The aerodynamics of the multi-rotor system with lifting-devices (MRSL), an innovative concept of wind energy harvesting machine, is preliminary investigated using Large Eddy Simulation (LES) with actuator techniques. In the current setup, turbulent inflow conditions are considered, but inflow wind shear is excluded. Consistent with previous studies, the results demonstrate faster wake recovery of the MRSL compared to its conventional counterpart, namely the wind turbine system without the lifting-devices. Additionally, a set of high-fidelity simulations further reveals that the enhanced wake recovery is robust under both laminar and turbulent inflow conditions, remaining largely unaffected by variations in the ambient turbulence level. The present work provides proof-of-concept evidence that the effectiveness of MRSLs is not significantly hindered by ambient turbulence, motivating future research to evaluate their performance within a realistic atmospheric boundary layer.

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.

This study presents the experimental validation of regenerative wind farms (RGWFs), a novel wind farm concept designed to enhance overall wind farm performance. RGWFs employ multi-rotor systems with lifting devices (MRSLs), an innovative wind energy harvester engineered to stimulate strong vertical energy entrainment, thereby accelerating wake recovery. In the experiments, MRSLs are scaled for wind tunnel testing, with their rotors modeled using porous disks and their lifting devices represented by wings. The tested RGWFs comprise up to 3 × 3 MRSLs. Flow quantities within RGWFs and aerodynamic loads on MRSLs are measured using volumetric particle tracking velocimetry and strain gauges. Compared to conventional wind farms, flow analysis indicates that vertical energy entrainment is significantly enhanced in RGWFs, as evidenced by a more than 200 % increase in thrust on the second-row MRSLs and so on. These experimental results, which are in line with the previous numerical predictions, highlight the promising potential of RGWFs.

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.