Wake interaction of dual surging FOWT rotors in tandem

To investigate the wake interaction between floating offshore wind turbines (FOWTs), this work presents large eddy simulations of two full-scale surging FOWT rotors in tandem. Rotors are modeled using actuator line technique with the possibility of prescribing surge degree-of-freedom. The study examines two main aspects: the different configurations of fixed and surging rotors, and the phase differences of surging motions when both upstream and downstream rotors are surging. Throughout the simulations, different spacings between the two rotors and different inflow conditions (laminar/turbulent) are explored, leading to a large database of highly resolved simulations. The analysis of different fixed-surging configurations suggests that surging motions are generally beneficial to the system’s power output (up to 2% at realistic turbulence intensities) compared to the fixed configuration. The power output increase is claimed to be associated with the surging motion itself and the faster wake recovery. Moreover, we discover that the phase differences of the surging motions have subtle effects on the rotor performance of the downstream rotor, especially for the cases with larger spacing between the two surging FOWTs. As an outcome, the relative difference between the power outputs are smaller than 0.4% when the rotor spacing is five rotor diameters. With the aim that this area can be further explored, selected animations, benchmark data, and the numerical solver developed during this study have been made publicly available through this article. • High fidelity CFD model to study the wake interaction of two moving wind turbine rotors in tandem is investigated. The corresponding source code and simulation data are made publicly available. • Effects of surging motion on the wake interaction are thoroughly explored with all four combinations of surging and fixed rotors. • Surging motion of the upstream rotor has positive impacts on both the power performance of the upstream and downstream rotors when the system is subjected to both laminar and turbulent inflows. • Identifying and quantifying the effects of the phase differences between the two surging motions of the two FOWTs rotor. Results show they are insignificant (the relative varying extents are less than 1%) and become even less with larger spacings.