Investigation Of Large Scale Wind Turbine Unsteady Loads Calculation And Alleviation

With the development of large-scale wind turbines, the stochastic wind velocity field and the complex working conditions make the wind turbine flow unsteadiness more serious, and thus the blade is prone to large deformation phenomenon, resulting in the obvious aerodynamic and structural coupling effect, and at the same time increasing the limit load and fatigue loads on the wind turbine. Therefore, in order to improve the design level of large-scale wind turbine and cost savings, it is of great significance that the unsteady load calculation accuracy and load alleviation are studied for large-scale wind turbines.Taking advantage of wavelet inverse transformation method, the independent stochastic wind speed field around the wind turbine is simulated, and the spatial correlation is made. The characteristics of three kinds of wind power spectra are analyzed. Based on an improved Von Karman power spectrum model and the Littlewood-Paley wavelet as the inverse transformation of wavelet orthogonal basis functions with the relationship of between the wavelet coefficients and power spectrum density function to correct the spatial correlation, the numerical simulation of the stochastic wind speed field of the large-scale wind turbine is carried out. Through the time domain, frequency domain and time-frequency analysis, it is found that the spectra of simulation are good agreement with the target spectrum, which reflects then on-stationary, local similarity and clearance characteristics of the stochastic wind speed field. The results also show that the stochastic wind speed field has high approximation of nonlinear wind power spectrum, and this method is effective and accurate in the stochastic wind speed field simulation for large-scale wind turbines.For the steady yaw, dynamic yaw, wind shear and stochastic wind speed field, the complex operational condition models are embedded into the free vortex wake method. The blade aerodynamic model is simplified with Weissinger-Llifting surface modeling. Based on Biot-Savart law for the solution of the induced velocity, the Lamb-Oseen vortex core model is used to enhance wake calculation convergence and accuracy. Then, the dynamic stall model and rotational effect model are use to correct the unsteady flow. Finally, the numerical calculation of complex operational condition of large-scale wind turbine is realized based on the free vortex wake method, and the result data are validated through NREL Phase VI experimental data. Compared the aerodynamic loads and wake result of the different complex conditions, the aerodynamic performance, loads and tip vortex line characteristics of wind turbine complex are concluded under the complex operational conditions, and the overshoot and lag time of the aerodynamic loads are obtained. This makes the free vortex wake method potential for a large number of wind turbine load calculations in the engineering to improve large-scale wind turbine load calculation precision and design level.Based on the linear finite element beam model and geometric nonlinear beam model, the finite element method is used to simplify the wind turbine blade. With the aerodynamic load, inertial load and gravity load of wind turbine blade considered, the dynamic equations of large-scale wind turbines are established, and are then solved using Newmark method, and Newton-Raphson method for structural internal iterative convergence of solution. Finally, the free vortex wake is appropriately coupled with the finite element method to calculate the unsteady dynamic loads on the large-scale wind turbine. The aeroelastic effect on wind turbine aerodynamic performance and wake is found. The difference between the linear finite element model and the geometric nonlinear finite element model is analyzed. The results show that the consideration of aeroelastic effect and geometric nonlinearity is important for large-scale wind turbine blades under the calculation of complicated operational conditions, which improve the dynamic response and unsteady loads calculation precision of the large wind turbine.Using the flexible trailing edge flap that install in near the tip of blade, set for ±20 ° deflection amplitude, the loads alleviation of wind turbine is achieved. The aerodynamic performance of trailing edge flap is investigated through the CFD(Computational Fluid Dynamics) method with the SST k ?? turbulence model. The spring mesh of the dynamic mesh technology is used to simulate the dynamic deflection of trailing edge flap, and the dynamic characteristics of the different trailing edge flap deflection rate and laws are analyzed. The aerodynamic performance database of tailing edge flap of NH1500 wind turbine is established, which is coupled to the free vortex wake method. Finally, the loads calculation and alleviation of wind turbine with the trailing edge flaps are realized. The results show that the trailing edge flap can be used for loads alleviation.Considering the flexible shaft and gear mesh effect, the two-mass, five-mass and included gear meshes modeling of drivetrain are built for NREL 750 KW wind turbine drivetrain as example. The calculation results compare well with the experimental data and other researcher’s calculation results, validating the reliability of the drivetrain model. Combined with the aeroelastic model, the dynamic response of the drivetrain is calculated. Based on the H∞ robust control theory, the control law of trailing edge flap is designed for reducing the vibration of blade and tower. The stability, dynamic response and natural frequencies of the drivetrain system are analyzed. Reductions in the deformation displacement and loads of the drivetrain using the trailing edge flap are investigated. The differences of stability and natural frequency of the three drivetrain model are concluded, and the Campbell diagram of the whole wind turbine is presented. The results show that the trailing edge flap has a good effect on the reducing loads and vibration of the drivetrain, blades and tower.