Wind tunnel experiments of a pair of interacting vertical-axis wind turbines

Abstract

Abstract.Vertical-axis wind turbines (VAWTs) have received a renewed interest in the wind energy research community, mainly for off-shore applications. One advantage is that installing a pair of counterrotating VAWTs on the same floating platform would result in thrust reduction and potential cancellation of the mooring yaw moment. In addition, such configurations could benefit from increased power output and reduced wake losses.In this article, we report on wind tunnel experiments to study the mechanical power output of a reference VAWT scale model, tested individually and in a closely-spaced pair of VAWTs. The power output of the individual VAWT configuration is compared with a pair of VAWTs spaced 1.3 diameters apart for two counterrotating directions. A net power increase in the power coefficient for the paired configuration of up to 17.0 % compared with two individual rotors has been observed.

Numerical Analysis of Dynamic Interaction Between Two Closely Spaced Vertical Axis Wind Turbines

“…It is unclear whether this was caused by the DFBI method. The results of the present DFBI-CFD analysis differed from the experimental results of Vergaerde et al [13], where the relation CU > CD was obtained for a pair of two-bladed VAWT rotors with small solidity (the exact value is unknown). Although the experimental results using the 3D-EXP rotors (σ = 0.38) are not explained herein, the wind tunnel experiments showed the common relation CD > CU for the present numerical simulation.…”

“…The angular velocity difference Δω varied by changing the sign at an almost constant period. This phenomenon corresponds to the phase synchronization observed experimentally by Vergaerde et al [13] and Jodai et al [16,17]; to the best of our knowledge, the results shown in Figure 16 are the first reproduction of the phase synchronization of two VAWT rotors via CFD analysis. The angular velocities (ω1 and ω2) of the two rotors and the difference Δω are illustrated for the CD layout with gap/D = 0.3, as shown in Figure 18.…”

“…As mentioned above, however, phase synchronization was observed in the case of gap/D = 0.3 of the CU layout. Vergaerde et al reported the instability of phase synchronization in a CD layout compared with that in a CU layout in their experiments [13]. The difference in the torque behavior between the CD and CU layouts in the region of short gap length shown in Figures 9(b) and (c) might be ascribed to the instability of the CD layout.…”

“…However, it is important to recognize the essential difference in the manner by which vortices are shed between a solid circular cylinder and a turbine rotor comprising blades. Recently, Vergaerde et al [13] performed experiments using a closely spaced pair of straight-bladed VAWTs that mutually revolved in opposite directions in a wind tunnel and observed their phase synchronization. The first author of this paper and his colleagues have proposed a concept named "Wind Oasis" [14], which applies a wind farm comprising small-scale vertical-axis-type butterfly wind turbines (BWTs) [15] for agriculture in drylands to pump water for crops and to generate electricity for people.…”

Performance Analysis of Hydrofoil Shaped and Bi-Directional Diffusers for Cross Flow Tidal Turbines in Single and Double-Rotor Configurations

“…The cheapest way to increase the energy production is placing pairs of counter-rotating CFTs in close proximity, as proved by the experimental texts documented in [4][5][6]. A much more efficient solution to improve the power extraction of tidal, river or small wind generators is the diffuser, namely a device capable of increasing the local flow velocity at the turbine location.…”