【作者】 陈刚；

【导师】 陈进；

【作者基本信息】 重庆大学 ， 机械设计及理论， 2018， 博士

【摘要】 随着化石能源的过度消耗,气候问题和能源危机促使人类更加重视可再生能源的开发。风能作为清洁的可再生能源之一,受到世界各国的广泛关注。叶片作为风力机的关键部件,其成本达到整机成本的20%以上,并且该比率随着单机容量的增大呈上升趋势。为了进一步降低发电成本,风轮尺寸越来越大,大型叶片的研究与开发将面临新的挑战:(1)柔性增加使得叶片的气弹效应更加显著,多向耦合振动和几何非线性行为凸显出来;(2)缓解载荷和振动,提高疲劳性能,降低风轮及其附属机构(比如主动变桨系统)的重量和复杂度变得更加重要。本文在国家自然科学基金项目“基于参数化的风力机叶片气动性能与结构一体化设计理论”(编号:51175526)、国家高技术研究发展计划(863计划)“先进风力机翼型族设计技术研究”(编号:2012AA051301)的资助下,对“大型风力机叶片气弹及其几何自适应研究”课题开展了相关研究,旨在为大型叶片的气弹研究与分析、新型自适应叶片的开发提供相应的理论基础和模型支撑。论文的相关工作和主要成果有:(1)通过坐标投影法,利用旋转矩阵取代经典叶素动量理论中的气动扭角,使得新叶素动量理论能够识别叶片多向耦合和几何非线性,从而有效处理柔性叶片的气动载荷计算问题。由于气弹效应的作用,翼型运行在非稳态工况下,本文将Beddoes-Leishman(B-L)模型嵌入到新的叶素动量理论中。由于原动态入流模型在计算动态阻力系数时缺乏准确性,本文使用切向力分离点来预测分离流切向力,从而提高模型对动态气动阻力的预测精度。本研究为后文气弹模型的建立提供气动载荷计算方面的理论基础。(2)为了分析各耦合形式对叶片气弹行为的影响,需要进行解耦分析。本文在深入分析叶片多向耦合内部机理的基础上,利用欧拉伯努利梁理论和虚功原理建立叶片多向耦合振动模型,结合新的叶素动量理论建立多向耦合气弹模型。引入NREL 5-MW叶片作为实例叶片,进行对比分析,探讨挥舞-摆振耦合、离心刚化效应以及旋转矩阵的选取对叶片气弹行为的影响。结果表明,挥舞-摆振耦合、离心刚化效应以及旋转矩阵的选取均会对叶片的气弹行为造成不同程度的影响。摆振方向的交变载荷会诱导挥舞方向的位移,使得挥舞方向的气动力出现波动,进一步影响挥舞方向的位移。叶片结构内部的挥舞-摆振耦合以及结构与气动上的气弹耦合使得叶片挥舞方向存在较大的载荷和位移波动,对疲劳性能不利。(3)借助弹性细杆非线性力学理论建立叶片几何非线性动力学控制方程,该控制方程囊括了叶片的拉伸、挥舞、摆振和扭转自由度,并能有效识别它们之间的耦合关系。结合新的叶素动量理论建立几何非线性气弹模型。为了对比分析不同量级叶片的几何非线性行为,利用尺度法外插生成更大量级的叶片(长度为100m,功率为13.2MW)。通过对比分析可知,小风速区,载荷小,挥舞变形小,基本无几何非线性现象。随着风速增加,挥舞方向的几何非线性凸显出来,且量级大的叶片更加显著。(4)利用气动特性对攻角的敏感性来衡量翼型的气弹性能,对攻角不敏感的翼型则具有好的气弹性能。基于该气弹性能指标,对NREL 5-MW叶片的外侧翼型NACA 64618进行优化。由于优化过程中常出现失效解的情况,使得优化效率低下。本文对粒子群算法进行改进,即让失效粒子反复学习直至跳出无解区域,并利用算例验证其优越性。接着利用改进的粒子群算法对NACA 64618翼型进行替代设计,得到新翼型CQU 64618。用CQU 64618翼型替代NREL 5-MW叶片的NACA64618翼型,得到新叶片。然后利用气弹模型分别对新叶片和原叶片进行对比仿真。仿真结果表明新叶片的挥舞位移和风轮功率均对阵风的敏感性降低,且扭转位移更接近0值,验证了新翼型CQU 64618的优越性。(5)结合微分几何曲线理论和Bezier曲线来定义预弯-后掠叶片,建立参数化模型,开展叶片的几何自适应研究。由于定义预弯-后掠的本质是定义叶片的松弛弯扭度,因此可将几何非线性气弹模型作为预弯-后掠叶片的气弹模型。为了验证预弯-后掠的自适应性能,利用参数化方法生成了3种叶片:直叶片、纯后掠叶片和预弯-后掠叶片。通过气弹仿真得到:预弯-后掠叶片相比其他两种叶片有更小的挥舞幅值(包括叶尖位移和叶根弯矩),并且叶根扭矩的幅值有大幅降低,从而验证了预弯-后掠叶片的自适应性能。为了分析预弯-后掠的关键参数(叶尖预弯量、预弯沿叶展的分布规律、叶尖后掠量、后掠沿叶展的分布规律)对叶片自适应性能的影响,以及不同量级对叶片自适应性能的影响,利用参数化方法定义了34支叶片,其中包括17支长61.5m的NREL 5-MW叶片和17支长100m的外插叶片。利用气弹仿真对比得到:(1)相同的后掠-预弯构型在不同量级叶片上的表现差异很小,说明预弯-后掠构型具有一定的拓展性;(2)对叶根扭矩而言,预弯构型和后掠构型能够解耦,能够对它们进行独立设计;(3)预弯-后掠构型对风轮的气动性能具有正向影响,合理的预弯-后掠能大幅提高风轮气动性能。此研究对大型自适应叶片的设计和开发具有指导意义。更多还原

【Abstract】 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.更多还原