Development of a multi rotor floating offshore system based on vertical axis wind turbines

Abstract

The upscaling of wind turbines results in fewer units per installed MW reducing infrastructure and maintenance costs of offshore wind farms. Multi rotor systems (MRS), comprising many wind turbine rotors on a single support structure, are potentially a means to maximize the upscaling benefit in achieving larger unit capacities than is feasible or economic with the conventional, 3-bladed horizontal axis wind turbine (HAWT). The MRS has an inherent upscaling advantage which, for a system with many rotors compared to a single rotor, reduces the total weight and cost of rotor-nacelle assemblies by a large factor. An innovative MRS design is presented based on vertical axis wind turbine (VAWT) rotors of the 2-bladed, H-type. Many disadvantages of VAWT design compared to HAWT in a single rotor system (reduced power performance and higher drive train torque, for example) are resolved in the MRS configuration. In addition, reduced component number and simpler components is advantageous for reliability and O&M cost. This MRS concept has many synergies arising from the choice of VAWT rotors. Results comprise a high-level evaluation of system characteristics and the first stage of more detailed investigation of aerodynamics of the high aspect ratio VAWT.

Lift-Induced Wake Re-Energization for a VAWT-Based Multi-Rotor System

“…From this table, it becomes evident that the wake region behind the MRS with wings recovers faster than the baseline con guration, as ū3 U 3 is larger at all three downstream locations. Furthermore, a large enhancement in wake recovery is found from x/D=1.5 to x/D=2.0 for the MRS con guration with wings as ū3 U 3 Wing recovers in this region from 0.36 to 0.49 compared to 0.33 to 0.34 for the MRS without wings. This enhanced recovery is attributed to the increased advection in the wake region of the MRS with wings.…”

“…For the experiment, a scaled VAWT-based Multi-Rotor System following a simpli ed design of Jamieson et al [3] was developed. In Figure 1 a sketch of the model and its main dimensions is shown.…”

“…Each individual VAWT rotor follows the design of Huang et al [12], having a diameter of d = 0.3m, and a height of h = 0.3m, with NACA0012 blades of chord c = 0.03m. Additionally, the rotors on each shaft are staggered 45 to each other to ensure a smooth, 8-phase torque input, in line with the work of Jamieson et al [3], and actively powered by a single Maxon DC motor. The two rotors on the left rotate in the clockwise direction and the two rotors on the right rotate counterclockwise when seen from the top.…”

“…While the concept of an MRS comprising HAWTs is not novel [2], its realization with Vertical Axis Wind Turbines (VAWTs) is innovative. Recent investigations into a VAWT-based MRS have shown remarkable potential, demonstrating power performance on par with large HAWTs, while simultaneously enhancing Operations and Maintenance (O&M) aspects [3]. However, despite the promise of this novel concept, the understanding of the wake structure within such systems remains limited, particularly concerning its implications for wind farm applications.…”

Wind-Tunnel Experiments on the Interactions among a Pair/Trio of Closely Spaced Vertical-Axis Wind Turbines

“…This interference between a trio and the other trios is essential for future research on the design of an optimal layout of the three-turbine array or multi rotor systems with very many rotors (e.g., [27]).…”