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Author: Eylül Bilgin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The study of turbulence has been ongoing for over seven decades now, and it is without a doubt one of the most challenging problems in classical physics. The immense difficulty of understanding and analyzing turbulent flows is why researchers have thrown all their resources at the problem, including supercomputers, in hopes of gaining some insight. While this thesis was written during the era of supercomputers and advanced CFD tools (in other words, in the 21st century), it takes on a different approach- we introduce analytical concepts to deal with turbulent flows, and we do so in a manner that encompasses all Reynolds number flows, from laminar to turbulent. It is our objective to show that the conventional view that turbulence cannot be analyzed analytically and that sophisticated numerical methods must be applied to solve fundamental turbulent flows of Newtonian fluids is not necessarily accurate. In this work, we develop physically meaningful and universal tools to analyze turbulent flows over smooth and rough walls, demonstrate their sufficiency in matching data very well and demonstrate their suitability for practical problems. As of now, direct numerical simulation is only suitable for very low Reynolds number and simple geometry investigations; we do not have enough computational power for the needs of most investigations. However, in far future developments might make it possible to supercompute the movement of each molecule in a fluid, providing a deeper understanding of the fluid dynamics of highly excited fluids. We can, in the meantime, gain a deeper understanding of turbulence through semi-analytical and practical methods. Incorporating semi-analytical models, such as those presented here, into numerical programs will also be extremely helpful for improving the computation of turbulence, since this can reduce computation times and improve the stability of numerical computations.
Author: Eylül Bilgin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The study of turbulence has been ongoing for over seven decades now, and it is without a doubt one of the most challenging problems in classical physics. The immense difficulty of understanding and analyzing turbulent flows is why researchers have thrown all their resources at the problem, including supercomputers, in hopes of gaining some insight. While this thesis was written during the era of supercomputers and advanced CFD tools (in other words, in the 21st century), it takes on a different approach- we introduce analytical concepts to deal with turbulent flows, and we do so in a manner that encompasses all Reynolds number flows, from laminar to turbulent. It is our objective to show that the conventional view that turbulence cannot be analyzed analytically and that sophisticated numerical methods must be applied to solve fundamental turbulent flows of Newtonian fluids is not necessarily accurate. In this work, we develop physically meaningful and universal tools to analyze turbulent flows over smooth and rough walls, demonstrate their sufficiency in matching data very well and demonstrate their suitability for practical problems. As of now, direct numerical simulation is only suitable for very low Reynolds number and simple geometry investigations; we do not have enough computational power for the needs of most investigations. However, in far future developments might make it possible to supercompute the movement of each molecule in a fluid, providing a deeper understanding of the fluid dynamics of highly excited fluids. We can, in the meantime, gain a deeper understanding of turbulence through semi-analytical and practical methods. Incorporating semi-analytical models, such as those presented here, into numerical programs will also be extremely helpful for improving the computation of turbulence, since this can reduce computation times and improve the stability of numerical computations.
Author: Haosen Xu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
This dissertation presents numerical and theoretical studies of wall-bounded turbulence. The dissertation is divided into three major parts. The first part focuses on flow physics and modeling of statistical quantities in turbulent boundary layers. We model pressure statistics. The modeling strategy is based on a combination of Townsend's attached eddy hypothesis with Komolgorov's 1941 theory on small-scale turbulence. Specifically, we account for small-scale motions related to pressure inside larger scale wall-attached eddies. With this strategy, we are able to model the even order moments and the scaling of pressure spectrum. In the second part of the dissertation, we study rough wall turbulent boundary layer with densely packed roughness elements. The roughness elements are cubes. Direct numerical simulations are carried out. We report mean flow statistics, Reynolds and dispersive stresses, as well as terms in the turbulent/dispersive kinetic energy budget equations. We show that roughness with high packing densities do not necessarily have similar behaviors and therefore they cannot simply be categorized as d-type roughness. The third part of this dissertation aims to apply computational fluid dynamics to realistic engineering problems. A few problems are considered. We start by studying turbulent boundary layers with heat transfer. We focus on low-speed flows(Mach number within 0.2) with heat transfer, and the performance of wall-modeled large eddy simulation with equilibrium wall model is assessed. The study shows that the Mach number limit for incompressible assumption for thermal fields is lower than the often-quoted value 0.2 due to the associated viscous heating. In addition, we show that the first grid point implementation of the equilibrium wall model outperforms the third grid point implementation for heat transfer problems. Next, we apply wall-modeled large eddy simulation for flows in turbo-machinery. The study focuses specifically on the return channel of a multistage centrifugal compressor. We compare the results from wall-modeled large eddy simulation with those from Reynolds-averaged Navier-Stokes equations and experimental measurements. We show the potential advantages of wall-modeled large eddy simulations for practical engineering applications.
Author: Jean-Pierre Minier
Publisher: Springer
ISBN: 3319415670
Category : Technology & Engineering
Languages : en
Pages : 268
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Book Description
The book presents an up-to-date review of turbulent two-phase flows with the dispersed phase, with an emphasis on the dynamics in the near-wall region. New insights to the flow physics are provided by direct numerical simuation and by fine experimental techniques. Also included are models of particle dynamics in wall-bounded turbulent flows, and a description of particle surface interactions including muti-layer deposition and re-suspension.
Author: T. B. Nickels
Publisher: Springer Science & Business Media
ISBN: 9048196310
Category : Technology & Engineering
Languages : en
Pages : 183
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Book Description
The study of wall-bounded turbulent ows is of considerable interest from both scienti c and practical view points. As such it has attracted a great deal of research over the last 100 years. Much research has concentratedon ows over smooth walls since these are simpler from experimental, numerical and theoretical standpoints. The ow over rough walls has still received considerable attention but progress has necessarilybeenslower.Perhapsthemostessentialproblem(certainlyfromaprac- cal point of view) is to be able to predict the skin-frictiondrag acting on a plate (or a body) given a certain known roughness characteristic of the surface. Unfortunately this has proved to be very dif cult since even the simplest rough surfaces can be characterised by a number of different parameters and we still cannot directly c- nectthese tothe uiddynamicdragin a givensituation.Varioustheoriesandmodels have been proposed in order to make progress but there is still some disagreement in the community as to the correct understanding of these important ows.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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Book Description
The dynamics of coherent structures in the wall region of a turbulent channel flow is considered. The Karhunen-Loeve eigenfunctions and Galerkin procedure are used to derive the dynamical description. In a previous treatment of this problem by Aubry et al1 the analysis required an inhomogeneous pressure term to be supplied from outside the theory. In the first part of this paper this theory is reconsidered on the basis of the construction of wall eigenfunctions that have a full channel validity. As a result of the methods developed here, a well-posed Hermitian theory is developed and convergence questions do not arise. Among a number of important consequences is the fact that no exterior pressure is required by the present theory. In the second part of this paper it is shown that the behavior of the resulting model equa- tions include intermittency, quasiperiodic and chaotic solutions. In the final portion part of this paper three dimensional effects are introduced into the dynamics in order to produce a physically more realistic dynamical theory. It is felt that the bursting and ejection events in turbulent boundary-layers is given a more satisfactory explanation within this framework.
Author: Martin Oberlack
Publisher: Springer
ISBN: 3709125642
Category : Science
Languages : en
Pages : 377
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Book Description
The term "turbulence” is used for a large variety of dynamical phenomena of fluids in motion whenever the details of the flow appear to be random and average properties are of primary interest. Just as wide ranging are the theoretical methods that have been applied towards a better understanding of fluid turbulence. In this book a number of these methods are described and applied to a broad range of problems from the transition to turbulence to asymptotic turbulence when the inertial part of the spectrum is fully developed. Statistical as well as nonstatistical treatments are presented, but a complete coverage of the subject is not attempted. The book will be of interest to scientists and engineers who wish to familiarize themselves with modern developments in theories of turbulence. The fact that the properties of turbulent fluid flow are addressed from very different points of view makes this volume rather unique among presently available books on turbulence.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 22
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Author: G. J. Brereton
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 24
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Author: Wolfgang Kollmann
Publisher: Springer Nature
ISBN: 3030318699
Category : Science
Languages : en
Pages : 744
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Book Description
The book serves as a core text for graduate courses in advanced fluid mechanics and applied science. It consists of two parts. The first provides an introduction and general theory of fully developed turbulence, where treatment of turbulence is based on the linear functional equation derived by E. Hopf governing the characteristic functional that determines the statistical properties of a turbulent flow. In this section, Professor Kollmann explains how the theory is built on divergence free Schauder bases for the phase space of the turbulent flow and the space of argument vector fields for the characteristic functional. Subsequent chapters are devoted to mapping methods, homogeneous turbulence based upon the hypotheses of Kolmogorov and Onsager, intermittency, structural features of turbulent shear flows and their recognition.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 52
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