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Enhanced drag-reduction over superhydrophobic surfaces with sinusoidal textures: A DNS study
Published in Elsevier Ltd
2019
Volume: 181
   
Pages: 208 - 223
Abstract
Direct Numerical Simulation (DNS) studies of a fully developed turbulent channel flow are performed with sinusoidal surface texture to assess its ability to enhance turbulent skin-frictional drag reductions over superhydrophobic surfaces (SHS). The streamwise sinusoidal microgroove structure generates asymmetric secondary flows to induce an in-plane stationary distribution of spanwise velocity that oscillates in the streamwise direction. The transverse motions over a sinusoidal texture behave analogously to an existing drag-reduction technique by spanwise wall oscillations. The friction-drag levels and slip-lengths are precisely quantified for various streamwise wavelength configurations, and an optimum wavelength for the maximum reduction in turbulent drag is determined. The response of the near-wall turbulent structures to the sinusoidal microgrooves is also analysed. The transverse Stokes strain generates spanwise tilting in the near-wall streaks for large wavelengths, inducing an apparent drop in the wall-normal ejections and sweeps, thereby reducing the turbulent contribution to the wall-shear-stress. The transverse shear strain above the sinusoidal microgroove is demonstrated to be resembling a Stokes spatial layer (SSL), by comparing with existing analytical solutions of strain profiles for wall-forcing by spanwise spatial oscillations. © 2019 Elsevier Ltd
About the journal
JournalData powered by TypesetComputers and Fluids
PublisherData powered by TypesetElsevier Ltd
ISSN00457930
Open AccessNo
Concepts (18)
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    Channel flow
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    Drag reduction
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    Flow control
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    Friction
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    Shear strain
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    Shear stress
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    Surface properties
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    Textures
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    Turbulence
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    MICROGROOVE STRUCTURES
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    SPANWISE WALL OSCILLATIONS
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    Stationary distribution
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    STOKES LAYER
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    Streamwise directions
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    Super-hydrophobic surfaces
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    TRANSVERSE SHEAR STRAINS
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    TURBULENT CHANNEL FLOWS
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    Hydrophobicity