1. ME 566 Computer Lab ANSYS–CFX Tutorial Oct. 5, 2009 2:30 – 4:30 pm
Wedge E2-1302B 1

2. 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:
ANSYS Mesh Generation (pages 17-19)
CFX Mesh Generation (pages 27-29)
You should focus on the CFX Mesh Generation method in the tutorial

3. Overview of ANSYS–CFX DesignModeler Create geometry CFX-Mesh
Generate mesh
ANSYS Workbench
CFX-Pre
Pre-processing
CFX-Solver
Solve equations
CFX-Post
Post-processing

4. ANSYS–CFX DesignModeler: CFX-Mesh: CFX-Pre: CFX-Solver: CFX-Post:
Define geometry dimensions
Name the faces of the solid body (e.g., inlet, outlet, wall, symmetry)
CFX-Mesh:
Specify mesh properties (e.g., mesh spacing, inflated boundary thickness)
CFX-Pre:
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:
Solve system of partial differential equations
CFX-Post:
Analyze results and create plots (e.g., vector plot)

5. Duct Bend Example
0.25 m
0.1 m
1 m
0.1 m
The radius of the inner wall bend is m
The average speed of the water flow through the duct is 3 m/s
0.1 m

6. DesignModeler
Create a solid body geometry

7. 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
Front
InnerWall
Inflow

8. CFX–Mesh Mesh generation methods
ANSYS Mesh Generation (pp ): generates a structured mesh
CFX Mesh Generation (pp ): generates an unstructured mesh
You will use CFX Mesh Generation for Assignment #1
structured mesh
unstructured mesh

9. CFX–Pre Fluid type and properties Simulation type Fluid models
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)

10. CFX–Pre continued Specify boundary conditions Advection scheme
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

11. 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:
0.125 m
0.025 m
0.25 m
0.1 m
0.1 m

12. CFX–Post
Flow visualization and analysis of results

13. Physical Geometry of Duct Bend

14. 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?
Choice #1: Use a full physical geometry
Choice #2: Use a half physical geometry
Choice #3: Use a thin slice of physical geometry
Choice #1
Choice #2
Choice #3 14

15. Solution Domain Choice #1: Full physical geometry
wall
wall
0.1 m
0.1 m
wall
wall

16. Solution Domain Choice #2: Half physical geometry
wall
0.1 m
symmetry
wall
0.1 m
wall

17. Solution Domain Choice #3: A thin slice of physical geometry
wall
0.1 m
symmetry
symmetry
0.1 m
wall