Microstructured Surfaces for Drag Reduction Purposes: Experiments and Simulations on Rectangular 2D Riblets

2005 ◽  
Vol 899 ◽  
Author(s):  
Håkan Rapp ◽  
Igor Zoric ◽  
Bengt Kasemo
Keyword(s):  
Drag Reduction ◽  
Plane Channel ◽  
Viscous Sublayer ◽  
Friction Drag ◽  
Frictional Drag ◽  
Navier Stokes Equation ◽  
Number Range ◽  
Structured Surfaces ◽  
Structured Surface ◽  
Wall Unit

AbstractIt is well established that properly structured surface exhibits a lower friction drag, when exposed to a turbulent boundary layer, than a smooth surface under the same flow conditions. The observed drag decrease is usually attributed to an increased thickness of the viscous sublayer. In this work we examine the friction drag reducing mechanism. Two parallel approaches towards achieving this goal are presented. Photolithography was used to manufacture rectangular riblets in the 10∝m range on a standard 4” silicon wafer. A special compact plane channel system was designed and used for measurements of the frictional drag on structured surfaces in the turbulent flow covering a wide Reynolds number range. Navier-Stokes equation, for the examined drag reducing geometry, was solved in the laminar regime with appropriate boundary conditions. The resulting velocity field was used to extract the protrusion heights difference for streamwise and spanwise flows over the structured surface. The latter was then related to the experimentally measured drag reduction slope. We show that in case of a rectangular riblet, with a size of the order of one wall unit, the observed drag reduction can be accounted for within the above model.

scholarly journals Experimental Analysis of The Effect of Hydrophobic Coating on Pressure Drop in Small Pipes

2020 ◽  
Vol 77 (1) ◽  
pp. 24-35
Author(s):  
Michael J Knights ◽  
Roy Donald ◽  
Diego Galletta ◽  
Pun Kul ◽  
Faik A Hamad
Keyword(s):  
Drag Reduction ◽  
Flow Condition ◽  
Surface Condition ◽  
Friction Drag ◽  
Frictional Drag ◽  
Pipe Surface ◽  
Hydrophobic Coating ◽  
Coated Surface ◽  
Inner Diameter ◽  
Laminar State

In this paper, experimental results are reported to quantify the effect of hydrophobic coating LT-8 on frictional drag of water flow in pipes of 450 mm length. Five pipes of 1, 2, 3, 4, and 5 mm inner diameter were tested. The results from 1, 2 and 3 mm diameter pipes demonstrated an average frictional drag reduction of 9%, 11.5% and 3%, respectively, while the results from 4mm and 5mm pipes showed an increase in frictional drag of 12% and 10%, respectively. The 2mm and 4mm pipes were also tested with a half application of hydrophobic coating. The half coated 2mm pipe showed decrease in drag while 4mm pipe showed increase in drag. The results indicate a relationship between drag reduction/ increase within the percentage of coated surface. The main conclusions are, the flow changed from laminar state to the liquid-air wetting surface condition (Cassie-Baxter wetting state) at the pipe surface and then destabilized by the turbulent boundary layer and entered the liquid wetting surface (Wenzel wetting state) will be appeared. This transition lead to a reduction in friction drag for laminar flow condition and increase in drag for turbulent flow condition.

Friction drag reduction based on a proportional-derivative control scheme

2021 ◽  
Vol 33 (7) ◽  
pp. 075115
Author(s):  
Chi Wai Wong ◽  
Xiaoqi Cheng ◽  
Dewei Fan ◽  
Wenfeng Li ◽  
Yu Zhou
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Control Scheme ◽  
Friction Drag Reduction ◽  
Derivative Control

Effects of the air layer of an idealized superhydrophobic surface on the slip length and skin-friction drag

2016 ◽  
Vol 790 ◽  
Author(s):  
Taeyong Jung ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Superhydrophobic Surface ◽  
Slip Length ◽  
Joint Probability ◽  
Turbulent Channel Flow ◽  
Water Interface ◽  
Friction Drag ◽  
Recirculating Flow ◽  
Air Water Interface

The anisotropy of the slip length and its effect on the skin-friction drag are numerically investigated for a turbulent channel flow with an idealized superhydrophobic surface having an air layer, where the idealized air–water interface is flat and does not contain the surface-tension effect. Inside the air layer, both the shear-driven flow and recirculating flow with zero net mass flow rate are considered. With increasing air-layer thickness, the slip length, slip velocity and percentage of drag reduction increase. It is shown that the slip length is independent of the water flow and depends only on the air-layer geometry. The amount of drag reduction obtained is in between those by the empirical formulae from the streamwise slip only and isotropic slip, indicating that the present air–water interface generates an anisotropic slip, and the streamwise slip length ($b_{x}$) is larger than the spanwise one ($b_{z}$). From the joint probability density function of the slip velocities and velocity gradients at the interface, we confirm the anisotropy of the slip lengths and obtain their relative magnitude ($b_{x}/b_{z}=4$) for the present idealized superhydrophobic surface. It is also shown that the Navier slip model is valid only in the mean sense, and it is generally not applicable to fluctuating quantities.

Drag Reduction of the Flow Past a Circular Cylinder in Surfactant Solution

2001 ◽  
Author(s):  
Satoshi Ogata ◽  
Keizo Watanabe
Keyword(s):  
Circular Cylinder ◽  
Drag Reduction ◽  
Sodium Salicylate ◽  
Tap Water ◽  
Pressure Coefficient ◽  
Surfactant Solution ◽  
Reduction Ratio ◽  
Number Range ◽  
Surfactant Solutions ◽  
Maximum Drag Reduction

Abstract The flow around a circular cylinder in surfactant solution was investigated experimentally by measurement of the pressure and velocity profiles in the Reynolds number range 6000 < Re < 50000. The test surfactant solutions were aqueous solutions of Ethoquad O/12 (Lion Co.) at concentrations of 50, 100 and 200 ppm, and sodium salicylate was added as a counterion. It was clarified that the pressure coefficient of surfactant solutions in the range of 10000 < Re < 50000 at the behind of the separation point was larger than that of tap water, and the separation angle increased with concentration of the surfactant solution. The velocity defect in surfactant solutions behind a circular cylinder was smaller than those in tap water. The drag coefficients of a circular cylinder in surfactant solutions were smaller than those of tap water in the range 10000 < Re < 50000, and no drag reduction occurred at Re = 6000. The drag reduction ratio increased with increasing concentration of surfactant solution. The maximum drag reduction ratio was approximately 35%.

Drag reduction in ultrahydrophobic channels with micro-nano structured surfaces

2010 ◽  
Vol 53 (7) ◽  
pp. 1298-1305 ◽  
Author(s):  
Si Lu ◽  
ZhaoHui Yao ◽  
PengFei Hao ◽  
ChengSong Fu
Keyword(s):  
Drag Reduction ◽  
Structured Surfaces

scholarly journals Investigation of the Impact of Micro-Structuring on the Bonding Performance of Beechwood (Fagus Sylvatica L.)

Forests ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 113
Author(s):  
Destin Bamokina Moanda ◽  
Martin Lehmann ◽  
Peter Niemz
Keyword(s):  
Bond Strength ◽  
Waiting Time ◽  
Type I ◽  
Bond Quality ◽  
Structured Surfaces ◽  
Structured Surface ◽  
Bonding Performance ◽  
Delamination Resistance ◽  
Micro Structuring ◽  
The Impact

Although glueing softwood is well mastered by the industry, predicting and controlling bond quality for hardwood is still challenging after years of research. Parameters such as the adhesive type, resin–hardener ratio, and the penetration behaviour of the wood are determinants for the bond quality. The aim of this work was to assess to what extent the glueing behaviour of beechwood can be improved by using structural planing. The different surfacing methods were characterised by their roughness. The bond strength of the micro-structured surfaces was determined according to EN 302-1, and the delamination resistance was tested as indicated by EN 302-2 for type I adhesives. Micro-structured surfaces were compared with different surfaces (generated by surfacing methods such as dull/sharp planing and sanding). In dry test conditions, all surfacing methods gave satisfying results. In the wet stage, the bond strength on the finer micro-structured surface slightly outperformed the coarse structure surface. For the delamination resistance, a clear improvement could be observed for melamine-formaldehyde-bonded specimens since, when using the recommended amount of adhesive, micro-structured surfaces fulfilled the requirements. Nevertheless, structural planing cannot lead to a reduction in the applied grammage since no sample with a smaller amount fulfilled EN 302-2 requirements even by observing the recommended closed assembly waiting time. Adhesion area enlargement of the micro-structuring is minor. The good delamination performance without waiting time (CAT) is not caused by surface enlargement, since finer micro-structured surface with negligible area increase and delivered even better delamination resistance. Subsurface analysis should be carried out to thoroughly investigate this phenomenon.

scholarly journals 710 Experimental Study on Friction Drag Reduction Effect of Flexible Tube(1)

2006 ◽  
Vol 2006 (0) ◽  
pp. _710-a_
Author(s):  
Zhigang GAO ◽  
Masatomo OHWAKI ◽  
Motoyuki ITOH ◽  
Shinji TAMANO ◽  
Kazuhiko YOKOTA
Keyword(s):  
Experimental Study ◽  
Drag Reduction ◽  
Friction Drag ◽  
Flexible Tube ◽  
Reduction Effect ◽  
Friction Drag Reduction

scholarly journals Discovery of riblets in a bird beak ( Rynchops ) for low fluid drag

2016 ◽  
Vol 374 (2073) ◽  
pp. 20160134 ◽  
Author(s):  
Samuel Martin ◽  
Bharat Bhushan
Keyword(s):  
Pressure Drop ◽  
Drag Reduction ◽  
Shear Stresses ◽  
Structured Surfaces ◽  
Mako Shark ◽  
Fluid Drag ◽  
Bird Beak ◽  
Modelling Studies ◽  
Flow Pressure ◽  
First Time

Riblet structures found on fast-swimming shark scales, such as those found on a mako shark, have been shown to reduce fluid drag. In previous experimental and modelling studies, riblets have been shown to provide drag reduction by lifting vortices formed in turbulent flow, decreasing overall shear stresses. Skimmer birds ( Rynchops ) are the only birds to catch fish in flight by flying just above the water surface with a submerged beak to fish for food. Because they need to quickly catch prey, reducing drag on their beak is advantageous. For the first time, riblet structures found on the beak of the skimmer bird have been studied experimentally and computationally for low fluid drag properties. In this study, skimmer replicas were studied for drag reduction through pressure drop in closed-channel, turbulent water flow. Pressure drop measurements are compared for black and yellow skimmer beaks in two configurations, and mako shark skin. In addition, two configurations of skimmer beak were modelled to compare drag properties and vortex structures. Results are discussed, and a conceptual model is presented to explain a possible drag reduction mechanism in skimmers. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’.

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