Theoretical and Numerical Study of Air Entrainment and Bubble Size Distribution in Strong Free-surface Turbulent Flow at Large Froude and Weber Number PDF Download

Author: Xiangming Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 192

View

Book Description
Strong turbulence near an air-water interface, characterized by large Froude (Fr) and Weber number (We), leads to significant interactions and exchanges between gas and liquid, resulting in measurable air entrainment. Air entrainment influences a number of physical processes in the nature, including air-sea gas transfer, production of the sea-salt aerosol and scavenging of biological surfactant. The key factor in controlling these processes is the size distribution of entrained bubbles. However, the underlying mechanisms/physics of air entrainment driven by free-surface turbulence (FST) and the resulted bubble size distribution still remain unclear. Therefore, detailed studies on air entrainment in strong free-surface turbulence (SFST) are of fundamental scientific interest. With recent interest in modeling the white bubbly water in ship wakes, these studies are also of practical importance to the design and analysis of modern surface vessels. In this thesis, we perform both theoretical and numerical studies on air entrainment and bubble size distribution in SFST at large Fr and We. The thesis work 1) characterizes the unique turbulence characteristics of SFST; 2) quantifies the entrainment volume and the corresponding size distribution of SFST air entrainment; 3) elucidates the mechanisms/physics of the bubble size distribution of SFST entrainment; 4) provides useful insight and guidance to the development of sub-grid air entrainment models ...

Author: Hubert Chanson
Publisher: Elsevier
ISBN: 0080526896
Category : Science
Languages : en
Pages : 403

View

Book Description
This book develops an analysis of the air entrainment processes in free-surface flows. These flows are investigated as homogeneous mixtures with variable density. Several types of air-water free-surface flows are studied: plunging jet flows, open channel flows, and turbulent water jets discharging into air. Experimental observations reported by the author confirm the concept that the air-water mixture behaves as a homogeneous compressible fluid in each case. This book will be of great interest to professionals working in many fields of engineering: chemical, civil, environmental, mechanical, mining, metallurgy, and nuclear. Covers new information on the air-water flow field: air bubble distributions, air-water velocity profiles, air bubble sizes and bubble-turbulence interactions Features new analysis is developed for each flow configuration and compared successfully with model and prototype data Includes over 372 references and more than 170 figures with over 60 photographs Presents useful information for design engineers and research-and-development scientists who require a better understanding of the fluid mechanics of air-water flows

Author: Milad Mortazavi
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
Bubble generation and air entrainment on ocean surfaces and behind ships are complex phenomena which usually accompany turbulent flows. Non-linear wave-breaking events entrain air and generate turbulence. Turbulence consequently fragments the entrained air into smaller bubbles. This process drastically increases the flux of air into the oceans and rivers, which is important for both aerating the water bodies and reducing greenhouse gases from the atmosphere. Wave breaking and bubble generation behind ships also have important effects on the hydrodynamics of ships and on their performance. The bubbly flow as a result of ship passage generates ship trails which remain for several minutes thereafter. Although turbulence is responsible for the fragmentation of larger bubbles into smaller ones, it cannot be the cause of the generation of micron-size bubbles. These bubbles are observed in ship wakes and natural waves and are associated with liquid-liquid impact events. These phenomena, due to their complexity, are far from being completely understood. In addition, there is missing quantitative connection between the large-scale non-linear wave-breaking events and the micron-size bubble generation as a result of impact events. There is a large-scale separation between these two phenomena which makes elucidation of the problem very challenging. The aim of this study is to use direct numerical simulations of turbulent hydraulic jumps as canonical representation of non-linear breaking waves, to study the air entrainment and large bubble generation. Furthermore, this study provides statistics of liquid-liquid impact events, which are precursors to micro-bubble generation in these flows. As far as we know, the present work is the first direct numerical simulation of turbulent hydraulic jumps, as well as the first attempt to obtain interface impact statistics in a stationary turbulent breaking wave. In addition to bubble generation, we investigate turbulence statistics such as mean and turbulent velocity fluctuations, Reynolds stress tensors, turbulence production terms, energy spectra and one-dimensional energy budget of the flow. Finally, we present investigation of the effect of relevant non-dimensional parameters such as Weber number and Reynolds number on both large bubbles and impact statistics in these flows.

Author: Peter S. Bernard
Publisher: John Wiley & Sons
ISBN: 9780471332190
Category : Technology & Engineering
Languages : en
Pages : 516

View

Book Description
Provides unique coverage of the prediction and experimentation necessary for making predictions. * Covers computational fluid dynamics and its relationship to direct numerical simulation used throughout the industry. * Covers vortex methods developed to calculate and evaluate turbulent flows. * Includes chapters on the state-of-the-art applications of research such as control of turbulence.

Author: G. Biswas
Publisher: CRC Press
ISBN: 9780849310140
Category : Technology & Engineering
Languages : en
Pages : 478

View

Book Description
This book allows readers to tackle the challenges of turbulent flow problems with confidence. It covers the fundamentals of turbulence, various modeling approaches, and experimental studies. The fundamentals section includes isotropic turbulence and anistropic turbulence, turbulent flow dynamics, free shear layers, turbulent boundary layers and plumes. The modeling section focuses on topics such as eddy viscosity models, standard K-E Models, Direct Numerical Stimulation, Large Eddy Simulation, and their applications. The measurement of turbulent fluctuations experiments in isothermal and stratified turbulent flows are explored in the experimental methods section. Special topics include modeling of near wall turbulent flows, compressible turbulent flows, and more.

Author: Hubert Chanson
Publisher:
ISBN: 9780867766110
Category : Air-supported structures
Languages : en
Pages : 368

View

Book Description

Author: Paul A. Libby
Publisher: CRC Press
ISBN: 9781560321002
Category : Technology & Engineering
Languages : en
Pages : 370

View

Book Description
Beginning with a description of turbulence, its various manifestations, and a brief history of study, this text also incorporates modern perspectives on turbulence. The text also covers such topics as intermittency and the resultant conditional sampling and averaging of turbulent flows, the role of large scale computation of the fundamental equations of fluid mechanics in providing information on variables, and asymptotic methods which are used to expose important features of turbulent flows. Meaningful exercises are included in every section.

Author: Jafar Mehdi Hassan
Publisher: Bentham Science Publishers
ISBN: 1681088126
Category : Science
Languages : en
Pages : 303

View

Book Description
Turbulent Flow and Boundary Layer Theory: Selected Topics and Solved Problems explains fundamental concepts of turbulent flow with boundary layer analysis. A general introduction to turbulent flow familiarizes the reader with the mechanics of turbulence in fluid flow in both nature and engineering applications. The book also explains related concepts including transient flow, methods for controlling transients, turbulent models and dynamic equations for unsteady flow through closed conduits. The contents of the book are designed to help both students and teachers in carrying out turbulent flow analysis and solving problems in engineering and hydraulic applications. Key Features - all the basic concepts in turbulent flow are clearly identified and presented in a simple manner with illustrative and practical examples. - includes a self-contained approach to the subject, indicating prerequisite materials and information needed from courses. - each chapter also has a set of questions and problems to test the student’s power of comprehending the topics. - provides an exhaustive appendix on interesting examples Turbulent Flow and Boundary Layer Theory: Selected Topics and Solved Problems a useful textbook for students of engineering. It also serves as a quick reference for professionals, researchers and project consultants involved with processes that require turbulent flow and boundary layer methods analysis.

Author: A.V. Boiko
Publisher: Springer Science & Business Media
ISBN: 3662047659
Category : Technology & Engineering
Languages : en
Pages : 273

View

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: Wolfgang Kollmann
Publisher: Springer Nature
ISBN: 3031595785
Category : Navier-Stokes equations
Languages : en
Pages : 848

View

Book Description
This updated/augmented second edition retains it class-tested content and pedagogy as a core text for graduate courses in advanced fluid mechanics and applied science. The new edition adds revised sections, clarification, problems, and chapter extensions including a rewritten section on Schauder bases for turbulent pipe flow, coverage of Cantwell’s mixing length closure for turbulent pipe flow, and a section on the variational Hessian. Consisting 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. The second segment, presented over subsequent chapters, is devoted to mapping methods, homogeneous turbulence based upon the hypotheses of Kolmogorov and Onsager, intermittency, structural features of turbulent shear flows and their recognition. Adds section on Plancherel’s theorem and a detailed problem on analytic solution of functional differential equations; Extends chapter nine on characteristic functionals to greater explain the role of convection; Reinforces concepts with problems on the theory and particular examples of turbulent flows such as periodic pipe flow. . .