Vortex flows around morphing foils: reshape yourself to effect a change

Martínez Carmena, Alfonso (2023) Vortex flows around morphing foils: reshape yourself to effect a change. PhD thesis, University of Glasgow.

Abstract

The unsteady production of vorticity is a unifying principle in biological locomotion in air and water. Shape-tailoring their aerodynamic/hydrodynamic surfaces, natural flyers/swimmers switch with ease between regimes of attached and separated flow. Modern engineering tries to mimic this shape control ability in applications such as micro air vehicles and oscillating energy harvesting devices. Owing to the complexity of morphing, fundamental research merits further efforts, to provide a clearer view of the link between shape variation and unsteady flow response.

In this dissertation, classical theories (potential flow) are combined with numerical methods (vortex methods) in the development of a physics-based low-order model to simulate complex unsteady flows around foils undergoing large camber variations, as a first step towards exploring the capability of camber morphing to alter vortex characteristics, like formation time and strength. Discrete-vortex methods have risen as one of the most suitable numerical tools to establish a relation between camber definition, flow characteristics and aerodynamic loads produced, involving a reasonably low number of parameters. An existing discrete-vortex model for rigid foils is extended to variable-camber foils. A time-varying chord line is proposed, where the boundary condition in thin-aerofoil theory is to be satisfied. This enables large deformations of the camber line to be modelled. Computational fluid dynamics simulations at Reynolds numbers of O(104) are used to test the performance of the model. Furthermore, a new method is introduced to determine the rate at which vorticity is fed into leading-edge vortices in vortex models. The strength of nascent particles at the leading edge is here computed with the velocity at the edge of the shear layer, formulated in terms of the leading-edge suction parameter (an inviscid parameter from unsteady thin-aerofoil theory). This novel formulation allows postseparation flow behaviour, like vortex sheets dynamics, to be correctly captured. Finally, morphing and vortex modelling are combined to demonstrate the potential of this technique to affect leading-edge vortices: the amount of vorticity produced at the leading edge is modulated by suitably tailoring the shape of the camber line.

This research aims to advance our theoretical understanding of the correlation between prescribed deflection at the trailing edge and alteration of flow properties at the leading edge, of interest to the design of flow control strategies inspired by nature.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Ramesh, Dr. Kiran
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83534
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Apr 2023 13:24
• Last Modified: 17 Apr 2023 14:18
• Thesis DOI: 10.5525/gla.thesis.83534
• URI: https://theses.gla.ac.uk/id/eprint/83534