Real-time prediction of aeroelastic loads of wind turbine blades in gusty and turbulent wind using an improved load model

The traditional method of flutter analysis of wind turbine blades employs a mixed-domain (frequency- and time- domain) formulation for self-excited aerodynamic loads, because flutter derivatives are functions of reduced frequencies. However, a time-domain formulation for self-excited and buffeting loads allows the equations of motion to be continuously solved for response time histories of wind turbine blades below flutter speed and captures the transient response in gusty and turbulent winds. The rational function coefficients and buffeting indicial function coefficients that appear in the time-domain formulation were previously extracted for the NREL S830 airfoil section model in a wind tunnel. The objective of the current study is to evaluate how well these experimentally extracted coefficients can predict the aerodynamic loads on a blade in different wind conditions, through a separate set of tests conducted on a much larger (3.3 times) section model of the blade in a larger wind tunnel than originally used. The measured loads (lift and moment) were used to validate simulated loads using the time domain load prediction procedure. To improve the correlation between the measured and predicted loads, an improved loads model was developed using an additional lag term and its performance is presented in smooth, gusty and turbulent wind. An aeroelastic model test of a HAWT blade in a wind tunnel was used for further validation showing the efficacy of the loads model.