ME 566 Computer Lab
ANSYS–CFX Tutorial
Oct. 5, 2009
2:30 – 4:30 pm
Wedge E2-1302B
1
ANSYS CFX Student User Manual
•
The manual can be downloaded from UW-ACE
•
In the tutorial, you will be working on the Duct Bend
Example (Sec. 2.2, pages 13-29) in the manual
•
Two mesh generation methods are presented in the
manual:
1. ANSYS Mesh Generation (pages 17-19)
2. CFX Mesh Generation (pages 27-29)
• You should focus on the CFX Mesh Generation method in the
tutorial
2
Overview of ANSYS–CFX
ANSYS
Workbench
DesignModeler
Create geometry
CFX-Mesh
Generate mesh
CFX-Pre
Pre-processing
CFX-Solver
Solve equations
CFX-Post
Post-processing
3
ANSYS–CFX
•
DesignModeler:
•
•
•
CFX-Mesh:
•
•
Specify fluid properties (e.g., density, viscosity)
Set simulation type (e.g., steady)
Select turbulence model (e.g., k- model, wall functions)
Specify boundary conditions (e.g., speed, turbulence intensity and length scale)
Select advection scheme (e.g., upwind)
Define convergence criterions (e.g., number of iterations, residual target)
CFX-Solver:
•
•
Specify mesh properties (e.g., mesh spacing, inflated boundary thickness)
CFX-Pre:
•
•
•
•
•
•
•
Define geometry dimensions
Name the faces of the solid body (e.g., inlet, outlet, wall, symmetry)
Solve system of partial differential equations
CFX-Post:
•
Analyze results and create plots (e.g., vector plot)
4
Duct Bend Example
0.25 m
0.1 m
1m
• The radius of the inner wall bend is 0.025 m
0.1 m
0.1 m
• The average speed of the water flow through
the duct is 3 m/s
5
DesignModeler
• Create a solid body geometry
6
DesignModeler – continued
• Name the faces of the solid body
• to make it easy to apply boundary conditions
• In the duct bend example, six faces of the solid body are named as:
Front, Back, Inflow, Outflow, InnerWall, OuterWall
Back
OuterWall
Outflow
InnerWall
Inflow
Front
7
CFX–Mesh
• Mesh generation methods
• ANSYS Mesh Generation (pp. 17-19): generates a structured mesh
• CFX Mesh Generation (pp. 27-29): generates an unstructured mesh
• You will use CFX Mesh Generation for Assignment #1
structured mesh
unstructured mesh
8
CFX–Pre
• Fluid type and properties
• Type: water/air
• Properties: density, dynamic viscosity
• Simulation type
• Steady/transient
• Fluid models
• Turbulence model (e.g., k- model/shear stress transport model)
• Turbulent wall functions (e.g., scalable)
9
CFX–Pre continued
• Specify boundary conditions
•
•
•
•
Wall: smooth/rough, stationary/translating/rotating
Inlet: fluid speed/mass flow rate/pressure
Outlet: fluid speed/mass flow rate/pressure
Symmetry:
• Advection scheme
• Upwind/High Resolution
• Timescale control
• Auto Timescale/Physical Timescale
• Convergence criterions
• Number of iterations
• Residual target
10
CFX–Pre continued
• Estimation of Physical Timescale
• The physical timescale is calculated using approximately 30% of the
average residence time for a fluid parcel to move across the flow domain
(see pages 47 and 48 of the student user manual for reference).
• For the duct bend case
•
•
•
•
Fluid travel length (average):
Flow speed:
Average residence time:
Physical timescale:
L  0.1 
  0.025  0.125 

2
2
  0.25  0.47 m

U  3m / s

L 0.47

s
U
3
t  0.3  0.047s
0.125 m
0.025 m
0.25 m
0.1 m
11
0.1 m
CFX–Post
• Flow visualization and analysis of results
12
Physical Geometry of Duct Bend
0.25 m
0.1 m
1m
0.1 m
0.1 m
13
Who Wants to Be a CFD Expert?
•
For the given physical geometry of the duct bend, which
of the following solution domain is the best choice for
modeling the duct bend flow?
A. Choice #1: Use a full physical geometry
B. Choice #2: Use a half physical geometry
C. Choice #3: Use a thin slice of physical geometry
Choice #1
Choice #2
Choice #3
14
Solution Domain
Choice #1: Full physical geometry
0.25 m
0.1 m
1m
wall
wall
0.1 m
0.1 m
wall
wall
15
Solution Domain
Choice #2: Half physical geometry
0.25 m
0.1 m
1m
0.5 m
wall
0.1 m
symmetry
0.1 m
wall
wall
16
Solution Domain
Choice #3: A thin slice of physical geometry
0.25 m
0.1 m
1m
0.02 m
wall
0.1 m
symmetry
symmetry
0.1 m
wall
17