Tall Tower Wind Shear Observations in the Stable Nocturnal Boundary Layer

Walter, Kevin; Weiss, Christopher C.; Chapman, Jamie; Kelley, Neil

doi:10.2514/6.2007-1224

Cited by 4 publications

(6 citation statements)

References 4 publications

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“…These results are consistent with Walter (2007) and Antoniou et al (2009) who carried out the same kind of simulations with BEM models and power law profiles. Moreover, it coincides with the measurements presented in (Albers et al, 2007), where high shears gave smaller power outputs than low shear.…”

Section: Consequences On the Power Productionsupporting

confidence: 80%

“…Similarly to the wind shear, the wind veer modifies the angle of attack of the wind on the turbine blade, which then varies with the altitude. However, the variation is different from that due to wind speed shear as direction shear involves a wind component that is parallel to the rotor plan (Walter, 2007). The influence of wind veer has so far been the subject of only a few investigations mainly because of the lack of measurements.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Numerical models of wind turbine aerodynamics make possible the investigation of the effect of various parameters independently of each other. Walter (2007) performed an advanced analysis of the variations of shear in Texas. Lacking power measurements, he used a blade element momentum (BEM) model to simulate the power output of a large wind turbine subjected to various inflows characterised by different shear exponents.…”

Section: Effect Of Speed Shearmentioning

confidence: 99%

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Accounting for the speed shear in wind turbine power performance measurement

Wagner¹,

Courtney²,

Gottschall³

et al. 2011

Wind Energy

147

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: Consequences On the Power Productionsupporting

confidence: 80%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Effect Of Speed Shearmentioning

confidence: 99%

See 1 more Smart Citation

Accounting for the speed shear in wind turbine power performance measurement

Wagner¹,

Courtney²,

Gottschall³

et al. 2011

Wind Energy

147

109

View full text Add to dashboard Cite

show abstract

“…The estimates for change in power because of wind shear and direction shear are compared with those presented by Walter using the National Renewable Energy (NREL) FAST software in Figure (see Figure 55 in Walter). It is observed that the two analyses show a similar trend in power variation with two important differences.…”

Section: Quantifying the Impact Of Turbulence On Wind Powermentioning

confidence: 99%

“…First, the results from Walter show that effect of direction shear is not symmetric about zero (see Walter for details on this), and the second is that the reduction in power estimated by the analytical formulation (equation ) is significantly higher. It should be noted that some differences are expected as using equation we estimate the differences in available energy in the wind given the presence of wind and direction shear while the results from Walter show differences in expected power production in presence of wind and direction shear as estimated by the FAST software which models the turbine response for a given inflow condition. That is, Figure (a) can be thought as modeled turbine response to difference in available energy shown in Figure (b).…”

Section: Quantifying the Impact Of Turbulence On Wind Powermentioning

confidence: 99%

A new formulation for rotor equivalent wind speed for wind resource assessment and wind power forecasting

et al. 2015

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The spurt of growth in the wind energy industry has led to the development of many new technologies to study this energy resource and improve the efficiency of wind turbines. One of the key factors in wind farm characterization is the prediction of power output of the wind farm that is a strong function of the turbulence in the wind speed and direction. A new formulation for calculating the expected power from a wind turbine in the presence of wind shear, turbulence, directional shear and direction fluctuations is presented. It is observed that wind shear, directional shear and direction fluctuations reduce the power producing capability, while turbulent intensity increases it. However, there is a complicated superposition of these effects that alters the characteristics of the power estimate that indicates the need for the new formulation. Data from two field experiments is used to estimate the wind power using the new formulation, and results are compared to previous formulations. Comparison of the estimates of available power from the new formulation is not compared to actual power outputs and will be a subject of future work.

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Modeling the effect of wind speed and direction shear on utility‐scale wind turbine power production

Mata,

Pena Martínez,

Bas Quesada

et al. 2024

Wind Energy

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Wind speed and direction variations across the rotor affect power production. As utility‐scale turbines extend higher into the atmospheric boundary layer (ABL) with larger rotor diameters and hub heights, they increasingly encounter more complex wind speed and direction variations. We assess three models for power production that account for wind speed and direction shear. Two are based on actuator disc representations, and the third is a blade element representation. We also evaluate the predictions from a standard power curve model that has no knowledge of wind shear. The predictions from each model, driven by wind profile measurements from a profiling LiDAR, are compared to concurrent power measurements from an adjacent utility‐scale wind turbine. In the field measurements of the utility‐scale turbine, discrete combinations of speed and direction shear induce changes in power production of −19% to +34% relative to the turbine power curve for a given hub height wind speed. Positive speed shear generally corresponds to over‐performance and increasing magnitudes of direction shear to greater under‐performance, relative to the power curve. Overall, the blade element model produces both higher correlation and lower error relative to the other models, but its quantitative accuracy depends on induction and controller sub‐models. To further assess the influence of complex, non‐monotonic wind profiles, we also drive the models with best‐fit power law wind speed profiles and linear wind direction profiles. These idealized inputs produce qualitative and quantitative differences in power predictions from each model, demonstrating that time‐varying, non‐monotonic wind shear affects wind power production.

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Tall Tower Wind Shear Observations in the Stable Nocturnal Boundary Layer

Cited by 4 publications

References 4 publications

Accounting for the speed shear in wind turbine power performance measurement

Accounting for the speed shear in wind turbine power performance measurement

A new formulation for rotor equivalent wind speed for wind resource assessment and wind power forecasting

Modeling the effect of wind speed and direction shear on utility‐scale wind turbine power production

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