Geometric and control optimization of a two cross-flow turbine array

Scherl, Isabel; Strom, Benjamin; Brunton, Steven L.; Polagye, Brian

doi:10.1063/5.0022428

Cited by 11 publications

(9 citation statements)

References 45 publications

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“…Combining these two methods resulted in enhancing turbine performance by 24.9% for two array turbines. The successful implementation of RPM control for optimal operation of two-array VAWTs was also shown by Scherl et al [23] using experiments.…”

Section: Introductionsupporting

confidence: 52%

Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine

Jafari

Sakib

Griffith

et al. 2022

J. Phys.: Conf. Ser.

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This study focuses on wind tunnel testing of a 3-bladed H-rotor vertical axis wind turbine (VAWT) under various conditions. Different performance metrics such as power coefficient (CP ), thrust load coefficient (CX ), and lateral load coefficient (CY ) are presented at four wind speeds. Parked loads, which are key parameters in designing VAWTs, are reported for the baseline case. Apart from presenting the benchmark results for the baseline model, the impact of two control strategies to boost the energy production of the VAWT are investigated. First, the effect of installing the plasma actuators on all blades is tested at four plasma input voltages. The results indicate that plasma actuators are an efficient approach to enhance the aerodynamic efficiency of VAWTs through modification of drag and lift loads acting on the blades. The second control strategy evaluated is intracycle RPM control. In this control method, the rotational speed of the turbine is varied with the azimuthal location of blades at each cycle so that the power production is increased. The results observed for this control strategy encourage further research development to expand the limited knowledge on its application for VAWTs.

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Section: Introductionsupporting

confidence: 52%

Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine

Jafari

Sakib

Griffith

et al. 2022

J. Phys.: Conf. Ser.

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“…Finally, for a fixedwidth channel, changing D changes both the spacing between adjacent turbines as well as the proximity of the turbines at the ends of the array to the channel side walls. For proximity on the order of the blade chord length, this alters the hydrodynamic interactions between adjacent rotors [36] as well as the lateral boundary effects on array performance [28].…”

Section: Introductionmentioning

confidence: 99%

Experimental techniques for evaluating the performance of high-blockage cross-flow turbine arrays

Hunt,

Polagye

2023

Proc. EWTEC

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Cross-flow turbines show great promise for extracting power from water currents since their rectangular projected area allows them to achieve high blockage. As a turbine’s blockage ratio—the ratio of the rotor projected area to the channel cross-sectional area—increases, its efficiency and structural loading increase since both kinetic and potential energy in the freestream are converted to mechanical power. For an array of turbines deployed in a river or tidal channel, the array blockage ratio will vary due to daily or seasonal fluctuations in the water level, as well as when individual turbines are deactivated for maintenance. Consequently, understanding how the performance characteristics of the array change as confinement is varied is of practical interest. Here, we characterize the performance of a laboratory-scale two-turbine array at various levels of confinement in a recirculating water channel. The array blockage ratio was varied from 30% to 60%—the upper end of what might be realizable in a natural channel. Two experimental approaches for varying the blockage were considered: 1) altering the channel cross-sectional area via a change in water depth, and 2) altering the array projected area by changing the blade span. Across all tested blockage ratios, the nominal chord-based Reynolds number (4.0 x 104) and nominal depth-based Froude number (0.22) were held constant, and the submergence-based Froude number was minimized to avoid ventilation of the turbine rotors at the upper end of the tested blockages. At each blockage ratio, the turbine performance was evaluated across a range of tip-speed ratios under a counter-rotating, phase-locked control scheme, wherein the turbines rotate at the same, constant speed but in opposite directions, with a constant angular phase offset, Δθ, between them. We focus this work on Δθ = 0°, an operating case in which the lateral forces and reaction torques for a pair of turbines are equal and opposite, which is advantageous for support structure design. As the array blockage ratio is increased, we observe significant increases in the array performance and thrust coefficients, as well as an increase in the range of tip-speed ratios over which the array produces power. For the highest confinements, peak power coefficients exceed unity and thrust coefficients are substantially higher than in conventional array designs. We observe disparities between the power and thrust coefficients for arrays with the same blockage ratio, but different blade spans. We attribute the higher performance for longer blade spans to differences in the relative magnitude of parasitic support structure losses between the two rotors, as well as free surface effects. Further, we explore the effectiveness of techniques for accounting for these performance differences through the estimation of blade-level performance. Overall, our results provide a solid foundation for understanding how the performance of cross-flow turbine arrays change as a function of the array blockage ratio, and highlight considerations for the design of cross-flow turbine experiments.

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“…Cooke et al (2015) conducted experiments in a wide channel with porous disks to emulate turbines to explore the principles of the partial fence theory of Nishino & Willden (2012) and determined that local constructive interference effects can be used to support higher disk thrusts in closely spaced arrays, leading to greater power extraction in the case of turbines. Scherl et al (2020) performed experiments for two vertical axis turbines varying the cross-stream and streamwise inter-turbine spacing in 64 different configurations. They concluded that a cross-stream arrangement, in which turbines are arrayed co-planar, provided the best performance enhancement, with diminishing performance as the streamwise separation increased and one turbine entered the wake of the other, relaxing local blockage effects.…”

Section: Introductionmentioning

confidence: 99%

Constructive interference effects for tidal turbine arrays

et al. 2022

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The performance benefits of deploying tidal turbines in close side-by-side proximity to exploit constructive interference effects are demonstrated experimentally using two 1.2 m diameter turbines. The turbines are arrayed side-by-side at 1/4 diameter tip-to-tip spacing, and their performance compared with that of a single rotor. Tests were completed in the 25 m diameter, 2 m deep wave and current FloWave Ocean Energy Research facility. A detailed assessment of inflow conditions at different control points is used to understand the impact that rotors, designed for high blockage conditions, have on the approach flow. After accounting for global blockage, a 10.8 % uplift in the twin-turbine-averaged power coefficient, relative to that for a single turbine, is found for the turbine design speed, at the expense of a 5.2 % increase in thrust coefficient and 3.1 % increase in tip-speed-ratio. Flowfield mapping demonstrated flow effects at array and device scale including array bypass flows and jetting between turbines. Azimuthal variation of blade root flapwise and edgewise bending moments show that the turbines interact in a beneficial manner, with additional and sustained loading peaks as the blades pass in close proximity to the neighbouring rotor. Peak performance for the twin turbines occurred at a higher tip-speed-ratio than for the single turbine, which is consistent with the twin turbines exerting a higher thrust on the flow to achieve maximum power. The twin turbine performance variation with tip-speed-ratio is found to be more gradual than for the single turbine. Using differential rotor speed control we observe that array performance is robust to small differences in neighbouring rotor operating point. Through these experiments we demonstrate that there is a substantial, achievable performance benefit from closely arraying turbines for side-by-side operation and designing them for constructive interference.

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Geometric and control optimization of a two cross-flow turbine array

Cited by 11 publications

References 45 publications

Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine

Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine

Experimental techniques for evaluating the performance of high-blockage cross-flow turbine arrays

Constructive interference effects for tidal turbine arrays

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