Experimental investigation of the wake characteristics behind twin vertical axis turbines

Müller, Stephanie; Muhawenimana, Valentine; Wilson, Catherine; Ouro, Pablo

doi:10.1016/j.enconman.2021.114768

Cited by 28 publications

(19 citation statements)

References 34 publications

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“…We note that the VAWT wind farm would still outperform the HAWT wind farm by 30% if the downwind direction was increased to 8D [49]. Furthermore, downwind spacing could be decreased to 5D if counter-rotation was to be employed [46]. This would automatically double ρ WF due to the pairs of turbines working at every node of the wind farm.…”

Section: Wind Farm Power Densitymentioning

confidence: 97%

“…Wind farm power density (ρ WF ) is a metric that quantifies how much power per square metre a wind farm produces. VAWTs can be placed next to each other in counter-rotation in the crosswind direction [46], whilst in the downwind direction a spacing between 4 to 8 diameters could be enough for the wake to recover above 80% [47][48][49]. In contrast HAWTs require a distance of 8 and 10 diameters in the cross-wind and in the downwind directions [50], respectively, to achieve C P, max .…”

Section: Wind Farm Power Densitymentioning

confidence: 99%

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Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

Arredondo-Galeana

2021

Energies

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The offshore wind sector is expanding to deep water locations through floating platforms. This poses challenges to horizontal axis wind turbines (HAWTs) due to the ever growing size of blades and floating support structures. As such, maintaining the structural integrity and reducing the levelised cost of energy (LCoE) of floating HAWTs seems increasingly difficult. An alternative to these challenges could be found in floating offshore vertical axis wind turbines (VAWTs). It is known that VAWTs have certain advantages over HAWTs, and in fact, some small-scale developers have successfully commercialised their onshore prototypes. In contrast, it remains unknown whether VAWTs can offer an advantage for deep water floating offshore wind farms. Therefore, here we present a multi-criteria review of different aspects of VAWTs to address this question. It is found that wind farm power density and reliability could be decisive factors to make VAWTs a feasible alternative for deep water floating arrays. Finally, we propose a way forward based on the findings of this review.

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Section: Wind Farm Power Densitymentioning

confidence: 97%

Section: Wind Farm Power Densitymentioning

confidence: 99%

Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

Arredondo-Galeana

2021

Energies

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“…However, an i th -device operating behind a number of n turbines can be affected by the impact of n i−1 upstream turbines whose low-velocity wakes overlap enhancing the velocity deficit. In a time-averaged sense, this wake interaction can be estimated using linear and quadratic wake superposition methods, as widely used in literature for both HATs (Stansby and Stallard 2016;Niayifar and Porté-Agel 2016;Lanzilao and Meyers 2021) and VATs (Mueller et al 2021). Taking into account that each individual turbine generates a velocity deficit U i , this is adopted to calculate the local incident velocity for every turbine (U i 0 ) in Eqs.…”

Section: Wake Superpositionmentioning

confidence: 99%

“…Furthermore, irrespective of the standalone turbine efficiency, the rectangular cross-section of VAT rotors allows to deploy two devices close to one another which induces a flow acceleration between them Posa (2019) that can increase the individual performance up to 5% (Hezaveh et al 2018). Mueller et al (2021) observed that the rotational direction of twin-VAT systems induces larger changes to the wake dynamics than the turbine spacing, with a counter-rotating forwards motion providing the fastest wake recovery. These synergistic effects means that in VAT arrays reduce detrimental wake effects to achieve large power densities, about 10-20 times larger than those achievable by HATs, meaning that a higher power capacity can be deployed per unit of planform area (Dabiri 2011).…”

Section: Introductionmentioning

confidence: 98%

Power density capacity of tidal stream turbine arrays with horizontal and vertical axis turbines

Ouro

Dené

Garcia-Novo³

et al. 2022

J. Ocean Eng. Mar. Energy

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Tidal and wind energy projects almost exclusively adopt horizontal axis turbines (HATs) due to their maturity. In contrast, vertical axis turbines (VATs) have received limited consideration for large-scale deployment, partly because of their earlier technology readiness level. This paper analyses the power density of turbine arrays comprising aligned and staggered configurations with decreasing turbine spacing of HATs and VATs with height-to-diameter aspect ratios from one to four at three real tidal sites. The VAT rotor has vertical blades extending over a portion of the water depth on a circular frame. Equivalent diameter is defined as $$D_0$$ D 0 = $$\sqrt{A}$$ A based on the projected rotor area for both VATs and HATs. The three-dimensional velocity field is computed using analytical wake models that capture cumulative wake effects. At highly energetic sites, e.g. Ramsey Sound (UK), HATs are the most suitable technology attaining power densities beyond 100 W m$$^{-2}$$ - 2 , whilst VATs provide higher power densities than HATs at those sites with low-to-medium velocities, e.g. Ría de Vigo (Spain) and Kobe Strait (Japan). At the latter site, VATs provided up to 35% larger energy yield than HATs over a 14-day tidal cycle. Our results show that VATs with height-to-diameter aspect ratios larger than three notably reduce wake effects even when deployed with a normalised turbine spacing of two $$D_0$$ D 0 , reaching an average power density capacity of 40.7 W m$$^{-2}$$ - 2 compared to HATs that attain 49.3 W m$$^{-2}$$ - 2 . This study outlines the higher efficiency of tidal stream energy compared to other renewable energy resources, e.g. offshore wind farms, reaching power densities at least one order of magnitude larger, and that VATs counterbalance their smaller individual performance with improved array synergy as wake effects are limited.

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“…As it can be seen, the computed maximum displacement agrees reasonably well with the results reported by [22] for both tip immersions. On the other hand, the study of wake development is of importance to determine the optimal spacing between HAHTs in a hydrokinetic farm [11,[39][40][41]. Time-averaged velocity deficit profiles downstream of the simulated HAHT are shown in Figure 11a and Figure 11b for the deep tip and shallow tip immersions, respectively.…”

Section: Wake and Free Surface Interactionsmentioning

confidence: 99%

Numerical Investigation of the Performance, Hydrodynamics, and Free-Surface Effects in Unsteady Flow of a Horizontal Axis Hydrokinetic Turbine

2021

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This paper presents computational fluid dynamics (CFD) simulations of the flow around a horizontal axis hydrokinetic turbine (HAHT) found in the literature. The volume of fluid (VOF) model implemented in a commercial CFD package (ANSYS-Fluent) is used to track the air-water interface. The URANS SST k-ω and the four-equation Transition SST turbulence models are employed to compute the unsteady three-dimensional flow field. The sliding mesh technique is used to rotate the subdomain that includes the turbine rotor. The effect of grid resolution, time-step size, and turbulence model on the computed performance coefficients is analyzed in detail, and the results are compared against experimental data at various tip speed ratios (TSRs). Simulation results at the analyzed rotor immersions confirm that the power and thrust coefficients decrease when the rotor is closer to the free surface. The combined effect of rotor and support structure on the free surface evolution and downstream velocities is also studied. The results show that a maximum velocity deficit is found in the near wake region above the rotor centerline. A slow wake recovery is also observed at the shallow rotor immersion due to the free-surface proximity, which in turn reduces the power extraction.

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Experimental investigation of the wake characteristics behind twin vertical axis turbines

Cited by 28 publications

References 34 publications

Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

Floating Offshore Vertical Axis Wind Turbines: Opportunities, Challenges and Way Forward

Power density capacity of tidal stream turbine arrays with horizontal and vertical axis turbines

Numerical Investigation of the Performance, Hydrodynamics, and Free-Surface Effects in Unsteady Flow of a Horizontal Axis Hydrokinetic Turbine

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