Mitigation of rotor thrust fluctuations through passive pitch

Model-scale experiments of passive pitch control for tidal turbines

“…It is therefore likely that simple modifications to existing low-order codes have the potential to dramatically improve the accuracy of their results. Moreover, these results show that the performance of a passive pitch system can be realistically improved to achieve results more similar to those of either CFD simulations (Dai et al, 2022) or low-order models (Pisetta et al, 2022) by minimising the friction around the pitching shaft. The results also show that a careful estimate of the preload moment provided by the pitching spring can decrease the thrust and the root-bending moment generated by the turbine without affecting the power generated by the turbine considerably.…”

“…Two main phenomena that have affected the results here presented were not forecast when developing the low-order code of Pisetta et al (2022): these are the friction generated by the bearings and the pitching spring, and the uncertainty in the average pitching angle whose effects on the mean loads was discussed in the last paragraph. Neither of these effects were present in the simulations of Dai et al (2022), which have modelled a similar tidal turbine in a similar inflow. In this work, the authors have indeed found a reduction in the unsteady thrust generated by the tidal turbine of 75 % in the worst-case scenario, a value that is compatible with the results of the reduced-order approach.…”

“…They verified that a flap with a hinge at 25% of the chord allows a 25% reduction of the unsteady loading. These results further motivated the numerical studies of Dai et al (2022) on the passive pitch of rigid blades, a mechanism that could theoretically lead to the total cancellation of the unsteady loads. Using computational fluid dynamics simulations of a turbine in a sheared current, the authors found that a turbine equipped with passively pitching blades experiences a reduction in the unsteady thrust of approximately 80 %, with no effect on its time-average value.…”

“…The authors however note that their results have neglected the effects of friction on the pitching motion on the turbine, and they stress the need to verify whether this assumption is practically achievable. The present paper is based on the previous works of Viola et al (2021Viola et al ( , 2022b; Pisetta et al (2022) and Dai et al (2022), and aims to demonstrate with physical experiments on a model scale turbine the unsteady load reduction potential of passively pitching rigid blades. Measurements of the instantaneous torque, thrust, and root-bending moment are provided for a range of tip speed ratios, and the effect of friction on the pitching motion is carefully analysed.…”

Control Strategies for Power Enhancement and Fatigue Damage Mitigation of Wave Cycloidal Rotors

“…Additionally, passive morphing foils are another appealing potential technological enhancement for cyclorotors. Foils that morph due to fluid forces have shown to reduce loading in cross flow [5,8,31,32] and tidal turbines [8,17,41], but a study on morphing foils remains to be reported in the literature of cyclorotors. We note that most of these studies represent a morphing foil through a passive pitching mechanism [41],…”