Laminar vortex dynamics around forward-swept wings

TL;DR

This study numerically investigates laminar vortex dynamics around forward-swept wings at low Reynolds numbers, revealing unique wake behaviors, vortex formations, and lift characteristics that differ from backward-swept wings, informing innovative wing design.

Contribution

It provides the first detailed numerical analysis of laminar separated flows over forward-swept wings at low Reynolds numbers, highlighting flow stabilization mechanisms and lift enhancement.

Findings

Wakes differ significantly from backward-swept wings.

Flow remains steady for low-aspect-ratio wings due to tip vortex downwash.

Larger aspect ratio wings exhibit unsteady vortex shedding and streamwise vortices.

Abstract

Forward-swept wings offer unique advantages in the aerodynamic performance of air vehicles. However, the low-Reynolds-number characteristics of such wings have not been explored in the past. In this work, we numerically study laminar separated flows over forward-swept wings with semi aspect ratios $sAR=0.5$ to 2 at a chord-based Reynolds number of 400. Forward-swept wings generate wakes that are significantly different from those of backward-swept wings. For low-aspect-ratio forward wings, the wakes remain steady due to the strong downwash effects induced by the tip vortices. For larger aspect ratio, the downwash effects weaken over the inboard regions of the wing, allowing unsteady vortex shedding to occur. Further larger aspect ratio allows for the formation of streamwise vortices for highly-swept wings, stabilizing the flow. Forward-swept wings can generate enhanced lift at high angles of attack than the unswept and backward-swept wings, with the cost of high drag. We show through force element analysis that the increased lift of forward-swept wings is attributed to the vortical structure that is maintained by the tip-vortex-induced downwash over the outboard region of wing span. The current findings offer a detailed understanding of the sweep effects on laminar separated flows over forward-swept wings, and invite innovative designs of high-lift devices.