Kynan Maley ey Volume Meshing Volume mesh shin ing is the basic - - PowerPoint PPT Presentation

Best st Practices: s: Volume e Meshing Kynan Maley ey

Volume mesh shin ing is the basic ic tool that allows s the creation ion of the space ce discr scretiz ization ion needed to solve most st of the CAE equ quation

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s for:

– CFD – Stress Analysis – Heat transfer – Electro-Chemistry – Magneto Hydro Dynamics – ...

Volume Meshing

Pipel eline e Meshing

Pipeli line meshing allows s you to:

– Change geometry, mesh type, refinements, location/number of prism layers, etc. – Automatically update the mesh and map the old solution – Rapidly evaluate multiple designs

Solu lution ion mappi ping

– Make changes to the geometry and mesh while retaining your solution – Physics is independent of mesh

3 Wrap appe per Remesher esher Polyh yhedral Meshe sher Surface ce Preparation / Meshing Volum ume e Mesh h Gener erat ation

• n

Trim Cell Meshe sher Prism sm Laye yer

General l Purpose

• se 3D Meshers:

– Polyhedral – Trimmer – Tet Mesher

General l purpose pose mesh shers on specia ial l geom

• metries

ies tend to produce ce non optim imal l mesh shes s in terms s of:

– Cell count – Quality

Volume Meshing g in ST STAR AR-CCM+ CM+

Exampl ples s of specia cial geometries: s:

– Thin objects/parts – Extruded parts – Long or curved pipes/ducts

Specia ciali lized (2.5D) 5D) Meshers:

– Prism Layer Mesher – Extruder – Thin Mesher – Generalized Cylinder Mesher – Advancing Layer Mesher

Volume Meshing g in ST STAR AR-CCM+ CM+

2.5D 5D meshin ing is a synthetic ic defin inition ition of those se mesh shin ing techniqu iques s that exploi ploit the fact that certain in specia cial geometries ies have a general l mesh in 2 dimensi sion

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s while le in the 3rd

rd dimension

• n the mesh

sh has some form of sim impli plifica ication ion:

– Extruded in a predetermined direction – Extruded along the local normal direction – Swept along a 3d curve or axis

Volume Meshing g in ST STAR AR-CCM+ CM+

Full l volume mesh shing pipeli line is parall llel l poly mesh sher Reducin cing memor

• ry and wall

l time

Volume Meshing g in ST STAR AR-CCM+ CM+

Golden rule of volume meshing in ST STAR-CCM+ Volume mesh shers have requ quirements s for the input surface ce:

– Closed – Manifold – Non-intersecting

Often cell qu quali lity issues in the volume mesh sh can be tracked dow

• wn to

face ce qu quality ity issues s in the surface ce mesh sh Recom

• mmendation
• n is to use the Surface

ce Remesh sher always s prior to volume mesh shing (with same size settings) s)

Volume Meshing

Quali lity of CAD determin ines path to close sed, , manif ifold

• ld,

, non interse sect ctin ing surface ce

– The surface wrapper is used for the worst quality CAD

• Also useful for de-featuring your model

– Other methods exist to fix minor CAD issues

Volume Meshing Surface Mesh

Polyhedral l mesher

– General purpose, reliable, robust – Capable of multi-region conformal meshing – Suitable for Conjugate Heat Transfer simulations

Trimmer

– Fast and high quality – Anisotropic refinement – Perfect for large domains such as:

• Cars in wind tunnels
• Airplanes
• Ships
• Trains

Gener eral Purpose

• se Mesher

er Polyhedral - Trimmer

Rule of thumb b here is to use a trimmed mesh for cases s that have large cartesia ian alig igned flow

• w direction
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Also so useful l when Trimmer Wake Refinement is needed (refinement foll llows shape pe of boundary)

– Can be done in a local coordinate system, allowing alignment with flow direction

Gener eral Purpose

• se Mesher

er Trimmer Mesher

In many situations s it is desirable le to have the possi sibil bility to accurately control

• l the mesh

sh size

– High gradient zones – Shocks – High error zones

This s can be accom

• mpl

plish shed by by placin cing appropr

• priate Volumetric

Controls

Gener eral Purpose

• se Mesher

er Refinement using Volumetric Controls

Volumetric c Controls

• ls allow a

numbe ber of refinement types: s:

– Surface Mesh – Volume Mesh

• Isotropic
• Anisotropic (Trimmer)

– Prism Layer Mesh

Gener eral Purpose

• se Mesher

er Refinement using Volumetric Controls

Surface ce mesh size can be set at individual

– Boundaries – Feature Curves

The volume mesh sh size is related to the surface ce size and grow

• wth rate

Gener eral Purpose

• se Mesher

er Refinement using Boundaries and Feature Curves

Refin inement levels ls prov

• vide

ide a qu quick k way to globa bally ly refine a polyhedral l mesh sh

– Activated within the Polyhedral Mesher model settings – One of two refinement levels selected in Reference Values

• Level 1: Splits each polyhedral cell into 6 or 7 new cells
• Level 2: Splits each polyhedral cell into 40 to 50 new cells
• Prism Layer unchanged

Gener eral Purpose

• se Mesher

er Polyhedra yhedral Refinement Level

Av Avoid

• id huge jumps

ps in volume ratio,

• ,

it will l cause se issues Keep p the ratio io as small ll as possi ssible ble Prism sm layers s can help impr prove blending from near wall ll to far field ld

Volume Mesh Volume Ratio

The volume ratio io for trimmed cells ls is influence ced through different Grow

• wth

Rate values On continuum level

– Trimmer > Properties: Template mesh growth rate – Reference Values > Template Growth rate > Properties: Default Growth rate

Volume Mesh Volume Ratio - Trimmer

On continuum, , boundary and interface ce level

– Boundary growth rate

It controls

• ls the rate of size changes

s between cells ls adjace cent to surface ces s and cells s in the core

Volume Mesh Volume Ratio - Trimmer

Example ple Templ plate Grow

• wth Rate option
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– Boundary Growth rate – Default Growth rate

Volume Mesh Volume Ratio - Trimmer

None Very y Slow Fast st

What are prism sm cells? ls?

– A polyhedral base, a copy of it at top and rectangular sides connecting both

Where are prism sm cells ls used?

– Wall Prism Layer (turbulence, heat transfer) – Extruder – Thin Mesher – Advancing Layer Mesher

Volume Mesh Prism Layer Mesher

The Prism sm Layer thickn kness ss is subtract cted from

• m the boundary

– Offset surface

A core mesh sh is created The Prism sm Mesh is extruded to the boundary

Wall Prism Laye yers rs Generation of Prism Layer Mesh

Where are Prism sm Layers s generated?

– Only at boundaries of type Wall

Why is no Prism Layer created at my fluid-soli solid interface ce?

– Although the boundaries forming an interface are often of type Wall, being an interface overrules this setting: At an interface no prism layers will be generated as default

Wall Prism Laye yers rs Locations of Prism Mesh

With the recent release ses of ST STAR AR-CCM+ + the creation ion of boundary layers s has s been further impr proved Today I will l show

• w you some of the Model

l Properties with which ch to influ luence ce the prism sm mesh sh in narrow

• w passa

ssages

– Gap Fill Percentage – Minimum Thickness Percentage – Layer Reduction Percentage

Wall Prism Laye yers rs Introduction to Properties Options

Wall Prism Laye yers rs

Default 25% 25% 10% 10% Default 10% 0% 25% 25% Default 50% 50% 85% 85%

Wall Prism Laye yers rs Expert Settings

The extruder mesh shin ing model l perfor

• rms an addition

itional l volume mesh shin ing step p once the core mesh sh has been generated The model l can be activated for any of the core mesh types s and enabled bled for any boundary Care should ld be take ken how

• wever that the extrusion

ion volume will l not interfere with the exist sting mesh sh by by intersec secting it in any way Generates prism sm cells ls which extends s the confines s of the starting surface ce Can use any coordin inate system:

– Cartesian – Cylindrical – Spherical

Ad Additiona

• nal Mesher

her Extruder

Extruder Mesher Option

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– Frozen Boundaries

Ad Additiona

• nal Mesher

her Extruder

Froze zen Boundaries On On Froze zen Boundaries Off Off

Infla late the compu putation

• nal

l domain in all direct ction

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– One possibility is to change the Part

• n the Geometry level

– Another is to ex extrude de the outer boundaries without the Frozen Boundaries option

Ad Additiona

• nal Mesher

her Extruder Example 1

Ad Additiona

• nal Mesher

her Extruder Example 2

3L-8L 8L L

Generates an Extruded mesh alon

• ng lengths

s of a part consi sidered a cylinder

– Automatic cylinder detection

Ad Additiona

• nal Mesher

her Generalized Cylinder

The thin meshin ing model l allows s thin region

• ns in the geom
• metry to have a

prism smatic ic type volume mesh sh Reason son is to improve the ov

• verall

ll cell l qu quality and reduce ce the cell l count when compa pared to an equ quivalen lent tetrahedral l or polyhedral type core mesh sh When very thin struct ctures cannot

• t be modele

led using baffles les – their thickn ckness s must be modeled led with a minimum of 3 cells ls through the thick ckness

Ad Adva vanced ed Mesher er Thin Mesher

Ad Adva vanced ed Mesher er Example - Thin Mesher

The advancin cing layer produce ces s prism smatic c cell ll layers s near wall boundaries Extruding the cells ls from the surface ce into the region

• n volume allows

s for a thick cker layer with a more unifor

• rm distribu

bution

• n than the

prism sm layer mesher

Ad Adva vanced ed Mesher er Advancing Layer

Ad Advancin cing Layer Option

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– Two options for Stretching Function – Several options for Stretching Mode

To influence ce the advancin cing layer mesh sh at convex corners, s, refine the Feat ature re Curve e at this edge

Ad Adva vanced ed Mesher er Advancing Layer

Ad Adva vanced ed Mesher er Advancing Layer Example - Shuttle

Direct cted mesh shin ing is a method

• d for creatin

ing swept mesh shes s from a 2D startin ing surface ce mesh The starting surface ce mesh may either be created by by:

– Patching the surface and creating quadrahedral elements – Using the surface of an existing volume mesh

The surface ce is then swept along a path descr cribe bed by by the CAD geom

• metry

This s results lts in a high qu quality struct ctured mesh

Direct ected d Mesher er

Electric Machines Engine Powertrain

Overse set Meshin ing:

– A background mesh enclosing the whole solution domain – Separate meshes enclosing each body – The regions overlap, and flow-field information is passed between them

No need to remesh sh during motion ion or after mov

• vin

ing geom

• metry!

Ove vers rset Mesher er

Ove vers rset Mesher er

Ove vers rset Mesher er

Any Questions

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Quest stion

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