Download or read book Flow Topology and Small scale Dynamics in Turbulent Rayleigh B nard Convection written by Firas Dabbagh and published by . This book was released on 2017 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Without fluid turbulence, life might have rather different look. The atmosphere and oceans could nearly maintain a much larger temperature differences resulting in ultimate heating or cooling to the earth surface. The water and air flow could rather run much faster at rates of the speed of sound. Turbulence is a highly active nature of chaotic, random and three-dimensionality of swirling fluid. Its nonlinear convective property transports the momentum and energy in a helical mechanism leading eventually to an enriched fluid mixing and generating of small scale motions. These scales chiefly rule the hairpin vorticity dynamics, the strain production and the cascade of kinetic energy mechanisms. Hence, the key feature in turbulence is around disclosing the small scale motions. Studying the fine-scale dynamics gives us fundamental perspectives of flow topology and thus, improves our knowledge of turbulence physics. The turbulence dynamo becomes more complex when the active thermal gradient constitutes into the pure generator of turbulence. This particularly happens in the so-called buoyancy-driven Rayleigh-Bénard convection (RBC), when an infinite/bounded lying fluid is heated from below and cooled from above in the field of gravity. The main goal of this thesis is investigating the flow topology and small-scale dynamics in turbulent RBC, in order to better understanding its thermal turbulence mechanism and improve/validate the turbulence modeling for the foreseeable Computational-Fluid-Dynamics future. To do so, a complete direct numerical simulation (DNS) of turbulent RBC in a rectangular air-filled cavity of aspect ratio unity and pi spanwise open-ended distance, has been presented at Rayleigh numbers Ra={1e8, 1e10}, in chapter 1. A global kinetic energy conservation is inherited using a fourth-order symmetry-preserving scheme for the spatial discretization, and the flow dynamics is explored by analysis of kinetic and thermal energy power spectra, probability density function (PDF) of viscous and thermal dissipation rates, and identification of the wind in RBC. In chapter 2, the DNS dataset is used to investigate several universal small-scale features observed in various turbulent flows and recaptured here in turbulent RBC through the bulk. For instance, the inclined "teardrop" shape of joint PDF velocity gradient tensor invariants (Q,R), the preferential alignment of vorticity with the intermediate eigenstrain vector, and the spiraling degenerated behavior of the average rates invariants (DQ/Dt,DR/Dt). It is found that a self-amplification of viscous straining -Qs results at Ra=1e10, helps in contracting the vorticity worms and enhances slightly the linear contributions of the vortex stretching mechanism. On the other hand, the evolution of relevant small-scale thermals has been addressed by investigating the average rate of invariants pertained to the traceless part of velocity-times-temperature gradient tensor i.e., (DQt/Dt,DRt/Dt). The new invariants are shown to follow correctly the evolution and lifetime of thermal plumes in RBC and hence disclose interactions of buoyant production and viscous dissipation. In chapter 3, the DNS dataset is employed to understand the underlying physics of the subgrid-scale (SGS) motions in turbulent RBC in the spirit of Large-eddy simulation (LES) turbulence modeling. To do so, the key ingredients of eddy-viscosity, eddy-diffusivity and turbulent Prandtl number, are calculated a priori and investigated in a topological point-of-view. As a result, it has been suggested the restricted application of the hypothesis of a constant turbulent Prandtl number only in the large-scale strain-dominated areas. More arguments have been attained through a priori investigation of the alignment trends imposed by existing parameterizations for the SGS heat flux. Finally, a new tensorial approach of modeling the SGS of thermal turbulence is sought, that opens new research trends in the future.
Download or read book Turbulent Convection in Rayleigh B nard Cells with Modified Boundary Conditions written by Andrés Alonso Castillo-Castellanos and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: One outstanding feature of the Rayleigh-Bénard problem which concerns a horizontal fluid layer heated from below and cooled from above, is the spontaneous establishment of spatial ordering and the formation of a coherent large-scale circulation. How different factors, such as the domain geometry and boundary conditions, influence the sizes and shapes of the large-scale flow remains an open question. Despite its apparent simplicity, Rayleigh-Bénard convection exhibits some incredibly rich and complex large-scale dynamics such as torsional modes, rotation, sloshing, and cessations, which often coexist and compete to each other. One approach, commonly used in the study of cessations is to constrain the large scale circulation to a plane by restricting the fluid domain to a (2-D) square cell or to a slim rectangular cell of small aspect ratio in the transversal direction. However, it is not entirely clear whether the 2-D and (quasi-)2-D reversals correspond to the same phenomenon. The present document is dedicated to the study of the large-scale flow patterns in turbulent Rayleigh-Bénard convection, and of the influence exerted by different factors on the flow structures and on their temporal evolution. The proposed characterization combines a statistical analysis with a physical approach relying on the angular momentum as well as the kinetic and potential energies to highlight the underlying physical mechanisms. We subsequently attempt to tie these mechanisms together to each of the distinctive flow patterns observed and to their evolution.
Download or read book On the Influence of Large Scale Forcing and Flow Topology on the Dynamics of Small scale Turbulent Transport written by Bertrand Rollin and published by . This book was released on 2008 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: The small-scale dynamics is analyzed with regards to the local topology of the flow, which is determined by the second and third invariant of the velocity gradient tensor. The phase-plane defined by these invariants allows an identification of the streamline patterns in the neighborhood of the location where they are computed. Probability density functions and conditioned statistics based on the local flow structure show that large scalar dissipation occurs in biaxial extensional regions located near vortices. Large scalar dissipation fluctuations pose a great challenge for traditional numerical simulations. Their scales, which could be several orders of magnitude smaller than the smallest velocity scales, may cause numerical errors that can significantly affect the accuracy of the solution. The study presented in this dissertation establishes the foundation for a new modeling strategy based on the flow topology and the combination of Eulerian and Lagrangian transport method.
Download or read book Introduction to Engineering Heat Transfer written by G. F. Nellis and published by Cambridge University Press. This book was released on 2020-07-30 with total page 1027 pages. Available in PDF, EPUB and Kindle. Book excerpt: Equips students with the essential knowledge, skills, and confidence to solve real-world heat transfer problems using EES, MATLAB, and FEHT.
Download or read book New Approaches and Concepts in Turbulence written by T. Dracos and published by Springer Science & Business Media. This book was released on 1993-09-01 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the proceedings of a colloquium held in Monte Verità from September 9-13, 1991. Special care has been taken to devote adequate space to the scientific discussions, which claimed about half of the time available. Scientists from all over the world presented their views on the importance of kinematic properties, topology and fractal geometry, and on the dynamic behaviour of turbulent flows. They debated the importance of coherent structures and the possibility to incorporate these in the statistical theory of turbulence, as well as their significance for the reduction of the degrees of freedom and the prospective of dynamical systems and chaos approaches to the problem of turbulence. Also under discussion was the relevance of these new approaches to the study of the instability and the origin of turbulence, and the importance of numerical and physical experiments in improving the understanding of turbulence.
Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Instabilities Chaos and Turbulence written by Paul Manneville and published by World Scientific. This book was released on 2010 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book (2nd edition) is a self-contained introduction to a wide body of knowledge on nonlinear dynamics and chaos. Manneville emphasises the understanding of basic concepts and the nontrivial character of nonlinear response, contrasting it with the intuitively simple linear response. He explains the theoretical framework using pedagogical examples from fluid dynamics, though prior knowledge of this field is not required. Heuristic arguments and worked examples replace most esoteric technicalities. Only basic understanding of mathematics and physics is required, at the level of what is currently known after one or two years of undergraduate training: elementary calculus, basic notions of linear algebra and ordinary differential calculus, and a few fundamental physical equations (specific complements are provided when necessary). Methods presented are of fully general use, which opens up ample windows on topics of contemporary interest. These include complex dynamical processes such as patterning, chaos control, mixing, and even the Earth's climate. Numerical simulations are proposed as a means to obtain deeper understanding of the intricacies induced by nonlinearities in our everyday environment, with hints on adapted modelling strategies and their implementation.
Download or read book Dynamics of Spatio Temporal Cellular Structures written by Innocent Mutabazi and published by Springer Science & Business Media. This book was released on 2005-12-15 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: The impact of Benard's discovery on 20th century physics is crucial to any modern research area such as fluid dynamics, nonlinear dynamics, and non-equilibrium thermodynamics, just to name a few. This centenary review shows the broad scope and development including modern applications, edited and written by experts in the field.
Download or read book Worlds of Flow written by Olivier Darrigol and published by Oxford University Press. This book was released on 2005-09 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides the first fully-fledged history of hydrodynamics, including lively accounts of the concrete problems of hydraulics, navigation, blood circulation, meteorology, and aeronautics that motivated the main conceptual innovations. Richly illustrated, technically competent, and philosophically sensitive, it should attract a broad audience and become a standard reference for any one interested in fluid mechanics.
Download or read book Internally Heated Convection and Rayleigh B nard Convection written by David Goluskin and published by Springer. This book was released on 2015-11-21 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Brief describes six basic models of buoyancy-driven convection in a fluid layer: three configurations of internally heated convection and three configurations of Rayleigh-Bénard convection. The author discusses the main quantities that characterize heat transport in each model, along with the constraints on these quantities. This presentation is the first to place the various models in a unified framework, and similarities and differences between the cases are highlighted. Necessary and sufficient conditions for convective motion are given. For the internally heated cases only, parameter-dependent lower bounds on the mean fluid temperature are proven, and results of past simulations and laboratory experiments are summarized and reanalyzed. The author poses several open questions for future study.
Download or read book Fundamentals of Multiphase Flow written by Christopher E. Brennen and published by Cambridge University Press. This book was released on 2005-04-18 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: Publisher Description
Download or read book Fluid Mechanics written by Pijush K. Kundu and published by Academic Press. This book was released on 2012 with total page 919 pages. Available in PDF, EPUB and Kindle. Book excerpt: Suitable for both a first or second course in fluid mechanics at the graduate or advanced undergraduate level, this book presents the study of how fluids behave and interact under various forces and in various applied situations - whether in the liquid or gaseous state or both.
Download or read book Nonlinear Dynamics and Chaos written by Steven H. Strogatz and published by CRC Press. This book was released on 2018-05-04 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook is aimed at newcomers to nonlinear dynamics and chaos, especially students taking a first course in the subject. The presentation stresses analytical methods, concrete examples, and geometric intuition. The theory is developed systematically, starting with first-order differential equations and their bifurcations, followed by phase plane analysis, limit cycles and their bifurcations, and culminating with the Lorenz equations, chaos, iterated maps, period doubling, renormalization, fractals, and strange attractors.
Download or read book Turbulence written by Uriel Frisch and published by Cambridge University Press. This book was released on 1995-11-30 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook presents a modern account of turbulence, one of the greatest challenges in physics. The state-of-the-art is put into historical perspective five centuries after the first studies of Leonardo and half a century after the first attempt by A. N. Kolmogorov to predict the properties of flow at very high Reynolds numbers. Such 'fully developed turbulence' is ubiquitous in both cosmical and natural environments, in engineering applications and in everyday life. The intended readership for the book ranges from first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, to professional scientists and engineers. Elementary presentations of dynamical systems ideas, of probabilistic methods (including the theory of large deviations) and of fractal geometry make this a self-contained textbook.
Download or read book Flow Control written by Mohamed Gad-el-Hak and published by Cambridge University Press. This book was released on 2000-08-15 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: A thorough treatment of the basics of flow control and flow control practices.
Download or read book Thermoacoustic Instability written by R. I. Sujith and published by Springer Nature. This book was released on 2021-12-14 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book systematically presents the consolidated findings of the phenomenon of self-organization observed during the onset of thermoacoustic instability using approaches from dynamical systems and complex systems theory. Over the last decade, several complex dynamical states beyond limit cycle oscillations such as quasiperiodicity, frequency-locking, period-n, chaos, strange non-chaos, and intermittency have been discovered in thermoacoustic systems operated in laminar and turbulent flow regimes. During the onset of thermoacoustic instability in turbulent systems, an ordered acoustic field and large coherent vortices emerge from the background of turbulent combustion. This emergence of order from disorder in both temporal and spatiotemporal dynamics is explored in the contexts of synchronization, pattern formation, collective interaction, multifractality, and complex networks. For the past six decades, the spontaneous emergence of large amplitude, self-sustained, tonal oscillations in confined combustion systems, characterized as thermoacoustic instability, has remained one of the most challenging areas of research. The presence of such instabilities continues to hinder the development and deployment of high-performance combustion systems used in power generation and propulsion applications. Even with the advent of sophisticated measurement techniques to aid experimental investigations and vast improvements in computational power necessary to capture flow physics in high fidelity simulations, conventional reductionist approaches have not succeeded in explaining the plethora of dynamical behaviors and the associated complexities that arise in practical combustion systems. As a result, models and theories based on such approaches are limited in their application to mitigate or evade thermoacoustic instabilities, which continue to be among the biggest concerns for engine manufacturers today. This book helps to overcome these limitations by providing appropriate methodologies to deal with nonlinear thermoacoustic oscillations, and by developing control strategies that can mitigate and forewarn thermoacoustic instabilities. The book is also beneficial to scientists and engineers studying the occurrence of several other instabilities, such as flow-induced vibrations, compressor surge, aeroacoustics and aeroelastic instabilities in diverse fluid-mechanical environments, to graduate students who intend to apply dynamical systems and complex systems approach to their areas of research, and to physicists who look for experimental applications of their theoretical findings on nonlinear and complex systems.
Download or read book An Introduction to Magnetohydrodynamics written by P. A. Davidson and published by Cambridge University Press. This book was released on 2001-03-05 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is an introductory text on magnetohydrodynamics (MHD) - the study of the interaction of magnetic fields and conducting fluids.
