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Author : Daniel Connell Haworth
Publisher :
ISBN 13 :
Total Pages : 286 pages
Book Rating : 4.:/5 (799 download)
Download or read book Developments in the Probability Density Function Method for Turbulent Flows written by Daniel Connell Haworth and published by . This book was released on 1988 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Daniel Connell Haworth
Publisher :
ISBN 13 :
Total Pages : 614 pages
Book Rating : 4.E/5 ( download)
Download or read book Developments in the Probability Density Function Method for Turbulent Flows written by Daniel Connell Haworth and published by . This book was released on 1986 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : David Clement Leslie
Publisher :
ISBN 13 :
Total Pages : 392 pages
Book Rating : 4.:/5 (43 download)
Download or read book Developments in the Theory of Turbulence written by David Clement Leslie and published by . This book was released on 1973 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : József Bakosi
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (233 download)
Download or read book PDF Modeling of Turbulent Flows on Unstructured Grids written by József Bakosi and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In probability density function (PDF) methods of turbulent flows, the joint PDF of several flow variables is computed by numerically integrating a system of stochastic differential equations for Lagrangian particles. Because the technique solves a transport equation for the PDF of the velocity and scalars, a mathematically exact treatment of advection, viscous effects and arbitrarily complex chemical reactions is possible; these processes are treated without closure assumptions. A set of algorithms is proposed to provide an efficient solution of the PDF transport equation modeling the joint PDF of turbulent velocity, frequency and concentration of a passive scalar in geometrically complex configurations. An unstructured Eulerian grid is employed to extract Eulerian statistics, to solve for quantities represented at fixed locations of the domain and to track particles. All three aspects regarding the grid make use of the finite element method. Compared to hybrid methods, the current methodology is stand-alone, therefore it is consistent both numerically and at the level of turbulence closure without the use of consistency conditions. Since both the turbulent velocity and scalar concentration fields are represented in a stochastic way, the method allows for a direct and close interaction between these fields, which is beneficial in computing accurate scalar statistics. Boundary conditions implemented along solid bodies are of the free-slip and no-slip type without the need for ghost elements. Boundary layers at no-slip boundaries are either fully resolved down to the viscous sublayer, explicitly modeling the high anisotropy and inhomogeneity of the low-Reynolds-number wall region without damping or wall-functions or specified via logarithmic wall-functions. As in moment closures and large eddy simulation, these wall-treatments provide the usual trade-off between resolution and computational cost as required by the given application. Particular attention is focused on modeling the dispersion of passive scalars in inhomogeneous turbulent flows. Two different micromixing models are investigated that incorporate the effect of small scale mixing on the transported scalar: the widely used interaction by exchange with the mean and the interaction by exchange with the conditional mean model. An adaptive algorithm to compute the velocity-conditioned scalar mean is proposed that homogenizes the statistical error over the sample space with no assumption on the shape of the underlying velocity PDF. The development also concentrates on a generally applicable micromixing timescale for complex flow domains. Several newly developed algorithms are described in detail that facilitate a stable numerical solution in arbitrarily complex flow geometries, including a stabilized mean-pressure projection scheme, the estimation of conditional and unconditional Eulerian statistics and their derivatives from stochastic particle fields employing finite element shapefunctions, particle tracking through unstructured grids, an efficient particle redistribution procedure and techniques related to efficient random number generation. The algorithm is validated and tested by computing three different turbulent flows: the fully developed turbulent channel flow, a street canyon (or cavity) flow and the turbulent wake behind a circular cylinder at a sub-critical Reynolds number. The solver has been parallelized and optimized for shared memory and multi-core architectures using the OpenMP standard. Relevant aspects of performance and parallelism on cache-based shared memory machines are discussed and presented in detail. The methodology shows great promise in the simulation of high-Reynolds-number incompressible inert or reactive turbulent flows in realistic configurations.
Author : F. Culick
Publisher : Springer Science & Business Media
ISBN 13 : 9400916205
Total Pages : 560 pages
Book Rating : 4.4/5 (9 download)
Download or read book Unsteady Combustion written by F. Culick and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 560 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains selected papers prepared for the NATO Advanced Study Institute on "Unsteady Combustion", which was held in Praia da Granja, Portugal, 6-17 September 1993. Approximately 100 delegates from 14 countries attended. The Institute was the most recent in a series beginning with "Instrumentation for Combustion and Flow in Engines", held in Vimeiro, Portugal 1987 and followed by "Combusting Flow Diagnostics" conducted in Montechoro, Portugal in 1990. Together, these three Institutes have covered a wide range of experimental and theoretical topics arising in the research and development of combustion systems with particular emphasis on gas-turbine combustors and internal combustion engines. The emphasis has evolved roughly from instrumentation and experimental techniques to the mixture of experiment, theory and computational work covered in the present volume. As the title of this book implies, the chief aim of this Institute was to provide a broad sampling of problems arising with time-dependent behaviour in combustors. In fact, of course, that intention encompasses practically all possibilities, for "steady" combustion hardly exists if one looks sufficiently closely at the processes in a combustion chamber. The point really is that, apart from the excellent paper by Bahr (Chapter 10) discussing the technology of combustors for aircraft gas turbines, little attention is directed to matters of steady performance. The volume is divided into three parts devoted to the subjects of combustion-induced oscillations; combustion in internal combustion engines; and experimental techniques and modelling.
Author : Tarek Echekki
Publisher : Springer Science & Business Media
ISBN 13 : 9400704127
Total Pages : 496 pages
Book Rating : 4.4/5 (7 download)
Download or read book Turbulent Combustion Modeling written by Tarek Echekki and published by Springer Science & Business Media. This book was released on 2010-12-25 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.
Author : Ashok Kumara Varma
Publisher :
ISBN 13 :
Total Pages : 54 pages
Book Rating : 4.:/5 (593 download)
Download or read book Modeling of Scalar Probability Density Functions in Turbulent Flows written by Ashok Kumara Varma and published by . This book was released on 1978 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent flows involving chemical reactions are a basic feature of many combustion and propulsion systems. The development of calculation procedures for turbulent reacting flows requires the understanding and modeling of the coupling between turbulence and combustion. Second-order closure modeling of turbulent flows provides a convenient framework for studying these interactions between turbulence and chemical reactions. Models for the scalar probability density function (pdf) have to be developed to achieve closure of turbulent transport equations for mixing and reacting flows. A delta function 'typical eddy' model has been developed for the joint pdf of the scalar variables. It has been demonstrated that delta functions are a necessary part of pdf's in order to attain the extremums of the statistical constraints on the moments. The statistical bounds on a number of moments of interest have been derived. It has been proven that a rational pdf composed of a set of delta functions alone can always be constructed at any point within the statistically valid moment space. The model provides a good representation of actual pdf's in two-species, variable-density mixing flows. The model has been directly compared to experimental pdf measurements and good agreement for higher-order moments has been demonstrated. It can be shown that the delta function pdf model is significantly simpler than other proposed pdf models and is more than adequate for the closure of the transport equations. (Author).
Author : Paul Richard Van Slooten
Publisher :
ISBN 13 :
Total Pages : 562 pages
Book Rating : 4.E/5 ( download)
Download or read book Velocity/wave-vector Probability Density Function Models for Inhomogeneous Turbulent Flows written by Paul Richard Van Slooten and published by . This book was released on 1998 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: Constructs and implements turbulence models for probability density function (PDF) methods for the computation of turbulent reacting flows. Treats the processes of convection and reaction without further assumptions at this level of closure, while the effects of the fluctuation pressure gradient and the diffusion of the fluctuating velocity by molecular viscosity require modeling. Effects correspond to the pressure-rate-of-strain correlations, the pressure transport, and the dissipation tensor in the Reynolds stress equation. Investigates models for each of these variables.
Author : National Aeronautics and Space Administration (NASA)
Publisher : Createspace Independent Publishing Platform
ISBN 13 : 9781722906252
Total Pages : 192 pages
Book Rating : 4.9/5 (62 download)
Download or read book A PDF Closure Model for Compressible Turbulent Chemically Reacting Flows written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the proposed research project was the analysis of single point closures based on probability density function (pdf) and characteristic functions and the development of a prediction method for the joint velocity-scalar pdf in turbulent reacting flows. Turbulent flows of boundary layer type and stagnation point flows with and without chemical reactions were be calculated as principal applications. Pdf methods for compressible reacting flows were developed and tested in comparison with available experimental data. The research work carried in this project was concentrated on the closure of pdf equations for incompressible and compressible turbulent flows with and without chemical reactions. Kollmann, W. Unspecified Center BOUNDARY LAYER COMBUSTION; COMPRESSIBLE FLOW; PREDICTION ANALYSIS TECHNIQUES; PROBABILITY THEORY; REACTING FLOW; TURBULENT FLOW; FLAME PROPAGATION; INCOMPRESSIBLE FLOW; STAGNATION POINT...
Author : R. Borghi
Publisher : Springer Science & Business Media
ISBN 13 : 146139631X
Total Pages : 958 pages
Book Rating : 4.4/5 (613 download)
Download or read book Turbulent Reactive Flows written by R. Borghi and published by Springer Science & Business Media. This book was released on 2013-03-08 with total page 958 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent reactive flows are of common occurrance in combustion engineering, chemical reactor technology and various types of engines producing power and thrust utilizing chemical and nuclear fuels. Pollutant formation and dispersion in the atmospheric environment and in rivers, lakes and ocean also involve interactions between turbulence, chemical reactivity and heat and mass transfer processes. Considerable advances have occurred over the past twenty years in the understanding, analysis, measurement, prediction and control of turbulent reactive flows. Two main contributors to such advances are improvements in instrumentation and spectacular growth in computation: hardware, sciences and skills and data processing software, each leading to developments in others. Turbulence presents several features that are situation-specific. Both for that reason and a number of others, it is yet difficult to visualize a so-called solution of the turbulence problem or even a generalized approach to the problem. It appears that recognition of patterns and structures in turbulent flow and their study based on considerations of stability, interactions, chaos and fractal character may be opening up an avenue of research that may be leading to a generalized approach to classification and analysis and, possibly, prediction of specific processes in the flowfield. Predictions for engineering use, on the other hand, can be foreseen for sometime to come to depend upon modeling of selected features of turbulence at various levels of sophistication dictated by perceived need and available capability.
Author : Katepalli R. Sreenivasan
Publisher :
ISBN 13 :
Total Pages : 12 pages
Book Rating : 4.3/5 (91 download)
Download or read book Developing New Generation of Models for Turbulent Flows written by Katepalli R. Sreenivasan and published by . This book was released on 1997 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of the study was to generate, from a simple set of rules, a stochastic signal in space-time that would closely resemble the real turbulent data. This goal has been achieved and the work is reported in a journal article (Phys. Rev. E. 49, 5179, 1994) and Chapter 4.4 of the Ph. D thesis by A. Juneja (May 1995). The paper explains the principles and deals with one dimensional signals whereas the thesis chapter deals with three dimensional signals. These synthetic signals possess most of the statistical properties of real turbulence, and have been used as initial conditions in a direct numerical simulation of homogeneous turbulence. A comparable scheme was attempted for wall bounded flows, and the principal hypothesis relating to this attempt was successfully verified in a high-Reynolds-number turbulent pipe flow and a moderate-Reynolds-number turbulent boundary layer.
Author : Brian Edward Launder
Publisher : Cambridge University Press
ISBN 13 : 9780521792080
Total Pages : 774 pages
Book Rating : 4.7/5 (92 download)
Download or read book Closure Strategies for Turbulent and Transitional Flows written by Brian Edward Launder and published by Cambridge University Press. This book was released on 2002-02-21 with total page 774 pages. Available in PDF, EPUB and Kindle. Book excerpt: Publisher Description
Download or read book Probability Density Function Method for Variable-density Pressure-gradient-driven Turbulence and Mixing written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Probability density function (PDF) methods are extended to variable-density pressure-gradient-driven turbulence. We apply the new method to compute the joint PDF of density and velocity in a non-premixed binary mixture of different-density molecularly mixing fluids under gravity. The full time-evolution of the joint PDF is captured in the highly non-equilibrium flow: starting from a quiescent state, transitioning to fully developed turbulence and finally dissipated by molecular diffusion. High-Atwood-number effects (as distinguished from the Boussinesq case) are accounted for: both hydrodynamic turbulence and material mixing are treated at arbitrary density ratios, with the specific volume, mass flux and all their correlations in closed form. An extension of the generalized Langevin model, originally developed for the Lagrangian fluid particle velocity in constant-density shear-driven turbulence, is constructed for variable-density pressure-gradient-driven flows. The persistent small-scale anisotropy, a fundamentally 'non-Kolmogorovian' feature of flows under external acceleration forces, is captured by a tensorial diffusion term based on the external body force. The material mixing model for the fluid density, an active scalar, is developed based on the beta distribution. The beta-PDF is shown to be capable of capturing the mixing asymmetry and that it can accurately represent the density through transition, in fully developed turbulence and in the decay process. The joint model for hydrodynamics and active material mixing yields a time-accurate evolution of the turbulent kinetic energy and Reynolds stress anisotropy without resorting to gradient diffusion hypotheses, and represents the mixing state by the density PDF itself, eliminating the need for dubious mixing measures. Direct numerical simulations of the homogeneous Rayleigh-Taylor instability are used for model validation.
Author : Geoff Hewitt
Publisher : Cambridge University Press
ISBN 13 : 9780521838993
Total Pages : 366 pages
Book Rating : 4.8/5 (389 download)
Download or read book Prediction of Turbulent Flows written by Geoff Hewitt and published by Cambridge University Press. This book was released on 2005-06-08 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: The prediction of turbulent flows is of paramount importance in the development of complex engineering systems involving flow, heat and mass transfer, and chemical reactions. Arising from a programme held at the Isaac Newton Institute in Cambridge, this volume reviews the current situation regarding the prediction of such flows through the use of modern computational fluid dynamics techniques, and attempts to address the inherent problem of modelling turbulence. In particular, the current physical understanding of such flows is summarised and the resulting implications for simulation discussed. The volume continues by surveying current approximation methods whilst discussing their applicability to industrial problems. This major work concludes by providing a specific set of guidelines for selecting the most appropriate model for a given problem. Unique in its breadth and critical approach, this book will be of immense value to experienced practitioners and researchers, continuing the UK's strong tradition in fluid dynamics.
Author : Stefan Heinz
Publisher : Springer Science & Business Media
ISBN 13 : 3662100223
Total Pages : 232 pages
Book Rating : 4.6/5 (621 download)
Download or read book Statistical Mechanics of Turbulent Flows written by Stefan Heinz and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: The simulation of technological and environmental flows is very important for many industrial developments. A major challenge related to their modeling is to involve the characteristic turbulence that appears in most of these flows. The traditional way to tackle this question is to use deterministic equations where the effects of turbulence are directly parametrized, i. e. , assumed as functions of the variables considered. However, this approach often becomes problematic, in particular if reacting flows have to be simulated. In many cases, it turns out that appropriate approximations for the closure of deterministic equations are simply unavailable. The alternative to the traditional way of modeling turbulence is to construct stochastic models which explain the random nature of turbulence. The application of such models is very attractive: one can overcome the closure problems that are inherent to deterministic methods on the basis of relatively simple and physically consistent models. Thus, from a general point of view, the use of stochastic methods for turbulence simulations seems to be the optimal way to solve most of the problems related to industrial flow simulations. However, it turns out that this is not as simple as it looks at first glance. The first question concerns the numerical solution of stochastic equations for flows of environmental and technological interest. To calculate industrial flows, 3 one often has to consider a number of grid cells that is of the order of 100 .
Author : Sharadha Viswanathan
Publisher :
ISBN 13 :
Total Pages : 240 pages
Book Rating : 4.:/5 (854 download)
Download or read book Advances in Modeling Mixing and Molecular Transport in Probability Density Function Methods of Turbulent Reacting Flows written by Sharadha Viswanathan and published by . This book was released on 2011 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: Modeling of turbulent reacting flow problems using Probability Density Function (PDF) methods yields transport and reaction in closed form while the processes related to the conditional dissipation of species compositions need to be closed using mixing models. First, we study the dispersion from line sources in decaying grid turbulence using a modified form of the Interaction by Exchange with the Conditional Mean (IECM) mixing model. These flows pose a significant challenge to statistical models, because the scalar length scale (of the initial plume) is much smaller than the turbulence integral scale. Consequently, this necessitates incorporating the effects of molecular diffusion in order to model laboratory experiments. The effects of molecular diffusion are modeled by adding a conditional mean scalar drift term and a laminar wake model is used to obtain an analytic expression for the mixing timescale at small times which is subsequently used as part of a general specification of the mixing timescale. Based on this modeling, PDF calculations are performed, and comparison is made primarily with existing experimental and numerical data on single and multiple line sources. A heated mandoline is also considered. This establishes the validity of the proposed model and the significant effect of molecular diffusion on the decay of scalar fluctuations. Next, various numerical implementations of mixing and molecular transport in LES/PDF studies of turbulent reacting flows are evaluated for accuracy using the Method of Manufactured Solutions (MMS). Mixing is modeled using the Interaction by Exchange with the Mean (IEM) model and the effects of molecular transport are incorporated as a mean drift term in the mixing step. This methodology avoids spurious production of scalar variance and also allows direct incorporation of differential diffusion effects. The implementation of the mixing model is shown to be successful in capturing the effects of differential diffusion accurately with the additional property of satisfying detailed conservation and realizability of species mass fractions. Additionally, we present a new variance reduction technique by way of an implicit smoothing methodology. This smoothing scheme is shown to satisfy conservation, boundedness and regularity criteria. Moreover, for an appropriate choice of the smoothing length scale, significant improvements in accuracy can be achieved for an incremental increase in computational cost. Also, it is shown that with smoothing, the bias and statistical errors due to finite number of particles in the Lagrangian Monte Carlo simulations now scale as N[-]1 and tot N[-]1/2 respectively, where Ntot is the total number of particles in the computatot tional domain. Finally, the numerical implementations described are applied to the study of a turbulent reacting jet flame (Sandia Flame D). It is shown that this implementation yields a consistent formulation between the LES and the PDF methods. Further, cross-validation is presented as a numerical technique to assist in the automatic choice of the smoothing length scale and the application of crossvalidation to smoothing of PDF fields is shown to improve the consistency between the LES and PDF fields.
Author : Pavel Petkov Popov
Publisher :
ISBN 13 :
Total Pages : 192 pages
Book Rating : 4.:/5 (913 download)
Download or read book Advances in Particle/finite Volume Algorithms for Turbulent Reactive Flows written by Pavel Petkov Popov and published by . This book was released on 2013 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the field of turbulent reactive flow simulations, hybrid particle/finite volume large eddy simulation/probability density function (LES/PDF) methods have been shown to be highly accurate in simulating laboratory-scale flames. Their strengths lie in the combination of the large eddy simulation procedure's ability to resolve the large, non-universal scales of turbulence, combined with the fact that probability density function models for turbulent combustion require no closure for the highly non-linear chemistry source term. This work presents advances in such hybrid particle/finite volume LES/PDF algorithms for turbulent reactive flows. New time stepping, interpolation, and coupling schemes have been proposed with the goal of reducing particle mass consistency (PMC) error (defined as the discrepancy between particle mass density and resolved finite volume density) and overall simulation error. The Multi-step Second-order Runge-Kutta (MRK2) integration scheme is an ODE integration scheme designed for reducing PMC errors when applied to discontinuous velocity fields. When applied to a discontinuous velocity field such as might be produced by a state-of-the art velocity interpolation scheme, MRK2 preserves the continuity of the Lagrangian position mapping and is second-order convergent in time, as opposed to a standard second-order Runge-Kutta scheme, which is only first-order convergent in time when applied to a discontinuous velocity field. The Direct Richardson p-th order (DRp) is a conceptually new family of SDE integration schemes which are weakly p-th order accurate in time, where p is an arbitrary positive integer. Unlike standard SDE integration schemes, which are based on matching appropriate terms in the Ito-Taylor expansion of the stochastic process, the DRp schemes work via Richardson extrapolation between the probability density functions of a set of first-order accurate Euler approximations with differing time steps. In the context of the Large Eddy Simulation/Probability Density Function (LES/PDF) code developed by the Turbulence and Combustion Group at Cornell University, a PDF to LES density coupling scheme via a transported specific volume (TSV) has been developed. While coupling approaches similar to TSV have been used previously in LES/PDF application, the present implementation is the first to allow overall second-order accuracy of the LES/PDF code in space and time. New implicit and explicit schemes for PMC error reduction schemes have been developed and tested in the context of the Sandia-Sydney bluff-body flame. Implicit PMC preservation schemes include new velocity and diffusivity interpolation algorithms, and explicit PMC error correction is achieved via a corrective velocity. While corrective velocity schemes have been used previously, the present algorithm, featuring a smoothed version of the PMC error field, is capable of maintaining the same PMC error levels with a corrective velocity of lower magnitude. Finally, the LES/PDF algorithm, developed by the Turbulence and Combustion group at Cornell, is applied to the Sandia-Sydney bluff-body flames. Comparison is made with experimental data, and the new code is in better agreement with experiment than previous simulations of the same series of flames.
