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Dispersion Of Finite Size Droplets And Solid Particles In Isotropic Turbulence
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Book Synopsis Dispersion of Finite Size Droplets and Solid Particles in Isotropic Turbulence by : Michele Rosso
Download or read book Dispersion of Finite Size Droplets and Solid Particles in Isotropic Turbulence written by Michele Rosso and published by . This book was released on 2016 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent disperse two-phase flows, of either fluid/fluid or fluid/solid type, are common in natural phenomena and engineering devices. Notable examples are atmospheric clouds, i.e. dispersed liquid water droplets and ice particles in a complex turbulent flow, and spray of fuel droplets in the combustion chamber of internal combustion engines. However, the physics of the interaction between a dispersed phase and turbulence is not yet fully understood. The objective of this study is to compare the dispersion of deformable finite size droplets with that of solid particles in a turbulent flow in the absence of gravity, by performing Direct Numerical Simulation (DNS). The droplets and the particles have the same diameter, of the order of the Taylor's microscale of turbulence, and the same density ratio to the carrier flow. The solid particle-laden turbulence is simulated by coupling a standard projection method with the Immersed Boundary Method (IBM). The solid particles are fully resolved in space and time without considering particle/particle collisions (two-way coupling). The liquid droplet-laden turbulence is simulated by coupling a variable-density projection method with the Accurate Conservative Level Set Method (ACLSM). The effect of the surface tension is accounted for by using the Ghost Fluid Method (GFM) in order to avoid any numerical smearing, while the discontinuities in the viscous term of the Navier-Stokes equation are smoothed out via the Continuum Surface Force approach. Droplet/droplet interactions are allowed (four-way coupling). The results presented here show that in isotropic turbulence the dispersion of liquid droplets in a given direction is larger than that of solid particles due to the reduced decay rate of turbulence kinetic energy via the four-way coupling effects of the droplets.
Book Synopsis The dynamics of finite-size settling particles by : Doychev, Todor
Download or read book The dynamics of finite-size settling particles written by Doychev, Todor and published by KIT Scientific Publishing. This book was released on 2015-01-27 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contributes to the fundamental understanding of the physical mechanisms that take place in pseudo turbulent particulate flows. In the present work we have considered the sedimentation of large numbers of spherical rigid particles in an initially quiescent flow field. We have performed direct numerical simulations employing an immersed boundary method for the representation of the fluid-solid interface. The results evidence that depending on the particle settling regime (i.e. Galileo number and particle-to-fluid density ratio) the particles may exhibit strong inhomogeneous spatial distribution. It is found that the particles are preferentially located in regions with downward fluid motion. The particles inside clusters experience larger settling velocities than the average. The flow in all flow cases is observed to exhibit characteristic features of pseudo-turbulence. The particle-induced flow field is further found to be highly anisotropic with dominant vertical components. The results indicate that, in the present flow configurations, the collective and mobility effects play significant role for the particle and fluid motion.
Book Synopsis Taylor Length-scale Size Particles in Isotropic Turbulence by : Francesco Lucci
Download or read book Taylor Length-scale Size Particles in Isotropic Turbulence written by Francesco Lucci and published by . This book was released on 2011 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present study investigates the two-way coupling effects of finite-size solid spherical particles on decaying isotropic turbulence using an immersed boundary method. study of the interactions between finite-size particles andisotropic turbulence. The conventional point particle assumption is valid only in the case of particles with a diameter, dp, much smaller than the Kolmogorov length scale, %eta. In a simulation with particles of diameter dp/sub” %eta the flow around each particle needs to be resolved. In this study, we use a method similar to that of Uhlmann(2005) that adapts the Immersed Boundary(IB) Method developed by Peskin to simulate the flow around suspended spherical solid particles. The main idea of the method is to distribute a number of Lagrangian points uniformly over the surface of the particle. A force is applied at each Lagrangian point to represent the momentum exchange between the particle and the surrounding fluid. An analytic three-point delta function is used to distribute the force to the Eulerian grid points saddling the spherical surface to satisfy the no-slip condition at each Lagrangian point. Decaying turbulence is simulated in a periodic box with a uniform mesh of up to (512)sup3/sup grid points and an initial microscale Reynolds number of up to Resub%lambda 0= 110. We compare the single phase flow (SPF) with particle-laden flows with particles of different diameters. The density of the particle varies from 2.56 to 10 times that of the fluid. The effects of the particles on the temporal development of turbulence kinetic energy E(t), its dissipation rate e(t), its two-way coupling rate of change Psi_p(t) and frequency spectra E(%omega) are discussed. In this study, in contrast to particles with d_p %eta, particles with d_p %eta always increase the dissipation rate of turbulence kinetic energy, e(t). In addition, \Psi_p(t) is always positive, whereas it can be positive or negative for particles with d_p
Book Synopsis Direct Numerical Simulation of Droplet-laden Isotropic Turbulence by : Michael S. Dodd
Download or read book Direct Numerical Simulation of Droplet-laden Isotropic Turbulence written by Michael S. Dodd and published by . This book was released on 2017 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: Interaction of liquid droplets with turbulence is important in numerous applications ranging from rain formation to oil spills to spray combustion. The physical mechanisms of droplet-turbulence interaction are largely unknown, especially when compared to that of solid particles. Compared to solid particles, droplets can deform, break up, coalesce and have internal fluid circulation. The main goal of this work is to investigate using direct numerical simulation (DNS) the physical mechanisms of droplet-turbulence interaction, both for non-evaporating and evaporating droplets. To achieve this objective, we develop and couple a new pressure-correction method with the volume-of-fluid (VoF) method for simulating incompressible two-fluid flows. The method's main advantage is that the variable coefficient Poisson equation that arises in solving the incompressible Navier-Stokes equations for two-fluid flows is reduced to a constant coefficient equation. This equation can then be solved directly using, e.g., the FFT-based parallel Poisson solver. For a $1024^3$ mesh, our new pressure-correction method using a fast Poisson solver is ten to forty times faster than the standard pressure-correction method using multigrid. Using the coupled pressure-correction and VoF method, we perform direct numerical simulations (DNS) of 3130 finite-size, non-evaporating droplets of diameter approximately equal to the Taylor lengthscale and with 5~\% droplet volume fraction in decaying isotropic turbulence at initial Taylor-scale Reynolds number $\Rey_\lambda=83$. In the droplet-laden cases, we vary one of the following three parameters: the droplet Weber number based on the r.m.s. velocity of turbulence ($0.1 \leq \Webrms \leq 5$), the droplet- to carrier-fluid density ratio ($1 \leq \rho_d/\rho_c \leq 100$) or the droplet- to carrier-fluid viscosity ratio ($1 \leq \mu_d/\mu_c \leq 100$). We derive the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. These equations allow us to explain the pathways for TKE exchange between the carrier turbulent flow and the flow inside the droplet. We also explain the role of the interfacial surface energy in the two-fluid TKE equation through work performed by surface tension. Furthermore, we derive the relationship between the power of surface tension and the rate of change of total droplet surface area. This link allows us to explain how droplet deformation, breakup and coalescence play roles in the temporal evolution of TKE. We then extend the code for non-evaporating droplets and develop a combined VoF method and low-Mach-number approach to simulate evaporating and condensing droplets. The two main novelties of the method are: (i) the VOF algorithm captures the motion of the liquid gas interface in the presence of mass transfer due to evaporation and condensation without requiring a projection step for the liquid velocity, and (ii) the low-Mach-number approach allows for local volume changes caused by phase change while the total volume of the liquid-gas system is constant. The method is verified against an analytical solution for a Stefan flow problem, and the $D^2$ law is verified for a single droplet in quiescent gas. Finally, we perform DNS of an evaporating liquid droplet in forced isotropic turbulence. We show that the method accurately captures the temperature and vapor fields in the turbulent regime, and that the local evaporation rate can vary along the droplet surface depending on the structure of the surrounding vapor cloud. We also report the time evolution of the mean Sherwood number, which indicates that turbulence enhances the vaporization rate of liquid droplets.
Book Synopsis Study of Turbulence Modulation by Finite-size Solid Particles with the Lattice Boltzmann Method by : Cheng Peng
Download or read book Study of Turbulence Modulation by Finite-size Solid Particles with the Lattice Boltzmann Method written by Cheng Peng and published by . This book was released on 2018 with total page 231 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent flows laden with finite-size solid particles are found in a variety of natural and engineering processes. However, the overall understanding of how the flow properties, such as turbulent intensity and flow drag, are modified by the addition of the particles is still limited. So far, the only rigorous approach to investigate the modulation mechanisms at the particle scale is to numerically solve the disturbance flow around each particle, known as the interface-resolved simulations (IRS). However, the application of IRS in the turbulent particle-laden flow is particularly challenging due to the requirements of resolving all the length and time scales in the turbulent flow, as well as the need to realize the no-slip boundary condition on the moving particle surfaces. ☐ In recent years, the lattice Boltzmann method (LBM) has emerged as an efficient and accurate numerical approach for computational fluid dynamics. Compared to the conventional approaches of directly solving the Navier-Stokes equations, LBM is simple to code, easy to parallelize, and flexible in treating boundary conditions. In particular, the no-slip boundary treatment based on bounce-back scheme and mesoscopic momentum exchange in LBM take full advantage of the gas kinetic description. However, the realization of these treatments in particle-laden turbulent flow simulations is still rare. So far, the majority of the particle-laden turbulent flow simulations relies on the smoothed-boundary treatments, such as the immersed boundary methods, which tends to induce artificial dissipation. In this dissertation, LBM with a sharp-interface treatment is developed to investigate turbulence modulation by finite-size solid particles. ☐ After a thorough validation, the method is applied to the simulations of a turbulent channel flow laden with both fixed and moving particles. The interactions between the dispersed particles and carrier turbulent flows, especially the modulation induced by the particles on the turbulence intensity and its parameter dependence are examined. The addition of particles is found to result in a more homogeneous distribution of turbulent kinetic energy (TKE) in the wall normal direction and a more isotropic TKE distribution among different spatial directions, comparing to the single-phase turbulent channel flow. To gain further insight, the budget equations of both the total TKE and component-wise TKE in the particle-laden turbulent flows are derived and analyzed using the simulation data. The budget analysis of the total TKE shows that the production rate of TKE from the mean flow is modified to become more uniform in the wall-normal direction by the presence of particles, which is responsible for the more homogeneous distribution of TKE. Specifically, in the buffer region where the TKE source is maximized in the single-phase flow, the TKE source due to the mean shear is reduced since both the mean flow velocity gradient and the Reynolds stress are reduced by the presence of particles. This reduction is found to be related to the particle inertia, where particles with larger inertia result in greater reduction of the TKE source. On the other hand, particles pump energy to turbulent fluctuations by doing work directly (moving particles) or inducing disturbances to the mean flow (fixed particles), converting more mechanical energy from the mean flow to the turbulent motion. The strength of this extra TKE source is related to the dynamics of the wake developed behind particles and therefore is particle-Reynolds-number dependent. The relative strength of the above two mechanisms determines whether the turbulence intensity of a turbulent channel flow is augmented or attenuated by the presence of particles. The budget analysis of component-wise TKE reveals that the more isotropic distribution of TKE among different spatial directions results from the enhanced inter-components transfer of TKE. This enhancement is found to originate from the spherical shape of the particles and particle rotation. ☐ In summary, the improved LBM simulation method based on the sharp-interface treatment provides a better alternative for particle-laden turbulent flow simulations than the commonly used smoothed-interface treatments. The physical results from this dissertation research advance our understanding of flow modulation induced by finite-size solid particles in turbulent flows, particularly in wall-bounded turbulent flows.
Book Synopsis Multiphase Flows with Droplets and Particles, Third Edition by : Efstathios E. Michaelides
Download or read book Multiphase Flows with Droplets and Particles, Third Edition written by Efstathios E. Michaelides and published by CRC Press. This book was released on 2022-12-30 with total page 478 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multiphase Flows with Droplets and Particles provides an organized, pedagogical study of multiphase flows with particles and droplets. This revised edition presents new information on particle interactions, particle collisions, thermophoresis and Brownian movement, computational techniques and codes, and the treatment of irregularly shaped particles. An entire chapter is devoted to the flow of nanoparticles and applications of nanofluids. Features Discusses the modelling and analysis of nanoparticles. Covers all fundamental aspects of particle and droplet flows. Includes heat and mass transfer processes. Features new and updated sections throughout the text. Includes chapter exercises and a Solutions Manual for adopting instructors. Designed to complement a graduate course in multiphase flows, the book can also serve as a supplement in short courses for engineers or as a stand-alone reference for engineers and scientists who work in this area.
Book Synopsis Particle Dispersion in Isotropic Turbulence and Unsteady Particle Dynamics at Finite Reynolds Number by : Renwei Mei
Download or read book Particle Dispersion in Isotropic Turbulence and Unsteady Particle Dynamics at Finite Reynolds Number written by Renwei Mei and published by . This book was released on 1990 with total page 636 pages. Available in PDF, EPUB and Kindle. Book excerpt: A solution to particle dispersion in an isotropic turbulence under Stokes drag, Basset force and gravitational force is obtained in closed form using the independence approximation. The Basset force has no effect on the fluid velocity structure seen by the particles or the long-time particle diffusivities. It does affect the intensities of particle motion for particles with large settling rate and with response time comparable to the turbulence integral time scale. A solution for particles dispersion in isotropic turbulence with non-Stokesian drag and gravitational force is obtained. The time constants of the particle fluctuation in the directions parallel and perpendicular to the gravity are anisotropic. Turbulence increases particle response time constants and reduces settling velocity. Influence of the nonlinear drag, particle response time constants and settling rate on particle dispersion are investigated. Monte-Carlo simulations are performed for particle motions in an isotropic turbulence with non-Stokesian drag. Pseudo-turbulence is generated using random Fourier modes representation. Statistical averages are obtained from more than 5000 particles. The results of the simulation validate the preceeding analysis in the non-Stokesian drag range. The influence of turbulence structure on the dispersions of fluid and particle is examined. In addition to the integral length and time scales, the functional form of the energy spectrum is also important in describing the dispersions of both fluid and particles. Numerical solution for unsteady flow over a sphere indicates that the added-mass force at finite Reynolds number is the same as in the creeping flow and the potential flow. The classical Stokes solution is not valid at small frequency, $omega$, and the corresponding Basset force is proportional to $omega$, instead of $sqrt{omega}$. The Basset-force term has a kernel decays faster than (t- $tau$)$sp{-1/2}$ at large time. The use of the steady state drag coefficient with the instantaneous velocity is justified to approximate the quasi-steady drag on particles. Limiting behavior of the unsteady drag on a sphere at small frequency and low Reynolds number is obtained using matched asymptotic expansions. The modified Basset-force term at finite Re is constructed. It has a kernel decays as (t- $tau$)$sp{-2}$ at large times.
Book Synopsis Fundamentals of Dispersed Multiphase Flows by : S. Balachandar
Download or read book Fundamentals of Dispersed Multiphase Flows written by S. Balachandar and published by Cambridge University Press. This book was released on 2024-03-31 with total page 675 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dispersed multiphase flows are everywhere, from a sneeze to a volcanic eruption. Discover the fundamental physics that connects them all.
Book Synopsis Analytical Prediction of Turbulent Dispersion of Finite Size Particles by : Goodarz Ahmadi
Download or read book Analytical Prediction of Turbulent Dispersion of Finite Size Particles written by Goodarz Ahmadi and published by . This book was released on 1970 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Interaction Between Decaying Isotropic Turbulence and Dispersed Solid Particles by : George Chris Truesdell
Download or read book The Interaction Between Decaying Isotropic Turbulence and Dispersed Solid Particles written by George Chris Truesdell and published by . This book was released on 1993 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Modification of Homogeneous and Isotropic Turbulence by Solid Particles by : Wontae Hwang
Download or read book Modification of Homogeneous and Isotropic Turbulence by Solid Particles written by Wontae Hwang and published by . This book was released on 2004 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dynamics of Non-Spherical Particles in Turbulence by : Luis Blay Esteban
Download or read book Dynamics of Non-Spherical Particles in Turbulence written by Luis Blay Esteban and published by Springer. This book was released on 2019-08-13 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book studies the dynamics of 2D objects moving through turbulent fluids. It examines the decay of turbulence over extended time scales, and compares the dynamics of non-spherical particles moving through still and turbulent fluids. The book begins with an introduction to the project, its aims, and its relevance for industrial applications. It then discusses the movement of planar particles in quiescent fluid, and presents the numerous methodologies used to measure it. The book also presents a detailed analysis of the falling style of irregular particles, which makes it possible to estimate particle trajectory and wake morphology based on frontal geometry. In turn, the book provides the results of an analysis of physically constrained decaying turbulence in a laboratory setting. These results suggest that large-scale cut-off in numerical simulations can result in severe bias in the computed turbulent kinetic energy for long waiting times. Combining the main text with a wealth of figures and sketches throughout, the book offers an accessible guide for all engineering students with a basic grasp of fluid mechanics, while the key findings will also be of interest to senior researchers.
Book Synopsis Simulations of Droplet Dispersion in the Wakes of Cylinders and Icing Tunnel Spray Bars by : Albert Y. Lee
Download or read book Simulations of Droplet Dispersion in the Wakes of Cylinders and Icing Tunnel Spray Bars written by Albert Y. Lee and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Simulations of droplet dispersion behind cylinder wakes and downstream of icing tunnel spray bars were conducted. In both cases, a range of droplet sizes were investigated numerically with a Lagrangian particle trajectory approach while the turbulent air flow was investigated with a hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations approach scheme. In the first study, droplets were injected downstream of a cylinder at sub-critical conditions (i.e. with laminar boundary layer separation). A stochastic continuous random walk (CRW) turbulence model was used to capture the effects of sub-grid turbulence. Small inertia droplets (characterized by small Stokes numbers) were affected by both the large-scale and small-scale vortex structures and closely followed the air flow, while exhibiting a dispersion consistent with that of a scalar flow field. Droplets with intermediate Stokes numbers were centrifuged by the vortices to the outer edges of the wake, yielding an increased dispersion. Large Stokes number droplets were found to be less responsive to the vortex structures and exhibited the least dispersion. Particle concentration was also correlated with vorticity distribution which yielded preferential bias effects as a function of different particle sizes. This trend was qualitatively similar to results seen in homogenous isotropic turbulence, though the influence of particle inertia was less pronounced for the cylinder wake case. A similar study was completed for droplet dispersion within the Icing Research Tunnel (IRT) at the NASA Glenn Research Center, where it is important to obtain a nearly uniform liquid water content (LWC) distribution in the test section (to recreate atmospheric icing conditions).. For this goal, droplets are diffused by the mean and turbulent flow generated from the nozzle air jets, from the upstream spray bars, and from the vertical strut wakes. To understand the influence of these three components, a set of simulations was conducted with a sequential inclusion of these components. Firstly, a jet in an otherwise quiescent airflow was simulated to capture the impact of the air jet on flow turbulence and droplet distribution, and the predictions compared well with experimental results. The effects of the spray bar wake and vertical strut wake were then included with two more simulation conditions, for which it was found that the air jets were the primary driving force for droplet dispersion, i.e. that the spray bar and vertical strut wake effects were secondary.
Book Synopsis An Eulerian Model of Droplet Dispersion in Turbulent Flow by : Sydney David Ryan
Download or read book An Eulerian Model of Droplet Dispersion in Turbulent Flow written by Sydney David Ryan and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Industrial sprays are common in many operations where liquid application to surfaces is required. Simulation of spray characteristics and surrounding flow conditions is crucial for maximizing spray efficacy. Traditionally, droplet modelling has been performed using a Lagrangian approach which requires tracking a sufficient number of droplets to form statistical estimates of droplet deposition. Alternatively, an Eulerian-based flow and droplet transport model using the Direct Quadrature Method of Moments (DQMOM) is applied to spray modeling. This model is coupled with the Reynolds Averaged N avier Stokes (RANS) equations and Shear Stress Transport (SST) turbulence model. The method described uses a novel turbulent diffusion coefficient model based on a full parametric study using Lagrangian particle tracking in a uniform, homogeneous and isotropic turbulent flow field. The model results are compared to: 1) Lagrangian tracking predictions of a log-normal particle size distribution injected into a homogeneous, isotropic turbulent flow field, and 2) full-scale experimental wind tunnel measurements in the anisotropic, non-homogeneous wake of a hollow cone hydraulic nozzle."--Page ii.
Book Synopsis New Approaches in Modeling Multiphase Flows and Dispersion in Turbulence, Fractal Methods and Synthetic Turbulence by : F.C.G.A. Nicolleau
Download or read book New Approaches in Modeling Multiphase Flows and Dispersion in Turbulence, Fractal Methods and Synthetic Turbulence written by F.C.G.A. Nicolleau and published by Springer Science & Business Media. This book was released on 2011-10-29 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains a collection of the main contributions from the first five workshops held by Ercoftac Special Interest Group on Synthetic Turbulence Models (SIG42. It is intended as an illustration of the sig’s activities and of the latest developments in the field. This volume investigates the use of Kinematic Simulation (KS) and other synthetic turbulence models for the particular application to environmental flows. This volume offers the best syntheses on the research status in KS, which is widely used in various domains, including Lagrangian aspects in turbulence mixing/stirring, particle dispersion/clustering, and last but not least, aeroacoustics. Flow realizations with complete spatial, and sometime spatio-temporal, dependency, are generated via superposition of random modes (mostly spatial, and sometime spatial and temporal, Fourier modes), with prescribed constraints such as: strict incompressibility (divergence-free velocity field at each point), high Reynolds energy spectrum. Recent improvements consisted in incorporating linear dynamics, for instance in rotating and/or stably-stratified flows, with possible easy generalization to MHD flows, and perhaps to plasmas. KS for channel flows have also been validated. However, the absence of "sweeping effects" in present conventional KS versions is identified as a major drawback in very different applications: inertial particle clustering as well as in aeroacoustics. Nevertheless, this issue was addressed in some reference papers, and merits to be revisited in the light of new studies in progress.
Book Synopsis Particle Dispersion in Homogeneous Isotropic Turbulence by : Thomas Burgener
Download or read book Particle Dispersion in Homogeneous Isotropic Turbulence written by Thomas Burgener and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Particles in Turbulent Flows by : Leonid I. Zaichik
Download or read book Particles in Turbulent Flows written by Leonid I. Zaichik and published by John Wiley & Sons. This book was released on 2008-12-04 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: The only work available to treat the theory of turbulent flow with suspended particles, this book also includes a section on simulation methods, comparing the model results obtained with the PDF method to those obtained with other techniques, such as DNS, LES and RANS. Written by experienced scientists with background in oil and gas processing, this book is applicable to a wide range of industries -- from the petrol industry and industrial chemistry to food and water processing.
