| Due to the reason of inflow wind velocity non-uniform in space and unsteady in time,with the addition of wind shear,strong turbulence,which will cause the load on the blade section changes in a random form when the wind turbine is working.Moreover,the load distribution of wind turbine blade is different under different inflow conditions,which makes the dynamic characteristics of fluid-solid interaction(FSI)of wind turbine blades become more complex and the low-frequency modes more concentration.So,it is of great significance for structural optimization design,fault diagnosis,treatment and prevention of wind turbines by studying the FSI of wind turbines blades under different inflow conditions.Therefore,based on the full-scale model of NREL 5MW wind turbine,the entry conditions of different wind shear indices were adopted and the fluctuating wind speed inlet was generated by the autoregressive linear filtration method in this paper.And then,the variation law of load characteristics,pressure,stress,strain and vibration response characteristics of blade under different inflow conditions was analyzed.The primary research projects are as follows:(1)we establish the full-scale model of NREL 5MW wind turbine,and then,we select three wind working conditions(5m/s,8m/s and 11.4m/s)to calculated thrust and torque to verified the feasibility of the discrete model by numerical simulation.In the meantime,we acquire the frequency of blade by modal analysis without prestressing,then,compared it with the results from literature to verify the reliability of the modeling and layup design of the blade structure.(2)The FSI numerically simulation of wind turbine under uniform flow condition is finished by using of delayed separation vortex-turbulence model.1)The influence of wind speed on the simulation results of wind turbine was studied.The results show that: the pressure,coverage area of the max positive pressure area,max negative pressure area and the pressure bias between pressure side and suction side of the blade were increased with the increase of the flow velocity.Besides,the max positive pressure area was diffused towards to the leading edge of the airfoil and the max negative pressure area was diffused towards to the trailing edge.Based on the above reasons,which testify that the effect of roundi ng treatment on the aerodynamic performance of the blade is small.2)By numerically method,the variation law of blade stress,strain and coupling deformation with flow ve locity were analyzed.The results show that the region of stress concentration and fatigue fracture point of the blade appear at the transition position between the root arc segment and the airfoil,which closed to the position of blade fracture in actual operation.With the increase of flow velocity,the max area of stress and the deformation amplitude of blades gradually increase,which may aggravate the fatigue failure of the blade.(3)The entry conditions of different wind shear indices were adopted.For each of the inflow cases,FSI numerical method are employed to acquire the blades surface load,pressure distribution and the variation of load with azimuth Angle.Th e numerical results show that the blade mainly bears the action of axial force,and the max fluid load of blades is mainly concentrated at the section of 85% to 90% of blades in the direction from root to top.Due to the influence of rotation,uneven distribution of flow velocity and the change of velocity profile with altitude,the pressure bias between suction side and pressure side increased with the increase of wind shear index,And the suction face pressure of the blade changed more.2)The coupled deformation,stress,strain and modal frequency of the structure under different working conditions were calculated by means of unidirectional FSI method.The results show that: the coupled deformation,stress,strain and modal frequency of the blade increase under the action of wind shear inflow.Therefore,when analyzing the FSI problem of wind turbine blades,considering the influence of wind shear can more accurately reflect the coupling effect of the fluid in the atmospheric boundary layer on the blades.(4)Based on AR linear filtration method,a type B turbulent wind field with shear and fluctuation characteristics was developed.1)Numerical simulation was conducted to compare and analyze the distribution law of surface load and pressure under different inflow conditions.The results show that the AR linear filter method is simpler and more reliable than the pre-simulation method,which can be used in our article to study the FSI characteristics of wind turbine blades under different inflow conditions.Since both wind shear and turbulence effects are considered in the turbulent wind field,so max surface pressure at the same section was accrued under the condition of type B wind field.Moreover,the leading edge of the blade is more sensitive with inflow pulsation characteristics,so under different inflow conditions,the most obvious pressure bias is consisted in the leading edge and it increases gradually along the blade span direction.2)The FSI dynamic behaviors of blade with different flow conditions were analyzed.The results have shown that: under different inflow conditions,the max coupling deformation,stress and strain of the blade were occurred in B-type turbulent wind field.In the low frequency between 0～3Hz,there are three resonant frequencies in the frequency domain response,which corresponding to the first second and third modal frequencies.And the vibration of blade is more intense at the first and thir d frequencies.It is suggested that the effective measures should be taken to avoid low freq uency resonance when we implementing optimization design of the blade. |
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