Numerical study on vortex-induced vibration of undulatory seal whiskers, part I: single degree of freedom

Seal whiskers are extraordinary hydrodynamic sensors with surface geometry specialized through evolution. However, it is not well understood what information is used by the seals for sensing. To answer this question, it is important to investigate the vortex-induced vibration (VIV) of whiskers systematically. In part I of this study, the single degree-of-freedom (cross flow) VIV of a harbor seal whisker is solved using direct numerical simulation for parametrically varied reduced velocity and angle of attack (AOA) at a constant Reynolds number of 300. The whisker is modeled as a rigid body with a mass ratio of 1 and a damping ratio of 0.02. Only one segment of the undulatory shape is considered by utilizing periodic boundary conditions. At 0° AOA, the wake is characterized by the hairpin vortices and the whisker shows a typical forced vibration response despite extremely low amplitude. At 15° AOA, in addition to the hairpin vortices, a Karman-like vortex shedding is introduced near the nodal plane at a higher frequency. The VIV amplitude is modulated at the beat frequency of these two modes. As the AOA further increases, the VIV amplitude increases significantly and lock-in regions appear. An infinite branch, where the VIV persists regardless of reduced velocity, is observed for AOAs greater than 60°.