Vortex-induced Vibration And Wake Tracing Mechanism Of A Slender Harbor Seal Whisker:A Numerical Study

Marine animals possess the exquisite sensitivity of detection in underwater environment,which provides new perspective for the detection systems of moving objects.Previous studies have shown that,under the condition of limited vision and hearing,harbor seals can still track the vortex wakes left by moving animals and identify objects through their unique shaped whiskers.In addition,even extremely weak disturbation can be perceived and tracked accurately.Therefore,the research on the vibration response and tracking mechanism of harbor seal whiskers in complex flow field has significant value in commercial application and scientific research.In this paper,flow-induced vibration of the harbor seal whisker in complex flow field is directly simultaed by using parallel hydrodynamic code Cg Les?IBM based on embedded iterative immersed boundary method.The corresponding vibration characteristics of the whisker and vortex structures in the wake are investigated.Through the comparison of the flow-induced vibrations of a circular cylinder and an elliptical cylinder with identical equivalent diameter,this paper analyzes the effects of different structural shapes on the vibration characteristics and vortex structures,studies the dynamic responses to upstream wake from different structure,and discusses the perceptive ability and tracking mechanism of harbor seal whiskers.The main findings are summarized as follows:1.Under the uniform inflow condition,the periodically undulant surface of the harbor seal whisker can modify the hydrodynamic features of the flow field.Compared with the circular cylinder case,this undulant surface significantly reduces the fluid forces on the whisker,thus leading to the drag reduction and vibration suppression.It also provides pure signal background for harbor seal whiskers to sense the upstream wake.2.In the wake of the fixed cylinder and paddle,the whisker can extract energy from the vortex in the flow field,resulting in an intensified vibration amplitude,and meanwhile its vibration frequency maintains equally to that of the upstream body.Compared with the circular and elliptical cylinder cases,the whisker has much higher signal to noise ratio(SNR)and sensitivity,materializing the exquisite perciption of the whisker.3.In the wake of the flapping paddle,two different vortex structure combinations appear in the wake of the harbor seal whisker(whisker model 2)and the other whisker with no offset angle(whisker model 1),namely " spanwise vortex + rib vortex + hairpin vortex " and "strong spanwise vortex +'S' type vortex + weak spanwise vortex ",respectively.In the reverse Kármán vortex street wake generated by the flapping paddle,there are two vortex types in the wake of the whisker model,and due to the significant difference of frequency,no vortex mergence occurs in the downstream.4.The separation line of the whisker under uniform inflow exhibits periodically three-dimensional distribution along the curved surface.With the addition of upstream hydrodynamic disturbance,the separation line is straightened and no longer shows obvious three-dimensional shape.5.The emergence of upstream disturbance can alter the stability of the whisker.The phase diagram is thus changing into a closed circle from an irregular spiral curve,and the hydrodynamic response is stable,leading to a periodically continuous oscillation of the whisker.