Experimental investigation on fluid–structure interaction in highly flexible wings

Abstract

This paper presents a comprehensive experimental investigation of fluid-structure interactions in a flexible, high-aspect-ratio wing during its post-critical phase, spanning a reduced velocity range of $U^{\ast }=1.47-35.34$ and corresponding Reynolds number range of $Re=146-3,499$. The angle of attack of the wing was systematically varied from 0° to 20° in increments of 2°. The structural dynamics results reveal that changes in the angle of attack significantly affect the onset of limit cycle oscillations, as well as the dominant oscillation frequencies and mode shapes. At higher flow velocities and angles of attack, a significant increase in tip deflection was observed, while minimal deflection occurred at lower or zero angles of attack. In addition to examining the structural responses, the study employs volumetric, time-resolved particle tracking velocimetry (TR-PTV) to investigate the three-dimensional (3-D) flow field around the wing and its wake. Vortex behavior and its interactions with the structural modes varied with different angles of attack and reduced velocities. Leading and trailing edge vortices adapt to wing deflection, particularly at higher angles, and the coherence of these vortical structures was shown to be influenced by the amplitude and mode shape of the wing’s oscillations.