Design optimisation of an offshore vertical axis wind turbine

Horizontal axis wind turbines have a number of limitations for offshore operations, particularly in deep water (i.e. over 50 m). For example, scalability restrictions, the necessity for high lift installations offshore requiring specialist vessels, high gravitational and aerodynamic moments on the support structure and a need to maintain rotary equipment at heights typically over 60–80 m. Conversely, vertical axis wind turbines have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. This paper describes the aerodynamic optimisation of a novel 10 MW vertical axis wind turbine rotor shape offering a low-stress design to minimise manufacturing and maintenance costs of the whole turbine assembly including the supporting structure and foundations. The Aerogenerator vertical axis wind turbine is self-supporting so does not require a supporting tower, giving a low centre of gravity and producing significantly lower aerodynamic over-turning moments than conventional vertical axis wind turbines or horizontal axis wind turbines, making it a credible option for a floating, deep water platform. A numerical optimisation procedure is described to minimise the Aerogenerator weight while imposing aerodynamic, mechanical and structural side constraints. The study proposes a novel ‘sycamore’-shaped rotor design that demonstrates a lower cost of energy compared with conventional offshore turbines.