Bionic Fluid Control Of Vortex-Induced Vibration Inspired By The Seal-Vibrissa-Shaped-Cylinder

The extraordinary ability of seals to hunt and survive in the dark,turbid sea has been found to heavily depend on their vibrissa's structural responses to the hydrodynamic trails of their upstream prey.The cylindrical vibrissa structure,which is subjected to its own vortex-induced vibration(VIV),is surprisingly stationary during high-speed motion in a uniform flow.As a seal approaches the wake far behind its upstream prey,its vibrissa exhibits an intensified structural vibration.This spatical quality is strongly related with the wake dynamic and fluid-induced vibriation response of the vibrissa,which will show a new way for control of the flow past bluff body and wake detection.This paper is focused on the complex wake dynamic and fluid-induced vibriation response of the vibrissa.The flow field behind an amplified vibrissa-shaped cylinder is captured by the time-resovled PIV system.Combined with dynamic mode decomposition,the spatial-temporal features of the Karman vortex is revealed.The fluid-induced vibriation responses of the vibrissa-shaped cylinder in unform flow and disturbed flow is captured and in the wind tunnel.The TR-PIV system based on continual wave laser is used to measure the flow structures shedding from the oscillating cylinder,to reveal the relation of vortex shedding and vibration response.To reveal the influence of the complex geometry of the vibrissa on the wake flow,TR-PIV is used to capture the flow field behind vibrissa-shaped cylinder and other three models.Combined with dynamic mode decomposition,the spatial-temporal features of the Karman vortex is revealed.The results show that the two-dimensional vortex shedding pattern are destroyed by the three-dimensional geometry of the vibrissa.The recirculation zone is shrank and more stable.The fluctuating intensity immersed in the flow field damps sufficiently.The intensity of the large-scale vortices shedding in saddle and nodal planes are strongly reduced and the shedding frequency is inconsistent.A pair of reversed vorticies are formed in the spanwise plane and destroy the two-dimensional vortex shedding pattern.The reveal the influence of the attack angle of the vibrissa on the wake flow.The flow field behind vibrissa-shaped cylinder with various attack angle arrangements are captured and compared by using TR-PIV and DMD analysis.The results show that the intensity of the vortex shedding in the saddle and nodal planes become more and more strong with the increasing of the attack angles.The fluctuating intensity is corresponding enhanced and the recirculaton zone become more unstable.The vortex shedding process in different spanwise plane become more synchronized in large attack angle configurations,and the shedding frequency reduces with the increasing of attack angle.The fluid-induced vibration response of the vibrissa-shaped cylinder in uniform flow and disturbed flow are captured in wind tunnel.The results show that in uniform flow,the vibrissa-shaped cylinder has a strong stability in small attack angle configurations(??30~0),no distinct VIV found in the test region.As the attack angle increasing to more than 30~0,VIV response occurs and the magnitude become lager with the increasing of attack angle,the'three-branch'lock in region move to the high reduced velocity region in large attack angle configurations.The spectra analysis of the velocity single behind fixed cylinder show that there is no dominant flow structures in small attack angle configurations(??30~0),so the model cann't be excited to oscillating.In large attack anlge configurations(?>30~0),the dominant flow structures occur in the wake flow but the frequency reduce with the increasing of attack angle.The responses of vibrissa-shaped cylinder to the vortex immersed in the incoming flow,which is achieved by installing a circular cylinder in the upstream,is also analysised.The results show that the vibrissa-shaped cylinder in all tested attack angle configurations are sufficiently responsed to the vortex immersed in the incoming flow.However,there is strong self-induced vibriation in attack angle configurations(?>30~0),which is caused by the vortex shedding from itself.The frequency of vortex shedding from upstream cylinder is identified in the spectra of vibration signal.The small attack angles(??30~0)were chosen for identifying the ability of wake detection by comparing the vibration responses in uniform flow and disturbed flow.The vibrissa-shaped cylinder had a high signal-to-noise level caused by the strong VIV suppression in uniform flow compared with that of circular cylinder.To measure the flow structures behind the oscillating cylinder in wind tunnel,a TR-PIV system based on a 25 Watt continuous wave laser is setup.Before the experiment of flow field behind oscillating vibrissa-shaped cylinder.The performance of the TR-PIV system is comprehensively revealed by the comparison with conventional PIV based on pulsed laser in different wind speed configurations.The influence of the exposure time arrangement of the high speed camera on the accuracy of the system is detailly tested to provide guidance to the subsequently experiments.The flow field behind the oscillating vibrissa-shaped cylinder in different response branches are measured by the TR-PIV system.Combined with the synchronized measurement of the vibration signal,the relation of the flow structures with the oscillating phase are comprehensively revealed.In the initial branch,the large-scale vortical structures occur in the far wake region and the intensity is quite low.As the cylinder moving to the top/bottom position,the vortical structures on the corresponding side occur.As the cylinder moving back to the middle position,the vortical structures have the strongest intensity.In the upper branch,the large-scale vortical structures occur immediately behind the model and the intensity grows substantially.Caused by the forceful movement of the model,the vortex expands distinctly in the longitudinal direction.As the attack angle keeping as 60~0,the cylinder moving to the top/bottom position,the vortical structures on the other side occur in the nodal plane,while the vortex shedding process in saddle plane is a little backward in the saddle plane.In the configuration of 90~0,the vortical structures in saddle and nodal planes occur as the cylinder moving to the middle position,and the intensity grow continually with the cylinder moving to the top/bottom sides.In lower branch,the vortical structures move to the downstream direction and the intensity decreases.As the cylinder moving to the top/bottom position,the vortical structures on the other side occur.As the cylinder moving back to the middle position,the vortical structures have the strongest intensity.