The sounds of high winds

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gas must keep flowing” . 1 I do not agree with the Minister: I think that a limited resource should require limited consumption, even at the cost of some discomfort to our spoiled society. If we can curb our Joule addiction, wind power may help us to produce part of the sustainable energy we need to satisfy basic needs. Figure I.1: history since 1980 and forecast until 2030 of global energy production (adapted from the ExxonMobil 2004 Energy Outlook); MBDOE = million barrels per day oil-equivalent = 620 TWh per year Wind turbine noise is a problem that may grow due to neglect by wind energy proponents and thus it may be another reason for part of the public, with politicians following, to turn away from wind power. This problem can be solved when it is also addressed at the level of local impact: sustainability must also apply at the local level. Some technical possibilities for noise reduction are given in this book and more competent, hardware oriented people may come up with better solutions. In addition to this, the social side of the problems must not be neglected. In a recent study [Van As et al 2005] it was concluded that “growing public resistance 1 NRC Handelsblad 8-11-2005, articles “Bezinning nodig over energiebeleid” (“Energy policy needs reflection” by W. van Dieren) and “Nieuw debat schept slechts onzekerheid” (“New debate only creates uncertainty” by Laurens Jan Brinkhorst); my translations 11
to onshore wind turbines” obstructs wind energy development in the Netherlands. According to the report this opposition is now the main bottle-neck: local communities and residents are faced with the disadvantages whilst others (proponents, society at large) reap the benefits. The report recommends that the former share in the benefits too. I.5 Microphone wind noise In contrast to the impact my wind turbine research has had in society, the same knowledge of atmospheric physics helped me solve a noncontroversial problem of interest to only a few: what is the nature of the noise that wind creates in a microphone? It occurred to me that if atmospheric turbulence was the cause, then one must be able to calculate the level of this noise. I was delighted when I found out how well theoretical considerations fitted hitherto only vaguely understood measurement results. Eureka!, such is the joy of work in science. Somewhat unexpectedly this second discovery turns out to be related to wind turbine sound, which is why it is in this book. Originally it was considered difficult to measure wind turbine sound, because the strong winds that were supposed to cause high wind turbine sound levels, also were believed to be responsible for a lot of microphone wind noise. Solutions to this problem were either to put the microphone out of the wind on the ground or use several microphones and decrease microphone noise by averaging over all microphone signals. A new solution offered in this book is to take measurements in a stable atmosphere where near-ground wind velocity is so low that microphone noise is far less of a problem. One can measure sound at distances from a wind farm most researchers would not now believe to be possible. The relationship is even stronger. In some countries the level of ambient background sound determines (part of) the limit imposed on sound exposure. To measure the level of this background sound the microphone must be put up in a place where residents stay outdoors, also in stronger winds. In this case it is important to discriminate between real ambient 12
Page 1 and 2: The sounds of high winds the effect
Page 3 and 4: Promotores: prof dr ir H. Duifhuis
Page 5 and 6: Contents I WIND POWER, SOCIETY, THI
Page 7 and 8: VII THINKING OF SOLUTIONS: measures
Page 10 and 11: I WIND POWER, SOCIETY, THIS BOOK: a
Page 12 and 13: esidents) noticed the discrepancy b
Page 14 and 15: that even though wind turbines did
Page 16 and 17: legitimate problems [Wolsink 1990].
Page 18 and 19: Thinking that this could perhaps be
Page 22 and 23: sound and the noise that wind produ
Page 24: combined with the corresponding sec
Page 27 and 28: calculated one and whether sound ch
Page 29 and 30: annoying turbine sound at distances
Page 31 and 32: was 57.9 dB, with a maximum deviati
Page 33 and 34: not correct at night, although the
Page 36 and 37: III BASIC FACTS: wind power and the
Page 38 and 39: 0.1. In a stable atmosphere vertica
Page 40 and 41: With regard to wind power some atte
Page 42 and 43: III.4 Main sources of wind turbine
Page 44 and 45: High frequency: trailing edge (TE)
Page 46: So, what's the sound like...? (....
Page 49 and 50: Figure IV.2: turbines (dots W1….W
Page 51 and 52: L Wj , assumed identical for all k
Page 53 and 54: IV.1. As explained above, the wind
Page 55 and 56: sound level in the measurement inte
Page 57 and 58: Leq,5 min in dB(A) 50 45 40 35 30 A
Page 59 and 60: The same lines as in figure IV.5B,
Page 61 and 62: at hub height, not to a variation i
Page 63 and 64: IV.10.1 Measured and calculated imm
Page 65 and 66: wind farm to the measurement locati
Page 67 and 68: spherical divergence, that is: prop
Page 69 and 70: Thus, the logarithmic wind profile,
Page 71 and 72:
There are now three factors influen
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direction may change significantly.
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V.2 Measurement results V.2.1 Locat
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P48 microphone. The sound was then
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1/3 octave band Lp in dB 1/3 octave
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1 1 0 1 0 0 1 0 0 0 1 0 0 0 0 A B 8
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same magnitude as close to the turb
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In figure V.5 the equivalent 1/3 oc
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Also plotted in figure V.7 is the v
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V.3 Perception of wind turbine soun
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kHz. For wind turbines we found tha
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V.4 Conclusion Atmospheric stabilit
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VI STRONG WINDS BLOW UPON TALL TURB
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(hub height) wind velocity is 4 m/s
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For the hourly progress of wind vel
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In figure VI.5 the frequency distri
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when V 80 was over 4 m/s. Such a de
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dunes on the North Sea coast, Vliss
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when based on extrapolated wind vel
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The differences between actual and
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hours. This corresponds to an avara
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VII THINKING OF SOLUTIONS: measures
Page 116 and 117:
stability. The turbine thus operate
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sound level was measured close to a
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This type of control can also be ac
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consecutive periods of 15 minutes i
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increase of blade pitch with tilt (
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elatively quiet areas as it control
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VIII RUMBLING WIND: wind induced so
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Finally, in this overview, Boersma
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The friction created by wind shear
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the eddy relative to the screen sur
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(L at,1/3 ~ -26.7·logf), but press
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VIII.3 Comparison with experimental
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the small size of the unscreened mi
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A B reduced pressure level Lred (dB
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microphone, in a 9 cm foam cylinder
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plotted is the calculated screening
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VIII.5 Applications As microphone w
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IX GENERAL CONCLUSIONS The research
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modulation frequencies close to 4 H
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Results from various onshore, relat
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limits, but nighttime immission lev
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X EPILOGUE This is the end of my to
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“….. about 80 per cent of the p
Page 162 and 163:
ACKNOWLEDGMENTS I want to express m
Page 164 and 165:
SUMMARY Ch. III Ch. II Ch. I This s
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and as a result layers of air are l
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500 kW. However, based on the real,
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well known for an unobstructed wind
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SAMENVATTING Bobby vraagt: 'Hoort u
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Vaak wordt aangenomen dat er een va
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gebleken dat de menselijke gevoelig
Page 178 and 179:
Bij een windpark kunnen de fluctuat
Page 180 and 181:
REFERENCES Archer C.L. and Jacobson
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Kerkers A.J. (1999): “Windpark Rh
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Petersen E.L., Mortensen N.G., Land
Page 186 and 187:
Van Ulden, A.P. and Wieringa J. (19
Page 188 and 189:
APPENDICES 179
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dB(G): unit of level after G-weight
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u f : rms longitudinal component of
Page 194 and 195:
downwind turbine with an 80 m tubul
Page 196 and 197:
and total trailing edge immission s
Page 198 and 199:
So for a modern turbine at high spe
Page 200 and 201:
45 wind E (100 gr) 20 Leq (A) Leq,5
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Wiens brood men eet, ….. Een plei
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Vochtproblemen in woningen Venuslaa
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Geluidsbelasting van een windturbin
Page 208 and 209:
Metingen van laagfrequent geluid in
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