Download or read book Stability Improvement of the One dimensional Two fluid Model for Horizontal Two phase Flow with Model Unification written by Kent C. Abel and published by . This book was released on 2005 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: The next generation of nuclear safety analysis computer codes will require detailed modeling of two-phase fluid flow. The most complete and fundamental model used for these calculations is known as the two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links the two phases together with six conservation equations. A major drawback is that the current two-fluid model, when area-averaged to create a one-dimensional model, becomes ill-posed as an initial value problem when the gas and liquid velocities are not equal. The importance of this research lies in obtaining a model that overcomes this difficulty. It is desired to develop a modified one-dimensional two-fluid model for horizontal flow that accounts for the pressure difference between the two phases, due to hydrostatic head, with the implementation of a void fraction distribution parameter. With proper improvement of the one-dimensional two-fluid model, the next generation of nuclear safety analysis computer codes will be able to predict, with greater precision, the key safety parameters of an accident scenario. As part of this research, an improved version of the one-dimensional two-fluid model for horizontal flows was developed. The model was developed from a theoretical point of view with the three original distribution parameters simplified down to a single parameter. The model was found to greatly enhance the numerical stability (hyperbolicity) of the solution method. With proper modeling of the phase distribution parameter, a wide range of flow regimes can be modeled. This parameter could also be used in the future to eliminate the more subjective flow regime maps that are currently implemented in today's multiphase computer codes. By incorporating the distribution parameter and eliminating the flow regime maps, a hyperbolic model is formed with smooth transitions between various flow regimes, eliminating the unphysical oscillations that may occur near transition boundaries in today's multiphase computer codes.
Download or read book Two Fluid Model Stability Simulation and Chaos written by Martín López de Bertodano and published by Springer. This book was released on 2016-11-09 with total page 367 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book addresses the linear and nonlinear two-phase stability of the one-dimensional Two-Fluid Model (TFM) material waves and the numerical methods used to solve it. The TFM fluid dynamic stability is a problem that remains open since its inception more than forty years ago. The difficulty is formidable because it involves the combined challenges of two-phase topological structure and turbulence, both nonlinear phenomena. The one dimensional approach permits the separation of the former from the latter.The authors first analyze the kinematic and Kelvin-Helmholtz instabilities with the simplified one-dimensional Fixed-Flux Model (FFM). They then analyze the density wave instability with the well-known Drift-Flux Model. They demonstrate that the Fixed-Flux and Drift-Flux assumptions are two complementary TFM simplifications that address two-phase local and global linear instabilities separately. Furthermore, they demonstrate with a well-posed FFM and a DFM two cases of nonlinear two-phase behavior that are chaotic and Lyapunov stable. On the practical side, they also assess the regularization of an ill-posed one-dimensional TFM industrial code. Furthermore, the one-dimensional stability analyses are applied to obtain well-posed CFD TFMs that are either stable (RANS) or Lyapunov stable (URANS), with the focus on numerical convergence.
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2006 with total page 860 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Stability Enhancing Two step Method for One dimensional Two phase Flow written by John H. Mahaffy and published by . This book was released on 1979 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modelling and Experimentation in Two Phase Flow written by Volfango Bertola and published by CISM International Centre for Mechanical Sciences. This book was released on 2003 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is an up-to-date review of recent advances in the study of two-phase flows, with focus on gas-liquid flows, liquid-liquid flows, and particle transport in turbulent flows. The book is divided into several chapters, which after introducing basic concepts lead the reader through a more complex treatment of the subjects. The reader will find an extensive review of both the older and the more recent literature, with abundance of formulas, correlations, graphs and tables. A comprehensive (though non exhaustive) list of bibliographic references is provided at the end of each chapter. The volume is especially indicated for researchers who would like to carry out experimental, theoretical or computational work on two-phase flows, as well as for professionals who wish to learn more about this topic.
Download or read book Closure Relations of the One dimensional Two fluid Model for the Simulation of Slug Flows written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Interface Stability of Vertical Two fluid Distinct phase Flows written by Charles Gordon Hodge (III.) and published by . This book was released on 1966 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book On the Formulation and Numerical Evaluation of a Set of Two phase Flow Equations Modelling the Cooldown Process written by Stephen Jarvis and published by . This book was released on 1965 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Stability of Two phase Flow Over a Swept wing written by Adrian V. Coward and published by . This book was released on 1994 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability of Finite Difference Approximations of Two Fluid Two Phase Flow Equations written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: It is well known that the basic single pressure, two fluid model for two phase flow has complex characteristics and is dynamically unstable. Nevertheless, common nuclear reactor thermal-hydraulics codes use variants of this model for reactor safety calculations. In these codes, the non-physical instabilities of the model may be damped by the numerical method and/or additional momentum interchange terms. Both of these effects are investigated using the linearized Von Neumann stability analysis. The stability of the semi-implicit method is of primary concern, because of its computational efficiency and popularity. It is shown that there is likely no completely stable numerical method, including fully implicit methods, for the basic single pressure model. Additionally, the momentum interchange terms commonly added to the basic single pressure model do not result in stable numerical methods for all the physically interesting reference conditions. Although practical stable approximations may be realized on a coarse computational grid, it is concluded that the assumption of instantaneously equilibrated phasic pressures must be relaxed in order to develop a generally stable numerical solution of a two fluid model. The numerical stability of the semi-implicit discretization of the true two pressure models of Ransom and Hicks, and Holm and Kupershmidt is analyzed. The semi-implicit discretization of these models, which possess real characteristics, are found to be numerically stable as long as certain convective limits are satisfied. Based on the form of these models, the general form of a numerically stable, basic two pressure model is proposed. The evolution equation required for closure is a volume fraction transport equation, which may possibly be determined based on void wave propagation considerations. 43 refs., 22 figs., 3 tabs.
Download or read book Statistical Hydrodynamic Models for Developed Mixing Instability Flows written by Antoine Llor and published by Springer Science & Business Media. This book was released on 2005-12-23 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Part textbook, part exploratory work, this book aims to raise the awareness of students, physicists, and engineers in turbulence on the modeling of gravitationally induced turbulent mixing flows as produced, for instance, by Rayleigh-Taylor instabilities. The discussion is centered on the differences between single-fluid and two-fluid approaches, and it is illustrated with a 0D analysis of two specific elementary models in common use. Important deviations are shown to appear on many features, among others the prominence of directed energy, the simultaneous restitution of test cases, the responses to variable acceleration and shocks, and the behavior of various length scales.
Download or read book On Stability of Solutions to the Two fluid Models for Dispersed Two phase Flow written by Reynir Levi Gudmundsson and published by . This book was released on 2002 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability Analysis of Implicit Multi fluid Schemes written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new implicit method has been developed for solving the viscous full multi-fluid equations, which incorporate transport and generation of mass and momentum for each component present in a system. This work presents stability analysis and application of the important full multi-fluid system in a fully implicit algorithm. The stability analyses presented demonstrate the performance of several iterative schemes applied to the solution of the linearized systems which arise in the formulation. These include block Jacobi and symmetric block Gauss-Siedel schemes with various preconditioners applied. A hierarchy of increasing physical complexity is pursued, starting with one-dimensional, two-fluid systems with minimum inter-field dynamic coupling and no mass transfer. These analyses are extended to systems employing physically important inter-field forces (drag, turbulence dispersion, virtual mass). The effects of mass transfer, multiple fields (i.e., n[phi]> 2) and multiple dimensions are also considered. A two-fluid Navier-Stokes code has been developed based on this new scheme. Results are presented which verify the validity of the stability analyses presented for the coupled scheme. Multi-phase flows which require full multi-fluid modeling arise in a wide class of engineering problems, where non-equilibrium dynamics and thermodynamics of the interfaces between constituents play important roles in the evolution of the ensemble averaged mean flow. Examples include cyclone separators, two-phase flow in jets and curved ducts and boiling flow in heat exchangers.
Download or read book Characteristics and Stability Analyses of Transient One dimensional Two Phase Flow Equations and Their Finite Difference Approximations written by and published by . This book was released on 1975 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Equation systems describing one-dimensional, transient, two-phase flow with separate continuity, momentum, and energy equations for each phase are classified by use of the method of characteristics. Little attempt is made to justify the physics of these equations. Many of the equation systems possess complex-valued characteristics and hence, according to well-known mathematical theorems, are not well-posed as initial-value problems (IVPs). Real-valued characteristics are necessary but not sufficient to insure well-posedness. In the absence of lower order source or sink terms (potential type flows), which can affect the well-posedness of IVPs, the complex characteristics associated with these two-phase flow equations imply unbounded exponential growth for disturbances of all wavelengths. Analytical and numerical examples show that the ill-posedness of IVPs for the two-phase flow partial differential equations which possess complex characteristics produce unstable numerical schemes. These unstable numerical schemes can produce apparently stable and even accurate results if the growth rate resulting from the complex characteristics remains small throughout the time span of the numerical experiment or if sufficient numerical damping is present for the increment size used. Other examples show that clearly nonphysical numerical instabilities resulting from the complex characteristics can be produced. These latter types of numerical instabilities are shown to be removed by the addition of physically motivated differential terms which eliminate the complex characteristics. (auth).
Download or read book Mathematical Modeling of Disperse Two Phase Flows written by Christophe Morel and published by Springer. This book was released on 2016-10-15 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, amongst others. This book is highly suitable for students in the subject area, but may also be a useful reference text for more advanced scientists and engineers.
Download or read book Two dimensional Flow Modeling written by Robert C. MacArthur and published by . This book was released on 1982 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability of Finite Difference Approximations of Two Fluid Two Phase Flow Equations written by Mark Alan Holmes and published by . This book was released on 1995 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:
