Finding the optimal soft material for the blades to improve wind turbine versatility.*

Although pitch angle control enlarges the working range of Horizontal Axis Wind Turbine (HAWT), this active method is expensive, energy consuming and requires maintenance. Passive pitch control, using soft materials for the blades, proposes an interesting alternative.

It has been shown that reconfiguration of flexible blades with respect to tip speed ratio λ is governed by three dimensionless numbers: the initial pitch angle θ₀, the Cauchy number C_Y (ratio between aerodynamic forces on the blade and elastic returning force), and the centrifugal number C_C (ratio between centrifugal force and elastic returning force) [1].

In this presentation, we introduce a new procedure which finds the optimal set (θ₀, C_Y, C_C)^opt corresponding to the soft materials able to passively reproduce the optimal deformation of the blade (ie the optimal variation of pitch angle θ with respect to λ) [2]. The procedure integrates BEM theory and works for constant wind velocity U, for constant angular velocity Ω, for constant resistive torque C, and for a torque proportional to angular velocity.

[1] V. Cognet et al. 2017. Bioinspired turbine blades offer new perspective for wind energy

[2] V. Cognet et al. 2017. Deformable blades to optimize rotors efficiency (Patent)