Classical BEM Analysis with CFD Simulation of Large Vertical Wind Turbine

The aerodynamic characteristics of vertical axis wind turbines (VAWTs) are determined by the complex interactions between the flow and the turbine blades. The complication mainly arises from the change of angle of attack, and Reynolds number of the blade airfoil during rotation and this leads to transient periodic aerodynamic forces on the blade. In this study, we analyze the torque and power output of large-scale wind turbines by using both the blade element method (BEM) and the numerical simulation. The aim is to determine the range of the tip speed ratio (TSR) in which the two methods agree. The parameters of calculations include TSR from 3 to 6, the number of blades from 2 to 4, and the solidity ratio (1/30 1/45 1/60). We found that the maximum power can be obtained around TSR=4. The turbine with two or three blades has the optimal power efficiency. When the solidity is smaller than 1/45, the numerical result and the BEM analysis are similar. Therefore, BEM is appropriate for prediction of large-scale, low solidity VAWTs.