Nacelle mounted profiling lidars have the potential of reducing the uncertainties in design load calculations, because profiling lidars can provide a more detailed parameterized description of the wind field compared to the parameters obtainable using a cup anemometer. In WP 5 we will define a spatial and temporal description of the wind field which is obtainable by means of profiling lidar measurements, and which results in reduction in the uncertainties in load predictions compared to predictions based on wind measured at hub height.
Task 5.1 Evaluation of standard loads assessment procedure
In this task we will establish a reference estimate of the uncertainties associated with load simulations using a standard, anemometer-based wind field description. Loads predicted by an aeroelastic model using a standard wind field parameterized with a single reference point at hub height, standard normal coherent turbulence and logarithmic wind shear law will be compared to the actually observed loads.
Task 5.2 Loads assessment procedure with a profiling nacelle lidar
The main goal of this step is to identify a parameterized wind field description obtainable by profiling lidars which minimizes the uncertainties in extreme loads and damage equivalent fatigue loads. The uncertainties in the loads obtained in Task 5.1 will serve as a reference. This will enable to quantify the benefits of nacelle lidar measurements for wind characterization as required for the prediction of design loads. The expected outcome of this task is a procedure for wind and loads measurement using a profiling nacelle mounted lidar which results in minimized uncertainty in the load predictions.
Task 5.3 Loads assessment based on near flow wind speed
Similarly to power curve measurement, using the near flow field can provide a method for loads assessment applicable in any type of terrain. The effect of using near-flow wind speed measurements on the load uncertainties will be compared to the use of the far-flow measurements, while implementing the wind field description obtained in Task 5.2.
Task 5.4 Derivation of wind parameters from the nacelle lidar measurements
This task will be to investigate how specific wind field parameters relevant for load simulations can be best measured with a nacelle-based profiling lidar. These parameters may be average wind speed, turbulence, wind shear, veer, and spatial coherence determined at multiple locations over the rotor area. Turbulence intensity retrieval has been investigated for ground based lidars and to some extent for nacelle mounted lidars. The derivation of relevant information from commercial lidars will be defined and detailed so as to fulfill the requirements for loads prediction.