Familiarity with the UI of ANSYS FLUENT. – CFD numerics and ... What can
ANSYS FLUENT be employed for? Across the ..... Tutorial HELP in ANSYS
FLUENT.
Inspire, Educate and Mentor engineers globally
CFD Modeling Using ANSYS FLUENT
www.LearnCAx.com
[email protected] +91 20 4009 8382
Course Notes Not for sale. Strictly for private circulation. Published 2015
Before First Simulation Lesson 02
Inspire | Educate | Mentor www.LearnCAx.com
Across the Table!!
•
The following background knowledge is expected from the candidates: – Familiarity with the UI of ANSYS FLUENT – CFD numerics and methodology
•
By the end of the lecture, you should be able to answer: – What and how to prepare before doing a simulation? – What can ANSYS FLUENT be employed for?
42
© LearnCAx.com : Inspire | Educate | Mentor
43
© LearnCAx.com : Inspire | Educate | Mentor
Overview
• • • • • • •
Precision and dimension File handling Units and geometry scale Mesh modifications Mesh nomenclature Available features Support options
ANSYS FLUENT Launcher
44
© LearnCAx.com : Inspire | Educate | Mentor
Single and double precision solver
•
For most cases single precision solvers are sufficiently accurate
•
Certain kind of problems need double precision – If your geometry has features of very disparate length scales – Mean pressure level is high but pressure driving the flow is small – For conjugate heat transfer problems involving high thermalconductivity ratios and/or high-aspect-ratio grids 2d (2D single precision ) 2ddp ( 2D double precision) 3d (3D single precision) 3ddp (3D double precision)
45
© LearnCAx.com : Inspire | Educate | Mentor
File I/O in ANSYS FLUENT
46
© LearnCAx.com : Inspire | Educate | Mentor
Data handling in ANSYS FLUENT
U
MESH file
• Uns. mesh info • Coordinates • Names of nodes/cells
CASE file • Uns. mesh info • Problem set-up • Numerical set-up • Display settings
47
DATA file • Dependent variables’ values at locations specified in the CASE file • u, v, w, p •T • Yi, k, e, …
© LearnCAx.com : Inspire | Educate | Mentor
Compressed Files
•
•
Reading – – – –
Fluent can read files compressed using compress or gzip If you select a file with .gz, it invokes gunzip If you select file with .Z extension, it invokes zcat On Windows, files with only .gz extension can be read
Writing – To compress the file, append .Z or .gz extension to the file name – Fluent invokes the appropriate compression tool and gives following message in case you have added .gz • Writing "| gzip -cfv > flow.cas.gz"...
– On Windows, compression can be performed only with gzip. • .gz extension can compress the file • .Z does not compress the file
48
© LearnCAx.com : Inspire | Educate | Mentor
Automatic Numbering
• •
You can include special characters in file name Provides shortcut for numbering the files based on various parameters (iteration no., time step etc.) – E.g. : For unsteady calculations, saving file that reflect the time step at which file is saved • contours-%t.ps : contours-0001.ps
– E.g. : File name which reflect the number of iteration • airfoil-%i : airfoil-005.cas
49
© LearnCAx.com : Inspire | Educate | Mentor
Automatic Saving of Case & Data
50
© LearnCAx.com : Inspire | Educate | Mentor
Automatic Saving of Case & Data
•
Case & Data file can be saved automatically at specified interval during calculation – – – –
Useful for time-dependent solution Useful to see how solution has progressed for steady solution Case file may or may not be written every time If Case file undergoes a change, it will always be saved along with the updated Data file
•
To Autosave
•
Frequency for saving case and data
•
In case of limited disc space
– File → Write → Autosave – For steady flow number of iterations – For unsteady flow number of time steps – Use Overwrite Existing File option – Specifies how many maximum files can be written – After saving specified number of files, earliest existing file will be overwritten
51
© LearnCAx.com : Inspire | Educate | Mentor
Automatic Saving of Case & Data
•
Specify the root name of file – .cas or .dat will be added automatically – If .gz or .Z is given, files will be written in compressed format – Iteration number/time-step/flow-time automatically appended to the name, dependent on the choice
Frequency for file saving
In case of limited disk space
Path for saving
52
© LearnCAx.com : Inspire | Educate | Mentor
Unit Systems
•
• • •
Fluent allows to work in any unit system, including inconsistent unit systems – You may work in British units with heat input in Watts (SI) OR you may work in SI units with length defined in inches This is accomplished by using appropriate conversion factors Fluent uses these conversion factors for input and output, internally storing all parameters and performing all calculations in SI units Units can be changed during problem setup or after calculation – If you have completed simulation in SI units but would like to see reports in any other units – Fluent converts all parameters in specified units and displays results Fluent always works in SI units internally and stores all results in SI units To be considered while generating Profile files, Journal files, UDFs, etc.
53
© LearnCAx.com : Inspire | Educate | Mentor
Built-In Unit Systems in FLUENT
•
Four built in unit systems – British, SI, CGS, and "default'' – You can convert all units from one system to another – Define → Units
Default is same as SI, but uses degrees instead of radians for angles Clicking on any system will immediately change all units in selected system
All future inputs will be in selected system 54
© LearnCAx.com : Inspire | Educate | Mentor
Customizing Units
•
•
Used in case of mixed unit systems – Select quantity, select unit from available list or specify your own conversion factor
Before changing any unit, you can list the units of all quantities that are currently used – Press List button in Set Unit form
55
© LearnCAx.com : Inspire | Educate | Mentor
Geometry/Mesh scaling • •
•
Some grid generators allow to define set of units for the mesh dimensions But when mesh is read into Fluent, it always assumes unit of length as meters You can change the unit of grid using – Mesh → Scale
56
© LearnCAx.com : Inspire | Educate | Mentor
Defining a New Unit •
To create new unit for selected quantity
– Select the quantity in list – Click New to open Define Unit panel – Set the name of new unit in Unit field – Conversion factor in Factor field – Offset in Offset field – Click OK
E.g. To use hour as unit of Time : Select Time, Select New, Enter Name as hour, Enter 3600 for factor
57
© LearnCAx.com : Inspire | Educate | Mentor
Mesh modifications in ANSYS FLUENT
58
© LearnCAx.com : Inspire | Educate | Mentor
Operations on Grid
• •
Fluent can import different types of gird Operations on grid – – – – – –
Modify the grid by translating or scaling node coordinates Partitioning the cells for parallel processing Reordering the cells in the domain to decrease bandwidth Merging or separating zones Adapt grid as per solution Diagnostic information on the grid • • • • •
Memory usage Simplex, topological, and domain information Number of nodes, faces, and cells in the grid Determine the minimum and maximum cell volumes in the domain Check for the proper number of nodes and faces per cell
59
© LearnCAx.com : Inspire | Educate | Mentor
Grid Topology • Fluent is an unstructured solver – It can accept • • • • •
2D tri and quad 3D hex, tet, pyramid, and wedge Single and multi-block structured grid Hybrid grid Grid with hanging nodes
Hanging Node 60
© LearnCAx.com : Inspire | Educate | Mentor
Choosing the Appropriate Grid Type
•
When choosing the mesh type, consider the following issues
•
Setup Time
– Setup time – Computational expense
– Creation of structured grid for complex geometries is time consuming if not impossible • Gives advantage to unstructured mesh
– If geometry is simple, setup time is almost same
•
Computational Expense
•
Mesh Quality
– Mesh generated using unstructured algorithm usually has a very high cell count
– Plays an important role in accuracy and stability of the numerical computation – Attributes associated with mesh quality are • Node point distribution • Smoothness • Skewness 61
© LearnCAx.com : Inspire | Educate | Mentor
Choosing the Appropriate Grid Type
•
Why go the hard way: structured mesh? – Grid aligned along the flow direction • Least numerical diffusion – accurate flow prediction
– Great control over the mesh quality and cell count
•
• Boundary layer capturing
Why go the easy way: unstructured mesh? – Can capture complex geometry with minimum user intervention – If flow is rapidly changing direction, grid alignment along the flow not possible to maintain – Fast computational power available
© LearnCAx.com : Inspire | Educate | Mentor
62
Choosing the Appropriate Grid Type L-grid type Multi-block Structured Mesh for flow through a Sector Grid aligned along the flow direction
Unstructured Mesh for flow through a Sector (Octree algorithm) Grid not aligned along the flow direction
63
© LearnCAx.com : Inspire | Educate | Mentor
Non-Conformal Grids
•
•
In FLUENT it is possible to use a grid composed of cell zones with non-conformal boundaries What is non-conformality ? – Grid node locations are not identical at the boundaries where two subdomains meet
Completely Overlapping Grid Interface Intersection
Partially Overlapping Grid Interface Intersection 64
© LearnCAx.com : Inspire | Educate | Mentor
Checking the Grid
•
The grid checking capability in FLUENT provides Domain extents Volume statistics Grid topology Periodic boundary information Verification of simplex counters, and (for axisymmetric cases) node position verification with respect to the axis – Accessible through – – – – –
• Grid → Check
– It is generally a good idea to check your grid right after reading it into the solver, in order to detect any grid trouble before you get started with the problem setup
65
© LearnCAx.com : Inspire | Educate | Mentor
Mesh terminology in ANSYS FLUENT
• • • • •
Cell center and Node Edge Face Cell Zone or Thread – Collection of faces – Face zone – Collection of volumetric cells – Cell zone
66
© LearnCAx.com : Inspire | Educate | Mentor
Basic Modeling capabilities in ANSYS FLUENT •
2D planar, 2D axi-symmetric, 2D axi-symmetric with swirl (rotationally symmetric), and 3D flows
•
Quadrilateral, triangular, hexahedral (brick), tetrahedral, prism (wedge), pyramid, and mixed element meshes with non-conformal interface
•
Steady-state or transient flows
•
Incompressible or compressible flows, including all speed regimes (low subsonic, transonic, supersonic, and hypersonic flows)
•
Inviscid, laminar, and turbulent flows
•
Heat transfer, including forced, natural, and mixed convection, conjugate
(solid/fluid) heat transfer
•
Multi-species and User-defined scalar/Additional variable simulation
67
© LearnCAx.com : Inspire | Educate | Mentor
Advanced Modeling capabilities in ANSYS FLUENT •
Radiation heat transfer modeling, Solar Load Model
•
Multiple reference frame (MRF) and sliding mesh options for modeling multiple moving frames
•
Mixing-plane model for modeling rotor-stator interactions, torque converters, and similar turbo-machinery applications with options for mass conservation and swirl conservation
•
Dynamic mesh model for modeling domains with moving and deforming mesh (IC Engine simulations, reciprocating pumps, flow induced rotations, etc.)
•
Volumetric sources of mass, momentum, heat
•
Multiphase flow modeling
•
Reacting flow modeling – Kinetics and PDF based combustion models
•
Material property database 68
© LearnCAx.com : Inspire | Educate | Mentor
Embedded HELP in ANSYS FLUENT
69
© LearnCAx.com : Inspire | Educate | Mentor
Content HELP in ANSYS FLUENT
70
© LearnCAx.com : Inspire | Educate | Mentor
Control Panel HELP in ANSYS FLUENT
71
© LearnCAx.com : Inspire | Educate | Mentor
Model User Guide HELP in ANSYS FLUENT
72
© LearnCAx.com : Inspire | Educate | Mentor
Theory HELP in ANSYS FLUENT
73
© LearnCAx.com : Inspire | Educate | Mentor
Tutorial HELP in ANSYS FLUENT •
Required Mesh and related files are available from the ANSYS Customer Portal
www1.ansys.com/customer
74
© LearnCAx.com : Inspire | Educate | Mentor
Summary
•
• • • •
Familiarity with file formats necessary to start with simulations FLUENT processes all data internally in SI unit system Appropriate mesh choice necessary for efficient and accurate simulations Mesh modifications possible in ANSYS FLUENT to some extent only ANSYS FLUENT offers on the fly HELP on theory and software specific topics
75
© LearnCAx.com : Inspire | Educate | Mentor
Inspire | Educate | Mentor
www.LearnCAx.com
[email protected] +91 20 4009 8382 www.facebook.com/LearnCAx in.linkedin.com/company/learncax twitter.com/info_learncax