Journal Article

Triglobal resolvent-analysis-based control of separated flows around low-aspect-ratio wings

Taira, Kunihiko, Ribeiro, Jean Hélder Marques

2024

Overview

We perform direct numerical simulations of actively controlled laminar separated wakes around low-aspect-ratio wings with two primary goals: (i) reducing the size of the separation bubble and (ii) attenuating the wing tip vortex. Instead of preventing separation, we modify the three-dimensional (3-D) dynamics to exploit wake vortices for aerodynamic enhancements. A direct wake modification is considered using optimal harmonic forcing modes from triglobal resolvent analysis. For this study, we consider wings at angles of attack of $14^\\circ$ and $22^\\circ$, taper ratios $0.27$ and $1$, and leading edge sweep angles of $0^\\circ$ and $30^\\circ$, at a mean-chord-based Reynolds number of $600$. The wakes behind these wings exhibit 3-D reversed-flow bubble and large-scale vortical structures. For tapered swept wings, the diversity of wake vortices increases substantially, posing a challenge for flow control. To achieve the first control objective for an untapered unswept wing, root-based actuation at the shedding frequency is introduced to reduce the reversed-flow bubble size by taking advantage of the wake vortices to significantly enhance the aerodynamic performance of the wing. For both untapered and tapered swept wings, root-based actuation modifies the stalled flow, reduces the reversed-flow region and enhances aerodynamic performance by increasing the root contribution to lift. For the goal of controlling the tip vortex, we demonstrate the effectiveness of actuation with high-frequency perturbations near the tip. This study shows how insights from resolvent analysis for unsteady actuation can enable global modification of 3-D separated wakes and achieve improved aerodynamics of wings.

• Publisher: Cambridge University Press
• Subject: Actuation / Aerodynamics / Aircraft / Angle of attack / Bubbles / Direct numerical simulation / Flow control / Flow separation / Fluid dynamics / Fluid flow / JFM Papers / Laminar flow / Laminar wakes / Leading edge sweep / Low aspect ratio wings / Reversed flow / Reynolds number / Separation / Sweep angle / Swept wings / Three dimensional analysis / Three dimensional flow / Unswept wings / Vortices / Wakes / Wing tip vortices / Wings