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On the Turbulent Drag Reduction Effect of the Dynamic Free-Slip Surface Method

Wang, Cong and Gharib, Morteza (2022) On the Turbulent Drag Reduction Effect of the Dynamic Free-Slip Surface Method. Journal of Marine Science and Engineering, 10 (7). Art. No. 879. ISSN 2077-1312. doi:10.3390/jmse10070879.

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The turbulent boundary layer (TBL) over the hull surface of a water vehicle significantly elevates the drag force on the water vehicle. In this regard, effectively controlling the TBL can lead to a drag reduction (DR) effect and therefore improve the energy efficiency of water transportation. Many DR methods have demonstrated promising DR effects but face challenges in implementation at the scale of engineering application. In this regard, the recently developed dynamic free-slip surface method can resolve some of the critical challenges. It employs an array of freely oscillating air–water interfaces to manipulate the TBL and can achieve a substantial DR effect under certain control conditions. However, the optimal setting of the control parameters that would maximize the DR effect remains unclear. To answer these questions, this study systematically investigates the effects of multiple control parameters for the first time, including the geometric size and curvature of the interface, the frequency of active oscillation, and the Reynolds number of TBL. Digital Particle Image Velocimetry was used to non-invasively measure the velocity and vorticity field of the TBL, and the Charted Clauser method was used to calculate the DR effect. The presented results suggest that the oscillating free-slip interfaces reduce the flow velocity near the wall boundary and lift the transverse vorticity (and the viscous shear stress) away from the wall. In addition, the shape factor of the TBL is elevated by the oscillating interfaces and slowly relaxes back in the downstream regions, which implies a partial relaminarization process induced in the TBL. Up to 36% DR effect was achieved within the current scope range of the control parameters. All of the results consistently suggest that a large DR effect is achieved when the free-slip interfaces oscillate with large Weber numbers. These discoveries shed light on the underlying DR mechanism and provide guidance for the future development of an effective drag control technique based on the dynamic free-slip surface method.

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Wang, Cong0000-0002-8271-5637
Gharib, Morteza0000-0003-0754-4193
Additional Information:© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( Received: 30 April 2022 / Revised: 20 June 2022 / Accepted: 21 June 2022 / Published: 27 June 2022. (This article belongs to the Special Issue Research on Dispersion and Transport of Non-spherical Particles in Turbulent Flows). The support from the United States Office of Naval Research is gratefully acknowledged. Cong Wang would like to thank the Stanback fellowship support from the Graduate Aerospace Laboratory at the California Institute of Technology (GALCIT). This research was funded by the United States Office of Naval Research under Grant No. N00014-15-1-2479. Author Contributions. Conceptualization, C.W.; investigation, C.W.; writing—review and editing, C.W.; supervision, M.G.; funding acquisition, M.G. All authors have read and agreed to the published version of the manuscript. The authors declare no conflict of interest. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable.
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-15-1-2479
Foster and Coco Stanback Postdoctoral FellowshipUNSPECIFIED
Subject Keywords:turbulent boundary layer control; drag reduction; multi-phase flow
Issue or Number:7
Record Number:CaltechAUTHORS:20220808-887233000
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Official Citation:Wang, Cong, and Morteza Gharib. 2022. "On the Turbulent Drag Reduction Effect of the Dynamic Free-Slip Surface Method" Journal of Marine Science and Engineering 10, no. 7: 879.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116179
Deposited By: George Porter
Deposited On:09 Aug 2022 19:51
Last Modified:09 Aug 2022 19:51

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