Aerodynamic Design and Modeling of Large-Scale Offshore Wind Turbines

Abstract

A large-scale offshore 2 MW wind turbine designed to operate in a proposed 120-MW North Sea windfarm project is investigated in this study. The wind resources at the proposed site and the power requirements of the wind farm have been established. Preliminary sizing and conceptual design of a 2 MW wind turbine has been carried out to achieve optimum aerodynamic performance. Aerodynamic performance of the proposed design has been independently analysed by classical blade element-momentum (BEM) theory and by an in-house computational fluid dynamics (CFD) analysis. The CFD analysis has in the past been used only for small scale 10KW class turbines and required a distributed computing platform. As part of the work, this approach has been extended to large-scale wind turbine systems, and implemented in a form suitable for efficient execution on modern multi-core desktop systems with the aid of message passing interface (MPI). The tip vortex model in earlier hybrid analyses has been extended to incorporate a full span wake model. In the event of unsteady stalled flow over the rotor at high wind speeds, the present approach also captures the shed wake effects. The results from both the BEM and CFD analyses agree well with each other in terms of performance. It is found that the proposed design is efficient in terms of power generation over a broad range of wind speeds, tip speed ratios, and blade pitch settings with a maximum coefficient of power around 0.47. An economic feasibility study of the proposed offshore windfarm has also been done. The cost of energy was found to be 9.7 cents per KW-hr in 2018 dollars, which is significantly lower than the prevailing cost of 18 cents per KW-hr. It is concluded that the windfarm project is economically viable.