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Laminar separated flows over finite-aspect-ratio swept wings

Published online by Cambridge University Press:  21 October 2020

Kai Zhang Open the ORCID record for Kai Zhang [Opens in a new window] ,
Shelby Hayostek ,
Michael Amitay Open the ORCID record for Michael Amitay [Opens in a new window] ,
Anton Burtsev ,
Vassilios Theofilis Open the ORCID record for Vassilios Theofilis [Opens in a new window]  and
Kunihiko Taira Open the ORCID record for Kunihiko Taira [Opens in a new window]
Kai Zhang*
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA90095, USA
Shelby Hayostek
Affiliation:
Department of Mechanical, Aeronautical, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY12180, USA
Michael Amitay
Affiliation:
Department of Mechanical, Aeronautical, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY12180, USA
Anton Burtsev
Affiliation:
Department of Mechanical, Materials and Aerospace Engineering, University of Liverpool, Brownlow Hill, LiverpoolL69 3GH, UK
Vassilios Theofilis
Affiliation:
Department of Mechanical, Materials and Aerospace Engineering, University of Liverpool, Brownlow Hill, LiverpoolL69 3GH, UK Department of Mechanical Engineering, Escola Politecnica, Universidade São Paulo, Avda. Prof. Mello Moraes 2231, CEP 5508-900São Paulo, Brasil
Kunihiko Taira
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA90095, USA
*
Email address for correspondence: kai.zhang3@rutgers.edu
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Abstract

We perform direct numerical simulations of laminar separated flows over finite-aspect-ratio swept wings at a chord-based Reynolds number of $Re = 400$ to reveal a variety of wake structures generated for a range of aspect ratios (semi aspect ratio $sAR=0.5\text {--}4$), angles of attack ($\alpha =16^{\circ }\text {--}30^{\circ }$) and sweep angles ($\varLambda =0^{\circ }\text {--}45^{\circ }$). Flows behind swept wings exhibit increased complexity in their dynamical features compared to unswept-wing wakes. For unswept wings, the wake dynamics are predominantly influenced by the tip effects. Steady wakes are mainly limited to low-aspect-ratio wings. Unsteady vortex shedding takes place near the midspan of higher-$AR$ wings due to weakened downwash induced by the tip vortices. With increasing sweep angle, the source of three-dimensionality transitions from the tip to the midspan. The three-dimensional midspan effects are responsible for the formation of the stationary vortical structures at the inboard part of the span, which expands the steady wake region to higher aspect ratios. At higher aspect ratios, the midspan effects of swept wings diminish at the outboard region, allowing unsteady vortex shedding to develop near the tip. In the wakes of highly swept wings, streamwise finger-like structures form repetitively along the wing span, providing a stabilizing effect. The insights revealed from this study can aid the design of high-lift devices and serve as a stepping stone for understanding the complex wake dynamics at higher Reynolds numbers and those generated by unsteady wing manoeuvres.

JFM classification

Wakes/Jets: Separated flows Wakes/Jets: Wakes Vortex Flows: Vortex dynamics
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 905 , 25 December 2020 , R1
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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Footnotes

†

Present address: Department of Mechanical and Aerospace Engineering, Rutgers University.

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