On the wake-body synchronization in flexible cylindrical cantilevers for sensing flow

Many animals navigate and explore their environment using complex, three-dimensional (3D) fluid flow information. Insects, crustaceans, rodents, and pinnipeds have specialized sensors that enable them to detect and localize flow sources and, in some cases, to track fluid currents and wakes. Notably, across all these species, the fluid-detecting sensors – hairs, antennae, and whiskers – take the form of slender, flexible cantilevers. These cantilevered sensors operate by undergoing self-sustained oscillations generally at low Reynolds number (Re) flows, often well below the critical Reynolds number of vortex-shedding (Re_cr). In this work, we conduct high-fidelity 3D numerical experiments to examine the wake-body synchronization of slender, flexible cylindrical cantilevers in air and water flow for Re<Re_cr. We pinpoint the origin of the underlying mechanism for cantilevers' self-sustained vibrations in this Re regime and outline how the synchronization/lock-in phenomenon, a universal concept in nonlinear physical systems, helps establish a general understanding of the coupled feedback mechanisms in fluid-structure systems. All the results presented in this work have significant implications for studying biologically-based flow sensing and engineered fluid sensors.