Numerical Analysis Method For Structure And Aerodynamic Performance Of Wind Turbine Swept Blades

Wind turbines are now becoming more and more large,which puts new and higher requirements on the safety and stability of the blades.As an adaptive passive de-loading aerodynamic layout,the wind turbine swept-back blade can reduce the extreme load and fatigue load of the unit through adaptive bending-torsion coupling,and at the same time improve the aerodynamic performance of the blade and improve the wind energy conversion efficiency and power output of the blade.In this paper,the finite element numerical analysis method,computational fluid dynamics(CFD)and fluid-solid coupling analysis were used to analyze the mechanism of the load-lifting synergy of the swept-back blade.Firstly,in order to more accurately simulate the mechanical properties of composite wind turbine blades,according to the geometrical characteristics of the blades and the mechanical properties of the composites,the method of establishing the finite element model of the blade with straight line and quadratic curve was studied.Using the APDL language in ANSYS,the parametric modeling of the three-dimensional shell element model of the composite blade was realized in a bottom-up manner,which makes the finite element modeling of the blade more efficient and accurate.Based on the established blade shell element model,the numerical modal analysis was carried out on the straight blade and the two swept blades.Firstly,the grid finite element model was verified by grid independence.By comparing the vibration modes and natural frequencies of the three grids,the finite element model with the appropriate number of grids was selected.Through the analysis of the dynamic characteristics of the swept-back blade,the variation law of the vibration modes of the straight blade and the swept blade was analyzed.The bending-torsion coupling coefficient derived from the node displacement method was used to describe the bending-torsion coupling characteristics of the blade.By applying a concentrated force at the tip of the blade,the displacement of each analytical section node was calculated numerically.Using the least squares principle to solve the six degrees of freedom of the section reference center of the blade equivalent beam model,calculate the bending-torsion coupling coefficient of each section,and calculate the equivalent bending-torsion coupling coefficient of the whole blade by weighted average method.After quantitative research The bending-torsion coupling characteristics of the swept blades and the influence of the amount of sweep.Based on FSI(Fluid-Structure Interaction),the solid finite element model and flow field finite element model of composite straight blade and swept blade wind wheel were established respectively.At the rated wind speed,the fluid-solid coupling analysis was carried out to analyze the load condition of the swept blade in the flow field and the deformation and stress distribution under the rated wind speed.The effects of blade sweep on the aerodynamic performance and structural performance of the blade were analyzed.Finally,the modal analysis of the pre-stress of the wind wheel was carried out to analyze the influence of the blade sweep on the vibration of the wind wheel.The research work in this paper was of great significance for the design of the new wind turbine swept-back blade and the strength check and fatigue load analysis method under rated wind conditions.