© 2015 CAE Associates
ANSYS CFD v16
Update Seminar
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Outline
ANSYS CFD Demo — CFX — Fluent — Icepak
ANSYS CFX v16 ANSYS Fluent v16
ANSYS Icepak v16
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CFX, Fluent, Icepak demo
CHT setup — Flow domain and solid parts — Automatic fluid-solid interface generation
Internal fan model
— Detail 3D fan blade geometry not modeled — Pressure jump condition
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Flow domain and solid parts
heat sink
transformer
fan
flow domain
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CHT with Fan Model
CFX — Pros : Easy to use, better tree outline structure, easy to identify
parts on fluid or solid side, GUI graphics to indicate which part is selected, auto contact detection for fluid-solid and solid-solid interfaces, multiple units available for each input, fan curve can be implemented
— Cons : need to write a CEL to implement fan swirl angle if needed
Fluent — Pros : auto contact detection for fluid-solid and solid-solid
interfaces, fan specific boundary page, easy to implement fan swirl angle if needed, fan curve can be implemented
— Cons : all fluid-solid interfaces are lumped into boundary condition page, takes effort to identify the parts (especially on a complex problem)
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Outline
ANSYS CFD Demo — CFX — Fluent — Icepak
ANSYS CFX v16 ANSYS Fluent v16
ANSYS Icepak v16
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HPC Performance Improvements
Background — Dramatic HPC scalability
advances were previously implemented, and required additional expert parameter settings for activation
R16 incorporates numerous HPC improvements and changes, to deliver excellent scalability ‘out-of-the-box’
— Note change: coupled partitioning is the new default in R16
• Can change convergence behavior!
Default HPC scaling on a transient water turbine simulation with 40M
nodes; benchmark in collaboration with Voith Hydro and HLRS in Stuttgart
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I/O: File Writing with MPICH Background
• File writing time found to be excessive and not scaling on some systems identified as an issue with MPICH-based MPI
• Affected Cray ES mode, Intel MPI and Microsoft’s MS-MPI
• IBM Platform Computing MPI not affected
R16 includes a dramatic
reduction in the file write time with MPICH-based MPI
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Turbulence Modeling
Background — Accurate CFD simulations
require accurate prediction of turbulent flow phenomena
New turbulence capabilities include:
— BSL-ω model — Stress-Blended Eddy
Simulation (SBES) model (β)
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Reattachment Modification
Background — RANS models may produce
exaggerated separation zones, at least when separation onset is correctly predicted
— Thought to be an inherent limitation of RANS models
R16 includes the release of an
option for the SST model to improve prediction of the re-attachment location
— Note: effect can be reduced with severe mesh refinement
Red arrows show the re-attachment location predicted with and without the
modification on a validation test case, and how it significantly improves agreement with the experimentally-measured re-
attachment location (black arrow)
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Improved Mass Flow Rate Specification
Background — Mass flow rate boundary
condition specified for meshed boundary area, not for machine
— Change in blade count can lead to inconsistent specified flow rate
R16 adds new Mass Flow Rate Area option with “Total for All Sectors”, allowing machine mass flow rate to be specified directly
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Improved Mass Flow Rate Specification
Total for All Sectors area
Mesh sector boundary area
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Fourier Transformation for Single Stage TRS Background
— Fourier Transformation Transient Rotor/Stator (FT-TRS) method was a beta feature in previous releases. Since its initial beta release, it has gone through a series of improvements, including accuracy and speed.
In R16 FT-TRS is a released feature — FT-TRS is best used on large pitch ratio
single stage turbomachines where the use of other pitch-change models is not possible
— FT-TRS supports simulations with incompressible fluids in rotating machines such as pumps
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● Beta: Extension to FT-TRS functionality to handle asymmetric flow situation. Connect rotor to 360 deg. domain
‒ Impeller in a Vaneless volute ‒ Fan in a crosswind
TBR in R16.0 FT Method
FT-TRS
FT-TRS
Reference FT
Impeller in Vanless Volute
Compressor off-design performance • Fan in crosswind • Boundary layer ingestion
• Ground vortex ingestion
• Inlet swirl distortion
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● Beta: Modeling multistage compressor/turbine with combination of TT-TRS and other interfaces (i.e. PT or Stage)
‒ Aerodynamic performance
‒ Position TT-TRS where the shock cross the interface. It will help in obtaining correct flow rate
TBR in R16.0 TT Method
IGV R1 S1 R2 S2
TT TT PT PT
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● Beta: Single Sided TT-TRS (STT) • Modeling multistage compressor/turbine
with combination of TT-TRS and STT-TRS • Further improvement to aerodynamic
performance prediction
TBR in R16.0 TT Method
STT
R1 S1
TT PT
IGV
TT
R2
TT
Entropy contour reconstruction Single passage per row TT/STT model
Entropy contour Reference full-wheel model
TT TT STT STT
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Provide Harmonic Forced Response Analysis in MAPDL
● Background — R15 provided export of pressure
harmonics for Mechanical cyclic Mode Superposition, but did not support user specification of the engine order to export
● CFX can now export pressure harmonic for:
— Arbitrary user-specified engine order (EO) from blade row interaction
— Blade vibration frequency from blade flutter analysis
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More Accurate Meridional Averaging
Background — Undefined values on a polyline
could skew quantities like meridional averages and there were limitations with TBR data instances
Meridional length averaging in R16 properly handles undefined points and works correctly with TBR data instances
R15 (top) shows discontinuities in meridionally-averaged pressure, much
improved in R16 (bottom)
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Precision Control for Auto-Annotation
Background — Animations of transient
with display of time could lead to ‘jumpy’ text output, depending on given time value
R16 adds user control for
the number precision, giving better and cleaner annotation display in the viewer
— Applies to time value and other numerical quantities
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Outline
ANSYS CFD Demo — CFX — Fluent — Icepak
ANSYS CFX v16 ANSYS Fluent v16
ANSYS Icepak v16
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Graphical User Interface
R16 introduces a new tree-based UI
— Branches of the tree provide an overview of the case set up
— New right-click menus allow quick access to most commonly used functionality
— Ability to save contour and vector definitions
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Workbench Integration
Background — Continued development
of capabilities that extend parametric simulation capabilities for Fluent in Workbench
R16 fully releases ability
have to multiple upstream mesh systems with Fluent
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User Interface Customization
Background — Many users have wanted to
user scheme and create custom user interface components, but little information has been available
New documentation for creation of custom user interface
— Instructions on how to use scheme to customize Fluent
— Examples for adding menu items and dialog boxes
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Extreme Parallel Scalability
Background — Continuously strive to improve solution scalability and stay
ahead of the competition R16 scales better than any other commercial CFD code
— 830 million cells — 86% efficiency at 36k cores, 1024 cores as base
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HPC Performance Improvements
Background — Many cases, particularly
unsteady moving mesh simulations, have suffered poor performance in parallel
Performance has been
improved for simulations that include
— Wall distance calculations — Sliding mesh
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Poor Mesh Numerics
Background — Users need to be able to
solve on efficiently generated meshes- often this means accepting poorer quality cells in some regions
Improved handling of poor
quality meshes — New cell quality-based
criteria for use of special ‘poor mesh’ numerics
— Improved user controls
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Polyhedral Conversion
Background: — Performance bottlenecks with
polyhedral conversion have been a common complaint from customers with large cases
Improvements include
— Removed parallel bottleneck for large meshes
— Improved parallel performance of optimization step
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Mapped Mesh Interfaces
Background — Robust methods are
needed to handle coupled boundaries in complex models
New mapped interface
option for coupled walls between zones
— Fluid-solid and fluid-fluid — Supports conjugate heat
transfer and radiation
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Acoustics Modeling
Background — Cabin noise
prediction is a key application for the automotive industry
Expanded capabilities include
— Frequency band post processing of sound sources
— 1-way coupling to harmonic and response analysis in ANSYS Mechanical (β)
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• 87 M tet/prism mesh • 15 prism-layers • Orthogonal Quality: 0.005 (use PMN)
Acoustic analysis – SAE bluff body
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Acoustics Pressure Loading in Frequency Domain
Freq. 455 Hz Freq. 455 Hz
Freq. 1575 Hz Freq. 1575 Hz
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Simulated SPL vs Experiments
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Freq. res= 10.8Hz or T=0.0925s Welch Average Periodogram, 50% overlap
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CFD Analysis Information
• Startup: • Ramping down the time-step from 1e-03s to 3e-05s for 0.35s
physical time • Sampling:
• 9,200 time-steps • dt = 3e-05 • Many tests: 2-4-8 iter per timesteps • T sampling = 0.2634 s • Max freq. = 16.67 kHz • Min (freq.-res.)= 3.6 Hz
• Computational Info:
• ~263h for 9,200 time-steps on 168 cores (Intel Xeon 2.93 GHz, SLES 11 SP1, 2016 GB RAM available (~300 GB used)
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Compressible Multiphase Flows
Background — Solver robustness
typically a bigger issue as physics become more complex
New numerical
treatments — Improved start-up and
run-time robustness for compressible multiphase flows
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Free Surface Flows (VOF)
Background — Broad range of free surface
flow applications – many requests for better ease-of-use and accuracy
VOF modeling adds a number
of enhancements in R16 — Enhanced Usability — More intuitive set up, less
error-prone — Enhanced numerics — Modified compressive scheme — Improved interface capturing
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Eulerian Multiphase Speed
Background — Long transient solution
times for multiphase simulations
Significant speedup for
Eulerian multiphase problems
— Non-Iterative Transient Advancement (NITA) is now available for multiphase flows
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System Coupling Improvements
Background: — Extend the range of
applications that can modeled using system coupling
Support for porous
zones with FSI — Porous media and
porous jumps are both supported
— 1 and 2-way coupling
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Wall Film Modeling
Background — Wide demand to expand
range of application for wall film models
LWF
— UDF for impingement and splashing
— Energy transfer from film to wall
— New film boiling model
EWF — Support for periodic
boundaries
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Wall Film Validation
• Cross Flow Injection • Primary Breakup • Secondary Breakup • Film Formation • Film Splashing, Stripping & Separation
Arienti et. Al. LES Simulations Arienti et. al. data and LES Simulations
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0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 Fi
lm T
hick
ness
(um
) Distance along Filmer (mm)
LWF
EXPT.
Comparison of wall film height
Cross-flow Velocity of Air: 82 m/s Jet Velocity: 12.7 m/s
Wall Film Validation
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Plotting Fluent Boundary Face Values
Background — Using interpolated nodal
values for contour plots may not always sufficiently accurately reflect boundary values applied in Fluent
R16 allows you to choose to
use face values from Fluent in the generation of contour plots, to create plots that are fully consistent with boundary values applied in the solver
Face Values
Interpolation from Nodes
Example of difference on a polyhedral mesh
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Outline
ANSYS CFD Demo — CFX — Fluent — Icepak
ANSYS CFX v16 ANSYS Fluent v16
ANSYS Icepak v16
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Maxwell to Icepak Coupling
• Maxwell Icepak • Both one way or
two way coupled • Heat flow density q”
is accurately mapped from Maxwell to Icepak
Planar transformer
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Cold plate & Busbar Assembly
Cold plate
Busbars
Fins
• Natural convection with side walls & top, bottom modeled as openings
• Heat generated in Busbar is carried away
by liquid cold plate system
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Server - Graphics Card
• Ease of use with auto settings of power map thresholds
• Icepak import preview and filter enhances workflow with Icepak
• Icepak trace modeling successfully validated against explicit trace models for simple non-standard mcm/anf based packages
• Explicit trace modeling for complete BGA and PCB not yet practical – successful with very high refinement of Icepak trace modeling instead
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