Large-eddy simulations (LES) were used to predict the neutral atmospheric boundary layer over a sparse and a dense forest, as well as over grass-covered flat terrain. The forest is explicitly represented in the simulations through momentum sink terms. Turbulence data extracted from the LES served then as inflow turbulence for the simulation of the dynamic structural response of a generic wind turbine. In this way, the impact of forest density, wind speed and wind-turbine hub height on the wind-turbine fatigue loads was studied. Results show for example significantly increased equivalent fatigue loads above the two forests. Moreover, a comparison between LES turbulence and synthetically generated turbulence in terms of load predictions was made and revealed that synthetic turbulence was able to excite the same spectral peaks as LES turbulence but lead to consistently lower equivalent fatigue loads. Copyright (c) 2016 John Wiley & Sons, Ltd.
A solution of the inviscid rapid distortion equations of a stratied flow with homogeneous shear is proposed, extending the work of Hanazaki and Hunt (J. Fluid Mech., 2004,vol. 507, pp. 1-42) to the ...
#2Lars Davidson(Chalmers University of Technology)H-Index: 51
A number of large-eddy simulations (LES) are performed for the calculation of the airflow over a horizontally homogeneous forest canopy for a wide range of thermal stability classes. For the first time, results from LES of a stably stratified canopy are also presented. Simulation results compare favourably to recent field measurements over a pine forest in south-eastern Sweden. The simple heat source model was found to perform adequately and to yield within-canopy heat-flux profiles typically ob...
An analysis and interpretation of measurements from a 138-m tall tower located in a forested landscape is presented. Measurement errors and statistical uncertainties are carefully evaluated to ensure high data quality. A 40\(^\circ \) wide wind-direction sector is selected as the most representative for large-scale forest conditions, and from that sector first-, second- and third-order statistics, as well as analyses regarding the characteristic length scale, the flux-profile relationship and su...
A velocity spectral tensor model was evaluated from the single-point measurements of wind speed. The model contains three parameters representing the dissipation rate of specific turbulent kinetic energy, a turbulence length scale and the turbulence anisotropy. Sonic anemometer measurements taken over a forested and an agricultural landscape were used to calculate the model parameters for neutral, slightly stable and slightly unstable atmospheric conditions for a selected wind speed interval. Th...
Most fluid flows of industrial interest are turbulent and their accurate representation may be of vital importance for the design process of new products. To date, steady RANS methods are usually employed for the simulation of turbulent flows of everyday engineering problems. These methods base the description of turbulence characteristics on mean-flow gradients and only provide a solution for the mean flow. However, there are applications that require instantaneous flow information, for which t...
#1Jinkyoo Park(University of Texas at Austin)H-Index: 13
#2Sukanta Basu(NCSU: North Carolina State University)H-Index: 20
Last. Lance Manuel(University of Texas at Austin)H-Index: 24
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Stochastic simulation of turbulent inflow fields commonly used in wind turbine load computations is unable to account for contrasting states of atmospheric stability. Flow fields in the stable boundary layer, for instance, have characteristics such as enhanced wind speed and directional shear; these effects can influence loads on utility-scale wind turbines. To investigate these influences, we use large-eddy simulation (LES) to generate an extensive database of high-resolution ( ∼ 10 m), four-di...
LIDAR systems are able to provide preview information of wind disturbances at various distances in front of wind turbines. This technology paves the way for new control concepts in wind energy such as feedforward control and model predictive control. This paper compares a nonlinear model predictive controller with a baseline controller, showing the advantages of using the wind predictions in the optimization problem to reduce wind turbine extreme and fatigue loads on tower and blades as well as ...
Efficient spatial and temporal resolution of simulated inflow wind fields is important in order to represent wind turbine dynamics and derive load statistics for design. Using Fourier-based stochastic simulation of inflow turbulence, we first investigate loads for a utility-scale turbine in the neutral atmospheric boundary layer. Load statistics, spectra, and wavelet analysis representations for different space and time resolutions are compared. Next, large-eddy simulation (LES) is employed with...
#2Sang Lee(NREL: National Renewable Energy Laboratory)H-Index: 18
Last. Patrick Moriarty(NREL: National Renewable Energy Laboratory)H-Index: 28
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Although the atmospheric sciences community has been studying the effects of atmospheric stability and surface roughness on the planetary boundary layer for some time, their effects on wind turbine dynamics have not been well studied. In this study, we performed numerical experiments to explore some of the effects of atmospheric stability and surface roughness on wind turbine dynamics. We used large-eddy simulation to create atmospheric winds and compute the wind turbine flows, and we modeled th...
The near-surface structure of atmospheric turbulence affects the design and operation of wind turbines and is especially difficult to predict under stably-stratified conditions. This study uses large-eddy simulation (LES) to explore properties of the stable boundary layer (SBL) using an explicit filtering and reconstruction turbulence modeling approach. Simulations of the atmospheric boundary layer over flat terrain, under both moderately and strongly stable conditions are performed. Results fro...
Last. Håkan Johansson(Chalmers University of Technology)H-Index: 8
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Abstract null null This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. As a case study, Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties like the Plant Area Density and the tree heights are extracted from the Airborne ...
To meet the increasing energy demand, renewable energy is considered the best option. Its patronage is being encouraged by both the research and industrial community. The main driving force for most renewable systems is solar energy. It is abundant and pollutant free compared to fossil products. Wind energy is also considered an abundant medium of energy generation and often goes hand in hand with solar energy. The last few decades have seen a sudden surge in wind energy compared to solar energy...
Last. Alfredo Peña(DTU: Technical University of Denmark)H-Index: 27
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Abstract. This study proposes two methodologies for improving the accuracy of wind turbine load assessment under wake conditions by combining nacelle-mounted lidar measurements with wake wind field reconstruction techniques. The first approach consists in incorporating wind measurements of the wake flow field, obtained from nacelle lidars, into random, homogeneous Gaussian turbulence fields generated using the Mann spectral tensor model. The second approach imposes wake deficit time-series, whic...
#1Hamidreza Abedi(Chalmers University of Technology)H-Index: 4
#2Saptarshi Sarkar(NITR: National Institute of Technology, Rourkela)H-Index: 5
Last. Håkan Johansson(Chalmers University of Technology)H-Index: 8
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This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. The Large-Eddy Simulation of the neutral atmospheric flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties are extracted from the Airborne Laser Scanning data. To emphasize the impact of the local topography and surface roughness on the wind field...
#1Chao Yan(CAS: Chinese Academy of Sciences)H-Index: 1
#2Shiguang Miao(CMA: China Meteorological Administration)H-Index: 27
Last. Guixiang Cui(THU: Tsinghua University)H-Index: 1
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Vegetation constitutes one of the fundamental types of land use on Earth. The presence of trees in urban areas can decrease local winds and exchange sensible and latent heat with the surrounding environments, thus exerting notable influences on the urban microenvironment. A better understanding of the turbulent transfer of momentum and scalars around vegetation canopy could significantly contribute to improvement of the urban environment. This work develops a large-eddy simulation (LES) method t...
Abstract. The presented work investigates the potential of large-eddy simulations (LES) of wind turbine wakes using the cumulant lattice Boltzmann method (CLBM). The wind turbine is represented by the actuator line model (ALM) that is implemented in a GPU-accelerated (Graphics Processing Unit) lattice Boltzmann framework. The implementation is validated and discussed by means of a code-to-code comparison to an established finite-volume Navier-Stokes solver. To this end, the ALM is subjected to a...
An increasing number of the offshore structures in the North Sea are being operated in a life extension phase, which means that their original design life has been exceeded. As the structures age, they are deteriorating, mainly due to fatigue and corrosion. In order to ensure that the structural integrity is maintained during the life extension phase, the remaining fatigue life of the structures needs to be assessed. While simple and conservative approximations are used in fatigue design, it wil...
