Research On Damping Blade Flutter Control Of Large Wind Turbine

In recent years,the trend of large-scale wind turbines has become more and more obvious.Therefore,the blades are designed to be more slender.When the wind wheel is rotating,the sweeping area of the blades increases,and the complex aerodynamic load it bears also increases.Under the interaction of inertial forces,self-excited vibration coupling will occur between the various modes of the blade.This coupling will strengthen each other and produce aeroelastic instability,which is called flutter.Blade flutter will have many adverse effects on the operation of the entire wind turbine.The alternating stress caused by flutter can easily cause blade fatigue,cracking,or even fracture damage.The flutter problem has severely restricted the development of large wind turbines.Aiming at the problem of blade flutter,this paper takes the 8MW large wind turbine blade as the research object from the perspective of improving t he ability of blade flutter,and establishes two finite element models of undamped blades and damped blades through ply design and damping layer laying position design.The modal analysis of the two models is carried out,and the optimal damping layer thickness of the damping blade is determined on the basis of comprehensive consideration of the natural frequency,structural loss factor,blade quality and other structural parameters.The static analysis and transient analysis are used to compare and study the two The vibration suppression effect of the blade is obtained,and the vibration suppression of the damping blade is obtained.Finally,the blade is equivalent to a cantilever beam,and a constrained damping structure cantilever beam dynamics experiment platform is built to explore the damping effect of the damping material on the flexible beam structure.The specific work is as follows :1.Analyze the blade flutter mechanism based on the force characteristics and load-bearing conditions of the blade,establish a simplified two-dimensional airfoil vibration model,and analyze the blade flutter from a mathematical point of view.2.According to the basic theory of the blade and the actual operating load,the wind wheel model of an 8MW large wind turbine is designed,and the flow field simulation calculation is carried out with ANSYS fluent software,and the surface pressure of the blade is obtained as the preload.3.Taking the number of plies,paving thickness,and paving area design parameters as the basic paving parameters,two paving schemes of full alternating symmetrical paving and partial alternating symmetrical paving are proposed,based on the effects of natural frequency,maximum relative displacement,maximum,etc.Comparing the modal calculation parameters such as force and modal shape,the full alternating symmetrical laying plan is selected as the finite element model laying plan in this paper,and the finite element model of the undamped blade of an 8MW wind turbine is established.4.According to the material characteristics,choose ZN-33 rubber as the damping material in this paper,and combine the mode shape and energy dissipation rate to determine the position of the damping layer to be between 70% and 100% of the blade span.The SHELL181 and SOLID185 elements are used to simulate the upper and lower blades.The skin and the damping layer are used to establish a finite element model of the damping blade of an 8MW wind turbine.When the thickness of the damping layer is 0.1 to 2.0mm,the blade natural frequency,structural loss factor,maximum relative displacement,blade quality and other parameters are analyzed.The parameters are combined to determine the best damping blade.The laying thickness of the best damping layer is 1.5mm.5.Establish a damping blade model based on the optimal damping layer thickness,and perform a parametric comparative analysis of the tremor suppression effects of the two finite element models of the undamped blade and the damped blade.Through modal analysis,it is found that the structural loss factor of the first-order modal damping blade is 26.99 times that of the undamped blade,and the maximum relative displacement is reduced by 1.42%.According to the static analysis of the applied pressure preload,it is found that the total displacement of the damping blade at different positions of the blade span The amplitude of fluctuation is lower than that of the undamped blade,the drop is smaller near the root of the blade,and the drop of the tip is the largest.After comparing the displacement in each direction of xyz,it is found that the swing displacement in the y-direction has the largest drop,followed by the shimmy displacement in the x-direction,and the displacement drop in the z-direction The smallest;through dynamic analysis by applying random wind load,it is found that the damping blade tip swing direction and the swing direction displacement and velocity amplitude are significantly reduced compared with undamped blades,and the effect of suppressing the swing direction is slightly higher than that of the swing vibration.direction.6.Use manual layup to make laminates and constrained damping structure laminates,use them as a cantilever beam model,build a cantilever beam dynamics experimental platform for vibration reduction research,and use the geometric model calculation result of the laminate frequency as the trigger frequency of the laminate.Comparing the displacement changes of constrained damping plates with different thicknesses under different frequency excitations,it is found that the first-order frequency is dominated by low-frequency and large amplitude,and the second and third-order frequencies are dominated by high-frequency and small amplitude.Compared with the original laminate,the constrained damping laminate is Both t he maximum and minimum values have decreased,which verifies the accuracy of the vibration suppression effect of the damping blade to a certain extent.At the same time,it is also found that as the thickness of th e damping layer increases,the vibration damping ability improves.In this thesis,by analyzing the flutter mechanism of large wind turbine blades,using the excellent dissipation effect of the damping material,a damping blade vibration suppression model is established,and the optimal damping layer thickness is determined under the premise of comprehensively considering the blade quality,vibration suppression performance,and structural rigidity.The vibration suppression effect of the damping blade is analyzed,and the vibration reduction performance of the damping material is explored through the cantilever beam dynamic experiment.It is found that the vibration suppression effect of the damping blade is obvious,and the damping material has a good vibration reduction effect on the flexible beam structure.