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Author: Publisher: ISBN: Category : Languages : en Pages : 44
Book Description
Earlier work of Sinclair and Jackson which treats the laminar flow of gas-solid suspensions is extended to model dilute turbulent flow. The random particle motion, often exceeding the turbulent fluctuations in the gas, is obtained using a model based on kinetic theory of granular materials. A two-equation low Reynolds number turbulence model is, modified to account for the presence of the dilute particle phase. Comparisons of the model predictions with available experimental data for the mean and fluctuating velocity profiles for both phases indicate that the resulting theory captures many of the flow features observed in the pneumatic transport of large particles. The model predictions did not manifest an extreme sensitivity to the degree of inelasticity in the particle-particle collisions for the range of solid loading ratios investigated.
Author: Publisher: ISBN: Category : Languages : en Pages : 44
Book Description
Earlier work of Sinclair and Jackson which treats the laminar flow of gas-solid suspensions is extended to model dilute turbulent flow. The random particle motion, often exceeding the turbulent fluctuations in the gas, is obtained using a model based on kinetic theory of granular materials. A two-equation low Reynolds number turbulence model is, modified to account for the presence of the dilute particle phase. Comparisons of the model predictions with available experimental data for the mean and fluctuating velocity profiles for both phases indicate that the resulting theory captures many of the flow features observed in the pneumatic transport of large particles. The model predictions did not manifest an extreme sensitivity to the degree of inelasticity in the particle-particle collisions for the range of solid loading ratios investigated.
Author: Publisher: ISBN: Category : Languages : en Pages : 18
Book Description
The successful prediction of particle-laden, turbulent flows relies heavily on the representation of turbulence in the gas phase. Several types of turbulence models for single-phase gas flow have been developed which compare reasonably well with experimental data. In the present work, a l̀̀ow-Reynolds̀̀ k-?, closure model is chosen to describe the Reynolds stresses associated with gas-phase turbulence. This closure scheme, which involves transport equations for the turbulent kinetic energy and its dissipation rate, is valid in the turbulent core as well as the viscous sublayer. Several versions of the low-Reynolds k-? closure are documented in the literature. However, even those models which are similar in theory often differ considerably in their quantitative and qualitative predictions, making the selection of such a model a difficult task. The purpose of this progress report is to document our findings on the performance of ten different versions of the low-Reynolds k-? model on predicting fully developed pipe flow. The predictions are compared with the experimental data of Schildknecht, et al. (1979). With the exception of the model put forth by Hoffman (1975), the predictions of all the closures show reasonable agreement for the mean velocity profile. However, important quantitative differences exist for the turbulent kinetic energy profile. In addition, the predicted eddy viscosity profile and the wall-region profile of the turbulent kinetic energy dissipation rate exhibit both quantitative and qualitative differences. An effort to extend the present comparisons to include experimental measurements of other researchers is recommended in order to further evaluate the performance of the models.
Author: Publisher: ISBN: Category : Languages : en Pages : 29
Book Description
An Eulerian two-fluid mathematical model is considered for the flow prediction of gas-particle systems. The model expands on the Sinclair and Jackson model by recognizing a turbulent continuous phase. Both the gas- and the particle-phase velocity fields are composed of by a mean and a fluctuating component, and the important physical phenomena arising from the interaction of these components are included in the model. The gas turbulence is modeled by a single-phase closure, namely the k-{var_epsilon} low Reynolds model by Myong and Kasagi, modified to account for the presence of a dilute particle phase. The solid phase is considered as a rapid granular flow; hence, a closure based on the kinetic-theory analogy is used for the description of the stresses associated with this phase. Along with the relation between the fluxes of both phases and the pressure drop, the model is capable of predicting features related to the local flow structure, such as the mean and fluctuating velocity components and the concentration of both phases. In this report, the model is applied to the case of steady, fully developed flow in a vertical cylindrical pipe. An extensive comparison of the model predictions with experimental data is included. The sensitivity of the model predictions to the properties describing the particle collisions is also explored.
Author: Shankar Subramaniam Publisher: Academic Press ISBN: 0323901344 Category : Science Languages : en Pages : 588
Book Description
Modelling Approaches and Computational Methods for Particle-laden Turbulent Flows introduces the principal phenomena observed in applications where turbulence in particle-laden flow is encountered while also analyzing the main methods for analyzing numerically. The book takes a practical approach, providing advice on how to select and apply the correct model or tool by drawing on the latest research. Sections provide scales of particle-laden turbulence and the principal analytical frameworks and computational approaches used to simulate particles in turbulent flow. Each chapter opens with a section on fundamental concepts and theory before describing the applications of the modelling approach or numerical method. Featuring explanations of key concepts, definitions, and fundamental physics and equations, as well as recent research advances and detailed simulation methods, this book is the ideal starting point for students new to this subject, as well as an essential reference for experienced researchers. Provides a comprehensive introduction to the phenomena of particle laden turbulent flow Explains a wide range of numerical methods, including Eulerian-Eulerian, Eulerian-Lagrange, and volume-filtered computation Describes a wide range of innovative applications of these models
Author: Publisher: ISBN: Category : Languages : en Pages : 22
Book Description
The excellent comparison between the data of Bader et al (1988) and the predictions using the fully-developed flow model of Sinclair and Jackson (1989) have not yet been repeated with any other experimental data set for riser flow. This may be due to the fact that the data sets investigated thus far have reflected gas-solid flow in a developing state (low L/D ratios). In addition, the model of Sinclair and Jackson (1989) neglected gas phase turbulence which should have an effect on the solid concentration distribution. Hence, a dilute, particle-laden, turbulent flow model is developed here. Model predictions highlight the importance of an independent measurement of the specularity factor, an appropriate representation of the kinetic contribution to the total particle phase stress for very low solid loadings in confined flows, and a correct representation of the interaction between the fluctuating velocity components for the two phases.
Author: Publisher: ISBN: Category : Aeronautics Languages : en Pages : 1028
Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author: Dennis Martin Dunn Publisher: ISBN: Category : Computational fluid dynamics Languages : en Pages : 178
Book Description
Conventional fluid dynamics models such as the Navier-Stokes equations are derived for prediction of fluid motion at or near equilibrium, classic examples being the motion of fluids for which inter-molecular collisions are dominant. Flows at equilibrium permit simplifications such as the introduction of viscosity and also lead to solutions that are single-valued. However, many other regimes of interest include "fluids"' far from equilibrium; for example, rarefied gases or particle-laden flows in which the dispersed phase can be comprised of granular solids, droplets, or bubbles. Particle motion in these flows is not typically dominated by collisions and may exhibit significant memory effects; therefore, is often poorly described using continuum, field-based (Eulerian) approaches. Non-equilibrium flows generally lack a straightforward counterpart to viscosity and their multi-valued solutions cannot be represented by most Eulerian methods. This strongly motivates different strategies to address current shortcomings and the novel approach adopted in this work is based on the Conditional Quadrature Method of Moments (CQMOM). In CQMOM, moment equations are derived from the Boltzmann equation using a quadrature approximation of the velocity probability density function (PDF). CQMOM circumvents the drawbacks of current methods and leads to multivariate and multidimensional solutions in an Eulerian frame of reference. In the present work, the discretized PDF is resolved using an adaptive two-point quadrature in three-dimensional velocity space. The method is applied to computation of a series of non-equilibrium flows, ranging from simple two-dimensional test cases to fully-turbulent three-dimensional wall-bounded particle-laden flows. The primary contribution of the present effort is on development, application, and assessment of CQMOM for predicting the key features of dilute particle-laden flows. Statistical descriptors such as mean concentration and mean velocity are in good agreement with previous results, for both collision-less and collisional flows at varying particle Stokes numbers. Turbulent statistics and measures of local accumulation agree less favorably with prior results and identify areas for improvement in the modeling strategy.
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Author: Shankar Subramaniam
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Author: Dennis Martin Dunn
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Author: Ying Xu