Aagaard Madsen , Helge

Bertagnolio, Franck

Fischer, Andreas

Kragh, Knud Abildgaard

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Analyses of the mechanisms of amplitude modulation of aero-acoustic wind turbinesoundFischer, Andreas; Aagaard Madsen , Helge; Kragh, Knud Abildgaard; Bertagnolio, FranckPublication date:2014Link back to DTU OrbitCitation (APA):Fischer, A., Aagaard Madsen , H., Kragh, K. A., & Bertagnolio, F. (2014). Analyses of the mechanisms ofamplitude modulation of aero-acoustic wind turbine sound European Wind Energy Association (EWEA).[Sound/Visual production (digital)]. European Wind Energy Conference & Exhibition 2014, Barcelona, Spain,10/03/2014Analyses of the mechanisms of amplitude modulation of aero-acoustic wind turbine sound  Andreas Fischer Helge Aagaard Madsen Knud Abildgaard Kragh Franck Bertagnolio   DTU Wind Energy Technical University of Denmark P.O. 49, DK-4000 Roskilde, Denmark asfi@dtu.dk  DTU Wind Energy, Technical University of Denmark           (Normal) Amplitude Modulation (NAM) of Wind Turbine Noise [1] • swishing sound radiated when the blade moves downwards • Peak to trough level a few dB • Normally only perceived close to the wind turbine (1-2D) • Can be explained by the directivity of trailing edge noise EWEA Conference 2014, Barcelona, Spain 2 25 March 2014 [2] Directivity of noise emitted from an airfoil with finite chord length [3] kc=10 kc=50 DTU Wind Energy, Technical University of Denmark           (Other) Amplitude Modulation (OAM) of Wind Turbine Noise [1] • Described as thumping sound • More low frequency content and higher peak to trough level than normal AM • Perceived at larger distance from the wind turbine • Perceive at up and downwind locations • Transient stall as a possible explanation EWEA Conference 2014, Barcelona, Spain 3 25 March 2014 Directivity of noise emitted from an airfoil with finite chord length [3] [2] kc=1 kc=5 DTU Wind Energy, Technical University of Denmark           Objectives  • Investigate the source of trailing edge noise and stall noise (surface pressure field) on a full scale wind turbine rotor  • Relate surface pressure field to emitted far field sound  • Identify wind conditions which can lead to OAM  • Outline control strategies to alleviate OAM EWEA Conference 2014, Barcelona, Spain 4 25 March 2014 DTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM  (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 5 25 March 2014 DTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM  (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 6 25 March 2014 DTU Wind Energy, Technical University of Denmark           NEG-Micon NM80 Wind turbine with inflow sensors DANAERO MW project [4], Vestas, Siemens, LM Wind Power, DONG Energy, DTU, 2007-2010 EWEA Conference 2014, Barcelona, Spain 7 25 March 2014 Four 5 hole pitot tubes installed on a NM80 turbine  • Pressure tabs at r=13m, 19m, 30m and 37m  • Pitot tubes at r= 14.5m, 20.3m, 31m and 36m  • 60 Microphones at r=37m for high frequency surface pressure measurements DTU Wind Energy, Technical University of Denmark           Campaign measurements from June to September 2009 – DANAERO MW project EWEA Conference 2014, Barcelona, Spain 8 25 March 2014 Microphone holes Pressure  holes DTU Wind Energy, Technical University of Denmark           NEG-Micon NM80 Wind Turbine (DANAERO MW project) EWEA Conference 2014, Barcelona, Spain 9 25 March 2014 • Technical Data: –Rated power 2.3MW –Hub height 57m –Rotor diameter 80m –LM38.8 blades • Unusual operational conditions: –Constant rotational speed (16.23rpm = 1.7rad/s) –Pitch -4.5°(towards higher AoAs, forced to stall) –High wind speed (above 12m/s at hub) –Yaw +/-10° DTU Wind Energy, Technical University of Denmark           Wind velocity profile measured at the met mast on Sept. 1, 2009 (10min average) EWEA Conference 2014, Barcelona, Spain 10 25 March 2014 6 7 8 9 10 11 12 13102030405060708090100110altitude [m]velocity [m/s]met mast mean wind speed  cupsonicHAWC2 pl7 8 9 10 11 12 13 14 15102030405060708090100110altitude [m]velocity [m/s]met mast mean wind speed  cupsonicHAWC2 pl10:00 11:40 Shear exponent 0.3 Shear exponent 0.3 DTU Wind Energy, Technical University of Denmark           Wind velocity profile measured at the met mast on Sept. 1, 2009 (10min average) EWEA Conference 2014, Barcelona, Spain 11 25 March 2014 6 7 8 9 10 11 12 13102030405060708090100110altitude [m]velocity [m/s]met mast mean wind speed  cupsonicHAWC2 pl7 8 9 10 11 12 13 14 15102030405060708090100110altitude [m]velocity [m/s]met mast mean wind speed  cupsonicHAWC2 pl10:00 11:40 Shear exponent 0.3 Shear exponent 0.3 DTU Wind Energy, Technical University of Denmark           Surface pressure level on suction side at x/c=0.84, Sept. 1, 2009 (evaluated every 0.5sec) EWEA Conference 2014, Barcelona, Spain 12 25 March 2014 10:05 11:48 time t [s]center frequency f c [Hz]Surface Pressure Level [dB1/12]  0 1 2 3 4 5 6 7 8 9 1020040060080010000 1 2 3 4 5 6 7 8 9 106789101112time t [s]angle of attack α [deg]  102104106108110112102030405060time t [s]center frequency f c [Hz]Surface Pressure Level [dB1/12]  0 1 2 3 4 5 6 7 8 9 1020040060080010000 1 2 3 4 5 6 7 8 9 10891011121314time t [s]angle of attack α [deg]  100105110115102030405060DTU Wind Energy, Technical University of Denmark           Aerofoil Pressure distribution Sept 1, 2009, 11:48 EWEA Conference 2014, Barcelona, Spain 13 25 March 2014 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-0.8-0.6-0.4-0.200.20.40.60.811.2x/c [-]-p [psi]  t=1.24s, α=8.7ot=4.74s, α=9.1ot=8.74s, α=9.3ot=3.74s, α=11.9ot=2.74s, α=12.9ot=6.24s, α=12.9oDTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM  (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 14 25 March 2014 DTU Wind Energy, Technical University of Denmark           Virginia Tech Stability Wind Tunnel EWEA Conference 2014, Barcelona, Spain 15 25 March 2014 Air exchange tower Control room 0.5MW Drive and Fan Flow Acoustic test section Anechoic chambers 3m DTU Wind Energy, Technical University of Denmark           Virginia Tech Stability Wind Tunnel EWEA Conference 2014, Barcelona, Spain 16 25 March 2014 Air exchange tower Control room 0.5MW Drive and Fan Flow Acoustic test section Anechoic chambers 3m DTU Wind Energy, Technical University of Denmark           Virginia Tech Stability Wind Tunnel EWEA Conference 2014, Barcelona, Spain 17 25 March 2014 Air exchange tower Control room 0.5MW Drive and Fan Flow Acoustic test section Anechoic chambers 3m DTU Wind Energy, Technical University of Denmark           Prediction of far field sound pressure with measured surface pressure 102103104202530354045505560center frequency f [Hz]far field sound spectrum Spp [dB1/12]NACA64-618, Re=1.5M  αE=-0.88oαE=0.93oαE=2.77oαE=6.52omic. arrayEWEA Conference 2014, Barcelona, Spain 18 25 March 2014 102103104253035404550556065center frequency f [Hz]far field sound spectrum Spp [dB1/12]NACA64-618, Re=1.9M  αE=6.27o (pre stall)αE=8.23o (post stall)αE=12.21o (deep stall)102103104707580859095100105110115120center frequency f [Hz]surface pressure spectrum Spp [dB1/12]NACA64-618, Re=1.9M  Trailing edge noise [5] : The effect of stall on noise emission: DTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM  (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 19 25 March 2014 DTU Wind Energy, Technical University of Denmark           DANAERO MW Project 2009 Vestas, Siemens, LM Wind Power, DONG Energy, DTU  EWEA Conference 2014, Barcelona, Spain 20 25 March 2014 Siemens 3.6 MW Turbine Pitot tube mounted at radial position r=36m DTU Wind Energy, Technical University of Denmark           DANAERO MW Project 2009 Vestas, Siemens, LM Wind Power, DONG Energy, DTU  EWEA Conference 2014, Barcelona, Spain 21 25 March 2014 Høvsøre Test Site  DTU Wind Energy, Technical University of Denmark           Correlation of wind shear to variations in angle of attack EWEA Conference 2014, Barcelona, Spain 22 25 March 2014 March 28, 2007 DTU Wind Energy, Technical University of Denmark           Correlation of wind shear to variations in angle of attack EWEA Conference 2014, Barcelona, Spain 23 25 March 2014 March 28, 2007 DTU Wind Energy, Technical University of Denmark           Correlation of wind shear to variations in angle of attack EWEA Conference 2014, Barcelona, Spain 24 25 March 2014 Difference between inflow angle (IA) and angle of attack (AOA)  DTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM   (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 25 25 March 2014 DTU Wind Energy, Technical University of Denmark           Mitigation - Decreasing mean angle of attack EWEA Conference 2014, Barcelona, Spain 26 25 March 2014 • HawcStab2 simulations with varying min pitch angle DTU Wind Energy, Technical University of Denmark           Mitigation - Decreasing angle of attack variations EWEA Conference 2014, Barcelona, Spain 27 25 March 2014 • HAWC2 simulations with individual pitch control, sheared inflow exp=0.5, no turbulence DTU Wind Energy, Technical University of Denmark           Mitigation - Decreasing angle of attack variations EWEA Conference 2014, Barcelona, Spain 28 25 March 2014 • Yaw misalignment DTU Wind Energy, Technical University of Denmark           Outline • Experimental noise source characterisation on a full scale rotor  (DAN-AERO MW project)  • Relation between noise source and emitted far field sound  (measurement in Virginia Tech Wind Tunnel)  • Critical atmospheric conditions to cause (Other)AM   (DAN-AERO MW project)  • Control strategies to alleviate (Other)AM  • Conclusions    EWEA Conference 2014, Barcelona, Spain 29 25 March 2014 DTU Wind Energy, Technical University of Denmark           Conclusions • Variation of the angle of attack during a revolution causes changes in the spectral energy of the noise sources on the blade  • Under normal conditions the variations of spectral energy are too small to lead to amplitude modulation far away from the turbine (NAM)  • If the blade undergoes transient stall the spectral energy in the low frequency range is significantly increased and it can lead to OAM  • Wind conditions leading to transient stall: high shear in combination with a mean wind speed close to rated wind speed  • Control strategies to mitigate OAM: –  reducing the mean angle of attack (collective pitch) –  reducing the angle of attack variations (individual pitch or yaw control)   EWEA Conference 2014, Barcelona, Spain 30 25 March 2014 DTU Wind Energy, Technical University of Denmark           References 1) Oerlemans S. An explanation for enhanced amplitude modulation of wind turbine noise. In: Wind Turbine Amplitude Modulation: Research to Improve Understanding as to its Cause and Effect. RenewableUK, Dec. 2013. 2) Brooks TF, Pope DS, Marcolini MA. Airfoil Self-Noise and Prediction. NASA Reference Publication 1218, 1989. 3) S. Moreau and M. Roger. Back-scattering correction and further extensions of Amiet’s trailing-edge noise model. Part II: Application. J. of Sound and Vib. 323 (2009) 397–425 4) H. A. Madsen et al. The DAN-AERO MW Experiments: Final report. Tech. Rep. Risoe-R-1726(EN), Risoe-DTU, Roskilde, Denmark, September 2010. 5) Roger M, Moreau S. Back-scattering correction and further extensions of Amiet’s trailing-edge noise model. Part 1: theory. J. Sound Vib. 2005; 286:477–506.      EWEA Conference 2014, Barcelona, Spain 31 25 March 2014 Thank you! 25 March 2014 

Analyses of the mechanisms of amplitude modulation of aero-acoustic wind turbine sound

This paper explores the source mechanism which cause amplitude modulation of the emitted sound of a wind turbine at large distances from the turbine, named as other amplitude modulation. Measurements of the fluctuating surface pressure on a 2.3MW wind turbine showed a considerable variation over a blade revolution in the presence of angle of attack variations. If the blade undergoes transient stall, the variation of the surface pressure spectrum was enhanced and shifted to frequencies below 200Hz. The surface pressure spectra could be directly related to the emitted far eld sound. These ndings give further evidence that transient stall is a main mechanism to cause other amplitude modulation. Wind shear was identified as a critical condition to cause angle of attack variations. Dierent control strategies to mitigate other amplitude modulation were proposed

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Analyses of the mechanisms of amplitude modulation of aero-acoustic wind turbine sound

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