Dynamics of harbor seal whiskers at different angles of attack in wake flow

Abstract

Harbor seals can exquisitely perceive and distinguish different hydrodynamic signals through their distinctive undulatory whiskers. In this study, an elastically supported Harbor seal whisker model undergoing one degree-of-freedom vibration in the cross-flow direction was positioned right downstream of a fixed cylinder and a flapping caudal fin model, respectively, as wake generators. The vibration responses, spectral frequencies, and fluid forces of the whisker model at different angles of attack (0° ≤ α ≤ 90°) are experimentally investigated. The reduced velocity, Ur, ranges from 4.0 to 26.0, and the Reynolds number, Re, varies within the range of 730–4770. The whisker model exhibits a combined vortex-induced vibration (VIV)—wake-induced vibration (WIV) response in the cylinder wake flow,whereas in the caudal fin wake flow, it displays a combination of VIV—wake-induced galloping response at α ≤ 45° and VIV–WIV response at α ≥ 60°. The frequency features of the wake generated by the fixed cylinder and the flapping caudal fin model, along with the increased VIV influence due to the angle of attack, cause the whisker model to exhibit different vibration characteristics. Understanding the vibration responses and fluid forces of the whisker model at various angles of attack in different wake flows is pivotal for future studies on developing whisker-inspired sensors.