Effects of aeroelasticity and wind direction on the aerodynamic characteristics and structural responses of blades for horizontal-axis wind turbines under typhoons

Flexible blades of horizontal-axis wind turbines (HAWTs) have severe aeroelastic issues under typhoons. Fluid-structure interaction studies which incorporated computational fluid dynamics (CFD) and finite element method (FEM) were conducted to investigate the effects of aeroelasticity and wind direction (B, relative to the normal of rotor's plane) on the aerodynamics and responses of blades under low-turbulence typhoons. Under the fully considered aeroelasticity, the increase in blade thrust fluctuation at B = 90 degrees was larger than those at B = 0 degrees and 180 degrees. The vortex shedding of upstream blade at B = 90 degrees increased the thrust variation of downstream blade. The flapwise thrust on Blade 3 (azimuth angle of 240 degrees, relative to the vertical direction in rotor's plane) increased by 109.30 % at B = 90 degrees under the fully considered aeroelasticity and upstream interference. Under the full consideration of aeroelasticity, the significant displacement-induced flow separation at B = 90 degrees increases the fluctuation in wind load. Large wind load variations increase aerodynamic damping, decreasing the fluctuations in blade-tip displacement (Delta) and blade-root moment (M). The decreases in Delta and M reduce the maximum stress of blade. The vortex shedding of flexible blades at B = 90 degrees increases the structural safety of HAWTs under typhoons.