De-risking hydrokinetic turbine projects by towing tank tests

The initial deployment of full-scale prototypes in the real environment represents the most critical phase gate in the development of offshore renewable energy systems. Operating conditions and key device components that could not be tested at model scale or adequately simulated by digital models often hold unforeseen problems with project delays and additional costs. Large basins and towing tank infrastructures offer a suitable environment where near to full-scale devices can be tested in repeatable and controlled conditions to de-risk system deployment in the real operating environment. In the tidal energy sector, an example of towing tank tests bridging the gap between model-scale experiments and sea trials has been undertaken in the EU-funded CRIMSON project (2021-2024). Aim of the project was to develop and demonstrate innovative solutions to increase the efficiency and reduce the LCoE of hydrokinetic turbines. The reference technology in the project was the RivGen Power System by ORPC, a TRL 8 crossflow turbine for riverine installations, also convenient for shallow water marine sites. In the proposed paper, the results of operational trails of the CRIMSON turbine will be presented. The fully equipped turbine had a 3-bladed, 1.8m diameter rotor with a 9m2 capture area. The activity was carried out at the large calm water towing tank at CNR-INM, one of the largest globally for research on marine renewable systems. Demonstration tests provided a comprehensive characterization of turbine performance and response of key system components (shaft bearings, composite foils and struts) over a full TSR range and flow speed from 1.0 to 2.25 m/s. The turbine was equipped with sensors to characterize the hydrodynamic performance (mechanical torque and power) and the efficiency of electrical power generation. An advanced fiber-optics strain sensors technology to measure strain on the blades was implemented and its application to foil structural monitoring equipment in real conditions was investigated. The hydrodynamic perturbation induced by the turbine in the confined-flow condition was characterized by Pitot velocimeters and ultra-sound wave probes. Considering the large hydrodynamic forces generated by the full-scale turbine, special attention was given to safety of operations. The loadings and vibrations transmitted from the rotor to the supporting frames and to the towing carriage were measured by load cells and accelerometers. Results allowed to validate the structural response of turbine and test-rig components predicted in the design-of-experiment phase by finite element analysis, with turbine loadings estimated by CFD. Part of the experimental dataset developed in the project is published on SEANOE for open access.