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ME 566 Computer LabANSYS–CFX Tutorial
Oct. 5, 2009
2:30 – 4:30 pm
Wedge E2-1302B
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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
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Overview of ANSYS–CFX
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ANSYS Workbench
DesignModeler
CFX-Mesh
CFX-Pre
CFX-Solver
CFX-Post
Create geometry
Generate mesh
Pre-processing
Solve equations
Post-processing
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ANSYS–CFX
• DesignModeler:• 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)
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Duct Bend Example
0.1 m
0.1 m
0.1 m
1 m
0.25 m
• The radius of the inner wall bend is 0.025 m
• The average speed of the water flow through the duct is 3 m/s
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DesignModeler
• Create a solid body geometry
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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
InnerWall
OuterWall
Inflow
Outflow
Front
Back
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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
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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)
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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
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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:
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0.1 m
0.1 m
0.25 m
0.025 m
0.125 m
0.025 0.1250.1 0.25 0.47
2 2L m
3 /U m s0.47
3
Ls
U
0.3 0.047t s
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CFX–Post
• Flow visualization and analysis of results
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Physical Geometry of Duct Bend
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0.1 m
0.1 m
0.1 m
1 m
0.25 m
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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
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Choice #1 Choice #2 Choice #3
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Solution DomainChoice #1: Full physical geometry
0.1 m
0.1 m
0.1 m
1 m
0.25 m
wall
wallwall
wall
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Solution DomainChoice #2: Half physical geometry
0.1 m
0.1 m
0.1 m
0.5 m
0.25 m
1 m
wall
wall
wall
symmetry
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Solution DomainChoice #3: A thin slice of physical geometry
0.1 m
0.1 m
0.1 m
1 m
0.25 m
0.02 m
wall
wall
symmetrysymmetry