Download or read book Bubble Generated Turbulence and Direct Numerical Simulations written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Air Entrainment and Micro bubble Generation by Turbulent Breaking Waves written by Milad Mortazavi and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Direct Numerical Simulations of Gas Liquid Multiphase Flows written by Grétar Tryggvason and published by Cambridge University Press. This book was released on 2011-03-10 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurately predicting the behaviour of multiphase flows is a problem of immense industrial and scientific interest. Modern computers can now study the dynamics in great detail and these simulations yield unprecedented insight. This book provides a comprehensive introduction to direct numerical simulations of multiphase flows for researchers and graduate students. After a brief overview of the context and history the authors review the governing equations. A particular emphasis is placed on the 'one-fluid' formulation where a single set of equations is used to describe the entire flow field and interface terms are included as singularity distributions. Several applications are discussed, showing how direct numerical simulations have helped researchers advance both our understanding and our ability to make predictions. The final chapter gives an overview of recent studies of flows with relatively complex physics, such as mass transfer and chemical reactions, solidification and boiling, and includes extensive references to current work.
Download or read book Evaluation of Interfacial Forces and Bubble Induced Turbulence Using Direct Numerical Simulation written by Jinyong Feng and published by . This book was released on 2017 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bubbly Flows written by Martin Sommerfeld and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book summarises the outcom of a priority research programme: 'Analysis, Modelling and Computation of Multiphase Flows'. The results of 24 individual research projects are presented. The main objective of the research programme was to provide a better understanding of the physical basis for multiphase gas-liquid flows as they are found in numerous chemical and biochemical reactors. The research comprises steady and unsteady multiphase flows in three frequently found reactor configurations, namely bubble columns without interiors, airlift loop reactors, and aerated stirred vessels. For this purpose new and improved measurement techniques were developed. From the resulting knowledge and data, new and refined models for describing the underlying physical processes were developed, which were used for the establishment and improvement of analytic as well as numerical methods for predicting multiphase reactors. Thereby, the development, lay-out and scale-up of such processes should be possible on a more reliable basis.
Download or read book Numerical Simulations of Bubbly Flows written by Asghar Esmaeeli-Koosej and published by . This book was released on 1995 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analysis and Modeling of Buoyancy Generated Turbulence Using Numerical Data written by and published by . This book was released on 1997 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rayleigh-Bernard convection offers a unique flow situation in which buoyancy-generated turbulence can be studied in isolation, free of the complicating influence of shear production of turbulence. The objective of this paper is to examine and model important aspects of buoyancy-generated turbulence using direct numerical simulation (DNS) data of Rayleigh-Bernard convection. In particular, we examine the pressure-strain and pressure temperature-gradient correlations, turbulent transport of Reynolds stress, and assumptions pertaining to algebraic modeling of thermal flux and Reynolds stress.
Download or read book Extending Bubble induced Turbulence Modeling Applicability in CFD Through Incorporation of DNS Understanding written by Benjamin Lawrence Magolan and published by . This book was released on 2018 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: Precise knowledge and understanding of the multiphase flow distribution is essential for light water reactor design. Multiphase Computational Fluid Dynamics (M-CFD) modeling and simulation techniques provide three-dimensional resolution of complex flow structures, which can be used to improve operation and safety in current systems, while driving optimization and performance enhancement in next generation designs. Introducing bubbles into liquid flow dramatically modifies the turbulent kinetic energy profile. Examination of experimental and Direct Numerical Simulation (DNS) research reveals a complicated, incomplete, and conflicting picture of bubble-induced turbulence (BIT). Incorporating these physical mechanisms into a BIT model compatible within the Eulerian-Eulerian framework remains a formidable challenge. Two-equation BIT models share a general formulation, manifesting as additional source terms in traditional turbulence models to account for production and dissipation of bubble-induced turbulence. Existing formulations struggle with reliably predicting the turbulent kinetic energy profile, routinely yielding non-physical results that subsequently worsen mean flow predictions. The present work encompasses two research objectives that include (1) advancing the understanding of the complex effects bubbles pose on liquid turbulence, and (2) proposing an approach to incorporate these physical phenomena into a BIT closure relation. Greater understanding of two-phase turbulent mechanisms is advanced through statistical analysis of upward bubbly channel flow DNS data generated by Bolotnov and Lu/Tryggvason. The impact of bubble deformability on the resulting turbulent distributions, energy budgets, and scales are quantified and examined. A methodology that incorporates these fundamental mechanisms into a new BIT model is proposed. The closure comprises five components that include new turbulent viscosity and time-scale formulations in addition to optimized values for the modulation parameter, dissipation coefficient, and newly proposed turbulent viscosity multiplier. Model performance and improvement is confirmed through simulation of the entire Liu (1989) experimental database and comparison with existing closures. The model is incorporated into the Bubbly And Moderate void Fraction (BAMF) formulation (Sugrue et al., 2017) in order to deliver best practices and guidelines for application of momentum closures with BIT modeling. This is accomplished through redefinition of the Wobble number, calibration of expressions for the turbulent dispersion coefficient and lift inversion function, and assessment via simulation of experimental databases.
Download or read book On the Effect of Turbulence on Bubbles written by Marcus Johannes Wilhelmus Harleman and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Micro bubble Dynamics in Turbulent Flow written by Zhentong Zhang (docteur en mécanique des fluides).) and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is devoted to the study of the motion of small bubbles in homogeneous isotropic turbulent flows. The work addresses several questions related to the statistical description of the hydrodynamic forces exerted on a bubble as well as the stochastic modeling of their high frequency fluctuations. First, we propose a model for the acceleration of micro-bubbles (smaller than the dissipative scale of the flow) subjected to the drag and the fluid inertia forces. This model, that depends on the Stokes number, the Reynolds number and the density ratio, reproduces the evolution of the acceleration variance as well as the relative importance and alignment of the two forces as observed from Direct Numerical Simulations (DNS). Second, based on the observation that acceleration statistics conditional to the local kinetic energy dissipation rate are invariant with the Stokes number and the dissipation rate, we propose a stochastic model for the instantaneous bubble acceleration vector accounting for the small-scale intermittency of the turbulent flows. The norm of the bubble acceleration is obtained by modeling the dissipation rate along the bubble trajectory from a log-normal stochastic process, whereas its orientation is given by two coupled random walk on a unit sphere in order to model the evolution of the joint orientation of the drag and inertia forces acting on the bubble. Furthermore, the proposed stochastic model for the bubble acceleration is used in the context of large eddy simulations (LES) of turbulent flows laden with small bubbles. It can effectively reproduce effect of turbulent motion at scales smaller than the mesh resolution by adding a random contribution depending on local average dissipation rate. Comparisons with DNS and standard LES, show that the proposed model improves significantly the statistics of the bubbly phase. Third, we extend the previous results in the case of bubbles with large Reynolds number by considering non-linear drag laws. We define an effective relaxation time based on the drag coefficient to characterize bubble motion (acceleration,velocity). Eventually we study the effect of buoyancy and lift force on the bubble dynamics, and analyze the reduction of the average rising velocity in turbulent flow compared to quiescent flows. It is observed that bubbles preferentially explore region having downward fluid acceleration which contributes through the inertia force to reduction of the rising velocity. In addition, as already observed, the lift force brings preferably bubbles into downstream fluid motion which also reduce their rising velocity.
Download or read book Advances of Computational Fluid Dynamics in Nuclear Reactor Design and Safety Assessment written by Jyeshtharaj Joshi and published by Woodhead Publishing. This book was released on 2019-06-15 with total page 888 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances of Computational Fluid Dynamics in Nuclear Reactor Design and Safety Assessment presents the latest computational fluid dynamic technologies. It includes an evaluation of safety systems for reactors using CFD and their design, the modeling of Severe Accident Phenomena Using CFD, Model Development for Two-phase Flows, and Applications for Sodium and Molten Salt Reactor Designs. Editors Joshi and Nayak have an invaluable wealth of experience that enables them to comment on the development of CFD models, the technologies currently in practice, and the future of CFD in nuclear reactors. Readers will find a thematic discussion on each aspect of CFD applications for the design and safety assessment of Gen II to Gen IV reactor concepts that will help them develop cost reduction strategies for nuclear power plants. Presents a thematic and comprehensive discussion on each aspect of CFD applications for the design and safety assessment of nuclear reactors Provides an historical review of the development of CFD models, discusses state-of-the-art concepts, and takes an applied and analytic look toward the future Includes CFD tools and simulations to advise and guide the reader through enhancing cost effectiveness, safety and performance optimization
Download or read book Analysis and Modeling of Buoyancy Generated Turbulence Using Numerical Data written by Sharath S. Girimaji and published by . This book was released on 1997 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Flow and Heat or Mass Transfer in the Chemical Process Industry written by Dimitrios V. Papavassiliou and published by MDPI. This book was released on 2018-09-28 with total page 215 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a printed edition of the Special Issue "Flow and Heat or Mass Transfer in the Chemical Process Industry" that was published in Fluids
Download or read book Multiphase Flows for Process Industries written by Vivek V. Ranade and published by John Wiley & Sons. This book was released on 2022-03-30 with total page 838 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discover the cutting-edge in multiphase flows used in the process industries In Multiphase Flows for Process Industries: Fundamentals and Applications, a team of accomplished chemical engineers delivers an insightful and complete treatment of the state-of-the-art in commonly encountered multiphase flows in the process industries. After discussing the theoretical background, experimental methods, and computational methods applicable to multiphase flows, the authors explore specific examples from the process industries. The book covers a wide range of multiphase flows, including gas-solid fluidized beds and flows with phase change. It also provides direction on how to use current advances in the field to realize efficient and optimized processes. Filling the gap between theory and practice, this unique reference also includes: A thorough introduction to multiphase flows and the process industry Practical discussions of flow regimes, lower order models and correlations, and the chronological development of mathematical models for multiphase flows Comprehensive explorations of experimental methods for characterizing multiphase flows, including flow imaging and visualization In-depth examinations of computational models for simulating multiphase flows Perfect for chemical and process engineers, Multiphase Flows for Process Industries: Fundamentals and Applications is required reading for graduate and doctoral students in the engineering sciences, as well as professionals in the chemical industry.
Download or read book Computational Methods for Multiphase Flow written by Andrea Prosperetti and published by Cambridge University Press. This book was released on 2009-06-25 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thanks to high-speed computers and advanced algorithms, the important field of modelling multiphase flows is an area of rapid growth. This one-stop account – now in paperback, with corrections from the first printing – is the ideal way to get to grips with this topic, which has significant applications in industry and nature. Each chapter is written by an acknowledged expert and includes extensive references to current research. All of the chapters are essentially independent and so the book can be used for a range of advanced courses and the self-study of specific topics. No other book covers so many topics related to multiphase flow, and it will therefore be warmly welcomed by researchers and graduate students of the subject across engineering, physics, and applied mathematics.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 692 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Studying Turbulence Using Numerical Simulation Databases III written by Center for Turbulence Research (U.S.) and published by . This book was released on 1990 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt:
