Investigate On The Structural Dynamic Characteristics Of Wind Turbine Composite Blade

As the most efficient mode of wind energy utilization,wind power plays an essential role in achieving carbon peak and carbon mitigation goals.The structure of flats,flexible,long spreading direction and chord direction short large wind turbine blade,under the time-varying load and strong wind gust impact effect,easy to cause collapse damage,so the composite blade static dynamic characteristics of higher requirements.Therefore,this work is funded by the National Natural Science Foundation of China "Research on the degradation mechanism of wind turbine blade structure performance with variable stiffness under typical wind resource environment in Northwest China(No.51965034)",and takes 5 MW horizontal axis wind turbine blade as the research object to study the structural dynamics of composite wind turbine blade.The work is carried out to investigate the blade lay-up scheme through the composite structure theory.On this basis,the static response and structural dynamics of the composite blade are investigated by the finite element method.The main research contents and research results are as follows:(1)The computational domain for the numerical simulation of the blade aerodynamics is constructed,and the reasonable mesh size is determined through the verification of mesh irrelevance to investigate the aerodynamic characteristics of the blade at different wind speeds and to solve the pressure-load distribution on the blade surface at the rated working condition of 11.4m/s.Firstly,construct the computational domain required for the numerical simulation calculation.Then,the calculation domain is meshed according to the grid size from small to large,and the most suitable number of grids for numerical calculation is 45.72 million by calculating the wind turbine output power for different numbers of grids.Finally,the thrust and torque of the blade are calculated to verify the accuracy of the blade aerodynamic numerical calculation model,and the velocity of the wake velocity and the pressure load on the blade surface is studied to obtain the flow characteristics of the airflow on the blade surface and the velocity distribution of the wake velocity and the pressure load on the blade surface at the wind speed of 11.4m/s.(2)The finite element model of the composite blade is constructed and the static response characteristics are investigated.Firstly,according to the composite blade structure theory and German Lloyd’s Register(GL)standards for blade certification,the blade lay-up scheme is conducted to determine the number of layers and lay-up angle of the composite blade,and the finite element modeling of the 5MW horizontal axis wind turbine blade is completed with the ACP module.Then,the blade surface pressure distribution at the rated working condition of 11.4m/s is loaded,and the static response of the blade in the rated working condition is examined according to the basic principles of statics,to explore the blade deformation and stress-strain distribution at this working condition.The research results show that the rated working condition blade deformation maximum place is located in the blade tip,the total deformation is2533 mm,not more than the lowest place when the wind turbine is stationary blade tip and tower barrel horizontal distance of 70%.And the blade equivalent force maximum position is located in the blade suction surface from the blade root 32250 mm,its value is 256 MPa,far less than the blade laying material allowable stress 1546 MPa,which meets the blade structure strength requirements.(3)The structural dynamics of the composite blade are researched.Firstly,based on the finite element model of the composite blade,the first six orders of the blade modalities are calculated by the Block Lanczos method,and the first six order vibration frequencies and corresponding modal vibration modes of the blade are obtained.Solve the blade vibration frequencies at different rotational speeds,and investigate the change of blade inherent frequency when the blade rotational speed increases.By calculating the blade’s inherent frequency,obtain the blade vibration Campbell diagram and evaluate whether the blade resonates in the actual operation process.Secondly,according to the modal analysis of the composite blade,the harmonic response characteristics of the blade are researched by using the modal superposition method.Finally,based on the results of the static analysis,the finite element method is applied to conduct a flexural stability analysis of the blade.The results show that the blade’s first-order intrinsic frequency is 0.887 Hz,the blade’s first six-order mode vibration patterns are first-order flatwise bending,first-order edgewise bending,second-order flatwise bending,second-order edgewise bending,third-order flatwise bending and third-order edgewise bending,and its torsional vibration doesn’t occur,indicating that the blade has excellent torsional resistance.The centrifugal force when the blade rotates makes the first six orders of the blade inherent frequency increase,including the first order of the blade inherent frequency increasing up to 3.6%,and the sixth order of the blade inherent frequency is only increased by 0.44%.The blade in the actual operation of the first order inherent frequency is higher than the blade rotation frequency 1P and 3P for 77.5% and 32.5% and doesn’t occur in resonance.The blade vibration frequency is 1.06 Hz and 5.86 Hz which is easy to appear as a hyper harmonic vibration phenomenon should make the blade operation stagger the frequency.The blade’s first-order buckling factor is 1.271,indicating that the blade’s critical load value is greater than the blade by the load,and the possibility of buckling is relatively small.