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Effect of the dynamic slip boundary condition on the near-wall turbulent boundary layer

Wang, Cong and Gharib, Morteza (2020) Effect of the dynamic slip boundary condition on the near-wall turbulent boundary layer. Journal of Fluid Mechanics, 901 . Art. No. A11. ISSN 0022-1120. https://resolver.caltech.edu/CaltechAUTHORS:20200917-145619942

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Abstract

The manipulation of near-wall turbulent structures in a turbulent boundary layer (TBL) is an effective way to reduce the turbulent frictional drag. This paper demonstrates the effectiveness of a novel approach for the manipulation of near-wall structures in a TBL with Reynolds number (R_eθ) set to 1200. The manipulation is achieved by employing a sustainable wall-attached air-film array. The static and dynamic interface configuration of the air film can be modulated, which generates a dynamic slip boundary condition. For modulation frequencies within the TBL receptivity, this approach shows that it can effectively modify the TBL near-wall velocity/vorticity field. For a typical modulation frequency of 50 Hz, the near-wall mean streamwise velocity decreases and the wall-normal velocity increases when compared to the canonical flat plate TBL. The mean transverse vorticity is suppressed in the near-wall region and its peak is ‘pushed’ outward away from the wall. In the vicinity of modulated air-film array, the phase-locked velocity/vorticity field demonstrates harmonic motions such as a Stokes-type oscillatory motion. The distribution of shear stresses indicates suppressed momentum transfer toward the wall. Estimation of the wall skin friction via the Clauser chart method indicates a reduction of the wall skin friction up to 40 % in the downstream region of the air-film array. A control volume analysis shows that the TBL gains a significant amount of momentum over the oscillating air films, which suggests that the oscillating air film acts like a source of momentum. This pumping effect could potentially explain the observed wall skin friction reduction effect.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1017/jfm.2020.514DOIArticle
ORCID:
AuthorORCID
Wang, Cong0000-0002-8271-5637
Gharib, Morteza0000-0003-0754-4193
Additional Information:© The Author(s), 2020. Published by Cambridge University Press. Received 3 November 2019; revised 11 May 2020; accepted 13 June 2020. Published online by Cambridge University Press: 24 August 2020. This work was supported by the Office of Naval Research under grant no. N00014-15-1-2479. C.W. was supported by the Stanback fellowship at GALCIT, Caltech. The authors appreciate the communication and discussion with Professor G.L. Brown. The authors report no conflict of interest.
Group:GALCIT
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-15-1-2479
CaltechUNSPECIFIED
Subject Keywords:turbulence control, turbulent boundary layers, drag reduction
Record Number:CaltechAUTHORS:20200917-145619942
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200917-145619942
Official Citation:Wang, C., & Gharib, M. (2020). Effect of the dynamic slip boundary condition on the near-wall turbulent boundary layer. Journal of Fluid Mechanics, 901, A11. doi:10.1017/jfm.2020.514
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105437
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:17 Sep 2020 23:37
Last Modified:17 Sep 2020 23:37

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