Validation of aeroelastic dynamic model of Active Trailing Edge Flap system tested on a 4.3 MW wind turbine

Abstract. Active Trailing Edge Flap (ATEF) is a promising technology for Wind Turbine load reduction and AEP improvement. However, this technology still needs extensive field validations to prove the reliability of the ATEF aeroelastic modeling codes. This article describes the validation of the dynamic response of the ATEF aeroelastic models developed for the BEM-based solvers HAWC2 and BHawC. The validation relied on field data from a 4.3 MW Wind Turbine (WT) equipped with an ATEFS on one blade and operating in normal power production. The validation consisted of three phases. At first, video recording of the ATEF deflection during WT operation allowed the tuning of the flap actuator model. In the second phase, the aerodynamic flap model was tuned and validated through the lift coefficient (Cl) transients measured with an innovative autonomous add-on measurement system placed on the blade in the middle of the spanwise extension of the ATEF. Finally, the aeroelastic ATEF model was validated based on the blade root moment (BMrM) transients over three months, from October to December 2020, with varying weather conditions. The validations showed that the simulations transient of Cl and MBrM are in good agreement with the corresponding measured transients, with a maximum difference for the blade-to-blade MBrM transients below 1 % of the mean blade load during flap activation and below 1.7 % during flap deactivation. An analysis of the possible root causes of these differences suggested additional measurements to improve the ATEF model tuning. The validation confirmed that the aeroelastic ATEF models provide a reliable and precise estimation of the impact of the flap on the wind turbine during flap actuation.