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© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
ANSYS Fluid
Structure Interactionfor ThermalManagement andAeroelasticity
Phil Stopford
Duxford Air Museum
11th May 2011
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© 2011 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
Fluid Structure Interaction (FSI)
• What is Fluid Structure Interaction? – Occurs when fluid flow interacts with solid structures, exerts
pressure and/or thermal loads that may cause structural
deformations and thus affecting the fluid flow itself
• Why is FSI important?
– Crucial in understanding many engineering problems• Material selection, fatigue, effect on fluid flow pa
rameters etc.
– For better designs!
– Can be catastrophic if neglected
Wind Turbine
Turbine
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© 2011 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary
FSI Modeling Approaches
• Two-way Coupling
– Coupling of FEA and CFD solvers
• Implicit and Explicit Approaches
• E.g. Vortex induced vibration, large time scale phenomenon
• One-way Coupling
– One-way interaction
– Fluid pressure/temperatures produces structural loads,
but strains too small to affect fluid flow field
– Superposition methods: modal analysis provides
deformed shape to flow field
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© 2011 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary
ANSYS Offerings for FSI
• Two-way Coupling – ANSYS Mechanical – CFX
• Iteratively implicit coupling
• Fully integrated environment
• Two-way coupling with FLUENT in ANSYS 14
• One-way Coupling
– ANSYS Mechanical – FLUENT or CFX
• Transient 1-way coupling is best performed using
the 2-way analysis approach
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© 2011 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
One-way Coupling – Overview
• Couple ANSYS Mechanicalwith FLUENT or CFX
– Coupling to thermal and structural
analysis in ANSYS
• Applications
– Any application involving thermal-
stresses or transfer of fluid
pressure/viscous forces
–
Steady state and transient analysis
Wing
Graphics Card
Tank Sloshing
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© 2011 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary
Integrated Process in Workbench
CHT Mesh
Project Schematic
CFD CHT SolutionGeometry
Thermal Loads Pressure Loads Thermal Stress Solution
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1-way Structural
• Transfer forces from CFD to
ANSYS
• Transfer displacements from
ANSYS to CFD
• Steady state – Transfer occurs after-the-fact
• Transient
– Can use scripting to create a series of
load files from a completed run• Use APDL or CEL to read the loads in at
the appropriate time
– Implemented more easily within the 2-
way framework by sending data in only
one direction
CAD
Pressure in CFX
Deformation in Mechanical
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1-way Time Averaged Data
• Time-averaged data is
useful in a number of
cases, e.g.
– Averaged pressure loads from
transient CFD simulations
• LES, DES, SAS
• Time-averaged data can
be generated and passed
to ANSYS as a static load
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9/52© 2011 ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary
Two-way Coupling: ANSYS – CFX
• Couples ANSYS Mechanical solver and ANSYS CFX – Retains advanced physics capabilities of both solvers
– Available in FLUENT in Version 14
• Option of Steady and Transient Coupling
• Force and/or Heat Flux/Temperature data transfer
– Any other field variable
• Unified and fully coupled environment in ANSYSWorkBench
• Semi-Implicit Matrix Coupling through Multi-field
Solver
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Two-way Coupling: ANSYS – CFX
Solid Mechanics
Structural
Fluid Dynamics
Mass
Momentum
Turbulence
Heat Transfer
• Coupling is achieved by transferring surface loads /displacements across physics interface
• An iterative coupling approach with in each timestep provides
implicit coupling at each timestep…
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• Physics fields calculated
by separate solvers
– Multiple data transfers within
timestep
– Implicit solution at end of
timestep
Semi-Implicit Matrix Coupling
Time Loop
End Time Loop
End Coupling / Stagger Loop
End Field Loop
Coupling / Stagger Loop
Field Loop
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Two-way Coupling: Key Features
• Easy to setup• Total Forces and Heat Fluxes are conservative across
FSI interface
• Non-conformal meshes
• Automatically morphs CFD mesh• Large Models
– Both sides can use parallel computing
• Third party coupling scheme not required
• Data transfer across TCP/IP internet sockets – Efficient; no intermediate files
– Heterogeneous architectures (Linux, Windows)
– Solvers can run on different machines (LAN, WAN, Internet)
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Two-way FSI Workflow
• The workflow is built on the WB Project page
Streaml ined p rocess integration wi thou t leav ing the Workbench envi ronment
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• Solid and Fluid geometry in ANSYS DesignModeler – Create and modify CAD geometry
– Bi-directional direct CAD connections
• ProE, SolidWorks, UG, CATIA, etc
– Parametric modeling capability
– Easy fluid volume extraction
Two-way FSI Workflow –
Geometry
Structural Part Fluid Volume
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Two-way FSI Workflow – Meshing
• Single meshing application forstructural and fluid meshes
– Swept, Tet, Inflation, Hex Dominant,
Hex Core, Multi-block
• Matching or non-matching
meshes at the FSI interface
– Fully conservative transfer
across interface
• Can use other Fluid mesh
generators
– ICEM for full Hex mesh
Fluid Domain
Solid Domain
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Two-way FSI Workflow –
Structural Setup
• Structural Problem setup in ANSYS Mechanical – Easy to use
– Setup like any other Transient Structural simulation
• Tag the FSI interface regions
– Library of solid materials, advanced material properties
– Also Modal, Random Vibration, Thermal Stress,
Harmonic Response, …
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• Coupled simulation set-up in
ANSYS CFX-Pre
• 2-way data/load transfer specified
• Simple & intuitive FSI interface
panels
– User-friendly, easy to use
Two-way FSI Workflow – Fluid
and FSI Setup
Interface transfer quantities
Coupling controlsTransient controls (common)
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Turbulence Transition ModelWind Turbine Blade
Transition
Transition
Tu Contour
Transition
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Two-way FSI Workflow – Solving
• Both solvers automatically started from the CFX Solver Manager
CFX-Solver Input ANSYS Solver Input
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Two-way FSI Workflow – Solving
• Single environment for solution monitoring
– Check interface quantities are converged within each timestep
– Monitor forces, displacements, custom expressions
1 timestep
Force monitor
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© 2011 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary
FSI ExamplesNREL Phase VI rotor
Rotor diameter 10.058 m
Blade are based on an aerofoil (S809)
Rotational speed 71.9 m/s
Measurements in NASA Ames wind tunnel
Cross section: 24.4 m x 36.6 m
Inlet speed 7 m/s
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© 2011 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary
FSI ExamplesNREL Phase VI rotor
Geometry imported Parasolid
Min angle > 20 deg
Nodes pr. passage 100,000
DirectCAD interfaces can be used
Using a script a high quality mesh is
generated in minutes
Blade region meshed in ICEM
HEX
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© 2011 ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary
FSI ExamplesNREL Phase VI rotor
Tower and nacelle parameterised in
DesignModeler Subtract solid from wind tunneldomain and meshed in Workbench
By using parameters a design change is implemented in a few minutes
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© 2011 ANSYS, Inc. All rights reserved. 26 ANSYS, Inc. Proprietary
FSI ExamplesNREL Phase VI rotor
• Solution
• Steady state
• Frozen rotor interface
• Timestep = 10/w
• Convergence criteria (RMS): 10-5
• Turbulence model: SST
• Transition is important
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© 2011 ANSYS, Inc. All rights reserved. 27 ANSYS, Inc. Proprietary
FSI ExamplesNREL Phase VI rotor
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© 2011 ANSYS, Inc. All rights reserved. 28 ANSYS, Inc. Proprietary
One way FSI – Von Mises Stresses
FSI ExamplesNREL Phase VI rotor
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© 2011 ANSYS, Inc. All rights reserved. 29 ANSYS, Inc. ProprietaryOne way FSI
–
Deformations
FSI ExamplesNREL Phase VI rotor
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© 2011 ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary
Transient Simulation• Steady state simulation as initial guess
• Temporal variation of fluid and structural
variables
– Temporal variation of wake
– FSI between tower and blade (two-way coupling)
– Noise (monopole, dipole, quadrupole)
• Time average quantities also generated – Expected to be similar to steady state
FSI ExamplesNREL Phase VI rotor
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© 2011 ANSYS, Inc. All rights reserved. 31 ANSYS, Inc. Proprietary
Transient: Max deformation=0.0012 Steady: Max deformation=0.00007
FSI ExamplesNREL Phase VI rotor
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© 2011 ANSYS, Inc. All rights reserved. 32 ANSYS, Inc. Proprietary
FSI Examples – Leaf Valve
• Pressure pulse passing through a leaf valve
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© 2011 ANSYS, Inc. All rights reserved. 33 ANSYS, Inc. Proprietary
FSI Examples – “Singing” Hydrofoil
• Hydrofoil simulated at a
free stream velocity that
produces a resonating
response
• 2 million cells for CFD
• DES with y+ ~ 25
• 22,000 elements for FEA
• Time step = 1.63 X 10-4 s
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© 2011 ANSYS, Inc. All rights reserved. 34 ANSYS, Inc. Proprietary
FSI Examples – “Singing” Hydrofoil
Displacements Magnified 5000x
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© 2011 ANSYS, Inc. All rights reserved. 35 ANSYS, Inc. Proprietary
FSI Examples – Bore Choking
• Bore Choking in Solid Rocket Motors
– Interaction between propellant grain and flow field
results in the radially inward deformation of the
propellant
– Difference in pressure P1 and P2 results in
deformation of the solid propellant
– Result in artificial throat and choking of the flow,leading to pressure build up and case failure
• Self-Sustaining phenomenon
– Deformation results in increase in difference in
pressure which further increases the deformation
P1
P2
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© 2011 ANSYS, Inc. All rights reserved. 36 ANSYS, Inc. Proprietary
FSI Examples – Bore Choking
• Results (no FSI)
– Pressure differential around corner
Pressure Contours
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© 2011 ANSYS, Inc. All rights reserved. 37 ANSYS, Inc. Proprietary
FSI Examples – Bore Choking
FSI Solid Deformation (as function of time)
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© 2011 ANSYS, Inc. All rights reserved. 39 ANSYS, Inc. Proprietary
FSI ExamplesWing Flutter
• Modal analysis
– Bending mode
– Torsional mode
Mode Experiment Simulation
1 9.59 Hz 9.37 Hz
2 38.16 Hz 39.07 Hz
S
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© 2011 ANSYS, Inc. All rights reserved. 40 ANSYS, Inc. Proprietary
FSI ExamplesWing Flutter
• Stagger loop: impliciteach timestep
• Benefit: time-step setby physics, not code
coupling
• Large timestep, more
stagger iterations• Small timestep, less
stagger iterations
• Optimize physics,
robustness, CPU time
12
13
14
15
16
1.E-04 1.E-03 1.E-02
Time step size [s]
F l u t t e r f r e q u e n c y [ H z
5 Stagger
3 Stagger
1 Stagger
-6.E-03
-4.E-03
-2.E-03
0.E+00
2.E-03
4.E-03
6.E-03
0 0.05 0.1 0.15 0.2 0.25Time [s]
A m p l i t u d e [ ]
dt=0.00025 [s], 1 Stagger
dt=0.005 [s], 5 Stagger
dt=0.005 [s], 1 Stagger
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 41 ANSYS, Inc. Proprietary
FSI ExamplesWing Flutter
Deformation increased by factor 200
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© 2011 ANSYS, Inc. All rights reserved. 42 ANSYS, Inc. Proprietary
FSI ExamplesStatic Aeroelastic Wing/Body Configuration
• 3D-simulation ofHIRENASD wing
– ‘High Re
Aerostructural
Dynamics’Workshop
– Transonic
– Span = 1.3 m
– Chord = 0.3445 m
https://heinrich.lufmech.rwth-aachen.de
Robert Selent, Technical University Dresden
Thorsten Hansen, ANSYS Germany
https://heinrich.lufmech.rwth-aachen.de/https://heinrich.lufmech.rwth-aachen.de/https://heinrich.lufmech.rwth-aachen.de/https://heinrich.lufmech.rwth-aachen.de/
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© 2011 ANSYS, Inc. All rights reserved. 43 ANSYS, Inc. Proprietary
FSI ExamplesStatic Aeroelastic Wing/Body Configuration
Solve CFD
Undeformed GridTransfer loads to CSM
Transfer deformationsSolve CFD
Deformed Grid
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 44 ANSYS, Inc. Proprietary
FSI ExamplesStatic Aeroelastic Wing/Body Configuration
• Aeroelastic Deformations
• Alpha 0°, 2°, 4° with aerodynamic load
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 45 ANSYS, Inc. Proprietary
FSI ExamplesStatic Aeroelastic Wing/Body Configuration
Cp @ Sections 1,4,7, a = 2°
Section 1 Section 4 Section 7
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 46 ANSYS, Inc. Proprietary
FSI ExamplesStatic Aeroelastic Wing/Body Configuration
Cp @ Sections 1,4,7 ,a
= 2°Section 1 Section 4 Section 7
Experiments
Simulation
Courtesy of RWTH Aachen
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 47 ANSYS, Inc. Proprietary
FSI ExamplesForced Vibration Analysis Using Mode Shapes
• Solve modalanalysis in
ANSYS
• Export the mode
shape
• CFD: transient
analysis with
prescribed mesh
motion
ANSYS Mode Shape
Apply as Mesh
Deformations inCFD
CFD Results
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 48 ANSYS, Inc. Proprietary
• Can use superposition method to combine mode shapes
1st mode 683 Hz 4th mode 3707 Hz2nd mode 1707 Hz 3rd mode 2248 Hz
FSI ExamplesForced Vibration Analysis Using Mode Shapes
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 49 ANSYS, Inc. Proprietary
• Can use superposition method to combine mode shapes
iiidisp t A x .sin A
i: constant amplitude for i th mode
i : frequency for i th mode
i
: i th mode shape
Deformation, scaled by factor
200
31
32
33
34
35
36
37
0 0.001 0.002 0.003 0.004
Time [s]
F o r c e
[ N ]
Amplitude 1
Amplitude 2
Normal force on blade
FSI ExamplesForced Vibration Analysis Using Mode Shapes
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 50 ANSYS, Inc. Proprietary
FSI ExamplesForced Vibration Analysis Using Mode Shapes
FSI E l
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© 2011 ANSYS, Inc. All rights reserved. 51 ANSYS, Inc. Proprietary
• Workbench Project Schematic
– 1-click project update for entire system!
FSI ExamplesForced Vibration Analysis Using Mode Shapes
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Summary
• ANSYS Workbench simplifies FSI simulations withFEA and CFD
– Single multiphysics environment
– Streamlined workflow
• Can be combined with industry-leading turbulenceand physical models
• Extensive experience in wind power and aeroelastic
simulations