Mechanical Engineering Fall Seminar Series: Class 530.803
“Pumping by oscillating plate arrays: viscous to inertial transitions in mayfly nymphs”
Presented by Professor Ken Kiger, Department of Mechanical Engineering, University of Maryland
Mayfly nymphs are aquatic insects, many of which can generate ventilation currents by beating two linear arrays of external plate-like gills. The oscillation Reynolds number associated with the gill motion changes with animal size, varying from Re ~ 2 to 30 depending on the age of the animal. This range of Re is interesting, as it represents an approximate boundary between the classical analytical realms of Stokesian and Eulerian dynamics. In this context, mayflies provide a novel system model for studying adaptations associated with transitions from a more viscous- to inertia-dominated flow. Observation of the gill plate kinematics and the mean flow field of the species C. triangulifer reveal that the mayfly makes a transition in stroke motion when Re > 5 (corresponding to a change from a “rowing” to a “flapping” type of motion), which is consistent with speculations in the literature that a boundary may exist for this transition. Our effort is directed to understand how the mayfly nymph effectively transits this intermediate regime using a combined technique of experimental measurement and numerical simulation. Time-resolved PIV measurements within the inter-gill space reveal the basic elements of the flow consist of vortex rings generated by the strokes of the individual gills. For the larger Re case, the phasing of the plate motion generates a complex array of small vortices that interact to produce an intermittent dorsally directed jet. For Re < 5, distinct vortices are still observed, but increased diffusion creates vortices that simultaneously envelope several gills, forcing a new flow pattern to emerge and preventing the effective use of the high Re stroke kinematics. Thus we argue the transition in the kinematics is a reflection of a single mechanism adapted over the traversed Re range, rather than a shift to a completely new mechanism.
Dr. Kiger is a Professor and Director of Undergraduate Studies in the Department of Mechanical Engineering and an Affiliate Faculty in the Fischell Department of Bioengineering at the University of Maryland where he has been a faculty member since 1995. Dr. Kiger’s research interests are in the area of experimental fluid mechanics and turbulence, with an emphasis on two-phase flows and biological fluid mechanics. His work in two-phase flows have focused on particle-turbulence interaction, which has required the development of novel instrumentation approaches to resolve the momentum coupling between the phases, primarily in solid-liquid flows. His research interests in biological applications relate to hemodynamics, cardiovascular mechanics pertaining to cardiogenesis, disease, and artificial pumping devices, as well as the study of bio-locomotion of animal flight and respiration.