Influence of aspect ratio on dynamic stall of a finite wing

The influence of aspect ratio (AR) on dynamic stall was studied by comparing experimental performance data and three-component velocity measurements acquired for wings of AR 3, 4, and 5, and an airfoil during an unsteady pitch maneuver. A NACA 0012 airfoil was used for all wing models, which were subject to a sinusoidal pitch oscillation between 4 and 22 deg at a reduced frequency of 0.1 and a Reynolds number of 4 × 10⁵. After acquiring the experimental performance data, it was found that decreasing the AR leads to a decrease in the nonlinear unsteady loading of the wing and postpones the dynamic stall process, which also leads to variations in the pitch damping characteristics. Velocity field measurements revealed that the dynamic stall vortex originates from flow separation at the leading edge across the wing inboard section and convects downstream across the chord, whereas the unsteady separation progresses toward the wing tips with increasing angle of attack. The formation of this vortex was delayed to higher angles of attack with reductions in AR, and the three-dimensional nature of the unsteady separation process led to a significant spanwise flow component identified in the acquired velocity fields.