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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: 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: Tapan K. Sengupta
Publisher: Springer
ISBN: 9811300380
Category : Technology & Engineering
Languages : en
Pages : 393
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Book Description
This book highlights by careful documentation of developments what led to tracking the growth of deterministic disturbances inside the shear layer from receptivity to fully developed turbulent flow stages. Associated theoretical and numerical developments are addressed from basic level so that an uninitiated reader can also follow the materials which lead to the solution of a long-standing problem. Solving Navier-Stokes equation by direct numerical simulation (DNS) from the first principle has been considered as one of the most challenging problems of understanding what causes transition to turbulence. Therefore, this book is a very useful addition to advanced CFD and advanced fluid mechanics courses.
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: 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: Chaoqun Liu
Publisher: Academic Press
ISBN: 0128190248
Category : Science
Languages : en
Pages : 458
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Book Description
Liutex and Its Applications in Turbulence Research reviews the history of vortex definition, provides an accurate mathematical definition of vortices, and explains their applications in flow transition, turbulent flow, flow control, and turbulent flow experiments. The book explains the term "Rortex" as a mathematically defined rigid rotation of fluids or vortex, which could help solve many longstanding problems in turbulence research. The accurate mathematical definition of the vortex is important in a range of industrial contexts, including aerospace, turbine machinery, combustion, and electronic cooling systems, so there are many areas of research that can benefit from the innovations described here. This book provides a thorough survey of the latest research in generalized and flow-thermal, unified, law-of-the-wall for wall-bounded turbulence. Important theory and methodologies used for developing these laws are described in detail, including: the classification of the conventional turbulent boundary layer concept based on proper velocity scaling; the methodology for identification of the scales of velocity, temperature, and length needed to establish the law; and the discovery, proof, and strict validations of the laws, with both Reynolds and Prandtl number independency properties using DNS data. The establishment of these statistical laws is important to modern fluid mechanics and heat transfer research, and greatly expands our understanding of wall-bounded turbulence. Provides an accurate mathematical definition of vortices Provides a thorough survey of the latest research in generalized and flow-thermal, unified, law-of-the-wall for wall-bounded turbulence Explains the term “Rortex as a mathematically defined rigid rotation of fluids or vortex Covers the statistical laws important to modern fluid mechanics and heat transfer research, and greatly expands our understanding of wall-bounded turbulence
Author: Thomas B. Gatski
Publisher: Springer Science & Business Media
ISBN: 1461227925
Category : Science
Languages : en
Pages : 609
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Book Description
This book contains contributions by former students, colleagues and friends of Professor John L. Lumley, on the occasion of his 60th birthday, in recognition of his enormous impact on the advancement of turbulence research. A variety of experimental, computational and theoretical topics, including turbulence modeling, direct numerical simulations, compressible turbulence, turbulent shear flows, coherent structures and the Proper Orthogonal Decomposition are contained herein. The diversity and scope of these contributions are further acknowledgment of John Lumley's wide ranging influence in the field of turbulence. The large number of contributions by the authors, many of whom were participants in The Lumley Symposium: Recent Developments in Turbulence (held at ICASE, NASA Langley Research Center on November 12 & 13, 1990), has presented us with the unique opportu nity to select a few numerical and theoretical papers for inclusion in the journal Theoretical and Computational Fluid Dynamics for which Professor Lumley serves as Editor. Extended Abstracts of these pa pers are included in this volume and are appropriately marked. The special issue of TCFD will appear this year and will serve as an additional tribute to John Lumley. As is usually the case, the efforts of others have significantly eased our tasks. We would like to express our deep appreciation to Drs. R.
Author: Tomás Chacón Rebollo
Publisher: Springer
ISBN: 1493904558
Category : Mathematics
Languages : en
Pages : 530
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Book Description
With applications to climate, technology, and industry, the modeling and numerical simulation of turbulent flows are rich with history and modern relevance. The complexity of the problems that arise in the study of turbulence requires tools from various scientific disciplines, including mathematics, physics, engineering and computer science. Authored by two experts in the area with a long history of collaboration, this monograph provides a current, detailed look at several turbulence models from both the theoretical and numerical perspectives. The k-epsilon, large-eddy simulation and other models are rigorously derived and their performance is analyzed using benchmark simulations for real-world turbulent flows. Mathematical and Numerical Foundations of Turbulence Models and Applications is an ideal reference for students in applied mathematics and engineering, as well as researchers in mathematical and numerical fluid dynamics. It is also a valuable resource for advanced graduate students in fluid dynamics, engineers, physical oceanographers, meteorologists and climatologists.
Author: A.V. Boiko
Publisher: Springer Science & Business Media
ISBN: 3662047659
Category : Technology & Engineering
Languages : en
Pages : 273
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Book Description
The Origin of Species Charles Darwin The origin of turbulence in fluids is a long-standing problem and has been the focus of research for decades due to its great importance in a variety of engineering applications. Furthermore, the study of the origin of turbulence is part of the fundamental physical problem of turbulence description and the philosophical problem of determinism and chaos. At the end of the nineteenth century, Reynolds and Rayleigh conjectured that the reason of the transition of laminar flow to the 'sinuous' state is in stability which results in amplification of wavy disturbances and breakdown of the laminar regime. Heisenberg (1924) was the founder of linear hydrody namic stability theory. The first calculations of boundary layer stability were fulfilled in pioneer works of Tollmien (1929) and Schlichting (1932, 1933). Later Taylor (1936) hypothesized that the transition to turbulence is initi ated by free-stream oscillations inducing local separations near wall. Up to the 1940s, skepticism of the stability theory predominated, in particular due to the experimental results of Dryden (1934, 1936). Only the experiments of Schubauer and Skramstad (1948) revealed the determining role of insta bility waves in the transition. Now it is well established that the transition to turbulence in shear flows at small and moderate levels of environmental disturbances occurs through development of instability waves in the initial laminar flow. In Chapter 1 we start with the fundamentals of stability theory, employing results of the early studies and recent advances.
Author: T. B. Nickels
Publisher: Springer
ISBN: 9789048196326
Category : Technology & Engineering
Languages : en
Pages : 184
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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 : 8
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Book Description
