Large wind turbines can experience significant vertical and horizontal shear and varying turbulence over blades span.Since, both these factors may result in flow separation over blades, active flow control devices such as plasma actuators(PA) have been receiving interest as they may alleviate the loadings on blades and maintain turbine efficiency. The current study investigates the overall effect of PA on the control response and performance of a wind turbine. To that end, aero-servo-elastic simulations with and without PA are performed for a 300 kW wind turbine for both steady and uniform, and turbulent inflow conditions. The effect of PA is implemented as lift and drag coefficients which were obtained from separate wind tunnel experiments. It is found that control parameters (rotor speeds and blade pitch angles) have no effect of PA and responses with and without PA overlapped in both steady and uniform, and turbulent cases. Similarly, thrust forces and power outputs as well as their fluctuations showed similar characteristic for the simulations with and without PA. Further analysis shows that the turbine mostly operated around the angle of attacks which are below the stall angles of the airfoils. Since PA is not effective at such lower angle of attack the difference between results with and without PA is negligible.

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In March 2023, a tower of a 1.5MW wind turbine was cut off and the upper part of the wind turbine fell to the ground. This paper presents the mechanism of the fracture. Detailed investigations of the fractured part of the tower were carried out by visual and macroscopic inspection and mechanical testing of specimens. The wind and operating conditions of the turbine were also investigated. It was found that there was misalignment of the center of thickness of two adjacent plates at the weld, and this caused an increase in stress at the weld. Furthermore, there is a dominant wind direction at the site and the direction was matched to the part where the misalignment of center lines was large. It is concluded that the misalignment and the dominant wind direction cause unexpected fatigue failure. The ultimate strength of the tower with fatigue fracture was analyzed by numerical simulation. When the circumferential length of the fatigue fracture is 3 m or more, the tower is cut off by ductile fracture and buckling of the tower. Preventive measures have already been implemented for the same type of tower and wind turbine.

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