Abstract
Abstract A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.
Highlights
The micro-structures fabricated on a mechanical surface show very practical value because of their special functions, such as drag reduction and anti-icing, dustproof, and self-cleaning abilities, among others [1, 2]
The drag reduction characteristics of the textured surface are presented in this article in terms of the profile geometries and friction coefficient
The literature review shows that the maximum drag reduction rate of more than 20% is possible for the hydrophobic, even super-hydrophobic surface
Summary
The micro-structures fabricated on a mechanical surface show very practical value because of their special functions, such as drag reduction and anti-icing, dustproof, and self-cleaning abilities, among others [1, 2]. In the aspect of a drag reduction experiment, Gruneberger and Hage [9] and Teo and Khoo [10] examined the momentum exchange of turbulent flow in the near wall region. The secondary vortex is considered to weaken the low-speed fluid ejection from the near-wall region, which impedes the momentum exchange and turbulent bursting intensity It can hinder the down-sweeping movement from the high-speed to the low-speed region with a consequent shear stress reduction on the solid wall, thereby stabilizing a lowspeed streak in the valley [15, 16]. The drag reduction characteristics of the textured surface are presented in this article in terms of the profile geometries and friction coefficient. Conclusions are drawn in light of the section types and drag reduction mechanism
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