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

TL;DR

This study investigates how Reynolds number influences flow separation, vortex shedding, and unsteady forces on low-aspect-ratio wings, revealing a transition in flow behavior and the stabilizing role of tip vortices across a range of Reynolds numbers.

Contribution

It bridges low and high Reynolds number flow studies on finite wings, highlighting the impact of Reynolds number on flow periodicity and vortex stabilization effects.

Findings

Flow becomes less periodic and more turbulent as Reynolds number increases from 600 to 2,500.

Flow diagnostics become less sensitive to Reynolds number beyond 2,500 due to tip vortex stabilization.

Tip vortices significantly influence flow behavior and force production on low-aspect-ratio wings.

Abstract

At high incidence, low-aspect-ratio wings present a unique set of aerodynamic characteristics, including flow separation, vortex shedding, and unsteady force production. Furthermore, low-aspect ratio wings exhibit a highly impactful tip vortex, which introduces strong spanwise gradients into an already complex flow. In this work, we explore the interaction between leading edge flow separation and a strong, persistent tip vortex over a Reynolds number range of $600 \leq Re \leq 10,000$. In performing this study, we aim to bridge the insight gained from existing low Reynolds number studies of separated flow on finite wings ($Re \approx 10^2$) and turbulent flows at higher Reynolds numbers ($Re \approx 10^4$). Our study suggests two primary effects of Reynolds number. First, we observe a break from periodicity, along with a dramatic increase in the intensity and concentration of small-scale eddies, as we shift from $Re = 600$ to $Re = 2,500$. Second, we observe that many of our flow diagnostics, including the time-averaged aerodynamic force, exhibit reduced sensitivity to Reynolds number beyond $Re = 2,500$, an observation attributed to the stabilizing impact of the wing tip vortex. This latter point illustrates the manner by which the tip vortex drives flow over low-aspect-ratio wings, and provides insight into how our existing understanding of this flowfield may be adjusted for higher Reynolds number applications.