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The power production of the Lillgrund wind farm is determined numerically using large-eddy simulations and compared with measurements. In order to simulate realistic atmospheric conditions, pre-generated turbulence and wind shear are imposed in the computational domain. The atmospheric conditions are determined from data extracted from a met mast, which was erected prior to the establishment of the farm. In order to allocate most of the computational power to the simulations of the wake flow, the turbines are modeled using an actuator disc method where the discs are imposed in the computational domain as body forces which for every time step are calculated from tabulated airfoil data. A study of the influence of imposed upstream ambient turbulence is performed and shows that higher levels of turbulence results in slightly increased total power production and that it is of great importance to include ambient turbulence in the simulations. By introducing ambient atmospheric turbulence, the simulations compare very well with measurements at the studied inflow angles. A final study aiming at increasing the farm production by curtailing the power output of the front row turbines and thus letting more kinetic energy pass downstream is performed. The results, however, show that manipulating only the front row turbines has no positive effect on the farm production, and therefore, more complex curtailment strategies are needed to be tested.

Understanding of the stall delay phenomenon on wind turbines remains, to this day, incomplete. A correct modelling of this phenomenon, which results from three-dimensional rotational effects, is essential in order to make reliable wind turbine simulations on the basis of two-dimensional airfoil data, such as with the widely used blade element momentum method. The present study addresses this issue by testing six existing models intended to correct for stall delay effects, namely those developed by Snel et al., Chaviaropoulos and Hansen, Raj, Bak et al., Corrigan and Schillings and Lindenburg. For this purpose, the models are implemented into a lifting-line-prescribed wake vortex scheme. Forces along the blades as well as power and root flap bending moment in a head-on flow configuration are predicted based on these models, and are compared to wind tunnel data from NREL's phase VI experiment. While load over-prediction in the presence of stall is in general observed from the use of the different models, significant differences between the models are still seen. Local over-prediction is generally seen in the tip region, while discrepancies are obtained, even at low wind speed, for the root flap bending moment. The results obtained are discussed in terms of deficiencies and strengths of the current correction schemes, and from there a basis is provided for the development of improved correction models.lift coeffi cients compared to the corresponding two-dimensional (2-D) case, and by a delay of the occurrence of fl ow separation to higher angles of attack.Ever since this phenomenon was fi rst observed by Himmelskamp on propeller blades, 3 it has captured the attention of many researchers in the helicopter and wind turbine fi elds, where computational, theoretical and experimental investigations have been performed. Among others, McCroskey, 4 and Savino and Nyland, 5 have performed fl ow vizualizations on rotating blades, investigating the separated fl ow along the blade. Milborrow 6 performed an analytical evaluation of existing experimental data to try and understand the mechanisms responsible for the stall delay phenomenon. Madsen and Christensen, 7 as well as Ronsten, 8 performed pressure measurements on rotating and non-rotating blades in order to quantify the importance of three-dimensional (3-D) fl ow effects. Sørensen et al.,9 in addition to Narramore and Vermeland, 10 used CFD computations to provide insight into 3-D rotational effects. Dumitrescu and Cardos 11 investigated the 3-D effects on the laminar boundary layer, trying to shed light on the stall delay phenomenon. Very recently, Schreck et al. 12 used CFD computations coupled with experimental data from the NREL phase VI experiment 13 to characterize the aerodynamic features in the rotating blade boundary layer, as well as to deduce mechanisms responsible for the rotational augmentation.The stall delay phenomenon is, however, still far from being completely understood. An illustration of this comes from the blind comparison exercise 14 that followed ...

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We report on the low-energy electron-induced production of aldehydes within thin solid films of tetrahydrofuran (THF) condensed on a solid Kr substrate. The aldehyde fragments, which remain trapped within the bulk of the THF film, are detected in situ via their 3,1(n-->pi*) and 3(pi-->pi*) electronic transitions and vibrational excitations in the ground state using high-resolution electron-energy-loss spectroscopy. The production of aldehyde is studied as a function of the electron exposure, film thickness, and incident electron energy between 1 and 18.5 eV. The aldehyde production is calibrated in terms of an electron scattering cross section, which is found to be typically 6-7 x 10(-17) cm(2) between 11 and 19 eV. Its energy dependence is characterized by a small feature around 3 eV, a strong rise from 6 eV up to a maximum at 12.5 eV, followed by two structures centered around 15 and 18 eV. The aldehyde production is discussed in terms of the formation of electron resonances or transient anion states, which may lead to the fragmentation of the molecule and explain the structures seen in the energy dependence of the measured cross section.