Numerical modeling of metachronal rowing for narrow and wide paddle designs

A considerable research effort has been devoted to understanding and quantifying swimming strategies in aquatic animals, ranging from microorganisms to large marine mammals. Metachronal rowing using multiple propulsors (paddles) is comparatively less studied, and organisms that employ this strategy show a broad variety of paddle morphologies. The paddle aspect ratio (length/width) varies between species, and we do not know how this affects flow physics and swimming performance. We develop a numerical model of a metachronal swimmer with a paddle-scale Reynolds number (Re) representative of adult krill (Re~100) using the immersed boundary method implemented in the open-source library IBAMR. We aim to capture the 3D flow characteristics that emerge from coordination among paddles and quantify the swimming performance. We test several paddle widths with a fixed paddle length, corresponding to aspect ratios ranging from 0.5 to 5.0. We find that narrow paddle regimes produce a smaller swimming velocity. Conversely, at larger paddle widths, swimming is enhanced, and interestingly, vertical swimming is more pronounced as vortex shedding increases. The results may help in the development of bio-inspired underwater vehicles that use fluid mechanical principles for design.