Passive flow control mechanisms with bioinspired flexible blades in cross-flow tidal turbines

Abstract

State-of-the-art technologies for wind and tidal energy exploitation focus mostly on axial turbines. However, cross-flow hydrokinetic tidal turbines possess interesting features, such as higher area-based power density in array installations and shallow water, as well as a generally simpler design. Up to now, the highly unsteady flow conditions and cyclic blade stall have hindered deployment at large scales because of the resulting low single-turbine efficiency and fatigue failure challenges. Concepts exist which overcome these drawbacks by actively controlling the flow, at the cost of increased mechatronical complexity. Here, we propose a bioinspired approach with hyperflexible turbine blades. The rotor naturally adapts to the flow through deformation, reducing flow separation and stall in a passive manner. This results in higher efficiency and increased turbine lifetime through decreased structural loads, without compromising on the simplicity of the design. Graphic abstract

Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

“…This deformation mitigates the change in loads sensed by the blades and therefore prolongs the fatigue life of the turbine. The effectiveness in load alleviation of morphing blades has been recently demonstrated [100][101][102]. Hence, it is foreseen that flexible material blades can extend the fatigue life of offshore floating VAWTs.…”

Design of a high fidelity Fluid–Structure Interaction solver using LES on unstructured grid

“…The case is inspired by the experimental work of Hoerner et al [6] to show how hyperflexible foils effectively adapt dynamically their shape and passively control the flow through deformation. The case consist to a pitched hydrofoil surrounded by a water stream.…”

“…However, Hoerner et al [5,6] showed in recent experimental studies that in the operational characteristics of a Vertical Axis Turbine (VAT), blades with high flexibility deliver significantly higher torque and can reduce structural loads, extending turbine lifetime. These potential improvements of turbine efficiency seem to be explained by the influence of the chordwise flexibility on dynamic stall which implies a drag reduction.…”

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

“…Results of Figure 9 show that the oscillating membrane has a higher impact in C D than in C L . Hence oscillating membranes could be complementary to load alleviation technology that modifies C L , for example, passive trailing edge flaps that mitigate peak loading in fluctuating flows [31,47].…”