Fluent用户手册

The

FLUENT

User's Guide tells you what you need to know to use

FLUENT

. At the end of the User's Guide,

you will find a Reference Guide, a nomenclature list, a bibliography, and an index.

!!

Under U.S. and international copyright law, Fluent is unable to distribute copies of the papers listed in the

bibliography, other than those published internally by Fluent. Please use your library or a document delivery

service to obtain copies of copyrighted papers.

A brief description of what's in each chapter follows:

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Chapter

1

, Getting Started, describes the capabilities of

FLUENT

and the way in which it interacts with

other Fluent Inc. and third-party programs. It also advises you on how to choose the appropriate solver

formulation for your application, gives an overview of the problem setup steps, and presents a sample

session that you can work through at your own pace. Finally, this chapter provides information about

accessing the

FLUENT

manuals on CD-ROM or in the installation area.

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Chapter

2

, User Interface, describes the mechanics of using the graphical user interface, the text interface,

and the on-line help. It also provides instructions for remote and batch execution. (See the separate

Text

Command List

for information about specific text interface commands.)

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Chapter

3

, Reading and Writing Files, contains information about the files that

FLUENT

can read and

write, including hardcopy files.

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Chapter

4

, Unit Systems, describes how to use the standard and custom unit systems available

in

FLUENT

.

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Chapter

5

, Reading and Manipulating Grids, describes the various sources of computational grids and

explains how to obtain diagnostic information about the grid and how to modify it by scaling, translating,

and other methods. This chapter also contains information about the use of non- conformal grids.

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Chapter

6

, Boundary Conditions, explains the different types of boundary conditions available

in

FLUENT

, when to use them, how to define them, and how to define boundary profiles and volumetric

sources and fix the value of a variable in a particular region. It also contains information about porous

media and lumped parameter models.

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Chapter

7

, Physical Properties, explains how to define the physical properties of materials and the

equations that

FLUENT

uses to compute the properties from the information that you input.

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Chapter

8

, Modeling Basic Fluid Flow, describes the governing equations and physical models used

by

FLUENT

to compute fluid flow (including periodic flow, swirling and rotating flows, compressible

flows, and inviscid flows), as well as the inputs you need to provide to use these models.

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Chapter

9

, Modeling Flows in Moving Zones, describes the use of single rotating reference frames,

multiple moving reference frames, mixing planes, and sliding meshes in

FLUENT

.

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Chapter

10

, Modeling Turbulence, describes

FLUENT

's models for turbulent flow and when and how to

use them.

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Chapter

11

, Modeling Heat Transfer, describes the physical models used by

FLUENT

to compute heat

transfer (including convective and conductive heat transfer, natural convection, radiative heat transfer,

and periodic heat transfer), as well as the inputs you need to provide to use these models.

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Chapter

12

, Introduction to Modeling Species Transport and Reacting Flows, provides an overview of

the models available in

FLUENT

for species transport and reactions, as well as guidelines for selecting

an appropriate model for your application.

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Chapter

13

, Modeling Species Transport and Finite-Rate Chemistry, describes the finite-rate chemistry

models in

FLUENT

and how to use them. This chapter also provides information about modeling species

transport in non-reacting flows.

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Chapter

14

, Modeling Non-Premixed Combustion, describes the non-premixed combustion model and

how to use it. This chapter includes details about using

prePDF

.

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Chapter

15

, Modeling Premixed Combustion, describes the premixed combustion model and how to use

it.

Chapter

16

, Modeling Partially Premixed Combustion, describes the partially premixed combustion

model and how to use it.

Chapter

17

, Modeling Pollutant Formation, describes the models for the formation of NOx and soot and

how to use them.

Chapter

18

, Introduction to Modeling Multiphase Flows, provides an overview of the models for

multiphase flow (including the discrete phase, VOF, mixture, and Eulerian models), as well as guidelines

for selecting an appropriate model for your application.

Chapter

19

, Discrete Phase Models, describes the discrete phase models available in

FLUENT

and how

to use them.

Chapter

20

, General Multiphase Models, describes the general multiphase models available

in

FLUENT

(VOF, mixture, and Eulerian) and how to use them.

Chapter

21

, Modeling Solidification and Melting, describes

FLUENT

's model for solidification and

melting and how to use it.

Chapter

22

, Using the Solver, describes the

FLUENT

solvers and how to use them.

Chapter

23

, Grid Adaption, explains the solution-adaptive mesh refinement feature in

FLUENT

and how

to use it.

Chapter

24

, Creating Surfaces for Displaying and Reporting Data, explains how to create surfaces in the

domain on which you can examine

FLUENT

solution data.

Chapter

25

, Graphics and Visualization, describes the graphics tools that you can use to examine

your

FLUENT

solution.

Chapter

26

, Alphanumeric Reporting, describes how to obtain reports of fluxes, forces, surface integrals,

and other solution data.

Chapter

27

, Field Function Definitions, defines the flow variables that appear in the variable selection

drop-down lists in

FLUENT

panels, and tells you how to create your own custom field functions.

Chapter

28

, Parallel Processing, explains the parallel processing features in

FLUENT

and how to use

them. This chapter also provides information about partitioning your grid for parallel processing.

18. Introduction to Modeling Multiphase Flows

A large number of flows encountered in nature and technology are a mixture of phases. Physical phases of matter

are gas, liquid, and solid, but the concept of phase in a multiphase flow system is applied in a broader sense. In

multiphase flow, a phase can be defined as an identifiable class of material that has a particular inertial response to

and interaction with the flow and the potential field in which it is immersed. For example, different- sized solid

particles of the same material can be treated as different phases because each collection of particles with the same

size will have a similar dynamical response to the flow field.

This chapter provides an overview of multiphase modeling in FLUENT, and Chapters 19 and 20 provide details

about the multiphase models mentioned here. Chapter 21 provides information about melting and solidification.

18.1 Multiphase Flow Regimes

Multiphase flow can be classified by the following regimes, grouped into four categories:

gas-liquid or liquid-liquid flows

bubbly flow: discrete gaseous or fluid bubbles in a continuous fluid

droplet flow: discrete fluid droplets in a continuous gas

slug flow: large bubbles in a continuous fluid

stratified/free-surface flow: immiscible fluids separated by a clearly-defined interface

gas-solid flows

particle- laden flow: discrete solid particles in a continuous gas

pneumatic transport: flow pattern depends on factors such as solid loading, Reynolds numbers, and particle

properties. Typical patterns are dune flow, slug flow, packed beds, and homogeneous flow.

fluidized beds: consist of a vertical cylinder containing particles where gas is introduced through a distributor. The

gas rising through the bed suspends the particles. Depending on the gas flow rate, bubbles appear and rise through

the bed, intensifying the mixing within the bed.

liquid-solid flows

slurry flow: transport of particles in liquids. The fundamental behavior of liquid-solid flows varies with the

properties of the solid particles relative to those of the liquid. In slurry flows, the Stokes number (see

Equation 18.4-4) is normally less than 1. When the Stokes number is larger than 1, the characteristic of the flow

is liquid- solid fluidization.

hydrotransport: densely-distributed solid particles in a continuous liquid

sedimentation: a tall column initially containing a uniform dispersed mixture of particles. At the bottom, the

particles will slow down and form a sludge layer. At the top, a clear interface will appear, and in the middle a

constant settling zone will exist.

three-phase flows (combinations of the others listed above)

Each of these flow regimes is illustrated in Figure 18.1.1.

Figure 18.1.1: Multiphase Flow Regimes

18.2 Examples of Multiphase Systems

Specific examples of each regime described in Section 18.1 are listed below:

Bubbly flow examples: absorbers, aeration, air lift pumps, cavitation, evaporators, flotation, scrubbers

Droplet flow examples: absorbers, atomizers, combustors, cryogenic pumping, dryers, evaporation, gas cooling,

scrubbers

Slug flow examples: large bubble motion in pipes or tanks

Stratified/free-surface flow examples: sloshing in offshore separator devices, boiling and condensation in nuclear

reactors

Particle-laden flow examples: cyclone separators, air classifiers, dust collectors, and dust-laden environmental

flows

Pneumatic transport examples: transport of cement, grains, and metal powders

Fluidized bed examples: fluidized bed reactors, circulating fluidized beds

Slurry flow examples: slurry transport, mineral processing

Hydrotransport examples: mineral processing, biomedical and physiochemical fluid systems

Sedimentation examples: mineral processing

18.3 Approaches to Multiphase Modeling