Analysis of turbulent exchange and coherent structures in the stable atmospheric boundary layer based on tower observations

Ferreres, E.; Soler, M. R.; Terradellas, Enric

doi:10.1016/j.dynatmoce.2013.10.002

Cited by 18 publications

(11 citation statements)

References 44 publications

(58 reference statements)

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“…In a decoupled SBL, wind speeds are generally low with occasional occurrences of large winds at all the levels. Wind profiles are frequently distorted by the occurrences of possible low‐level wind maxima and thus associated intermittent events, consistent with previous studies (Conangla et al, ; Ferreres et al, ). Once the SBL becomes fully coupled as a result of increased wind speeds, the intrusion of low‐level wind maxima is absent and linear relations between U 2 m and the upper levels become more evident (Figure d).…”

Section: Resultssupporting

confidence: 90%

“…The considerable vertical flux divergence in strongly stratified SBLs results from intermittent turbulent events that can lead to nonstationary or enhanced vertical advection of momentum and scalar fluxes thereby invalidating MOST assumptions (Sun et al, ). The origin for these intermittent events can be partly attributed to formation of low‐level jet (Karipot et al, ; Oldroyd et al, ), gravity wave (Sorbjan & Czerwinska, ), density current (Sun et al, ), solitary wave (Ferreres et al, ), and other complicated wave‐like motions (Cava et al, ). Elevated turbulence sources such as low‐level jets result in turbulence intensity that increases with z .…”

Section: Introductionmentioning

confidence: 99%

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Distinct Turbulence Structures in Stably Stratified Boundary Layers With Weak and Strong Surface Shear

Lan

et al. 2018

JGR Atmospheres

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Turbulence structures and exchange of momentum and heat in the nocturnal stable boundary layer (SBL) show distinct features under different stability conditions prompting interest in their connection.Here eddy covariance data collected at four different heights on a 62-m meteorological tower over a large open flat terrain are used to characterize different SBL states and associated turbulence structures. In a SBL characterized by strong near-surface winds, turbulent eddy sizes scale with their observational heights and the SBL experiences enhanced turbulent mixing of momentum and heat throughout (a state hereafter referred to as a "coupled" state). Conversely, in a decoupled SBL, weak winds occur near the surface and turbulent eddies are depressed and detached from the boundary leading to suppressed vertical mixing and layered SBL profiles. Because the transport of momentum and heat to the surface across SBL layers is determined by turbulent eddies, cross-layer correlation and the aforementioned SBL coupling states can be delineated by distinct turbulence structures.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Distinct Turbulence Structures in Stably Stratified Boundary Layers With Weak and Strong Surface Shear

Lan

et al. 2018

JGR Atmospheres

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“…One advantage of using meteorological towers is the ability to concentrate measurements closer to the ground. Ferreres et al (2013) investigated whether tower observations could capture the main features of several coherent structures found in atmospheric stable conditions, one of those structures being a LLJ. Although the spatial and temporal resolutions of the instrumentation were not high, the structures were correctly detected and analyzed by using wavelet methods.…”

Section: Previous Experiences On Data Collectionmentioning

confidence: 99%

Impacts of the low-level jet's negative wind shear on the wind turbine

et al. 2017

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Abstract.Nocturnal low-level jets (LLJs) are defined as relative maxima in the vertical profile of the horizontal wind speed at the top of the stable boundary layer. Such peaks constitute major power resources for wind turbines. However, a wind speed maximum implies a transition from positive wind shears below the peak to negative ones above. The effect that such a transition has on wind turbines has not been thoroughly studied.This research study employed a methodical approach to the study of negative wind shear's impacts on wind turbines. Up to now, the presence of negative shears inside the turbine's rotor in relation to the presence of positive shears has been largely ignored. A parameter has been proposed to quantify that presence in future studies of LLJ-wind-turbine interactions. Simulations were performed using the NREL aeroelastic simulator FAST code. Rather than using synthetic profiles to generate the wind data, all simulations were based on real data captured at the high frequency of 50 Hz, which allowed us to perform the analysis of a turbine's impacts with real-life, small scales of wind motions.It was found that the presence of negative wind shears at the height of the turbine's rotor appeared to exert a positive impact on reducing the motions of the nacelle and the tower in every direction, with oscillations reaching a minimum when negative shears covered the turbine swept area completely. Only the tower wobbling in the spanwise direction was amplified by the negative shears; however, this occurred at the tower's slower velocities and accelerations. The forces and moments were also reduced by the negative shears. The aforementioned impacts were less beneficial in the rotating parts, such as the blades and the shafts. Finally, the variance in power production was also reduced. These findings can be very important for the next generation of wind turbines as they reach deeper into LLJ's typical heights.The study demonstrated that the presence of negative shears is significant in reducing the loading on wind turbines. A major conclusion of this study is that the wind turbines of the future should probably be designed with the aim of reaching the top of the nightly boundary layer more often and therefore the altitudes where negative shears are more frequent. Doing so will help to reduce the positive shear's associated damage and to capture the significant LLJ energy.

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“…For the statistical study of the behaviour of the turbulence strength relationship with the wind speed we set a temporal average of 5 min as done in Sun, 2011;Sun et al, 2012;Mahrt, 2014. We used this temporal average because reducing the averaging period, or using other methods, such as multi-resolution decomposition or wavelet, might potentially eliminate the contribution of non-turbulent mesoscale motions to the calculated turbulence quantities (Terradellas et al, 2005;Udina et al, 2013;Ferreres et al, 2013;Soler et al, 2014). However, to obtain a broad picture of the patterns, a constant averaging time of 5 min seemed sufficient.…”

Section: Introductionmentioning

confidence: 99%

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Yus-Díez¹,

Udina²,

Soler³

et al. 2019

Atmos. Chem. Phys.

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Abstract. A night-time turbulence regime classification, the so-called “HOckey-Stick Transition ” (HOST) theory, proposed by Sun et al. (2012) from the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) is explored using data from the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign which took place during summer 2011 in the central French Pyrenean foothills. Results show that the HOST turbulence relationships for the BLLAST field campaign data are strongly dependent on both the meteorological and orographic features. The HOST pattern only appears for nights when a stably stratified boundary layer can be developed, corresponding to fair-weather and clear-sky nights, when the flow is generated by the nearby orography, from the south and the south-east. Those flows strongly influenced by the orography may generate intermittent or enhanced turbulence. When considering the whole nocturnal dataset for these flow directions, several enhanced turbulence points are found to be associated with sudden wind speed and directional shear transitions. In contrast, flows from other directions do not reproduce the HOST relationships and the turbulence relationship is almost linear, independent of vertical temperature gradients, corresponding to flows driven by synoptic scales. In addition we identify examples of gravity waves and top-down turbulent events that lead to transitions between the turbulence regimes.

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Analysis of turbulent exchange and coherent structures in the stable atmospheric boundary layer based on tower observations

Cited by 18 publications

References 44 publications

Distinct Turbulence Structures in Stably Stratified Boundary Layers With Weak and Strong Surface Shear

Distinct Turbulence Structures in Stably Stratified Boundary Layers With Weak and Strong Surface Shear

Impacts of the low-level jet's negative wind shear on the wind turbine

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

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