Numerical Investigation on Evolution of Tip Vortices Generated by Low-Aspect Ratio Rectangular Wings at High Angle of Attack

Abstract

The onset and evolution of tip vortices generated by the vertical tip of a straight half wing, with a NACA 0012 airfoil section, were studied at a Reynolds number of 1 × 105 by a steady-state calculation at high angles of attack, namely, 10°, 18°, and 42°, where the maximum lift, deep stall, and second peak of the lift coefficient occur, respectively, with three different aspect ratios: 2, 3, and 4. It was found that the counter-rotating vortex wrap initiated within the short wake period at higher angles than the deep stall and affected the contraction of the core trail, as well as resulting in the calculated swirl velocity component exhibiting a significant deviation from the conventional model fit. It was noted that the swirl strength of tip vortices increased continuously, even up to the deep stall phase, where the lift started to decrease immediately after the first peak. Wake contraction was found to follow an exponential decay in the earlier wake region. Compared to both the infinite wing and the elliptical wing, the finite square wing seems to have an offset in the lift coefficient, which could represent the tip loss.