Study of vortex stability in swept wing configurations

Cavanagh, Alexander J. (2026) Study of vortex stability in swept wing configurations. PhD thesis, University of Glasgow.

Abstract

The aerodynamic performance of small flapping and plunging wings operating at low Reynolds numbers is strongly influenced by the formation and evolution of leading-edge vortices (LEVs). While the role of LEVs in lift enhancement is well established for unswept wings, the combined effects of sweep angle and unsteady kinematics on LEV stability and force production remain less well understood, particularly in the Reynolds number regime relevant to micro air vehicles (MAVs).
This thesis investigates the influence of wing sweep angle and reduced frequency on LEV dynamics for finite wings undergoing prescribed plunging motions at Reynolds number 2 × 10^4. High-fidelity improved delayed detached eddy simulations (IDDES) are performed for wings with sweep angles of Λ = 0◦,30◦, and 60◦, spanning quasi-steady to highly unsteady motion regimes. The resulting flow fields are analysed to characterise LEV formation, growth, convection, and breakdown across the wing span.
Two distinct LEV breakdown modes are identified and characterised: burst-type breakdown at low reduced frequency, involving abrupt collapse of a coherent LEV, and spiral-type breakdown at higher reduced frequency, in which three-dimensional helical instabilities lead to progressive deformation and downstream convection of the vortex. These modes correspond to established breakdown behaviours in the literature and are shown here to be robustly distinguished by reduced frequency for the present finite-wing configurations, with each breakdown mode associated with a distinct aerodynamic response.
The leading-edge suction parameter (LESP) is assessed as a predictive metric for LEV initiation on swept wings and is shown to remain qualitatively applicable, with important modifications arising from three-dimensional effects and spanwise transport. Force and moment partitioning methods are employed to quantify the spanwise distribution of vorticity-induced lift and thrust contributions, enabling direct links between flow structure and aerodynamic loading.
The results demonstrate that increasing reduced frequency promotes earlier LEV detachment and more rapid downstream convection, leading to pronounced transient lift peaks associated with impulsive acceleration effects. Wing sweep fundamentally alters LEV stability by enhancing spanwise vorticity transport, promoting sustained LEV attachment near the wing root whilst modifying the spanwise distribution of aerodynamic loading. These findings regarding wing sweep provide new insight into the coupled roles of unsteadiness and sweep in LEV-dominated flows and offer guidance for the aerodynamic design of bio-inspired MAVs operating in gust-sensitive environments.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by the UK Engineering and Physical Sciences Research Council (EPSRC) through a DTA scholarship, grant EP/T517896/1. This work used the Cirrus UK National Tier-2 HPC Service at EPCC (http://www.cirrus.ac.uk) funded by the University of Edinburgh and EPSRC (EP/P020267/1). This work used the ARCHER2 UK National Supercomputing Service (https://www.archer2.ac.uk).
• Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Mallik, Dr. Wrik
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86021
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 Jun 2026 09:22
• Last Modified: 10 Jun 2026 09:22
• Thesis DOI: 10.5525/gla.thesis.86021
• URI: https://theses.gla.ac.uk/id/eprint/86021

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