Assessing the rotor blade deformation and tower-blade tip clearance of a 3.4 MW wind turbine with terrestrial laser scanning

Abstract. Wind turbines have grown in size in recent years, making an efficient structural health monitoring of all of their structures ever more important. Wind turbine blades deform elastically under the loads applied to them by wind and inertial forces acting on the rotating rotor blades. In order to properly analyze these deformations, an earthbound system is desirable that can measure the blade deformation, as well as the tower-blade tip clearance from a large measurement working distance of over 150 m and a single location. To achieve this, a terrestrial laser scanner (TLS) in line-scanning mode with vertical alignment is used to measure the distance to passing blades and the tower for different wind loads over time. In detail, the blade deformations for two different wind load categories are evaluated and compared. Additionally, the tower-blade tip clearance is calculated and analyzed with regard to the rotor speed. Using a Monte-Carlo simulation, the measurement uncertainty is determined to be in the mm-range for both the blade deformation analysis and the tower-blade tip clearance. The in-process applicable measurement methods are applied and validated on a 3.4 MW wind turbine with a hub height of 128 m. As a result, the deformation of the blade increases with higher wind speed in wind direction, while the tower-blade tip clearance decreases with higher wind speed. Both relations are measured not only qualitatively but also quantitatively. Furthermore, no difference between the three rotor blades is observed, i.e. each of the three blades is shown to be separately measurable. The tower-blade tip clearance is compared to a reference video measurement, which recorded the tower-blade tip clearance from the side, with validated the novel measurement approach. Therefore, the proposed setup and methods are proven to be effective tools for the in-process structural health monitoring of wind turbine blades.