The effect of Reynolds number on the separated flow over a low-aspect-ratio wing*

The flow over a low-aspect-ratio wing is rich and complex. Particularly at high incidence, low-aspect-ratio wings are driven by an intricate interaction between shed vortices, which originate from flow separation at the wing’s leading edge, and a strong, persistent tip vortex, which imparts downwash across much of the wing span. In this talk, we explore how this interaction develops over a range of Reynolds numbers, with the goal of tracking the flow as it transitions from coherent, periodic vortex shedding (Re ≈ 10²) to disorganization and irregularity (Re ≈ 10⁴). Using a combination of direct numerical simulation (DNS) and large-eddy simulation (LES), we find that an increase in Reynolds number yields two seemingly opposing effects: (1) a growing tendency toward instability in the leading edge shear layer, and (2) a strengthening of the wing tip vortex, which acts to attenuate instability in outboard regions of the wing. The result is an inboard-to-outboard spread of unsteadiness, with a breakdown in coherence emerging near Re = 10³ and gradually spreading outward toward the tip. Broadly, these observations highlight the degree to which the tip vortex drives the flow over a low-aspect-ratio wing, and marks a crucial step toward advancing our understanding of tip vortex interactions in higher Reynolds number regimes and applications.