Download or read book Role of Stable Eigenmodes in Shear flow Instability Saturation and Turbulence written by Adrian Everett Fraser and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A flow in which two fluids slide by one another or two layers of a single fluid flow at different speeds is called a shear flow. These flows are of interest in a broad range of physical systems, including atmospheric and astrophysical ones. Their potential to be unstable, with small perturbations growing by feeding off the flow's kinetic energy, motivates their study. Particularly in astrophysical systems, these instabilities often drive turbulence that dramatically modifies the rate at which heat, particles, and momentum are transported across the flow. This thesis studies the nature of these instabilities and the ensuing turbulence, investigating the canonical shear-flow instability, the Kelvin-Helmholtz (KH) instability, in three systems. Specifically, large-scale stable modes are explored, which transfer energy from perturbations back to the shear flow and tend to decay in time, in contrast to unstable modes which take energy away from the flow and tend to grow. In systems where stable modes were investigated prior to this work, the same nonlinear interactions that transfer energy from large to small scales were shown to transfer energy from unstable to stable modes. Thus, they can potentially reach significant amplitudes despite their tendency to decay in the absence of nonlinear interactions. At large amplitudes, the energy sink they present can significantly modify the turbulent state, and accounting for them can significantly improve reduced models of turbulent transport. These prior studies all concerned plasma micro-instabilities or systems that were otherwise quasi-homogeneous. The KH instability is importantly macroscopic and inhomogeneous. Thus, this thesis presents a significant expansion to the set of systems in which stable modes have been investigated. Three studies are described in this thesis. Each study concerns a different flow configuration and a different set of physical effects: a piecewise-linear, fixed shear layer in hydrodynamics, a reinforced, sinusoidal shear flow in gyrokinetics, and a smooth, freely-evolving shear layer in MHD. It is shown that stable modes are nonlinearly coupled to unstable modes in each system. When stable modes are not suppressed by added physical effects, the transfer of energy from unstable to stable modes plays an important role in saturation, and stable modes are expected or directly shown to be excited to significant amplitudes in the ensuing turbulence. The excitation of stable modes is linked to the transport of momentum against its gradient, an effect previously observed in experiments. It is shown that accounting for stable modes can significantly improve reduced models of momentum transport in regimes where they reach significant amplitude. The major contributions of this work are twofold. First, nonlinear coupling to large-scale stable modes is shown to be a generic feature of KH-unstable shear flows. Stable modes are shown to provide a valuable interpretive framework for explaining how features of the turbulence change with system parameters (e.g.~understanding why adding a magnetic field in the direction of the shear flow enhances small-scale fluctuations), and they inform improvements to reduced models. Second, in carrying out this work, tools developed for studying stable modes in quasi-homogeneous systems have been extended to apply to inhomogeneous systems, with stable modes shown to be relevant in inhomogeneous systems for the first time. Thus, this work motivates investigations into stable modes more broadly in inhomogeneous systems and provides the necessary tools for these investigations. Further details of each study are given in the abstracts of Chapters 2, 3, and 4.
Download or read book Physics of Transitional Shear Flows written by Andrey V. Boiko and published by Springer Science & Business Media. This book was released on 2011-09-15 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Starting from fundamentals of classical stability theory, an overview is given of the transition phenomena in subsonic, wall-bounded shear flows. At first, the consideration focuses on elementary small-amplitude velocity perturbations of laminar shear layers, i.e. instability waves, in the simplest canonical configurations of a plane channel flow and a flat-plate boundary layer. Then the linear stability problem is expanded to include the effects of pressure gradients, flow curvature, boundary-layer separation, wall compliance, etc. related to applications. Beyond the amplification of instability waves is the non-modal growth of local stationary and non-stationary shear flow perturbations which are discussed as well. The volume continues with the key aspect of the transition process, that is, receptivity of convectively unstable shear layers to external perturbations, summarizing main paths of the excitation of laminar flow disturbances. The remainder of the book addresses the instability phenomena found at late stages of transition. These include secondary instabilities and nonlinear features of boundary-layer perturbations that lead to the final breakdown to turbulence. Thus, the reader is provided with a step-by-step approach that covers the milestones and recent advances in the laminar-turbulent transition. Special aspects of instability and transition are discussed through the book and are intended for research scientists, while the main target of the book is the student in the fundamentals of fluid mechanics. Computational guides, recommended exercises, and PowerPoint multimedia notes based on results of real scientific experiments supplement the monograph. These are especially helpful for the neophyte to obtain a solid foundation in hydrodynamic stability. To access the supplementary material go to extras.springer.com and type in the ISBN for this volume.
Download or read book Stability Study on Shear Flow and Vortices in Late Boundary Layer Transistion written by Jie Tang and published by . This book was released on 2017 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence is still an unsolved scientific problem, it has been regarded as “the most important unsolved problem of classical physics”. Dr. Liu proposed a new mechanism about turbulence generation and sustenance after decades of research on turbulence and transition. His new idea challenged the classical theorem in many aspects. One of them is the flow stability of transition. Dr. Liu believes that inside the flow field, shear (dominant in laminar) is very unstable while rotation (dominant in turbulence) is relative stable. This inherent property of flow creates the trend that non-vertical vorticity must transfer to vertical vorticity, and causes the occurrence of transition. To verify this new idea, this dissertation analyses the linear stability on twodimensional shear flow and quasi-rotation flow. 1) Chebyshev collocation spectral method is discussed to solve Orr-Sommerfeld equation, the famous eigenvalue function describing the linear modes of disturbance. Several typical parallel shear flows are tested as the basicstate flows in the equation. The instability of shear flow is demonstrated by the existence of positive eigenvalues associated with disturbance modes (eigenfunctions), i.e. the growth of these linear modes. 2) Quasi-rotation flow is considered under Cylindrical coordinate. An eigenvalue perturbation equation is derived to study the stability problem with symmetric flows. Shifted Chebyshev polynomial with Gauss collocation points is used to solve the equation. To investigate the stability of vortices generation in real-world case, I tracked a ring-like vortex and a leg-like vortex over time from our Direct Numerical Simulation (DNS) data. The result shows that, with the generation over time, both ring-like vortex and leg-like vortex become more stable in the fact of decreasing positive eigenvalues.
Download or read book Stability and Transition in Shear Flows written by Peter J. Schmid and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 561 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed look at some of the more modern issues of hydrodynamic stability, including transient growth, eigenvalue spectra, secondary instability. It presents analytical results and numerical simulations, linear and selected nonlinear stability methods. By including classical results as well as recent developments in the field of hydrodynamic stability and transition, the book can be used as a textbook for an introductory, graduate-level course in stability theory or for a special-topics fluids course. It is equally of value as a reference for researchers in the field of hydrodynamic stability theory or with an interest in recent developments in fluid dynamics. Stability theory has seen a rapid development over the past decade, this book includes such new developments as direct numerical simulations of transition to turbulence and linear analysis based on the initial-value problem.
Download or read book The Structure of Turbulent Shear Flow written by A. A. R. Townsend and published by Cambridge University Press. This book was released on 1976 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: Develops a physical theory from the mass of experimental results, with revisions to reflect advances of recent years.
Download or read book Constructive Modeling Of Structural Turbulence And Hydrodynamic Instabilities written by Oleg Mikhailovich Belotserkovskii and published by World Scientific. This book was released on 2009-01-05 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book provides an original approach in the research of structural analysis of free developed shear compressible turbulence at high Reynolds number on the base of direct numerical simulation (DNS) and instability evolution for ideal medium (integral conservation laws) with approximate mechanism of dissipation (FLUX dissipative monotone “upwind” difference schemes) and does not use any explicit sub-grid approximation and semi-empirical models of turbulence. Convective mixing is considered as a principal part of conservation law.Appropriate hydrodynamic instabilities (free developed shear turbulence) are investigated from unique point of view. It is based on the concept of large ordered structures with stochastic core of small scale developed turbulence (”turbulent spot”). Decay of “turbulent spot” are simulated by Monte Carlo method. Proposed approach is based on two hypotheses: statistical independence of the characteristic of large ordered structures (LOS) and small-scale turbulence (ST) “and” weak influence of molecular viscosity (or more generally, dissipative mechanism) on properties of large ordered structures.Two versions of instabilities, due to Rayleigh-Taylor and Richtmyer-Meshkov are studied detail by the three-dimensional calculations, extended to the large temporal intervals, up to turbulent stage and investigation turbulent mixing zone (TMZ).The book covers both the fundamental and practical aspects of turbulence and instability and summarizes the result of numerical experiments conducted over 30 years period with direct participation of the author.In the book are cited the opinions of the leading scientists in this area of research: Acad. A S Monin (Russia), Prof. Y Nakamura (Japan, Nagoya University) and Prof. F Harlow (USA, Los-Alamos).
Download or read book Tokamaks written by John Wesson and published by Oxford University Press. This book was released on 2011-10-13 with total page 828 pages. Available in PDF, EPUB and Kindle. Book excerpt: The tokamak is the principal tool in controlled fusion research. This book acts as an introduction to the subject and a basic reference for theory, definitions, equations, and experimental results. The fourth edition has been completely revised, describing their development of tokamaks to the point of producing significant fusion power.
Download or read book Mathematical Reviews written by and published by . This book was released on 2007 with total page 804 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Magnetohydrodynamic Turbulence written by Dieter Biskamp and published by Cambridge University Press. This book was released on 2003-07-31 with total page 313 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressible (in particular, supersonic) turbulence. Because of the similarities in the theoretical approach, these chapters start with a brief account of the corresponding methods developed in hydrodynamic turbulence. The final part of the book is devoted to astrophysical applications: turbulence in the solar wind, in accretion disks, and in the interstellar medium. This book is suitable for graduate students and researchers working in turbulence theory, plasma physics and astrophysics.
Download or read book The Origin of Turbulence in Near Wall Flows written by A.V. Boiko and published by Springer Science & Business Media. This book was released on 2002-01-22 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a comprehensive survey of the origin of turbulence in near-wall shear layer flows. Instead of going too far into details modern approaches to the problem are discussed in a conceptual treatment. The transition from laminar to turbulent flows in shear layers is described including the generation of flow perturbations, their amplification and development, the breakdown of the initial laminar state, and transformation to a turbulent regime. This book also presents new approaches to boundary-layer transitions with strong external-flow perturbations and to the prediction and control of the presented near-wall transitions to turbulence. This book is addressed to researchers, lecturers and students in engineering, physics and mathematics.
Download or read book Turbulent Shear Flows 8 written by Franz Durst and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 419 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains a selection of the papers presented at the Eighth Symposium on Turbulent Shear Flows held at the Technical University of Munich, 9-11 September 1991. The first of these biennial international symposia was held at the Pennsylvania State Uni versity, USA, in 1977; subsequent symposia have been held at Imperial College, London, England; the University of California, Davis, USA; the University of Karlsruhe, Ger many; Cornell University, Ithaca, USA; the Paul Sabatier University, Toulouse, France; and Stanford University, California, USA. The purpose of this series of symposia is to provide a forum for the presentation and discussion of new developments in the field of turbulence, especially as related to shear flows of importance in engineering and geo physics. From the 330 extended abstracts submitted for this symposium, 145 papers were presented orally and 60 as posters. Out of these, we have selected twenty-four papers for inclusion in this volume, each of which has been revised and extended in accordance with the editors' recommendations. The following four theme areas were selected after consideration of the quality of the contributions, the importance of the area, and the selection made in earlier volumes: - wall flows, - separated flows, - compressibility effects, - buoyancy, rotation, and curvature effects. As in the past, each section corresponding to the above areas begins with an introduction by an authority in the field that places the individual contributions in context with one another and with related research.
Download or read book On Lower Branch Exact Coherent Structures in Turbulent Shear Flows written by Jue Wang and published by . This book was released on 2007 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Global Stability Analysis of Shear Flows written by Rameshkumar Bhoraniya and published by Springer Nature. This book was released on 2023-03-10 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the fundamentals and advanced research on the global stability analysis of the shear flows. The contents investigate the results of global stability analysis for different configurations of internal and external shear flows. The topics covered are global stability analysis of converging-diverging channel flows, axisymmetric boundary layer developed on a circular cylinder, cone and inclined flat-plate boundary layer, and wall jets. It further explains the effect of divergence, convergence, transverse curvature, and pressure gradients on the global stability of the different configurations of shear flows. The book is a valuable reference for beginners, researchers, and professionals working in the field of aerodynamics and marine hydrodynamics.
Download or read book Fundamental Problematic Issues in Turbulence written by Albert Gyr and published by Springer Science & Business Media. This book was released on 1999-08-01 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt: A collection of contributions on a variety of mathematical, physical and engineering subjects related to turbulence. Topics include mathematical issues, control and related problems, observational aspects, two- and quasi-two-dimensional flows, basic aspects of turbulence modeling, statistical issues and passive scalars.
Download or read book On the Consistency of Reynolds Stress Turbulence Closures with Hydrodynamic Stability Theory written by Charles G. Speziale and published by . This book was released on 1995 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Wave guide Model for Turbulent Shear Flow written by Mårten Landahl and published by . This book was released on 1965 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Turbulent Shear Flows 8 written by F. Durst and published by Springer. This book was released on 1993 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains a selection of the papers presented at the Eighth Symposium on Turbulent Shear Flows held at the Technical University of Munich, 9-11 September 1991. The first of these biennial international symposia was held at the Pennsylvania State Uni versity, USA, in 1977; subsequent symposia have been held at Imperial College, London, England; the University of California, Davis, USA; the University of Karlsruhe, Ger many; Cornell University, Ithaca, USA; the Paul Sabatier University, Toulouse, France; and Stanford University, California, USA. The purpose of this series of symposia is to provide a forum for the presentation and discussion of new developments in the field of turbulence, especially as related to shear flows of importance in engineering and geo physics. From the 330 extended abstracts submitted for this symposium, 145 papers were presented orally and 60 as posters. Out of these, we have selected twenty-four papers for inclusion in this volume, each of which has been revised and extended in accordance with the editors' recommendations. The following four theme areas were selected after consideration of the quality of the contributions, the importance of the area, and the selection made in earlier volumes: - wall flows, - separated flows, - compressibility effects, - buoyancy, rotation, and curvature effects. As in the past, each section corresponding to the above areas begins with an introduction by an authority in the field that places the individual contributions in context with one another and with related research.
