Blade strain analysis from field measurements on a vertical axis wind turbine

In this paper, the 10 kW WindQuest Vertical Axis Wind Turbine (VAWT) has been instrumented by strain gauges during its trials in the Ifremer in situ test site of Brest to study the effects of the structural dynamic response of the blades under operating conditions. Static and dynamic effects have been investigated as a function of the rotational speed when the rotor operates under stable wind conditions. The analysis segregates the influence of the gravitational, inertial, and aerodynamic loading components on the flapwise bending stress of the blades. The study of the cyclic variations on the blade strain at different Tip-Speed Ratios leads to the identification of the dynamic stall effect on the unsteady loads, while the spectral analysis describes the system eigenfrequencies excited by the interaction of the wind and the structure's motion. The results provide useful data to validate numerical models for VAWT blades with similar design and evaluate the structural fatigue.