1. 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

2. 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

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. 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

11. Acoustic array measurements: Some observationsGE
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

12. 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

13. 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

14. 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

15. 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

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

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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=
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

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

25. 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

26. 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: dB and 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