Hydrodynamics of Metachronal Rowing at Low-to-Intermediate Reynolds Numbers

Metachronal rowing is commonly found among small swimming invertebrates. Animals that locomote via this mechanism feature rows of appendages that perform propulsive strokes sequentially with a constant phase lag from their neighbor. In this study, ctenophores (comb jellies, the largest animals in the world to locomote via cilia) are used to explore the effects of varying propulsive configuration and Reynolds numbers on hydrodynamics. We reconstruct the beating motion of ctenophore appendages based on high-speed video recordings. To model the metachronal wave and the movement of appendages, beating kinematics are represented by the truncated Fourier series. An in-house immersed-boundary-method-based computational fluid dynamics solver is used to simulate the flow field and associated hydrodynamic performance. A parametric study is conducted to investigate the vortex structures and propulsive characteristics of metachronal rowing over a range of key parameters, including the number of appendages, phase lag, space between neighbor appendages, and Reynolds number. Our simulation results aim to provide fundamental fluid dynamic principles for guiding the design of bio-inspired miniaturized robots swimming in the low-to-intermediate Reynolds number regime.