Linear modal instabilities around post-stall swept finite-aspect ratio wings at low Reynolds numbers



Burtsev, Anton ORCID: 0000-0002-8268-9088, He, Wei ORCID: 0000-0002-2633-6114, Hayostek, Shelby, Zhang, Kai, Theofilis, Vassilios ORCID: 0000-0002-7720-3434, Taira, Kunihiko and Amitay, Michael
(2022) Linear modal instabilities around post-stall swept finite-aspect ratio wings at low Reynolds numbers. Journal of Fluid Mechanics, 944. a6-.

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Abstract

Linear modal instabilities of flow over finite-span untapered wings have been investigated numerically at Reynolds number 400, at a range of angles of attack and sweep on two wings having aspect ratios 4 and 8. Base flows have been generated by direct numerical simulation, marching the unsteady incompressible three-dimensional Navier-Stokes equations to a steady state, or using selective frequency damping to obtain stationary linearly unstable flows. Unstable three-dimensional linear global modes of swept wings have been identified for the first time using spectral-element time-stepping solvers. The effect of the wing geometry and flow parameters on these modes has been examined in detail. An increase of the angle of attack was found to destabilize the flow, while an increase of the sweep angle had the opposite effect. On unswept wings, TriGlobal analysis revealed that the most unstable global mode peaks in the midspan region of the wake; the peak of the mode structure moves towards the tip as sweep is increased. Data-driven analysis was then employed to study the effects of wing geometry and flow conditions on the nonlinear wake. On unswept wings, the dominant mode at low angles of attack is a Kelvin-Helmholtz-like instability, qualitatively analogous with global modes of infinite-span wings under same conditions. At higher angles of attack and moderate sweep angles, the dominant mode is a structure denominated the interaction mode. At high sweep angles, this mode evolves into elongated streamwise vortices on higher aspect ratio wings, while on shorter wings it becomes indistinguishable from tip-vortex instability.

Item Type: Article
Additional Information: 41 pages, 27 figures
Uncontrolled Keywords: physics.flu-dyn, physics.flu-dyn
Divisions: Faculty of Science and Engineering > School of Engineering
Depositing User: Symplectic Admin
Date Deposited: 26 Jul 2022 15:56
Last Modified: 15 Mar 2024 11:46
DOI: 10.1017/jfm.2022.420
Open Access URL: https://doi.org/10.1017/jfm.2022.420
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3158410

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