Study On Dynamic Responses Of Aerodynamic-structure Coupling For The Pitch Fault Of Large Horizontal Axis Wind Turbine

With the rapid development of wind power and large-scale installation,running and grid-connected generation of wind turbines,ensuring the structural safety of wind turbine has become a top priority.In many factors that lead to structural failure and damage accidents of blades,whenever wind turbine runs or reaches the cut-out wind speed and halts,pitch fault is easy to cause ultra-high aerodynamic load.But now,there are few related aerodynamic and structural research.For this reason,aiming at state of wind turbine when pitch fault occurs and blade structural performance requirements,according to aerodynamic and sturcture features of different pitch fault situations,this paper proposed two aerodynamic-structure coupling models based on static link library and database respectively,and used two-way strong fluid-structure interaction method.Damage mechanism research of wind turbine blade with pitch fault under multi-physics coupling was carried out,and new configuration blade of fractal structure was proposed to improve its structural mechanical performance.Main works of this paper are shown as followed:1.Three-dimensional solid model of NREL 5 MW wind turbine was constructed based on the parametric modeling,and detailed lay-up scheme of blade was proposed according to actual manufacturing process requirements,ultimately the finite element analysis model of composite blade can be obtained.Therefore,aerodynamic-structure coupling numerical simulation accuracy and result practicability of wind turbine blade with pitch fault can be ensured.2.Research on fluid domain characteristics of pitch fault blade of single blade model and full rotor model under cut-out wind speed when wind turbine halts was carried out,including information such as blade torque,load time-domain fractal feature,frequency-domain main stimulus frequency,velocity field and vorticity field.Results analysis indicate for megawatt-class level horizontal axis wind turbine,basing the single blade model can accurately characterize the aerodynamic characteristics of blade with pitch fault and improve computational efficiency.3.Aerodynamic characteristic and structural response of the blade with pitch fault under high coupling of multi-physics was analysed using the two-way strong fluid-structure interaction method.The results show that the fluctuation range of the blade flapwise torque under the two-way strong fluid-structure interaction is wider than that without fluid-structure interaction.At the same time,the aerodynamic torque and tip displacement of the blade with pitch fault are all larger one order than the blade with pitch success.Therefore,the transient instability of the blade with pitch fault occurs under all four typical azimuths,and the 0°azimuth is the most severe.In addition,the quasi-static structural response analysis was used to study the structure characteristics of blade with pitch fault under cut-out wind speed.The results prove that,although the two-way weak fluid-structure interaction can obtain the stress concentration position,stress magnitude and tip displacement of the blade with pitch fault using less computing resources,the quasi-static structural response analysis cannot consider the influence of inertia effect and geometric nonlinearity on the structure in the dynamic response process.4.Influence of atmospheric boundary layer on megawatt large horizontal axis wind turbine cannot be ignored.Adding buoyancy term based on Boussinesq hypothesis and Coriolis force term from earth rotation to standard N-S equation using the open source computational fluid dynamics software Open FOAM,real atmospheric boundary layer that can be applied to wind turbine wind field numerical simulation was generated.In addition,allying Open FOAM with the open source wind turbine aeroelastic software FAST to realize aerodynamic-structure coupling calculation of multiple running state wind turbines was proposed.For this reason,it was necessary to compile more than 40 Fortran source program of FAST into a static link library.At the same time,the dynamic link library of the actuator line method was written based on Open FOAM bottom code as data communication approach between FAST and flow field variables.5.Combing the aerodynamic-structure coupling method that based on static link library with atmospheric boundary layer data,research on aerodynamic load and structure dynamic response of blade with pitch fault of running state wind turbine within wind farm was carried out.The results show that the flapwise torque,edgewise torque and torsional torque of blade with pitch fault are significantly greater than t blade with normal pitch,and load pulsation curve fractal dimension of the former is higher,indicating that the aerodynamic moment time domain data of blade with pitch fault has the small self-similarity but large irregularity.The tip displacement is similar to the situation of load,because the aerodynamic characteristic is the root of the structure response.In addition,it is also found that the output power of upstream wind farm wind turbine including blade with pitch fault is lower than that with normal pitch angle,but the influence of its wake on the downstream wind turbine is weakened,thus the total power of the wind farm can be improved.6.Fractal blade and a new aerodynamic-structure coupling method based on database were proposed.First,aeroelastic of blade with pitch fault was analysed using FAST.The 17-segment load information of blade was stored in the way of database,which was loaded into the structure finite element model based on Python language secondary development function of Abaqus software.Then,comparative analysis of fractal blade with original blade under the same condition was carried out based on the new method.The results show that the tip displacement of the former is reduced by19.7 % compared with the latter,which proves the fractal blade can achieve better structural mechanical properties on the basis of material saving and weight reducing of the blade.In addition,the structural buckling calculation of fractal blade and original blade was also carried out.The results show that the first-order buckling factor of the former is 1.8583,which is 3.6 % higher than the latter,so the fractal blade has higher structural safety.