Aerodynamic Modeling of Offshore Vertical Axis Wind Turbines using the Actuator Cylinder Method

Abstract

Recently the interest in developing vertical axis wind turbines (VAWTs) for offshore application has been increasing. Among the aerodynamic models of VAWTs, double multi-streamtube (DMST) and actuator cylinder (AC) models are two favorable methods for fully coupled modeling and dynamic analysis of floating VAWTs in view of accuracy and computational cost. This paper deals with the development of an aerodynamic code to model floating VAWTs using the AC method developed by Madsen. It includes the tangential load term when calculating induced velocities, addresses two different approaches to calculate the normal and tangential loads acting on the rotor, and proposes a new modified linear solution to correct the linear solution. The effect of dynamic stall is also considered using the Beddoes-Leishman dynamic stall model. The developed code is verified to be accurate by a series of comparisons against other numerical models and experimental results. It is found that the effect of including the tangential load term when calculating induced velocities on the aerodynamic loads is very small. The proposed new modified linear solution can improve the power performance compared with the experiment data. Finally, a comparison of the developed AC method and the DMST method is performed using two rotors and shows that the AC method can predict more accurate aerodynamic loads and power than the DMST method, at least for the considered rotors.