| Wind energy has broad prospects for development and utilization as an abundant and clean renewable energy source.Wind power is rapidly developing as an important method of wind energy utilization.However,as for the key wind energy absorption component of wind turbine,the blades operating in cold conditions face icing problems.Coupling with aerodynamic,elastic and inertial forces,blade icing influences its aerodynamic performance and service life directly.Therefore,the blade of a 1.5 MW horizontal axis wind turbine in a Hexi wind farm is selected as the research object,and then the dynamic effects of ice accretion on blade is studied and explored.The specific content and the obtained research conclusions are as follows:(1)The effect of ice accretion on the aerodynamic performance of the blade.The icing morphology of the airfoil at the cross section of r/R=0.8 under different conditions was predicted in rated operating condition.The lift and drag coefficients of the iced airfoil at multiple attack angles were solved quantitatively.Combined with the velocity distribution of the airflow around the airfoil,the stalling law of the iced airfoil was investigated.The results show that the ice accretion of the blade decrease the lift coefficient and increase the drag coefficient.The lift coefficient of the numerical simulation is reduced by up to 20%,and the drag coefficient is increased by 2.45 times of clean airfoil.Ice accretion changes the profile of the airfoil and causes the airfoil to enter a stall state in advance.Under the same conditions,the glaze icing enters the stall state earlier than the rime icing.(2)The effect of ice accretion on blade loading.The inflow parameters of 28 sections and the ice mass distribution of the blade for two hours were accurately calculated in rated operating condition.Combined with the wind resource model of a wind field in Hexi Corridor,the steady-state load before and after the blade icing were calculated.The results show that the ice mass of a single blade in two hours is only 156 kg,which is an augment of 2.5% relative to the mass of the blade.The ice accretion increases the load on the blade.The shear forces at the root of iced blade were boosted by 0.93%,1.02% in flapping and swing directions,respectively.The flapping moment at the root of iced blade decreased by 0.1%,and the swing moment escalated by 1.53%.(3)Finite element modeling for quasi-three-dimensional ice accretion of rotating blade and research on the static characteristics of the blade before and after icing.With the support of the ACP module of the finite element software ANSYS-Workbench,the finite element model of composite blade and the quasi-three-dimensional ice accretion finite element model of rotating blade in rated working condition were constructed,respectively.The complex loads on blade surface were converted into concentrated forces and coupled to the torsional center of the blade element,meanwhile,the stress and strain contours of the blade before and after icing were computed.The results show that the accreted ice on blade aggrandizes the stiffness of the entire blade and results in a reduction of the maximum tip displacement of 65%.Meanwhile,it is easy to cause stress concentration in the bonded part of the ice body and the leading edge of the blade due to the irregularity of the ice body and the adhesion between the blade.(4)Based on the finite element model,quantitatively,the first 6 natural frequencies and mode shapes of the blade were calculated without prestress when influenced by ice mass or by ice mass and stiffness together.Considering the effect of prestress,the modal frequencies of the ice-free and iced blade at different angular velocity were calculated,and then the influence of the angular velocity on the natural frequency of the blade was investigated.The results show that assuming the influence of ice mass only is considered and without the prestress,the maximum reduction of the first-order flapping frequency is about 12.5%,which indicates that ice accretion will increase the probability of blade resonance under the complex loading.If the combined influence of ice mass and stiffness is considered together,the maximum increase of the first-order flapping frequency is about 9.0%,which indicates that the stiffness of the ice body can greatly reduce the decrease amplitude of the blade natural frequency due to the increase of ice mass.The natural frequency of the blade will be kept away from the resonance frequency and is beneficial to the safe operation of wind turbine.The natural frequency of the blade increases with the escalation of the wind wheel angular velocity,which indicates that the pre-stress can aggrandize the entire stiffness of the blade,and then affect the natural frequency of the blade.The project has certain reference value for the design and development of antiicing systems for wind turbine blades in cold regions. |
PDF Full Text Request