Vortex method based on the potential theory is applied to unsteady aerodynamic modeling of co-axial dual-rotor wind turbines（DRWT）. In the model, the lifting surface method is used to calculate the blade circulation, and the free vortex wake model is used to calculate wake skewness, aerodynamic load and wake of front and rear wind turbine blades are coupled through the induced velocity. Two NREL 5 MW wind turbines are axial-linked as the reference DRWT, with two rotors rotating at the same speed and opposite directions. Power output is calculated under various rotation speeds to analyze period-averaged and dynamic characteristics. The results indicate that the optimal power coefficient of DRWT is 34% higher than SRWT, and decreases at high rotation speeds. Power of DRWT fluctuates periodically. Front and rear rotors interfere each other by blade induction, and wake of front rotor affects rear rotor, resulting in significant power troughs.
Key words
wind turbines /
dual-rotor /
vortex method /
power characteristic /
aerodynamic interference
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