The Challenges of Fluid-Structure Interaction

Alan Mueller, CD-adapco

STAR Japan Conference Nov 28, 2012 Yokohama

What is FSI?

Air Interaction with a Flexible Structure

What is FSI?

• Water/Air Interaction with a Structure

What is FSI?

• Vortex Induced Vibration and Galloping

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What is FSI?

• Aeroelastic Flutter

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What is FSI?

• Hydroplaning

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What is FSI?

• Gulping

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What is FSI?

• Ask 20 engineers “What is FSI?” and you will likely get 20 different answers

• There is not simply one approach valid for all FSI problems

• The analyst must be presented with a range of options and chose the most suitable

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The Challenges of FSI

• Mapping data techniques – Finding neighbors and interpolating

• Protocols and formats for exchanging data – Getting data from Code A to Code B

• Coupling methods – Algorithms for accuracy, stability

• Dynamic fluid mesh evolution – Topology changes in the fluid domain

• Validation of FSI results 9

The Challenges of FSI

MAPPING

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The 3 steps of “Mapping”

• Searching for opposing neighbors • Interpolating source stencil data on a

target point – Source and targets may be face or vertex

• Often requires integration (quadratures) – intensive extensive variables – pressure force – heat flux heat – FEA nodal loads: integration of intensive

variables against the shape function.

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Source Neighbor Search Imperative

• Search requires little user intervention • The search excludes potential neighbors

based on proximity and orientation • Critically important for sheet metal parts

– resolve ambiguities of poor geometry – thin solid parts may be on the wrong side of

the fluid surface • Parallel Mapping is a must!

– Takes advantage of distributed memory 12

Co-Simulation Vehicle Thermal Management

Mapping Displacement in Low Y+ Prism Meshes

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C0 continuous mapping very important for low y+ meshes

Otherwise very easy for morpher to invert high aspect ratio cells in prism layer

The Challenges of FSI

DATA EXCHANGE

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Methods for Exchanging Data

• File Based Transfer: Import/Map/Export – Data exchange via files on a hard-disk – CAE codes need not be resident in memory – Often called “Loose Coupling” – User responsible for exchange synch

• Socket Based Transfer: Co-Simulation API – CAE code and STAR-CCM+ in memory – Data exchanged via sockets – API controls exchange synchronization

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Abaqus/STAR-CCM+ Co-Simulation

• Coupling via Abaqus Co-Simulation API of SIMULIA – Manages Coupling Synchronization/Exchange/Mapping – Abaqus v6.12/STAR-CCM+ v7.04 (implicit coupling)

• STAR-CCM+ Abaqus (explicit or standard) – Initial geometry – Pressure(relative or absolute pressure) – Shear traction – Surface heat flux

• Abaqus STAR-CCM+ – Displacement, velocity – Temperature

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Abaqus/Star-CCM+ Co-Simulation Interface

Hit the Step or Run button to commence the co-simulation

The Challenges of FSI

Coupling Technique

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Degrees of Coupling

• Two-way coupling for aeroelastic or hydroelastic equilibrium

• One way static coupling for thermal stresses – structural temperature computed by CFD CHT

• One way dynamic coupling – Loads only go from fluid to structure – Loads only go from structure to fluid

• Two way dynamic coupling – explicit (exchange once per time step) – or implicit (multiple exchange per time step)

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The Challenges of FSI

Dynamic Mesh Evolution

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Dynamic Mesh Evolution

• Completely define a good quality fluid mesh – Using as little user intervention as possible

• Options within STAR-CCM+ – Rigid body motion, sliding interfaces – Morphing – User Defined Motion

• Overset Mesh

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Overset Mesh Motion and Fluid Flow : Stop Valve

The Challenges of FSI

Validations

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AeroElastic Prediction Workshop: HIRENASD

2.3M cells

53K nodes

Aerodynamic Equilibrium at different AOA

• Static Structure, Steady airflow at deformed shape • Ma=0.8, Re=23.5x106, q/E=0.48x10-6

Wing Tip Displacement Lift Coefficient

Windoff Vibration Modes : Abaqus vs Experiment

f=25.55 Hz (26.25)

f=80.25 Hz (78.20)

f=106.20 Hz

f=160.35 Hz (165.25)

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FUN3D

Cp: AOA 2°

STAR-CCM+/Abaqus

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x/c

Cp: AOA 2°, Station 7

STAR-CCM+/Abaqus NASA FUN3D

AeroElastic Prediction Workshop: Forced Vibration of 2nd Flap Bending Mode

Wing Tip Response

Flow Instabilities in a Tube Bundle

• Yeung and Weaver, “The Effect of Approach Flow Direction on the Flow-Induced Vibrations of a Triangular Tube Array”

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Co-Simulation DOT Tank Impact

Experimental Test Impact

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DOT Tank Impact Simulations

Von Mises Stress (Abaqus Explicit) STAR-CCM+ Pressure

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0

200

400

600

800

1000

1200

1400

Star-CD/AbaqusDirect Coupling

0 0.1 0.2 0.3 0.4 0.5

Time (seconds)

Test

Impa

ct F

orce

(kip

s)

DOT Tank Impact Comparisons

__STAR-CCM+/Abaqus

The Challenges of FSI

• Mapping Data Techniques • Procedures for Exchanging Data • Coupling Methods • Dynamic Fluid Mesh Evolution • Validations

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Thank You For Your Attention & Enjoy