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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
© 2011 ANSYS, Inc. February 23, 20125
• Poly
• CutCell
NACA4412 Study
Results
© 2011 ANSYS, Inc. February 23, 20126
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
© 2011 ANSYS, Inc. February 23, 201211
NASA C3X Transonic Turbine Vane
Structured Hex Mesh (SHM) Structured Hex Mesh Fine
(SHMF)Unstructured Hex Mesh
(UHM)
© 2011 ANSYS, Inc. February 23, 201212
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%
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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
© 2011 ANSYS, Inc. February 23, 201215
Stairmand Cyclone
Tangential Velocity (m/s)
@ 0.41 m
© 2011 ANSYS, Inc. February 23, 201216
Tangential Velocity (m/s)
@ 0.41 m
-�- Cut Cell, -�- Course Block Hex, -�- poly, -�- tet, � Experimental
Stairmand Cyclone
Axial Velocity (m/s)
@ 0.41 m
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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