LES modelling of wake vortex surfing for formation flight applications

Chan, Jia Cheng (2026) LES modelling of wake vortex surfing for formation flight applications. PhD thesis, University of Glasgow.

Abstract

The industry mission toward sustainable aviation has intensified interest in wake surfing operation as a potential method for reducing carbon emissions. Wingtip vortices constitute the fundamental aerodynamics mechanism governing the wake interactions between aircraft. However, the prediction of wake-vortex evolution over extended distances remains technically challenging due to the highly unsteady nature of vortical flows, which are sensitive to turbulence dissipation and inflow specification. This research investigates the characterisation, modelling, and efficient computational simulation of wingtip vortex behaviour, with specific emphasis on vortex surfing in extended longitudinal fields. A combined experimental-computational approach is adopted to address the challenges of accurately predicting vortex development over long distances at reduced computational cost.

A novel perspective upright correction technique for wind tunnel test is introduced to enable geometrically upright vortex images from a single camera positioned at arbitrary viewing angles. This method greatly simplifies experimental setup and improves the precision of wake-spiral characterisation. Experimental results reveal that the true vortex core may behave differently from the visible wake spiral, underscoring the importance of numerical analysis for vortex core characterisation.

To address the numerical characterisation, a Computational Fluid Dynamic (CFD) methodology is developed using OpenFOAM to resolve the wake vortex dynamics from the leading wing using Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) turbulence models. The CFD framework is constructed to capture the spiral morphology of the vortex core, the tangential velocity magnitudes, axial velocity deficits and downstream trajectory and evolution. The more recent formation flights have a substantial longitudinal separation of up to a few kilometres. Resolving the flight dynamics using LES is computationally prohibitive due to the vast spatial and temporal scales. For efficient simulation for repetitive upstream flow field over the extended flight formation, inlet conditioning framework was developed. The precursor method successfully transfers fully developed LES vortex inflow to a downstream main domain, retaining coherent turbulence with negligible dissipation. A complementary synthetic method, based on Fourier-series reconstruction of velocity fluctuations, demonstrates feasibility but encounters limitations within the vortex core where fluctuation behaviour is highly unstable.

In wake surfing simulations, the leading wing remains largely unaffected, whereas the trailing wing benefits substantially from the induced upwash. The optimal configuration identified in this study corresponds to a lateral overlap of approximately 10% wingspan at matched flight level, yielding a significant improvement in lift-to-drag ratio.

To further reduce the computational cost, the inflow conditions can be initialised through the combination of the mean vortex fields derived from the Unsteady Vortex Lattice Method (UVLM) and the turbulent fluctuations from the LESs. Although the UVLM tends to accelerate the vortex core growth, the simulation case may achieve the realistic vortex representation through a careful selection of the inlet plane from the UVLM.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Economic Development Board of Singapore (EDB) and ST Engineering Aerospace Ltd.
• Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Economic Development Board of Singapore (EDB), ST Engineering Aerospace Ltd
• Supervisor's Name: Hesse, Dr. Henrik, Wang Peng Cheng, Mr. Victor and Ramesh, Dr. Kiran
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86229
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 Sep 2026 10:56
• Last Modified: 10 Sep 2026 12:01
• Thesis DOI: 10.5525/gla.thesis.86229
• URI: https://theses.gla.ac.uk/id/eprint/86229

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