Effect of Aspect Ratio on Finite-Wing Dynamic Stall

• Published in: AIAA journal 2022-12, Vol.60 (12), p.6581-6593
• Main Authors: Hammer, Patrick R., Garmann, Daniel J., Visbal, Miguel R.
• Format: Article
• Language: English
• Subjects: Angle of attack; Aspect ratio; Cellular structure; Fluid flow; Large eddy simulation; Mach number; Peak load; Reynolds number; Three dimensional flow; Topology; Vortices
• ISSN: 0001-1452; 1533-385X
• DOI: 10.2514/1.J062109

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 wings (NACA 0012 cross section) at chord Reynolds number Rec=2×105 and freestream Mach number M∞=0.1. The wings pitch sinusoidally from initial incidence of 4° to a maximum angle of attack of 22° with reduced frequency k=πfc/U∞=π/16 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 Λ vortex (AR=4), 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.