The sounds of high winds

More documents

Recommendations

Info

A third reason may be partiality to the outcome of the results. Wind turbine operators are not keen on spending money that may show that sound levels do not comply with legal standards. And if, as expected, they do comply, the money is effectively wasted. Apart from this, we have the experience that at least some organisations that advocate wind energy are not interested in finding out why residents oppose wind farms. II.4 The use of standard procedures Although our objective was to measure immission sound levels, we also wanted to understand what was going on: if levels were higher than expected, was that because emission was higher or attenuation less? Could there be focussing or interference? We therefore also measured sound emission as a function of rotational speed of the variable speed turbines. An interesting point that came up with the emission measurement was that compliance with the recommended standard [Ljunggren 1997 or IEC 1998] was impossible. As the farm operator withdrew the co-operation that was previously agreed upon, we had to measure emission levels with the full wind farm in operation, as we obviously did not have the means to stop all turbines except the one to be measured, as the standard prescribes. To measure ambient background sound level, even the last turbine should be stopped. According to the recommended standard the sound emission should be measured within 20% of the distance to the turbine equal to hub height + blade length. However, to prevent interference from the sound from other turbines the measurement location had to be chosen closer to the turbine. The primary check on the correctness of the distance (i.e. not too close to other turbines) was by listening: the closest turbine should be the dominant source. If not, no measurement was done, and usually a measurement near another turbine was possible. Afterwards we were able to perform a second check by comparing the measured sound immission of the wind farm at a distance of 400 m with the level calculated with a sound propagation model with the measured emission level of all (identical) turbines as input. The calculated difference between a single turbine sound power level and the immission level was 58.0 dB (assuming a constant spectrum this is independent from the power level itself). The measured average difference 21
was 57.9 dB, with a maximum deviation of individual measurement points of 1.0 dB. So our measurements proved to be quite accurate, deviating only 0.1 ± 1.0 dB from the expected value! In fact, from our measurements one may conclude that, to determine turbine sound power level, it is easier and cheaper to determine total sound emission by measurements at some distance from a wind farm than measuring separate turbines. The wind induced ambient sound, that easily spoils daytime measurements, is not an important disturbance in many nights! Using a 1 m diameter round hard board, again to comply with the standard, was quite impractical and sometimes impossible. E.g. at one place potato plants would have to be cleared away, at another place one would have to create a flat area in clumps of grass in a nature reserve, both unnecessarily. Instead of the large board we used the side (30·44 cm 2 ) of a plastic sound meter case. We convinced ourselves that (in this case) this was still a good procedure by comparing at one location sound levels measured on the case on soft ground with sound levels measured on a smooth tarmac road surface a few meters away, both at the same distance to the turbine as in the other measurements: there was no difference. Whether a turbine produces impulsive sound is usually determined by listening to and measuring the sound near a single turbine (along with measurements to determine sound power and spectral distribution). In the Netherlands impulsivity is judged subjectively (by ear), not by a technical procedure as in Germany, though judgement can be supported with a sound registration showing the pulses. Interestingly, in Dutch practice only an acoustician’s ear seems reliable, though even their opinions may disagree. From our measurements the impulsive character can be explained by the wind profile and the interaction of the sound of several turbines. Even at a time the impulsive character can be heard near residents’ dwellings, it cannot clearly be heard close to the turbines in the wind farm (as explained in section II.2). So here also there was need to do measurements where people are actually annoyed, and not to rely on source measurements only, certainly not from a single turbine. 22
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 20 and 21: gas must keep flowing” . 1 I do n
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: annoying turbine sound at distances
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
Page 73 and 74: direction may change significantly.
Page 75 and 76: V.2 Measurement results V.2.1 Locat
Page 77 and 78: P48 microphone. The sound was then
Page 79 and 80: 1/3 octave band Lp in dB 1/3 octave
Page 81 and 82:
1 1 0 1 0 0 1 0 0 0 1 0 0 0 0 A B 8
Page 83 and 84:
same magnitude as close to the turb
Page 85 and 86:
In figure V.5 the equivalent 1/3 oc
Page 87 and 88:
Also plotted in figure V.7 is the v
Page 89 and 90:
V.3 Perception of wind turbine soun
Page 91 and 92:
kHz. For wind turbines we found tha
Page 93 and 94:
V.4 Conclusion Atmospheric stabilit
Page 96 and 97:
VI STRONG WINDS BLOW UPON TALL TURB
Page 98 and 99:
(hub height) wind velocity is 4 m/s
Page 100 and 101:
For the hourly progress of wind vel
Page 102 and 103:
In figure VI.5 the frequency distri
Page 104 and 105:
when V 80 was over 4 m/s. Such a de
Page 106 and 107:
dunes on the North Sea coast, Vliss
Page 108 and 109:
when based on extrapolated wind vel
Page 110 and 111:
The differences between actual and
Page 112 and 113:
hours. This corresponds to an avara
Page 114 and 115:
VII THINKING OF SOLUTIONS: measures
Page 116 and 117:
stability. The turbine thus operate
Page 118 and 119:
sound level was measured close to a
Page 120 and 121:
This type of control can also be ac
Page 122 and 123:
consecutive periods of 15 minutes i
Page 124 and 125:
increase of blade pitch with tilt (
Page 126 and 127:
elatively quiet areas as it control
Page 128 and 129:
VIII RUMBLING WIND: wind induced so
Page 130 and 131:
Finally, in this overview, Boersma
Page 132 and 133:
The friction created by wind shear
Page 134 and 135:
the eddy relative to the screen sur
Page 136 and 137:
(L at,1/3 ~ -26.7·logf), but press
Page 138 and 139:
VIII.3 Comparison with experimental
Page 140 and 141:
the small size of the unscreened mi
Page 142 and 143:
A B reduced pressure level Lred (dB
Page 144 and 145:
microphone, in a 9 cm foam cylinder
Page 146 and 147:
plotted is the calculated screening
Page 148 and 149:
VIII.5 Applications As microphone w
Page 150 and 151:
IX GENERAL CONCLUSIONS The research
Page 152 and 153:
modulation frequencies close to 4 H
Page 154 and 155:
Results from various onshore, relat
Page 156 and 157:
limits, but nighttime immission lev
Page 158 and 159:
X EPILOGUE This is the end of my to
Page 160 and 161:
“….. 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
Page 166 and 167:
and as a result layers of air are l
Page 168 and 169:
500 kW. However, based on the real,
Page 170 and 171:
well known for an unobstructed wind
Page 172 and 173:
SAMENVATTING Bobby vraagt: 'Hoort u
Page 174 and 175:
Vaak wordt aangenomen dat er een va
Page 176 and 177:
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
Page 182 and 183:
Kerkers A.J. (1999): “Windpark Rh
Page 184 and 185:
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
Page 190 and 191:
dB(G): unit of level after G-weight
Page 192 and 193:
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
Page 202 and 203:
Wiens brood men eet, ….. Een plei
Page 204 and 205:
Vochtproblemen in woningen Venuslaa
Page 206 and 207:
Geluidsbelasting van een windturbin
Page 208 and 209:
Metingen van laagfrequent geluid in
show all

The sounds of high winds

Create successful ePaper yourself

Delete template?

Save as template?