Analysis of Wake Induced Dynamic Stall on Wind Turbine Blades

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Dynamic stall phenomena on wind turbine blades generated by unsteady inflow conditions from upstream turbine wakes or atmospheric boundary layer fluctuations will be investigated. In the first project phase, wind turbine wakes were analyzed with the focus on the tip and hub vortices. The wake was predicted based on large-eddy simulations. Active control has been applied to excite unstable modes in the turbulent wake to minimize dynamic loads on turbine blades in wind farm installations. A major source of unsteady loads on wind turbine blades is flow separation which frequently happens under unsteady inflow conditions caused by wakes generated by upstream installed turbines or atmospheric turbulence. That is, detailed data of dynamic stall on wind turbine blades are necessary to extend dynamic stall models to perturbed inflow conditions and rotating configurations. The objective of this proposal is to improve the understanding and modeling of dynamic stall phenomena for typical wind turbine applications. In addition, the influence of dynamic stall on the wake turbulence will be analyzed. This knowledge will enable more accurate predictions of structural loads and the power output of a wind turbine. The dynamic stall on the turbine blade will be investigated by large-eddy simulations based on hybrid structured body-fitted and unstructured Cartesian meshes, such that the flow features including boundary layer growth, separation, transition to turbulence and flow reattachment can be captured accurately. Dynamic mode decomposition will be used to analyze the individual modes occurring at stall and in the wake dynamics. These simulations complement the measurements conducted by the TU Darmstadt and Univ. Oldenburg to reduce dynamic stall effects by an adaptive camber also for sweep conditions. Furthermore, simulations for the wind turbine model from the TU Berlin will be performed.