Effect of Aspect Ratio on Finite-Wing Dynamic Stall

Abstract

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 ([Formula: see text], 8, and 16) are explored for wings (NACA 0012 cross section) at chord Reynolds number [Formula: see text] and freestream Mach number [Formula: see text]. The wings pitch sinusoidally from initial incidence of 4° to a maximum angle of attack of 22° with reduced frequency [Formula: see text] over one pitching cycle. The three-dimensional unsteady flowfields show similarity among the three wings through laminar separation bubble formation/bursting. The flow topology during dynamic stall exhibits distinctly different evolutions at the higher aspect ratio relative to the lower, baseline aspect ratio. Rather than evolving into a [Formula: see text] vortex ([Formula: see text]), the higher-aspect-ratio wings show dramatic three-dimensional deformation of the vortex tube that resembles cellular structures. The vortical structure eventually interacts with the trailing-edge vortex, which contrasts with the lower aspect ratio. Examination of the unsteady loads shows an increase in lift slope, average loads, peak loads, and earlier stall with aspect ratio.