the surface, their wetted wings lose the ability to generate aerodynamic thrust. However, they adequately locomote, reaching a speed up to three body lengths·s-1. Honeybees use their wetted wings as hydrofoils for their water surface propulsion. Their locomotion imparts hydrodynamic momentum to the surrounding water in the form of asymmetric waves and a deeper water jet stream, generating approximately 20 μN average thrust. The wing kinematics show that the wing’s stroke plane is skewed, and the wing supinates and pronates during its power and recovery strokes, respectively. The flow under a mechanical model wing mimicking the motion of a bee’s wing further shows that non-zero net horizontal momentum is imparted to the water, demonstrating net thrust. Moreover, a periodic acceleration and deceleration of water are observed, which provides additional forward movement by ‘recoil locomotion’. Scaling analysis of the hydrodynamic forces associated with the wing motion indicates that the wings utilize added mass force (unsteady inertial force associated with the pulling of the water attached to the wing). Hydrofoiling highlights the versatility of their flapping-wing systems that are capable of generating propulsion with fluids whose densities span three orders of magnitude. This discovery inspires a novel aerial-aquatic hybrid vehicle.
Chris Roh received his B.S. in Bioengineering from Cornell University in 2012, M.S. and PhD degree in Aeronautics from California Institute of Technology (Caltech) in 2013 and 2017. He is currently Assistant Professor in Biological and Environmental Engineering at Cornell University. From his youth, Chris has been fascinated by the diversity of insects and the different stories each insect tell. The old passion combined with his newly found love for the intricate ways fluid flow led him to study hydrodynamics of insects at Caltech under the guidance of Professor Mory Gharib. In his thesis work, he studied the jet vectoring ability of aquatic dragonfly larva’s tri-leaflet valve, as well as how honeybees swim using their wings. These studies have broad implications, as the tri-leaflet valve of dragonfly larvae helps us imagine a new prosthetic heart valve and honeybee’s swimming demonstrates the versatility of flapping wing systems. Chris continues to observe interesting ways insects interact with fluid surrounding them with engineering applications in mind.
Meeting ID: 943 4469 7811