Skin-friction drag reduction in a high-Reynolds-number turbulent boundary layer via real-time control of large-scale structures

Abbassi, M, Baars, W, Hutchins, N and Marusic, I 2017, 'Skin-friction drag reduction in a high-Reynolds-number turbulent boundary layer via real-time control of large-scale structures', International Journal of Heat and Fluid Flow, vol. 67, pp. 30-41.


Document type: Journal Article
Collection: Journal Articles

Title Skin-friction drag reduction in a high-Reynolds-number turbulent boundary layer via real-time control of large-scale structures
Author(s) Abbassi, M
Baars, W
Hutchins, N
Marusic, I
Year 2017
Journal name International Journal of Heat and Fluid Flow
Volume number 67
Start page 30
End page 41
Total pages 12
Publisher Elsevier Inc.
Abstract While large-scale motions are most energetic in the logarithmic region of a high-Reynolds-number turbulent boundary layer, they also have an influence in the inner-region. In this paper we describe an experimental investigation of manipulating the large-scale motions and reveal how this affects the turbulence and skin-friction drag. A boundary layer with a friction Reynolds number of 14 400 is controlled using a spanwise array of nine wall-normal jets operated in an on/off mode and with an exit velocity that causes the jets in cross-flow to penetrate within the log-region. Each jet is triggered in real-time with an active controller, driven by a time-resolved footprint of the large-scale motions acquired upstream. Nominally, the controller injects air into large-scale zones with positive streamwise velocity fluctuations; these zones are associated with positive wall-shear stress fluctuations. This control scheme reduced the streamwise turbulence intensity in the log-region up to a downstream distance of more than five times the boundary layer thickness, 6, from the point of actuation. The highest reduction in spectral energy more than 30%-was found for wavelengths larger than 5 delta in the log-region at 1.7 delta downstream of actuation, while scales larger than 2 delta still comprised more than 15% energy reduction in the near-wall region. In addition, a 3.2% reduction in mean skin-friction drag was achieved at 1.7 delta downstream of actuation. Our reductions of the streamwise turbulence intensity and mean skin-friction drag exceed a base line control-case, for which the jet actuators were operated with the same temporal pattern, but not synchronised with the incoming large-scale zones of positive fluctuating velocity.
Subject Aerodynamics (excl. Hypersonic Aerodynamics)
Keyword(s) Drag reduction
Flow control
Large-scale structure
Turbulent boundary layer
DOI - identifier 10.1016/j.ijheatfluidflow.2017.05.003
Copyright notice © 2017 Elsevier Inc. All rights reserved.
ISSN 0142-727X
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