Analysis and parameterisation of wind profiles in the low atmosphere

Pérez, Isidro A.; García, M. Ángeles; Sánchez, M. Luisa; Torre, B. de

doi:10.1016/j.solener.2004.08.024

Cited by 38 publications

(31 citation statements)

References 19 publications

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“…The exponent increases with the roughness of the terrain, and decreases with increasing geometric mean height (Tielmann, 2008). By suitable choice of α, the power law profile closely corresponds to a considerable range of wind profiles compared to the other less empirical forms, and it was found to provide a reasonable fit to the observed wind speed profiles over a wide range of surface roughness and stability conditions (Perez et al, 2005). Based on measurements, Davenport (1960) suggested typical shear exponent values of 1/7,1/3.5 and 1/2.5 for three roughness classes: grassland, forest and city, respectively.…”

Section: The Power Law Profilementioning

confidence: 81%

Accounting for the speed shear in wind turbine power performance measurement

Wagner¹,

Courtney²,

Gottschall³

et al. 2011

Wind Energy

146

109

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Abstract:The power curve of a wind turbine is the primary characteristic of the machine as it is the basis of the warranty for it power production. The current IEC standard for power performance measurement only requires the measurement of the wind speed at hub height and the air density to characterise the wind field in front of the turbine. However, with the growing size of the turbine rotors during the last years, the effect of the variations of the wind speed within the swept rotor area, and therefore of the power output, cannot be ignored any longer. Primary effects on the power performance are from the vertical wind shear and the turbulence intensity. The work presented in this thesis consists of the description and the investigation of a simple method to account for the wind speed shear in the power performance measurement. Ignoring this effect was shown to result in a power curve dependant on the shear condition, therefore on the season and the site. It was then proposed to use an equivalent wind speed accounting for the whole speed profile in front of the turbine. The method was first tested with aerodynamic simulations of a multi-megawatt wind turbine which demonstrated the decrease of the scatter in the power curve. A power curve defined in terms of this equivalent wind speed would be less dependant on the shear than the standard power curve. The equivalent wind speed method was then experimentally validated with lidar measurements. Two equivalent wind speed definitions were considered both resulting in the reduction of the scatter in the power curve. As a lidar wind profiler can measure the wind speed at several heights within the rotor span, the wind speed profile is described with more accuracy than with the power law model. The equivalent wind speed derived from measurements, including at least one measurement above hub height, resulted in a smaller scatter in the power curve than the equivalent wind speed derived from profiles extrapolated from measurements at hub height and below only. It is well established that the turbulence intensity also influences the power performance of a wind turbine. Two ways of accounting for the turbulence were tested with the experimental data: an adaptation of the equivalent wind speed so that it also accounts for the turbulence intensity and the combination of the equivalent wind speed accounting for the wind shear only with the turbulence normalising method for turbulence intensity suggested by Albers. The second method was found to be more suitable for normalising the power curve for the turbulence intensity. Using the equivalent wind speed accounting for the wind shear in the power performance measurement was shown to result in a more repeatable power curve than the standard power curve and hence, in a better annual energy production estimation. Furthermore, the decrease of the scatter in the power curve corresponds to a decrease of the category A uncertainty in power, resulting in a smaller uncertainty in estimated AEP.The thesis is submitted to the Danish Tec...

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Section: The Power Law Profilementioning

confidence: 81%

Accounting for the speed shear in wind turbine power performance measurement

Wagner¹,

Courtney²,

Gottschall³

et al. 2011

Wind Energy

146

109

View full text Add to dashboard Cite

show abstract

“…This model is widely (and, as yet, only) used in relation to wind turbine sound (see, e.g., [8] or [14] [9] or [13]). Equation (l) has no theoretical basis, but often provides a good fit to the vertical wind profile, especially when the atmosphere is non-neutral.…”

Section: Effect Of Atmospheric Stability On Wind Turbine Soundmentioning

confidence: 99%

The Beat is Getting Stronger: The Effect of Atmospheric Stability on Low Frequency Modulated Sound of Wind Turbines

Berg

2005

Journal of Low Frequency Noise, Vibration and Active Control

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SUMMARYSound from wind turbines involves a number of sound production mechanisms related to different interactions between the turbine blades and the air. An important contribution to the low frequency part of the sound spectrum is due to the sudden variation in air flow which the blade encounters when it passes the tower: the angle of attack of the incoming air suddenly deviates from the angle that is optimized for the mean flow. Hitherto, low-frequency sound from wind turbines has not been shown to be a major factor contributing to annoyance. This seems reasonable as the blade passing frequency is of the order of one hertz where the human auditory system is relatively insensitive. This argument, however, obscures a very relevant effect: the blade passing frequency modulates well audible, higher-frequency sounds and thus creates periodic sound: blade swish. This effect is stronger at night because in a stable atmosphere there is a greater difference between rotor averaged and near-tower wind speed. Measurements have shown that additional turbines can interact to further amplify this effect. Theoretically the resulting fluctuations in sound level will be clearly perceptible to human hearing. This is confirmed by residents near wind turbines with the same common observation: often late in the afternoon or in the evening the turbine sound acquires a distinct 'beating' character, the rhythm of which is in agreement with the blade passing frequency. It is clear from the observations that this is associated to a change toward a higher atmospheric stability. The effect of stronger fluctuations on annoyance has not been investigated as such, although it is highly relevant because a) the effect is stronger for modern (that is: tall) wind turbines, and b) more people in Europe will be living close to these wind turbines as a result of the growth of wind energy projects.

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“…Ray et al (2006) found significant variation with wind direction at Boulder, a site in complex terrain. Other recent studies include those by (Motta et al, 2005;Perez et al, 2005;Rogers et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Adequacy of the Wind Speed Extrapolation Laws for Two Different Roughness Meteorological Sites

Khalfa

Benretem

Herous

et al. 2014

American Journal of Applied Sciences

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Increasing knowledge on wind shear models to strengthen their reliability appears as a crucial issue, markedly for energy investors to accurately predict the average wind speed at different turbine hub heights and thus the expected wind energy output. This is particularly helpful during the feasibility study to abate the costs of a wind power project. The extrapolation laws were found to provide the finest representation of the wind speed according to heights, thus avoiding installation of tall towers, or even more expensive devices such as LIDAR or SODAR. The proposed models are based on theories that determine the vertical wind profile from implicit relationships. However, these empirical extrapolation formulas have been developed for specific meteorological conditions and appropriate sites for wind turbines; reason that several studies have been made by various authors to determine the best suited formula to their own conditions. This study is aimed at proceeding the research issue addressed within a previous study, where some extrapolation models were tested and compared by extrapolating the energy resources at different heights. However, comparable results are returned by the power law and the log law which indeed proved to be preferable. In this context, this study deals the assessment of several wind speed extrapolation laws (six laws), by comparing the analytical results obtained with real data for two different meteorological Sites, different roughness, different altitudes and different measurement periods. The first site studied is an extremely rough site with daily measurements of March 2007, wind speed measurements are available at four different heights of Gantour/Gao site, obtained by the water, energy and environment company Senegal. The second site studied is a feeble rough site with monthly measurements for 2005, wind speed measurements are available at three different heights of Kuujjuarapik Site obtained by Hydro-Quebec Energy Helimax Canada. The study aims to determine the effectiveness and concordance between the extrapolation laws and the real measured data. The results show that the adjusted law is efficiently adequate for an extremely rough site and the modified laws with two other laws are efficiently adequate for a feeble rough site. The experimental results and numerical calculations exploited for the evaluation of the Weibull parameters fall the shape factors k greater than 9. The increase in altitude often causes an increase in the Weibull parameters values, however, our results show that the shape factor k can take lower values to those established in the reference altitude.

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Analysis and parameterisation of wind profiles in the low atmosphere

Cited by 38 publications

References 19 publications

Accounting for the speed shear in wind turbine power performance measurement

Accounting for the speed shear in wind turbine power performance measurement

The Beat is Getting Stronger: The Effect of Atmospheric Stability on Low Frequency Modulated Sound of Wind Turbines

Evaluation of the Adequacy of the Wind Speed Extrapolation Laws for Two Different Roughness Meteorological Sites

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