A Study of Hydraulically Actuated Oscillating Pitch to Increase Energy Production in Wind Turbines

Abstract

The focus of this paper is to oscillate the pitch of the wind turbine blades using hydraulic actuation to increase the power captured by a hydrostatic wind turbine. This is based on the fact that oscillating an airfoil under specific conditions increases the instantaneous lift coefficient by up to 97%. Different conditions were investigated by varying airfoil shape, waveform shape, waveform amplitude, waveform frequency and average angle of attack. The following conditions were found to give the best performance: a low camber airfoil, a lower average angle of attack than used for a non-oscillating airfoil, and an optimized waveform shape called a “tilted sinusoid.” A multi-level factorial experiment determined the most impactful variables were frequency, amplitude, and average angle of the tilted sinusoid. The best frequencies and amplitudes were studied through numerical simulations and hill climbing optimization. Results showed that oscillating the pitch of the wind turbine blades would, under all conditions tested, never outperform steady-state turbine operation, the main reason being the higher drag coefficients that are also present when oscillating the pitch of the blade.