Lidar & Wakes
Lidar (Light detection and ranging) is an established remote sensing technology for measuring the wind flow, used in industrial applications as well as in academic wind energy research. The wind industry mainly uses lidar for resource assessment and power curve measurement. Universities employ lidars for e.g. the measurement of complex wind flows in the direct vicinity of single wind turbines or the entire wind farm. These measurements can be used to improve wind turbine and wind farm efficiency by extending the knowledge about the interaction of wind turbines with the flow.
When the wind passes through the wind turbine rotor, mechanical energy is extracted from the wind, causing a wake which propagates downstream. An accurate knowledge of wakes, with their characteristic lower wind speeds and impact on downstream turbines, plays a major role in the optimization of the wind farm layout. Information about the position and the propagation of wakes can also be used to optimize the power output of existing wind farms by clever wind farm control strategies. We investigate the dynamic behaviour of wakes and develop computationally inexpensive wake models for these objectives.
In order to measure the flow in and around wind farms and in the far wake of wind turbines, we operate three Leosphere WLS-200S long-range scanning lidar systems. This type of lidar is well suited to measure the wind over a large area, such as a wind farm, in a relatively short time frame. Another research area in which we employ these lidars is short-term wind forecasting.
Apart from the investigation of wake effects, our research group also employs lidars for the measurement of wind turbine inflow. In order to understand the interaction between the wind turbine and the flow better, the wind imposing on the wind turbine has to be characterised. For measuring the inflow wind field in front of a turbine, we mainly operate a short-range SpinnerLidar. This lidar uses a fast (1 second) scan trajectory to quickly measure the wind field in front of the wind turbine. This information can be used to define wind field parameters such as wind speed, wind direction, wind shear and turbulence, which can be correlated with sensors on the wind turbine.