【作者】 范忠瑶；

【导师】 康顺；

【作者基本信息】 华北电力大学（北京） ， 热能工程， 2011， 博士

【摘要】 深入系统地研究和掌握风力机的能量吸收规律是保证风力机的安全可靠性、提高风力机性能的关键。目前,CFD方法以其突出的优势在风力机空气动力学问题研究和工程应用的各个方面发挥着越来越重要的作用,保证风力机数值模型的计算精度至关重要。由于运行工况下风力机叶片转捩类型多样,对边界层发展、流动分离及气动力等影响显著,因此转捩研究及其模型的发展和应用有助于进一步提高CFD计算精度,提升风力机设计水平。而鉴于风切变和塔影效应对风力机性能的剧烈影响,采用接近实际情况的风轮乃至整机模型,系统分析这些因素的影响规律和影响机理,将为风场选址、风力机设计和选型乃至发电量出力预报等各方面提供详细指导和参考。为此,本文采用CFD商用软件Fine/TurboTM,系统研究了均匀风速下叶片定常绕流场,切变风速对风轮气动性能、以及均匀和切变风速条件下整机塔影效应对风力机气动性能的非定常影响。均匀风速下叶片定常绕流数值模拟的研究从计算域尺度、网格数目、湍流和转捩模型以及风力机机舱的影响几个方面展开。首先以失速型风力机NORDTANK 500/41为研究对象,在高风速条件下,分析了计算域尺度和网格数目对叶片定常气动载荷数值模拟结果的影响；进而采用全湍流Spalart-Allmaras (S-A)模型、k-ωSST模型以及在S-A模型中计及转捩Abu-Ghannam & Shaw (AGS)模型,对风力机翼型FFA-W3-241和NORDTANK500/41风力机叶片进行多个工况下的边界层流态、性能参数和流动细节的详细分析；最后以NREL Phase VI风力机为研究对象,进行了机舱对叶片气动性能影响的数值分析。以上研究的结果显示：当计算域外边界距离旋转中心10倍风轮旋转半径以上时,基本可以满足气动计算结果与计算域尺度的无关性；当定常计算的性能参数收敛曲线呈大幅振荡的周期性收敛时,可靠的数值结果应为振荡周期内的平均值而非某一个迭代步上的计算结果；全湍流S-A模型及其转捩AGS模型可以较好的预计风力机气动性能及流场细节；机舱会影响叶根流动分离和旋涡结构,以及径向流动沿叶片展向的发展,尤其是分离区的流态,进而影响风轮气动性能和载荷预估值,在研究模型中加入机舱将提高数值模拟准确性。在对切变风速下风轮的非定常气动性能研究中,除了对NREL Phase VI风力机进行三维非定常CFD模拟分析外,还提出了一种准三维非定常数值模型并进行了验证,进而采用这种模型分析了不同风速廓线指数和展向位置处风切变的影响规律及影响机理,并与三维风轮模型的非定常CFD模拟结果进行了对比分析。结果显示：准三维模型可以很好的反映截面气动特征,适用于叶片边界层无分离或分离较小的展向截面处风切变下的气动性能分析；切变风速使得风力机性能、载荷和流动参数波动振幅增大,随方位角呈近似余弦函数型式的周期性波动,波动波幅随风速廓线指数和展向位置而增加,在整个风轮旋转平面内呈上下不对称式分布,且幅值方位角普遍滞后风速极值；与不同展向位置处线性增加的线速度引起的流动参数变化相比,风切变影响相对较小,不改变载荷的展向分布规律,对叶片结构稳定性的影响也不至于过大。在对均匀和切变风速条件下整机塔影效应的非定常数值模拟中,以上风向风力机DF90为研究对象,详细分析了包括叶片和风轮总体性能参数、压力分布、壁面极限流线图和截面流线图谱等流场细节。结果显示,均匀风速条件下,塔架的阻碍作用导致叶片载荷的剧烈变化,呈现塔前的突然增加,继而快速下降,进而是相对缓慢的回复过程。风轮的旋转作用使得塔前来流始终发生偏转,引起塔架两侧受力的不均匀以及塔后涡街3p脱落。塔影效应下的周期性脉冲载荷容易引起叶片和塔架的动态响应,对机组的寿命和运行安全不利。切变风速条件下,载荷波动幅值增加,相对均匀风速条件下增长近倍,并呈上部较大、下部较小,沿展向增加的趋势。同时,切变风速波动缓和了塔架附近载荷的剧烈波动,而三叶片相位差的叠加作用使得切变前后风轮载荷平均值及波动波幅变化不大。综上,本文所研究的几何模型自叶片、风轮到整机,物理现象自均匀风速下的定常流动到切变风速下的非定常流动,再到更为复杂的风切变与塔影非线性综合作用,层层递进,逐渐接近真实物理模型。研究结果为采用CFD数值方法进行翼型和叶片气动载荷分析与设计提供参考,为认识风切变、塔影等复杂非定常空气动力学问题的影响提供依据,为深入系统的掌握风力机的能量吸收规律,保证风力机的安全可靠性、提高风力机性能提供支持。更多还原

【Abstract】 The development of wind energy is a long-term strategic task in China. Systemic investigations and good understanding of the energy transform to ensure the reliability of wind turbine and to improve wind turbine performance are keystones of the sustainable development of wind energy industry. Due to the importance of CFD applications in wind turbine aerodynamics, a very important issue is the accuracy of CFD simulations. However, there exist many types of transition which has considerable impact on the development of boundary layer, separation flow and the aerodynamic performance. The investigation on transition and the development of transition models may improve the accuracy of CFD simulations and the design of wind turbine. In view of the dramatic impact of the wind shear and tower shadow effect on wind turbine performance, a numerical model close to the actual wind turbine, which contains the rotor, nacelle as well as the tower, should be used to analysis the influence of laws and mechanism systematically. The analysis results could provide detailed guidance and reference for wind farm micro-siting, turbine design and type selection as well as wind power prediction. Therefore, the present thesis is devoted to the investigation of the steady flow field under uniform wind speed, the unsteady influence of wind shear on rotor performance, and further the unsteady influence of tower shadow effect on turbine performance under uniform and shear wind speeds, by using commercial CFD software Fine/TurboTM.The steady simulations on wind turbine blade under uniform wind speed focus on the computational domain scale, grid size, turbulence and transition models, as well as the influence of turbine nacelle. Firstly, the influences of computational domain scale and grid size on the aerodynamic performance and load distributions of steady simulations under high wind speed is investigated, where the stall-controlled wind turbine NORDTANK 500/41 is taken as the test case. Detailed analysis on the boundary layer, performance and details of the flow field of the FFA-W3-241 airfoil and NORDTANK 500/41 wind turbine blade are performed using full turbulence Spalart-Allmaras (S-A) model、k-ωSST model, as well as the transition model Abu-Ghannam & Shaw (AGS) in S-A. The influence of nacelle on the aerodynamic performance of the blade are analysised using the model of NREL Phase VI wind turbine. The simulation results show that the simulated aerodynamic performance is independent to the computational domain scale when the computational domain is larger than 10 rotor radii. When the performance convergence history of steady computations has large periodic variations, the result averaged of a period is more reliable than one of the certain time step. Full turbulence S-A model and transition AGS model have good performance on the predication of aerodynamic performance and flow details. The nacelle has influence on the separated flow and vortex structure at the hub of blade, as well as the spanwise development of radial flow, especially the flow in the separation region. Taking the influence of nacelle into account will improve the accuracy of CFD simulations。A quasi-three dimensional unsteady numerical module is imposed and validated on the wind shear influence investigation of rotor performance. Based on this model, the influence law and mechanism of different wind profiles and the wind shear effects on different spanwise locations are analysised. The results are further validated by full three-dimensional unsteady simulations. The test case used above is NREL Phase VI wind turbine. The comparison shows that the quasi-three dimensional model proposed can capture the aerodynamic characteristics, which can be used in the aerodynamic analysis of wind shear at specific spanwise position without boundary layer separation or with small separation region. The wind shear increases the fluctuations of wind turbine performance and loads, as well as the flow parameters, with their variations along azimuth angle is of periodic approximately in cosine function, and the amplitude increases with the wind shear exponent and along the span, which cause an asymmetric feature in the rotating plane and phase lagged compared with the peak of wind speed. Nonetheless, The effect of wind shear is relatively small on the flow parameters compared with that of linear velocity increase along span, which will not change the load distribution along span, and do harmless impact on the blade structural stability.An upwind wind turbine DF90 is used as the simulation model in the unsteady simulations on the tower shadow effect. The analysis focus on the variation of total performance parameter, distribution of pressure, limiting streamline close to the wall and section streamline patterns. The results show that the block of tower will cause dramatic changes of blade load when the wind speed is uniform, showing a sudden increase before the tower and then decrease rapidly and slow recovery afterwards. Income flow deflection always exists due to the rotating of turbine, which results in the unbalance of forces at both sides of tower and 3p vortex shedding after tower. The periodic load under the impact of tower easily leads to the dynamic response of blade and tower, which will do harm to the operation and life of machine. Under the wind shear, the increase of the load amplitude is nearly two times than that of the uniform wind speed, with the fluctuation increases along span. This results in imbalance load distributions of the rotor plane, where the upper half is larger then that of the lower. Meanwhile, the shear winds reduce the load dramatic variation acceleration near the tower, and the mean value and variation of load before and after the wind shear effect change little due to the phase difference of three blades.The present thesis investigates systematically on both steady and unsteady flows of wind turbine based on the model from single blade to rotor, and finally the turbine contains tower. The complicated wind shear and nonlinear effect of tower also investigated, which prove a more accurate model close to the real physical one. The simulated results can be used as the guidance and reference for the load analysis and aerodynamic design from airfoil to blade by using CFD simulations, which also give the basis of understanding of the complicated unsteady aerodynamic features of wind shear and tower shadow effects, so as to the support to the reliable and high performance design of wind turbine.更多还原