Experiments on Vortex Shedding From Reconfigured Flexible Filaments Vibrating in Flow

This paper describes an experimental study of the spanwise vortex shedding frequencies from cantilever flexible filaments which are bent (reconfigured) when exposed to air crossflow. At a reduced velocity of approximately U* = 1500 (based on filament diameter) the filaments started to vibrate in the inline direction. Hot-wire anemometry was thus employed to investigate the wake flow of filaments of three aspect ratios (L/D = 38, 80, and 113) at Reynolds numbers Re < 300. Despite the large relative inclination angles between the filament and the flow direction, the vortex shedding frequency measured along the span of the filaments remained close to those of a cylinder in pure crossflow. Moreover, it was found that as the aspect ratio (axial length) of the filaments was increased, vortex shedding lost coherence towards the free end of the filaments, whereas this was not the case for the shortest aspect ratio filament currently tested. This is thought to be due to the interaction between the crossflow vortex shedding and the axial flow component developing along the wake of the inclined filaments. Through comparisons with stiff inclined wires it was confirmed that the spanwise vortex shedding behaviors observed (frequency and coherence) were not modulated by the motions of the filaments.