Flow Examples Illustrating Benefits of Automated Meshing

© 2011 ANSYS, Inc. February 23, 20121

Dr Jasper KidgerANSYS UK Ltd

Human time to

generate Mesh

Conflicting Priorities

Absolute accuracy

of results

© 2011 ANSYS, Inc. February 23, 20122

Cell Count

Rationale

• Top on the list of challenges engineering companies are

facing is shortened product development schedules

while at the same time the product designs themselves

are becoming increasingly complex

• Companies have increasingly complex products for

© 2011 ANSYS, Inc. February 23, 20123

• Companies have increasingly complex products for

which they need to make more CFD simulations in a

shorter time frame

• How to increase the CFD simulation throughput with

acceptable accuracy?

Courtesy Siemens AG.

ANSYS Workbench Meshing

• Automated meshing environment for various mesh types

incl. tetrahedral, hexahedral, prismatic inflation layer,

hexahedral inflation layer, hexahedral core, body fitted

Cartesian, cut cell Cartesian

ANSYS Meshing

© 2011 ANSYS, Inc. February 23, 20124

ANSYS Extended Meshing

• Geometry acquisition/repair, mesh generation, mesh

editing and mesh diagnostics for large complex CFD

>250

Million

Cells

NACA4412 at 13.86° Angle of Attack and Re = 1.5 x 106

Meshing with typical mesh types

• Block Hex

• Tet

• Poly

NACA4412 Study

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• Poly

• CutCell

NACA4412 Study

Results

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Hex Block Mesh Prism-Tet Mesh

Prism-Poly Mesh Prism-CutCell Mesh

No. of prism layers: 10

Steady State, k-εεεε realizable w/ enhanced wall treatment

SIMPLE scheme

2nd order spatial discretisation

Ahmed Body, 25 Deg Slant

© 2011 ANSYS, Inc. February 23, 20127

Result

• CutCell (18M Cells): Cd = 0.3125

• Block Hex (30M Cells): Cd = 0.324

k-εεεε realizable turbulence model

Pressure based coupled solver with defaults

PRESTO! for pressure discretisation and 2nd order for all

other equations (momentum, turbulence)

Comparison between results obtained by using Body Fitted

Transition Duct Study

© 2011 ANSYS, Inc. February 23, 20128

Comparison between results obtained by using Body Fitted

Hex mesh and a similarly sized CutCell meshComparison of Pressure Coefficient Along Centerline of the Duct

- FLUENT simulation using Body Fitted Hex mesh

Transition Duct Study

Velocity on Centerline

Static Pressure Comparison

© 2011 ANSYS, Inc. February 23, 20129

Pressure on Centerline

CutCell Body Fitted Hex

CutCell

Body Fitted Hex

Transition Duct Study

Pressure Monitor on Walls

100

iterations62

iterations

© 2011 ANSYS, Inc. February 23, 201210

Faster Convergence

Body Fitted Hex CutCell

Transition Duct Study

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NASA C3X Transonic Turbine Vane

Structured Hex Mesh (SHM) Structured Hex Mesh Fine

(SHMF)Unstructured Hex Mesh

(UHM)

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CutCell Hex Mesh (CHM)Unstructured Tri-Prism Mesh

(UTM)

Unstructured Poly-Prism Mesh

(UPM)

CutCell Hex Mesh Fine (CHMF)

NASA C3X Transonic Turbine Vane

Suction side shock wave

© 2011 ANSYS, Inc. February 23, 201213

Ps/P0 = static-pressure/inlet-total-pressure

NASA C3X Transonic Turbine Vane

• P02/P01 = Ptotal-avg-outlet / Ptotal-avg-inlet• T02/T01 = Ttotal-avg-outlet / Ttotal-avg-inlet

• Mass flow rate = mass flow per passage

0.2

0.4

0.6

0.8

1

1.2

C3X Turbine Vane Results

SHM SHMF UHM CHM CHMF UTM UPM

Mass Flow 0.09% 0.00% 1.24% 1.07% 1.16% 1.42% 1.33%

P02 / P01 0.20% 0.00% -0.99% 0.04% 0.20% -0.39% -0.50%

© 2011 ANSYS, Inc. February 23, 201214

SHM SHMF UHM CHM CHMF UTM UPM

mass flow rate (kg/s) 1.126 1.125 1.139 1.137 1.138 1.141 1.14

P02/P01 0.9329 0.931 0.9218 0.9314 0.9329 0.9274 0.9263

T02/T01 0.9965 0.9957 0.996 0.9961 0.9963 0.9961 0.9962

0

0.2

•Mass flow rates and total pressure and temperature ratios within 1%SHM had slightly lower mass flow – may be due to mesh resolution.

•Mid-span pressure distributions in close agreementSome differences observed near suction side shock, which should reduce

if mesh resolution is enhanced

T02 / T01 0.08% 0.00% 0.03% 0.04% 0.06% 0.04% 0.05%

Stairmand Cyclone

CutCell Mesh

Hex Mesh

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Stairmand Cyclone

Tangential Velocity (m/s)

@ 0.41 m

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Tangential Velocity (m/s)

@ 0.41 m

-�- Cut Cell, -�- Course Block Hex, -�- poly, -�- tet, � Experimental

Stairmand Cyclone

Axial Velocity (m/s)

@ 0.41 m

© 2011 ANSYS, Inc. February 23, 201217

Axial Velocity (m/s)

@ 0.41 m

-�- Cut Cell, -�- Course Block Hex, -�- poly, -�- tet, � Experimental

Hex Mesh count: 875K

BERL Combustor

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CutCell Mesh count: 1.7M

Temperature Distribution

BERL Combustor

CutCell

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Hex

BERL Combustor

Axial Velocity

Hex

CutCell – fine mesh

© 2011 ANSYS, Inc. February 23, 201220

CutCell – fine mesh

CutCell – coarse mesh

Experiment

Conclusions

• ANSYS offers a wide variety of types of meshes

• Not all types of meshes are appropriate for all applications

• Inflation Layers and proper mesh distribution are extremely

important for accurate solutions for all types of meshes

• Unstructured meshes can be a reliable alternative to hand-

crafted hex meshes as they

© 2011 ANSYS, Inc. February 23, 201221

crafted hex meshes as they

o Offer competitive accuracy

o In general they are faster to generate

o Often provide faster convergence

o They are more automated-require less setup time

Any Questions

© 2011 ANSYS, Inc. February 23, 201222