Measurement of Drag Reduction on Parallel Trench Superhydrophobic Surfaces in a High-Speed Water Tunnel

Measurement of Drag Reduction on Parallel Trench Superhydrophobic Surfaces in a High-Speed Water Tunnel
Author: Gintare Kerezyte
Publisher:
Total Pages: 95
Release: 2017
Genre:
ISBN:

Superhydrophobic (SHPo) surfaces are capable of trapping air under water, and this air plastron may lubricate the shearing of the water flowing by and reduce its skin-friction drag. While the slip effect and the resulting drag reduction on SHPo surfaces have been well understood in laminar flows, the results have been controversial and inconsistent in regard to turbulent flows. This thesis describes the progressive modification and adaptation of a low-profile testing module that measures the relative drag of two surfaces for flow tests in a high-speed water tunnel. After a series of experiments at Naval Undersea Warfare Center (NUWC) in Newport, Rhode Island to improve the testing module until it functions reliably in their water tunnel, we obtain a functional prototype and complete successful measurements. Testing a set of SHPo surfaces in boundary layer flows along the parallel trenches at Reynolds numbers up to 9.7x106, we obtain drag reduction up to ~34% compared with a smooth surface. The results support previous numerical studies predicting that the rate of drag reduction increases with Reynolds number, visualize the wetting phenomena of SHPo surfaces in high-speed water tunnel tests, and lay the groundwork to study the effect of SHPo surface trench parameters.

Plastron State and Drag Reduction of High-Performance Superhydrophobic (SHPo) Surfaces in High-Speed Turbulent Flows on Open Water

Plastron State and Drag Reduction of High-Performance Superhydrophobic (SHPo) Surfaces in High-Speed Turbulent Flows on Open Water
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.

Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows

Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows
Author: Muchen Xu
Publisher:
Total Pages: 191
Release: 2017
Genre:
ISBN:

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.

Flat Plate Reduction in a Water Tunnel Using Riblets

Flat Plate Reduction in a Water Tunnel Using Riblets
Author: L. W. Reidy
Publisher:
Total Pages: 22
Release: 1987
Genre:
ISBN:

Streamwise microgroove surface modifications, known as riblets, are known to alter the structure of the turbulent boundary layer such that the skin friction drag over the surface is reduced. For this investigation, velocity profile measurements were used to calculate the drag on a flat plate, both with and without riblets, in a high-speed water tunnel. The vinyl riblet surface produced a maximum drag reduction of 8.1% + or - 2.5% at a nondimensional groove spacing, + or - of 13.1. If the results obtained in the laboratory can be realized for torpedoes and other submersibles, significant improvements in vehicle speed or fuel economy will be achieved.

Passive and Active Approaches to Sustained Turbulent Hydrodynamic Drag Reduction Using Superhydrophobic Surfaces

Passive and Active Approaches to Sustained Turbulent Hydrodynamic Drag Reduction Using Superhydrophobic Surfaces
Author: Dhananjai V. Saranadhi
Publisher:
Total Pages: 139
Release: 2015
Genre:
ISBN:

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.

Drag Reduction Caused by High Polymer Solutions Injected Into Water Flowing Around Cylindrical Bodies

Drag Reduction Caused by High Polymer Solutions Injected Into Water Flowing Around Cylindrical Bodies
Author: C. N. Baronet
Publisher:
Total Pages: 26
Release: 1966
Genre:
ISBN:

It was clearly demonstrated that high polymer solutions of a few parts per million by weight substantially reduce the drag on cylindrical bodies, with spherical ends, which are suspended in water flowing in a pipe. The finding is similar to that obtained by investigators for the reduction of resistance to flow of liquids in pipes alone. It is demonstrated that the water tunnel, the measuring equipment, and the method of study are extremely convenient and effective for studying the important phenomena associated with drag reduction caused by dilute solutions of high polymers. (Author).

The Biology of Bats

The Biology of Bats
Author: Gerhard Neuweiler
Publisher: Oxford University Press, USA
Total Pages: 326
Release: 2000
Genre: Bats
ISBN: 0195099508

Well adapted to numerous habitats, bats comprise almost one quarter of all species of mammals. This book is a comprehensive introduction to their biology. Suitable as a textbook for undergraduates and written by one of the world's leading researchers, the book offers an accessible summary of the extensive body of research on bats. The book takes a broad physiological perspective and devotes separate chapters to specific physiological systems as well as to bat ecology and phylogeny. It features a thorough discussion of echolocation, which continues to be the subject of intense research, and describes many European and neotropical bats, as well as North American species. "Biology of Bats" is an important resource both for students and researchers.

Characterization of Minerals, Metals, and Materials 2019

Characterization of Minerals, Metals, and Materials 2019
Author: Bowen Li
Publisher: Springer
Total Pages: 782
Release: 2019-02-13
Genre: Technology & Engineering
ISBN: 3030057496

This collection gives broad and up-to-date results in the research and development of materials characterization and processing. Topics covered include characterization methods, ferrous materials, non-ferrous materials, minerals, ceramics, polymer and composites, powders, extraction, microstructure, mechanical behavior, processing, corrosion, welding, solidification, magnetic, electronic, environmental, nano-materials, and advanced materials The book explores scientific processes to characterize materials using modern technologies, and focuses on the interrelationships and interdependence among processing, structure, properties, and performance of materials.

Sustainable Winter Road Operations

Sustainable Winter Road Operations
Author: Xianming Shi
Publisher: John Wiley & Sons
Total Pages: 476
Release: 2018-08-27
Genre: Technology & Engineering
ISBN: 1119185068

The first and only comprehensive guide to best practices in winter road operations Winter maintenance operations are essential to ensure the safety, mobility, and productivity of transportation systems, especially in cold-weather climates, and responsible agencies are continually challenged to provide a high level of service in a fiscally and environmentally responsible manner. Sustainable Winter Road Operations bridges the knowledge gaps, providing the first up-to-date, authoritative, single-source overview and guide to best practices in winter road operations that considers the triple bottom line of sustainability. With contributions from experts in the field from around the world, this book takes a holistic approach to the subject. The authors address the many negative impacts on regional economies and the environment of poorly planned and inadequate winter road operations, and they make a strong case for the myriad benefits of environmentally sustainable concepts and practices. Best practice applications of materials, processes, equipment, and associated technologies and how they can improve the effectiveness and efficiency of winter operations, optimize materials usage, and minimize cost, corrosion, and environmental impacts are all covered in depth. Provides the first up-to-date, authoritative and comprehensive overview of best practices in sustainable winter road operations currently in use around the world Covers materials, processes, equipment, and associated technologies for sustainable winter road operations Brings together contributions by an international all-star team of experts with extensive experience in designing, implementing, and managing sustainable winter road operations Designed to bring professionals involved in transportation and highway maintenance and control up to speed with current best practice Sustainable Winter Road Operations is essential reading for maintenance professionals dealing with snow and ice control operations on highways, motorways and local roads. It is a valuable source of information and guidance for decision makers, researchers, and engineers in transportation engineering involved in transportation and highway maintenance. And it is an ideal textbook for advanced-level courses in transportation engineering.