Wind turning in the atmospheric boundary layer over land

Lindvall, Jenny; Svensson, Gunilla

doi:10.1002/qj.3605

Cited by 18 publications

(31 citation statements)

References 27 publications

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“…Veering and backing inflow are characteristic nighttime situations of the boundary layer flow if no other processes such as topographically induced circulations or large-scale weather systems prevent the establishment of an SBL regime. Veer within the wind-turbine rotor layer has been observed with several field campaigns with towers and lidars (Walter et al, 2009;Sanchez Gomez and Lundquist, 2020;Bodini et al, 2019Bodini et al, , 2020, and veer throughout the boundary layer has been observed globally using radiosonde datasets (Lindvall and Svensson, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…In a convective regime during the daytime above the surface layer, there is no significant change in the incoming wind direction or wind speed with height and the inflow conditions are uniform over the whole rotor area. A nocturnal stably stratified regime, however, often generates wind profiles with changing magnitude (vertical wind shear) and direction (wind veer; Lindvall and Svensson, 2019). Vertical variations in both quantities reflect the balance between Coriolis force and friction.…”

Section: Introductionmentioning

confidence: 99%

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Changing the rotational direction of a wind turbine under veering inflow: a parameter study

2020

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Abstract. All current-day wind-turbine blades rotate in clockwise direction as seen from an upstream perspective. The choice of the rotational direction impacts the wake if the wind profile changes direction with height. Here, we investigate the respective wakes for veering and backing winds in both hemispheres by means of large-eddy simulations. We quantify the sensitivity of the wake to the strength of the wind veer, the wind speed, and the rotational frequency of the rotor in the Northern Hemisphere. A veering wind in combination with counterclockwise-rotating blades results in a larger streamwise velocity output, a larger spanwise wake width, and a larger wake deflection angle at the same downwind distance in comparison to a clockwise-rotating turbine in the Northern Hemisphere. In the Southern Hemisphere, the same wake characteristics occur if the turbine rotates counterclockwise. These downwind differences in the wake result from the amplification or weakening or reversion of the spanwise wind component due to the effect of the superimposed vortex of the rotor rotation on the inflow's shear. An increase in the directional shear or the rotational frequency of the rotor under veering wind conditions increases the difference in the spanwise wake width and the wake deflection angle between clockwise- and counterclockwise-rotating actuators, whereas the wind speed lacks a significant impact.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Changing the rotational direction of a wind turbine under veering inflow: a parameter study

2020

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“…Shu et al [37] examined the dependence of the wind veer profile on upstream terrain conditions and mean wind speed. Lindvall and Svensson [38] reported that there is clear latitudinal dependence of wind veer, with angles increasing with latitude. Moreover, seasonal and diurnal cycles are also apparent, which is mostly related to the variations in thermal stratification.…”

Section: Introductionmentioning

confidence: 97%

Investigation of Marine Wind Veer Characteristics Using Wind Lidar Measurements

Shu

et al. 2020

Atmosphere

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A proper understanding of marine wind characteristics is of essential importance across a wide range of engineering applications. While the offshore wind speed and turbulence characteristics have been examined extensively, the knowledge of wind veer (i.e., turning of wind with height) is much less understood and discussed. This paper presents an investigation of marine wind field with particular emphasis on wind veer characteristics. Extensive observations from a light detection and ranging (Lidar) system at an offshore platform in Hong Kong were examined to characterize the wind veer profiles up to a height of 180 m. The results underscored the occurrence of marine wind veer, with a well-defined two-fold vertical structure. The observed maximum wind veer angle exhibits a reverse correlation with mean wind speed, which decreases from 2.47° to 0.59° for open-sea terrain, and from 7.45° to 1.92° for hilly terrain. In addition, seasonal variability of wind veer is apparent, which is most pronounced during spring and winter due to the frequent occurrence of the low-level jet. The dependence of wind veer on atmospheric stability is evident, particularly during winter and spring. In general, neutral stratification reveals larger values of wind veer angle as compared to those in stable and unstable stratification conditions.

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“…Regarding the wind field within the boundary layer, observational studies that are based on campaigns limited to a few days report a large range of values for the wind turning angle with small values up to 10-15 degrees for convective conditions [2] and larger values reaching up to 35 degrees for stable boundary layers [45]. Lindvall and Svensson [26] derived a forty-year global climatology for the wind turning angle using the IGRA sounding data set. They found a strong dependence of turning angle with latitude, so for the range of latitudes of the three sites in our study they found a slight veering of the wind with a median value for the global average of the wind turning angle of 15 degrees with little seasonal variation.…”

Section: Comparison To Results From Previous Studiesmentioning

confidence: 99%

“…In this study, we expand the climatology over a period of 32 years and over two additional sites in Greece. In addition, climatologies of the wind field have recently been reported on a global scale [26] but this study focuses on the region of Greece.…”

Section: Introductionmentioning

confidence: 99%

Climatology of the Boundary Layer Height and of the Wind Field over Greece

2020

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In this study, a climatology of two key boundary layer features, the Planetary Boundary Layer Height (PBLH) and the wind field over Greece is derived. The climatology is based on daily soundings collected in Athens, Thessaloniki and Heraklion and spanning a 32-year period. The PBLH is estimated using a method based on the gradient of potential temperature and a method based on the bulk Richardson number. The wind field is analyzed by calculating the wind shear and the turning angle of the wind vector between the surface and the top of the boundary layer. The PBLH of the daytime boundary layer over Athens and Thessaloniki is found to exhibit seasonal variability with summer maxima and winter minima and has annual median values in the range of 1.4–1.7 km estimated using the gradient method. The PBLH over Heraklion is found to exhibit weak seasonal variability with a lower median value of 1.2 km. The nighttime boundary layer over all three sites is found to be much shallower with PBLH values in the range of 150–200 m with no seasonal variations. In addition, the bulk Richardson number method is found to systematically underestimate the PBLH compared to the gradient method. The wind field in the daytime boundary layer at all three sites is found to have small shear of the order of 1 ms−1 and wind turning angles that are lower than 15 degrees, while in the nocturnal boundary layer it has larger shear of the order of 5–10 ms−1 with turning angles lower than 20 degrees. In addition, for both the daytime and the nighttime boundary layer there is no general preference for veering or backing.

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Wind turning in the atmospheric boundary layer over land

Cited by 18 publications

References 27 publications

Changing the rotational direction of a wind turbine under veering inflow: a parameter study

Changing the rotational direction of a wind turbine under veering inflow: a parameter study

Investigation of Marine Wind Veer Characteristics Using Wind Lidar Measurements

Climatology of the Boundary Layer Height and of the Wind Field over Greece

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