Wake dynamics of tapered wings. Part I: a computational study

Abstract

As the first of our three-part joint paper series, we study the effects of wing taper on laminar wakes behind NACA 0015 wings at post-stall angles of attack using direct numerical simulations. We consider semi aspect ratio 2 wings at angle of attack α = 18 with taper ratios δ from 0.5 and 1, leading edge sweep angles from 0 to 40. The mean-chord-based Reynolds number is set to 600 and Mach number is fixed at 0.1. This work explores the wing taper effects on the separated wake dynamics. At high angles of attack, unswept and untapered wings develop wake shedding near the wing root with a streamwise steady vortex core near the wing tip. Swept and untapered wings exhibit wake shedding near the wing tip at moderate sweep angles, while steady wakes are observed around highly swept wings. This wake behavior is related to the formation of coherent structures at the leading and the trailing edges. For tapered wings, leading and trailing edge sweep angles are not the same and they have a distinct influence on the wake characteristics of low-Reynolds number separated flows. For instance, by keeping the trailing edge unswept, a backward-swept leading edge is observed to promote unsteadiness at the wing root and near the wing tip. This feature suggests an influence of the leading edge vortex to transport vorticity from the wing root towards the tip region. An opposite effect is observed for tapered wings with forward-swept trailing edges and unswept leading edges. For such wing planform geometry, the wake shedding concentrates near the root. We further analyze how wing taper influences the wakes of highly swept wings. For wings with high leading edge sweep angles, the wake is steady. However, for tapered wings, wake oscillations appear near the wing tip region, as the trailing edge sweep angle is smaller than that of the leading edge. The current results provide novel insights on the effect of wing taper on wake dynamics of finite wings.