Browsing by Subject "Large-eddy simulation"

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On characteristics of stable boundary layer flow fields and their influence on wind turbine loads
(2011-08) Park, Jinkyoo; Manuel, Lance; Basu, Sukanta
Fourier-based stochastic simulation of wind fields commonly used in wind turbine loads computations is unable to account for contrasting states of atmospheric stability. Flow fields in the stable boundary layer (SBL), for instance, have characteristics such as enhanced wind shear and veering wind direction profiles; the influence of such characteristics on utility-scale wind turbine loads has not been studied. To investigate these influences, we use large-eddy simulation (LES) to generate inflow wind fields and to estimate load statistics for a 5-MW wind turbine model. In the first part of this thesis, we describe a procedure employing LES to generate SBL wind fields for wind turbine load computations. In addition, we study how large-scale atmospheric conditions affect the characteristics of wind fields and turbine loads. Next, in the second part, we study the contrasting characteristics of LES-SBL and stochastic NBL flow fields and their influences on wind turbine load statistics by isolating effects of the mean wind (shear) profile and of variation in wind direction and turbulence levels over the rotor sept area. Among large-scale atmospheric conditions, the geostrophic wind speed and surface cooling rate have the greatest influence on flow field characteristics and, thus, on wind turbine loads. Higher geostrophic winds lead to increased mean and standard deviation values of the longitudinal wind speed at hub height. Increased surface cooling rates lead to steeper shear profiles and appear to also increase fatigue damage associated with out-of-plane blade root moments. In summary, our studies suggest that LES may be effectively used to model wind fields in the SBL, to study characteristics of turbine-scale wind fields, and to assess turbine loads for conditions that are not typically examined in design standards.
Wind turbine loads in thunderstorm downbursts using large-eddy simulation
(2019-05-10) Lu, Nan-You; Manuel, Lance; Basu, Sukanta; Kinnas, Spyros; Passalacqua, Paola; Vizy, Edward
To meet the U.S. Department of Energy’s goals of delivering 20% of the nation’s energy needs from wind, it is expected that an increasing number of turbines will be sited in resource-rich areas. The Great Plains, in particular, have contributed substantially with wind power for years due to favorable climate conditions. At the same time, severe weather events, such as thunderstorms and downbursts that accompany them follow, are unfortunately also common in this region and pose threats to the structural integrity of wind turbine components. To limit the risk of turbine damage or failure in strong winds during downbursts, it is important to develop a framework for the computation of turbine loads under simulated inflows with physically realistic ABL (atmospheric boundary layer) conditions that exist during such severe weather events. Accordingly, in this study, we propose such a framework and develop the required computational methodology for the generation of thunderstorm-related inflow fields using large-eddy simulation (LES) models. The evening transition (ET) period is one where the atmospheric boundary layer is undergoing changes in turbulence and stability. This ET period, that can last a few hours, is often a precursor to late-afternoon thunderstorm downbursts. Because of its trnasitional nature and an accompanying ABL that can vary from convective through neutral to stable, careful consideration of the ET period and these distinct stability states is important in simulation of downburst wind fields and associated loads on wind turbines. In this dissertation, a three-part study is undertaken that seeks to investigate characteristics of downburst-related wind fields and associated turbine loads. How turbine loads change during the ET period as a result of contrasting ABL conditions is first discussed, both physically and through a series of statistical analyses. Next, downburst-related wind fields, initialized within different stability regimes, are generated using LES with a cooling source approach; these wind fields and turbine loads are compared to pre-downburst values in the preceding ET period to assess the impact of the downburst. Finally, risks to individual turbine units in a rectilnear array representing a typical wind farm under the influence of downbursts, initiated in stability-varied turbulence fields, are estimated using the same LES framework for inflow generation