Aspect Ratio Effect on Finite Wing Dynamic Stall

View Video Presentation: https: //doi. org/10. 2514/6. 2021-1089. vid The role of aspect ratio on the dynamic stall process of an unswept finite wing is investigated using high-fidelity large-eddy simulations. Three aspect ratios (AR = 4, 8, and 16) are explored for a finite wing with a NACA 0012 profile and rounded wing-tips. Following previous work, the finite wing at chord-Reynolds number Rec = 2 10⁵ and freestream Mach number M_ = 0. 1 pitches sinusoidally from an initial incidence of 4^ to a maximum angle of attack of 22^ with reduced frequency k = f c /U_ = /16 over one pitching cycle. Examination of the 3D unsteady flow-fields show distinctly different evolutions of the dynamic stall flow structure at the higher AR in contrast to the lower, baseline AR. Rather than evolving into a Lambda-vortex following the bursting of the laminar separation bubble observed at AR = 4, the higher AR show multiple arch-like cells forming across the DSV core from instabilities generated by the DSV's interaction with the wing. These structures eventually break down as they interact with a more span-wise coherent trailing edge vortex in contrast to forming into an arch-vortex that ejects into the wake as a ring-like structure seen at the lower AR. Examination of the unsteady loads show an increase in maximum lift and minimum pitching moment, earlier onset of stall, and the emergence of a secondary minimum peak in the pitching moment indicative of an increasingly coherent trailing edge vortex with increasing AR.