Icemcfd Tips&Tricks2010

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© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary


ICEM CFD

Tips and Tricks2010…

ICEM CFD

Tips and Tricks2010…

SimonPereira




Guiding principles of Workbench

CAD Model

WorkbenchModel

Thisimagecann otcurrently bedisplayed.

• Parametric; update in theCAD, DM or Spaceclaim

• Persistent; meshingkeeps up with modelchanges





• Highly-automated

– Physics aware

intelligent defaults

– Context sensitivemeshing (prism,

contact, etc.)

Automatic Contact(FEA),

Non-conformalinterfaces (CFD), etc.

Automated Meshing

Apply loads on geometryGo straight to solution!





• Flexibility:

– Breadth of mesh

methods/controls– Depth of

basic/advanced tools

Hex-Dominant

Tet

Swept

Free Mesh Type = Tetra

Free Mesh Type = Hexa Dominant

Free Mesh Type = Hexa Core




Workbench IntegratedMeshing

►Sold as part of integrated solver

solution►Can Add additional dedicatedseats

The Future of Meshing

►Combination of best in classtechnologies and concepts

►Integrated in a user friendlysimulation environment

►For all Physics (CFD, FEA, etc.)

Workbench Guiding Principles

►Parametric and Persistent

►Highly Automated, Physics Aware

►

Flexible Controls►Adaptive Architecture

CFD with“programcontrolled

” inflation

!"#" Meshing

GAMBIT

CFX-Mesh

ANSYS MAPDL

ICEM CFD

TGrid

Supports instances

FEA

Combine

meshmethods




E x t e n d e d

F u n

c t i o n a l i t y

Mesh from

►Facets and/or Mesh

►Poor or complex data

Efficiently Mesh large/complex models

►Greater than 20 million cells

►Extended mesh controls

Advanced Mesh options

►Intelligent automated Prism

►HexCore to far-field planes

►

Wrapper technology►GoCart technology

Extended mesh diagnostics

Interactive Mesh Editing

►Remeshing, etc.

ComplexGeometry

AdvancedCartesian Hexa

Core and Inflation

Cavity

Re-meshing

Testdrive

GoCart

now!

!"#" TGrid E$%ends !"#" Meshing

Capabili%ies Wi%h &o'er To(

Wrap anyComplexGeometry




Mesh from

►Dirty CAD, Third Party Geometry, etc.

►Faceted Data, Scan Data, STL

►Combinations of CAD, Facets & Mesh

E

x t en d e d

F un c t i on al i t y

Efficiently Mesh large/complex models

►Greater than 20 million cells

►Extended mesh controlsHexa mesh

►Structured or Unstructured

►Advanced blocking control

Extended mesh diagnostics

Advanced Interactive Mesh Editing

Output to a wide variety of solver formats

►CFD, FEA, neutral formats

StructuredHexa mesh

>250MillionCells

Interactive

MeshEditing

!"#" ICEM CFD E$%ends !"#"

Meshing Capabili%ies Wi%h &o'er To(



© 2010 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary © 2010 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary

ICEM CFD Tips andTricks 12)1ICEM CFD Tips andTricks 12)1

Simon PereiraSimon Pereira




genda

• Tips and Tricks

– General, Tetra/Prism– Hexa




Workbench *eaders

• Workbench readers are available foruse in ICEM CFD

– Use the same license keys as the ICEMCFD CAD interfaces

– Available for CATIA, SolidWorks, UG,Pro/E, Inventor, OneSpace, SolidEdge,Bladegen, SpaceClaim, JTOpen, etc.

• *.sat, *.x_t, *.dsdb, *.stp, *.step, *.igs,*.CATPart, *.ps, *.prt, *.dwg, *.sldprt, *.asm,*.agdb, *.model, *.par, *.scdoc, etc.)

– Also read Workbench formats such as

Design Modeler, Simulation, etc.• *.dsdb, *.agdb

• Read in Mesh and/or Geometry!




I+por% geo+e%r, using

Workbench *eaders• You can import Geometry from Workbench Design

Modeler

– Only active bodies are imported (Bone Marrow was not

active)– Named selections are imported

• Create Subset from Named Selection

– Named Selections can be setup in DM, Simulation orCAD packages such as UG, Pro/E or SolidWorks

– SpaceClaim too! – Option to filter by “Named Selection Prefixes”

• Accept the Defaults and apply

1

2

3

Often easier to do CAD creation,

simplification or repair in WorkbenchDesign modeler and transfer thedata to ICEM CFD




!a+ed "elec%ions as "ubse%s

• Each Body comes in as a Part

• The named Selections can appear as Geometry Subsets

– These can be used to control display or selection

– These can be turned into Parts

• Make sure all the Subsets are active

• Right Click on “Subsets” and choose “Create Part

• The new parts can be displayed

1

2




*epair Geo+e%r,

• Build Topology establishes connectivity

– Hole detection…• helpful for flood fill

• But not required for patch independent methods

– MultiZone

– Patch Dependent Meshing

– Etc.• Can cause trouble, use carefully

• Single curve cleanup allows you to use twodifferent tolerances,

– Small size for the majority so you don’tcollapse good features

– Larger size for stubborn gaps




*epair Geo+e%r,

• Once Diagnostic Topology is built options such as Floodfill and feature detection become available




*epair Geo+e%r,

• Detection tools have obvious use

for extracting, selecting and even

removing features– Hole tool has advanced options to

remove holes or set sizes for patchbased surface meshing

– Fillet tool is usefull for putting fillets ina different subset or part so you canapply a different meshing method

• But what about nasty models where Build topology can’t

help or causes more trouble then it is worth?




*epair Geo+e%r, -'.o /uild Topo

• The Check Geometry option does *surface based* featuredetection (not topology based)

• If you have a scary model, such as a large complex castengine block,

– don’t build topology, it may take too long or cause trouble.– delete all the curves and points– extract all the flat items to a new part

• Low curvature

– Extract points and curves from the flat parts– Complete parameter setup and proceed to Octree tetra…

Area andNormal canhelp filterprecisely




o%ke,s

• Hotkeys can make you much more efficient

• Search the Help to get hotkey maps•There is consistency tothe hotkeys

•For instance “s” is forsplit.

•On the geometrypanel, it is splitcurve.

•On the Mesh EditPanel, it is for SplitEdge

•Control-hotkey is aspecial ability, such ascontrol-s for splitw/propagate

•Shift-hokey is an alternate

•“?” to list hotkeys

Hotkeys are Tab specific




*e+inder abou% c%ree "i3es

• With Octree, it is important to understand mesh size…– Many long time users waste time setting wrong sizes

• Sizes carefully set to 0.75, 0.5 and some 0.3

• Max deviation set to 0.05 and Min size set to 0.45…

• The 0.75 and 0.5 both round downto 0.5.

• The smaller 0.3 would round down to0.25, but since it is sill much largerthan the small detail it is placed on,why no just set the entire part to 0.5

• The Min Size rounds down to 0.25

– Since this is the smallest size set, allother sizes are related to this size

– Local Size = (Smallest Size)*2n forn=0 to ∞




Densi%, regions…

• A density region sets the Max local size within the volume

– Use with Geometry Translation tool to copy/translate/rotate

– Use line and point densities when advantageous

– Use Width on surfaces to refine near the wall




Working 'i%h Densi%, regions

• More here about various density types, show

how to create a cone and a torus.




Edge Cri%erion 4 Thin Cu%s

– Edge Criterion• Determines if a node projects to surface or the edge is

split

• Range from 0 to 1– 0.2 ok for most cases.

• To increase nodes moving to fit to geometry, increasethis criterion

– Ideal for planned tet to hex conversion

• To increase refinement near entities, reduce this– Reduces non manifold verts in trailing edges

Edge Criterion = 0.2

Edge Criterion = 0.01Handy when thin cuts failor are difficult to setup




Edge Cri%erion 4 Thin Cu%s

– Define Thin cuts• Tool for resolving gaps based on pairs

of parts.

• It is made necessary by the octreeprocess– One way to avoid the problem is to use

patch based meshing

• Thin cuts have limits

– If two surfaces approach asymptotically,this may eventually break down

– If the separation rule of thin cuts isviolated at any point, all thin cuts aredeactivated

B

A

c

If the face of a tetra elementhas a surface/line node onpart “A” then it may nothave a surface/line node in

part “B ”

Note; If the surfaces of thetwo parts, A and B , meet,then the contact curvemust be in a third part, c , orthe thin cut will fail.




Ignore Wall Thickness

• You don’t always want thin gaps refined

• FEA – higher Aspect Ratio

• CFD – ignore wall thickness

Off

On

FEA CFD




ccurac,

• The mesh projection module inICEM CFD facets b-spline

surfaces and curves• Tri tolerance determines the

degree of facetization, accuracy

Tri t olerance = 0.1

Facetizedbehind thescenes




ccurac,

Lower tri tolerance = more precise curvature

Greater accuracy

Slower Rendering

Tri tolerance =0.1 Tri tolerance =0.01

Increase tri tolerance to work on large models, but put it

back at the default when computing the meshTri tolerance =0.001

(default)




ccurac,

• For greater accuracy withoutincreasing tri-tolerance, thereis a hexa option to projectdirectly to B-Splines (no

facetization)

Important for Highresolution Navier-

Stokes grids with veryfine near wall spacing(1e-6)




"urface Mesh T,pe

• Mesh Type• Mesh Method

– Transitions between mesh methods andtypes are handled automatically

Surface based meshing controls:

Set different mesh methodsor types for each surface?

Mapped/paved bosses,patch independent tetra

everywhere else?




!"#" ICEM CFD De5elop+en%

• Use Patch Independent on surfaces with poor connectivity.

– Common edges are meshed with Octree method.

• Paved with quads or tris onmore important regions,

– fillets, bosses, etc.

Surface based meshing controls:

Note; For High aspect ratioelements along wings, etc.

We recommend the Hexamerge method

This method can be usedto pave fillets, thinregions, etc.




&a%ch Independen% "urface Meshing

• Need a surface mesh for rough geometry?

– Patch Independent uses Octree approach for all

the Octree advantages– Huge time saver




e$a for "urface +eshing

• It is a little more work, but for stamped parts, Hexamay be well worth while.

• Controlled wrapping

Just use Remesh tofix any difficult

areas




Co+ple$ Geo+e%r,

• Often we have complex geometry, but the detailsare not critical to our analysis.

• Try shrinkwrap.– Essentially it is a Cartesian based surface mesher

ICEM CFDShrinkwrap is

good forcapturing roughblockage quickly

TGrid

Shrinkwrap isgood forcapturing detailsmore precisely

(more like ICEM

Octree Tetra)




/o%%o+ 6p Te%ra +e%hods

• Use these methods in conjunction with the other ICEMCFD methods

– “top down” or “patch independent” tetra

– Patch based surface meshing

• Each method has its own specific requirements/Benefits

– All require a closed outer volume (no single edges).

• Run all the checks on the surface mesh• Internal single edges are ok (baffles)

– No sudden changes either along a surface or across agap• use Laplace smooth to prep the surface

– Advancing Front mesher only works with all Tris






ICEM Te%ra Meshing

Octree

Expansion Ratio=1.2

Delaunay

Advancing Front

Mix and Matchwith Hexa Core or

Prism




TGrid Te%ra

• TGrid Tetra was also added toICEM CFD at V11.

• At R12, we also include thenew TGrid AF algorithm whichis advancing front based

(instead of skewness based)– It actually generates more

quickly that the previous

scheme

– Greater memory requirements

than Standard Delaunay




Te%2e$

• Tet2Hex (12 to 1) works with Octree tetra mesh andconverts it back to cartesian

• Transitions and smoothed mesh are not easily converted

– Turn off smoothing– Increasing Edge Criterion can help somewhat




*12 I+pro5e+en%

• Orient Octree by LCS

• Tet to Hex by LCS

Oriented Octree Tetra moreeasily converts to orientedANSYS ICEM CFD Hexahybrid mesh




Mesh Edi%ing 'i%h "ubse%s

• Subsets are non exclusive groups that youcan use to work with geometry and Mesh

• Experts use Subsets for mesh editing

– Display mesh Quality• Use Histogram to create subsets of the worst elements

• Add layers to subsets to get a better view

• Repair a few of the worst elements and stuck elements

• Run smoother– Check Mesh

• For many of the checks a Subset is the best option

• Add layers to the subset

• Repair issues

• Right click on subsets to add a layer orremove elements or choose modify for moreoptions, such as adding volume elements.




e$a FarField

• Hybridize your models– tunnel is usually simple and doesn’t change from run to run

• Use hexa for max efficiency

– Detailed region may be complex in shape• Use Tetra/Prism for max ease of mesh generation

– Merge together

Run Prism thru Both

Convert Tetrato Hexa




e$a Far Field

Some Models haveregions of complexityand regions where Hexawould be more

appropriate andrelatively easy to apply




&u%%ing i% all %og%her




e$a Wings.irfoils

• Here it is in reverse

– Hexa mesh inside the airfoils, Tetra mesh outside.

Then merge mesh together– Delete Hexas, Pyramids and Tetras, grow prisms

from quads and tris, then generate tetras again.




6nderhood

• In this case, a hexa region around the coolingsystem has been merged into the rest of this

under hood model (done with octree tetra)




7e, *ules for a successful Merge

• Perimeter must match

– Merged surface parts must share a perimeter 100%

– Both meshes must be projected to this perimeter• Curves in tetra, curves plus edge associations in hexa

• Can not simply merge the bottom of the cylinder with thetop of the box. They do not share a perimeter.

• Must first intersect them to subdivide the top of the box.Then mesh. Then merge the circle on the top of the boxwith the bottom of the cylinder

• Check for green nodes/edges around perimeter

– Size diff between Hexa/tetras will reduce quality.

• Try to stay within 3 to 1 either way; 1 to 1 or

0.7 (hexa) to 1 (tetra) is best.




"lide abou% Merging

• More to come




e$a Tunnels

• For External Aero,– tunnel is usually simple geometrically and doesn’t change from run to

run

• Use hexa for max efficeincy– Vehicle changes frequently and can be complex in shape

• Use Tetra for max ease of mesh generation

– Merge together

Tetra Vehicle

Hexa Tunnel

T l




e$a Tunnels

• For External Aero,

– Merge together

– Also hybridize the Tetraportion with Tet to hex…

Merge Hexa and Tetra

Flexible Hybrid Mesh




Mul%i8one Meshing

• Automatic hybrid blocking

consisting of Unstructured, Sweptand Structured Blocks to handleanisotropic meshing of wings etc.

• Unstructured blocks can be filledwith tetra, hexa core or hex dominantmesh

• O-grid boundary layers

• control mesh at the block level

• Flexible blocking structure makes itthe ultimate flexible hybrid mesh






Mul%i8one Meshing


M l%i8 &




Mul%i8one &rocess

Geometry Import & Repair Mesh Params

Bottom Up(automatic patch

based)

Top Down (Manual

patch Independent)

Interactively modifysurface blocking and

adjust edge params

2D to 3D Fill wBoundary layersMore

interactive

adjustment

Generate Mesh

Check Mesh

Output to

Solver

AdjustGeometry




• Sometimes a Simple shape iscomplicated by unnecessarypatches.

• Use Top Down blocking instead

• It will save time in the long runPatchwork wing

AutomaticBottom upapproach maygive a very

complex blocking

Manualcomponentapproach may bemuch cleaner,

then “sew” intorest of blocking

Mul%i8one "'eep De+o




Mul%i8one "'eep De+o

• Sweep with multiple sources and targets…

Mul%i8one De+o




Mul%i8one De+o

• Tidal Turbine

&ris+ &repara%ion




&ris+ &repara%ion

– Start with good tetra or tri-surface mesh

• It may be difficult to smooth prism after it is generated, it is relatively easy to improve thesurface mesh before hand

– Check aspect ratios / quality

– Check and fix all diagnostics• Single/multiple edges, Non-manifold vertices, Duplicate elements

• Laplace smooth• often better without tetra, then fill w/ Delaunay after smooth

• Delaunay mesh will have fewer nodes and smoother transitions; easierfor prism – Visually scan the surface mesh

– Look for kinks or sharp tent-like structures in the mesh

– Diagnostics may not reveal all surface discrepancies

– Make sure part associations are correct– Look for a few elements in one part scattered among another part

– Extruding from a few isolated elements and none of their neighbors will likely crash

– Modify part assignments of offending elements

Mesh "+oo%hing




g

• Use the Laplacian Smoother

• Moves the point towards an “ideal” location defined asthe average of the surrounding nodes

– Has the effect of averaging the surface mesh transitions andtriangles become more equilateral

• Better for bottom up fill and prism

•Laplacian smootherrp= Avg (ri)

p

1

2i

&ris+ "e%%ings




&ris+ "e%%ings

• Leave initial height as “0”

– This causes the initial height to float in order toreduce the volume change between the last prismand adjacent tetra.

&,ra+ids due %o in%ersec%ion




&,ra+ids due %o in%ersec%ion

• If the height is floating, you canrefine the mesh to control the prismheight and prevent intersection

from being resolved with pyramids

•Before refinement, prism

layers intersected andpyramids were used

•after refinement there is lotsof clearance (no pyramids)

Auto reduction (discussedlater) can also prevent

collision without pyramids

&ris+ "e%%ings




&ris+ "e%%ings

• Min Prism quality = 0.000001

– Default is 0.01; If you set this closer

to zero, prism will permit lowerquality prisms without resorting to

pyramids.

• Solver preference• If Min Prism Quality is too high, it

may adjust Max Prism angle down to

keep quality up, this will result inpyramids near sharp trailing edges.

– Common mistake

&ris+ "e%%ings




Max Prism Angle = 140 Max Prism Angle = 180

&ris+ "e%%ings

• Max Prism Angle keeps the prism layers connectedaround tight bends.

– Set this at 180 to prevent pyramids

&ris+ "e%%ings




s "e%% gs

• Advanced prism params, Auto Reduction

– Proximity can cause prism to stop and give pyramidsinstead.

– This option causes the prisms to squeeze down– This is fixed with redistribute prisms

Pyramids

Reduced (Squished) prismsRedistributed andNo Pyramids

*edis%ribu%e &ris+




• Redistribute prism improvements at R12

– Mesh more quickly with fewer layers, then split andredistribute prisms for a fixed initial height or ratio.

– The new distribution is calculated column by column

• Works on partial layers, etc.

"+oo%h &ris+




• Prism is difficult to smooth which is why we try tostart with as good a surface mesh as possible.

• Once the mesh is done, we recommend smoothing

without the prisms (Penta_6). Set them to frozen.This will only improve the tetra mesh. Do this untilyou don’t see any further improvements.

– Turning on the allow refinement option may help also, butuse judiciously or you may add many new elements.

• If you want to smooth some more turn on thesmooth for the Penta_6 elements, set the “up toValue” very low (< 0.05) so that most of the prismmesh is left alone.

– I also recommend saving before smoothing prisms incase you don’t like the result.

• In ICEM CFD prism quality is judged more harshlythan TGrid and other meshers.

– 0.01 or even 0.0001 is ok depending on your solver

Infla%ion fro+ 9uads




• You can Inflate from quads.

– Prism will not move pyramids (yet) so you

must delete the volume mesh first, or just startwith a surface mesh.

– Grow Prism without

a volume mesh– Tetra mesh using

the Delaunay

mesher• It will fill the void

without damaging

the inflation layers

6se E$is%ing 9uad :a,ers




• You can grow Prism along quads.

– Need to turn on Prism advanced

option for “Use Existing QuadLayers”

– Tricky to set up…

6se E$is%ing 9uad :a,ers




• Generate Hexa portion and tetra portion, Merge

– This is to connect the surface tris with the quads

• Delete all the hexas, keep only the envelope around the

tetra region, also delete the tetras– It will not align if there are Hexas behind the quads

– It will not inflate along Pyramids

– Be careful not to smooth QUAD faces so we can merge with Hexasagain later

– We hope to remove these tricky requirements at R13

• Setup prism params to ~match quad layers.

• Run Prism without volume mesh• Fill remaining volume with Delaunay tetra

• Load previous Hexa portion and Merge nodes with a

small tolerance.

"e%%ing &ris+ &ara+e%ers on

Cur5es




• Mesh > Curve Mesh Setup

• You can get Prism to transition linearly acrossa surface by not setting a height on thesurface, but instead set a different height on

each curve on the opposite sides of the prismsurface

• Height ratio and Num. of layers have no affecton prism for curve settings

Cur5es

Height = 0.003

Height =0.01

Height = 0 onsurface

&ris+ Transi%ion




• You can get Prism to transition linearly by notsetting a height on the wall, but instead set a

different height on each curve on theopposite edges of the prism surface…

Height =

0.01 Height = 0.003Height = 0 onsurface

igh spec% *a%io +esh




• Several ways

– Stretch and squish works if the high aspect ratio isin one direction only• Squish geometry, mesh with uniform mesh and then

stretch (scale in one direction) the mesh to get highaspect ratio.

– Surface mesh with high aspect ratio quads, growprisms and bottom up tetra… Good for someexternal aero applications

– MultiZone, use hexa edge params to adjust meshaspect ratio. Works on certain cases if thegeometry is good quality.

";uish and "%re%ch




– Stretch and squishworks if the highaspect ratio is in onedirection only• Squish geometry (in

one or two directions)

• mesh with uniformmesh

• then stretch (scaleback) the mesh to get

high aspect ratio.

Octree generatesUniform tetras

Which can thenbe stretched out

igh spec% ra%io Tri<s




• Best made by subdividing mapped quads

– Start with the Hexa merge method (discussed later)

– tri algorithms do not produce these well

• OCTREE Tetra produces uniform Tri’s (not high aspect ratio)

On convex features,

Aspect ratio is lesssevere as Prismradiates tris outward

Fill volume withbottom up tetramethod

=olu+e Change




• With bottom up tetra methods, highaspect ratio tri’s, quads or prismsresult in adjacent high aspect ratio

tetras or pyramids.• However the Elements between and

adjacent to those high aspect ratio

elements may have a lower aspectratio and therefore much morevolume.

• TGrid Pyramids may be better…

– (hope to improve for R12)

&ris+




• Prism can run from Quads or Tris

– But not from pyramids (yet), so run prism before tetra if starting with a quad mesh

– You can see that as the prism radiates outward, the element length stays thesame, but the width increases, which reduces the aspect ratio on convex surfaces

Mul%i8one




• Semi-automatic blocking (discussed later)

– Easy control of distribution, shape, etc. of the zones

– Zones can be structured, swept or unstructured

Mul%i8one




• Change the shape of mesh by simply contouringthe “ZONE” edges.

"+oo%hing




• Smoothing can adjust the angle or volume ratio ofelements

e$a /locking in si+ple s%eps…




• Once you decide on the blocking topology you want (the hardest part),generating the Hexa blocking is just a series of the same steps

– Split blocks (could be an Ogrid split) to get the topology you want.

– Delete blocks that are not part of your topology

– Associate the blocks with the geometry

– Move the vertices into place so they fit to the geometry and blocks are goodquality

– Adjust edge params for quality and transition

• There is a lot of iteration, but generally, it pays to go as far as you can witheach split before things go to complicated…

– Delete unneded blocks as soon as you can to reduce complexity

– Associated the blocking as soon as an edge can be matched with a curve (or

chain of curves) so you will have less work to do after you make further splits.– Move the verts into place while you only have a few splits so future splits will

already be aligned.

– Get as much done before you add a boundary OGrid so you won’t have tomove OGrid verts later.

Grids




• 2 main uses for OGRID…

– Capture Topology:

• OGrid can be used to get the basic blocking shape laid out. Is

your basic topology an OGrid or a Cgrid? Do you havefeatures within your model (such as drilled holes) that wouldbest be captured with an Ogrid?

• Use these as early in the blocking process as possible

– Boundary layer:

• OGrid used to aling mesh with the walls. Solves problem ofHexas mapped to a curve and helps align the besh forboundary layer analysis.

• Best if used late in the blocking process after all other stepsare complete.

>Grid Defini%ion




• An O-grid is a series of blocks created in one step which arranges grid linesinto an “O” shape or a wrapping nature

• 3 basic types created through the same operation all referred to as “O-grids”

• O-grid

• C-grid (half O-grid)

• L-grid (quarter O-grid)

• Reduce skew where a block corner must lie on a continuous curve/surface

• Cylinders

• Complex geometries

• Improves efficiency of node clustering near walls for CFD applications

O-grid C-grid L-grid

No O-grid(H-grid)

O-grid

Crea%ing an >Grid




• Select blocks for O-grid – Can select by visible, part, around face, around

edge, around vertex, 2 corner method, or individualselection

Note: Internal block has all internal (blue) edges and vertices

7 blocks in 3D

5 blocks in 2D

Select specific blocksor around face, edge,or vertex

>Grid>dding Faces




O-grid passesthrough this face

• Adding faces during O-grid creation – O-grid “passes through” the selected block faces

– In general, add faces on the “flat parts”

– Adding a face actually adds blocks on both sides of the face

• Examples of uses – Pipe ends

– Symmetry planes

– Complexgeometries

O-grid passesthrough this face

Half O-grid(C-grid)

dding Mul%iple Faces




• Any number of faces can be added around a selected block – If all the faces are added around a block, the result is no change

since the O-grid passes through all the faces

Quarter O-grid(L-grid)

Seen as a C-grid in onedirection andan L-grid inanotherdirection

Quarter O-grids

can be used toblock triangularshapes

>Grid>round /locks




• Select Around block(s) to create the O-grid around theselected blocks

– Useful for creating wrap-around grid around a solid object

– Examples

• Opposite order of creation from block around/O-grid inside

• Flow over a cylinder

• Boundary layer resolution around an airplane or car body

"caling an >Grid




• O-grids can be re-sized after or during creation – By default the O-grid size is set to minimize block

distortion

– You are actually scaling all parallel O-grid (radial) edgesto the selected edge

– The selected edge is given a factor of 1 – Numbers < 1 will shrink the edge and thus create a

larger inner block

Selected edge

factor = 1

Factor = 0.3

Wh, >Grid?




This mesh can be improved by using an O-grid

– An example of bad mesh in the block corners

Before O-grid

Right mouse click on the histogram to

access options like show, replot, ordone

Mul%iple Wa,s of /locking %he

"a+e Geo+e%r,




• Creating a fork by Merge vertices

#1 #2

#3 #4 #5

Mergevertices

Splits

Deleteblock

OrCollapse

Block

Mul%iple Wa,s of /locking %he "a+e

Geo+e%r,




• Creating a fork by Extrude faces

Extrude 1

Extrude 2

Associate

#1 #2 #3

#4 #5

Mul%iple Wa,s of /locking %he "a+e

Geo+e%r,

C i f k i h T d h d




split

• Creating a fork with Top-down methods

Two

quarterO-grids

OnequarterO-grid

OnequarterO-grid

Deleteblocks

Move

vertices

Topolog,




•What is common inthese?

– Their block topology

Topolog,

All these parts ha e the same

Thi h li l bl ki




• All these parts have the samebasic topology

– Blocking strategy for all pipes aresimilar.

– Single block with o-grid

– The only difference is the number ofsplits added to help control theblocking

– Create the one block, then split, andadd O-grid last

Single blockwith o-grid

Single block with 5splits and o-grid

splitsSingle block withmultiple splits and o-grid

This helical blockingis quickly createdwith extrude alongcurve

/asic /lock "%ruc%ures




Meshinsidefillet

O-grid isrequired unlessapproximatinga corner usinglarge mesh size

Badquality O-grid necessary

Acceptablequality

Badquality

O-grid necessary

Badquality O-gridnecessary

O-grid

Quality is

However, an

O-grid makes





Meshoutsidefillet

Quality isgood withoutan O-grid

O grid makesnormal gridlines forboundarylayerresolution

Meshinside andoutsidefillet.Combinepreviousexamples

This method needs large mesh size

Vertex atend of fillet

This is notpreferablebecausequality islower

There should beone vertex at thecenter of everyapproximate 90degree bend

Mesh onlyin ring

Mesh inboth

Split anyradialedge

Deletecenterblock





Split Split

Deleteblocks

Meshinsidetube

Tubes are

one-blocktopologies

Splits canbe addedfor morecontrol

Meshinsideandoutsidetube

Manystudentsmistakenly just split atgeometryfeatures

Badquality

O-grids canmake this workalthough it is notthe preferredtopology

Badangle


We must use thestraight-through split

Bad

angle




g g pstrategy as in theprevious example forgrid lines to flow withthe inner tube

Deleteblock

g

Add O-grid formeshing insidecurvature

BlocksselectedforcreatingO-grid

2 splits

Split forbetterblockingcontrol

There are multiple methodsof producing the Y-blockstructure

Method 1Quarter O-grid

Movevertices

These may also be called wedge blocks.They can be used to effectively terminate meshfrom continuing through the geometry


Method 2

splitMovevertices

Create

block




Method 3InsideH-grid

( bottom-up)

Delete blocks“permanently”

2 splits

Movevertices

Createblock

Collapseblock

Method 4InsideH-grid (top-down)

1stquarterO-grid

2ndquarterO-grid

Movevertices

Method 5Createblockfunction(quarter O-grid)

1

2

3

4

5

6


Add

quarterO-grid

Move

vertices




Add O-gridfor round

Since the round iscloser to 180degrees than 90degrees, having twoblock corners maybe better

Add O-grid

for round

A Y-blockstructurecan also beused for acircle

Useful for fillingthe center ofgeometry that isperiodic inmultiples of 3

Add O-grid Movevertices

g


splitDelete blocks“permanently” Merge

vertices




Movevertices

p y vertices

Createblocks

Add moresplits forcontrol

Method 2

Method 1

O-grid

Movevertices

Deleteblock

Splits formorecontrol


Thinthicknesses

First

block theoutside

Then put an

O-grid insideall blocks




are easily donewith an O-grid

(addappropriatefaces)

Deletethe insideblocks

ScanplaneResulting blocks

Method 1

Method 2

Vertex moved slightly offintersection for better angles


Method 3Using Y-

Half O-gridO-grid

Deleteblocks




Using Yblocks

Method 4Leavingsmallledge

Delete edgeassociation

In 3D model, interpolate

face association

Method 5Degenerateblocks

Start frommethod 4above

Mergevertices

Faceinterpolationnot necessarywhen mergingvertices

Method 6Convertblock Start from

method 5above

Alltri

QuaddominantConvert

block to freefor 2D orswept for 3D


O-grid




Filleted wings are easilydone with a simpleblock.The block can be made

larger than the wing andan O-grid made inside,or the block can be onthe wing and the O-gridmade around.

Edge splits to shape edges

Filleted wings are easily done witha block on the wing then add an

O-grid around

Knife-edge wings pose a problem if you collapse.The collapse behind the wing must propagate through theblocking, or invalid elements result in a corner.

Mesh region beyond theblade-tip is bad quality

This means mesh beyond the blade tip will have the same mesh pattern as onthe blade tip, as if the blade were meshed inside.

Very low angles and unnecessary mesh densityresult from a simple collapse





Create 4 blocks

Collapseblocks

Collapseblock

Delete blockspermanently Move

vertices

3 splits

O-gridwithsplit


A knife-edge blade can also be handledby collapsing all around the blade if the




by collapsing all around the blade if thecomplicated strategy of the previousexample is not wanted.

i l sHigh or low curvature, etc.

o' To




V a r i e t y o f A i r f o►May require different blocking strategy (Topology)

►Requires some robust scripting

o i l sTrailing edge?

o' To




V a r i e t y o f A i r f o►Blunt

►Deal with size transitions

►Sharp

►Collapse trailing edge block

l d sFar Fields

o' To




V

a r i e t y o f

F a r F i e l

►Square, round, half circle, Wedge etc.

►HGrid, OGrid, CGrid, YGrid, etc.

►Periodic?

Note: the FF scale hasbe dramaticallyreduced for illustration



l d sPeriodic?A d Bl d B Bl d

o' To




V

a r i e t y o f

F a r F i e

►Around Blades or Between Blades

►Between Blades if NO Tip Gap

Channel between blades?

►Multi-Block with OGrid

►HGrid converted to a single output block

PeriodicV a

"hif%ed &eriodic…




►High curvature or blade angle?

►Try Shifted periodic

ar i e t y

of F ar F

i el d s

No Tip Gap makes it much easier

►Edges don’t need to cross the airfoil

►More careful with a tip gap

r%hogonali%, "+oo%her

• Improves volume transition• Equalizes angles between elements




Equalizes angles, smoothesvolume transitions, makes themesh orthogonal

• Equalizes angles between elements

• Can affect just the mesh or adjustblocking

• Saves time otherwise spent onadjusting edge parameters• Can be used to set orthogonal initial

height• Works on many mesh types

– Structured Multi-block Hexa– Unstructured Hexa– hexa dominant– BF-Cart– Hybrid mesh

r%hogonali%, "+oo%her

• Users run into trouble because not




all the mesh is supposed to beorthogonal

– Release orthogonality

• Also can use this to set initialheight off the wall

• Note: this may reduce min quality…Its goal is to improve transitionsand the overall quality of the mesh

E$%ended Meshing(

ICEM CFD In%erac%i5e




• Options under

MultiZone Method

Yes: Writes ICEM CFD Files for usein ICEM CFDInteractive: Runs interactiveICEM CFDBatch: Runs ICEM CFD in Batch

Using ICEM CFD Interactive w/replay control, user can blockout a mesh and commit it back to Meshing

Change model parameters, and run ICEM CFD inbatch to update parameter change

/F>Car%

• Works well for models withouth d




sharp edges



Car%esian Mesh

• Do you have complex aerospace geometry, earlyd i h




design phase

• Consider Cart3D

– Inviscid flow Analysis package

– Cartesian Mesh based

– Developed at NASA AmesResearch center

– Integrated into ANSYS ICEMCFD (6dof)

– Extensively validated insubsonic and low supersonicregimes

After you narrow down your design, finalizewith more labor intensive /accurate body fittingmesh and solve in ANSYS CFD.

"elf Training

*esources

"elf Training

*esources



© 2010 ANSYS, Inc. All rights reserved. 114 ANSYS, Inc. Proprietary © 2010 ANSYS, Inc. All rights reserved. 114 ANSYS, Inc. Proprietary

"elf Training *esources




• ICEM CFD has many options.

– Flexibility, Power

– Harder to learn on yourown

• Ideally, you can get trainingfrom an instructor, but noteveryone has this option.

• Self training resources include

– Built in tutorials and Help

– Programmers Guide



Thank,ou

• Thank you




Thank you

• Don’t forget to contact support for assistance

or advanced suggestions

Documents

Icemcfd Tips&Tricks2010