Wake-Body Synchronization and Sustained Oscillation of Flexible Cantilevers without Vortex Shedding

Certain species including seals and rats possess unique hydrodynamic sensing abilities, enabling them to locate prey, follow trails, and navigate in total darkness. This sensing involves detecting minute flow changes through sensory organs that convert flow energy into electrical signals in the animal's brain. Our research focuses on the fluid-structure interaction (FSI) of sensory organs, specifically whiskers, to understand the physical phenomena governing their dynamic response. Using a high-fidelity 3D numerical framework, we examine the FSI of a flexible cylindrical cantilever—a whisker model—at subcritical flows, i.e., no periodic vortex-shedding. Fundamental questions addressed include (i) the mechanism behind the sustained oscillation of the cantilever under subcritical flows, (ii) the effect of an upstream wake on the response characteristics, and (iii) the impact of base excitation on the oscillatory dynamics. Emphasizing the significance of the synchronization phenomenon, widely observed in nonlinear physical systems, we provide a general understanding of the cantilever's coupled motion in subcritical flows. Knowledge gained through this work can lead to the development of artificial flow sensors used in diverse applications for self-guided navigation.