Rotor Performance and Wake Interaction of Controlled Dual Surging FOWT Rotors in Tandem

Using Large Eddy Simulation (LES) with Actuator Line Model (ALM), this work investigates the system of two surging wind turbine rotors operating under realistic turbulent inflow conditions (TI = 5.3%). The two rotors are placed in tandem with a spacing of 5D and the surging motions are harmonic. A widely used torque controlling strategy, MPPT (Maximum Power Point Tracking), is implemented to ensure a maximium power extraction under all conditions. The rotor performances as well as the field data are surveyed to examine the effectiveness and impacts of the controller. It is found that the power performances of the surging rotors are benefited by the controller with a small margin (∼1%) when the surging motions are moderate. The results also show that the controller reacts much slower than the considered surging frequency, making the power performances of the rotors worse than the quasi-steady predictions (targeted values) and complicating the system dynamics. In general, the implementation of the controller has minor impacts on the wake characteristics; however, the strengths of Surging Induced Periodic Coherent Structures (SIPCS) are found to be enhanced.