Turbulent Flow Over A Superhydrophobic Surface With Isotropic Slip
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| Author | : Babak Vajdi Hokmabad |
| Publisher | : |
| Total Pages | : 107 |
| Release | : 2015 |
| Genre | : Hydrophobic surfaces |
| ISBN | : |
Superhydrophobic surfaces are proven to be capable of reducing the skin friction in laminar and turbulent flows. These surfaces consist of micro/nano-scale hydrophobic roughness features which make the surface render a non-wetting property due to the entrainment of air pockets between the solid surface and the liquid phase. This shear free air-water interface reduces the frictional drag force. This flow control method has two distinct effects in turbulent flow: drag reduction due to effective slip velocity and drag reduction associated with the modification of the turbulent flow structures (Rastegari & Akhavan, 2015). In the current research, the turbulent structure of the inner layer of a turbulent channel flow over a non-wetted superhydrophobic (SHO) surface with random pattern is experimentally studied. The results are compared with the wetted counterpart and also a smooth reference surface. Two planar particle image velocimetry (PIV) measurements are carried out in the streamwise/spanwise and streamwise/wall-normal planes. The vector fields are obtained from both ensemble averaging and individual cross-correlations of double-frame PIV images. The results showed a small increase (~5%) of the mean velocity profile at y+=10 over the non-wetted surface in comparison with the wetted and the smooth surfaces. Up to 15% reduction of normal and shear Reynolds stresses is observed in the inner layer over the non-wetted SHO surface. The wetted SHO counterpart demonstrates no effect on the mean velocity and Reynolds stresses in comparison with the smooth surface implying that the surface is hydrodynamically smooth. A noticeable suppression of the sweep and ejection events, increase of the spanwise spacing of the low and high speed streaks, and attenuation of vortical structures are observed over the non-wetted SHO. These indicate attenuation of the turbulence regeneration cycle due to the slip boundary condition over the non- iii wetted SHO surfaces with random texture. Tomographic PIV (tomo-PIV) and 3D particle tracking velocimetry (3D-PTV) as three-dimensional flow measurement techniques can unravel the relevant physics by revealing the flow modifications across the third dimension. The performance of these measurements is evaluated through comparison with DNS data in the literature. The results show that 3D-PTV is more accurate compared to tomo-PIV especially in near-wall region where noise increases for all PIV measurements.
| Author | : K. L. Mittal |
| Publisher | : John Wiley & Sons |
| Total Pages | : 308 |
| Release | : 2019-10-16 |
| Genre | : Technology & Engineering |
| ISBN | : 1119593301 |
This is the fourth volume in the series "Advances in Contact Angle, Wettability and Adhesion" initiated to consolidate information and provide commentary on certain recent research aspects dealing with this important topic. Its predecessor Volumes 1, 2 and 3 were published in 2013, 2015 and 2018 respectively. This new book comprising 14 research and review articles is divided into four parts: Part 1: Contact Angle and Wettability Aspects; Part 2: Surface Free Energy and Surface Tension Determination; Part 3: Applied Aspects. The topics covered include: Contact Angle Determination of Talc Powders from Heat of Immersion Surface Wetting at Macro and Nanoscale Wettability of Wood Surfaces with Waterborne Acrylic Lacquer Stains Modulated by DBD Plasma Treatment in Air at Atmospheric Pressure Wettability of Ultrafiltration Membranes Determination of the Surface Free Energy of Solid Surfaces: Can the Best Model be Found Surface Free Energy Characterization of Talc Powders Determination of the Surface Free Energy of Skin and the Factors Affecting it by the Contact Angle Method Determination of Surface Tension Components of Aqueous Solutions using Fomblin HC/25 R Perfluoropolyether Liquid Film as a Solid Substrate Enhancing the Wettability of Polybenzimidazole (PBI) to Improve Fuel Cell Performance Evaluation of Sebum Resistance for Long-Wear Face Make-Up Products Using Contact Angle Measurements Contact Angle Hysteresis of Pressure-Sensitive Adhesives due to Adhesion Tension Relaxation The Potential of Surface Nano-Engineering and Superhydrophobic Surfaces in Drag Reduction Laser Surface Engineering of Polymeric Materials for Enhanced Mesenchymal Stem Cell Adhesion and Growth Sisal-Green Resin Interfaces in Green Composites.
| Author | : Guoxiang Hou |
| Publisher | : Springer Nature |
| Total Pages | : 265 |
| Release | : |
| Genre | : |
| ISBN | : 9819703492 |
| Author | : Pranesh Muralidhar |
| Publisher | : |
| Total Pages | : 57 |
| Release | : 2012 |
| Genre | : Hydrophobic surfaces |
| ISBN | : |
Superhydrophobic surfaces are a class of surfaces that have a microscale roughness imposed on an already hydrophobic surface, akin to a lotus leaf. These surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. The goal of this thesis was to explore how these surfaces alter the vortex shedding dynamics of a cylindrical body when coated on its surface, thus leading to an alteration in drag and lift on these surfaces. A cylindrical body was chosen as it is a very nice representative bluff body and sets the stage for predicting the behavior of hydrofoils and other bluff bodies under flow with a slip boundary condition. In this work, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from PDMS with well-defined micron-sized patterns of surface roughness or random slip surfaces fabricated by sanding Teflon cylinders or spray painting superhydrophobic paint on a smooth cylinder. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. The vortices shed from these surfaces were found to be weaker and less interlaced leading to reduced circulation and lift forces on these cylinders. The effect of slip on bluff bodies and separating flow was dealt with in detail in this thesis and the results could be used to predict the impact of these surfaces on the flow past hydrofoils which combine skin friction dominated flow with separating flow.
| Author | : Thomas Jelly |
| Publisher | : |
| Total Pages | : |
| Release | : 2013 |
| Genre | : |
| ISBN | : |
| Author | : |
| Publisher | : ScholarlyEditions |
| Total Pages | : 2526 |
| Release | : 2012-01-09 |
| Genre | : Technology & Engineering |
| ISBN | : 1464963754 |
Issues in Mechanical Engineering / 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Mechanical Engineering. The editors have built Issues in Mechanical Engineering: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Mechanical Engineering in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Mechanical Engineering: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
| Author | : William Layton |
| Publisher | : MDPI |
| Total Pages | : 229 |
| Release | : 2018-05-04 |
| Genre | : Mathematics |
| ISBN | : 3038428094 |
This book is a printed edition of the Special Issue "Turbulence: Numerical Analysis, Modelling and Simulation" that was published in Fluids
| Author | : Ning Yu |
| Publisher | : |
| Total Pages | : 162 |
| Release | : 2022 |
| Genre | : |
| ISBN | : |
Superhydrophobic (SHPo) surfaces, which may capture a thin air layer (called plastron) on them underwater, have been studied over the last two decades most notably due to their potential drag-reducing ability for water vessels. Despite many reports of successful drag reduction in laboratory settings, no success has been reported for highly turbulent flows on the open water in natural environment until just two years ago. While reporting around 30% of reduction under a boat, the recent success indicated that the plastron was the culprit for most of the failures and the resulting controversies about SHPo drag reduction. The current study is motivated by our finding that the common practice of confirming the plastron with the silvery sheen appearance is not sufficient and may be seriously misleading for SHPo drag reduction research. Since drag reduction requires a plastron pinned on top of the surface asperities while depinned plastron may still appear bright, we develop a convenient observation strategy that can discern the pinned from the depinned plastron in field studies such as under a boat. By further revamping the 13 foot motorboat retrofitted for drag-reduction experiments, we study the behavior of plastron on micro-trench SHPo surfaces in highly turbulent flows on a natural sea environment. A unified theory is developed and experimentally confirmed to predict the maximum trench length that allows for a full plastron in the typical flow conditions of watercraft. Furthermore, high-performance SHPo surfaces are developed with micro electro mechanical systems (MEMS) technology to maintain a full plastron at typical boat speeds (tested up to 14 knots). In addition to testing the effect of slip length and obtaining about 30% of drag reduction with longitudinal trench SHPo surfaces, transverse trench and aligned post SHPo surfaces are also tested to reveal the effect of transverse slip on drag reduction in the turbulent flows under the boat.
| Author | : Michael B. Martell |
| Publisher | : |
| Total Pages | : 129 |
| Release | : 2009 |
| Genre | : Hydrophobic surfaces |
| ISBN | : |
| Author | : Wole Soboyejo |
| Publisher | : Cambridge University Press |
| Total Pages | : 374 |
| Release | : 2020-09-17 |
| Genre | : Technology & Engineering |
| ISBN | : 1108963447 |
Master simple to advanced biomaterials and structures with this essential text. Featuring topics ranging from bionanoengineered materials to bio-inspired structures for spacecraft and bio-inspired robots, and covering issues such as motility, sensing, control and morphology, this highly illustrated text walks the reader through key scientific and practical engineering principles, discussing properties, applications and design. Presenting case studies for the design of materials and structures at the nano, micro, meso and macro-scales, and written by some of the leading experts on the subject, this is the ideal introduction to this emerging field for students in engineering and science as well as researchers.
