Ansys Fluent 12.0 Getting Started Guide: January 2009
Ansys Fluent 12.0 Getting Started Guide: January 2009
Ansys Fluent 12.0 Getting Started Guide: January 2009
0
Getting Started Guide
January 2009
Copyright
c 2009 by ANSYS, Inc.
All Rights Reserved. No part of this document may be reproduced or otherwise used in
any form without express written permission from ANSYS, Inc.
ANSYS, Inc.
Centerra Resource Park
10 Cavendish Court
Lebanon, NH 03766
Contents
Preface 1
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Preface
• The User’s Guide contains detailed information about how to use ANSYS FLUENT,
including information about the user interface, reading and writing files, defining
boundary conditions, setting up physical models, calculating a solution, and ana-
lyzing your results.
• The Theory Guide contains reference information for how the physical models are
implemented in ANSYS FLUENT.
• The Tutorial Guide contains a number of example problems with detailed instruc-
tions, commentary, and postprocessing of results.
• The UDF Manual contains information about writing and using user-defined func-
tions (UDFs).
• The Text Command List provides a brief description of each of the commands in
ANSYS FLUENT’s text interface.
• The following addon module manuals offer additional applications within ANSYS
FLUENT:
– Continuous Fiber Module Manual
– Fuel Cell Modules Manual
– Magnetohydrodynamics (MHD) Module Manual
– Population Balance Module Manual
Typographical Conventions
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Preface
Technical Support
If you encounter difficulties while using ANSYS FLUENT, please first refer to the section(s)
of the manuals containing information on the commands you are trying to use or the
type of problem you are trying to solve. The product documentation is available from
the online help, or from the User Services Center.
If you encounter an error, please write down the exact error message that appeared and
note as much information as you can about what you were doing in ANSYS FLUENT.
Then refer to the following resources available on the User Services Center:
• Installation and System FAQs—a link is available from the main page on the User
Services Center. The FAQs can be searched by word or phrase, and are available
for general installation questions as well as for product questions.
• Known Defects for ANSYS FLUENT—a link is available from the product page.
The defects can be searched by word or phrase, and are listed by categories.
• Online Technical Support—a link is available from the main page on the User
Services Center. From the Online Technical Support Portal page, there is a link to
the Search Solutions & Request Support page, where the solutions can be searched
by word or phrase and where you have the ability to enter a technical support
request.
• Note what you were doing when the problem or error occurred.
• Save a journal or transcript file of the ANSYS FLUENT session in which the problem
occurred. This is the best source that we can use to reproduce the problem and
thereby help to identify the cause.
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Chapter 1. Introduction to ANSYS FLUENT
ANSYS FLUENT is a state-of-the-art computer program for modeling fluid flow, heat
transfer, and chemical reactions in complex geometries.
ANSYS FLUENT is written in the C computer language and makes full use of the flexibil-
ity and power offered by the language. Consequently, true dynamic memory allocation,
efficient data structures, and flexible solver control are all possible. In addition, ANSYS
FLUENT uses a client/server architecture, which allows it to run as separate simultaneous
processes on client desktop workstations and powerful compute servers. This architec-
ture allows for efficient execution, interactive control, and complete flexibility between
different types of machines or operating systems.
ANSYS FLUENT provides complete mesh flexibility, including the ability to solve your
flow problems using unstructured meshes that can be generated about complex geome-
tries with relative ease. Supported mesh types include 2D triangular/quadrilateral, 3D
tetrahedral/hexahedral/pyramid/wedge/polyhedral, and mixed (hybrid) meshes. ANSYS
FLUENT also allows you to refine or coarsen your mesh based on the flow solution.
After a mesh has been read into ANSYS FLUENT, all remaining operations are performed
within ANSYS FLUENT. These include setting boundary conditions, defining fluid prop-
erties, executing the solution, refining the mesh, and postprocessing and viewing the
results.
The ANSYS FLUENT serial solver manages file input and output, data storage, and flow
field calculations using a single solver process on a single computer. ANSYS FLUENT
also uses a utility called cortex that manages ANSYS FLUENT’s user interface and basic
graphical functions. ANSYS FLUENT’s parallel solver allows you to compute a solution
using multiple processes that may be executing on the same computer, or on different
computers in a network.
Parallel processing in ANSYS FLUENT involves an interaction between ANSYS FLUENT,
a host process, and a set of compute-node processes. ANSYS FLUENT interacts with the
host process and the collection of compute nodes using the cortex user interface utility.
Figures 1.0.1 and 1.0.2 illustrate the serial and parallel ANSYS FLUENT architectures.
For more information about ANSYS FLUENT’s parallel processing capabilities, please
refer to the User’s Guide.
All functions required to compute a solution and display the results are accessible in
ANSYS FLUENT through an interactive interface.
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Introduction to ANSYS FLUENT
CORTEX
CORTEX
Data: Data:
Cell Cell
Face FLUENT FLUENT Face
Node MPI MPI Node
Socket
MP
Data: FLUENT FLUENT Data:
Cell MPI MPI Cell
Face Face
Node Node
COMPUTE NODES
Figure 1.0.2: Parallel ANSYS FLUENT Architecture
• Heat transfer, including forced, natural, and mixed convection, conjugate (solid/fluid)
heat transfer, and radiation
• Free surface and multiphase models for gas-liquid, gas-solid, and liquid-solid flows
• Cavitation model
• Porous media with non-isotropic permeability, inertial resistance, solid heat con-
duction, and porous-face pressure jump conditions
• Lumped parameter models for fans, pumps, radiators, and heat exchangers
• Multiple reference frame (MRF) and sliding mesh options for modeling multiple
moving frames
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Introduction to ANSYS FLUENT
ANSYS FLUENT is ideally suited for incompressible and compressible fluid-flow simula-
tions in complex geometries. ANSYS FLUENT’s parallel solver allows you to compute
solutions for cases with very large meshes on multiple processors, either on the same
computer or on different computers in a network. ANSYS, Inc. also offers other solvers
that address different flow regimes and incorporate alternative physical models. Addi-
tional CFD programs from ANSYS, Inc. include ANSYS CFX, Airpak, ANSYS Icepak, and
ANSYS POLYFLOW.
⇓
path\ANSYS Inc\v120\fluent\fluent12.0.x \help\index.htm
where path is the folder in which you have installed ANSYS FLUENT (by default, the
path is C:\Program Files), and x is replaced by the appropriate number for the release
(e.g., 9 for fluent12.0.9).
On UNIX/Linux:
⇓
path/ansys inc/v120/fluent/fluent12.0.x/help/index.htm
where path is the directory in which you have installed ANSYS FLUENT, and x is replaced
by the appropriate number for the release (e.g., 9 for fluent12.0.9).
This will bring up the ANSYS FLUENT documentation “home” page (Figure 1.2.1),
from which you can select the HTML or PDF version of the particular ANSYS FLUENT
manual you want to view. For large manuals, PDF files are provided for the individual
chapters in addition to a single PDF file for the entire manual on the User Services Center
(www.fluentusers.com).
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Introduction to ANSYS FLUENT
Return to Home takes you to the ANSYS FLUENT documentation home page (Fig-
ure 1.2.1).
Previous takes you to the page just before the current one in the manual. Note that
this is not the same function as the “Back” button of your browser.
Up takes you to the first page of the current manual division (chapter or section).
Next takes you to the next page in the manual. Note that this is not the same function
as the “Forward” button of your browser.
Note that these buttons do not necessarily appear on all pages. Sometimes they appear
but are inactive; in such cases they are “grayed out”, as the Previous and Up buttons are
in Figure 1.2.2.
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Introduction to ANSYS FLUENT
Index
The index gives an alphabetical list of keywords, each linked to the relevant section(s) of
the manual. You can access the index by clicking the Index button that appears at the
top and bottom of the page. Note that the Index button does not appear if the manual
does not have an index.
In a larger manual, the index is split into a number of pages, each containing keywords
starting with a particular letter; in this case, the Index button will take you to the “A”
index page.
Table of Contents
The table of contents gives a list of the titles of the chapters, sections, and subsections of
the manual in the order in which they appear. Each title is linked to the corresponding
chapter or section. You can access the table of contents by clicking the Contents button
that appears at the top and bottom of the page. Note that the Contents button does not
appear if the manual does not have a table of contents.
Browser Search
The full text search engine (Figure 1.2.3) allows you to search the HTML manual for
either single or multiple keywords. You can access the full text search engine by clicking
the Search button that appears at the top of the page. To display the popup window
and use the search engine, Javascript should be enabled in your web browser.
To use the search engine, enter a specific term or keyword(s) in the text field and click the
Search button. By default, the search engine will look for pages that contain any keyword
input (Boolean OR). If you insert a + before the keyword input, then the search engine
will look for pages that contain all of the keywords provided in the text field (Boolean
AND). Search results appear in the lower half of the search engine popup window. When
search results extend below the bottom edge of the window, you can access those results
by selecting the lower portion of the window and pressing the <Page Down> button on
the keyboard in order to activate scroll bars in the window.
You can also use the search capability provided by your browser to find words or expres-
sions on a single page. For example, you can use the Edit/Find (on This Page)... menu
item in Internet Explorer to search for the word “turbulence” on a page of the manual.
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Introduction to ANSYS FLUENT
Font Size
The absolute size of the text that you see when viewing your ANSYS FLUENT docu-
mentation is dependent on a number of factors, including the resolution of your monitor
screen. You can adjust the text size by changing the default font size of your browser.
In Internet Explorer, for example, you can change the font size by selecting an option
from the View/Text Size menu. Try several sizes to see the effect on the appearance of
the manuals, and choose the one that is best for you.
Page Width
While reading a manual, you may find a figure that is wider than your browser’s window.
As a result, part of the figure will be hidden from view. To see all of the figure, you can
use the horizontal scroll bar at the bottom of your browser’s window, or increase your
browser’s window size.
You might also want to adjust the window size to increase or decrease the page width to
a comfortable reading width.
Tool Tips
When viewing the manuals with certain browsers, information about a figure will be
displayed if you put your cursor over it. However, this information is not meaningful
for most users, and you might find it somewhat distracting. On some browsers, you can
disable the display of “Tool Tips” in the preferences menu.
Before you begin your CFD analysis using ANSYS FLUENT, careful consideration of the
following issues will contribute significantly to the success of your modeling effort. Also,
when you are planning a CFD project, be sure to take advantage of the customer support
provided to all ANSYS FLUENT users.
Step 2 of the solution process requires a geometry modeler and mesh generator. You can
use the geometry and meshing capabilities within ANSYS Workbench, or a separate CAD
system for geometry modeling and mesh generation. Alternatively, you can use supported
CAD packages to generate volume meshes for import into ANSYS FLUENT (see the User’s
Guide). For more information on creating geometry and generating meshes using each
of these programs, please refer to their respective manuals.
The details of the remaining steps are covered in the User’s Guide.
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Basic Steps for CFD Analysis using ANSYS FLUENT
The following questions should be considered when you are generating a mesh:
– Can you benefit from other ANSYS, Inc. products such as ANSYS CFX, ANSYS
Icepak, or Airpak?
– Can you use a quad/hex mesh or should you use a tri/tet mesh or a hybrid
mesh?
∗ How complex is the geometry and flow?
∗ Will you need a non-conformal interface?
– What degree of mesh 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?
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Basic Steps for CFD Analysis using ANSYS FLUENT
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Basic Steps for CFD Analysis using ANSYS FLUENT
The following guidelines can help you make sure your CFD simulation is a success. Before
logging a technical support request, make sure you do the following:
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Guide to a Successful Simulation Using ANSYS FLUENT
You can also monitor lift, drag, or moment forces as well as pertinent variables or
functions (e.g., surface integrals) at a boundary or any defined surface.
7. Run the CFD simulation using second order discretization for better accuracy
rather than a faster solution.
A converged solution is not necessarily a correct one. You should use the second-
order upwind discretization scheme for final results.
8. Monitor values of solution variables to make sure that any changes in the solution
variables from one iteration to the next are negligible.
11. Check to see that the solution makes sense based on engineering judgment.
If flow features do not seem reasonable, you should reconsider your physical models
and boundary conditions. Reconsider the choice of the boundary locations (or the
domain). An inadequate choice of domain (especially the outlet boundary) can
significantly impact solution accuracy.
You are encouraged to collaborate with your technical support engineer in order to de-
velop a solution process that ensures good results for your specific application. This type
of collaboration is a good investment of time for both yourself and the ANSYS FLUENT
support engineer.
This glossary contains a listing of terms commonly used throughout the documentation.
• adaption
• case files
• cell types
• computational fluid dynamics (CFD)
• console
• convergence
• cortex
• data files
• dialog boxes
• discretization
• GUI
• mesh
• models
• node
• postprocessing
• residuals
• skewness
• solvers
• terminal emulator
• TUI
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Glossary of Terms
adaption
A technique useful in improving overall mesh quality. The solution-adaptive mesh refine-
ment feature of ANSYS FLUENT allows you to refine and/or coarsen your mesh based on
geometric and numerical solution data. In addition, ANSYS FLUENT provides tools for
creating and viewing adaption fields customized to particular applications.
case files
Files that contain the mesh, boundary conditions, and solution parameters for a prob-
lem. A case file also contains the information about the user interface and graphics
environment.
cell types
The various shapes or units that constitute the base elements of a mesh. ANSYS FLUENT
can use meshes comprised of tetrahedral, hexahedral, pyramid, wedge, or polyhedral cells
(or a combination of these).
2D Cell Types
Triangle Quadrilateral
3D Cell Types
Tetrahedron Hexahedron
The science of predicting fluid flow, heat transfer, mass transfer (as in perspiration or
dissolution), phase change (as in freezing or boiling), chemical reaction (e.g., combustion),
mechanical movement (e.g., fan rotation), stress or deformation of related solid structures
(such as a mast bending in the wind), and related phenomena by solving the mathematical
equations that govern these processes using a numerical algorithm on a computer.
console
The console is part of the ANSYS FLUENT application window that allows for text
command input and the display of information.
convergence
The point at which the solution is no longer changing with each successive iteration.
Convergence criteria, along with a reduction in residuals, also help in determining when
a solution is complete. Convergence criteria are pre-set conditions on the residuals that
indicate that a certain level of convergence has been achieved. If the residuals for all
problem variables fall below the convergence criteria but are still in decline, the solution
is still changing to a greater or lesser degree. A better indicator occurs when the resid-
uals flatten in a traditional residual plot (of residual value vs. iteration). This point,
sometimes referred to as convergence at the level of machine accuracy, takes time to
reach, however, and may be beyond your needs. For this reason, alternative tools such
as reports of forces, heat balances, or mass balances can be used instead.
cortex
A utility that manages ANSYS FLUENT’s user interface and basic graphical functions.
data files
Files that contain the values of the flow field in each grid element and the convergence
history (residuals) for that flow field.
dialog boxes
The separate windows that are used like forms to perform input tasks. Each dialog box
is unique and employs various types of input controls that make up the form.
discretization
The act of replacing the differential equations that govern fluid flow with a set of algebraic
equations that are solved at distinct points.
GUI
The graphical user interface, which consists of the main ANSYS FLUENT application
window, dialog boxes, graphics windows, etc.
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Glossary of Terms
mesh
A collection of points representing the flow field, where the equations of fluid motion
(and temperature, if relevant) are calculated.
models
node
The distinct points of a mesh at which the equations of fluid motion are solved.
postprocessing
The act of analyzing the numerical results of your CFD simulation using reports, inte-
grals, and graphical analysis tools such as contour plots, animations, etc.
residuals
The small imbalance that is created during the course of the iterative solution algorithm.
This imbalance in each cell is a small, non-zero value that, under normal circumstances,
decreases as the solution progresses.
skewness
The difference between the shape of the cell and the shape of an equilateral cell of
equivalent volume. Highly skewed cells can decrease accuracy and destabilize the solution.
solvers
ANSYS FLUENT has two distinct solvers, based on numerical precision (single-precision
vs. double-precision). Within each of these categories, there are solver formulations:
pressure based; density based explicit; and density based implicit.
terminal emulator
See console.
TUI
The text user interface, which consists of textual commands that can be entered into the
terminal emulator.