Journal ArticleDOI
A numerical study of the effects of superhydrophobic surface on skin-friction drag in turbulent channel flow
TLDR
In this paper, the effects of a superhydrophobic surface, consisting of microgrates aligned in the flow direction, on skin-friction drag in turbulent flows were investigated through direct numerical simulation of turbulent channel flows.Abstract:
Superhydrophobic surfaces have attracted much attention lately as they present the possibility of achieving a substantial skin-friction drag reduction in turbulent flows. In this paper, the effects of a superhydrophobic surface, consisting of microgrates aligned in the flow direction, on skin-friction drag in turbulent flows were investigated through direct numerical simulation of turbulent channel flows. The superhydrophobic surface was modeled through a shear-free boundary condition on the air-water interface. Dependence of the effective slip length and resulting skin-friction drag on Reynolds number and surface geometry was examined. In laminar flows, the effective slip length depended on surface geometry only, independent of Reynolds number, consistent with an existing analysis. In turbulent flows, the effective slip length was a function of Reynolds number, indicating its dependence on flow conditions near the surface. The resulting drag reduction was much larger in turbulent flows than in laminar flows, and near-wall turbulence structures were significantly modified, suggesting that indirect effects resulting from modified turbulence structures played a more significant role in reducing drag in turbulent flows than the direct effect of the slip, which led to a modest drag reduction in laminar flows. It was found that the drag reduction in turbulent flows was well correlated with the effective slip length normalized by viscous wall units.read more
Citations
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Journal ArticleDOI
Superhydrophobic drag reduction in laminar flows: a critical review
TL;DR: In this paper, the authors provide a global picture of the liquid slip on structured surfaces to assist in rational design of superhydrophobic surfaces for drag reduction and discuss the recent efforts to prevent its loss.
Journal ArticleDOI
Superhydrophobic turbulent drag reduction as a function of surface grating parameters
TL;DR: In this paper, a set of bias-free reduction data obtained by measuring the skin-friction drags on a superhydrophobic surface and a smooth surface at the same time and location in a turbulent boundary layer (TBL) flow is presented.
Journal ArticleDOI
Turbulent drag reduction over air- and liquid- impregnated surfaces
TL;DR: In this paper, turbulent skin friction reduction over air-and liquid-impregnated surfaces for aqueous Taylor-Couette flow is presented for the case of super-hydrophobic surfaces.
Journal ArticleDOI
Buoyancy increase and drag-reduction through a simple superhydrophobic coating
TL;DR: Buoyance testing showed that the reduction of surface energy by superhydrophobic coating made it feasible that glass, a high density material, was supported by the surface tension of water.
Journal ArticleDOI
Turbulence and skin friction modification in channel flow with streamwise-aligned superhydrophobic surface texture
TL;DR: In this paper, the effects of the surface texture on the turbulence and skin-friction coefficient were examined, and the SHS is modeled as a planar boundary comprised of spanwise-alternating regions of no-slip and free-slink boundary conditions.
References
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Journal ArticleDOI
Natural and biomimetic artificial surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reduction
Bharat Bhushan,Yong Chae Jung +1 more
TL;DR: In this paper, the theoretical mechanisms of the wetting of rough surfaces are presented followed by the characterization of natural leaf surfaces and a comprehensive review is presented on artificial super-hydrophobic surfaces fabricated using various fabrication techniques and the influence of micro-, nano-and hierarchical structures on superhydrophobicity, self-cleaning, low adhesion, and drag reduction.
Journal ArticleDOI
Wetting and self-cleaning properties of artificial superhydrophobic surfaces
TL;DR: The wetting and the self-cleaning properties (the latter is often called the "Lotus-Effect") of three types of superhydrophobic surfaces have been investigated: silicon wafer specimens with different regular arrays of spikes hydrophobized by chemical treatment, replicates of water-repellent leaves of plants, and commercially available metal foils which were additionally hydrophobic by means of a fluorinated agent.
Journal ArticleDOI
Recent developments in superhydrophobic surfaces and their relevance to marine fouling: a review
Jan Genzer,Kirill Efimenko +1 more
TL;DR: The formation of responsive/“smart” surfaces, which adjust their physico-chemical properties to variations in some outside physical stimulus, including light, temperature, electric field, or solvent, is also described.
Journal ArticleDOI
Slip on Superhydrophobic Surfaces
TL;DR: A review of the use of the combination of surface roughness and hydrophobicity for engineering large slip at the fluid-solid interface is given in this paper, with an eye toward implementing these surfaces in a wide range of applications.
Journal ArticleDOI
Laminar drag reduction in microchannels using ultrahydrophobic surfaces
TL;DR: In this paper, a series of experiments are presented which demonstrate significant drag reduction for the laminar flow of water through microchannels using hydrophobic surfaces with well-defined micron-sized surface roughness.