Performance Improvement of a Darrieus Tidal Turbine with Active Variable Pitch

Pierre-Luc Delafin,François Deniset,Frédéric Hauville,Jacques André Astolfi

doi:10.3390/en14030667

Abstract

Vertical axis turbines, also called Darrieus turbines, present interesting characteristics for offshore wind and tidal applications but suffer from vibrations and a lower efficiency than the more conventional horizontal axis turbines. The use of variable pitch, in order to control the angle of attack of the blades continuously during their rotation, is considered in this study to overcome these problems. 2D blade-resolved unsteady Reynolds-Averaged Navier–Stokes (RANS) simulations are employed to evaluate the performance improvement that pitching blades can bring to the optimal performance of a three-straight-blade vertical axis tidal turbine. Three pitching laws are defined and tested. They aim to reduce the angle of attack of the blades in the upstream half of the turbine. No pitching motion is used in the downstream half. The streamwise velocity, monitored at the center of the turbine, together with the measurement of the blades’ angle of attack help show the effectiveness of the proposed pitching laws. The decrease in the angle of attack in the upstream half of a revolution leads to a significant increase in the power coefficient (+40%) and to a better balance of the torque generated in the upstream and downstream halves. Both torque and thrust ripples are therefore significantly reduced.

Highlights

The installed capacity of renewable energy in the world has been increasing continuously over the past fifteen years [1,2]
(6◦, 8◦ or 10◦, as defined by Equation (4)) while traveling through the upstream half, the blade pitches to maintain the target value until the azimuthal angle where the angle of attack (as defined by Equation (4)) becomes lower than the target value (Figure 10a). Those pitching laws are based on the simplified angle of attack defined by Equation (4), which is considered valid as we focus on the upstream half only
The three pitching laws proposed lead to a significant increase in power coefficient, with PL2 performing the best (+40.9% compared to the fixed pitch case)

Summary

Introduction

The installed capacity of renewable energy in the world has been increasing continuously over the past fifteen years [1,2]. The will to find energy sources available on a long-term basis with stable costs and lower atmospheric pollutant emissions has led to a growing interest in renewable energies like solar photovoltaics (PV), wind turbines, and biomass (hydro-power was already well developed). Onshore wind and solar PV represent currently the largest additions of installed capacity per year (+60 GW and +115 GW, respectively, in 2019) and are forecast to lead the capacity growth until 2025 at least [1,3]. Ocean power consists in only 535 MW of installed capacity at the end of 2019 with an addition of 3 MW during the year [1]. Research is necessary to help with the development of this source of energy

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Conclusion