Modal Test Of Small Wind Turbine Blades Under Thin Ice Cover

In winter,the icing on the surface of wind turbine blades affects the structural dynamic characteristics and aerodynamic performance of wind turbine blades,so that the blades cannot work normally.In severe cases,the blades may break off,causing heavy losses to wind farms.Therefore,it is of great significance to study the structural dynamic characteristics of wind turbine blades after icing.In this paper,the small wind turbine blade as the research object,in the winter on the blades under different ice state modal test,the blade is obtained under different ice condition of the first four order vibration mode and natural frequency and damping ratio.The research results show that:(1)The effect of icing on the tip and middle of the blade on the fourth order shape is not obvious.The effect of blade root icing on the first 3 order modes is not obvious,while the 4th order node changes from torsion mode to flap-wise mode.(2)The natural frequencies of the first,second and fourth order of the blades decrease with the increase of icing thickness,while the natural frequencies of the third order of the blades increase with the increase of icing thickness.There is ice in the middle of the blade.The natural frequency of order 1 and 4 decreases with the increase of icing thickness;the natural frequency of order 2 increases with the increase of icing thickness;the natural frequency of order 3 decreases first and then increases with the increase of icing thickness.When the roots of leaves freeze,the 1st and 4th natural frequencies increase with the increase of icing thickness,while the 2nd and 3rd natural frequencies decrease with the increase of icing thickness.(2)Icing at the tip,the 1st order damping ratio first decreases and then increases with the increase of icing thickness;the second-order damping ratio decreases with the increase of icing thickness;and the third-order and fourth-order damping ratio first increases and then decreases with the increase of icing thickness.Icing in the middle of the blade,the 1st damping ratios,second and fourth orders first increased and then decreased with the increase of icing thickness,while the damping ratios of the third order increased with the increase of icing thickness.The first,second and fourth order damping ratios first increase and then decrease with the increase of icing thickness,while the third order damping ratios increase with the increase of icing thickness.