Aerodynamic Characteristics And Wake Analysis Of Large-scale Horizontal-axis Wind Turbines Based On IDDES Method

The aerodynamic problems involved in the actual operation of wind turbines are extremely complex.The wind speed and wind direction are unstable,and the wind turbine operating environment is always accompanied by high turbulence and wind shear,which not only affects the aerodynamic characteristics of the wind turbine,but also forms a very complex wake field,which leads to changes in the wake conditions of wind turbines operating in the middle and lower reaches of wind farms.Numerical simulations of wind turbine aerodynamic characteristics and wake field flow characteristics mostly adopt Reynolds-averaged Navier-Stokes(RANS)method,Large Eddy Simulation(LES)method and Detach ed Eddy Simulation(DES)combining the advantages of these two methods,but these three methods are difficult to meet the requirements of computational accuracy and computational resources for numerical simulations of large wind turbine aerodynamic charact eristics and wake field at the same time.The Improved Delayed Detached Eddy Simulation(IDDES),which is improved on the basis of DES method,is more effective in simulating complex flow separation problems in wind turbine flow fields.Therefore,in this thesis,the numerical simulation of the wake flow and aerodynamic characterist ics of a large horizontal axis wind turbine under different incoming flow conditions is carried out using the IDDES method with the NH1500 three-blade large horizontal axis wind turbine as the research object.The main work is as follows:(1)Structured meshes for horizontal axis wind turbines based on IDDES and RANS methods,verifying the feasibility of IDDES method in the field of large horizontal axis wind turbine aerodynamic characteristics and wake flow stu dies.For the full-scale model of NH1500 wind turbine,a structured mesh of horizontal axis wind turbine based on IDDES and RANS methods is established to carry out numerical simulations of the aerodynamic characteristics of large wind turbine and the flow characteristics of wake field under uniform incoming flow at rated wind speed.The simulation results of the two methods are compared with the calibration results of GH Bladed software,and it is found that the IDDES method has advantages in describing the aerodynamic characteristics of wind turbine blade surface pressure,blade surface flow characteristics,blade and wind turbine thrust and torque,as well as the mean velocity,turbulent kinetic energy,vortex structure and other flow characteristics of wind turbine wake area.The relative errors of the wind turbine thrust and power obtained by the IDDES method are less than 5%;comparing the pressure coefficient and streamline distribution of the blade surface calculated by the RANS and IDDES methods,it is found that the IDDES method can better predict the airflow separation;the axial mean velocity of the wake field simulated by the two methods is approximately the same,but the results of the RANS method are more stable,while the results of the IDDES method show obvious fluctuations;compared with the RANS method,the The IDDES method can depict the separation and fragmentation of unstable vortices in the wake field more clearly than the RANS method.(2)Numerical simulations of shear flow conditions ba sed on different wind shear indices were carried out to reveal the influence of shear flow on the aerodynamic characteristics and wake characteristics of horizontal axis wind turbines.Shear incoming flow has wind speed inhomogeneity,which will affect the distribution of aerodynamic loads during wind turbine operation to a certain extent,and also affect the flow structure of the wind turbine wake field,which is an important factor to be considered in the wind turbine operating environment.The IDDES method is used to develop the simulation analysis of the aerodynamic characteristics of the wind turbine and the flow characteristics of the wake field under the rated wind speed shear incoming flow.The analysis shows that when the wind shear index changes,the surface pressure coefficient and flow distribution of the suction surface of the blade at 0° azimuth change significantly,and the flow separation point of the airflow in the suction surface of the blade gradually moves forward with the increase of the wind shear index,and the closer to the tip of the blade,the more significant the forward phenomenon,with the wind shear index becomes larger,the root mean square of blade/wind turbine thrust and torque are reduced,and the relative fluctuations are inc reased.The change of wind shear index has a greater effect on the axial velocity and turbulent kinetic energy in the vertical plane of the wake field.Below the rotation axis of the wind turbine,the larger the wind shear index is,the greater the velocit y loss,and the faster the turbulent kinetic energy in the central vortex area and the tower vortex area is reduced;while above the rotation axis,the larger the wind shear index is,the smaller the velocity loss,and the greater the turbulent kinetic energy in the vortex of the blade tip.(3)Numerical simulations of uniform turbulence based on different turbulence intensities were carried out to reveal the influence law of turbulent incoming flow on the aerodynamic characteristics and wake characteristic s of horizontal axis wind turbines.A simulation study of the aerodynamic characteristics of wind turbines with wake flow field flow characteristics was carried out under uniform turbulence conditions using the IDDES method.The study shows that: the chang e of turbulence intensity has almost no effect on the pressure distribution on the pressure surface of the blade,while the pressure on the suction surface of the blade near the trailing edge part is more significant,and the closer to the root of the blad e the greater the effect,with the increase of turbulence intensity,the root mean square of the blade or wind turbine thrust and torque and the fluctuation amplitude are increased,but the fluctuation amplitude changes are small.When the turbulence inten sity changes,the blade-tip vortex and tower vortex in the wake field mix with each other and form complex and variable vortex behind the tower,and the greater the turbulence intensity,the more violent the vortex velocity fluctuation and the greater the mixing intensity along the radial direction between each vortex system.