(c) Coria

The facts & the project

With seas and oceans accounting for 71% of the surface of the planet, marine energy sources represent a potential future solution for the generation of “clean” electricity. Offshore wind turbines are an example of this, located at sea on anchored or floating platforms to best capture and convert wind energy. Just like the land-based ones, most of these wind turbines operate on the horizontal axis and rotate slowly, at fewer than 10 revolutions a minute, for the largest of these.

The floating vertical axis offshore wind turbine, an innovation developed by the French company, Nenuphar, with the support of Bpifrance, Areva Wind and EDF-EN, offers a highly promising alternative: Using blades with a variable wind-determined pitch, it can capture the wind from any direction and is not overly sensitive to swell - which should help increase its efficiency and the stability of installation.

This innovative concept however encountered a major problem: Dynamic stalling, which occurs when the speed of the wind turbine blades gets close to that of the incident wind and results in the generation of numbers of vortices that perturb the performance of the whole unit. And this is where Ghislain Lartigue and Vincent Moureau, researchers at Coria and specialists in high resolution simulation of subsonic flows, came in.

The results

They were responsible for conducting Large-Eddy Simulations, using the YALES2 code and 2.5 million hours, to reach a better understanding and mastery of this phenomenon that can lead to significant fatigue in the structures and thus reduce the working life of the turbine.

First simulations ever run with a 2.4 billion element mesh and a resolution size of 2.5 cm (the wind turbine is 30 meters high), they led the scientists to reproduce, as closely as possible, the phenomenon and its impacts, in particular on the rotor wake generated by the wind turbine.