On the Large-Scale Structure in Turbulent Free Shear Flows PDF Download
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Author: J. T. C. Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
The existence of organized structures in turbulent shear flow has been the subject of recent observational discoveries in both the laboratory and in the atmosphere and ocean. The resent work on modeling such structures in a temporally developing, horizontally homogeneous turbulent free shear layer has been extended to the spatially developing mixing layer, there being no available rational transformation between the two nonlinear problems. The basis for the consideration is the kinetic energy development of the mean flow, large-scale structure and fine-grained turbulence with a conditional average, supplementing the usual time average, to separate the nonrandom from the random part of the fluctuations. The integrated form of the energy equations and the accompanying shape assumptions, is used to derive amplitude equations for the mean flow, characterized by the shear layer thickness, the nonrandom and random components of flow which are characterized by their respective energy densities. In general, the large-scale structure augments the spreading of the shear layer and enhances the fine-grained turbulence by taking energy from the mean flow and transferring it to the turbulence as it amplifies and subsequently decays. The maximal amplitude of the large-scale structure is attained by the initially most amplified mode, however, the relative enhancement of the fine-grained turbulence is achieved by both the magnitude of the large-scale structure and its streamwise lifetime. Thus a greater enhancement of the turbulence is achievable by the lower frequency mdoes which have longer streamwise lifetimes. The large-scale structure can also be controlled by increasing the initial level of turbulence, which would render its decay more rapidly. (Author).
Author: J. T. C. Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
The existence of organized structures in turbulent shear flow has been the subject of recent observational discoveries in both the laboratory and in the atmosphere and ocean. The resent work on modeling such structures in a temporally developing, horizontally homogeneous turbulent free shear layer has been extended to the spatially developing mixing layer, there being no available rational transformation between the two nonlinear problems. The basis for the consideration is the kinetic energy development of the mean flow, large-scale structure and fine-grained turbulence with a conditional average, supplementing the usual time average, to separate the nonrandom from the random part of the fluctuations. The integrated form of the energy equations and the accompanying shape assumptions, is used to derive amplitude equations for the mean flow, characterized by the shear layer thickness, the nonrandom and random components of flow which are characterized by their respective energy densities. In general, the large-scale structure augments the spreading of the shear layer and enhances the fine-grained turbulence by taking energy from the mean flow and transferring it to the turbulence as it amplifies and subsequently decays. The maximal amplitude of the large-scale structure is attained by the initially most amplified mode, however, the relative enhancement of the fine-grained turbulence is achieved by both the magnitude of the large-scale structure and its streamwise lifetime. Thus a greater enhancement of the turbulence is achievable by the lower frequency mdoes which have longer streamwise lifetimes. The large-scale structure can also be controlled by increasing the initial level of turbulence, which would render its decay more rapidly. (Author).
Author: J. P. Bonnet
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: M. A. Badri Narayanan
Publisher:
ISBN:
Category :
Languages : en
Pages : 21
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Book Description
The basic understanding of the physics of turbulence has undergone many radical changes in the last few years. Turbulent fluctuations which were considered to be purely random in nature is no more accepted to behave in that fashion but made up of somewhat coherent and orderly structures mixed with noise like random disturbances. The major difficulty experienced in the experimental investigations is the identification of these coherent structures from the overall signal. New methods are being developed to identify them. These orderly motions are large in scale and seem to play an important role in the dynamics of the mixing and the transport processes which are the essential features of turbulence. In this paper the properties of the large scale fluctuations in boundary layers as well as in shear flows are discussed. (Author).
Author: A. A. R. Townsend
Publisher: Cambridge University Press
ISBN: 9780521298193
Category : Mathematics
Languages : en
Pages : 450
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Book Description
Develops a physical theory from the mass of experimental results, with revisions to reflect advances of recent years.
Author: Thomas B. Gatski
Publisher:
ISBN:
Category :
Languages : en
Pages : 37
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Author: Franz Durst
Publisher: Springer Science & Business Media
ISBN: 3642714358
Category : Science
Languages : en
Pages : 367
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Book Description
The first four symposia in the series on turbulent shear flows have been held alternately in the United States and Europe with the first and third being held at universities in eastern and western States, respectively. Continuing this pattern, the Fifth Symposium on Turbulent Shear Flows was held at Cornell University, Ithaca, New York, in August 1985. The meeting brought together more than 250 participants from around the world to present the results of new research on turbulent shear flows. It also provided a forum for lively discussions on the implications (practical or academic) of some of the papers. Nearly 100 formal papers and about 20 shorter communications in open forums were presented. In all the areas covered, the meeting helped to underline the vitality of current research into turbulent shear flows whether in experimental, theoretical or numerical studies. The present volume contains 25 of the original symposium presentations. All have been further reviewed and edited and several have been considerably extended since their first presentation. The editors believe that the selection provides papers of archival value that, at the same time, give a representative statement of current research in the four areas covered by this book: - Homogeneous and Simple Flows - Free Flows - Wall Flows - Reacting Flows Each of these sections begins with an introductory article by a distinguished worker in the field.
Author: Lee-Or Merkine
Publisher:
ISBN:
Category :
Languages : en
Pages : 494
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Author: J.P. Bonnet
Publisher: Springer Science & Business Media
ISBN: 9401120986
Category : Technology & Engineering
Languages : en
Pages : 504
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Book Description
The existence and crucial role played by large-scale, organized motions in turbulent flows are now recognized by industrial, applied and fundamental researchers alike. It has become increasingly evident that coherent structures influence mixing, noise, vibration, heat transfer, drag, etc... The accelera tion of the development of both experimental and computational programs devoted to this topic has been evident at several recent international meet ings. One of the first questions which experimentalists or numerical analysts are faced with is: how can these structures be separated from the background turbulence? This is a nontrivial task because the coherent structures are gen erally embedded in a random field and the technique used to determine when and where certain structures are passing, or their averaged characteristics (in the more probable or dominant role sense) is directly related to the definition of the coherent structure. Several methods or approaches are available and the choice of a particular one is generally dependent on the desired informa tion. This choice depends not only on the definition of the structure, but also on the experimental and numerical capabilities available to the researcher.
Author: P. Bradshaw
Publisher: Springer Science & Business Media
ISBN: 3662225689
Category : Science
Languages : en
Pages : 345
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Book Description
Turbulent transport of momentum, heat and matter dominates many of the fluid flows found in physics, engineering and the environmental sciences. Complicated unsteady motions which mayor may not count as turbulence are found in interstellar dust clouds and in the larger blood vessels. The fascination of this nonlinear, irreversible stochastic process for pure scientists is demonstrated by the contributions made to its understanding by several of the most distinguished mathematical physicists of this century, and its importance to engineers is evident from the wide variety of industries which have contributed to, or benefit from, our current knowledge. Several books on turbulence have appeared in recent years. Taken collectively, they illustrate the depth of the subject, from basic principles accessible to undergraduates to elaborate mathematical solutions representing many years of work, but there is no one account which emphasizes its breadth. For this, a multi-author work is necessary. This book is an introduction to our state of knowledge of turbulence in most of the branches of science which have contributed to that knowledge. It is not a Markovian sequence of unrelated essays, and we have not simply assembled specialized accounts of turbulence problems in each branch; this book is a unified treatment, with the material classified according to phenomena rather than application, and freed as far as possible from discipline-oriented detail. The approach is "applied" rather than "pure" with the aim of helping people who need to under stand or predict turbulence in real life.
