Download or read book Passive and Active Approaches to Sustained Turbulent Hydrodynamic Drag Reduction Using Superhydrophobic Surfaces written by Dhananjai V. Saranadhi and published by . This book was released on 2015 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Superhydrophobic surfaces have been shown to trap a pocket of air (or a "plastron") in between the features of their rough texture when submerged in water. A partial slip condition is created at the interface between the water and the submerged body, allowing for a reduction in skin friction drag. I begin by identifying and fabricating several superhydrophobic surfaces, and testing their ability to reduce skin friction in turbulent flows using a bespoke Taylor-Couette apparatus. These superhydrophobic surfaces possess different surface topographies and chemistry, and exhibit different amount of drag reduction, leading to a deeper investigation of the role of surface chemistry and the roughness on the robustness of the plastron. The mean square slope as the driving roughness parameter in promoting plastron stability, and suggest methods by which it may be increased in order to optimize drag-reducing performance. The air plastron captured by a passive superhydrophobic surface represents one way of creating a slip boundary condition. An active approach can be used to augment slip at the boundary. With this approach, a submerged body is heated past its Leidenfrost temperature to form a thick, continuous film of steam between itself and the water. I continue to employ superhydrophobic surfaces, but now exploit their unique heat transfer properties (i.e. the insulation to heat transfer provided by the minimal contact area between the body and the surrounding water) to drastically reduce the Leidenfrost Temperature and Critical Heat Flux, and by extension the energy input required to create and sustain such a boiling film. In the active case, vapor film completely envelops the heated body and is thicker than a typical passive plastron, which allows for a significant increase in obtained drag reduction relative to a passive superhydrophobic surface. I design and fabricate a mechanism by which a Taylor-Couette rotor can be heated past its Leidenfrost point and continuously supplied with power to maintain a boiling film under rotation rates of 60 rad/s. The results show that skin friction can be reduced by over 90% relative to an unheated superhydrophobic surface at Re = 52,200, and I derive a boundary layer and slip theory to fit the data to a model that calculates a slip length of 1.04 ± 0.3 mm. This indicates that the boiling film has a thickness of 37 ± 9.5 [mu]m, which is consistent with literature.
Download or read book Mitigation Of Hydrodynamic Resistance Methods To Reduce Hydrodynamic Drag written by Marc Perlin and published by World Scientific. This book was released on 2014-11-18 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text presents the state of the art in friction drag/resistance reduction technologies for BODIES and crafts operating in liquids at and beneath the free surface. It is useful for professionals with backgrounds in advanced fluid dynamics as well as by academics teaching introductory graduate courses in this area. Active control of resistance will include a discussion of friction reduction, for example through the injection of gas that can form air layers and polymers that initially reside adjacent to the hull, including the use of partial and super cavities. The book discusses passive resistance control achieved through changes in the overall hull shape and appendages, including the application of lifting bodies, bulbous bows, and stern flaps. It also addresses passive reduction of skin friction through the application of hull coatings and other elements of hull husbandry.
Download or read book Turbulence Control by Passive Means written by E. Coustols and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the 4th European Drag Reduction Meeting
Download or read book Drag Reduction of Turbulent Flows by Additives written by A. Gyr and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 243 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drag Reduction of Turbulent Flows by Additives is the first treatment of the subject in book form. The treatment is extremely broad, ranging from physicochemical to hydromechanical aspects. The book shows how fibres, polymer molecules or surfactants at very dilute concentrations can reduce the drag of turbulent flow, leading to energy savings. The dilute solutions are considered in terms of the physical chemistry and rheology, and the properties of turbulent flows are presented in sufficient detail to explain the various interaction mechanisms. Audience: Those active in fundamental research on turbulence and those seeking to apply the effects described. Fluid mechanical engineers, rheologists, those interested in energy saving methods, or in any other application in which the flow rate in turbulent flow should be increased.
Download or read book Drag Reduction in Turbulent Flows Over Micropatterned Superhydrophobic Surfaces written by Robert J. Daniello and published by . This book was released on 2009 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Viscous Drag Reduction written by C. Sinclair Wells and published by Springer. This book was released on 2013-12-20 with total page 497 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laminar Drag Reduction written by Keizo Watanabe and published by . This book was released on 2015-06-05 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: The phenomenon of resistance to motion through a fluid is believed to be a function of fluid-wall interaction. This theory is based on the assumption that under certain conditions a real fluid does not usually slip on the wall in contact with it and displ
Download or read book Turbulent Drag Reduction by Surfactant Additives written by Feng-Chen Li and published by John Wiley & Sons. This book was released on 2012-01-10 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent drag reduction by additives has long been a hot research topic. This phenomenon is inherently associated with multifold expertise. Solutions of drag-reducing additives are usually viscoelastic fluids having complicated rheological properties. Exploring the characteristics of drag-reduced turbulent flows calls for uniquely designed experimental and numerical simulation techniques and elaborate theoretical considerations. Pertinently understanding the turbulent drag reduction mechanism necessities mastering the fundamentals of turbulence and establishing a proper relationship between turbulence and the rheological properties induced by additives. Promoting the applications of the drag reduction phenomenon requires the knowledge from different fields such as chemical engineering, mechanical engineering, municipal engineering, and so on. This book gives a thorough elucidation of the turbulence characteristics and rheological behaviors, theories, special techniques and application issues for drag-reducing flows by surfactant additives based on the state-of-the-art of scientific research results through the latest experimental studies, numerical simulations and theoretical analyses. Covers turbulent drag reduction, heat transfer reduction, complex rheology and the real-world applications of drag reduction Introduces advanced testing techniques, such as PIV, LDA, and their applications in current experiments, illustrated with multiple diagrams and equations Real-world examples of the topic’s increasingly important industrial applications enable readers to implement cost- and energy-saving measures Explains the tools before presenting the research results, to give readers coverage of the subject from both theoretical and experimental viewpoints Consolidates interdisciplinary information on turbulent drag reduction by additives Turbulent Drag Reduction by Surfactant Additives is geared for researchers, graduate students, and engineers in the fields of Fluid Mechanics, Mechanical Engineering, Turbulence, Chemical Engineering, Municipal Engineering. Researchers and practitioners involved in the fields of Flow Control, Chemistry, Computational Fluid Dynamics, Experimental Fluid Dynamics, and Rheology will also find this book to be a much-needed reference on the topic.
Download or read book Design Fabrication and Evaluation of Superhydrophobic SHPo Surfaces for Drag Reduction in Turbulent Boundary Layer Flows written by Muchen Xu and published by . This book was released on 2017 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sustaining a gas layer on them in liquid, superhydrophobic (SHPo) surfaces have attracted enormous attention due to the possibility of reducing friction drag in numerous flow applications. Although many SHPo surfaces proved to reduce drag significantly (e.g., > 10%) in microchannel flows and certain SHPo surfaces proved to have an unprecedentedly large slip length (e.g., > 100 microns), a significant drag reduction is still elusive in turbulent flows that reflect most applications, such as watercraft in marine environment. Recognizing the gas layer (called plastron) as the key and studying its robustness under water of varying depths, we first conclude that the SHPo surfaces capable of a significant drag reduction cannot maintain the plastron indefinitely if submerged deeper than a few centimeters. By developing a high-resolution shear sensor for centimeters-size sample surfaces and using silicon SHPo surfaces that keep plastron more robust than others, we obtain up to ~25% drag reduction in turbulent boundary layer flows at Reynolds numbers up to 1.1x107. Obtained at a high-speed water tunnel and a high-speed tow tank, the results also indicate that the drag reduces more with increasing Reynolds number, corroborating the numerical studies in the literature. Moreover, we develop and conduct SHPo drag experiments using a real boat in marine conditions for the first time, achieving ~20% drag reduction. Finally, a scalable fabrication process is developed for scale-up manufacturing of both passive and semi-active SHPo surfaces. For the semi-active SHPo surfaces, i.e., SHPo surfaces with self-regulating gas restoration capability, we propose and demonstrate a gas generation mechanism that does not require any external power input.
Download or read book Experimental Investigation of Turbulent Boundary Layer with Uniform Blowing at Moderate and High Reynolds Numbers written by Gazi Hasanuzzaman and published by Cuvillier Verlag. This book was released on 2022-01-18 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental investigation in turbulent boundary layer flows represents one of the canonical geometries of wall bounded shear flows. Utmost relevance of such experiments, however, is applied in the engineering applications in aerospace and marine industries. In particular, continuous effort is being imparted to explore the underlying physics of the flow in order to develop models for numerical tools and to achieve flow control. Flow control experiments have been widely investigated since 1930’s. Several flow control technique has been explored and have shown potential benefit. But the choice of control technique depends largely on the boundary condition and the type of application. Hence, friction drag of subsonic transport aircraft is intended to be reduced within the scope of this Ph. D. topic. Therefore, application of active control method such as microblowing effect in the incompressible, zero pressure gradient turbulent boundary layer was investigated. A series of experiments have been performed in two different wind tunnel facilities. Wind tunnel from Department of Aerodynamics and Fluid Mechanics (LAS) was used for the measurements for moderate Reynolds number range in co-operation with the wind tunnel from Laboratoire de M´ecanique de Feiret Lille for large Reynolds number range. Measurements are conducted with the help of state-of-the-art techniques such as Laser Doppler Anemometry, Particle Image Velocimetry and electronic pressure sensors.
Download or read book Turbulent Drag Reduction by Passive Means written by Royal Aeronautical Society and published by . This book was released on 1987 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Sustainable Drag Reduction by Utilizing Superhydrophobic Surface and Leidenfrost Effect written by Yi Tian and published by . This book was released on 2021 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Experimental Study of Passive Drag Reduction in a Turbulent Boundary Layer by a Riblet Surface written by Seong-Ryong Park and published by . This book was released on 1992 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Boundary layer Drag Reduction Using Passive Manipulators written by John Benjamin Anders and published by . This book was released on 1984 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigation of Passive and Active Friction Drag Reduction written by Wenfeng Li and published by . This book was released on 2017* with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Survey of the Turbulent Drag Reduction Using Passive Devices written by Kwing-So Choi and published by . This book was released on 1984 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulations for Turbulent Drag Reduction Using Liquid Infused Surfaces written by Isnardo Arenas-Navarro and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerical simulations of the turbulent flow over Super Hydrophobic and Liquid Infused Surfaces have been performed in this work. Three different textured surfaces have been considered: longitudinal square bars, transversal square bars and staggered cubes. The numerical code combines an immersed boundary method to mimic the substrate and a level set method to track the interface. Liquid Infused Surfaces reduce the drag by locking a lubricant within structured roughness to facilitate a slip velocity at the surface interface. The conceptual idea is similar to Super Hydrophobic Surfaces, which rely on a lubricant air layer, whereas liquid-infused surfaces use a preferentially wetting liquid lubricant to create a fluid-fluid interface. This slipping interface has been shown to be an effective method of passively reducing skin friction drag in turbulent flows. Details are given on the effect of the viscosity ratio between the two fluids and the dynamics of the interface on drag reduction. An attempt has been made to reconcile Super-Hydrophobic, Liquid Infused and rough wall under the same framework by correlating the drag to the wall normal velocity fluctuations.
