scholarly journals Superhydrophobic drag reduction in turbulent flows: a critical review

2021 ◽  
Vol 62 (11) ◽  
Author(s):  
Hyungmin Park ◽  
Chang-Hwan Choi ◽  
Chang-Jin Kim
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Large Scale ◽  
Water Environment ◽  
Experimental Studies ◽  
Open Water ◽  
Laminar Flows ◽  
Turbulent Regime ◽  
Frictional Drag ◽  
Factors Affecting

AbstractSuperhydrophobic (SHPo) surfaces have been investigated vigorously since around 2000 due in large part to their unique potential for hydrodynamic frictional drag reduction without any energy or material input. The mechanisms and key factors affecting SHPo drag reduction have become relatively well understood for laminar flows by around 2010, as has been reviewed before [Lee et al. Exp Fluids 57:176 (2016)], but the progress for turbulent flows has been rather tortuous. While improved flow tests made positive SHPo drag reduction in fully turbulent flows more regular since around 2010, such a success in a natural, open water environment was reported only in 2020 [Xu et al. Phys Rev Appl 13:034056 (2020b)]. In this article, we review studies from the literature about turbulent flows over SHPo surfaces, with a focus on experimental studies. We summarize the key knowledge obtained, including the drag-reduction mechanism in the turbulent regime, the effect of the surface roughness morphology, and the fate and role of the plastron. This review is aimed to help guide the design and application of SHPo surfaces for drag reduction in the large-scale turbulent flows of field conditions. Graphic abstract

Experimental Study of Air Layer Sustainability for Frictional Drag Reduction

2014 ◽  
Vol 58 (01) ◽  
pp. 30-42 ◽  
Author(s):  
Bhat Nikhil Jagdish ◽  
Tay Zhi Xian Brandon ◽  
Tiaw Joo Kwee ◽  
Arun Kr. Dev
Keyword(s):  
Drag Reduction ◽  
Experimental Studies ◽  
Hydrophobic Surface ◽  
Viscous Drag ◽  
Total Resistance ◽  
Frictional Drag ◽  
Form Drag ◽  
Friction Resistance ◽  
Slow Steaming ◽  
Pressure Drag

Frictional drag reduction by microbubbles is a promising engineering method for reducing ship fuel consumption, especially for large, slow steaming vessels. Total resistance can be broken down into frictional drag and form drag (also known as pressure drag or profile drag). Ship's hull form optimization is commonly to reduce the form drag of a ship. Another technique would be required to deal with the frictional (viscous) portion of the total resistance. One such technique that reduces the friction resistance is the air lubrication technique. This research looks at possible enhancement for the microbubbles drag reduction technique with the use of hydrophobic plates to trap and retain an air layer. The hydrophobic surface cannot sustain bubbles by itself. Laser-machined microstructure coupled with hydrophobic coatings allows the rapid formation of air layer rapidly and sustainability of the air layer is recorded. With extensive experimental studies, we have shown that an air layer can be entrained around a moving flat plate thereby reducing friction. This could pave the way for applying this technique around the wall of moving ship hulls thereby minimizing the viscous drag and reducing the shipping costs.

scholarly journals Superhydrophobic Drag Reduction for Turbulent Flows in Open Water

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Muchen Xu ◽  
Andrew Grabowski ◽  
Ning Yu ◽  
Gintare Kerezyte ◽  
Jeong-Won Lee ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Open Water

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 Study on turbulence drag reduction of riblet plate in hypersonic turbulent flows

2020 ◽  
Vol 31 (03) ◽  
pp. 2050046
Author(s):  
Hao Zhou ◽  
Xinliang Li ◽  
Changping Yu
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Large Scale ◽  
Three Dimensional ◽  
Turbulence Control ◽  
Eddy Simulation ◽  
Number Formula ◽  
Large Scale Vortex ◽  
Reduction Effect ◽  
Parameter Values

This paper focuses on turbulence drag reduction of riblet plate in hypersonic turbulent flows. We use direct numerical simulation (DNS) and large eddy simulation (LES) to simulate three-dimensional spatially-developing boundary layer over the flat plate and riblet plate with a free-stream Mach number [Formula: see text]. The results reveal the influence of different riblet heights [Formula: see text] and riblet distances [Formula: see text] on drag reduction effect. The drag reduction effect increases with the increase of riblet height and the decrease of riblet distance within suitable range of parameter values. Through analysis, it can be seen that the riblet plate affects the turbulent contribution of the skin friction by suppressing or destroying the large-scale vortex structure. Combined with the actual engineering design requirements, we can use the riblet plate with appropriate parameters to achieve the purpose of turbulence control.

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.

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.

scholarly journals Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Anoop Rajappan ◽  
Gareth H. McKinley
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Large Scale ◽  
Molar Mass ◽  
Raw Material ◽  
Large Reynolds Number ◽  
Frictional Drag ◽  
High Molar Mass ◽  
Plant Seeds ◽  
Cost Constraints

AbstractThe high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.

scholarly journals Dynamics and evolution of turbulent Taylor rolls

2019 ◽  
Vol 870 ◽  
pp. 970-987 ◽  
Author(s):  
Francesco Sacco ◽  
Roberto Verzicco ◽  
Rodolfo Ostilla-Mónico
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Fluid Motion ◽  
Domain Size ◽  
Turbulent Regime ◽  
Computational Domain ◽  
Mean Flow ◽  
Concentric Cylinders ◽  
Angular Velocities ◽  
High Reynolds

In many shear- and pressure-driven wall-bounded turbulent flows secondary motions spontaneously develop and their interaction with the main flow alters the overall large-scale features and transfer properties. Taylor–Couette flow, the fluid motion developing in the gap between two concentric cylinders rotating at different angular velocities, is not an exception, and toroidal Taylor rolls have been observed from the early development of the flow up to the fully turbulent regime. In this manuscript we show that under the generic name of ‘Taylor rolls’ there is a wide variety of structures that differ in the vorticity distribution within the cores, the way they are driven and their effects on the mean flow. We relate the rolls at high Reynolds numbers not to centrifugal instabilities, but to a combination of shear and anti-cyclonic rotation, showing that they are preserved in the limit of vanishing curvature and can be better understood as a pinned cycle which shows similar characteristics as the self-sustained process of shear flows. By analysing the effect of the computational domain size, we show that this pinning is not a product of numerics, and that the position of the rolls is governed by a random process with the space and time variations depending on domain size.

scholarly journals Coupled SPH–FEM Modeling of Tsunami-Borne Large Debris Flow and Impact on Coastal Structures

2021 ◽  
Vol 9 (10) ◽  
pp. 1068
Author(s):  
Anis Hasanpour ◽  
Denis Istrati ◽  
Ian Buckle
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fem Modeling ◽  
Vertical Column ◽  
Initial Water ◽  
Modeling Approach ◽  
Non Linear ◽  
The Impact

Field surveys in recent tsunami events document the catastrophic effects of large waterborne debris on coastal infrastructure. Despite the availability of experimental studies, numerical studies investigating these effects are very limited due to the need to simulate different domains (fluid, solid), complex turbulent flows and multi-physics interactions. This study presents a coupled SPH–FEM modeling approach that simulates the fluid with particles, and the flume, the debris and the structure with mesh-based finite elements. The interaction between the fluid and solid bodies is captured via node-to-solid contacts, while the interaction of the debris with the flume and the structure is defined via a two-way segment-based contact. The modeling approach is validated using available large-scale experiments in the literature, in which a restrained shipping container is transported by a tsunami bore inland until it impacts a vertical column. Comparison of the experimental data with the two-dimensional numerical simulations reveals that the SPH–FEM models can predict (i) the non-linear transformation of the tsunami wave as it propagates towards the coast, (ii) the debris–fluid interaction and (iii) the impact on a coastal structure, with reasonable accuracy. Following the validation of the models, a limited investigation was conducted, which demonstrated the generation of significant debris pitching that led to a non-normal impact on the column with a reduced contact area and impact force. While the exact level of debris pitching is highly dependent on the tsunami characteristics and the initial water depth, it could potentially result in a non-linear force–velocity trend that has not been considered to date, highlighting the need for further investigation preferably with three-dimensional models.

DIESEL ENGINE OPERATION IN USE OF FUEL WITH ADDITIVES

2018 ◽  
pp. 18-24
Author(s):  
Petar Kazakov ◽  
Atanas Iliev ◽  
Emil Marinov
Keyword(s):  
Diesel Engine ◽  
Fuel Consumption ◽  
Diesel Fuel ◽  
Internal Combustion Engines ◽  
Experimental Studies ◽  
Combustion Engines ◽  
Engine Operation ◽  
Factors Affecting ◽  
Operating Modes ◽  
Positive Effects

Over the decades, more attention has been paid to emissions from the means of transport and the use of different fuels and combustion fuels for the operation of internal combustion engines than on fuel consumption. This, in turn, enables research into products that are said to reduce fuel consumption. The report summarizes four studies of fuel-related innovation products. The studies covered by this report are conducted with diesel fuel and usually contain diesel fuel and three additives for it. Manufacturers of additives are based on already existing studies showing a 10-30% reduction in fuel consumption. Comparative experimental studies related to the use of commercially available diesel fuel with and without the use of additives have been performed in laboratory conditions. The studies were carried out on a stationary diesel engine СМД-17КН equipped with brake КИ1368В. Repeated results were recorded, but they did not confirm the significant positive effect of additives on specific fuel consumption. In some cases, the factors affecting errors in this type of research on the effectiveness of fuel additives for commercial purposes are considered. The reasons for the positive effects of such use of additives in certain engine operating modes are also clarified.

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