Download or read book Design Advantages of Skin Friction Drag Reduction Using Riblets written by John Michael Gregory and published by . This book was released on 2013 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geometry Mediated Drag Reduction Using Riblets and Wrinkled Surface Textures written by Shabnam Raayai Ardakani and published by . This book was released on 2018 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: The surfaces of many plants and animals are covered with a variety of micro-textures such as ribs or 3D tubules which can control surface-mediated properties such as skin friction. Inspired by the drag reducing ability of these natural structures, especially the ribbed features on shark denticles, passive drag reduction strategies such as micro-fabricated riblet surfaces have been developed and studied. Microgroove textures on the surface of objects such as hulls, wings or inner surface of pipes which are aligned in the stream-wise direction have been shown to reduce the wall friction by 4 − 8%. The mechanisms suggested for this form of drag reduction are viscous retardation of the flow in the grooves (both laminar and turbulent) and the displacement of vortical structures away from the wall in turbulent flows. Due to their effectiveness in altering the boundary layer structure and reducing the viscous drag force, use of riblets have been banned in various competitions such as the America’s Cup. The current thesis work is partly focused on theoretical and numerical modelling (using the open source CFD package OpenFOAM) of the evolution of viscous boundary layers in the presence of various-shaped riblets (V-grooves as well as sinusoidal wrinkled surfaces) in high Reynolds laminar flow. We explore the effect of the dimensionless height to spacing of the grooves (aspect ratio) as well as the length of the wetted surface in the streamwise direction and how these change the total drag compared with a corresponding flat wall. We show that riblets retard the viscous flow inside the grooves and reduce the shear stress inside the grooves. But for this reduction to result in overall drag reduction, the riblet wall needs to be longer than a critical length. The total drag reduction achieved is a non-monotonic function of the aspect ratio of the riblets, with aspect ratios of order unity offering the largest reduction in the total drag. To eliminate the role of entrance effects, we additionally investigate the effect of stream-wise aligned riblet structures on fully-developed Taylor-Couette flow. We perform both experimental studies as well as time-dependent numerical simulations in both the laminar Couette and the Taylor vortex regime. We again explore the effect of the size of the riblets with respect to the geometry of the Taylor-Couette cell, as well as the aspect ratio of the riblet grooves and the shape of the grooves (V-groove, Rectangular, semi-circular, etc.). For the experiments, the cylindrical textured rotors are fabricated using 3D printing techniques and the rest of the Taylor-Couette cell is custom built using CNC machining. The test cell is then aligned and mounted on a stress-controlled rheometer to measure the velocity and the torque on the rotating inner cylinder. The numerical studies are performed using the open source CFD software package OpenFOAM to compare results and understand the physical mechanisms contributing to this drag reduction phenomenon. Again we observe a non-monotonic behavior for the reduction in torque as a function of the aspect ratio of the riblets tested, similar to the trend observed in the boundary layer analysis and we discuss the effect of changing the geometry of the flow as well as the riblet spacing on the changes in the total torque. When viewed holistically the results of these two studies show that, through careful design, a net reduction in viscous drag force can be robustly realized on micro-textured surfaces in high Reynolds number laminar flows through complex changes in near-wall stream-wise velocity profiles even in the absence of turbulent effects. The understanding of these changes can be effective in guiding the design of internal flows (pipes or ducts) and external flows (such as ship hulls, micro air vehicles or unmanned underwater vehicles) that are tailored and optimized to result in low frictional drag over the entire wetted surface in both laminar and turbulent regions.

Download or read book An Assessment of the Drag Reduction Properties of Riblets and the Penalties of Off design Conditions written by L. Gaudet and published by . This book was released on 1987 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: An assessment is given of the performance of riblets in reducing skin friction in turbulent flow. The data of Sawyer and Winter is used to develop skin-friction relationships derived from the velocity profile for a turbulent boundary layer as modified by a riblet surface. The maximum percentage drag reduction is shown to vary with Reynolds number R sub x. At large values of the non-dimensional riblet height the riblet surface acts as a uniform roughness and a value for the equivalent sand-grain roughness height is given. Examples of the estimated drag reductions which might be achieved for two current aircraft by incorporating riblet surfaces are presented.

Download or read book Flow Control Techniques and Applications written by Jinjun Wang and published by Cambridge University Press. This book was released on 2018-12-13 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master the theory, applications and control mechanisms of flow control techniques.

Download or read book Special Course on Skin Friction Drag Reduction written by and published by . This book was released on 1992 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Summary of Low Speed Airfoil Data written by Michael S. Selig and published by Soartech. This book was released on 1995 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Biomimetics written by Bharat Bhushan and published by Springer. This book was released on 2016-02-19 with total page 607 pages. Available in PDF, EPUB and Kindle. Book excerpt: This revised, updated and expanded new edition presents an overview of biomimetics and biologically inspired structured surfaces. It deals with various examples of biomimetics which include surfaces with roughness-induced superomniphobicity, self-cleaning, antifouling, and controlled adhesion. The focus in the book is on the Lotus Effect, Salvinia Effect, Rose Petal Effect, Oleophobic/philic Surfaces, Shark Skin Effect, and Gecko Adhesion. This new edition also contains new chapters on the butterfly wing effect, bio- and inorganic fouling and structure and Properties of Nacre and structural coloration.

Download or read book Liutex and Its Applications in Turbulence Research written by Chaoqun Liu and published by Academic Press. This book was released on 2020-10-29 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: Liutex and Its Applications in Turbulence Research reviews the history of vortex definition, provides an accurate mathematical definition of vortices, and explains their applications in flow transition, turbulent flow, flow control, and turbulent flow experiments. The book explains the term "Rortex" as a mathematically defined rigid rotation of fluids or vortex, which could help solve many longstanding problems in turbulence research. The accurate mathematical definition of the vortex is important in a range of industrial contexts, including aerospace, turbine machinery, combustion, and electronic cooling systems, so there are many areas of research that can benefit from the innovations described here. This book provides a thorough survey of the latest research in generalized and flow-thermal, unified, law-of-the-wall for wall-bounded turbulence. Important theory and methodologies used for developing these laws are described in detail, including: the classification of the conventional turbulent boundary layer concept based on proper velocity scaling; the methodology for identification of the scales of velocity, temperature, and length needed to establish the law; and the discovery, proof, and strict validations of the laws, with both Reynolds and Prandtl number independency properties using DNS data. The establishment of these statistical laws is important to modern fluid mechanics and heat transfer research, and greatly expands our understanding of wall-bounded turbulence. Provides an accurate mathematical definition of vortices Provides a thorough survey of the latest research in generalized and flow-thermal, unified, law-of-the-wall for wall-bounded turbulence Explains the term “Rortex as a mathematically defined rigid rotation of fluids or vortex Covers the statistical laws important to modern fluid mechanics and heat transfer research, and greatly expands our understanding of wall-bounded turbulence

Download or read book Convective Heat and Mass Transfer written by S. Mostafa Ghiaasiaan and published by CRC Press. This book was released on 2018-06-12 with total page 788 pages. Available in PDF, EPUB and Kindle. Book excerpt: Convective Heat and Mass Transfer, Second Edition, is ideal for the graduate level study of convection heat and mass transfer, with coverage of well-established theory and practice as well as trending topics, such as nanoscale heat transfer and CFD. It is appropriate for both Mechanical and Chemical Engineering courses/modules.

Download or read book Spinoff written by and published by . This book was released on 1983 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulent Skin friction Drag Reduction Via Spanwise Wall Oscillations written by Davide Gatti and published by . This book was released on 2015 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Investigation of Skin Friction Drag Reduction on a Flat Plate Using Microbubbles written by Zachary A. Grabe and published by . This book was released on 2007 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aircraft Excrescence Drag written by Alec David Young and published by . This book was released on 1981 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Boundary Layer Flow Over Elastic Surfaces written by Viktor V. Babenko and published by Butterworth-Heinemann. This book was released on 2012-10-23 with total page 635 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coverage includes: Experimental findings around coherent vortical structures (CVS) in turbulent boundary layers and methods of controlling them Static and dynamic mechanical characteristics of elastic composite coatings, as well as new techniques and devices developed for their measurement Combined methods of flow control and drag reduction, including the effect of injection of polymer solutions, elastic coatings and generated longitudinal vortical structures on hydrodynamic resistance Intended as a reference for senior engineers and researchers concerned with the drag reduction and the dynamics of turbulent boundary layer flows, Boundary Layer Flow over Elastic Surfaces provides a unique source of information on compliant surface drag reduction and the experimental techniques around it that have shown measurable and repeatable improvements over recent years.

Download or read book Special Course on Skin Friction Drag Reduction written by North Atlantic Treaty Organization. Advisory Group for Aeronautical Research and Development and published by . This book was released on 1992 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Viscous Drag Reduction in Boundary Layers written by and published by AIAA. This book was released on 1990 with total page 542 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aerodynamic Drag Reduction Technologies written by Peter Thiede and published by Springer Science & Business Media. This book was released on 2001-05-22 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains the proceedings of the CEAS/DragNet European Drag Reduction Conference 2000. The conference addressed the recent advances in all areas of drag reduction research, development, validation and demonstration including laminar flow technology, adaptive wing concepts, turbulent and induced drag reduction, separation control and supersonic flow aspects. This volume is of particular interest to engineers, scientists and students working in the aeronautics industry, research establishments or academia.