scholarly journals Polymers and Plastrons in Parallel Yield Enhanced Turbulent Drag Reduction

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 197 ◽  
Author(s):  
Anoop Rajappan ◽  
Gareth H. McKinley
Keyword(s):  
Drag Reduction ◽  
Couette Flow ◽  
Turbulent Flows ◽  
Polymer Additives ◽  
Frictional Drag ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Reduction Effect ◽  
Friction Measurements ◽  
Wall Bounded Turbulence

Despite polymer additives and superhydrophobic walls being well known as stand-alone methods for frictional drag reduction in turbulent flows, the possibility of employing them simultaneously in an additive fashion has remained essentially unexplored. Through experimental friction measurements in turbulent Taylor–Couette flow, we show that the two techniques may indeed be combined favorably to generate enhanced levels of frictional drag reduction in wall-bounded turbulence. We further propose an additive expression in Prandtl–von Kármán variables that enables us to quantitatively estimate the magnitude of this cooperative drag reduction effect for small concentrations of dissolved polymer.

Turbulent Drag Reduction Effect by Hydrogen and Oxygen Microbubbles Made by Electrolysis

2006 ◽  
Author(s):  
Xinlin Lu ◽  
Hiroharu Kato ◽  
Takafumi Kawamura
Keyword(s):  
Drag Reduction ◽  
Void Fraction ◽  
Bubble Diameter ◽  
Water Electrolysis ◽  
Air Injection ◽  
Air Bubbles ◽  
Turbulent Drag Reduction ◽  
Circulating Water ◽  
Turbulent Drag ◽  
Reduction Effect

Turbulent drag reduction by very small hydrogen microbubbles was investigated experimentally. The method for generating microbubbles of 10–60 μm by water electrolysis was established firstly. Experiments were carried out using a circulating water tunnel, and it was observed that the small microbubbles generated by electrolysis can achieve the same drag reduction as the injected air bubbles at much lower void fraction. The distribution of microbubble was examined using the microscope photography. The peak of local void fraction was found to be very close to the wall, while no correlation was found between the average bubble diameter and the distance from the channel wall. The present experimental results suggest that the very small microbubbles produced by electrolysis are 10∼100 times more effective in terms of the drag reduction than large bubbles made by air injection. So it is considered that the diameters of microbubbles play an important role to drag reduction.

0304 Turbulent Drag-Reduction Effect by Blowing Polymer Solution from a Wall using Discrete-Element Model

2009 ◽  
Vol 2009 (0) ◽  
pp. 157-158
Author(s):  
Masahiko KOSHI ◽  
Kaoru IWAMOTO ◽  
Akira MURATA ◽  
Yasuo KAWAGUCHI ◽  
Hirotomo ANDO ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Polymer Solution ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Reduction Effect

scholarly journals Interpretation of the mechanism associated with turbulent drag reduction in terms of anisotropy invariants

2007 ◽  
Vol 577 ◽  
pp. 457-466 ◽  
Author(s):  
B. FROHNAPFEL ◽  
P. LAMMERS ◽  
J. JOVANOVIĆ ◽  
F. DURST
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Viscous Sublayer ◽  
Direct Numerical Simulations ◽  
Wall Region ◽  
Turbulent Drag Reduction ◽  
High Anisotropy ◽  
Turbulent Drag ◽  
Reduction Mechanisms ◽  
Long Chain

A central goal of flow control is to minimize the energy consumption in turbulent flows and nowadays the best results in terms of drag reduction are obtained with the addition of long-chain polymers. This has been found to be associated with increased anisotropy of turbulence in the near-wall region. Other drag reduction mechanisms are analysed in this respect and it is shown that close to the wall highly anisotropic states of turbulence are commonly found. These findings are supported by results of direct numerical simulations which display high drag reduction effects of over 30% when only a few points inside the viscous sublayer are forced towards high anisotropy.

scholarly journals Superhydrophobic turbulent drag reduction as a function of surface grating parameters

2014 ◽  
Vol 747 ◽  
pp. 722-734 ◽  
Author(s):  
Hyungmin Park ◽  
Guangyi Sun ◽  
Chang-Jin “CJ” Kim
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Turbulent Flows ◽  
Smooth Surface ◽  
Continuous Monitoring ◽  
Laminar Flows ◽  
Turbulent Drag Reduction ◽  
Surface Grating ◽  
Turbulent Drag ◽  
Slip Flows

AbstractDespite the confirmation of slip flows and successful drag reduction (DR) in small-scaled laminar flows, the full impact of superhydrophobic (SHPo) DR remained questionable because of the sporadic and inconsistent experimental results in turbulent flows. Here we report a systematic set of bias-free reduction data obtained by measuring the skin-friction drags on a SHPo surface and a smooth surface at the same time and location in a turbulent boundary layer (TBL) flow. Each monolithic sample consists of a SHPo surface and a smooth surface suspended by flexure springs, all carved out from a $2.7 \times 2.7 {\mathrm{mm}}^{2}$ silicon chip by photolithographic microfabrication. The flow tests allow continuous monitoring of the plastron on the SHPo surfaces, so that the DR data are genuine and consistent. A family of SHPo samples with precise profiles reveals the effects of grating parameters on turbulent DR, which was measured to be as much as ${\sim }75\, \%$.

scholarly journals Turbulent Drag Reduction. Effect of Implanted Fiber.

1996 ◽  
Vol 62 (596) ◽  
pp. 1383-1387 ◽  
Author(s):  
Takashi TAKATA ◽  
Keiji KYOGOKU ◽  
Tsunamistu NAKAHARA
Keyword(s):  
Drag Reduction ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Reduction Effect

Liquid-infused surfaces as a passive method of turbulent drag reduction

2017 ◽  
Vol 824 ◽  
pp. 688-700 ◽  
Author(s):  
M. K. Fu ◽  
I. Arenas ◽  
S. Leonardi ◽  
M. Hultmark
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Experimental Studies ◽  
Turbulent Channel Flow ◽  
Superhydrophobic Surfaces ◽  
Fluid Interfaces ◽  
Turbulent Drag Reduction ◽  
Liquid Lubricant ◽  
Passive Method ◽  
Turbulent Drag

Liquid-infused surfaces present a novel, passive method of turbulent drag reduction. Inspired by the Nepenthes Pitcher Plant, liquid-infused surfaces utilize a lubricating fluid trapped within structured roughness to facilitate a slip at the effective surface. The conceptual idea is similar to that of superhydrophobic surfaces, which rely on a lubricating air layer, whereas liquid-infused surfaces use a preferentially wetting liquid lubricant to create localized fluid–fluid interfaces. Maintaining the presence of these slipping interfaces has been shown to be an effective method of passively reducing skin friction drag in turbulent flows. Given that liquid-infused surfaces have only recently been considered for drag reduction applications, there is no available framework to relate surface and lubricant characteristics to any resulting drag reduction. Here we use results from direct numerical simulations of turbulent channel flow over idealized, liquid-infused grooves to demonstrate that the drag reduction achieved using liquid-infused surfaces can be described using the framework established for superhydrophobic surfaces. These insights can be used to explain drag reduction results observed in experimental studies of lubricant-infused surfaces. We also demonstrate how a liquid-infused surface can reduce drag even when the viscosity of the lubricant exceeds that of the external fluid flow, which at first glance can seem counter-intuitive.

Turbulent Drag Reduction by Polymer Containing Paint: Simultaneous Measurement of Skin Friction and Release Rate

2010 ◽  
Author(s):  
Masaaki Motozawa ◽  
Toshihisa Ito ◽  
Ayumu Matsumoto ◽  
Hirotomo Ando ◽  
Toshihiko Ashida ◽  
...  
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Release Rate ◽  
Performance Test ◽  
Reynolds Shear Stress ◽  
Antifouling Paint ◽  
Laser Doppler Velocimeter ◽  
Frictional Drag ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag

Performance test for polymer containing trial antifouling paint was carried out experimentally. This trial paint is made by adding a polymer (PEO) to commercial antifouling paint for ship hull. Our developing paint has a function of leaching out the polymer and eventually reduces the skin frictional drag by the effect of dissolved polymer when the ship cruises. As the performance test, we examined the release rate of the polymer from the trial paint and measured the skin frictional drag at the same time. In addition, the velocity distribution near the painted wall was measured by Laser Doppler Velocimeter (LDV). As a result, in the first stage, the large drag reduction was obtained with releasing polymer. The Reynolds shear stress near the painted wall largely decreases comparing with the commercial antifouling paint in the water flow. However, after several hours, this drag reducing effect was hardly lost.

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