Abstract
In this study, large-eddy simulations (LESs) were performed to investigate the effects of changing wind direction on the turbine wakes and associated power losses in the Horns Rev offshore wind farm. In the LES framework, the turbulent subgrid-scale stresses are parameterized using a tuning-free Lagrangian scale-dependent dynamic model, and the turbine-induced forces are computed using a dynamic actuator-disk model with rotation (ADM-R). This dynamic ADM-R couples blade-element theory with a turbine-specific relation between the blade angular velocity and the shaft torque to compute simultaneously turbine angular velocity and power output. A total of 67 simulations were performed for a wide range of wind direction angles. Results from the simulations show a strong impact of wind direction on the spatial distribution of turbine-wake characteristics, such as velocity deficit and turbulence intensity. This can be explained by the fact that changing the wind angle can be viewed as changing the wind farm layout relative to the incoming wind, while keeping the same wind turbine density. Of particular importance is the effect of wind direction on the distance available for the wakes to recover and expand before encountering other downwind turbines (in full-wake or partial-wake interactions), which affects the power losses from those turbines. As a result, even small changes in wind direction angle can have strong impacts on the total wind farm power output. For example, a change in wind direction of just 10° from the worst-case full-wake condition is found to increase the total power output by as much as 43%. This has important implications for the design of wind farms and the management of the temporal variability of their power output.
Highlights
The production of electrical power from wind energy has experienced a remarkable expansion in the last two decades, reaching a total installed capacity of 283 GW in 2012 and growing exponentially at an average annual rate of about 25% [1,2]
large-eddy simulations (LESs) were performed to study the effect of wind direction on the power output from a large wind farm
The Horns Rev offshore wind farm was chosen as a case study since the LES code used here was previously validated to predict power output from this farm for some selected wind conditions [12]
Summary
The production of electrical power from wind energy has experienced a remarkable expansion in the last two decades, reaching a total installed capacity of 283 GW in 2012 and growing exponentially at an average annual rate of about 25% [1,2]. Besides maximizing wind farm power output, it is important to understand and predict its variability in order to optimize its integration to the electrical grid. This involves predicting the inherently turbulent atmospheric boundary layer (ABL) flow, its spatial and temporal variability and its interaction with the wind farms. Barthelmie et al [5] reported power data measured at the Horns Rev and the Nysted wind farms for seven wind directions, and showed an obvious increase in the power output from the downwind turbines when the incoming wind angle departs from the full-wake condition. Large-eddy simulations (LESs) are used to explore the effect of wind direction on the turbine wakes and power output from the Horns Rev wind farm.
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