Dilute Turbulent Gas-solid Flow with Particle Interactions and Turbulence Modulation PDF Download

Author: Eduardo Jose Bolio
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description

Author: Mark Pepple
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
The turbulence of both phases becomes increasingly flat near the center of the pipe with increasing Re and solids concentration. This is in agreement with the flat profiles of both fluid and solid turbulence in inertia-dominated gas-solid flows. In general, the 0.5 mm particles damp the fluid turbulence while the 1.0 mm and 1.5 mm particles are either neutral or enhance the turbulence. These data give insight into the fluid-particle interactions over a wide range of flow conditions.

Author: Cheng Peng
Publisher:
ISBN: 9780438241909
Category :
Languages : en
Pages : 231

View

Book Description
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.

Author: Aleksei Y. Varaksin
Publisher: Springer Science & Business Media
ISBN: 3540680543
Category : Science
Languages : en
Pages : 204

View

Book Description
This book presents results of experimental and theoretical studies of "gas-solid particles" turbulent two-phase flows. It analyzes the characteristics of heterogeneous flows in channels (pipes), as well as those in the vicinity of the critical points of bodies subjected to flow and in the boundary layer developing on their surface. Coverage also treats in detail problems of physical simulation of turbulent gas flows which carry solid particles.

Author: Ying Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 134

View

Book Description
Many particle-laden flows in engineering applications involve turbulent gas flows. Modeling multiphase turbulent flows is an important research topic with applications in fluidized beds and particle conveying. A predictive multiphase turbulence model can help CFD codes to be more useful for engineering applications, such as the scale-up in the design of circulating fluidized combustor and coal gasifications. It is reasonable to expect that multiphase turbulence models should at least satisfy some basic modeling and performance criteria and give reasonable predictions for the canonical problems in dilute particle-laden turbulent flows. In this research, a comparative assessment of predictions from Simonin and Ahmadi's turbulence models is performed with direct numerical simulation (DNS) for two canonical problems in particle-laden turbulent flows. Based on the comparative assessment, some criteria and the areas for model improvement are identified: (i) model for interphase TKE transfer, especially the time scale of interphase TKE transfer, and (ii) correct prediction of TKE evolution with variation of particle Stokes number. Some deficiencies that are identified in the Simonin and Ahmadi models limit the applicability. A new multiphase turbulence model, the Equilibration of Energy Model (EEM), is proposed in this work. In EEM, a multiscale interaction time scale is proposed to account for the interaction of a particle with a range of eddy sizes. EEM shows good agreement with the DNS results for particle-laden istropic turbulence. For particle-laden homogeneous shear flows, model predictions from EEM can be further improved if the dissipation rate in fluid phase is modeled with more accuracy. This new time scale is incorporated in the interphase TKE transfer terms of the Simonin and Ahmadi models. For canonical problems in particle-laden turbulent flows, this time scale improves the predictions from these two models. Although EEM is a simple model, it has a clear physical interpretation and gives reasonable predictions for two canonical problems in particle-laden turbulent flows. It can be a useful engineering tool for CFD calculations of gas-solid two phase flows.

Author: Leonid I. Zaichik
Publisher: John Wiley & Sons
ISBN: 3527626263
Category : Science
Languages : en
Pages : 318

View

Book Description
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.

Author: Rouholluh Shokri
Publisher:
ISBN:
Category : Granular flow
Languages : en
Pages : 271

View

Book Description
The turbulent motion of particles and their interactions with the turbulence of the carrier phase make a complex system. Hence understanding the physics and consequently developing a well-stablished model becomes very difficult. With insufficient computational power to numerically resolve all the scales of these kinds of flows using Direct Numerical Simulation (DNS), experimental investigations still remain the sole source of information for these systems, especially at high Reynolds numbers. Lack of comprehensive experimental data for solid-liquid flows as well as limitation of the existing experimental data to low Reynolds numbers are the motivations for this investigation. The main goal of this research is to experimentally investigate solid-liquid turbulent flows in a vertical pipe and provide some insight into these flows, especially for an extended range of Reynolds numbers. To fulfil the abovementioned goal, a 50.6 mm vertical pipe loop was constructed and dilute mixtures of water and glass beads were used. The glass bead diameters were 0.5, 1 and 2 mm and the volumetric concentration ranged from 0.05 to 1.6% depending on the particle size. The experiments were performed at three Reynolds numbers: 52 000, 100 000, and 320 000 which are referred to here as low, medium and high Re. A combined technique of Particle Image/Tracking velocimetry (PIV/PTV) was employed to perform the measurements. The measured and reported flow parameters are: mean axial velocity profiles of the solid and liquid phases, particle distribution over the cross section of the pipe (concentration profile), particle-particle interaction index, axial and radial fluctuating velocity profiles of both phases, and shear Reynolds stress and its correlation for both phases. The relatively wide range of different parameters tested here provided interesting and novel experimental results. The results showed that the turbulent motions of the fluid and particles and their interactions varied drastically as Re increased. Moreover, the behavior of the particles and their impact on the fluid can be very different in the axial and radial directions. The results proved that the well-known criteria for axial turbulence modulation of the carrier phase could not perform well at high Reynolds numbers and their performance was much poorer for the radial direction modulation. The new data sets provided by the present study offer valuable insight into the processes or phenomena heavily influenced by turbulence, such as pipe wear rate, oil sand lump ablation, and pressure loss/energy consumption. In addition, these data sets can be utilised to evaluate and improve the existing correlations and models for particulate turbulent flows. In addition, a quantitative analysis of the particle and carrier phase turbulence modulation was conducted. Particle turbulence intensities in present study were combined with other experimental data from the literature to propose a novel empirical correlation was proposed for axial particle turbulence in solid-liquid flows. Moreover, a novel empirical criterion/correlation was proposed to classify the carrier phase turbulence attenuation/augmentation phenomenon for both gas-solid and liquid-solid flows by employing a wide range of data from the present study and from the literature. Two major improvements of the proposed criterion/correlation are the prediction of the onset and the magnitude of the carrier phase turbulence augmentation. These new empirical correlations will assist the researchers in this field to effectively design and coordinate their experimental or numerical efforts.

Author: Shankar Subramaniam
Publisher: Academic Press
ISBN: 0323901344
Category : Science
Languages : en
Pages : 588

View

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: Richard W. Johnson
Publisher: CRC Press
ISBN: 1439849579
Category : Science
Languages : en
Pages : 1544

View

Book Description
Handbook of Fluid Dynamics offers balanced coverage of the three traditional areas of fluid dynamics—theoretical, computational, and experimental—complete with valuable appendices presenting the mathematics of fluid dynamics, tables of dimensionless numbers, and tables of the properties of gases and vapors. Each chapter introduces a different fluid dynamics topic, discusses the pertinent issues, outlines proven techniques for addressing those issues, and supplies useful references for further research. Covering all major aspects of classical and modern fluid dynamics, this fully updated Second Edition: Reflects the latest fluid dynamics research and engineering applications Includes new sections on emerging fields, most notably micro- and nanofluidics Surveys the range of numerical and computational methods used in fluid dynamics analysis and design Expands the scope of a number of contemporary topics by incorporating new experimental methods, more numerical approaches, and additional areas for the application of fluid dynamics Handbook of Fluid Dynamics, Second Edition provides an indispensable resource for professionals entering the field of fluid dynamics. The book also enables experts specialized in areas outside fluid dynamics to become familiar with the field.

Author: Bart Merci
Publisher: Springer Science & Business Media
ISBN: 9400714092
Category : Technology & Engineering
Languages : en
Pages : 180

View

Book Description
This book reflects the outcome of the 1st International Workshop on Turbulent Spray Combustion held in 2009 in Corsica (France). The focus is on reporting the progress of experimental and numerical techniques in two-phase flows, with emphasis on spray combustion. The motivation for studies in this area is that knowledge of the dominant phenomena and their interactions in such flow systems is essential for the development of predictive models and their use in combustor and gas turbine design. This necessitates the development of accurate experimental methods and numerical modelling techniques. The workshop aimed at providing an opportunity for experts and young researchers to present the state-of-the-art, discuss new developments or techniques and exchange ideas in the areas of experimentations, modelling and simulation of reactive multiphase flows. The first two papers reflect the contents of the invited lectures, given by experts in the field of turbulent spray combustion. The first concerns computational issues, while the second deals with experiments. These lectures initiated very interesting and interactive discussions among the researchers, further pursued in contributed poster presentations. Contributions 3 and 4 focus on some aspects of the impact of the interaction between fuel evaporation and combustion on spray combustion in the context of gas turbines, while the final article deals with the interaction between evaporation and turbulence.