Study On Dynamic Properties Of Wind Turbine Blades Under Pe-Riodic And Aerodynamic Loads

This thesis is focused on dynamic properties of wind turbine blades under pe-riodic and aerodynamic loads in operation. Apart from theoretically exploiting the impacts that these two types of loads exert on blades, a series of modal tests and analysis of a 300W rated power wind turbine in different wind speeds, rotating speeds and damage states were conducted to verify theoretical counterparts. The main work could be summarized as the following:At first, such periodic loads on wind turbine as gravity, centrifugal resultant force owing to dynamic imbalance, wind shear, vortex induced forces etc. were formulated mathematically and their impacts on blade dynamic properties when acting together were given subsequently based on harmonic analysis. Then, the aero-damping of a typical section of blades was derived, which was used to ex-plain the reason why the modal parameters of blades even non-rotating were still varying in changing wind speeds.Secondly, a modal experiment of a small-scale wind turbine was systemati-cally designed and completed during different wind speeds, rotating speeds and damage states, in which acceleration and strain were obtained by acceleration sen-sors of piezoelectric type and using strain gauges and FBGs, respectively. Test ob-jects included the integral components of wind turbine like tower, blades and rotor, as well as the whole turbine system under different wind speeds, rotating speeds and damage states. Electrical and optical signals were respectively sent to data ac-quisition (modem) devices through an electrical slip ring and an optical slip ring. After some preliminary process of acceleration signals, some evenly distributed frequencies were found in frequency spectrogram of acceleration responses.Lastly, through further analyzing of test data and together with the theories in the second chapter, the evenly distributed frequency peaks found in both non-rotational and rotational cases were interpreted. Then, based on the simple expres-sion derived for aero-damping, combined with lift and drag coefficient curve, it was qualitatively explained that the influence of aerodynamic loads on modal pa-rameters of wind turbine blades. Moreover, through statistical analysis of FBGs'time-strain data, FBG sensors were found pretty sensitive to the simulated damage in the experiment, which indicates that FBGs can be used to monitor similar dam-ages (delaminating damage) of operating wind turbine blades.