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 Bubble Dynamics and Interface Phenomena written by John R. Blake and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains papers presented at the IUTAM Symposium on Bubble Dynamics and Interface Phenomena held at the University of Birmingham from 6-9 September 1993. In many respects it follows on a decade later from the very successful IUTAM Symposium held at CALTECH in June 1981 on the Mechanics and physics of bubbles in liquids which was organised by the late Milton Plesset and Leen van Wijngaarden. The intervening period has seen major development with both experiment and theory. On the experimental side there have been ad vances with very high speed photography and data recording that provide detailed information on fluid and interface motion. Major developments in both computer hardware and software have also led to extensive improvement in our understand ing of bubble and interface dynamics although development is still limited by the sheer complexity of the laminar and turbulent flow regimes often associated with bubbly flows. The symposium attracts wide and extensive interest from engineers, physical, chemical, biological and medical scientists and applied mathematicians. The sci entific committee sought to achieve a balance between theory and experiment over a range of fields in bubble dynamics and interface phenomena. It was our intention to emphasise both the breadth and recent developments in these various fields and to encourage cross-fertilisation of ideas on both experimental techniques and theo retical developments. The programme, and the proceedings recorded herein, cover bubble dynamics, sound and wave propagation, bubbles in flow, sonoluminescence, acoustic cavitation, underwater explosions, bursting bubbles and ESWL.
Download or read book Direct Numerical Simulations of Bubbles in Turbulent Flows with Heat Transfer written by Claudio Santarelli and published by Tudpress Verlag Der Wissenschaften Gmbh. This book was released on 2015-08-12 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bubbly flows are essential in many industrial and environmental applications and several methodologies have been employed to investigate the complex phenomena involved. In the present book Direct Numerical Simulations of bubble swarms in channel flow configuration are reported and several cases are presented. The focus is on the mutual interaction between fluid turbulence and bubble dynamics and the impact on the heat transfer in the two-phase mixture. This analysis concerns flow visualizations and quantitative statistical data regarding the fluid as well as the bubbles which can now be used as reference data for model developing and validation.
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 Assessments of Bubble Dynamics Model and Influential Parameters in Microbubble Drag Reduction written by and published by . This book was released on 2006 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the course of this research effort computational parametric studies of the microbubble drag reduction phenomena were conducted. The effects of mixture density variation, free stream turbulence intensity, free stream velocity, and surface roughness on the microbubble drag reduction were studied using a single phase model based on Reynolds-averaged Navier-Stokes transport equations. Additionally, predictions of Eulerian multiphase model for microbubble laden flow were compared with Direct Numerical Simulation from the open literature. Good agreement was achieved between the simulations with the single phase model and experimental data of Deutsch et al. (2003). This good agreement was observed for both free stream velocity as well as surface roughness effect studies. Increased free stream turbulence intensity was observed to result in lower drag reduction, and this effect was stronger for higher density ratios of water and injected gas. For the same free stream velocity increase, the drag reduction was higher for higher density ratio. For fixed gas injection rate, lower drag reduction was predict for higher free stream velocity, and increased drag reduction was obtained with increased surface roughness. The drag reduction predicted by the multiphase model was substantially lower than that predicted by the Direct Numerical Simulation model of Ferrante and Elghobashi (2004). However, gas volume fraction and turbulent kinetic energy profiles predicted by the multiphase model were similar but not identical to those predicted by the DNS of Ferrante and Elghobashi (2004).
Download or read book Fluid Dynamics of Particles Drops and Bubbles written by and published by Cambridge University Press. This book was released on with total page 573 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mathematical Modeling of Bubble Growth in Turbulent Flow written by Ali F. Abu-Bakr and published by LAP Lambert Academic Publishing. This book was released on 2014-12-25 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mathematical modeling of bubbles dynamics is presented in turbulent flow to study the behaviour of vapour growth bubble between two phases (vapour-superheated liquids) flow. Theoretical study of the growth problem is solved analytically in terms of initial void fraction and initial bubble velocity. The growth problem in a viscous superheated liquid is investigated under the proposed pressure of Plesset and Zwick. The growth of bubble radius in a constant and variable dynamical viscosity is studied. The effect of constant and variable dynamical viscosity for two different cases of pressure is studied. The initial time of growth of vapour bubbles between two phase laminar-turbulent flow is introduced in thermal stage. This book is suitable and will be interesting for all researchers in related fields.
Download or read book Engineering Turbulence Modelling and Experiments 3 written by G. Bergeles and published by Newnes. This book was released on 2012-12-02 with total page 932 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents and discussses new developments in the area of turbulence modelling and measurements, with particular emphasis on engineering-related problems. At present, turbulence is one of the key issues in tackling engineering flow problems. Powerful computers and numerical methods are now available for solving the flow equations, but the simulation of turbulence effects which are nearly always important in practice, is still in an unsatisfactory state and introduces considerable uncertainities in the accuracy of CFD calculations. These and other aspects of turbulence modelling and measurements are dealt with in detail by experts in the field. The resulting book is an up-to-date review of the most recent research in this exciting area.
Download or read book Bubble Wake Dynamics in Liquids and Liquid Solid Suspensions written by Liang-Shih Fan and published by Butterworth-Heinemann. This book was released on 1990-08-21 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is devoted to a fundamental understanding of the fluid dynamic nature of a bubble wake, more specifically the primary wake, in liquids and liquid-solid suspensions, an dto the role it plays in various important flow phenomena of multiphase systems. Examples of these phenomena are liquid/solids mixing, bubble coalescence and disintergration, particle entrainment to the freeboard, and bed contraction.
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 Multiphase Flow Dynamics 3 written by Nikolay Ivanov Kolev and published by Springer Science & Business Media. This book was released on 2007-06-08 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to allow the application of the theory from all the three volumes also to processes in combustion engines a systematic set of internally consistent state equations for diesel fuel gas and liquid valid in broad range of changing pressure and temperature are provided also in Volume 3. Erlangen, October 2006 Nikolay Ivanov Kolev Table of contents 1 Some basics of the single-phase boundary layer theory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. 1 Flow over plates, velocity profiles, share forces, heat transfer. . . . . . . . . . . . . . . . . . . . 1 1. 1. 1 Laminar flow over the one site of a plane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. 1. 2 Turbulent flow parallel to plane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. 2 Steady state flow in pipes with circular cross sections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. 2. 1 Hydraulic smooth wall surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. 2. 2 Transition region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1. 2. 3 Complete rough region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1. 2. 4 Heat transfer to fluid in a pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1. 3 Transient flow in pipes with circular cross sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2 Introduction to turbulence of multi-phase flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2. 1 Basic ideas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2. 2 Isotropy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2. 3 Scales, eddy viscosity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2. 3. 1 Small scale turbulent motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2. 3. 2 Large scale turbulent motion, Kolmogorov-Pandtl expression. . . . . . . . . 42 2. 4 k-eps framework. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3 Sources for fine resolution outside the boundary layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3. 1 Bulk sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3. 1. 1 Deformation of the velocity field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3. 1. 2 Blowing and suction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 Bubble Dynamics in a Compressible Viscous Liquid written by Wenke Liu and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microbubble dynamics are associated with cavitation damage to pumps, turbines and propellers, as well as applications in biomedical ultrasonics, sonochemistry and cavitation cleaning. The compressible effects of liquid are essential, which are associated with acoustic radiation at the inception of a bubble and the end of collapse. Viscous effects are important for microbubbles. This thesis is concerned with microbubble dynamics in a viscous compressible liquid near a rigid boundary. The compressible effects are modelled by using the weakly compressible theory. The viscous effects are approximated using the viscous potential flow theory, because the flow field is characterised as being an irrotational flow in the bulk volume but with a thin viscous boundary layer at the bubble surface. Consequently, the phenomenon is modelled by using the boundary integral method. The numerical results are shown in good agreement with the Keller-Miksis equation, experiments and computations based on the Navier-Stokes equations. Numerical studies were carried out for microbubble dynamics near a rigid boundary as well as subject to an acoustic wave. The bubble oscillation, topological transform, jet development and penetration through the bubble and the energy of the bubble system are simulated and analysed regarding the compressible and viscous effects.
Download or read book Bubble Dynamics in Microchannel Flow Boiling written by David W. Fogg and published by . This book was released on 2007 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microchannel flow boiling is a very promising solution to the thermal management problem facing the microprocessor industry. In macroscale systems, such as nuclear reactors, flow boiling has been successful in removing large amounts of power. Unfortunately, microscale flows deviate from conventional theory. Large fluctuations in pressure, temperature, and flow distribution are generated by single bubbles due to channel confinement.
Download or read book Micro and Nanobubbles written by Hideki Tsuge and published by CRC Press. This book was released on 2014-08-04 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microbubbles and nanobubbles have several characteristics that are comparable with millimeter- and centimeter-sized bubbles. These characteristics are their small size, which results in large surface area and high bioactivity, low rising velocity, decreased friction drag, high internal pressure, large gas dissolution capacity, negatively charged surface, and ability to be crushed and form free radicals. Microbubbles and nanobubbles have found applications in a variety of fields such as engineering, agriculture, environment, food, and medicine. Microbubbles have been successfully used in aquacultures of oysters in Hiroshima, scallops in Hokkaido, and pearls in Mie Prefecture, Japan. This field has shown a strong potential for growth. This book comprehensively discusses microbubbles and nanobubbles and their application in aquaculture, environment, engineering, medicine, stock raising, agriculture, and marine industry. It presents their potential as a new technology that can be utilized globally.
Download or read book Cavitation and Bubble Dynamics written by Phoevos Koukouvinis and published by Elsevier. This book was released on 2021-09-24 with total page 355 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cavitation and Bubble Dynamics: Fundamentals and Applications examines the latest advances in the field of cavitation and multiphase flows, including associated effects such as material erosion and spray instabilities. This book tackles the challenges of cavitation hindrance in the industrial world, while also drawing on interdisciplinary research to inform academic audiences on the latest advances in the fundamentals. Contributions to the book come from a wide range of specialists in areas including fuel systems, hydropower, marine engineering, multiphase flows and computational fluid mechanics, allowing readers to discover novel interdisciplinary experimentation techniques and research results. This book will be an essential tool for industry professionals and researchers working on applications where cavitation hindrance affects reliability, noise, and vibrations. Covers a wide range of cavitation and bubble dynamics phenomena, including shock wave emission, jetting, and luminescence Provides the latest advice about applications including cavitation tunnels, cavitation testing, flow designs to avoid cavitation in pumps and other hydromachinery, and flow lines Describes novel experimental techniques, such as x-ray imaging and new computational techniques
Download or read book Particles in Wall Bounded Turbulent Flows Deposition Re Suspension and Agglomeration written by Jean-Pierre Minier and published by Springer. This book was released on 2016-07-26 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
