Research On Aeroelasticity And Geometrical Adaptiveness Of Large-scale Wind Turbine Blades

With the excessive consumption of fossil energy,climate issues and energy crises have promoted human to develop renewable energy.Wind energy,as one of the clear and renewable energies,has been payed much attention to.Blades,as key components of wind turbines,account for more than 20% of the total cost of wind turbine.This ratio increases with the increasement of the wind turbine capacity.In order to further reduce the cost,the size of the turbine is more and more big,the blade is becoming dramatically large which induces new challenges in research and development:(1)increased flexibility makes the aeroelastic effect more significant,multi-coupled vibration and geometrical nonlinear behavior stand out;(2)alleviation of vibrations and loads,improvement of fatigue performance,saving in weight and complexity in the rotor design and its auxiliary mechanisms(i.e.the pitch control actuators)become more important.This research,supported by the grant from the National Natural Science Foundation of China(No.51175526)and the National High Technology Research and Development program of China(No.2012AA051301,863 Program),focuses on the research about topic” Research on Aeroelasticity and Geometrical Adaptiveness of Large-scale Wind Turbine Blades”,and aims at providing theoretical and model supports for aeroelastic research of large-scale blade and new geometrically adaptive blades.The relevant work and main achievements of the thesis are as follows:(1)Through projection,a rotation matrix is introduced to replace the aerodynamic twist angle,which was originally used in classical blade element momentum theory(BEM).This process makes the new BEM enable to recognize the blade's multi-coupling and geometrical nonlinear behavior,so that the new BEM is able to calculate the aerodynamic loads of flexible blade.Due to aeroelastic effects,the airfoils operate under unsteady conditions.Therefore,Beddoes-Leishman(B-L)model is embedded into the new BEM.As the original B-L model is inaccurate in predicting drag coefficient,The B-L model is improved to predict the tangent force using the tangent separating point,which makes the predicting of the drag force more accuracy.This chapter provides theoretical fundamentals about aerodynamic force's computations for latter aeroelastic models.(2)In order to analyze the influence of coupling forms on the behavior of aeroelasticity,decoupling analysises are needed.Based on thorough analysises of internal mechanism of multi-coupling,multi-coupled vibration model is established using Euler-Bernoulli beam theory and virtual work principle.And the multi-coupled aeroelastic model is established combining the new BEM.NREL 5-MW blade is used as the study case.Contrastive analysises are carried out to analyze the influences of flap-edge coupling,centrifugal rigid effect and rotation matrix on aeroelastic behavior.The results indicates that flap-edge coupling,centrifugal rigid effect and rotation matrix will have different influence on aeroelastic behavior.(3)By using nonlinear mechanics theory of thin elastic rod,the geometrical nonlinear governing equations are established,and these equations involve the degrees of freedom such as tension,flap,edge and torsion and can identify the coupling relationship among them.The geometrical nonlinear aeroelastic model is established combining the new BEM.In order to compare the geometrical nonlinearity of different scale blades,a larger scaled blade(100m with a power of 13.2MW)is generated by up-scale method.Through contrastive analysises,it is concluded that when wind speed is small,loads are small,flap displacements are small,no nonlinear phenomena appear,while wind speed is large enough,nonlinear phenomena are outstanding,and are more significantly for larger-scale blade,at the same time,slight nonlinearity are observed in edge direction.(4)The airfoil's aeroelastic performance is measured by the sensitivity of the aerodynamic characteristics to the angle of attack,less sensitivity means better aeroelastic performance.Based on the aeroelastic performance,the outer airfoil NACA 64618 of the NREL 5-MW blade is optimized.Due to the failure positions in the optimization process,the optimization efficiency is low.In this paper,the PSO(particle swarm algorithm optimization)is improved.The failure particle is repeatedly studied until the unsolved region is broken out.The advantage of improved PSO is verified by an example.Then,the improved PSO is used to alternative-optimize NACA 64618 of NREL 5-MW blade,and a new airfoil named CQU 64618 is obtained.Then,replace the NACA 64618 by CQU 64618 and get a new blade.The new blade and the original blade are simulated by geometrical nonlinear aeroelastic model.The simulation results show that the flap loads,flap displacement and rotor power of the new blade are less sensitive to gust,and the torsion displacement is closer to 0,which proves the superiority of CQU 64618.(5)The pre-bend and sweep coupled blade is defined by combining of the curves theory and Bezier curve.The parameterization model is establish to study the geometrical adaptiveness.As the fact that defining of pre-bend and sweep coupled is defining of loose curvature and twisting vector,therefore the geometrical nonlinear aeroelastic model is naturally suitable for pre-bend and sweep coupled blade.In order to verify the adaptive performance of pre-bend and sweep coupled blade,three blades are built by the parameterization model: straight blade,purely swept blade and pre-bend and sweep coupled blade.It is concluded by the aeroelastic simulation that pre-bend and sweep coupled blade has smaller wave amplitude(including tip displacement and blade root bending moment),and its hub torque amplitude is greatly reduced,these can verify the the adaptive performance of pre-bend and sweep coupled blade.In order to analyze the influences of the key parameters of pre-bend and sweep coupled blade(tip bending value,distribution of bending along blade,tip sweep value and distribution of sweep along blade)on adaptive performance,34 blades are built by the parametrization model,17 for NREL 5-MW blade and 17 for extrapolated blade.It is concluded by the aeroelastic simulation that:(1)the same pre-bend and sweep configuration has similar behavior at different scaled blade,it proves that the pre-bend and sweep configuration is expansible;(2)for torsion moment,the pre-bend configuration and sweep configuration can be decoupled;(3)pre-bend and sweep configuration has positive influences on rotor's aerodynamic performance.This study is helpful to design of large-scale adaptive blades.