Performance Analytical Model of Vertical Axis Wind Turbines for Floating Offshore Systems

摘要

Floating offshore wind turbine-generator systems are expected to install in areas that have very deep waters. In current demonstrating projects to commercialize floating offshore systems, conventional horizontal axis wind turbines are employed. However, vertical axis wind turbines possess great potential for floating offshore systems. This is because they excel in stability of a floating platform due to a generator and gearbox installed near its oscillation center. The present study develops a performance analytical model of vertical axis wind turbines for floating offshore systems by extending a conventional double-multiple streamtube model to inclined axis conditions. The feature of the developed model is characterized by the consideration of blow-up and blow-down behaviors of the wind after passing through the upstream blade and the inflow wind speed distribution in the downstream part due to the blow-up and blow-down winds under inclined axis conditions to the leeward and windward sides, respectively. The validity of the developed model is verified through the comparison with an wind tunnel result and calculation results using models developed in previous studies. Then, the impact of the inclined axis angle on the performances of a straight-wing vertical axis wind turbine for a floating offshore system is analyzed. The calculation result reveals the mechanism of increase in the generated power under inclined axis conditions.