SIROCCO, SIlant ROtors by aCoustiC Optimisation Participants: Energy Research Centre of the Netherlands, ECN (Gerard Schepers and Toine Curvers) National Aerospace Laboratory, NLR (Stefan Oerlemans) University of Stuttgart, Ustutt (Kurt Braun, Andreas Herrig, Thorsten Lutz, Werner Wuerz) Gamesa Aeólica, Gamesa (Beatriz Mendez López, Alvaro Matesanz) GE Wind Energy/Global Research, GE (Rainer Arelt, Thierry Maeder) Funded by: EU 5th Framework SenterNOVEM (ECN/NLR) IMTS meeting Madrid 18th-19th October 1999

OUTLINE OBJECTIVE PROJECT SET-UP (Period, participants, tasks) MAIN RESULTS RESULTS FROM PHASE 1: ACOUSTIC ARRAY MEASUREMENTS RESULTS FROM PHASE 2: DESIGN AND VALIDATION OF ACOUSTIC AIRFOIL DESIGN CONCLUSIONS/FUTURE WORK IMTS meeting Madrid 18th-19th October 1999

SIROCCO, OBJECTIVE To develop ‘tip’-airfoils (r/R >0.75) by which aerodynamic noise of wind turbines can be reduced significantly without loss in aerodynamic performance; Focus is on reduction of trailing edge noise! Background: Previous EU project ‘DATA’: Noise reduction of 3-6dB(A) on model wind turbine in the DNW wind tunnel; Trailing edge noise dominant IMTS meeting Madrid 18th-19th October 1999

SIROCCO, OBJECTIVE Ctd. Two ‘baseline’ turbines: Gamesa (G58, D=58 m, 850 kW, at Zaragoza) GE (2.3 MW, D=94 m, at ECN test field) IMTS meeting Madrid 18th-19th October 1999

OUTLINE OBJECTIVE PROJECT SET-UP (Period, participants, tasks) MAIN RESULTS RESULTS FROM PHASE 1: ACOUSTIC ARRAY MEASUREMENTS RESULTS FROM PHASE 2: DESIGN AND VALIDATION OF ACOUSTIC AIRFOIL DESIGN CONCLUSIONS/FUTURE WORK IMTS meeting Madrid 18th-19th October 1999

Sirocco: Project period January 1st 2003 until February 28th 2007 GE joined project in May 2005 IMTS meeting Madrid 18th-19th October 1999

February 2006 SIROCCO, 4 phases Start-up phase: Is acoustic behaviour of baseline turbines as expected, i.e. is trailing edge noise dominant? Acoustic array measurements: Location and quantification of noise sources on wind turbine blade 2D design phase: Design and test acoustically optimised airfoils Development of aero-acoustic design method Supported by 2D wind tunnel measurements 3) 3D design and manufacturing 4) Final validation in the field: Compare acoustic and ‘aerodynamic’ behaviour of optimised turbine and reference turbine February 2006 IMTS meeting Madrid 18th-19th October 1999

SIROCCO: Participants, main role Energy Research Centre of the Netherlands, ECN: Coordination, design consultancy, ‘aerodynamic’ field measurements National Aerospace Laboratory, NLR: Acoustic measurements: Field and wind tunnel (2D) University of Stuttgart: Development design methodology for acoustically optimised airfoils; Design of acoustically optimised airfoils; Validation: Wind tunnel (2D): Aerodynamic and acoustic Gamesa: Design of blades with optimised airfoils and manufacturing GE Wind Energy IMTS meeting Madrid 18th-19th October 1999

OUTLINE OBJECTIVE PROJECT SET-UP (Period, participants, tasks) MAIN RESULTS RESULTS FROM PHASE 1: ACOUSTIC ARRAY MEASUREMENTS RESULTS FROM PHASE 2: DESIGN AND VALIDATION OF ACOUSTIC AIRFOIL DESIGN CONCLUSIONS /FUTURE WORK IMTS meeting Madrid 18th-19th October 1999

Is trailing edge noise the dominant noise source? Answer yes as derived from NLR’s acoustic array measurements on GE2.3 turbine/G58 turbine Assume monopole source at scan point Location and quantification of noise sources on rotating wind turbine blades GE Scan points Microphone array G58 Delay&sum Sound rays IMTS meeting Madrid 18th-19th October 1999

Acoustic array measurements: Some observations GE Turbine noise dominated by rotor blades Noise radiated from outer part of blades (but not the very tip) Practically all blade noise (emitted to ground) produced during downward movement G58 IMTS meeting Madrid 18th-19th October 1999

Dominance of down-going blades The down-going blades are dominant for all frequencies and all measurements Indication for trailing edge noise to be dominant Can be explained by combination of: Convective amplification Trailing edge noise directivity sin2(/2) IMTS meeting Madrid 18th-19th October 1999

Noise sources on individual G58 blades (clean, untreated, tripped) Typical source plots for individual blades Rotating focus plane for each blade Averaged over downward part of one rotation Clean Untreated Tripped 12 dB 0 dB Tripped blade significantly noisier than other two Indication for TE-noise to be dominant IMTS meeting Madrid 18th-19th October 1999

TE-noise dominant in calculations, but how good are the calculations? Spin-off: Use measurements to validate wind turbine noise prediction code SILANT IMTS meeting Madrid 18th-19th October 1999

SILANT Originally developed by Stork Product Engineering, NLR and TNO ECN Divide blade in a number of blade elements Calculate noise spectrum per element: Inflow noise: Amiet and Lowson Trailing edge noise: Brooks Pope and Marcolini d*p and d*s at trailing edge from XFOIL and blade element momentum model Sum over elements IMTS meeting Madrid 18th-19th October 1999

SILANT/meas (noise vs. power) IMTS meeting Madrid 18th-19th October 1999

Measured spectrum vs SILANT spectrum: Total noise, trailing edge noise, inflow noise IMTS meeting Madrid 18th-19th October 1999

Indications for TE-noise to be dominant Practically all blade noise (emitted to the ground) produced during downward movement Directivity of trailing edge noise Tripped blade significantly noisier than other two Tripping influences trailing edge noise Calculated results show TE noise to be dominant above inflow noise Blade noise levels scale with 5th power of local speed Dependancy of trailing edge noise Broadband TE noise is the dominant noise source IMTS meeting Madrid 18th-19th October 1999

OUTLINE OBJECTIVE PROJECT SET-UP (Period, participants, tasks) MAIN RESULTS RESULTS FROM PHASE 1: ACOUSTIC ARRAY MEASUREMENTS RESULTS FROM PHASE 2: DESIGN AND VALIDATION OF ACOUSTIC AIRFOIL DESIGN CONCLUSIONS/FUTURE WORK IMTS meeting Madrid 18th-19th October 1999

Main results: Phase 2: 2D design phase Design philosophy: Modify boundary layer at trailing edge Improved noise airfoil prediction code coupled to an aerodynamic airfoil prediction code and optimizer Requirements/constraints of manufacturers implemented Aerodynamics Acoustics Mean boundary layer profile + turbulent properties at trailing edge Using boundary layer wind tunnel measurements on airfoil with Variable Trailing Edge (VTE) IMTS meeting Madrid 18th-19th October 1999

ORIGINAL LINK BETWEEN AERODYNAMIC/AERO-ACOUSTIC MODELLING Mean boundary layer profile assumed to be a Coles profile: Derived from integral boundary-layer parameters Turbulence properties: v’2 ,Kt derived from mean boundary layer profile with mixing length approach Vertical integral length scale (Λ2) from mixing length scale and scaling law Equilibrium approach!! Anisotropy is constant factor IMTS meeting Madrid 18th-19th October 1999

DESIGN METHOD: IMPROVEMENTS MADE DURING SIROCCO PROJECT History and anisotropy effects important for flow regions with acceleration/deceleration EDDYBL FD boundary-layer code with stress-ω model (Wilcox) Vertical integral length scale Λ2 is not provided by available turbulence models adequate scaling laws required Directly found from Λ2 measurements in the wind tunnel IMTS meeting Madrid 18th-19th October 1999

Aerodynamic/Acoustic validation in windtunnel Aerodynamic validation LWT tunnel of USTUTT closed test section 0.73x2.73 m2 Acoustic validation: 1) AWB tunnel (NLR): Array technique Open jet 1.2x0.8 m2 2) LWT tunnel (USTUTT): CPV technique Re=1.6 106 Clean/tripped airfoils CPV: Coherent Particle Velocimetry: Measurement of particle velocities with hot-wire at pressure and suction side of airfoil TE, instead of (microphone) measurement of pressure fluctuations LWT AWB IMTS meeting Madrid 18th-19th October 1999

Drag polars Noise polars GE Gamesa IMTS meeting Madrid 18th-19th October 1999

OUTLINE OBJECTIVE PROJECT SET-UP (Period, participants, tasks) MAIN RESULTS RESULTS FROM PHASE 1: ACOUSTIC ARRAY MEASUREMENTS RESULTS FROM PHASE 2: DESIGN AND VALIDATION OF ACOUSTIC AIRFOIL DESIGN CONCLUSIONS/FUTURE WORK IMTS meeting Madrid 18th-19th October 1999

Conclusions/Future work Acoustic array measurements very successfully applied on full scale turbine: Trailing edge noise is dominant Design methodology for acoustically optimised airfoil has been improved and validated successfully in wind tunnel New airfoils: Noise reduction: 1-1.5 dB and 2.5-2.9 dB Aerodynamic characteristics hardly changed Blade design/manufacturing underway Full scale validation with hybrid rotor in April 2006/Autumn 2006 IMTS meeting Madrid 18th-19th October 1999