**New Assessment Scales for Evaluating the Degree of Risk of Wind Turbine Blade Damage Caused by Terrain-Induced Turbulence**

#### **Takanori Uchida 1,\* and Yasushi Kawashima 2**


Received: 4 June 2019; Accepted: 2 July 2019; Published: 8 July 2019

**Abstract:** The present study scrutinized the impacts of terrain-induced turbulence on wind turbine blades, examining measurement data regarding wind conditions and the strains of wind turbine blades. Furthermore, we performed a high-resolution large-eddy simulation (LES) and identified the three-dimensional airflow structures of terrain-induced turbulence. Based on the LES results, we defined the Uchida-Kawashima Scale\_1 (the U-K scale\_1), which is a turbulence evaluation index, and clarified the existence of the terrain-induced turbulence quantitatively. The threshold value of the U-K scale\_1 was determined as 0.2, and this index was confirmed to not be dependent on the inflow profile, the influence of the horizontal grid resolution, and the influence of the computed azimuth. In addition, we defined the Uchida-Kawashima Scale\_2 (the U-K scale\_2), which is a fatigue damage evaluation index based on the measurement data and the design value obtained by DNV GL's Bladed. DNV GL (Det Norske Veritas Germanischer Lloyed) is a third party certification body in Norway, and Bladed has been the industry standard aero-elastic wind turbine modeling software. Using the U-K scale\_2, the following results were revealed: the U-K scale\_2 was 0.86 < 1.0 (within the designed value) in the case of northerly wind, and the U-K scale\_2 was 1.60 > 1.0 (exceeding the designed value) in the case of easterly wind. As a result, it was revealed that the blades of the target wind turbine were directly and strongly affected by terrain-induced turbulence when easterly winds occurred.

**Keywords:** wind turbine blade; complex terrain; terrain-induced turbulence; large-eddy simulation; turbulence evaluation index; fatigue damage evaluation index
