Numerical study on vortex-induced vibration of undulatory seal whiskers, part II: two degrees of freedom

Seal whiskers are extraordinary hydrodynamic sensors with surface geometry specialized through evolution. Previous research has found that the unique undulatory shape of seal whiskers reduces the oscillation of lift force and consequently suppresses vortex-induced vibration (VIV). 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 VIV of seal whiskers systematically. In part II of this study, the two degrees of freedom (DOFs, cross flow and inline) VIV of a harbor seal whisker is solved using direct numerical simulation for parametrically varied reduced velocity and angle of attack (AOA, from 0° to 90°) at a constant Reynolds number of 300. The whisker is modeled as an elastically mounted 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. Preliminary analysis of the results shows that the inline degree of freedom has a very small effect on the cross-flow VIV when the AOA or reduced velocity is low. More detailed 2 DOF VIV responses and comparison with single DOF VIV will be presented. Together, the results give implications for the signal detection mechanisms of seal whiskers.