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Author : R. L. Wardlaw
Publisher :
ISBN 13 :
Total Pages : 64 pages
Book Rating : 4.:/5 (354 download)
Download or read book On Coupling Two-dimensional Bluff Body Potential Flow to the Periodic Vortex Wake written by R. L. Wardlaw and published by . This book was released on 1966 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 : 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 : Jose V. Nebres
Publisher :
ISBN 13 :
Total Pages : 362 pages
Book Rating : 4.:/5 (265 download)
Download or read book Wake Similarity and Vortex Formation for Two-dimensional Bluff Bodies written by Jose V. Nebres and published by . This book was released on 1992 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Rajeev Jaiman
Publisher : Springer Nature
ISBN 13 : 9811985782
Total Pages : 1028 pages
Book Rating : 4.8/5 (119 download)
Download or read book Mechanics of Flow-Induced Vibration written by Rajeev Jaiman and published by Springer Nature. This book was released on 2023-06-10 with total page 1028 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses various passive and active techniques for controlling unsteady flow dynamics and associated coupled mechanics of fluid-structure interaction. Coupled multiphysics and multidomain simulations are emerging and challenging research areas, which have received significant attention during the past decade. One of the most common multiphysics and multidomain problems is fluid-structure interaction (FSI), i.e., the study of coupled physical systems involving fluid and a structure that have a mechanical influence on each other. Regardless of the application area, the investigation toward modeling of fluid-structure interaction and the underlying mechanisms in dealing with coupled fluid-structure instability with real-world applications remains a challenge to scientists and engineers. This book is designed for students and researchers who seek knowledge of computational modeling and control strategies for fluid-structure interaction. Specifically, this book provides a comprehensive review of the underlying unsteady physics and coupled mechanical aspects of the fluid-structure interaction of freely vibrating bluff bodies, the self-induced flapping of thin flexible structures, and aeroelasticity of shell structures. Understanding flow-induced loads and vibrations can lead to safer and cost-effective structures, especially for light and high-aspect ratio structures with increased flexibility and harsh environmental conditions. Using the body-fitted and moving mesh formulations, the physical insights associated with structure-to-fluid mass ratios, Reynolds number, nonlinear structural deformation, proximity interference, near-wall contacts, free-surface, and other interacting physical fields are covered in this book. In conjunction with the control techniques, data-driven model reduction approaches based on subspace projection and deep neural calculus are covered for low-dimensional modeling of unsteady fluid-structure interaction.
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 : Helmut Eckelmann
Publisher : Springer Science & Business Media
ISBN 13 : 3662004143
Total Pages : 390 pages
Book Rating : 4.6/5 (62 download)
Download or read book Bluff-Body Wakes, Dynamics and Instabilities written by Helmut Eckelmann and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bluff-body wakes play an important role in many fluid dynamics problems and engineering applications. This book gives and up-to-date account of recent results obtained in the study of bluff-body wakes. Experimental, theoretical and numerical approaches are all comprehensively covered and compared. Topics of particular interest include hydrodynamic instability analyses, three-dimensional pattern formation problems, flow control methods, bifurcation analyses, numerical simulations and turbulence modelling. The main originality of thisvolume is that recent conceptual advances made to describe nonlinear phenomena in general are put to the test on a classical problem in fundamental fluid mechanics, namely the wake structure generated behind a bluff object.
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 : Vijay Matheswaran
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (136 download)
Download or read book Vortex Induced Vibrations written by Vijay Matheswaran and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vortex shedding and Vortex Induced Vibrations (VIV) of bluff bodies is a fundamental problem in fluid mechanics. The ubiquity of vortex shedding and VIV in several engineering fields has meant that a significant amount of research has centered on this subject. Recent studies have focused on the extraction of energy from steady flow using bodies undergoing VIV. In this dissertation, a new model for flow around a circular cylinder called the Hybrid Potential Flow (HPF) model is presented. The HPF model incorporates potential flow methods, experimental data and von Karman’s representation of the vortex wake to construct a complete solution for flow around a circular cylinder in the sub-critical Reynolds number regime $300 \leq Re \leq 1.5 x 10^5).$ Shedding frequencies and forces due to vortex shedding are calculated and compared to published results. The HPF model is extended to other bluff body geometries using conformal mapping. A composition of Karman-Trefftz transformations and Fornberg’s method is used to construct a conformal map between the physical domain and the circle plane. The combination of the HPF model and conformal mapping can thus be used to quickly calculate vortex shedding behavior for various bluff bodies. Validation of theoretical results is done through experimental methods. A flow visualization technique to view the time-averaged wake behind bluff bodies is developed and presented. Wind tunnel tests are done to validate predicted shedding frequencies for various bluff body geometries. A proof-of-concept prototype of a device that extracts energy from steady flow using VIV is developed. Emphasis is laid on the device being of low cost and complexity. Finally, principal conclusions of this dissertation and recommendations for future work are presented.
Author :
Publisher :
ISBN 13 :
Total Pages : 704 pages
Book Rating : 4.:/5 (31 download)
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : G. A. Dobrodzicki
Publisher :
ISBN 13 :
Total Pages : 60 pages
Book Rating : 4.:/5 (359 download)
Download or read book Flow Visualization Water Tunnel written by G. A. Dobrodzicki and published by . This book was released on 1982 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: The intention of this report is to demonstrate the utility of theflow visualization water tunnel in the field of experimentalfluid dynamics and also provide guidance to its prospectiveusers. A brief description of the facility and its ancillaryequipment is followed by a short description of the flowvisualization techniques. To emphasize the diversity of subjectstested in the water tunnel, a list of typical experiments and anumber of photographs are presented.
Author : Angela White Bakkom
Publisher :
ISBN 13 :
Total Pages : 178 pages
Book Rating : 4.:/5 (376 download)
Download or read book A Numerical Study of Two-phase Flow Involving Mass and Energy Coupling in the Wake of a Bluff-body written by Angela White Bakkom and published by . This book was released on 1996 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : K. T. Wiese-Nielsen
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (11 download)
Download or read book Vortex Formation in a Two-dimensional Periodic Wake written by K. T. Wiese-Nielsen and published by . This book was released on 1970 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Negar Nabatian
Publisher :
ISBN 13 :
Total Pages : 143 pages
Book Rating : 4.:/5 (11 download)
Download or read book Dynamics and Control of Bluff-body-wake-structure Interaction written by Negar Nabatian and published by . This book was released on 2014 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fluid-structure interaction is encountered in most of the engineering and industrial flow applications. The interaction can lead to generation of undesirable forces acting on structures and causing fatigue or damage. One approach to understanding the fundamental wake flow dynamics and stability is to conduct simulations using forced oscillation of a cylinder. Two aspects of such a flow are considered. The first is the dependence of vortex shedding pattern symmetries on the forced oscillation amplitude, forcing frequency ratios and the direction of the oscillation relative to flow direction. The forced oscillation, depending on the amplitude and frequency of the oscillation, causes formation of various patterns which have specific symmetries. Numerical simulations and stability analysis are employed to determine the unstable wake flow modes and their bifurcations. The forced inline oscillation of a circular cylinder is studied to predict the wake modes over a prescribed range of amplitudes and frequencies. The two-dimensional numerical computations of the Navier-Stokes equations are performed using forced periodic boundary condition method in the range of forcing-to-shedding frequency ratios / [1 2] e s f f ; covering the harmonic and superharmonic excitation regimes with amplitude ratio in the range A/ DÎ[0-0.5]. Symmetric and asymmetric lock-on modes are observed for three different oscillation amplitudes and frequency ratios. The asymmetric 2S mode when / 1 e s f f = for A/D=[0.35-0.5], P+S mode at / 1.5 e s f f = for A/D=[0.175,0.5] and S mode at / 2 e s f f = for A/D=[0.175,0.5] are confirmed. Due to the nonlinearity of the Navier-Stokes équations and the complexity of the infinite dimensional flow dynamics, the primary modes are calculated by the proper orthogonal decomposition (POD) tool. A Galerkin procedure is the used to project the Navier-Stokes equations onto a low-dimensional space spanned by the first two POD modes. This method reduces the problem size from an infinite-dimensional space to a finite number of modes (degree-offreedom)representing the wake dynamics. The vortex shedding dominant modes are invariant Under their symmetry groups. The equivariant bifurcation theory is employed to develop the low order model using the symmetry properties of the primary modes. Thus, equivariant bifurcation and normal form theories are combined with numerical computations of the Navier-Stokes equations to precisely describe the spatio-temporal properties of the wake flow modes and their bifurcations. A linear analysis of the analytical low order model near the bifurcation point is performed to predict the bifurcation sequences observed in simulations.
Author :
Publisher :
ISBN 13 :
Total Pages : 354 pages
Book Rating : 4.:/5 (319 download)
Download or read book Aeronautical Report written by and published by . This book was released on 1972 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Nielson K. Th Wiese
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (258 download)
Download or read book Vortex formation in a two-dimensional periodic wake written by Nielson K. Th Wiese and published by . This book was released on 1970 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book รายงานผลการสํารวจข้าวนาปรังปี 2547 written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
