Abstract
With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected.
Highlights
Offshore wind, tidal and waves energies are economically and technically feasible ways of producing renewable energy and meet our sustainability targets
cross flow turbine (CFT) suffer of low starting-torque and lower efficiency respect to horizontal axis turbines, it is of great interest to find technologies to increase the production of a turbine having a certain cross-sectional area
The k-ω SST (Shear Stress Transport) model that is widely used in the simulation of wind or tidal
Summary
Tidal and waves energies are (in the order) economically and technically feasible ways of producing renewable energy and meet our sustainability targets. Tidal currents energy is characterised by predictability and low visual impact of the energy converters, and is considered one of the most favourable renewable resources in Europe. Horizontal axis or cross flow turbines (CFTs), known as vertical axis turbines, can be employed. The platform motion would negligibly affect power output, as CFTs exhibit good performance in skewed flow [1,2,3]. CFTs suffer of low starting-torque and lower efficiency respect to horizontal axis turbines, it is of great interest to find technologies to increase the production of a turbine having a certain cross-sectional area
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
