Vibration of an S-shaped bluff sheet in uniform flow

Abstract

The dynamics of flexible sheet flapping in uniform flow are profoundly influenced by the boundary conditions imposed upon the sheet. This study introduces an innovative configuration featuring an S-shaped bluff sheet characterized by asymmetric clamp angles relative to the centerline and clamp directions oriented perpendicular to the flow. This unique design enables the sheet to undergo largeamplitude periodic oscillation. Experimental investigations are conducted to explore the oscillatory behaviour of the sheet in uniform flow, aiming to unravel the intricate relationships among various parameters that impact its dynamics. The objective is to enhance our understanding of the oscillating dynamics of elastic sheets and uncover the key mechanism responsible for driving the periodic motion. The motion characteristics of the sheet are classified into three distinct modes based on the flow velocity. Notably, variations in the vicinity of the clamps are observed to trigger a sharp increase in the sheet’s amplitude. In order to elucidate the behaviour of the sheet, scaling analyses were conducted on governing equations and essential-physical quantities. Successful analysis was carried out on the dynamics of the sheet, including the prediction of the moment when the amplitude increases. Moreover, substantial variations in bending energy were observed near both clamps, and a quantitative calculation of the energy amount was performed, presenting the potential for a novel energy harvester. Significantly, the advantage of strong vibrations occurring at relatively low flow velocities was demonstrated compared to previous studies with fixed-fixed boundary conditions.