A synchronization phenomenon of two closely spaced vertical axis wind turbines and the mathematical analysis

Hara, Yutaka; Furukawa, Masato; Jodai, Yoshifumi; Okinaga, Tomoyuki; Sogo, Yuki

doi:10.1299/jsmefed.2020.os09-10

Cited by 3 publications

(12 citation statements)

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“…Last, in the CD configuration presented in Figure 8c, both Rotor 1 and 2 demonstrate a significant increase in the rotational speed with a decrease in gap until the smallest gap tested is reached. The most interesting finding is the "phase-synchronized rotation" (Jodai et al [19]; Hara et al [20]; Hara and Jodai [21]) between both rotors when the gap is equal to or less than 15 mm (g/D ≤ 0.3), as a result of the dynamic interaction between VAWTs. The synchronized rotation has also been reported by Vergaerde et al [15] based on an experiment at g/D = 0.3 using two-bladed Darrieus turbines with NACA 0018 airfoil.…”

Section: Rotational Speeds and Power Of Closely Spaced Vawtsmentioning

confidence: 99%

Wind Tunnel Experiments on Interaction between Two Closely Spaced Vertical-Axis Wind Turbines in Side-by-Side Arrangement

Jodai

Hara

2021

Energies

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This study aimed to determine the optimal rotor spacing of two vertical-axis wind turbines, which are simulated by miniature models arranged side-by-side with a relatively low aspect ratio. Wind tunnel experiments with a pair of 3-D printed model rotors were conducted at a uniform velocity. A series of experiments were conducted involving both incremental adjustments to the rotor gaps, g, and the rotational direction of each rotor. Increases in the power and the related flow patterns were observed in all three arrangements: Co-Rotating (CO), Counter-Up (CU), and Counter-Down (CD). The maximum phase-synchronized rotational speed occurs at the narrowest gap in the CD arrangement. Meanwhile, local maxima arise in the CO and CU arrangements at g/D < 1, where D is the rotor diameter. From an engineering perspective, the optimal rotor spacing is g/D = 0.2 with the CO arrangement, using the same two rotors rotating in the same direction. Based on flow visualization using a smoke-wire method at a narrower gap opening of 0.2D, the wake width in the case of the CU arrangement was remarkably narrower than those obtained in the CO and CD arrangements. In the CU arrangement, a movement towards the center of the rotor pair of the nominal front-stagnation point of each rotor was confirmed via flow visualization. This finding explains a reduction tendency in the rotational speed of the rotors via a reduction in the lift in the CU arrangement.

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Section: Rotational Speeds and Power Of Closely Spaced Vawtsmentioning

confidence: 99%

Wind Tunnel Experiments on Interaction between Two Closely Spaced Vertical-Axis Wind Turbines in Side-by-Side Arrangement

Jodai

Hara

2021

Energies

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“…This CFD analysis using the DFBI is equivalent to experiments involving variable-speed wind turbines. Although some of the results have been reported in several oral presentations [20][21][22][23] and in a commentary article [15], they are integrated herein and new considerations and results are included; furthermore, the calculation times of some cases were prolonged until the rotor angular velocities converged within the new criteria. The details of the revised data acquisition are explained in the following section.…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis of the Dynamic Interaction between Two Closely Spaced Vertical-Axis Wind Turbines

et al. 2021

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To investigate the optimum layouts of small vertical-axis wind turbines, a two-dimensional analysis of dynamic fluid body interaction is performed via computational fluid dynamics for a rotor pair in various configurations. The rotational speed of each turbine rotor (diameter: D = 50 mm) varies based on the equation of motion. First, the dependence of rotor performance on the gap distance (gap) between two rotors is investigated. For parallel layouts, counter-down (CD) layouts with blades moving downwind in the gap region yield a higher mean power than counter-up (CU) layouts with blades moving upwind in the gap region. CD layouts with gap/D = 0.5–1.0 yield a maximum average power that is 23% higher than that of an isolated single rotor. Assuming isotropic bidirectional wind speed, co-rotating (CO) layouts with the same rotational direction are superior to the combination of CD and CU layouts regardless of the gap distance. For tandem layouts, the inverse-rotation (IR) configuration shows an earlier wake recovery than the CO configuration. For 16-wind-direction layouts, both the IR and CO configurations indicate similar power distribution at gap/D = 2.0. For the first time, this study demonstrates the phase synchronization of two rotors via numerical simulation.

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“…where c 1 and c 2 are constants. As shown in Appendix A, we chose these expressions by observing the CFD [13,14], as well as the experimental [7,8] data. The actual values used in our simulation are given in the next section.…”

Section: Modelmentioning

confidence: 99%

“…VAWTs accept wind from all directions; thus, it is possible to place them in proximity to each other. In order to investigate the performance and characteristics of such closely spaced VAWTs, wind tunnel experiments [3][4][5][6][7][8] and computational fluid dynamics (CFD) simulations of a pair of VAWTs were performed in two dimensions [9][10][11][12][13][14], as well as in three dimensions [6,15].…”

Section: Introductionmentioning

confidence: 99%

“…Hara et al performed a two-dimensional CFD analysis [13,14] to simulate the experiments by Jodai et al They adopted a dynamic fluid-body interaction (DFBI) model that enabled the angular velocities of the rotors to change dynamically. The simulation results showed that phase synchronization also occurred in the CFD analysis for both the CD and CU layouts.…”

Section: Introductionmentioning

confidence: 99%

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Analytical Model for Phase Synchronization of a Pair of Vertical-Axis Wind Turbines

2022

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The phase-synchronized rotation of a pair of closely spaced vertical-axis wind turbines has been found in wind tunnel experiments and computational fluid dynamics (CFD) simulations. During phase synchronization, the two wind turbine rotors rotate inversely at the same mean angular velocity. The blades of the two rotors pass through the gap between the turbines almost simultaneously, while the angular velocities oscillate with a small amplitude. A pressure drop in the gap region, explained by Bernoulli’s law, has been proposed to generate the interaction torque required for phase synchronization. In this study, an analytical model of the interaction torques was developed. In our simulations using the model, (i) phase synchronization occurred, (ii) the angular velocities of the rotors oscillated during the phase synchronization, and (iii) the oscillation period became shorter and the amplitude became larger as the interaction became stronger. These observations agree qualitatively with the experiments and CFD simulations. Phase synchronization was found to occur even for a pair of rotors with slightly different torque characteristics. Our simulation also shows that the induced flow velocities influence the dependence of the angular velocities during phase synchronization on the rotation directions of the rotors and the distance between the rotors.

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A synchronization phenomenon of two closely spaced vertical axis wind turbines and the mathematical analysis

Cited by 3 publications

References 0 publications

Wind Tunnel Experiments on Interaction between Two Closely Spaced Vertical-Axis Wind Turbines in Side-by-Side Arrangement

Wind Tunnel Experiments on Interaction between Two Closely Spaced Vertical-Axis Wind Turbines in Side-by-Side Arrangement

Numerical Analysis of the Dynamic Interaction between Two Closely Spaced Vertical-Axis Wind Turbines

Analytical Model for Phase Synchronization of a Pair of Vertical-Axis Wind Turbines

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