Research On Influence Of Aerodynamic Mistuning On Horizontal Axis Wind Turbines

In recent years, with the development of wind power technology, wind turbine blades, which is the main parts of the wind wheel,absorb wind energy, and have frequent accidents, thus become the focus of attention for the safe operation of wind turbines. The design and performance analysis of wind machine are based on coor-dination wind wheels system. However, human factors such as the material, manu-facture, installation errors, run wear and pollution etc,and also the physics factors such as gust, non-uniform flow and non-axis etc, will both lead to structure detun-ing and pneumatic detuning. Computational Fluid Dynamic(CFD), applied with its unique advantages in airfoil analysis and design, blades and wind turbine aerody-namic performance analysis have been more widely used. The main generator type of domestic wind turbines include the 1.5MW and 2MW.The paper mainly study the pneumatic detuning including wind shear and yaw, based on the study objects about the NREL Phase VI and 2MW three blades Tj(?)reborg for horizontal axis wind turbine, carried out the aerodynamic characteristics simulation of axial uni-form flow conditions and compare with the experimental data, finally analyzes the factors that affect accuracy. On this basis, perform the simulation about the aerody-namic detuning characteristic and fluid solid coupling characteristic of wind turbine under the wind shear and yaw condition.Under axial uniform flow wind speed circumstance, use Tj(?)reborg wind ma-chine as research object, discuss both process method of steady numerical simula-tion results and grid number,which do effect numerical results.As the results show, select the sliding mesh; and split the blade into segments, gives different grid numbers on the different segment. Choose the suitable initial grid density and reasonable CFL number, can reduce the mesh numbers, increase time step, shorten calculation time; Take NREL Phase VI wind machine for examples, do the research on the aerodynamic characteristic with or without nacelle under different axial flow wind speed condition. Judged on the result, pressure coefficient distribu-tion have no big difference between with nacelle and without one, and both have fitted well with the experimental result.However, tangent force coefficient and normal force coefficient at the root of blade has large changes between with nacelle and without one, while that at the middle and top of blade have not big difference.In addition, with or without nacelle do have impact on the flow separation and vortex structure concentrating in the range of the root of blade, while not in the main flow.In the case of wind shear condition, use NREL Phase VI wind turbines and Tj(?)reborg as object of study analyze the influence rule and influence mechanism of wind shear in the different wind profile indexes and span-wise position wind shear, and compare with the experimental results. As the results demonstrated, shear wind speed makes wind turbine aerodynamic performance, load and flow parameter fluctuation amplitude increase, and fluctuation amplitude augments with wind speed profile line index increases and span-wise position more close to blade top,which can more accurately reflect the reduce of pneumatic power. Pneumatic power, thrust and torque etc the overall performance parameters change cyclically; wake expanses constantly, and the asymmetry of wake speed loses causing by the wind shear will become indistinct with the augment ofwake distance.In the case of yaw velocity condition, use NREL Phase VI wind turbine and Tj(?)reborg wind turbine as the study object, analyze yaw effect rule and mechanism under different conditions of yawing.As the result shows:yaw wind speed presents obvious periodicity in the unsteady operation process; with the increase of yaw an-gle, torque reduces, and decrement is relevant to yaw angle; when azimuth angle and yaw angle is not the same, separation situation has big differences; With the increase of blade span-wise position, the effect by the yaw more closely to blade top have been more smaller.The oblique and asymmetric of wake indicate more sensi-tive with increase of yaw angle.In the case of yaw wind speed of Wind turbine flow structure coupling simula-tion, use NREL Phase Ⅵ wind machine as research object, compare the flow and structure characteristic between 7m/s axial uniform flow and 7m/s with yaw angle 30°conditions two-way flow structure coupling.It can be obtained that perfor-mance parameters of fluid structure coupling presents fast cyclical to stable value under axial uniform flow condition;The blade deformation in the direction of flap-wise, edgewise and span-wise render out first order vibration form, and in-creases from root to blade top gradually. And what’s more, the flap-wise defor-mation is most striking, the stress mainly concentrating near the middle of blade span-wise,and the chord-wise stress focus on the vicinity of the maximum thick-ness of the blade.Under the condition of yaw wind speed flow structure coupling, wind wheel load and blade deformation presents cyclical shock, but wind wheel overall load and amplitude change smaller by the coupling; coupling effect makes blade twist angle reduce at the inner span, and load increase; the blade twist an-gle increases at the outer part, and reduces the load, thus extreme load value have decreased; The blade azimuth angle of load extreme value and that of wind speed extreme value have not corresponded o each other within the wind wheel rotating plane.As has been stated above, this paper studies two kinds of wind turbine mod-els, from steady flow of the axial uniform velocity condition to the unsteady flow of pneumatic detuning with the wind shear and yaw velocity, then to the more complex fluid-structure coupling synthetic simulation, go forward one by one,and gradually close to the reality physical model. Research results will provide a refer-ence to the analysis and design of the airfoil and blade aerodynamic load applied with CFD numerical method. It also provide the basic for being aware of wind shear, yaw and other complex unsteady aerodynamic mistuned issues, and also flu-id-structure coupling characteristic. Furthermore, the study provide technical sup-port to the active control separation and to guarantee the safety and reliability of wind turbines operation.