SIROCCO, SIlant ROtors by aCoustiC OptimisationParticipants:

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)

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

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

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)

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

Sirocco: Project period

January 1st 2003 until February 28th 2007

GE joined project in May 2005

SIROCCO, 4 phases

1) 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

2) 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 manufacturing4) Final validation in the field: Compare acoustic and ‘aerodynamic’

behaviour of optimised turbine and reference turbine

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 Design of blades with optimised airfoils and manufacturing

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

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

Sound rays

Scan points

Microphone array

Delay&sum

GE

G58

-70

-65

-60

-55

-50

-10 -5 0 5 10

[m]

[m]

Platform: 15 x 18 m2

152 mics

Acoustic array measurements: Some observations

•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

GE

G58

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)

4

22

)cos1(

sin )2/(sin2

MD

0 60 120 180 240 300 360-10

-5

0

5

10

Rotor azimuth (degrees)

dirconvtotal

dSP

L (d

B)

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

– Tripped blade significantly noisier than other two

– Indication for TE-noise to be dominant

Clean Untreated Tripped

0 dB

12 dB

TE-noise dominant in calculations, but howgood are the calculations?

Spin-off: Use measurements to validate wind turbine noise prediction code SILANT

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–

p and s at trailing edge from XFOIL and

blade element momentum model Sum over elements

SILANT/meas (noise vs. power)

90

95

100

105

110

0 100 200 300 400 500 600 700 800 900

Power (kW)

OA

SP

L (

dB

A)

measured (cleanblades)

SILANT

2nd order fit (SILANT)

2nd order fit (measured)

Measured spectrum vs SILANT spectrum: Total noise, trailing edge noise, inflow noise

Indications for TE-noise to be dominant

1. Practically all blade noise (emitted to the ground) produced during downward movement Directivity of trailing edge noise

2. Tripped blade significantly noisier than other two Tripping influences trailing edge noise

3. Calculated results show TE noise to be dominant above inflow noise

4. Blade noise levels scale with 5th power of local speed Dependancy of trailing edge noise

Broadband TE noise is the dominant noise source

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

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)

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

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

Aerodynamic validationLWT tunnel of USTUTT

closed test section 0.73x2.73 m2

Aerodynamic/Acoustic validation in windtunnel

LWT AWB

Acoustic validation: 1) AWB tunnel (NLR): Array technique

•Open jet•1.2x0.8 m2

2) LWT tunnel (USTUTT): CPV technique

CPV: Coherent Particle Velocimetry:Measurement of particle velocitieswith hot-wire at pressure and suction side of airfoil TE, instead of(microphone) measurement of pressure fluctuations

Re=1.6 106

Clean/tripped airfoils

GE Gamesa

Dragpolars

Noisepolars

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

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