Collaborative Research: Hydrodynamic Mechanisms and Scalability of Metachronal Swimming Across Viscous to Inertial Flow Regimes

Many aquatic organisms use a technique called metachronal rowing to swim. They use their paddle-like appendages to row in a coordinated rhythm, starting from the rear and moving toward the front of the organism. Metachronal rowing is observed in organisms that range in size from single cells to large crustaceans such as shrimp and krill. This project will use experiments and computational modeling on live animals and metachronal rowing vehicles to explain why this swimming technique works regardless of organism size. By examining how animals of different sizes optimize their swimming appendages, this research will help design underwater vehicles that can efficiently operate over broad ranges of sizes and speeds. Undergraduate and graduate students will receive cross-disciplinary training in fluid mechanics, robotics, and scientific computing. New summer camps on bio-inspired engineering will be developed for high school students. This project will elucidate the fluid dynamic principles that enable thrust and lift generation by metachronal rowing across an astounding seven orders of magnitude in paddle-scale Reynolds number from strongly viscous (0.01) to inertially dominated (10,000) flow regimes. Previous studies of metachronal rowing have considered tethered paddling without body motion for a limited Reynolds number range. Flow visualization and force measurements will be performed on state-of-the-art dynamically similar remotely operated vehicles to examine the flow physics, swimming performance and scalability of metachronal rowing across the biologically relevant range of Reynolds numbers. Computational simulations will be conducted to examine fluid-structure interaction in untethered metachronal swimming and evaluate the cost of transport for varying Reynolds number, paddle geometry and kinematics. The integrated experimental and computational approach will be used to test whether differences in the mechanical design and paddling kinematics of natural metachronal swimmers can facilitate efficient locomotion in their specific flow regime. The findings can guide the development of new bio-inspired autonomous underwater vehicles that provide efficient propulsive performance across broad ranges of sizes and speeds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.