Numerical Simulation And Aerodynamic Noise Characteristic For Wind Turbine Blade Fault

The blade is the key component of wind turbine to obtain wind energy.Because of the bad operating environment and the long-term stress of complex alternating loads,blade failure occurs frequently,not only can lead to long downtime,even cause serious accident and huge economic losses.The noise signal radiated by the faulty blade is significantly different from that of the normal blade.Aiming at the unknown aerodynamic and noise characteristics of wind turbine failure blades,this paper focused on the numerical simulation and aerodynamic noise characteristics research of wind turbine blade faults.The main contents and results are as follows:(1)This paper proposed a fault simulation method based on computational fluid dynamics.Combined with the fault characteristics of fan blades,the fault models of NACA0012 airfoil at different angles of attack and NREL 5 MW wind turbine blades was established.Combined with wind turbine working conditions and rotating region modeling theory,the space model of flow field and the simulation model of wind wheel rotation process based on slip mesh was established.Based on boundary layer theory and spatial topological method,the flow field grid model of blade near wall was established.By y+judgment,it was confirmed that the numerical model can fully capture the flow process in the viscous bottom region.The reliability of the numerical simulation model was verified by lift coefficient curve and rotor torque analysis.(2)Aiming at the unclear aerodynamic performance of turbine failure blades,the pressure distribution in the flow field of the numerical simulation model of the failed blade under steady condition was obtained based on the Reynolds time-homogeneous turbulence model.Large eddy simulation(LES)method was used to study the pressure pulsation and eddy current phenomena under unsteady conditions,and the flow field distribution characteristics of faulty blades were analyzed.It was found that the pressure coefficient oscillates on the pressure surface and suction surface of the airfoil due to the fault,and the oscillation mainly occurs in the fault area.At high Angle of attack,the amplitude and region of oscillation gradually decrease,and flow transition or separation is more likely to occur in the airfoil fault area and the upper surface area close to the trailing edge.The failure will lead to the expansion of the maximum static pressure area at the leading edge of the blade,the decrease of the pressure difference amplitude,the severe pressure pulsation near the trailing edge,and the decrease of the aerodynamic performance of the wind turbine.(3)Aiming at the ambiguous problem of noise characteristics of wind turbine failed blades,the FW-H sound analogy method was used to solve the transient sound field data.Based on vortex-acoustic theory,the relationship between flow field and sound field of faulty blade was established,and the influence of turbine blade faults on aerodynamic noise characteristics was studied.It was found that under the condition of large Angle of attack,the unstable vortex structure in the fault area and at the front of trailing edge is the main noise source of the fault airfoil,and the noise increases in different frequency bands,especially in middle and high frequency bands.The aerodynamic noise of the faulty blade of the wind turbine presents a broadband characteristic,and the noise energy is mainly concentrated in the 400-2000Hz frequency band.The fault mainly promotes tip vortex shedding,leading to more unstable flow near the tip,and the aerodynamic noise pressure level increases significantly.