3C1futur Flutter Free Turbomachinery Blades

7/30/2019 3C1futur Flutter Free Turbomachinery Blades

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Aero Days 2011, Madrid .

FUTUREFlutter-Free Turbomachinery Blades

Torsten Fransson, KTH

Damian Vogt, KTH

2011-03-31


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RR Trent 1000

A Typical Turbomachine

Picture courtesy of RR


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What is it flutter?


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Blades oscillate in traveling wave mode

Neighbor blades usually lead to instability

An isolated blade would not flutter

Turbomachinery Flutter

Flutter denotes a self-excited and self-sustainedaeroelastic instabilityVery harmful unless properly damped


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Why do turbomachinery blades flutter?


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Underlying Mechanisms

Flutter involves the interaction offluid and structureUpon the motion of a component, the surrounding fluid will

respond with an aerodynamic force

The direction and phase of this force will lead to having themotion damped or augmented

In case of augmentation, flutter will establish

The character of the fluid response depends on manyfactors such asGeometrical aspects (i.e. profile shape, blade size, blade count)

Operating point (idle, take-off, cruise)

Ambient conditions (air temperature, etc)

Dynamics (engine acceleration, deceleration)

Flutter might establish only at very few of the aboveconditions. Due to its harmful character it must howeverbe avoided at any cost


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How can we ensure flutter-free

turbomachinery blades?


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Flutter-Free Turbomachinery Blades

A good design does not flutter

How to ensure a good design?Design for stability performing accurate predictions of the

unsteady behavior of the structural dynamics (FEM) andaerodynamics (CFD) in a turbomachine

Ensure large-enough stability limits (i.e. moderate changes inoperating conditions, profile shape, etc will not directly leadto a flutter instability)

A good design must also be economically viableEngine development costs and time

Fulfilling other objectives such as performance, weight,

manufacturing cost, maintainability etc

During component design, industry nowadays largelyrelies on numerical simulations at affordable analysiscosts (model size and run time)


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How well are we to date doing on

aeroelastic predictions?


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Prediction Accuracy

Test case: transonic compressorEach industry partner is using their own (trusted) aeroelastic

analysis tool to analyze the aeroelastic behavior

Variation of minimum aerodynamic damping with operatingpoint

mass flow


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Background

Despite the high level of sophistication in todaysnumerical prediction tools, it is not uncommon that wehave to deal with an accuracy of+-40% of predictedminimum aerodynamic dampingIn the present test case: 2 out of 5 predict flutter, 3 do not

Test cases exist but these do not fully cover the spectrumneeded for modern turbomachine designsComponent types (blisks, bladed disks)

Flow conditions (transonic flow, high loading, separations)

Combinations of unsteady pressure and vibration data

This empty spot shall be filled-in by the FUTURE projectEstablishing ofnew experimental test cases

Extensive validation of state-of-the-art prediction tools


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Flutter-Free Turbomachinery Blades

www.future-project.eu

Presentation of FUTURE Project
http://www.future-project.eu/http://www.future-project.eu/


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EU FP7 Project FUTURE

Project aiming at the acquiring new sets of relevantvalidation data on turbomachinery aeroelasticity(compressor, turbine) and validating numerical tools

Project coordinator: KTH, Prof Torsten Fransson

Partners: 25 partners from industry, research institutes,academia

Budget: 10.6M

Duration: July 2008 June 2012


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FUTURE Project Partners

Industry ResearchInstitutes

Academia


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Project Concept

Aeroelastic experiments

Aeroelastic computations

Synthesis of experimentsand computations

x x

x x

x x

Fan Compressor

Turbine

Picture courtesy of RR


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Project Structure

Two main streaks ofvalidation test cases as followsTransonic compressor

High subsonic Low-Pressure Turbine (LPT)

These test cases have been conceived within FUTURE

Interconnected experimentsNon-rotating cascade tests, controlled blade oscillation

Rotating tests, multi-blade row, free and forced oscillation

Mechanical characterizations of components (blisk, bladed disks)

Application ofnovel measurement techniques such as PSP

Interconnected computationsPerformed by virtually all partners in the project

Pre-test predictions

Post-test predictions


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Work Package Structure

WP1: Turbine and compressor cascade flutterPaolo Calza, Avio

WP2: LPT Rotating rig flutterRoque Corral, ITP

WP3: Multi-row compressor flutterJan stlund, Volvo Aero

WP4: Synthesis of experiments and computationsDetlef Korte, MTU

WP5: Project managementDamian Vogt, KTH

Shortcut to Benefits


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Presentation of FUTURE Test Cases


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Transonic Compressor

Design intentAeroelastic stable operation at design point

N 18000rpm, ~ 0.6

Reduction of positive aerodynamic damping as stall line isapproached


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Compressor Flow Field

ADP, 1.412

50% span

90% span


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Compressor - Overview of Tests

Non-rotating tests (isolated blade row, EPFL)Detailed steady aerodynamics

Aerodynamic damping (controlled oscillation, free oscillation)

Data: inlet/outlet flow parameters, blade loading, time-resolvedblade surface pressure

Rotating tests (1 stage compressor, TUD)Detailed steady aerodynamics (blade loading, probe traverses)

Mechanical characterization of rotor blisk (ECL)

Damping measurements at various operating points

Data: inlet/outlet flow parameters, blade loading, time-resolvedblade surface pressure, blade vibration (tip-timing)


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Non-Rotating Compressor TestFacility (EPFL)

Annular cascade module


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Rotating Compressor Test

Facility (TUD)

Rotor blisk


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High Subsonic LPT Rotor

Design intentControlled aeroelastic instability at design point Limit CycleOscillations (LCO)

N 2416rpm, M2 ~ 0.75

Goal: measurable LCO amplitudes

displacement


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LPT Rotor Flow Field

Mach number50% span

Outlet ptot

SS PS

Surface oil flow


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LPT - Overview of Tests

Non-rotating tests (isolated blade row sector, KTH)Detailed steady aerodynamicsAerodynamic damping (controlled oscillation influence

coefficients)

Data: inlet/outlet flow parameters, blade loading, time-resolvedblade surface pressure

Rotating tests (1 stage LPT, CTA)Detailed steady aerodynamics (probe traverses)

Two test objects: 1) cantilever 2) interlock

Mechanical characterization of rotor bladed disks (AVIO)

Damping measurements at various operating points

Data: inlet/outlet flow parameters, blade vibration (tip-timing)


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Non-Rotating LPT Test Facility(KTH)

Annular sectorcascade module


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Cascade Flow Field

Annular sector cascade5 blades, 6 passages

70% span loading of rotating rig matched

Outlet Mach numberdistribution

Fig with midspan

loading


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Rotating LPT Test Facility (CTA)

Assembled rotorbladesInterlock

configuration

Cantileverconfiguration


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What are the expected benefits of the

FUTURE project?


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Expected Benefits

The FUTURE project shall contribute to makingturbomachinery aeroelastic predictions more reliable

Numerical tools validated on new, relevant and uniqueaeroelastic test cases that shall lead to best practiceguidelines

Achieving this will help making turbomachinery blades flutter-free

make new aircraft engines more efficient

cut development costs and time frames

The FUTURE project will provide key enabling technologiestowards a green, safe, reliable and affordable air transportof the future


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Dissemination

Great attention is given to the dissemination of projectfindingsFeeding-back findings to education and life-long learning

ExamplesSharing of audiovisual instruction material from industry

partners with universities

Development ofe-learning tools

THRUST TurbomacHinery AeRomechanical UniverSity Training

The worlds first Masters programme in turbomachineryaeromechanics

UpcomingTHRUST+ Joint PhD programme on aeromechanics

EXPLORE Aero World Virtual University

www.explorethrust.eu
http://www.explorethrust.eu/http://www.explorethrust.eu/


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What do we envision after FUTURE?


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Within the FUTURE project many questions will beanswered but there might be unresolved topics at the end

Having a strong project consortium and unique hardwarein place, we envision research in the following directions

Control of flutter (active, mistuning, novel damping concepts)

Influence of flow distortion and impedance

Flutter in the presence of other unsteady aerodynamic

phenomena

Development of new improved numerical models


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3C1futur Flutter Free Turbomachinery Blades