Yudin, DavidFloryan, DanielVan Buren, Tyler2023-10-122023-10-122023-03-22Yudin, David, Daniel Floryan, and Tyler Van Buren. “Propulsive Performance of Oscillating Plates with Time-Periodic Flexibility.” Journal of Fluid Mechanics 959 (2023): A31. doi:10.1017/jfm.2023.166.1469-7645https://udspace.udel.edu/handle/19716/33542This article was originally published in Journal of Fluid Mechanics. The version of record is available at: https://doi.org/10.1017/jfm.2023.166. © The Author(s), 2023. Published by Cambridge University PressWe use small-amplitude inviscid theory to study the swimming performance of a flexible flapping plate with time-varying flexibility. The stiffness of the plate oscillates at twice the frequency of the kinematics in order to maintain a symmetric motion. Plates with constant and time-periodic stiffness are compared over a range of mean plate stiffnesses, oscillating stiffness amplitudes and oscillating stiffness phases for isolated heaving, isolated pitching and combined leading-edge kinematics. We find that there is a profound impact of oscillating stiffness on the thrust, with a lesser impact on propulsive efficiency. Thrust improvements of up to 35 % relative to a constant-stiffness plate are observed. For large enough frequencies and amplitudes of the stiffness oscillation, instabilities emerge. The unstable regions may confer enhanced propulsive performance; this hypothesis must be verified via experiments or nonlinear simulations.en-USArticle