Wind-tunnel experimental study on aeroelastic response of flexible wind turbine blades under different wind conditions

The long and flexible blades of the offshore wind turbine are easily damaged during extreme wind conditions (e. g. typhoons or tornados). For this reason, a continuous aeroelastic model of a 5 MW wind turbine blade from National Renewable Energy Laboratory is designed and processed to depth analyze the aeroelastic response of flexible wind turbine blades. The effects of different pitch angles, wind speeds and spanwise positions on the aeroelastic response characteristics of wind turbine blades are studied by the model wind-tunnel experiments. The experimental results show that the aeroelastic model of flexible blades is reasonably designed for simulating the aeroelastic response under different wind speeds and directions. The pitch angles ranging from - 120 degrees to - 105 degrees and 45 degrees -105 degrees are unfavorable for this wind turbine blade. The root-mean-square (RMS) acceleration of the blade is significantly increased, which is considered to be a sensitive region for wind vibration. It has been observed that the blade is more susceptible to lock-in phenomenon when the blade profile is at incidences presenting shallower characteristic length (theta = 90 degrees and 105 degrees). In addition, the large deformation is measured after the blade tip deflection exceeds the cut-out wind speed, which in turn aggravates the geometric nonlinearity and greatly reduces the aeroelastic stability. Besides, the aeroelastic response of blades is reduced by optimizing the twist angle distribution in spanwise position. This experimental study aims to further the understanding of the aeroelastic response of flexible blades for reduction of windstorm damage to wind turbines in the typhoon-prone regions.