An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt...

An efficient Approach for Determining the

Flutter Characteristicsof Rotor Blades for

Multi-Megawatt Wind TurbinesEWEC 2006 - Presentation No. 627

CS4: Aerodynamics, Aeroelasticity and LoadsDipl.-Ing. Raphael Haas

EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH, Berlin

haas@euros.de

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Introduction – Problem definitionIntroduction – Problem definitionEUROS manufactures blades ranging from 10m to 56m for WEC from 100kW to 5.0MWTrend in development of large rotor blades:longer, lighter and narrower blades.Aeroelastically critical designs

Risk of flutter

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

What is flutter ?What is flutter ?

Flutter – an explanation:resonant (unstable) motion interaction of structural mass, stiffness, and aerodynamic forcesusually present above some limiting (rotor) speed.

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

OverviewOverviewSystem equation and structural modelUnsteady aerodynamics – GreenbergUnsteady aerodynamics – LoewyReduction of system sizeResults – Development of dampingResults – Influencing Factors

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

System equationSystem equation

Matrices:M: mass matrixD: damping matrixK: stiffness matrix

azgazgelaat pppxKKKKxDxMM

pxKxDxM

)()()(

Inidices:t: inertia mass termsa: aerodynamic termsel: elastic stiffness termsg: pretension stiffening termsz: centrifugal stiffening terms

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Structural model (1)Structural model (1)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Structural model (2)Structural model (2)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

)t(i0 exx

Unsteady Aerodynamics–Unsteady Aerodynamics–Greenberg(1)Greenberg(1)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Unsteady Aerodynamics–Unsteady Aerodynamics–Greenberg(2)Greenberg(2)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Unsteady Aerodynamics – Loewy Unsteady Aerodynamics – Loewy (1)(1)

Pict. source: Loewy: „A Two-Dimesional Approximation to the Unsteady Aerodynamics of Rotary Wings“Journal of the Aeronautical Sciences, Vol. 24, No. 2, pp. 81-92, Feb. 1957.

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Unsteady Aerodynamics – Loewy Unsteady Aerodynamics – Loewy (2)(2)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Static CondensationReduction of system size (1)Reduction of system size (1)

Pict. source: Gasch: „Strukturdynamik, Band 2: Kontinua und ihre Diskretisierung.“ Springer. Berlin. 1989.

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Modal CondensationReduction of system size (2)Reduction of system size (2)

Pict. source: Gasch: „Strukturdynamik, Band 2: Kontinua und ihre Diskretisierung.“ Springer. Berlin. 1989.

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Example blade EU80:Length: 39mWeight: 6.5 tons

DiagramsFirst order elastic beamHalf torsional stiffness (2nd o. beam)Full torsional stiffness (2nd o. beam)

Results-Trend of damping Results-Trend of damping coefficients(1)coefficients(1)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Damping coefficients vs. Rotor speed, first order elastic beam.

Results-Trend of damping Results-Trend of damping coefficients(2)coefficients(2)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Damping vs. rotor speed, 2nd order el. Beam, full torsional stiffness.

Results-Trend of damping Results-Trend of damping coefficients(3)coefficients(3)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Damping vs. rotor speed, 2nd order el. Beam, half torsional stiffness.

Results-Trend of damping Results-Trend of damping coefficients(4)coefficients(4)

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Results – Influencing FactorsResults – Influencing Factors

Higher torsional stiffness significantly shifts the flutter onset rotor speed

Usage of a second order FEM blade model is mandatory

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Present status and outlookPresent status and outlook

Natural frequencies and modeshapes evaluated for each blade

Fast and easy to use tool

Integration into an iterative design loop

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt An efficient Approach for Determining the Flutter Characteristics of Rotor Blades for Multi-Megawatt Wind TurbinesWind Turbines

Raphael Haas – EUROS Entwicklungsgesellschaft für Windkraftanlagen mbH – Berlin – Germany

Natural frequ. vs. rotor speed, cons. system – no aerodynamic loads.Natural frequ. vs. rotor speed, 2nd order el. Beam, no returning wake.Damping vs. rotor speed, 2nd order el. Beam, no returning wake.

Results – No returning wakeResults – No returning wake

azgazgelaat pppxKKKKxDxMM

pxKxDxM

)()()(