Active Micro-Tabs for Load Control on Wind Turbine Blades

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Modern large wind turbine blades are affected by strong local and unsteady wind conditions such as wind shear, gusts, and blade-tower interaction. These effects lead to dynamic stall and thereby accelerate the fatigue of various structural components. Therefore, a wind turbine's life time is significantly reduced which increases the overall cost of energy. The means of controlling dynamic load changes is provided through flow control with active elements. However, transient effects of their application as well as the effects of dynamic stall on the control elements have not been properly addressed yet. Therefore, additional research is required on these subjects to enable the application of active load control methods on full-scale wind turbines. A promising tool for effective load control is offered through so-called micro-tabs which may be deployed and retracted to counteract sudden load changes. The micro-tab system is advantageous because of its mechanical simplicity, uncomplicated implementation within the blade structure, and substantial control authority. Micro-tabs are applied at the trailing edge region where they reduce lift when deployed on the suction side and enhance lift when deployed on the pressure side. However, due to the occurrence of dynamic stall, the tab on the suction is embedded in separated flow which renders the tab ineffective. Therefore, an experimental approach to study a combination of micro-tabs with stall delaying vortex generators is proposed. The main focus of this project is the investigation of transient effects during the deployment and retraction process as well as the effects of dynamic stall. Furthermore, the feasibility of instantaneous load control in a closed-loop configuration under realistic conditions is examined.