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Wake-induced transition in the low-Reynolds-number flow over a multi-element airfoil

Published online by Cambridge University Press:  11 March 2021

Jiang-Sheng Wang  and
Jin-Jun Wang Open the ORCID record for Jin-Jun Wang [Opens in a new window]
Jiang-Sheng Wang
Affiliation:
Fluid Mechanics Key Laboratory of Education Ministry, Beijing University of Aeronautics and Astronautics, Beijing100191, China
Jin-Jun Wang*
Affiliation:
Fluid Mechanics Key Laboratory of Education Ministry, Beijing University of Aeronautics and Astronautics, Beijing100191, China
*
†Email address for correspondence: jjwang@buaa.edu.cn
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Abstract

Time-resolved particle image velocimetry and hydrogen bubble visualization are used to investigate the wake-induced transition of a 30P30N multi-element airfoil at a fixed angle of attack of 4° within the stowed chord Reynolds-number range of 1.38 × 104 to 3.05 × 104. A special transition routine, strongly affected by the slat wake, is observed in the confluent boundary layer over the 30P30N airfoil. In particular, the effects of slat-wake-triggered double-secondary vortices on the whole transition process are explored in detail. At the initial transition stage, the strong slat-wake disturbances penetrate the boundary layer of the main element and are then amplified by double-exponential growth to generate double-secondary vortices. Compared to the scenarios of simplified geometries (He et al., J. Fluid Mech., vol. 718, 2013, pp. 116–130; He & Wang, Phys. Fluids, vol. 27, 2015, 024106), the double-exponential growth provides stronger fluctuations for the transition. At the intermediate transition stage, the wake disturbances trigger the three-dimensional destabilization of these secondary vortices by direct injection or indirect induction, leading to Λ vortices. The spanwise wavelength of the consequent Λ vortices is therefore locked on by the wake disturbances. At the late transition stage, the Λ vortices evolve into hairpin vortex packets and finally contribute to an attached turbulent boundary layer above the main element. Throughout the transition process, no obvious separation occurs in the mean flow above the main element, revealing potential aerodynamic benefits.

JFM classification

Vortex Flows: Vortex dynamics Vortex Flows: Vortex interactions Turbulent Flows: Turbulent transition
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 915 , 25 May 2021 , A28
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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