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- Title
Turbulent drag reduction by spanwise wall forcing. Part 2. High-Reynolds-number experiments.
- Authors
Chandran, D.; Zampiron, A.; Rouhi, A.; Fu, M.K.; Wine, D.; Holloway, B.; Smits, A.J.; Marusic, I.
- Abstract
We present measurements of turbulent drag reduction (DR) in boundary layers at high friction Reynolds numbers in the range of $4500 \le Re_\tau \le 15\ 000$. 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- $Re_\tau$ 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.
- Subjects
DRAG reduction; REYNOLDS number; BOUNDARY layer (Aerodynamics); PARTICLE image velocimetry; TURBULENT boundary layer; BOUNDARY layer control; OSCILLATIONS; PARTICLE motion
- Publication
Journal of Fluid Mechanics, 2023, Vol 968, p1
- ISSN
0022-1120
- Publication type
Article
- DOI
10.1017/jfm.2023.498