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Chandran, D., Zampiron, A., Rouhi, A. 
ORCID: 0000-0002-7837-418X, Fu, M.K., Wine, D., Holloway, B., Smits, A.J. 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
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 | ||||||
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| 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 |
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