For axial-flow turbines, passive adaptive blades designed to passively feather in response to increasing thrust have the potential to decrease peak loads without the need for active pitch mechanisms, which come at the cost of additional failure modes and system complexity. In this study, we tested a 1-meter diameter axial-flow turbine in open water with two sets of composite blades: one blade set with a bend–twist coupling and a second, neutral blade set with no bend–twist coupling for comparison. Both blade sets were tested over a range of tip-speed ratios from λ = 2 to 9, inflow speeds from 0.9 to 1.8 m/s, and yaw angles of 0°, 15°, and 25°. The neutral blades were also tested over a range of preset blade pitch angles from –3° to 20°. Testing over this wide range of operating conditions allowed us to assess the benefits of passive adaptive blades under low-frequency flow fluctuations in above-rated flow speeds (like those experienced during a tidal cycle) as well as cyclic, once-per-revolution loading. The bend–twist coupled blades were observed to achieve the same peak power coefficient as the neutral blades with a 7% reduction in thrust when operating at peak efficiency, and up to a 15% reduction in thrust at high tip-speed ratios. Interpolating across the experimental data, we simulated multiple off-design control strategies which estimate even greater load reduction potential. Further comparisons under yawed inflow are also discussed.

In 2023, a first-generation prototype of a small-scale marine current turbine was operated in Sequim Bay, Washington (USA) for 141 days. The system, referred to as the Turbine Lander, was the product of a laboratory-to-field effort to develop a system that enables enhanced ocean sensing or vehicle recharge in remote, energetic settings. The turbine consists of a vertical-axis, cantilevered rotor (1.19 m x 0.85 m) with four foils installed on a gravity foundation. A broader range of constraints including the deployment strategy, site characteristics, and estimated loads, drove the system's design. This work presents the design, characterization, operation, and post-recovery engineering assessment of the Turbine Lander. Pre-deployment characterization efforts yielded a peak power coefficient of approximately 0.3 for the rotor, although system losses resulted in much lower water-to-wire efficiencies under most operating conditions. The results demonstrate the importance of co-design among key components of the powertrain and control systems to achieve acceptable system efficiency across operating conditions.