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Author : John Clifford Owen
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (593 download)
Download or read book Passive Control of Vortex Shedding in the Wakes of Bluff Bodies written by John Clifford Owen and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Andre Sirilutporn Chan
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (821 download)
Download or read book Control and Suppression of Laminar Vortex Shedding Off Two-dimensional Bluff Bodies written by Andre Sirilutporn Chan and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this research is on the control and suppression of vortex shedding of flow past bluff bodies. The motivation of this research stems from the aerodynamic problems encountered in the design and development of hard disk drives (HDD's). Two different computational fluid dynamic methods have been used in this research-- the Semi-Implicit Method for Pressure Linked Equation (SIMPLE), that is widely employed in today's commercial incompressible flow solvers, and the high-order spectral difference (SD) method, recently developed for compressible flow solution. In addition to numerical simulation and verification, complementary experimental measurements have been performed to further validate the results. This research leads to two very different suppression techniques: 1) a passive control using a thin splitter plate positioned downstream of the bluff body; 2) an active control by way of counter rotating a cylinder pair. The passive suppression technique places a thin splitter plate downstream of the bluff body in order to interfere with the vortex wakes and thereby suppress the vortexinduced forces on the bluff body itself. The present investigation examines the suppression of wake instabilities in the laminar shedding regime. Both bounded and unbounded flow conditions are examined. It is found that in the bounded flow condition, the channel walls have an additional stabilizing effect on the shedding control. With proper positioning of the splitter plate, vortex shedding is completely suppressed in a bounded flow with moderate blockage factor. Wind tunnel empirical experiments have also confirmed the effectiveness of a splitter plate in a bounded flow. Active flow control by counter-rotating a pair of cylinders has been numerically investigated. It has also been investigated experimentally in partnership with the Gas Dynamics Laboratory at Princeton University. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to 200. The degree of unsteady wake suppression is proportional to the speed and the direction of rotation, and there is a critical rotation rate where a complete suppression of flow unsteadiness can be achieved. In the doublet-like configuration at higher rotational speeds, a virtual elliptic body that resembles a potential doublet is formed, and the drag is reduced to zero. The shape of the elliptic body primarily depends on the gap between the two cylinders and the speed of rotation. Prior to the formation of the elliptic body, a second instability region is observed, similar to that seen in studies of rotating single cylinders. It is also shown that the unsteady wake suppression can be achieved by rotating each cylinder in the opposite direction, that is, in a reverse doublet-like configuration. This tends to minimize the wake interaction of the cylinder pair and the second instability did not make an appearance over the range of speeds investigated here.
Author : National Research Council
Publisher : National Academies Press
ISBN 13 : 0309058791
Total Pages : 1100 pages
Book Rating : 4.3/5 (9 download)
Download or read book Twenty-First Symposium on Naval Hydrodynamics written by National Research Council and published by National Academies Press. This book was released on 1997-09-11 with total page 1100 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :
Publisher :
ISBN 13 :
Total Pages : 6 pages
Book Rating : 4.:/5 (227 download)
Download or read book Vortex Shedding and Vortex Wakes: Dynamics, Instabilities and Modifications written by and published by . This book was released on 1994 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: RESEARCH OBJECTIVES: To study nonlinear and secondary instability properties of wake flows behind bluff bodies and their control and modification. (KAR) p. 2.
Author :
Publisher :
ISBN 13 :
Total Pages : 11 pages
Book Rating : 4.:/5 (227 download)
Download or read book Control of Two and Three-Dimensional Wake Instabilities from Bluff-Bodies written by and published by . This book was released on 1995 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The detailed, instantaneous flow structure of the near-wake of a cylinder subjected to various classes of active (open-loop) and passive control has been characterized using both qualitative flow visualization and high-image-density particle image velocimetry (piv) developed in our laboratories. The first cinema PIV system allows acquisition of images that are highly resolved in both space and time. Concepts of timing of vortex formation, period-doubled patterns of vortices, and modulated and phase-locked systems of vortices are addressed for controlled oscillations of the cylinder. Three-dimensional patterns of instantaneous vorticity allow classification of the modes of response of the near-wake, providing a basis for formulating concepts for attenuation of vortex formation.
Author : Jinjun Wang
Publisher : Cambridge University Press
ISBN 13 : 1107161568
Total Pages : 293 pages
Book Rating : 4.1/5 (71 download)
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.
Author : Lakshmana Sampat Doddipatla
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (17 download)
Download or read book Wake Dynamics and Passive Flow Control of a Blunt Trailing Edge Profiled Body written by Lakshmana Sampat Doddipatla and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Wake flows behind two-dimensional bodies are dominated mainly by two types of coherent structures, namely, the Karman Benard vortices and the streamwise vortices, also referred to as rolls and ribs respectively. The three-dimensional wake instabilities lead to distinct instability modes (mode-A, mode-B and mode-C or mode S) depending on the flow Reynolds number and geometric shape. The present investigation explores the mechanism by which the flow transitions take place to three-dimensionality in the near wake of a profiled leading edge and blunt trailing edge body. Experiments consisting of a combination of Planar Laser Induced Fluorescence visualizations and Particle Image Velocimetry measurements are conducted for Reynolds numbers ranging from 250 to 46000. The results indicate that three instability modes, denoted by mode-A, mode-B and mode-C, appear in the wake transition to three-dimensionality, but their order of appearance does not occur through the traditional route as observed in circular cylinder flows. It is found that mode-C instability with a spanwise spacing varying between 1.2 to 2.8D (D being the trailing edge thickness) dominates the near wake development. This result is explored further with the aim to devise a simple passive control method to mitigate vortex shedding for blunt trailing edge bodies. The effect of a trailing edge spanwise sinusoidal perturbation (SSP) is investigated for a range of Reynolds numbers (ReD) spanning the transition range from ReD = 550 up to 46000. PIV measurements at different vertical and horizontal locations are performed to study changes in the streamwise and spanwise vortices. The base drag and strength of vortex shedding decrease with wavy trailing edge compared to the straight trailing edge. Proper Orthogonal Decomposition (POD) of the obtained PIV data indicates that the spanwise sinusoidal perturbation redistributes the relative energy, enhancing the streamwise vortices and, as a result, suppressing the Karman Benard rolls.
Author : Anne Emily Corlett
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (67 download)
Download or read book A Near Wake Study of Vortex Shedding from Bluff Bodies at Low Reynolds Numbers written by Anne Emily Corlett and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Zachary John Taylor
Publisher :
ISBN 13 :
Total Pages : 314 pages
Book Rating : 4.:/5 (16 download)
Download or read book Vortex Shedding from Elongated Bluff Bodies written by Zachary John Taylor and published by . This book was released on 2011 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the spans of suspension bridges increase, the structures become inherently flexible. The flexibility of these structures, combined with the wind and particular aerodynamics, can lead to significant motions. From the collapse due to flutter of the Tacoma Narrows Bridge to the case of vortex-induced vibrations (VIV) of the Storebælt Bridge, it is evident that a better understanding of the aerodynamics of these geometries is necessary. The work herein is motivated by these two problems and is presented in two parts. In the first part, the focus is on the physical mechanisms of vortex shedding. It is shown that the wake formation for elongated bluff bodies is distinct from shorter bluff bodies due to the leading edge separating-reattaching flow. Pressure data are then used to propose a mechanism of competition between the flow at the leading and trailing edges rather than synchronization which occurs at low Reynolds numbers. Within the context of this framework, the wakes are orthogonally decomposed and it was discovered that new modes appear not previously observed for shorter bluff bodies. In Part II, a timeresolved Particle Image Velocimetry (PIV) system is developed. This system is used to capture both the high and low frequency dynamics of flutter due its uniquely long recording length. It is shown that, contrary to conventional understanding, the vortex shedding does not significantly change during flutter. Thus, the fact that these bodies shed vortices is only a secondary effect in relation to the flutter instability. There is a distinct contrast between flutter and VIV: the latter is known to be governed by the vortex shedding wake and it has been shown herein that the former is not. Regarding the problem of VIV, it is shown that the wakes of these bodies are formed due to interaction with the leading edge separating-reattaching flow. As the leading edge separation angle grows, it is shown to disturb the trailing edge vortex shedding altering many of the key parameters including fluctuating lift force and shedding frequency.
Author :
Publisher :
ISBN 13 :
Total Pages : 8 pages
Book Rating : 4.:/5 (227 download)
Download or read book Research on Bluff-Body Vortex Wakes written by and published by . This book was released on 1995 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Comparison of laboratory experiments and computational results for two dimensional flows showed that, in impulsively started flows, laboratory flows are two dimensional in the early stages and that three dimensional effects develop after acceleration is complete. In fully developed flow the mean and fluctuating forces are considerably lower (up to 50%) in the laboratory flows (ie with three dimensionality) than in the two dimensional numerical simulations. The experiments in tow tank and water tunnel also revealed the existence of long-time modulations of vortex shedding forces. These have the form of bursts with duration of order 10 vortex shedding periods. A novel method of introducing controlled spanwise components of velocity into otherwise two dimensional flow, at low Reynolds number was to give the cylinder an axial (spanwise) motion, either a steady translation or a periodic oscillation. For unsteady, periodic axial oscillation of the cylinder, the experiments showed how the ratio of the spanwise period to the vortex shedding period determines the patterns of vortex dislocation in the wake, how regimes of chaos are formed and how shedding frequency and wake spectra are affected. (AN).
Author :
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (227 download)
Download or read book Vortex Shedding from Stationary and Vibrating Bluff Bodies in a Shear Flow written by and published by . This book was released on 1980 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: If a fluid is in relative motion past a stationary bluff, or unstreamlined, structure and the vortex shedding frequency approaches one of the natural frequencies of the structure, then resonant flow-induced oscillations of the structure can occur when the damping of the system is sufficiently low. These resonant oscillations are accompanied by a 'lock-on' or capture of the vortex shedding frequency by the vibration frequency over a range of flow speeds, and this lock-on effect causes the wake and the structure to oscillate in unison. The periodic lift and the mean drag forces are amplified as a result of the vibrations, and changes in these fluid forces are closely related to the changes that occur in the flow field in the near wake of the body. Many practical ocean and wind engineering situations involve lightly-damped structures that are located in flows of air or water that are nonuniform along the length of the structure. The primary difference between a uniform flow and a shear flow is the presence and added complexity, in a shear flow, of vorticity whose vector is normal to the plane of the flow. When the incident flow approaches the body this vorticity is turned into the flow direction and interacts with the vortices which are shed from the body into the wake.
Author : Georges-Henri Cottet
Publisher : Cambridge University Press
ISBN 13 : 9780521061704
Total Pages : 0 pages
Book Rating : 4.0/5 (617 download)
Download or read book Vortex Methods written by Georges-Henri Cottet and published by Cambridge University Press. This book was released on 2008-04-24 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vortex methods have matured in recent years, offering an interesting alternative to finite difference and spectral methods for high resolution numerical solutions of the Navier Stokes equations. In the past three decades, research into the numerical analysis aspects of vortex methods has provided a solid mathematical background for understanding the accuracy and stability of the method. At the same time vortex methods retain their appealing physical character, which was the motivation for their introduction. This book presents and analyzes vortex methods as a tool for the direct numerical simulation of impressible viscous flows. It will interest graduate students and researchers in numerical analysis and fluid mechanics and also serve as an ideal textbook for courses in fluid dynamics.
Author : Min Zhao
Publisher : Springer Nature
ISBN 13 : 9813365269
Total Pages : 257 pages
Book Rating : 4.8/5 (133 download)
Download or read book Prediction and Validation Technologies of Aerodynamic Force and Heat for Hypersonic Vehicle Design written by Min Zhao and published by Springer Nature. This book was released on 2021-03-01 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides an overview of advanced prediction and verification technologies for aerodynamics and aerothermodynamics and assesses a number of critical issues in advanced hypersonic vehicle design. Focusing on state-of-the-art theories and promising technologies for engineering applications, it also presents a range of representative practical test cases. Given its scope, the book offers a valuable asset for researchers who are interested in thermodynamics, aircraft design, wind tunnel testing, fluid dynamics and aerothermodynamics research methods, introducing them to inspiring new research topics.
Author : Thomas J. Mueller
Publisher : Springer Science & Business Media
ISBN 13 : 3642840108
Total Pages : 456 pages
Book Rating : 4.6/5 (428 download)
Download or read book Low Reynolds Number Aerodynamics written by Thomas J. Mueller and published by Springer Science & Business Media. This book was released on 2013-03-08 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: Current interest in a variety of low Reynolds number applications has focused attention on the design and evaluation of efficient airfoil sections at chord Reynolds numbers from about 100,000 to about 1,000,000. These applications include remotely piloted vehicles (RPVs) at high altitudes, sailplanes, ultra-light man-carrying/man powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers. The purpose of this conference was to bring together those researchers who have been active in areas closely related to this subject. All of the papers presented are research type papers. Main topics are: Airfoil Design and Analysis, Computational Studies, Stability and Transition, Laminar Separation Bubble, Steady and Unsteady Wind Tunnel Experiments and Flight Experiments.
Author : Ilteris Koc
Publisher :
ISBN 13 :
Total Pages : 362 pages
Book Rating : 4.:/5 (318 download)
Download or read book Experimental Investigation of Active Control of Bluff Body Vortex Shedding written by Ilteris Koc and published by . This book was released on 2008 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :
Publisher :
ISBN 13 :
Total Pages : 4 pages
Book Rating : 4.:/5 (227 download)
Download or read book Three-Dimensional Aspects of Nominally 2-D and 3-D Bluff Body Wakes written by and published by . This book was released on 1995 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last decade, there has been much work carried out to understand three-dimensional effects at low Reynolds numbers (Re) in the wake of bluff bodies, yielding the reaction that end effects can influence the vortex shedding across large spanwise lengths. Wake patterns such as parallel shedding, oblique shedding, cellular shedding, transient patterns, such as 'phase shocks' and 'phase expansions', as well as the existence of large-scale 'vortex dislocations', have been investigated, aspects of this research being spearheaded by me studies at Cornell under the above Contract. In particular, we have discovered a new mechanism for oblique wave resonance in the far wake. We have found a means to control the near wake by using suction at the spanwise ends of a body, which has enabled much more precise phenomena to be investigated including the critical conditions for turbulence inception, and a careful study of 3-D wake transition. We have combined our research at Cornell with studies by Dr. Peter Monkewitz at Ecole Polytechnique, Lausanne, who has effectively laid much of the foundation of the description of these near wake patterns in terms of a Guinzburg-Landau equation. For example, the now transient phenomenon known as a 'phase expansion' has been found to be directly analogous to a Prandtl-Meyer expansion found in gas dynamics. Clearly, the work under the support of the ONR has led to a surprisingly rich new understanding of three-dimensional effects in nominally two-dimensional wake flows.
Author : Chenfeng Li
Publisher : Springer Nature
ISBN 13 : 9811384681
Total Pages : 345 pages
Book Rating : 4.8/5 (113 download)
Download or read book Advances in Engineering Design and Simulation written by Chenfeng Li and published by Springer Nature. This book was released on 2019-10-03 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book consists of selected peer-reviewed papers presented at the NAFEMS India Regional Conference (NIRC 2018). It covers current topics related to advances in computer aided design and manufacturing. The book focuses on the latest developments in engineering modelling and simulation, and its application to various complex engineering systems. Finite element method/finite element analysis, computational fluid dynamics, and additive manufacturing are some of the key topics covered in this book. The book aims to provide a better understanding of contemporary product design and analyses, and hence will be useful for researchers, academicians, and professionals.
