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Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers

Li, Mogeng and de Silva, Charitha M. and Chung, Daniel and Pullin, Dale I. and Marusic, Ivan and Hutchins, Nicholas (2021) Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers. Journal of Fluid Mechanics, 923 . Art. No. A18. ISSN 0022-1120. doi:10.1017/jfm.2021.577. https://resolver.caltech.edu/CaltechAUTHORS:20210821-001444301

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Abstract

This study presents an experimental dataset documenting the evolution of a turbulent boundary layer downstream of a rough-to-smooth surface transition. To investigate the effect of upstream flow conditions, two groups of experiments are conducted. For the Group-Re cases, a nominally constant viscous-scaled equivalent sand grain roughness k⁺_(s0)≈160 is maintained on the rough surface, while the friction Reynolds number Re_(τ0) ranges from 7100 to 21 000. For the Group-ks cases, Re_(τ0)≈14000 is maintained while k⁺_(s0) ranges from 111 to 228. The wall-shear stress on the downstream smooth surface is measured directly using oil-film interferometry to redress previously reported uncertainties in the skin-friction coefficient recovery trends. In the early development following the roughness transition, the flow in the internal layer is not in equilibrium with the wall-shear stress. This conflicts with the common practise of modelling the mean velocity profile as two log laws below and above the internal layer height, as first proposed by Elliott (Trans. Am. Geophys. Union, vol. 39, 1958, pp. 1048–1054). As a solution to this, the current data are used to model the recovering mean velocity semi-empirically by blending the corresponding rough-wall and smooth-wall profiles. The over-energised large-scale motions leave a strong footprint in the near-wall region of the energy spectrum, the frequency and magnitude of which exhibit dependence on Re_(τ0) and k⁺_(s0), respectively. The energy distribution in near-wall small scales is mostly unaffected by the presence of the outer flow with rough-wall characteristics, which can be used as a surrogate measure to extract the local friction velocity.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1017/jfm.2021.577DOIArticle
ORCID:
AuthorORCID
Li, Mogeng0000-0002-9875-6468
de Silva, Charitha M.0000-0001-9517-4318
Chung, Daniel0000-0003-3732-364X
Marusic, Ivan0000-0003-2700-8435
Hutchins, Nicholas0000-0003-1599-002X
Additional Information:© The Author(s), 2021. Published by Cambridge University Press. Received 8 December 2020; revised 20 April 2021; accepted 21 June 2021. This research was partially supported under the Australian Research Council's Discovery Projects funding scheme (project DP160103619). The authors report no conflict of interest.
Group:GALCIT
Funders:
Funding AgencyGrant Number
Australian Research CouncilDP160103619
DOI:10.1017/jfm.2021.577
Record Number:CaltechAUTHORS:20210821-001444301
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210821-001444301
Official Citation:Li, M., De Silva, C., Chung, D., Pullin, D., Marusic, I., & Hutchins, N. (2021). Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers. Journal of Fluid Mechanics, 923, A18. doi:10.1017/jfm.2021.577
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110341
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 Aug 2021 17:35
Last Modified:21 Aug 2021 17:35

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