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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

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

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)

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

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