An overview of recent research on AM and OAM of wind turbine … · H Aa Madsen -- WTN 2015 Glasgow 20 April 20-23, 2015 Madsen HAa et. al. , The DANAERO MW Experiments, paper AIAA

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An overview of recent research on AM and OAM of wind turbine noise

Aagaard Madsen , Helge; Bertagnolio, Franck; Fischer, Andreas

Publication date:2015

Link back to DTU Orbit

Citation (APA):Aagaard Madsen , H. (Author), Bertagnolio, F. (Author), & Fischer, A. (Author). (2015). An overview of recentresearch on AM and OAM of wind turbine noise. Sound/Visual production (digital)

https://orbit.dtu.dk/en/publications/57510a18-88a3-4887-bd75-014157e249f0

An overview of recent research on AM and OAM of wind turbine noise

Helge Aagaard Madsen

Franck Bertagnolio

Andreas Fischer

DTU Wind Energy

Technical University of Denmark

P.O. 49, DK-4000 Roskilde, Denmark

[email protected]

mailto:[email protected]

DTU Wind Energy, Technical University of Denmark

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Introduction

H Aa Madsen -- WTN 2015 Glasgow April 20-23, 2015 2

Bullmore A, Cand M, Oerlemans S, Smith MG, White P, von Hünerbein S, King A, Piper B, et al.. ReneawableUK. Wind Turbine Amplitude Modulation: Research to Improve Understanding as to its Cause and Effect. RenewableUK, United Kingdom;2013.

Madsen HAa, Fischer A, Abildgaard K. Phase 2, Mechanisms and causes of Amplitude Modulation (AM) and Other Amplitude Modulation (OAM) of aero-acoustic wind turbine noise. Report DTU Wind Energy I-0095 (EN), DTU Wind Energy August 2013. In RenewableUK 2013 report: Wind Turbine Amplitude Modulation: Research to Improve Understanding as to its Cause & Effect.

A comprehensive research project: ” Wind Turbine Amplitude Modulation:

Research to Improve Understanding as to its Cause and Effect”

coordinated and funded by Renewable UK

carried out in the period 2010-2013

final report released in December 2013

DTU involved in last part



DTU background for conducting the AM research in the Renewable UK study

Expertise on:

inflow measurements on a blade (since 1987)

noise source measurements with microphones

on the blade surface (since 2006)

these techniques applied in The DAN-AERO

project 2007-2010*

rotor noise modeling

modeling wind turbine aeroelasticity and control

3 H Aa Madsen -- WTN 2015 Glasgow

April 20-23, 2015

* The DANAERO project was conducted in corporation between Vestas, Siemens, LM, DONG Energy and DTU Wind Energy in 2007-2010. Funded by the Danish Ministry of Energy



Inflow measurements

First measurements on a 100 kW turbine in the period from 1987-1993


April 20-23, 2015



Mechanism of amplitude modulation (AM) of noise – from the Ren. UK study

caused by 1p variations of the level of trailing edge

noise and change in directivity during blade rotation

variation of a few dB over one blade revolution

AM

5

Bullmore A, Cand M, Oerlemans S, Smith MG, White P, von Hünerbein S, King A, Piper B, et al.. ReneawableUK. Wind Turbine Amplitude Modulation: Research to Improve Understanding as to its Cause and Effect. RenewableUK, United Kingdom;2013.

Measured about 50 m upwind from a 93-m diameter pitch-controlled wind turbine

H Aa Madsen -- WTN 2015 Glasgow April 20-23, 2015



6

horizontal coordinate x [m]

altitude h

[m

]

integrated SPL [dB] for TE noise

-30 -20 -10 0 10 20 30

30

40

50

60

70

80

90

40

42

44

46

48

50

52

54

56

58

60

AM simulation - Shear exponent 0.2


altitude h

[m

]

angel of attack [deg]

-30 -20 -10 0 10 20 30

30

40

50

60

70

80

90

6

7

8

9

10

11

12

13

14

15


altitude h

[m

]

directivity factor for TE noise

-30 -20 -10 0 10 20 30

30

40

50

60

70

80

90

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

Directivity for TE noise AOA variation causing TE noise variation




Characteristics of extreme AM - also called EAM or OAM

the modulation depth significantly greater than that of normal

blade swish (AM)

modulation depths up to 10 dB have been measured

increased level at frequencies below 400 Hz

the effect is generally strongest in the downwind direction

Figures from Renewable UK study on AM and OAM (EAM), December 2013

EAM


April 20-23, 2015



Characteristics of extreme AM - also called EAM or OAM


April 20-23, 2015

commonly termed ‘blade swish’

part of normal WTN

~5dB modulation at source

dominant crosswind effect

decreases away from source

dominated by mid frequencies

(400Hz to 1000Hz) ‘swish’

source mechanism understood

more impulsive ‘thump’

atypical, intermittent

>5dB (>10dB) amplitude at times?

audible/noticeable at large distances

downwind to >1km?

additional lower frequency content

(200 Hz to 500 Hz)? ‘whooomp’

source mechanism?

Normal AM OAM

Jeremy Moon, RES, 2014



Causal factors raised in the Renew. UK AM and OAM study


April 20-23, 2015

OAM due to transient stall ?

is it possible that transient stall occurs on a pitch regulated turbine in normal operation ?

characteristics of angle of attack (AoA) variations on a real full scale turbine ?

stall noise characteristics ?

the causes of variability of the occurence of OAM ?

is there a scaling effect ?



Limits of the present overview


April 20-23, 2015

the noise source characteristics of AM and OAM

But many other important subjects related to AM and OAM identification of all important factors influencing mechanisms behind AM and OAM

propagation effects

quantification of AM and OAM

annoyance characteristics of AM and OAM

mitigation



Outline

the noise sources in relation to AM and OAM

the measurement techniques

inflow – (AoA and magnitude of the relative velocity)

high frequency surface pressure measurements

measurements on full scale turbines

results from two experimental data sets

scaling effect and blade leading edge degradation

conclusions


April 20-23, 2015



Noise sources behind AM and OAM

12

Trailing edge (TE) noise important for AM, (OAM ?)

Stall (ST) noise

important for OAM Turbulent inflow (TI) noise

important for AM ? and OAM ?




TE Noise Mechanism


2y

3y

1y

1 2( )U y

( , )P k

1 2 3, ,u u u Far field sound

by scattering ( )PS

Turbulent boundary layer

Surface pressure fluctuations (SPF)




Turbulent Inflow (TI) Noise

Idealized Airfoil as an Half-Plane

2y3y

1y

Far field sound

Turbulent Inflow

P2gustu

U1





Stall (ST) noise





Experimental characterization of the TE, TI and ST noise sources

and

the measurement techniques




Experimental characterization of the source of TE, TI and ST noise

1y


Surface microphones to measure SFP

Five hole pitot tube to measure magnitude and direction (AOA) of U

AoA

17




What are the noise sources influenced by ?

TE noise > function(AOA, U, blade roughness, transition, vortex generators)

AOA function ( inflow turbulence and shear, blade elastic torsion, blade

pitch)

TI noise > function(U, inflow turbulence and shear, leading edge geometry,

AOA ?)

ST noise > function(AOA, U, blade roughness, transition, vortex generators)

AOA function ( inflow turbulence and shear, blade elastic torsion, blade

pitch)

18



Measurement of SPF with microphones mounted on the blade




Measurement on a full scale rotor blade, 80m rotor, 2MW turbine - - DANAERO MW project 2009

surface pressure and

inflow with five hole pitot

tubes measured at 4 radial

stations

60 flush mounted

microphones for high

frequency surface

pressure measurements

measurement

campaigns from June to

September 2009


Madsen HAa et. al. , The DANAERO MW Experiments, paper AIAA 2010-645 presented at 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 4 - 7 January 2010, Orlando, Florida



Installation of the 38.8m instrumented blade in May 2009

Microphone holes


A new test blade was manufactured and instrumented



Measurement of inflow (AOA) with a five hole pitot

4 pitot tubes on the 80m, 2MW, NM80 turbine

One pitot tube on the Siemens 3.6 MW turbine


April 20-23, 2015

The DANAERO MW experiment 2009



Experimental data sets


1. High frequency surface pressure data correlated with inflow

(AoA) data measured on an 80m diameter wind turbine rotor – the DANAERO experiment in 2009

provides insight into change of noise source characteristics at transition from attached flow to separated flow (stall)

2. Measurement of inflow (AoA) on the rotating blade over three weeks on the same turbine in 2003 provides statistics on the occurrence of high angle of attack (stall)

on a wind turbine in normal operation – (2014 study)



1. Measurement of SPF on a full scale rotor blade, 80m diameter rotor, 2MW

SPF spectra derived at each red dot

Wind shear measured in the met mast


April 20-23, 2015



TE spectra measured during free inflow at 9-11m/s -- amplitude modulation

Each spectrum is based on 0.5sec


April 20-23, 2015



time t [s]

cente

r fr

equency f

c [

Hz]

Surface Pressure Level [dB1/12

]

0 1 2 3 4 5 6 7 8 9 10

200

400

600

800

1000

0 1 2 3 4 5 6 7 8 9 106

7

8

9

10

11

12

time t [s]

angle

of

att

ack

[deg]

102

104

106

108

110

112

10

20

30

40

50

60

Surface pressure level on suction side at x/c=0.84, Sept 1, 2009, 10:05


April 20-23, 2015

Below stall



Surface pressure level on suction side at x/c=0.84, Sept 1, 2009, 10:05 binned on AoA

102

103

104

80

85

90

95

100

105

110

115

center frequency fc [Hz]

Spp [

dB

1/1

2]

=7o

=8o

=9o

=10o

=11o


April 20-23, 2015

Below stall



time t [s]

cente

r fr

equency f

c [

Hz]

Surface Pressure Level [dB1/12

]

0 1 2 3 4 5 6 7 8 9 10

200

400

600

800

1000

0 1 2 3 4 5 6 7 8 9 108

9

10

11

12

13

14

time t [s]

angle

of

att

ack

[deg]

100

105

110

115

10

20

30

40

50

60

DANAERO – NM80 turbine - forced operation at high angle of attack (AOA) by negative pitch and constant rpm – transient stall

High 1p modu-lation (15 dB) at the low frequencies. Microphone close to the trailing edge


Strong wind shear causing variations of AOA reaching stall



DANAERO – NM80 turbine - forced operation at high angle of attack by negative pitch and constant rpm


Stall

[Hz]




2. Measurement of inflow (AOA) on the rotating blade over three weeks

on the same turbine in 2003 provides statistics on the occurrence of high angle of attack

(stall) on a wind turbine in normal operation



2. Inflow measurements with one five hole pitot tube on same turbine – 2003 - 3 weeks with normal operation – basis for statistics of inflow (AOA)


Turbine situated in a small wind farm with 8 turbines



Inflow measurements – 2003 - about 2000 of 10 min. time series




Inflow measurements – 2003 - analysis of about 2000 10 min. series


AOA amplitude is max to min

Free inflow Wake operation

Madsen H Aa, Bertagnolio F, Fischer A, Bak C, Correlation of amplitude modulation to inflow characteristics. Proceedings of INTERNOISE 2014, Melbourne, Australia, November 16-19, 2014.



Inflow measurements - 2003 - 10 min. statistics of AOA variations - the risk of transient stall

5 degrees between grid lines




An example of high AOA


Mx is flapwise blade root moment



A scale effect due to rotational sampling of turbulence


Spectrum of the wind seen from the tip of the rotating blade



A scale effect due to rotational sampling of atmospheric turbulence


1p

Increase in 1p content of AoA when upscaling rotors



Blade leading edge roughness


Leading edge rough-ness will decrease Clmax and increase risk for transient stall

http://www.nacleanenergy.com/articles/17870/reliability-centered-maintenance-for-wind-turbine-blades NM80 turbine – DANAERO project



Conclusions

strong 1p modulation seen in measured SPF spectra on

rotating 38m blade

a shift in SPF spectra to lower frequencies when transient stall occurs

very likely that trailing edge separation causing stall noise is a major mechanism of OAM

wake and shear effects increase AoA variations

transient stall seems closely linked to the variable speed operation of the turbine

the intermittent character of the AoA variations corresponds well to observed characteristics of OAM

upscaling of rotors will increase 1p AoA variations




Thank you for your attention


April 20-23, 2015

Documents

An overview of recent research on AM and OAM of wind turbine … · H Aa Madsen -- WTN 2015 Glasgow 20 April 20-23, 2015 Madsen HAa et. al. , The DANAERO MW Experiments, paper AIAA