Abstract
In the current study, an Actuator-Line Model (ALM) is implemented in our in-house pseudo-spectral LES solver SP-WIND, including a turbine controller. Below rated wind speed, turbines are controlled by a standard-torque-controller aiming at maximum power extraction from the wind. Above rated wind speed, the extracted power is limited by a blade pitch controller which is based on a proportional-integral type control algorithm. This model is used to perform a series of single turbine and wind farm simulations using the NREL 5MW turbine. First of all, we focus on below-rated wind speed, and investigate the effect of the farm layout on the controller calibration curves. These calibration curves are expressed in terms of nondimensional torque and rotational speed, using the mean turbine-disk velocity as reference. We show that this normalization leads to calibration curves that are independent of wind speed, but the calibration curves do depend on the farm layout, in particular for tightly spaced farms. Compared to turbines in a lone-standing set-up, turbines in a farm experience a different wind distribution over the rotor due to the farm boundary-layer interaction. We demonstrate this for fully developed wind-farm boundary layers with aligned turbine arrangements at different spacings (5D, 7D, 9D). Further we also compare calibration curves obtained from full farm simulations with calibration curves that can be obtained at a much lower cost using a minimal flow unit.
Highlights
Modeling approaches such as the Actuator Disc Model (ADM) and the Actuator Line Model (ALM) [1] are quite common for the representation of wind turbines in wind farm simulations
We show that this normalization leads to calibration curves that are independent of wind speed, but the calibration curves do depend on the farm layout, in particular for tightly spaced farms
The grid density required by these models is not much larger than the ones required for the Large Eddy Simulation (LES) of atmospheric boundary layers and even large wind farm simulations can be performed with an acceptable computational time and cost
Summary
Modeling approaches such as the Actuator Disc Model (ADM) and the Actuator Line Model (ALM) [1] are quite common for the representation of wind turbines in wind farm simulations. With these models, boundary layer over the turbine geometries is not required to be resolved since the turbine induced forces are calculated as integral quantities. The rotational speed of the rotor is controlled by a blade pitch controller based on a proportional-integral (PI) type controller algorithm Within this framework, first, a set of simulations are performed so as to examine the operation of the controllers in response to the changing wind speeds.
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