Aquatic bodies, such as a fish, leave behind different footprints or waterborne disturbances that consist of trails of flow vortices with a complex shedding frequency content. Harbor seals remarkably accomplish tracking their prey using their whiskers, functioning as a sensor. They possess the ability to detect the waterborne disturbances through interaction of the surrounding wake flow of the left-behind footprint with their flexible whisker structure. When the major axis of the whisker geometry is aligned with the flow, lengthwise undulations of the whisker model break the spatial coherence of vortex formation in the wake of the whisker, which in turn minimize or eliminate self-induced vortex-induced vibration (VIV) of whisker. This unique orientation-sensitive feature of the whisker allows the seal to move forward at steady speed with small self-induced noise from VIV.While the vortex-induced vibration and wake flow dynamics behind harbor seal whisker models are well-studied in the literature, their interaction with the oncoming vortex flow from upstream hydrodynamic objects is not well-understood and sparse in literature. In this study, water tunnel experiments are conducted to study flow-induced vibration response of an elastically mounted whisker model, when placed in the wake of an upstream circular cylinder in tandem arrangement. Flow-induced vibration response in terms of amplitudes and frequencies of oscillation were studied in the crossflow direction for a reduced velocity range of U* = 4.7 - 36.5, corresponding to a Reynolds number range of Re = 8,075 - 62,582. The reduced velocity was defined as U*=U/D×f, where U is the flow velocity, D is the average whisker diameter, and f is the natural frequency of the system. Effects of a wide range of distances between the upstream cylinder and whisker as well as the angle at which the whisker faces the oncoming flow (angle of attack) on the flow-induced vibration response characteristics were studied. Instantaneous volumetric flow field behind the whisker model was measured using Particle Tracking Velocimetry (PTV) data processed by the Shake The Box (STB) algorithm that allowed for the time resolved, three dimensional (3D) 3 components (3C) measurement of flow field in the wake of the whisker model. The wake dynamics of the tandem pair of the whisker model and the upstream cylinder were studied at different angles of attack of the whisker model. Also, the correlation between the whisker’s frequency of oscillation and the vortex shedding frequency in the wake of the upstream cylinder was studied.

Flow-Induced Vibration and Wake Flow Dynamics Behind Harbor Seal Whisker Model in Tandem Arrangement With an Upstream Cylinder

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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