Lamar Low-Level Jet Program Interim Report

Kelley, Neil; Shirazi, Mostafa A.; Jäger, D.; Wilde, S.; Adams, J.; Buhl, M. L.; Sullivan, Patrick; Patton, Edward G.

doi:10.2172/15006544

Cited by 79 publications

(72 citation statements)

References 18 publications

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“…A comprehensive study about LLJ-induced damage to wind turbines was conducted by Kelley et al (2004). The research was based on the collection of real wind data from a tower and a sodar and also on measurements of resulting loads on real wind turbines.…”

Section: Previous Work On Wind Shearmentioning

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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Section: Previous Work On Wind Shearmentioning

confidence: 99%

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

et al. 2017

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“…The GP_LLJ model reflects conditions seen over the Great Plains with and without the presence of a low-level jet stream that occurs at a height between 70 and 490 m AGL. Local turbulence scaling and low-level jet vertical wind profiles used with the GP_LLJ model have been derived from measurements collected on a 120-m tower and with a medium range Doppler acoustic wind profiler (SODAR) located in the southwestern Great Plains near Lamar, Colorado [4]. The GP_LLJ model allows the user to specify the jet height and peak wind speed (intensity) or to let the code randomly choose a jet height and/or wind speed based on the other specified boundary conditions.…”

Section: Gp_llj Spectral Modelmentioning

confidence: 99%

“…Typically the size of the structures have a higher probability of being scaled to the dimensions of the requested rotor diameter but the user may request the placement of the coherent disturbance in either the upper or lower half of the specified rotor disk for rotor diameters of 30 m or larger. The presence of superimposed coherent structures can induce transient loading events on simulated turbine rotors and supporting structures [4,5]. The simulation of such structures is not adequately provided for in the inflow simulators up to now because of basic limitations in the mathematical procedures used.…”

Section: Coherent Turbulent Structuresmentioning

confidence: 99%

“…KH instability (KHI) is known to be more or less ubiquitous in the stable, nocturnal boundary layer. A more complete discussion of KHI and its impact on wind turbines is available in Sections 1-3 of [4] and in [5]. The coherent structures generated are then superimposed on the more random background similar to what occurs in natural flows.…”

Section: Coherent Turbulent Structuresmentioning

confidence: 99%

“…Modeled as a combination of non-homogenous Poisson and lognormal stochastic processes, the randomized scaling of the coherent structures in this version of TurbSim is based on measurements taken from the anemometer array upwind of the NWTC ART Turbine as part of the LIST program [4,6]. A flow chart of the TurbSim code is shown in Figure 2.…”

Section: Coherent Turbulent Structuresmentioning

confidence: 99%

See 2 more Smart Citations

Overview of the TurbSim Stochastic Inflow Turbulence Simulator: Version 1.10

Kelley¹,

Jonkman²

2006

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Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

et al. 2012

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The existence of vertical wind shear in the atmosphere close to the ground requires that wind resource assessment and prediction with numerical weather prediction (NWP) models use wind forecasts at levels within the full rotor span of modern large wind turbines. The performance of NWP models regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by the Weather Research and Forecasting model using seven sets of simulations with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights.Winds speeds at heights ranging from 10 to 160 m, wind shears, temperatures and surface turbulent fluxes from seven sets of hindcasts are evaluated against observations at Høvsøre, Denmark. The ability of these hindcast sets to simulate mean wind speeds, wind shear, and their time variability strongly depends on atmospheric static stability. Wind speed hindcasts using the Yonsei University PBL scheme compared best with observations during unstable atmospheric conditions, whereas the Asymmetric Convective Model version 2 PBL scheme did so during near-stable and neutral conditions, and the Mellor-Yamada-Janjic PBL scheme prevailed during stable and very stable conditions. The evaluation of the simulated wind speed errors and how these vary with height clearly indicates that for wind power forecasting and wind resource assessment, validation against 10 m wind speeds alone is not sufficient. Evaluation of wind shear in the WRF model C. Draxl et al.the overall power losses by a wind farm. Furthermore, when the output from mesoscale models is used for wind resource assessment, information about the wind profile across the rotor area will lead to more accurate resource estimates.Because the grid resolution in mesoscale numerical weather prediction (NWP) models is too large to explicitly resolve the processes responsible for small-scale fluxes in the planetary boundary layer (PBL), sub-grid-scale turbulent fluxes, which are mostly unknown, and vertical mixing are calculated by PBL parameterizations. 4 PBL parameterizations use the distribution of wind, temperature, and water vapor mixing ratio with height and the surface fluxes calculated from a land surface model (LSM) and/or surface layer scheme to determine, amongst many others, the time tendencies of wind, temperature and water vapor mixing ratio. The choice of PBL scheme thus plays a significant role in the evolution of the low-level wind structure and therefore can heavily impact the quality of the forecast winds.Many aspects of the mesoscale model determine the quality of the forecast PBL structure. In the Weather Research and Forecasting (WRF) model, surface momentum, heat and moisture fluxes are c...

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Lamar Low-Level Jet Program Interim Report

Cited by 79 publications

References 18 publications

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

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

Overview of the TurbSim Stochastic Inflow Turbulence Simulator: Version 1.10

Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

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