Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- 1 Introduction: A computational approach to multiphase flow
- 2 Direct numerical simulations of finite Reynolds number flows
- 3 Immersed boundary methods for fluid interfaces
- 4 Structured grid methods for solid particles
- 5 Finite element methods for particulate flows
- 6 Lattice Boltzmann models for multiphase flows
- 7 Boundary integral methods for Stokes flows
- 8 Averaged equations for multiphase flow
- 9 Point-particle methods for disperse flows
- 10 Segregated methods for two-fluid models
- 11 Coupled methods for multifluid models
- References
- Index
2 - Direct numerical simulations of finite Reynolds number flows
Published online by Cambridge University Press: 07 December 2009
- Frontmatter
- Contents
- Preface
- Acknowledgments
- 1 Introduction: A computational approach to multiphase flow
- 2 Direct numerical simulations of finite Reynolds number flows
- 3 Immersed boundary methods for fluid interfaces
- 4 Structured grid methods for solid particles
- 5 Finite element methods for particulate flows
- 6 Lattice Boltzmann models for multiphase flows
- 7 Boundary integral methods for Stokes flows
- 8 Averaged equations for multiphase flow
- 9 Point-particle methods for disperse flows
- 10 Segregated methods for two-fluid models
- 11 Coupled methods for multifluid models
- References
- Index
Summary
In this chapter and the following three, we discuss numerical methods that have been used for direct numerical simulations of multiphase flow. Although direct numerical simulations, or DNS, mean slightly different things to different people, we shall use the term to refer to computations of complex unsteady flows where all continuum length and time scales are fully resolved. Thus, there are no modeling issues beyond the continuum hypothesis. The flow within each phase and the interactions between different phases at the interface between them are found by solving the governing conservation equations, using grids that are finer and time steps that are shorter than any physical length and time scale in the problem.
The detailed flow field produced by direct numerical simulations allows us to explore the mechanisms governing multiphase flows and to extract information not available in any other way. For a single bubble, drop, or particle, we can obtain integrated quantities such as lift and drag and explore how they are affected by free stream turbulence, the presence of walls, and the unsteadiness of the flow. In these situations it is possible to take advantage of the relatively simple geometry to obtain extremely accurate solutions over a wide range of operating conditions. The interactions of a few bubbles, drops, or particles is a more challenging computation, but can be carried out using relatively modest computational resources. Such simulations yield information about, for example, how bubbles collide or whether a pair of buoyant particles, rising freely through a quiescent liquid, orient themselves in a preferred way. Computations of one particle can be used to obtain information pertinent to modeling of dilute multiphase flows, and studies of a few particles allow us to assess the importance of rare collisions.
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- Computational Methods for Multiphase Flow , pp. 19 - 36Publisher: Cambridge University PressPrint publication year: 2007