am 12 appendix b

B-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

April 28, 2009Inventory #002645

Appendix B

CFX-Mesh

ANSYS MeshingApplication Introduction

Appendix B: CFX-Mesh



Training Manual

• CFX-Mesh provides automated mesh generation• Unstructured triangular surface mesh generation• Volume mesh is created from the surface mesh• Tetrahedral/prismatic/pyramidal volume mesh generation• Extruded meshes can also be created– If quad faces exist on the extruded face due to inflation, hex elements

will be created for those quad elements

• Advancing Front and Inflation (AFI)

Introduction




Training Manual

• Valid element types for the CFX-Solver include tetrahedra, prisms (wedges), pyramids, and hexes

Element Types




Training ManualAccessing CFX Mesh

1. Launch ANSYS Workbench

2. Double click on Mesh under component systems.

3. This will create a ‘Mesh component’ in the Project Schematic area.

4. Right click on select “Import Geometry” and click on “Browse…” to load a previously created geometry or click “New Geometry” to open DesignModeler and create a new geometry.

5. Once the geometry is loaded double click on to open the meshing application.




Training Manual

• In the Project environment go to Tools > Options…– Select “Geometry Import”– Select Analysis Type as “3D”– Ensure “Solid Bodies” is chosen

• Only solid bodies are relevant to CFX Mesh

– Check the “Named Selection” box to get Design Modeler defined named selections

– Set the filtering prefix (keep the “Filtering Prefixes” box blank to import all named selections regardless of prefix)

Accessing CFX Mesh





• Right-click on Mesh and Insert Method

• Select the Body of interest

• Now edit the method and choose CFX Mesh

• Then right Click on resulting CFX-Mesh Method and Choose Edit in CFX-Mesh





• Note that the meshing environment is now modified




Training Manual

• Geometry used for meshing in CFX-Mesh must consist of one or more Solid Bodies

• In CFX-Mesh, the body will have the units specified in DM

• Surface Bodies and Line Bodies are not supported in CFX-Mesh – On import of certain file formats, Workbench will convert sets of surfaces which fully

enclose to a volume into Solid Bodies (see DM documentation for details)

• Solid Bodies must not overlap each other

• Where Solid Bodies in a multi-body part touch, they must have common faces

• Bodies which are Frozen in DM will appear in CFX-Mesh and can be meshed

• To exclude a Solid Body from meshing, you can either suppress/delete it in DM, or suppress it in CFX-Mesh

Geometry Requirements




Training Manual

wrong

• Example 1:– When Solid Bodies in a multi-body part touch, they must have

common faces

– If two bodies contact as shown, the face at the end of pipe is not one of the faces of the cylinder, CFX-Mesh will fail in generating mesh if the two bodies are in a single part

– How to meet CFX-Mesh topology requirements?





Training Manual

right

– To make a common face between pipe and cylinder, the cylinder needs to have the cylinder face that touches the pipe split into two: one face is the circular face which matches the end of the pipe, the other face is the remaining annular ring.

– This can be done with an Imprint Face body operation in DM.





Training Manual

• Example 2:– When part of pipe intrudes into the cylinder, part of the side

surface is external to the cylinder, while the other part is internal to it.

– What should the two bodies look like if they are in a single part?





Training Manual

wrong

– Again, the rule to remember is that adjacent solid bodies in a multi-body part must meet at shared faces

– If two bodies contact as shown, where the side surface of the pipe is a single face, it does not match up with cylindrical cut-out in the bottom cylinder and CFX-Mesh will fail in generating mesh.

Single Side Surface

CylindricalCut-Out





Training Manual

right

– To make sure the pipe and cylinder meet at a shared face, the pipe needs to have its side face segmented into the part that’s external to the bottom cylinder and the part that’s internal to it (via an Imprint Face body operation in DM).

External Side Surface

Internal Side SurfaceCylindricalCut-Out





Training Manual

• The CFX-Mesh Help provides many useful examples of what can and cannot be handled in CFX-Mesh, and some ways around difficult geometries, including:– Bodies Joined by a Common Face– Bodies Touching at a Face– Body with a Hole– Body with an Enclosed Body– Bodies with an Enclosed Body and a Hole– Body with an Enclosed Body Touching the Face– Non-Manifold Geometry– Closed Faces (ie. Cylinders)– Thin Surface Topology– Poorly Parameterized Surfaces– Degenerate Geometry

Other Geometry Requirements




Training Manual

• Geometry Update allows for quick modification of geometry and mesh regeneration.– Updates geometry while retaining most or all CFX-

Mesh settings.– Updates from CAD systems in plug-in mode is

faster and cleaner.– If importing in reader mode, then you must save

the new geometry into the appropriate file before updating.

– Most geometry updates work with the minimum required modification to your mesh settings

• Depends on the complexity of the changes made to the geometry, the CAD format and the method of import

– Look at status symbols on each entity at the end of the update. If there are problems, you should correct them before regenerating the mesh.

Geometry Update

Right-click on Geometry in Tree View

Status Symbols

Error

OK

or




Training Manual

• Geometry Checking checks for the presence of certain undesirable features in faces and edges which can cause poor mesh quality or failure of the mesher.

• Can be accessed from the Go menu, by right-clicking on Geometry in Tree View, or in the top right toolbar.

• Note: the “lock” symbol means the item must remain.

• Results of check can be viewed under Errors in Tree View– If a Warning or Error refers to a specific curve or face,

it will be highlighted when selected– Last warning gives a summary of

the checks

Geometry Checking




Training Manual

• Failed check does not necessarily result in poor mesh

• Worth checking the mesh on any faces which failed the checks

• Doesn’t check for ALL problems which can be present, just a few specific problems:– Sliver Edge Checking– Sliver Face Checking– Parameterization Face Checking

• Verify Options determine values which generate errors

Geometry Checking




Training Manual

• Looks for short edges in the geometry

• Short edges can produce a mesh which is over-refined in regions near the short edges

• To remove short edges, change the default from NO to YES for Remove Short Edges in Fix Options

• You can change the tolerance used for the check by using Verify Options

Sliver Edge Checking




Training Manual

• Computes a ratio of perimeter length to area for each face

• Faces with a high sliver factor can result in a poor quality surface mesh

• You can change the limit used for the check by using Verify Options

• Default of 25 is usually sensible

• Each face identified will be highlighted when the individual warning message is selected

Sliver Face Checking




Training Manual

• Provides guidance on the parameterization of the surfaces

• Each potentially poorly parameterized surface will be highlighted when the individual warning message is selected

Parameterization Face Checking




Training Manual

• By Default CFX-Mesh resolves every edge using a minimum of 3 vertices and meshes every face

• Results is large mesh when there are many short edges and narrow faces in the CAD data

Virtual Topology

• May not require a fine mesh in these areas for CFD

• If proper mesh controls are not used in these areas, the resulting mesh may be of poor quality or the mesher might fail

• Virtual Topology allows users to combine faces and edges into Virtual Faces and Virtual Edges. Can be added in CFX-Mesh or the Meshing Application.

78 Surfaces represent car body




Training Manual

• CFX-Mesh only sees the combined Virtual Face or Virtual Edge

• Mesher does not resolve the constituent faces or edges, giving higher quality mesh with the required refinement

• Does NOT modify the underlying CAD

• Virtual topology will be discussed in more detail later

Virtual Topology

A single virtual surface




Training Manual

• To change the appearance of your geometry, left-click on Geometry in the Tree View

• Transparency (%)– 100% means completely transparent– 0% means completely opaque

• Shine (%)– Controls how much light is reflected by

the faces of the mesh– 0% gives lowest reflection and looks

matt– 100% gives highest reflection and

looks very bright

Geometry Display

Transparency can be very useful for selecting hidden surfaces since there isn’t a wireframe view




Training Manual

• You can use 2D Regions to give meaningful names to parts of the geometry which may comprise many faces

• Composite Regions can be used for:– Specifying Locations in CFX-Mesh– Defining Boundary Conditions in CFX-

Pre

• Default and additional Regions available– To create a new Region, right-click on

Regions and choose Insert>Composite 2D Region

• No primitive 2D Region can be assigned to more than one Composite 2D Region

Composite 2D Regions




Training Manual

• Named Selections are imported from DM as Composite Regions– Select Named Selection under Default

Geometry Options on the Project tab before proceeding to CFX-Mesh.

– Can be set as default option in the Geometry Import options panel

• Composite 2D Regions can be hidden!!– Removes the constituent faces from the

viewer– Hidden faces cannot be selected

Composite 2D Regions




Training Manual

• Where two Solid Bodies meet at a common face:– There is just one face present in the

geometry– There are two 2D Regions

• Each meshing feature that requires you to specify a location has its own rules about 2D Regions on the same face– Ex. Face Spacing: Do not try to apply

different Face Spacings to 2D Regions which are the two sides of a common face (surface mesh is generated on the common face, not 2D Regions)

– Ex. Inflated Boundary: You can have different settings for the two different 2D Regions which make up a common face

2D Regions and Faces




Training Manual

• Use attached Selection Rectangles to select individual 2D Regions easily and accurately

• CFX-Mesh will not allow you to select locations for meshing features which break the rules given for each feature

2D Regions and Faces




Training ManualSaving the Volume Mesh

• Two formats– .CMDB file

• Contains mesh and mesh settings• Larger file which takes longer to

generate for large meshes– .GTM file

• Suitable for import directly into CFX-PRE

• Access Options from the Tools Menu

• The right panel will show various CFX options.




Training ManualSaving the Volume Mesh

• You may choose to write .cmdb or .gtm or both• User Defined location for .gtm will produce a dialog box to save choose a

location when you Generate the Volume Mesh




Training ManualLength Scales

• The process of setting an element length scale for CFX-Mesh can be viewed as a 3 step process

– Default Body Spacing– Face Spacing– Other Mesh Controls (Point Spacing, Periodicity, Inflation, etc)

• Smallest effecting length scale is chosen




Training ManualFace Spacing

• Face Spacing can be set to one of 4 types:– Angular resolution - curvature sensitive, discussed next– Relative error - curvature sensitive, discussed next– Constant - constant length scale, overriding the Body Spacing (must be less than

Default Body Spacing)– Volume Spacing - uses the same spacing on the face as the Body Maximum

Spacing




Training ManualFace Spacing

• Face spacings have a volumetric effect. The region over which theyact are determined by the following settings:– Radius of Influence: extent of the Face Spacing influence, after which it will

expand according to the Expansion Factor– Expansion Factor: rate of expansion of mesh scale from surface to interior

• Location: Faces where the Face Spacing values will be applied– Can be selected from the Model View or Tree View Regions– Unnecessary for Default Face Spacing




Training Manual

• Angular Resolution [Degrees]– CFX-Mesh chooses edge length such

that the set angle is subtended at the center of circle with radius equal to smallest radius of curvature

– Default is 30 degrees (recommended 5 to 60 degrees)

• Relative Error [Δr/r]– Deviation of mesh from surface as a

fraction of local radius of curvature

• Minimum edge length - lower bound on length scale

• Maximum edge length - upper bound on length scale (default same as volume background scale)

Curvature Sensitive Mesh




Training Manual

Without surface curvature sensitive meshingWith surface curvature sensitive meshing

Curvature Sensitive Mesh




Training ManualEdge Spacing

• Edge Spacing specifies the mesh length scale on an edge (or edges) and in the volume adjacent to the selected edges

• To create a new Edge Spacing, right-click on Spacing and choose Insert>Edge Spacing

• Parameters and effect on mesh are the same as with Face Spacing




Training ManualEdge Spacing




Training ManualMesh Controls

• Mesh Controls are used to refine the surface and volume mesh in specific regions of your model

• Location can be defined using any point on the model or by specifying coordinates– Can be located anywhere in the

3D space of model (inside, outside or on the edge)

• 3 types of volumetric Controls are available:– Point – Line– Triangle

• Remember: Face Spacing also available for volumetric control




Training ManualPoint Spacing

• Each of the 3 volumetric Controls requires you to specify a Point Spacing for the control at appropriate points.Any number of mesh controls can reference the same point Spacing

• Length Scale– For the mesh size where the Point

Spacing is applied– Must be less than Body Spacing

Max

• Radius of Influence– Radial extent of the fixed local

length scale influence

• Expansion Factor– Geometric rate of increase of

local element length scale beyond radius




Training ManualPoint Control

• Point Control controls the mesh spacing in a spherical region

• Point– Select either a vertex from the

model or coordinates

• Spacing– Select a Point Spacing which

defines the attributes for the Point Control (Length Scale, Radius of Influence and Expansion Factor)

• Figure to right shows a Point Control on a 1m cube with:– Length Scale=0.05m– Radius of Influence=0.2m– Expansion Factor=1.2




Training ManualLine Control

• Line Control controls the mesh spacing in a region defined by a cylindrical volume between 2 spheres

• Point– Select either a vertex from the model or

coordinates for both Points

• Spacing Definitions– Uniform requires only one Spacing– Non Uniform requires a Spacing for

each end

• Spacing– Select a Point Spacing which defines

the attributes for the Line Control (Length Scale, Radius of Influence and Expansion Factor)

• Figure to right shows a Line Control on a 1m cube with:– Length Scale=0.05m– Radius of Influence=0.2m– Expansion Factor=1.2




Training ManualTriangle Control

• Triangle Control controls the mesh spacing in a region defined by a prismatic volume between 3 spheres

• Point– Select either a vertex from the model or

coordinates for all 3 Points

• Spacing Definitions– Uniform requires only one Spacing– Non Uniform requires a Spacing for each

corner of the triangle

• Spacing– Select a Point Spacing which defines the

attributes for the Triangle Control (Length Scale, Radius of Influence and Expansion Factor)

• Figure to right shows a Triangle Control on a 1m cube with:– Length Scale=0.05m– Radius of Influence=0.2m– Expansion Factor=1.2




Training ManualPeriodicity

• Using Periodicity allows you to generate identical meshes for faces that will be specified as part of a periodic boundary condition in ANSYS CFX

• The CFX Solver makes more accurate calculations when mesheson periodic pairs are identical (one-to-one)

• Periodicity can be either Translation by a fixed vector or Rotation

• Rules/Limitations:– Each face in the Location 1 face list must map to an equivalent face in the Location

2 face list– Multiple faces can be selected for each of Location 1 and Location 2, provided

each face in the Location 1 face list maps onto a face in the Location 2 face list using the specified transformation

– Inflation cannot be applied to a face which is part of a Periodic Pair

• See the documentation for further details on Periodicity




Training ManualPeriodic Pairs

• Periodic Pairs create identical meshes on the 2 locations selected

• Location– Select face(s) either directly from the

Model View or select a Composite 2D Region from the Tree View

– All faces selected must be on the external boundary of the model and must not be included in an Inflated Boundary

• Periodic Type– Rotational requires 2 points to define

an axis, and possibly an Angle of Rotation

• Points can be either a vertex from the model or coordinates

– Translational requires no further input




Training ManualInflation

• Inflation is the generation of prismatic element layers by “inflating” triangular surface elements

• Purpose:– Prism elements more effectively and efficiently captures

boundary layer effects– Node density near the wall is increased– Velocity profile is captured by the prism layer– Tetrahedral elements efficiently fill the volume region





• You can control the number, thickness and expansion rate of inflation layers

• You can inflate from any surface or boundary condition, except those included in a Periodic Pair

• Inflation layers can be viewed within CFX-Mesh





• Number of Inflated Layers– If First Layer Thickness Option is used, this is a

maximum number of layers– If Total Thickness Option is used, this is the

actual number of layers (unless layers are removed to improve mesh quality)

• Expansion Factor– Each layer, moving away from the face, is one

Expansion Factor thicker than the previous.

• Number of Spreading Iterations– Advanced quality control, see documentation

for details

• Minimum Internal Angle– Advanced quality control, see documentation

for details

• Inflation Option– Total Thickness– First Layer Thickness




Training ManualInflation Option - Total Thickness

• Total Thickness– The total thickness of the inflation is

controlled by the:• Thickness Multiplier• Local element edge length

– Determined by Face Spacing and Controls

• Maximum Thickness– Set individually for each Inflated

Boundary– Creates a less smooth transition from the

inflated prism mesh elements to the tetrahedral mesh elements

– The number of inflated layers is more constant, and you have some control over height of layers on face-by face basis




Training ManualInflation Option - Total Thickness

• Process used for creating the layers of prisms when using the Total Thickness option is given below:– CFX-Mesh calculates the total thickness of the inflation layers as follows:

• Multiply the Thickness Multiplier by the local element edge length• Where this is less than the specified Maximum Thickness, then this gives the

total thickness of the layers• Where this is greater than the specified maximum Thickness, then the

Maximum Thickness is taken to be the total thickness of the layers– Use the specified Number of Inflated Layers and Expansion Factor to calculate the

height of each layer, given the total thickness that has just been calculated

• Inflation thickness will not be constant over the inflated edge if the element edge length changes in the region of the inflation layer




Training ManualInflation Option - First Layer Thickness

• First Layer Thickness– Does not control the overall height of

the inflation layers– Prisms based on First Prism Height or

y+, Expansion Factor and Number of Inflated Layers

– Creates smoother transition from inflated prism mesh elements to the tetrahedral mesh elements

– First Prism Height must be less than the Max Spacing under Body Spacing

– You should examine the mesh to visualize the extent of the inflation and the quality of the transition from prisms to tetrahedral elements




Training Manual

y = Ly+ 80 Re(-13/14)

Inflation Option - First Layer Thickness

• Define First Layer By y+– Computes First

Prism Height based on user inputs

– Desired y+, Flow Reynolds Number and Reference Length

First Prism Height = Reference Length * (Desired) y+ * 80 * Reynolds Number(-13/14)




Training ManualInflation Option – Extended Layer Growth

Process used for creating the layers of prisms when using the First Layer Thickness option is given below

• Put a single layer of prisms against the faces of the inflated boundary, of a height equal to the First Prism Height

Extended Layer Growth = No

• Check the aspect ratio of the prisms

– If height < base length, add another layer of prisms of height (Previous Height) X (Expansion Factor)

– If height ≥ base length, stop adding prisms

• Repeat until aspect ratio for all the prisms ≈ 1 or until the Number of Inflated Layers is reached

Extended Layer Growth = Yes

• Check the aspect ratio of the prisms

– If height < base length, add another layer of prisms of height (Previous Height) X (Expansion Factor)

– If height ≥ base length keep adding layers of unit aspect ratio until the Number of Inflated Layers is reached




Training Manual

Extended Layer Growth = No Extended Layer Growth = Yes

Number of Inflated layers = 25

Inflation Option – Extended Layer Growth




Training ManualInflation Option – Layer Smoothing

• Available when using First Layer Thickness option

• Allows prisms to grow out normal to the surface, i.e. orthogonal to the surface

• Layer normals and heights are then progressively smoothed, during the creation of each layer

• Maximizes the number of layers obtained

• Result in longer mesh generation times




Training ManualInflation Option – Layer Smoothing

Layer by Layer Smoothing = No Layer by Layer Smoothing = Yes

Prism growth is orthogonal




Training ManualInflated Boundary

• Creation of an Inflated Boundary is how you specify which faces you want Inflation to apply to

• Location– Select face(s) either directly from the Model View

or select a Composite 2D Region from the Tree View

– A face cannot be in more than one Inflated Boundary, or in both an Inflated Boundary and a Periodic Pair

• Maximum Thickness– The Maximum Thickness for the whole inflation

layer, when Inflation Option is set to Total Thickness

– Not used if Inflation Option is set to First Layer Thickness




Training ManualStretch

• Stretch can be used to expand or contract the mesh elements in a particular direction– The geometry is expanded by the specified factors, meshing takes place, then the

geometry is contracted back to its original size– The max and min stretches allowed are 0.2 and 5 (factors below 0.6 are not

recommended)

Stretch in X = 1.0

Stretch in Y = 1.0

Stretch in Z = 2.0

Stretch in X = 0.5

Stretch in Y = 3.0

Stretch in Z = 1.0

Before Stretching




Training ManualCombined Mesh Control and Stretch

• The effective influence of a Mesh Control, which is treated as a spherical mesh control while meshing takes place, will NOT be modified to elliptical

• Therefore, a Point Control will appear to influence an elliptical region when the mesh is examined

x

y

z




Training ManualProximity

• Proximity settings control automatic refinement of the mesh when edges or faces are near to other edges or faces, but not connected

– Edge proximity• ON by default• Adjusts mesh based on

mesh size on neighboring edges

– Surface proximity• OFF by default• Adjusts mesh based on gap

between neighboring surfaces




Training Manual Edge Proximity

• Edge Proximity is used to automatically modify mesh elements in regions where curves are in close proximity– Bounding curves of surface “sense” nearby

curves and increase mesh density locally– Only available when Delaunay Surface

Mesher is used (meshers discussed soon)

Edge Proximity OFF Edge Proximity ON

Edge Proximity OFF

Edge Proximity ON




Training ManualSurface Proximity

• Surface Proximity is used to automatically reduce the mesh size in regions where surfaces are in close proximity and the original mesh does not resolve the gap sufficiently

• Number of Elements Across Gap– Recommend at least 4– Generates higher quality prismatic

and tetrahedral elements in the gap region

• Maximum Number of Passes– Number of times the surface mesher

will run to try to meet the Number of Elements Across Gap

• Available for both Delaunay and Advancing Front Surface Meshers




Training ManualOptions – Global Mesh Scaling

• Allows easy scaling of each length scale for the mesh, except those applied to Face Spacing’s

• Decreasing this factor decreases mesh length scales and increases number of elements

• Does not affect anything other than mesh length scales (i.e. Radius of Influence is not affected)

• Stretch affects all lengths (including Radius of Influence)

• Global Mesh Scaling factor is only applied during meshing– Display of size of Controls will show the size

as if the factor is 1




Training ManualOptions – Surface Meshing

• Both methods are well recognized and have established track records

• Both mesh individual surfaces

• Delaunay (default)– works on “closed” surfaces– Delaunay mesh quality is not good

on poorly parameterized surfaces

• Advancing Front– produces higher quality elements

at boundaries– traditionally slower than Delaunay– cannot mesh “closed” surfaces




Training ManualOptions – Meshing Strategy

• Advancing Front and Inflation 3D– Includes Inflation– Quickly generates a mesh with

tetrahedra, prisms and pyramids with low memory usage

– New elements created from advancing “front” of triangles

– Creates tetrahedral elements by point (node) placement

– Identify exposed faces which now form the new “front”

• Extruded 2D Mesh– See next two slides




Training ManualExtruded Meshes

• When “Extruded 2D Mesh” is selected, the user is prompted to define the “Extruded Periodic Pair”

• Pick the two sets of faces from the model view or the object tree

– You can also select composite 2D regions from the Tree View

• Select the “Periodic Type” – Translational or Rotational

– If there are no vertices on the selected faces, you will be asked for a translation distance or a rotation angle

• Extruded meshes in CFX-Mesh are not as flexible as those that the Swept Mesher can generate

– The difference in the Periodic Pair must be a simple translation or rotation

– However, the source and target faces can consist of multiple (matching) faces




Training Manual

Extrusion Options

• 2D Extrusion Option

– Full = extrude through the full extent of the geometry

– Partial = thickness of elements determined automatically such that element quality is high. Will not necessarily fill geometry for a given number of layers

• Number of Layers

• Distribution

– distribution of element heights along the extrusion can be uniform or biased

• Expansion Factor

– Set the growth rate for the thickness of elements in non-uniform extrusion

Extruded Meshes




Training ManualOptions – Volume Meshing

• This option is only available with the Advancing Front and Inflation 3D meshing strategy

• Advancing Front options is default– Runs as a single process on a single

CPU

• Parallel Advancing Front– Multiple processes (multiple CPU’s) on the same or different machines– Faster mesh generation for large models– Overcomes memory limitations of a single processor / machine, especially on 32

bit system– Have at least 500,000 tetrahedral elements per partition. Do not run small models

in parallel. – Uses the CFX-Parallel (Solver) licenses if available. Else can be separately

licensed.




Training ManualOptions – Volume Meshing

• Set the Number of Partitions along the X,Y and Z coordinates– Divides the geometry based on the number

of partitions along each coordinate– Each partition is meshed independently and

then combined– Combined mesh will be same as that

generated by a single process

• Parallel Meshing can be:– Local Parallel, on the same machine– Distributed Parallel, on different machines– Distributed Parallel requires a Hosts List– Refer to CFX-Mesh Help for details on

setup and limitations of Distributed Parallel Meshing




Training Manual

• Allows you to look at the mesh on a particular face or faces before creating the entire surface or volume mesh

• Select face(s) for Preview Group either directly from the Model View or select a Composite 2D Region from the Tree View

• Can choose whether to generate mesh on selected faces or all at once

• Can view only surface mesh in CFX-Mesh, volume mesh may be viewed in CFX-Post

Mesh Preview




Training ManualMesh Preview Display

• Mesh Render Mode– Wire on Face Mesh shows the mesh faces

and the mesh lines– Solid Face shows the mesh faces– Wire Mesh shows just the mesh lines

• Display Mesh

– Mesh Before Inflation

– Mesh After Inflation

– Inflated Front shows triangles across the top of the inflated elements

– Inflated Mesh shows the inflation layers only

• Transparency (%)– 100% means completely transparent– 0% means completely opaque

• Shine (%)– Controls how much light is

reflected by the faces of the mesh– 0% gives lowest reflection and looks

matt– 100% gives highest reflection and looks

very bright

• Face Color Mode– Body shows mesh the same colour as

body– Uniform allows you to pick a color– Rainbow shows the mesh on each face

in a different colour, as different as possible




Training ManualMesh Statistics

• Mesh Statistics– Shows Number of Quads and

Triangles (Surface Elements) in the Preview Group

• Warning Messages or Errors– Non-fatal warning messages or errors

will be shown under the Errors item in the Tree View

– Fatal errors produce a pop-up message and are also shown under Errors

– Clicking on an Error or Warning highlights the related face or element if appropriate




Training Manual

• Generate Volume Mesh

– Once mesh is set up, you can generate the Volume Mesh

– The Volume Mesh is written to the GTM file for import into CFX-Pre GTM file automatically written when volume mesh is generated

– Contains all the mesh and region information

– Uses double-precision coordinates

– Not viewable in CFX-Mesh, use CFX-Post

– Can be repeated after any change to the mesh settings

Volume Mesh




Training Manual

• To abort surface mesh or volume mesh generation, use the Interrupt or Halt Current Processing button– This button is active only during mesh

generation and geometry verification

Stopping Mesh Generation

• Limitation: Interrupt takes effect only when underlying process exchanges data with user interface– In some circumstances the mesh process may go on for a long time without

exchanging data with the user interface– In these cases, if you want to terminate the process immediately, you can use

Task Manager (Windows) or kill command (Unix) to end the following processes. (Use with care)

• srfmsh_wb.exe • nsurf3d_wb.exe • inflate_wb.exe • nvol3d.exe • nvol2d_wb.exe




Training Manual

• By Default CFX-Mesh resolves every edge using a minimum of 3 vertices and meshes every face

• Results in a large mesh when there are many short edges and narrow faces in the CAD data

Virtual Topology

• Virtual Topology allows users to combine faces and edges into Virtual Faces and Virtual Edges

• CFX-Mesh only sees the combined Virtual Face or Virtual Edge

78 Surfaces represent car body

A single virtual surface




Training ManualCreating Virtual Topology

• Creating Virtual Topology:– Virtual Topology includes Virtual Face and Virtual Edge – Virtual Topology can be created either automatically or manually– Virtual Topology can be created in CFX-Mesh or in the Meshing Application

• Automatic Virtual Topology Creation:– CFX-Mesh automatically detect candidate edges and faces that could be merged based on

geometric parameters such as contact angle between faces, relative areas of faces, aspect ratios and shared boundary ratio

– Once these candidates have been detected, virtual edges and faces are created automatically– Where possible, external edges of Virtual Faces will be automatically merged together to form

Virtual Edges

• Manual Virtual Topology Creation:– User manually create Virtual Topology by inserting Virtual Faces or Virtual Edges – In the Virtual Face creation, user can turn on and off the option of automatic merging possible

external edges of Virtual Faces to from Virtual Edges

Automatic Virtual Topology creation

Manual Virtual Topology creation




Training ManualAutomatic Virtual Topology

• Automatic Virtual Topology creation:– User controls for this feature are very simple

Select Virtual Topology in the Tree View. Controls are available in the Details View

Automatic Merge Strategy controls the aggressiveness of the automatic Virtual Topology algorithm. The Low option merges the worst faces and edges in the model, while the High option attempts to merge much more of the geometry.

Automatic Merge Option defines whether the automatic Virtual Topology operation should be applied to the whole model (the default) or whether it should only apply to a selection of faces.

The face selection can be defined by selecting the faces directly from the graphics window or by selecting a Region name in the tree view.




Training ManualVirtual Topology Example

• Automatic Virtual Topology example:– Create a Virtual Face which includes 3 faces at the top– Several ways of doing this automatically

Method 1: Generate Virtual Topology on Entire Model

Right Click on Virtual Topology in the Model Tree and select Generate Virtual Topology on Entire Model

Select Automatic merge Option as Entire Model





Method 2: Generate Virtual Topology on Selected Set

Right Click on Virtual Topology in the Model Tree and select Generate Virtual Topology on Selected Set

Select Automatic Merge Option as Selected Set

Select three top faces and apply





Method 3: Generate Virtual Topology on on a control (Composite 2D region, inflated boundary, etc)

Create a Composite 2D Region which contains 3 faces at the top

Right Click on the created Composite 2D Region Select Simplify Location using Virtual Topology

Final results for these three methods are the same – One virtual face and two virtual edges will be created.

Virtual EdgesVirtual Face




Training ManualVirtual Face Example

• Manually creating a Virtual Face:– Right Click on Virtual Topology in the Model Tree and Insert a Virtual Face– Select the required faces from the graphics window and Apply– Can select Composite 2D regions as well– Selected faces must be adjacent

• Virtual Face example:

Fine mesh due to sliver surface

Select 3 faces

Mesh on Virtual Face




Training ManualVirtual Edges

• Virtual Face …– Where possible, CFX-Mesh will automatically merge external edges to form Virtual Edges.– This behavior can be turned off from the Options panel

Single Edge

Mesh with auto generation of Virtual

Edge turned off.




Training ManualVirtual Edge Example

• Creating a Virtual Edge:– Right Click on Virtual Topology in the Model Tree and Insert a Virtual Edge– Select the required edges from the graphics window and Apply– Selected edges must be adjacent

• Virtual Edge example:

Mesh with Virtual Edge




Training ManualVirtual Topology Restrictions

• Limited to “developable surfaces”– A developable surface has the property that it can be made out of sheet metal– A virtual surface can be created for a group of surfaces that can be unfolded or unrolled

into a flat plane

• Virtual Faces cannot form a closed region– All six sides of a cube cannot be combined into a Virtual Face




Training ManualVirtual Topology Rules

• Virtual Topology Rules:– Constituent faces of a Virtual Faces will not be available for selection. You can only

select the Virtual Face. • Should consider boundary conditions requirements before defining Virtual

Faces– Look for the status symbols of features in the Model Tree after creating or deleting

virtual entities.• Some features may become invalid or may require verification

– Virtual Topology definitions are persistent for geometry updates• If a location or CAD face does not exist after geometry update, the virtual entity

will become invalid– You can add more faces/edges to an existing Virtual Face or Virtual Edge– You can include an existing Virtual Face or Edge in a new Virtual Face or Edge



Aircraft Engine-Airframe

Workshop B.1

WS B.1: Aircraft Engine-Airframe



Training Manual

This workshop will take you through the process of importing an aircraft engine and airframe model prepared in DesignModeler, setting the mesh spacings, and generating a surface mesh for a CFD analysis. You will return to this workshop later (Workshop A.4) and add virtual topology.

• Goals:– Import the DM model file. – Define 2D regions for boundary conditions.– Define mesh spacings

Goals




Training ManualOpening the Geometry File

1. Copy the file Aircraft_Engine-Airframe.agdb to your working directory




5. Right click on and “Import Geometry” and click on “Browse…”.

6. Locate and open the file Aircraft_Engine-Airframe.agdb.





Training ManualImported Geometry

Only half the model will be meshed to take advantage of the

symmetry in the flow field




Training ManualChoosing the CFX-Mesh Method

8. Right-click on Mesh and select Insert Method• Select the body• Change the Method to CFX-Mesh

9. Right-click on the method in the tree and select Edit Mesh in CFX-Mesh




Training ManualCreating Composite Regions

Now create composite 2D regions:10.Right-click on Regions in the Tree View and Insert a Composite 2D Region

called Symmetry on the upper- Y surface11.Create the remaining 2D Region's as shown in the right figure

Symmetry

Outlet

Top

Bottom

Right

Inlet




Training ManualHiding Composite Regions

Now hide the newly created 2D Regions:

12. Under Tree View > Regions, right click on Symmetry and select Hide

13. Similarly hide all other 2D Regions except the Default 2D Region. You can do them all at once.Note: Hiding the external boundaries makes it easier to see

the aircraft surfaces and also makes it easier to pick the surfaces of the aircraft




Training ManualSetting Global Spacings

Set the Default Body Spacing:

14. Under Tree View > Mesh > Spacing, select Default Body Spacing and set Maximum Spacing to 0.08 [m]

Set the Default Face Spacing:

15. Under Tree View > Mesh > Spacing, select Default Face Spacing and set the parameters as shown

Generate surface mesh:

16. Under Tree View >Preview, right click on Default Preview Group and select Generate Surface Meshes




Training ManualSurface Mesh Preview

17. Review the surface mesh




Training ManualCAD Model Issues– The CAD model has many narrow surfaces which are not significant to the flow

analysis– The CAD model has many short edges because of the way the surfaces are

constructed– By default CFX-Mesh, resolves these narrow surfaces and short edges, resulting in

unnecessary mesh refinement and poor quality elements– We will revisit this geometry in Workshop B.4 and create virtual faces and virtual

edges to remove the unnecessary narrow faces and edges, thereby by reducing the mesh size and improving quality

18.For now, save the CFX-Mesh database (File > Save Project)



Static Mixer: Basic Settings, Mesh Controls and Inflation

Workshop B.2

WS B.2: Static Mixer: Basic Settings, Mesh Controls and Inflation



Training Manual

• This workshop will take you through the process of meshing a Static Mixer geometry with CFX-Mesh. Line mesh controls and inflationlayers will be added to better refine the mesh

• The basic steps involved in this workshop are:

– 1. Start a new instance of the ANSYS Meshing Application and open the geometry file to be meshed

– 2. Set the Mesh Method to CFX-Mesh and edit the Method

– 3. Define any desired composite regions

– 4. Set global mesh spacings (Body Spacing and Face Spacing)

– 5. Preview the initial surface mesh

– 6. Define Point Spacings and Line Mesh Controls

– 7. Define Inflation Boundaries

– 8. Generate the Volume Mesh and save the meshing database

Goals




Training ManualStarting the Meshing Application

1. Copy the file staticmixer.agdb to your working directory





6. Locate and open the file staticmixer.agdb.





Training ManualMeshing Options Form

8. When the Meshing Application comes up, go to the Meshing Options Panel which appears at the right of the screen• Set the Physics Preference to CFD• Set the Mesh Method to CFX-

Mesh• Make sure that Set Meshing

Defaults toggle is enabled• Click OK




Training ManualCFX-Mesh

9. Note that the model is now displayed in the CFX meshing environment.




Training ManualMaking the Model Transparent

10. In CFX-Mesh, click on the Geometry entry in the Tree View.

11. In the Details View and move the Transparency slider to 50% to make the model partially transparent• This makes it easier to see hidden faces in the model




Training ManualDefining Composite Region in1

12.Right-click on Regions in the Tree View and select Insert Composite Region• Create a Composite Region named in1 at the side pipe inlet as shown




Training ManualDefining Composite Region in2

13.Create a Composite Region named in2 at the other side pipe inlet as shown




Training ManualDefining Composite Region out

14.Create a Composite Region named out at the bottom pipe outlet as shown




Training ManualSetting the Global Body Spacing

15.Click on the + sign next to the Spacing entry in the Tree View to expand it

16.Set the Default Body Spacing to 0.20 m• Note the mesh size preview icon in the viewport




Training ManualSetting the Global Face Spacing

17.Set the Default Face Spacing Option to Angular Resolution with a setting of 18°

18.Set the Minimum Edge Length to 0.015 m and the Maximum to 0.20 m• Again note the mesh size preview icon




Training ManualInitial Mesh Preview

19.Click on the + sign next to Preview in the Tree View to expand it

20.Right-click on the Default Preview Group and select Generate Surface Meshes




Training ManualGenerating a Volume Mesh

The initial mesh is rather coarse for CFD purposes although it illustrates the basics steps involved in generating a tetrahedral mesh.

21.Right-click the Mesh entry in the Tree View and select Generate Volume Mesh• CFX-Mesh will create the volume mesh• The information panel at the bottom right will display the

node and element count for the mesh




Training ManualMesh Refinement

• The first part of this tutorial resulted in a rather coarse mesh with no resolution of the boundary layer near walls

• Although a better quality mesh for CFD purposes could be generated by defining finer global mesh spacings, the global mesh spacings will be left as they are

• Instead, a mesh control will be defined to refine the mesh in the area of the two pipe inlets. Also, an inflation layer will be added to the all walls in the geometry to better resolve the boundary layer




Training Manual

22. In the tree view right click on Controls under the Mesh listing and Insert a Point Spacing

23. In the Details View for the Point Spacing enter the following:

• Length Scale = 0.1• Radius of Influence = 0.5• Expansion Factor = 1.2

This defines a point spacing which describes the element size and the region of influence over which it will be applied

Mesh Control: Point Spacing




Training Manual

Line Control 1

24.Right-click on Controls in the Tree View, and select Insert > Line Control

25. In the Details View for the Line Control, click on Cancel in the box next to the first Point. Right-click the red bar in the box next to the first Point and select Edit in the pop-up menu

26. In the white text box, clear None and type in 1,-3,-1• You can hit Enter from the keyboard or click in

the model view to finish• Units are entered automatically

27.Similarly set the coordinates of the second Point to 1,-1,-1

28.Leave the Option as Uniform

29.Click in the empty Spacing box and select Point Spacing 1 from the Tree View and then click Apply




Training ManualLine Control 2 and Inflation

30. In the Tree View, right-click on Controls under the Mesh listing and Insert another Line Control

31.For Line Control 2:• Enter 1, 3 ,1 for the first Point• Enter 1, 1 , 1 for the second Point• Select Point Spacing 1 as the Spacing

32. In the Tree View right-click on Inflation and Insert an Inflated Boundary

33. In the Details View for Inflated Boundary 1, click in the Location box marked None, select Default 2D Region from the Tree View as the Location and click Apply• This will inflate from all walls in the

model

34.Set the Maximum Thickness for the inflated boundary to 0.2 m




Training ManualMesh Preview for Refined Mesh

35.Right-click on Preview > Default Preview Group and select Generate This Surface Mesh

• Notice the finer mesh in the two side pipes

• You can modify the Length Scale of Point Spacing 1 to refine the mesh further

• Also note the quad faces on the faces normal to the inflated boundary




Training Manual

You are now ready to create and save the volume mesh:

36.Select Tools > Options > CFX-Mesh Options

• Check that Volume Mesh Output is set to Add to CMDB File

• Click OK

37.Click on the Generate Volume Mesh icon on the task bar

38.When the process finishes, save your CFX-Mesh database (File > Save)

• The volume mesh is now stored in the Meshing Application cmdb file

• Note the change in the node and element count in the Information window and the addition of prisms from inflation

Final Volume Mesh



Extruded Mesh

Workshop B.3

WS B.3: Extruded Mesh



Training Manual

• This workshop will take you through the process of meshing a simplebox geometry with an extruded 2D mesh. The Full extrusion option will be demonstrated.

• The basic steps involved in this workshop are:

– 1. Start a new instance of the ANSYS Meshing Application and open the geometry file to be meshed

– 2. Set the Mesh Method to CFX-Mesh and edit the Method

– 3. In CFX-Mesh, change the mesh options to Extruded 2D Mesh and set the extrusion options

– 4. Define the faces for the 2D periodic pair

– 5. Set global mesh spacings (Body Spacing and Face Spacing)

– 6. Define an inflation layer on the side walls

– 7. Preview the surface mesh

– 8. Generate the Volume Mesh and save the meshing database

Goals




Training ManualStarting the Meshing Application

1. Copy the file box.agdb to your working directory





6. Locate and open the file box.agdb.





Training ManualMeshing Options Form

8. When the Meshing Application comes up, go to the Meshing Options Panel which appears at the right of the screen• Set the Physics Preference to CFD• Set the Mesh Method to CFX-

Mesh• Make sure that Set Meshing

Defaults toggle is enabled• Click OK




Training ManualCFX-Mesh

9. The model is now displayed in the CFX meshing environment.

10.Note that there are two faces on either end of the bar. As is, this would not be a general sweepable body in the Meshing Application Swept Mesher.




Training ManualMesh Options

11. Click on the Options entry under Mesh in the Tree View

12. In the Details View, set the Meshing Strategy Option to Extruded 2D Mesh

13.Leave the 2D Extrusion Option set to Full

14.Change the Number of Layers to 50 with a Uniform distribution




Training ManualExtruded Periodic Pair

• Note the addition of an Extruded Periodic Pair in the Tree View. This entry has a red X next to it since the faces which comprise it have yet to be defined.

15.Click on the Extruded Periodic Pair entry in the Tree View

16.In the Details View, select the two faces at the high Z end of the box and click Apply in the Location 1 entry box

17.Similarly select the two faces at the other side of the box and click Apply in the Location 2 entry box




Training ManualSetting the Global Body Spacing

18.Click on the + sign next to the Spacing entry in the Tree View to expand it

19.Set the Default Body Spacing to 0.10 in• Note the mesh size preview icon in the viewport




Training ManualSetting the Global Face Spacing

20.Set the Default Face Spacing Option to Constant with a setting of 0.10 in




Training ManualInitial Mesh Preview

21.Select Preview > Default Preview Group > Generate Surface Meshes

• Note the extrusion in the length direction




Training ManualAdding Inflation

22. In the Tree View right-click on Inflation and Insert > Inflated Boundary

23. In the Details View for Inflated Boundary 1, select the four sides of the box from the viewport and click Apply in the Location box.

• This will inflate the mesh from the four sides.

24. Set the Maximum Thickness to 0.20 in




Training ManualFinal Mesh Preview

25.Right-click on the Default Preview Group and select Generate Surface Meshes• Since there are now quad faces on the ends from the inflated layer, a combination of

hex and prism elements will be generated when the mesh is extruded




Training Manual

You are now ready to create and save the volume mesh:

26. Click on the Generate Volume Mesh icon on the task bar

27. When the process finishes, save your CFX-Mesh database (File > Save).

• The volume mesh is now stored in the Meshing Application cmdb file

• Note that the Mesh Information Window shows that the volume mesh contains a combination of hexahedral (extruded quads) and prismatic (extruded tris) elements

Final Volume Mesh



Virtual Topology for Geometry and Mesh

Workshop B.4

WS B.4: Virtual Topology for Geometry and Mesh



Training Manual

• This workshop will take you through the process of using virtual topology to create a better quality mesh for the aircraft engine geometry imported in Workshop B.1

• Goals:– Use Automatic Virtual Topology to improve mesh quality

1. Open the CFX-Mesh database that you saved at the end of Workshop B.1

Goals




Training ManualCAD Issues and Virtual Topology

– The CAD model has many narrow surfaces which are not significant to the flow analysis

– CAD model has many short edges because of the way the surfaces are constructed

– By default CFX-Mesh, resolves these narrow surfaces and short edges, resulting in unnecessary mesh refinement and poor quality elements

–We will create virtual faces and virtual edges to remove the unnecessary narrow faces and edges, thereby by reducing the mesh size and improving quality

– The automatic method of creating virtual topology will be demonstrated in the workshop




Training ManualInitial Surface Mesh (Before VT)




Training ManualAutomatic Virtual Topology

2. Select Virtual Topology in the Tree View

• Set the Automatic Merge Strategy to Low

• Set the Automatic Merge Option to Entire Model

3. Right-click on Virtual Topology and select Generate Virtual Topology on the Entire Model




Training Manual

• You should see that a number of virtual faces and edges have been created

• These appear in the Tree View below the Virtual Topology object

• You can click on the various virtual faces and edges. They are color coded so that different faces and edges appear differently.

• The leading and trailing edge of the wing are areas of interest for CFD. You will find that they have been grouped into virtual faces which is not desirable

Viewing Virtual Faces




Training ManualDeleting Virtual Faces

4. Find any virtual faces which include the wing leading edge faces and delete them • These are Virtual Face 8 and Virtual Face 11




Training ManualDeleting Virtual Faces

5. Find the virtual face which include the wing trailing edge and delete it• This is Virtual Face 7




Training ManualPreview Surface Mesh with VT

6. Regenerate the surface mesh to see the effect of adding virtual topology




Training Manual

• You could further modify the mesh by creating virtual faces and edges in selected areas manually to further improve the mesh quality

7. Generate the volume mesh and save the CFX-Mesh database

Creating the Volume Mesh

am 12 appendix b

Documents

basic steps

meshing takes

composite

final volume

project schematic

meshing options

composite

automatic