Best st Practices: s: Volume e Meshing Kynan Maley ey
Volume Meshing 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 ons s for: – CFD – Stress Analysis – Heat transfer – Electro-Chemistry – Magneto Hydro Dynamics – ...
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 Polyh yhedral Meshe sher Prism sm Wrap appe per Remesher esher Laye yer Trim Cell Meshe sher 3 Surface ce Preparation / Meshing Volum ume e Mesh h Gener erat ation on
Volume Meshing g in ST STAR AR-CCM+ CM+ General l Purpose ose 3D Meshers: – Polyhedral – Trimmer – Tet Mesher General l purpose pose mesh shers on specia ial l geom ometries 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 ons s while le in the 3 rd rd dimension on 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 ory and wall l time
Volume Meshing 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 own to face ce qu quality ity issues s in the surface ce mesh sh Recom ommendation on is to use the Surface ce Remesh sher always s prior to volume mesh shing (with same size settings) s)
Volume Meshing Surface Mesh Quali lity of CAD determin ines path to close sed, , manif ifold old, , 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
Gener eral Purpose ose Mesher er Polyhedral - Trimmer 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 ose Mesher er Trimmer Mesher Rule of thumb b here is to use a trimmed mesh for cases s that have large cartesia ian alig igned flow ow direction ons 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 ose Mesher er Refinement using Volumetric Controls In many situations s it is desirable le to have the possi sibil bility to accurately control ol the mesh sh size – High gradient zones – Shocks – High error zones This s can be accom ompl plish shed by by placin cing appropr opriate Volumetric Controls
Gener eral Purpose ose Mesher er Refinement using Volumetric Controls Volumetric c Controls ols allow a numbe ber of refinement types: s: – Surface Mesh – Volume Mesh • Isotropic • Anisotropic (Trimmer) – Prism Layer Mesh
Gener eral Purpose ose Mesher er Refinement using Boundaries and Feature Curves 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 owth rate
Gener eral Purpose ose Mesher er Polyhedra yhedral Refinement Level Refin inement levels ls prov ovide 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
Volume Mesh Volume Ratio Avoid Av oid huge jumps ps in volume ratio, o, 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 - Trimmer The volume ratio io for trimmed cells ls is influence ced through different Grow owth 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 ols 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 owth Rate option ons – Boundary Growth rate Fast st Very y Slow None – Default Growth rate
Volume Mesh Prism Layer Mesher 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
Wall Prism Laye yers rs Generation of Prism Layer Mesh The Prism sm Layer thickn kness ss is subtract cted from om the boundary – Offset surface A core mesh sh is created The Prism sm Mesh is extruded to the boundary
Wall Prism Laye yers rs Locations of Prism 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 Introduction to Properties Options 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 ow you some of the Model l Properties with which ch to influ luence ce the prism sm mesh sh in narrow ow passa ssages – Gap Fill Percentage – Minimum Thickness Percentage – Layer Reduction Percentage
Wall Prism Laye yers rs Default Default Default 25% 25% 50% 50% 10% 0% 85% 85% 10% 10% 25% 25%
Wall Prism Laye yers rs Expert Settings
Ad Additiona onal Mesher her Extruder The extruder mesh shin ing model l perfor orms 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 owever 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 onal Mesher her Extruder Extruder Mesher Option ons – Frozen Boundaries Froze zen Boundaries On On Froze zen Boundaries Off Off
Ad Additiona onal Mesher her Extruder Example 1 Infla late the compu putation onal l domain in all direct ction ons – One possibility is to change the Part on the Geometry level – Another is to ex extrude de the outer boundaries without the Frozen Boundaries option
Ad Additiona onal Mesher her Extruder Example 2 L 3L-8L 8L
Additiona Ad onal Mesher her Generalized Cylinder Generates an Extruded mesh alon ong lengths s of a part consi sidered a cylinder – Automatic cylinder detection
Ad Adva vanced ed Mesher er Thin Mesher The thin meshin ing model l allows s thin region ons in the geom ometry to have a prism smatic ic type volume mesh sh Reason son is to improve the ov overall 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 ot 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 Example - Thin Mesher
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