Fluent Ppt

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INTRODUCTION TO COMPUTATIONAL

FLUID DYNAMICS

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Fluid dynamics is a discipline that encompasses a wide variety of

scientific and technical systems.

Historically, fluid dynamics analyses have been carried out by

means of analytical approximations with a narrow range of

applicability and of expensive experimental studies.

The numerical integration of the fluid dynamics governing

equations allows us to solve complex flow problems with ease.

Currently, there exists both open source and commercial general-

purpose models that may deal with a wide variety of problems.

These software packages are called CFD (Computational Fluid

Dynamics) solvers and are rapidly spreading in many disciplines.

Introduction

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What is CFD?

Computational Fluid Dynamics (CFD) is the science of predicting fluid

flow, heat transfer, mass transfer, chemical reactions, and related

phenomena by solving mathematical equations that represent physical

laws, using a numerical process.

The result of CFD analyses is relevant engineering data:

conceptual studies of new designs

detailed product development

troubleshooting

Redesign

CFD analysis complements testing and experimentation.

Reduces the total effort required in the laboratory.

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Why CFD?

Experimental methods are costly

Data available throughout the domain

Scale up issues are eliminated

Complex problems can be addressed.

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CFD capabilities

Steady state and transient flows

Laminar and turbulent flows

Compressible flows

Heat transfer

Non Newtonian flows

Variable boundary conditions

Rotating frame of reference

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Components of CFD The main stages in a CFD simulation are:

1. Preprocessing

This initial step consists of defining the problem geometry, discretize it in

small control volumes (mesh) and determine the suitable boundary conditions

as well as initial conditions

2. Solver

This step refers to the code execution and includes the monitorization of the

solution..

3. Post processing

This is the final step where we analyze the results obtained from the

simulation.

Some commercial meshing packages

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Gambit

Ansys-ICEM

Hyper mesh

Pointwise

ADINA

NISA

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Some commercial CFD packages

Ansys-Fluent

CFX

Star CCM

COMSOL

FLUIDyn

ANSYS - AQWA

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Tools:

Gambit - preprocessor

To create the geometry

Fluent - solver manager

To solve the flow equations and

post processing

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Creating the geometry

Meshing the geometry

Specifying the boundary conditions

Exporting the mesh

What can you do with Gambit?

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Flow problems in 2D and 3D

Compressible & Incompressible

Steady state and time dependent

Variety of material properties

Complex physics & chemistry

Inviscid, viscous, and turbulence models

Multiple and non-inertial reference frames

What can you do with FLUENT ?

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GAMBIT AND FLUENT

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A single, integrated preprocessor for CFD

analysis:

Geometry construction and import

Using ACIS solid modeling capabilities

Using STEP, Parasolid, IGES, etc. import

Cleanup and modification of imported data

Mesh generation for all Fluent solvers

Structured and Unstructured hexahedral, tetrahedral,

pyramid, and prisms.

Mesh quality examination

Boundary zone assignment

What is Gambit?

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General sequence of operations Geometry Creation (ACIS, STEP, Parasolid, IGES

or Mesh import )

Create full geometry

Decompose into mesh-able sections

Meshing

Local meshing: Edge and Boundary layers

Global meshing: Face and/or Volume

Mesh examination

Operation

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GAMBIT directory and files When GAMBIT starts up, it creates a directory called GAMBIT.#

# = the process number

It also creates a lock file, ident.lok, in the working directory

ident.lok prevents any user from starting up another session

using the same identifier in the same directory. If the code

crashes, this file needs to be manually removed.

Three files are created inside this directory

ident.dbs =

jou =

trn =

the database. All information will be saved

in this

file. This file is NOT retrievable upon a

crash

the journal file. This file is directly

accessible from

the Run journal form

the transcript file. Output from GAMBIT

Files in Gambit

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Journal File:

Executable list of Gambit commands

Created automatically by Gambit from GUI and TUI.

Can be edited or created externally with text editor.

Journals are small - easy to transfer, e-mail, store

Uses:

Can be parameterized, comments can be added

Easy recovery from a crash or power loss

edit existing commands to create new ones

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Main Menu

bar

Global Control

Operation toolpad

Command line Description

window

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Vertex

Edge

Face

Volume

Group

Boundary Layer

Edge

Face

Volume

Group

Boundary Types

Boundary Entity

Continuum

Types

Continuum

Entity

Coordinate

Systems

Sizing Function

G/Turbo

User-Defined Tools

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How will you isolate a piece

of the complete physical

system?

Where will the

computational domain begin

and end?

Do you have boundary

condition information at

these boundaries?

Can the boundary condition

types accommodate that

information?

Problem Identification and Pre-

Processing

1. Define your modeling goals.

2. Identify the domain you will model.

3. Design and create the grid

Gas

Riser

Cyclon

e

L-valve

Gas

Defining the Model

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What results are you looking for, and how will they

be used?

What are your modeling options?

What physical models will need to be included in your

analysis?

What simplifying assumptions can you make?

Do you require a unique modeling capability?

User-defined functions (written in C) in FLUENT 6

What degree of accuracy is required?

How quickly do you need the results?


Processing



3. Design and create the grid.

Defining the Model

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Can you use a quad/hex grid or should you

use a tri/tet grid or hybrid grid?

How complex is the geometry and

flow?

Will you need a non-conformal

interface?

What degree of grid resolution is required

in each region of the domain?

Is the resolution sufficient for the

geometry?

Can you predict regions with high

gradients?

Will you use adaption to add

resolution?

Do you have sufficient computer

memory?

How many cells are required?

How many models will be used?

triangle quadrilateral

tetrahedro

n

pyramid prism/wedge

hexahedro

n


Processing



3. Design and create the grid.

Defining the Mesh

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For a given problem, you will need to:

Select appropriate physical models.

Turbulence, combustion,

multiphase, etc.

Define material properties.

Fluid

Solid

Mixture

Prescribe operating conditions.

Prescribe boundary conditions at all

boundary zones.

Provide an initial solution.

Set up solver controls.

Set up convergence monitors.

Solver Execution

4. Set up the numerical model.

5. Compute and monitor the

solution.

Solving initially in 2D will

provide valuable experience

with the models and solver

settings for your problem in

a short amount of time.

Defining the solver - FLUENT

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The discretized conservation equations are

solved iteratively.

A number of iterations are usually required to reach a

converged solution.

Convergence is reached when:

Changes in solution variables from one iteration

to the next are negligible.

Residuals provide a mechanism to help

monitor this trend.

Overall property conservation is achieved.

The accuracy of a converged solution is dependent

upon:

Appropriateness and accuracy of physical models.

Grid resolution and independence

Problem setup

Solver Execution

4. Set up the numerical model.

5. Compute and monitor the

solution.

A converged and grid-

independent solution on a

well-posed problem will

provide useful

engineering results!

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Examine the results to review solution and

extract useful data.

Visualization Tools can be used to answer

such questions as:

What is the overall flow pattern?

Is there separation?

Where do shocks, shear layers, etc.

form?

Are key flow features being resolved?

Numerical Reporting Tools can be used to

calculate quantitative results:

Forces and Moments

Average heat transfer coefficients

Surface and Volume integrated

quantities

Flux Balances

Post-Processing

6. Examine the results.

7. Consider revisions to the model.

Examine results to ensure

property conservation and

correct physical behavior.

High residuals may be

attributable to only a few

cells of poor quality.

Visualizing the Results

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THANK YOU

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