Investigation on dynamic performance of wind turbines using different scaling methods in wind tunnel tests

The relationship between rotor thrust (T) and tip speed ratio (TSR) directly influences the response of the scaled offshore wind turbine in the wind tunnel test. In this paper, a series of 1:100 scaled wind tunnel tests based on NREL 5 MW wind turbine are designed to study the dynamic performance of the wind turbine based on two different T-TSR scaling methods: (1) geometrically scaled blade with increased wind speed (GB-IW) and (2) redesigned blade with scaled wind speed (RB-SW). Test result indicates that the GB-IW method can meet the requirement of T, but unavoidably result in the distortion of TSR (40.2 % to 61.7 % lower than the target). However, using the RB-SW method, the T-TSR curve can be simulated well under different operational conditions. The amplitudes of structural response including base moment, nacelle acceleration and displacement from the GB-IW method are much lower than those from the RB-SW method, indicating that the GB-IW method leads to an overestimation of damping ratio but underestimation of the fluctuation of both natural frequency and structural response. The RB-SW method can provide a more reasonable estimation of structural dynamic performance, compared with the GB-IW method. This study confirms the importance of selecting reasonable scaling method for wind tunnel test, which is critical to the understanding of the complex aerodynamic and structural dynamic performance of offshore wind turbines.