Underwater Flight of the Pteropod

Abstract: A portable tomographic particle image velocimetry (tomo-PIV) system was used to study fluid dynamics and kinematics of pteropods (aquatic snails nicknamed ‘sea butterflies’) in Antarctica.  These pteropods (Limacina helicina antarctica) swim with a pair of parapodia (or “wings”) via a unique flapping propulsion mechanism that incorporates similar techniques as observed in small flying insects.  The swimming velocity is typically 14 – 30 mm/s for pteropod size ranging 1.5 – 5 mm, and the pteropod shell pitches forward-and-backward at 1.9 – 3 Hz.  It has been shown that pitching motion of the shell effectively positions the parapodia such that they flap downwards during both power and recovery strokes.  The tomo-PIV measurements reveal the influence of the vortex structure created and shed from the parapodia on the generated lift forces.  The non-dimensional variables characterizing the motion of swimming pteropods are flapping, translating, and pitching Reynolds numbers (i.e. Re_f, Re_U, and Re_Ω).  The observed specimens swim within the same optimal Strouhal number range as observed for a broad range of species in air and water.  Further, we found that the relationship between these Reynolds numbers show an existence of a critical Re_Ω, below which pteropods fail to swim successfully.

Bio: Donald Webster, Ph.D., P.E. is the Karen & John Huff School Chair and Professor in the School of Civil & Environmental Engineering (CEE) at the Georgia Institute of Technology in Atlanta, Georgia.  Dr. Webster earned a B.S. from the University of California, Davis (1989), and M.S. (1991) and Ph.D. (1994) degrees from the University of California, Berkeley. He joined the Georgia Tech faculty in September 1997 after completing a postdoctoral research appointment at Stanford University and holding a non-tenure-track faculty position at the University of Minnesota.  Dr. Webster’s research expertise lies in environmental fluid mechanics focused on the influence of fluid motion and turbulence on biological systems.  His contributions have been in three arenas: 1) illuminating the fluid mechanics processes related to sensory biology and biomechanics; 2) developing advanced experimental techniques and facilities; and 3) translating research results into bio-inspired design.  In recognition of these contributions, Dr. Webster is a Sustaining Fellow of the Association for the Sciences of Limnology and Oceanography (ASLO) and has won numerous awards including the Felton Jenkins, Jr. Hall of Fame Faculty Award, Class of 1934 Outstanding Innovative Use of Education Technology Award, the Eichholz Faculty Teaching Award, and the British Petroleum Junior Faculty Teaching Excellence Award.

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