Velocity and Temperature Statistics in Reacting Droplet-laden Homogeneous Shear Turbulence PDF Download
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Author: Farzad Mashayek
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Farzad Mashayek
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Gabriel D. Roy
Publisher: CRC Press
ISBN: 1420040685
Category : Science
Languages : en
Pages : 553
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Book Description
Written by the scientists who performed the research, this book reports on the progress achieved by the outstanding team of researchers participating in the ONR Propulsion Program. It covers all aspects of the combustion process, from chemical synthesis, reaction pathways of the fuel, and combustor performance to the reduction of emissions, thrust vectoring, and control. The chapter authors discuss the relevant issues, describe their approach and results, and explain how the findings can be extended to practical applications. Richly illustrated and carefully edited for clarity, uniformity, and readability, this book offers a comprehensive survey of the field, from pre- to post-combustion.
Author: Michael S. Dodd
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Book Description
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.
Author: Jeng-Horng Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 404
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Author: Jovan Jovanovic
Publisher: Springer Science & Business Media
ISBN: 9783540203360
Category : Computers
Languages : en
Pages : 156
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Book Description
This short but complicated book is very demanding of any reader. The scope and style employed preserve the nature of its subject: the turbulence phe nomena in gas and liquid flows which are believed to occur at sufficiently high Reynolds numbers. Since at first glance the field of interest is chaotic, time-dependent and three-dimensional, spread over a wide range of scales, sta tistical treatment is convenient rather than a description of fine details which are not of importance in the first place. When coupled to the basic conserva tion laws of fluid flow, such treatment, however, leads to an unclosed system of equations: a consequence termed, in the scientific community, the closure problem. This is the central and still unresolved issue of turbulence which emphasizes its chief peculiarity: our inability to do reliable predictions even on the global flow behavior. The book attempts to cope with this difficult task by introducing promising mathematical tools which permit an insight into the basic mechanisms involved. The prime objective is to shed enough light, but not necessarily the entire truth, on the turbulence closure problem. For many applications it is sufficient to know the direction in which to go and what to do in order to arrive at a fast and practical solution at minimum cost. The book is not written for easy and attractive reading.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 646
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Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 482
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 128
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Book Description
This report studies the dynamics of particle-laden turbulent flows. Specifically, it addresses the effect of the turbulence on the concentration field and drift velocity of spherical particles. The coupling between the particle accumulation and the modification of the drift velocity is also investigated. Turbulent flows with and without mean shear are analyzed and the effect of the turbulent length scales on the behavior of the particles is described. The effect of the density ratio between the disperse and the continuous phase was considered in the two extreme cases of water droplets in air (1000) and air bubbles in water (1/1000).
Author: John R. Schwab
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Author: Efstathios Michaelides
Publisher: CRC Press
ISBN: 1315354624
Category : Science
Languages : en
Pages : 1559
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Book Description
The Multiphase Flow Handbook, Second Edition is a thoroughly updated and reorganized revision of the late Clayton Crowe’s work, and provides a detailed look at the basic concepts and the wide range of applications in this important area of thermal/fluids engineering. Revised by the new editors, Efstathios E. (Stathis) Michaelides and John D. Schwarzkopf, the new Second Edition begins with two chapters covering fundamental concepts and methods that pertain to all the types and applications of multiphase flow. The remaining chapters cover the applications and engineering systems that are relevant to all the types of multiphase flow and heat transfer. The twenty-one chapters and several sections of the book include the basic science as well as the contemporary engineering and technological applications of multiphase flow in a comprehensive way that is easy to follow and be understood. The editors created a common set of nomenclature that is used throughout the book, allowing readers to easily compare fundamental theory with currently developing concepts and applications. With contributed chapters from sixty-two leading experts around the world, the Multiphase Flow Handbook, Second Edition is an essential reference for all researchers, academics and engineers working with complex thermal and fluid systems.
