fluent4
TRANSCRIPT
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Edge and Face Meshing
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Meshing - General
To reduce overall mesh size, confine small cells to areas where
they are needed (e.g., where high gradients are expected).
Controlling cell size distribution
Edges, Faces and Volumes can be directly meshed A uniform mesh is generated unless pre-meshing or sizing functions
are used.
Pre-meshing
Edge meshes can be graded (varying interval size on edge)
Graded edge mesh can be used to control distribution of cell size in
face mesh.
Controlling distribution of cell size in face mesh also controls
distribution of cell size in volume mesh.
Sizing Functions
New feature to control cell size in faces and volumes directly.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Edge Meshing
Edge mesh distribution is controlled through
the spacing and grading parameters.
Using the Edge meshing form
Picking
Temporary graphics
Links, Directions
Grading/Spacing
Special characteristics
Apply and Defaults
Invert and Reverse
Options
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Picking Edges for Meshing
Picking
Temporarily meshed edges
When you pick an edge, the edge is
temporarily meshed using white nodes
Displayed edge mesh is based on current grading and spacing parameters If you modify the scheme or spacing, the temporary mesh will be
immediately updated
When youApply, the mesh nodes will turn blue
Sense
Sense is used to show direction of grading Every picked edge will show its sense direction using an arrow
The sense can be reversed by a shift-middle click on the last edge picked
(this is in addition to the "next" functionality) or by clicking on the
Reverse button
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Soft Links
Picking and soft links
Pick with links
By enabling this option, Soft-linked edges can be selected in a single pick
Linked edges share the same information and can be picked in a single
pick
Modifying soft links
You can anytime:
Form links
Break links
Maintain links
By default, GAMBIT will form links between unmeshed edges that arepicked together
By default, GAMBIT will maintain links between meshed edges that are
picked together
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Grading Controls mesh density distribution along an edge.
Grading can produce single-sided or double-sided
mesh
Doubled-sided mesh can be symmetric or asymmetric.
Symmetric schemes produce symmetric mesh about
edge center.
Asymmetric schemes can produce asymmetric mesh
about edge center.
Single-sided grading:
Uses a multiplicative constant, R, to describe the ratio of
the length of two adjacent mesh elements, i.e., R = l(i+1) / li
R can be specified explicitly (Successive Ratio) or
determined indirectly
Gambit also uses edge length and spacing information to
determine R.
Single-sided grading
Symmetric grading
Asymmetric grading
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Double Sided Grading
Symmetric grading schemes implicitly
generate double sided grading that is
symmetric.
Asymmetric schemes are accessible when
Double-Sided Option is used with: Successive Ratio, First Length, Last Length,
First-Last Ratio, and Last-First Ratio
The mesh is symmetric if R1 and R2 are
equal.
The mesh is asymmetric if R1 and R2 are not
equal.
Edge center is determined automatically.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Spacing
Spacing
In all meshing forms, the following spacing functions can be specified:
Interval count - recommended for edge meshing only
A value of 5 creates 5 intervals on the edge (6 nodes, including ends)
% of edge length - recommended for edge meshing only An edge length of 10 and a value of 20 creates 5 intervals on the edge
Interval size - the default setting
Identifies the interval size relative to overall dimensions of geometry
Identifies "average" interval size if used with grading
An edge-length of 10 and a value of 2 creates 5 intervals on the edge
Average size of elements/grid is 2
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
First Edge Settings
Use first edge settings enabled
First edge selected in pick list updates form
Useful to copy settings from one meshed
edge to other edges.
Use first edge settings disabled Any time you pick two or more meshed edges
where there is a difference in:
the Type
the Spacing
the localApply button for that option willbe turned off
This allows you to maintain pre-existing grading and/or spacing settings for
each edge.
Enforce a change in grading and/or spacing by enablingApply button.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Mesh Options
Apply without meshing
This option is useful in cases where you
want to impose a scheme without fixing
the number of intervals
The higher level meshing scheme will decide
(and match) the intervals Example
Specify fixed interval and no grading
Specify double sided grading and
Apply without Meshing on bottom edges
Face meshing will automatically match mesh
Remove Old Mesh Deletes old mesh
Ignore Sizing Function
Sizing function has precedence on meshing
unless this option is enabled.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Face Meshing Face Meshing form
Upon picking a face
GAMBIT automatically chooses Quad elements
GAMBIT chooses the Type based on the
Solver/face vertex types
Available element/scheme type combinations Quad
Map
Submap
Tri-Primitive
Pave
Tri
Pave
Gambit also has quad-to-tri conversion utility.
Quad/Tri
Map
Pave
Wedge
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Face Meshing - Quad Examples
Quad: Map
Quad: Submap
Quad: Tri-Primitive
Quad: Pave
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Face Meshing - Quad/Tri and Tri Examples
Quad/Tri: Map
Quad/Tri: Pave
Quad/Tri: Wedge
Tri: Pave
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Deleting Old Mesh
Existing mesh must be removed before remeshing.
Mesh can be deleted using
delete mesh form.
Lower topology mesh can also be deleted (default)
Existing mesh can also be removed in all Create
mesh forms without the need for Delete mesh
Remove mesh
Leaves all lower topology mesh Remove mesh + lower mesh
Removes all lower mesh that is not shared
with another entity
Undo after meshing operation also works!
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Hard Linking
Mesh Links (Hard Links) Mesh linked entities have identical mesh
created for periodic boundary conditions
Applicable to Edge, Face, and Volume entities
Best to use soft links for edge meshing
To link volume meshes, all faces must be meshhard linked first.
Setting up Hard Links for Faces
Select faces and reference vertices
Edge sense will appear
Reverse orientation on by default for sense Periodic option can be used for split edges
Mesh one face before orafter hard link is defined
mesh on second face generated automatically
Multiple pairs of hard links can be created.
+ + + +
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Assessing Mesh Quality
Default measure of quality is based on EquiAngle Skew.
Definition of EquiAngle Skew:
where:
max = largest angle in face or cell
min = smallest angle in face or cell
e
= angle for equiangular face or cell
e.g., 60 for triangle, 90 for square
Range of skewness:
e
mine
e
emax ,180
max
min
max
0 1
best worst
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Examining the MeshExamine Mesh Form Display Type
Plane/Sphere
View mesh elements that fall in plane or sphere.
Range
View mesh elements within quality range. Histogram shows quality distribution.
Show worst elementautomatically zooms into
worst element
Select 2D/3D and Element Type
Select Quality Type
Display Mode
Change cell display attributes.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Striving for Quality
A poor quality grid will cause inaccurate solutions and/or slow convergence.
Minimize EquiAngle Skew:
Hex and Quad Cells
Skewness should not exceed 0.85.
Tris Skewness should not exceed 0.85.
Tets
Skewness should not exceed 0.9
Minimize local variations in cell size:
e.g., adjacent cells should not have size ratio greater than 20%.
If Examine Mesh shows such violations:
Delete mesh
Perform necessary decomposition and/or pre-mesh edges and faces.
Remesh
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Mesh Smoothing
Gambit generally incorporates default smoothing scheme after initial
mesh on face or in volume is created.
Default scheme can be changed in Edit - Defaults
Different scheme can be selected and
applied after meshing. Face mesh smoothing
Length-weighted Laplacian
Centroid Area
Winslow
Volume mesh smoothing Length-weighted Laplacian
Equipotential
Boundary mesh by default is fixed.
Option allows frees boundary mesh.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Assigning Boundary and Continuum Types
The Boundary Type Form
Enter entities to be grouped into single zone in
entity list box.
First choose entity type as face or edge.
Select boundary type for zone (entity group). Available types depend on Solver
Name zone if desired.
Apply defines zone and boundary type.
Can also modify and delete zone/boundary.
By default, External faces/edges are walls
Internal faces/edges are interior
The Continuum Type Form
Similar operation.
All continuum zones are by default, fluid.
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
FLUENT 5/6 Example: Flow over a Heated Obstacle
Boundary: Name = inlet
Type = VELOCITY_INLET
Boundary: Name = outlet
Type = PRESSURE_OUTLET
Continuum: Name = step
Type = SOLID
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Introductory GAMBIT Notes
GAMBIT v2.1 Jul 2003
Fluent User Services Center
www.fluentusers.com
Defaults: Example: Flow over a Heated Obstacle
By default, the 4 remaining external
faces have the Name and Type:
Boundary: Name = wall
Type = WALL
By default, the one remainingvolume has the Name and Type
Continuum: Name = fluid
Type = FLUID