Turbulent drag reduction by spanwise wall forcing. Part 2. High-Reynolds-number experiments

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Chandran, D, Zampiron, A, Rouhi, A ORCID: https://orcid.org/0000-0002-7837-418X, Fu, MK, Wine, D, Holloway, B, Smits, AJ and Marusic, I, 2023. Turbulent drag reduction by spanwise wall forcing. Part 2. High-Reynolds-number experiments. Journal of Fluid Mechanics, 968: A7. ISSN 0022-1120

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Official URL: https://doi.org/10.1017/jfm.2023.498

Abstract

We present measurements of turbulent drag reduction (DR) in boundary layers at high friction Reynolds numbers in the range of 4500≤Reτ≤15 000. The efficacy of the approach, using streamwise travelling waves of spanwise wall oscillations, is studied for two actuation regimes: (i) inner-scaled actuation (ISA), as investigated in Part 1 of this study, which targets the relatively high-frequency structures of the near-wall cycle, and (ii) outer-scaled actuation (OSA), which was recently presented by Marusic et al. (Nat. Commun., vol. 12, 2021) for high- Reτ flows, targeting the lower-frequency, outer-scale motions. Multiple experimental techniques were used, including a floating-element balance to directly measure the skin-friction drag force, hot-wire anemometry to acquire long-time fluctuating velocity and wall-shear stress, and stereoscopic particle image velocimetry to measure the turbulence statistics of all three velocity components across the boundary layer. Under the ISA pathway, DR of up to 25 % was achieved, but mostly with net power saving (NPS) losses due to the high-input power cost associated with the high-frequency actuation. The low-frequency OSA pathway, however, with its lower input power requirements, was found to consistently result in positive NPS of 5–10 % for moderate DRs of 5–15 %. The results suggest that OSA is an attractive pathway for energy-efficient DR in high-Reynolds-number applications.

Item Type:	Journal article
Publication Title:	Journal of Fluid Mechanics
Creators:	Chandran, D., Zampiron, A., Rouhi, A., Fu, M.K., Wine, D., Holloway, B., Smits, A.J. and Marusic, I.
Publisher:	Cambridge University Press
Date:	2023
Volume:	968
ISSN:	0022-1120
Identifiers:	Number Type 10.1017/jfm.2023.498 DOI 1787834 Other
Rights:	This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Divisions:	Schools > School of Science and Technology
Record created by:	Jonathan Gallacher
Date Added:	07 Aug 2023 08:07
Last Modified:	07 Aug 2023 08:07
URI:	https://irep.ntu.ac.uk/id/eprint/49505