Suppression of Classical Flutter Using a 'Smart Blade'

Abstract

Future horizontal axial wind turbines that approach the 10MW capacity will have a rotor diameter somewhere in the order of 170m. Their loads could be much higher and their blades more flexible compared to current multi-MW wind turbines, most probably resulting in aeroelastic instabilities not commonly seen in the machines of today. The likely design drivers for future 10MW+ wind turbines are fatigue life and aeroelastic stability. To help improve the fatigue life and the aeroelastic stability, load control could be applied to future wind turbines. This paper concerns the load control concept of an actuated trailing edge flap (TEF), focusing on the effects they have on the aeroelastic stability of a blade. In particular, the two degree of freedom Flap-Torsion Flutter instability-Classical Flutter-is studied.

Adaptive Aeroelastic Suppression of a Wind Turbine Blade Using Trailing-edge Flap

“…The quasi-steady aerodynamic lift and moment, denoted by L and M in (1), are given as (2) where β is the flap angle of trailing-edge flap, V is free-stream wind velocity, ρ is air density, b is semi-chord, a is non-dimensional distance between mid-chord and elastic axis, C l,θ , C m,θ , lift and moment coefficients per angle of attack, can be derived from aerodynamic model and C l,β , C m,β are lift and moment coefficients per flap angle. The parameters of the system are given in Table I.…”

“…The parameters of the system are given in Table I. The structural parameters are based on airfoil NACA0012 [2].…”

“…eroelastic flutter instability has been an issue in wind turbine design with the trend of larger-capacity wind turbines with relatively flexible blades [1,2]. Large-sized blades produce bending and twisting, which again affect the aerodynamic forces by changing angle of attack, so as to make structural damping insufficient to damp the vibrations induced by aerodynamic loads when flutter occurs.…”

Flutter performance of large-scale wind turbine blade with shallow-angled skins

“…Upon reaching the flutter limit, however, the vibrations start to grow exponentially in the amplitude. Beyond the flutter limit, the blade response becomes unstable because of negative aero-elastic damping, and high-amplitude vibrations become self-exciting and sustainable, subsequently, leading to rapid structure failure [6,[14][15][16].…”

Aeroelastic Control of Wind Turbine Blade Using Trailing-Edge Flap

“…Aeroelastic flutter instability has been an issue in wind turbine design with the trend of largercapacity wind turbine and relatively flexible blades [1][2]. Large-sized blade produces bending and twisting, which again affect the aerodynamic forces by changing of angle of attack, so as to make structural damping insufficient to damp the vibrations induced by aerodynamic loads when flutter occurs.…”