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.

COMPUTATIONAL AND EXPERIMENTAL STUDIES OF AN ACTIVE SKIN FOR TURBULENT DRAG REDUCTION

2002 ◽  
Author(s):  
Othon Rediniotis ◽  
Dimitris Lagoudas ◽  
Raghavendran Mani ◽  
Lance Traub ◽  
George Karniadakis ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Experimental Studies ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag

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.

Turbulent Drag Reduction Using Superhydrophobic Surfaces

2006 ◽  
Author(s):  
Charles Henoch ◽  
Tom Krupenkin ◽  
Paul Kolodner ◽  
J. Taylor ◽  
M Hodes ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Superhydrophobic Surfaces ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag

Simulation Results for Micro-Bubbles and Turbulent Drag Reduction (Keynote)

2003 ◽  
Author(s):  
M. R. Maxey ◽  
J. Xu ◽  
S. Dong ◽  
G. E. Karniadakis
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turbulent Drag Reduction ◽  
Void Fractions ◽  
Turbulent Drag ◽  
Simulation Results ◽  
Small Bubbles ◽  
Near Wall

A series of numerical simulations of small bubbles seeded in a turbulent channel flow have been made at average void fractions up to 10%. Initial near-wall seeding in general leads to a transient reduction in drag while smaller bubbles are more effective in producing sustained drag reduction.

Numerical simulation of turbulent drag reduction using micro-bubbles

2002 ◽  
Vol 468 ◽  
pp. 271-281 ◽  
Author(s):  
JIN XU ◽  
MARTIN R. MAXEY ◽  
GEORGE EM KARNIADAKIS
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Turbulent Channel Flow ◽  
Supporting Evidence ◽  
Average Volume ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Spherical Bubbles ◽  
Small Bubbles ◽  
Over Time

While turbulent drag reduction through the injection of micro-bubbles into a turbulent boundary layer is well established in experiments, there is a lack of corresponding supporting evidence from direct numerical simulations. Here we report on a series of numerical simulations of small bubbles seeded in a turbulent channel flow at average volume fractions of up to 8%. These results show that even for relatively large bubbles, an initial transient drag reduction can occur as bubbles disperse into the flow. Relatively small spherical bubbles will produce a sustained level of drag reduction over time.

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 ${\sim }75\, \%$.

On the mechanism of turbulent drag reduction with super-hydrophobic surfaces

2015 ◽  
Vol 773 ◽  
Author(s):  
Amirreza Rastegari ◽  
Rayhaneh Akhavan
Keyword(s):  
Reynolds Number ◽  
Surface Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Free Fraction ◽  
Turbulent Channel Flow ◽  
Governing Equations ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Effective Slip

The mechanism of turbulent drag reduction (DR) with super-hydrophobic (SH) surfaces is investigated by direct numerical simulation (DNS) and analysis of the governing equations in channel flow. The DNS studies were performed using lattice Boltzmann methods in channels with ‘idealized’ SH surfaces on both walls, comprised of longitudinal micro-grooves (MG), transverse MG, or micro-posts. DRs of $5\,\%$ to $83\,\%$, $-4\,\%$ to $20\,\%$, and $14\,\%$ to $81\,\%$ were realized in DNS with longitudinal MG, transverse MG, and micro-posts, respectively. By mathematical analysis of the governing equations, it is shown that, in SH channel flows with any periodic SH micro-pattern on the walls, the magnitude of DR can be expressed as $DR=U_{slip}/U_{bulk}+O({\it\varepsilon})$, where the first term represents the DR resulting from the effective slip on the walls, and the second term represents the DR or drag increase (DI) resulting from modifications to the turbulence dynamics and any secondary mean flows established in the SH channel compared to a channel flow with no-slip walls at the same bulk Reynolds number as the SH channel. Comparison of this expression to DNS results shows that, with all SH surface micro-patterns studied, between 80 % and 100 % of the DR in turbulent flow arises from the effective slip on the walls. Modifications to the turbulence dynamics contribute no more than 20 % of the total DR with longitudinal MG or micro-posts of high shear-free fraction (SFF), and a DI with transverse MG or micro-posts of moderate SFF. The effect of the SH surface on the normalized dynamics of turbulence is found to be small in all cases, and confined to additional production of turbulence kinetic energy (TKE) within a thin ‘surface layer’ of thickness of the order of the width of surface micro-indentations. Outside of this ‘surface layer’, the normalized dynamics of turbulence proceeds as in a turbulent channel flow with no-slip walls at the friction Reynolds number of the SH channel flow.

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.

scholarly journals Prediction of Drag Reduction Rate in Turbulent Channel Flow Based on BP Neural Network

2020 ◽  
Vol 194 ◽  
pp. 05049
Author(s):  
Yuchen Cao ◽  
Yongwen Yang
Keyword(s):  
Neural Network ◽  
Drag Reduction ◽  
Polymer Solution ◽  
Channel Flow ◽  
Bp Neural Network ◽  
Reduction Rate ◽  
Turbulent Channel Flow ◽  
Solution Concentration ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag

The technology of turbulent drag reduction by viscoelastic additives cannot be widely applied in practical engineering due to the difficulty in judging the effect of drag reduction. To solve this problem, the experiment of drag-reducing channel flow of polymer solution was carried out based on the comprehensive analysis of the factors affecting the drag reduction rate. Abundant drag reduction rate data were obtained. A three-layer BP neural network prediction model was established with polymer solution concentration, Reynolds number and injection flow rate as input parameters. Based on the test results, the prediction accuracy on drag reduction rate of the model was analysed. The prediction and model validation of drag reduction rate are carried out further according to the historical data in literature. The results show that the predicted drag reduction rate of BP neural network is close to the real drag reduction rate in the drag-reducing flow of polymer solution. The prediction is with high accuracy and with good generalization ability. It is expected to be applied to practical projects and to promote the development of turbulent drag reduction technology by additives.

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