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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A3: Wind, Wave and Tidal Energy".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 20903

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Prof. Dr. Yutaka Hara

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Guest Editor

Faculty of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori 680-8552, Japan
Interests: vertical-axis wind turbines; horizontal-axis wind turbines; cost reduction of wind turbines; aerodynamics; computational fluid dynamics; blade element momentum theory; over-speed control of wind turbines; wind turbine wake; closely spaced arrangements of VAWT; interaction between wind turbines; phase synchronization; aeroelastic analysis; fatigue analysis; wind power; fluid mechanics; renewable energy
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Prof. Dr. Yoshifumi Jodai

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Guest Editor

Department of Mechanical Engineering, National Institute of Technology (KOSEN), Kagawa College, 355 Chokushi, Takamatsu 761-8058, Japan
Interests: energy saving; educational technology; fluid mechanics; turbulence; wind tunnel experiment
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Wind power is becoming the main power source for electricity generation as expectations for renewable energy increase toward the realization of carbon neutrality. Currently, large propeller-type horizontal-axis wind turbines (HAWTs) have become mainstream, and development is progressing toward further increasing their size; however, this is not easy. For floating offshore wind turbines, vertical-axis wind turbines (VAWTs), in which the tilt of the axis of rotation is not an issue, could prove to be superior to HAWTs. In addition, there have been proposals for increasing the wind turbine power of small VAWTs owing to the proximity arrangement, and the development of small VAWT wind farms that can effectively utilize the land is expected. Furthermore, owing to the inherent characteristics of VAWTs (i.e., no wind direction dependence, resulting in a simple structure), low-cost wind power generation equipment can be developed, regardless of the size and application of the VAWT. As we move toward a carbon-free society, it is important to investigate various possibilities and have many options, such as lift-type/drag-type, Darrieus-type, Savonius-type, cross-flow-type, and paddle-type VAWTs. This is important for advancing the research and development of VAWTs, which have great potential with their wide variety of sizes.

In consideration of the abovementioned points, the purpose of this Special Issue is to collect original research and review papers on various topics related to VAWTs and to explore new possibilities of VAWTs.

Prof. Dr. Yutaka Hara
Prof. Dr. Yoshifumi Jodai
Guest Editors

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Keywords

vertical-axis wind turbines (VAWTs)
aerodynamics of VAWTs
computational fluid dynamics of VAWTs
blade element momentum theory of VAWTs
cost reduction of VAWTs
control of VAWTs
wake analysis of VAWTs
wind farm of VAWTs
closely spaced arrangements of VAWTs
interaction between VAWTs
phase synchronization of VAWTs
aeroelastic analysis of VAWTs
fatigue analysis of VAWTs
new designs of VAWTs
offshore applications of VAWTs
practical applications of VAWTs
advanced measurement techniques for VAWTs
new theoretical models for VAWTs

Published Papers (10 papers)

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Research

15 pages, 8589 KiB

Open AccessArticle

Numerical Simulation of the Effects of Blade–Arm Connection Gap on Vertical–Axis Wind Turbine Performance

by Yutaka Hara, Ayato Miyashita and Shigeo Yoshida

Energies 2023, 16(19), 6925; https://doi.org/10.3390/en16196925 - 2 Oct 2023

Viewed by 848

Abstract

Many vertical-axis wind turbines (VAWTs) require arms, which generally provide aerodynamic resistance, to connect the main blades to the rotating shaft. Three–dimensional numerical simulations were conducted to clarify the effects of a gap placed at the blade–arm connection portion on VAWT performance. A VAWT with two straight blades (diameter: 0.75 m, height: 0.5 m) was used as the calculation model. Two horizontal arms were assumed to be connected to the blade of the model with or without a gap. A cylindrical rod with a diameter of 1 or 5 mm was installed in the gap, and its length varied from 10 to 30 mm. The arm cross section has the same airfoil shape (NACA 0018) as the main blade; however, the chord length is half (0.04 m) that of the blade. The simulation shows that the power of the VAWT with gaps is higher than that of the gapless VAWT. The longer gap length tends to decrease the power, and increasing the diameter of the connecting rod amplifies this decreasing tendency. Providing a short gap at the blade–arm connection and decreasing the cross–sectional area of the connecting member is effective in increasing VAWT power. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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27 pages, 18936 KiB

Open AccessArticle

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

by Yoshifumi Jodai and Yutaka Hara

Energies 2023, 16(3), 1088; https://doi.org/10.3390/en16031088 - 18 Jan 2023

Cited by 1 | Viewed by 1697

Abstract

To elucidate the wind-direction dependence of the rotor performance in closely spaced vertical-axis wind turbines, wind-tunnel experiments were performed at a uniform wind velocity. In the experiments, a pair/trio of three-dimensional printed model turbines with a diameter of D = 50 mm was used. The experiments were performed systematically by applying incremental adjustments to the rotor gap g and rotational direction of each rotor and by changing the wind direction. For tandem layouts, the rotational speed of the downwind rotor is 75–80% that of an isolated rotor, even at g/D = 10. For the average rotational speed of the rotor pair, an origin-symmetrical and a line-symmetrical distribution are observed in the co-rotating and inverse-rotating configurations, respectively, thereby demonstrating the wind-direction dependence for the rotor pair. The inverse-rotating trio configuration yields a higher average rotational speed than the co-rotating trio configuration for any rotor spacing under the ideal bidirectional wind conditions. The maximum average rotational speed should be obtained for a wind direction of θ = 0° in the inverse-rotating trio configuration. The wind-direction dependence of the rotational speeds of the three turbines was explained via flow visualization using a smoke-wire method and velocity field study using two-dimensional computational fluid dynamics. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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21 pages, 2809 KiB

Open AccessArticle

Shades of Green: Life Cycle Assessment of a Novel Small-Scale Vertical Axis Wind Turbine Tree

by Duong Minh Ngoc, Montri Luengchavanon, Pham Thi Anh, Kim Humphreys and Kuaanan Techato

Energies 2022, 15(20), 7530; https://doi.org/10.3390/en15207530 - 12 Oct 2022

Cited by 2 | Viewed by 2301

Abstract

Are small-scale wind turbines green? In this study, we perform a ‘cradle to grave’ life cycle assessment of a novel domestic-scale 10 kW vertical axis wind turbine tree which uses combined Savonius and H-Darrieus blades. Situated at a test site in Surat Thani, Thailand, SimaPro software was used to evaluate the environmental impact profile of the tree. Comparisons to the Thai grid mix were made, using both with and without end-of-life treatments. Impact profiles were calculated using wind data collected over two years at Surat Thani, and from wind data from a higher capacity factor (C_F) site at Chiang Mai, Thailand. Energy and greenhouse gas payback times were estimated for both locations. The relative magnitudes of impacts were compared with environmental prices protocol, and we investigated reductions in impacts using three mitigative scenarios: changes to design, transportation and materials. The results showed that Chiang Mai had a C_F = 7.58% and Surat Thani had a C_F = 1.68%. A total of 9 out of 11 impacts were less than the grid values at Chiang Mai, but at Surat Thani, 9 of 11 impacts were more than the grid values. End-of-life treatments reduced impacts by an average of 11%. The tower and generator were majority contributors to impacts (average 69%). Greenhouse gas and energy payback times were 28.61 and 54.77 years, and 6.50 and 12.50 years for Surat Thani and Chiang Mai, respectively, with only the Chiang Mai times being less than the turbine’s estimated lifetime. Location changes mitigated impacts most, followed by design, transportation, and then materials. We make recommendations to further improve the environmental impact profile of this turbine tree. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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17 pages, 6507 KiB

Open AccessArticle

Verification of Tilt Effect on the Performance and Wake of a Vertical Axis Wind Turbine by Lifting Line Theory Simulation

by Hidetaka Senga, Hiroki Umemoto and Hiromichi Akimoto

Energies 2022, 15(19), 6939; https://doi.org/10.3390/en15196939 - 22 Sep 2022

Cited by 4 | Viewed by 1900

Abstract

Renewable energy has received a lot of attention. In recent years, offshore wind power has received particular attention among renewable energies. Fixed-type offshore wind turbines are now the most popular. However, because of the deep seas surrounding Japan, floating types are more preferable. The floating system is one of the factors that raises the cost of floating wind turbines. Vertical axis wind turbines (VAWT) have a low center of gravity and can tilt their rotors. As a result, a smaller floating body and a lower cost are expected. A mechanism called a floating axis wind turbine (FAWT) is expected to further reduce the cost. FAWT actively employs the features of VAWT in order to specialize itself in the area of offshore floating-type wind turbines. The lifting line theory simulation was used in this study to discuss the performance of the FAWT under the tilted conditions and its wake field. The results show that a tilted VAWT recovers faster than an upright VAWT. This suggests that FAWTs can be deployed in high density and efficiently generate energy as an offshore wind farm using VAWTs. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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26 pages, 10431 KiB

Open AccessArticle

Investigation into the Aerodynamic Performance of a Vertical Axis Wind Turbine with Endplate Design

by Shern-Khai Ung, Wen-Tong Chong, Shabudin Mat, Jo-Han Ng, Yin-Hui Kok and Kok-Hoe Wong

Energies 2022, 15(19), 6925; https://doi.org/10.3390/en15196925 - 21 Sep 2022

Cited by 9 | Viewed by 2478

Abstract

For the past decade, research on vertical axis wind turbines (VAWTs) has garnered immense interest due to their omnidirectional characteristic, especially the lift-type VAWT. The H-rotor Darrieus VAWT operates based on the lift generated by aerofoil blades and typically possesses higher efficiency than the drag-type Savonius VAWT. However, the open-ended blades generate tip loss effects that reduce the power output. Wingtip devices such as winglets and endplates are commonly used in aerofoil design to increase performance by reducing tip losses. In this study, a CFD simulation is conducted using the sliding mesh method and the k-ω SST turbulence model on a two-bladed NACA0018 VAWT. The aerodynamic performance of a VAWT with offset, symmetric V, asymmetric and triangular endplates are presented and compared against the baseline turbine. The simulation was first validated with the wind tunnel experimental data published in the literature. The simulation showed that the endplates reduced the swirling vortex and improved the pressure distribution along the blade span, especially at the blade tip. The relationship between TSR regimes and the tip loss effect is also reported in the paper. Increasing VAWT performance by using endplates to minimise tip loss is a simple yet effective solution. However, the improvement of the power coefficient is not remarkable as the power degradation only involves a small section of the blades. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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22 pages, 3300 KiB

Open AccessArticle

Investigations of Vertical-Axis Wind-Turbine Group Synergy Using an Actuator Line Model

by Ji Hao Zhang, Fue-Sang Lien and Eugene Yee

Energies 2022, 15(17), 6211; https://doi.org/10.3390/en15176211 - 26 Aug 2022

Cited by 7 | Viewed by 1582

Abstract

The presence of power augmentation effects, or synergy, in vertical-axis wind turbines (VAWTs) offers unique opportunities for enhancing wind-farm performance. This paper uses an open-source actuator-line-method (ALM) code library for OpenFOAM (turbinesFoam) to conduct an investigation into the synergy patterns within two- and three-turbine VAWT arrays. The application of ALM greatly reduces the computational cost of simulating VAWTs by modelling turbines as momentum source terms in the Navier–Stokes equations. In conjunction with an unsteady Reynolds-Averaged Navier–Stokes (URANS) approach using the k-

ω

shear stress transport (SST) turbulence model, the ALM has proven capable of predicting VAWT synergy. The synergy of multi-turbine cases is characterized using the power ratio which is defined as the power coefficient of the turbine cluster normalized by that for turbines in isolated operation. The variation of the power ratio is characterized with respect to the array layout parameters, and connections are drawn with previous investigations, showing good agreement. The results from 108 two-turbine and 40 three-turbine configurations obtained using ALM are visualized and analyzed to augment the understanding of the VAWT synergy landscape, demonstrating the effectiveness of various layouts. A novel synergy superposition scheme is proposed for approximating three-turbine synergy using pairwise interactions, and it is shown to be remarkably accurate. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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19 pages, 7172 KiB

Open AccessArticle

A Study on a Casing Consisting of Three Flow Deflectors for Performance Improvement of Cross-Flow Wind Turbine

by Tadakazu Tanino, Ryo Yoshihara and Takeshi Miyaguni

Energies 2022, 15(16), 6093; https://doi.org/10.3390/en15166093 - 22 Aug 2022

Cited by 1 | Viewed by 1861

Abstract

We investigated the effective use of cross-flow wind turbines for small-scale wind power generation to increase the output power by using a casing, which is a kind of wind-collecting device, composed of three flow deflector plates having the shape of a circular-arc airfoil. Drag-type vertical-axis wind turbines have an undesirable part of about half of the swept area where the inflow of wind results in low output performance. To solve this problem, we devised a casing consisting of three flow deflector plates, two of which were to block the unwanted inflow of wind and the remaining flow deflector plate having an angle of attack with respect to the wind direction to increase the flow toward the rotor. In this study, output performance experiments using a wind tunnel and numerical fluid analysis were conducted on a cross-flow wind turbine with three flow deflector plates to evaluate the effectiveness of the casing on output performance improvement. As a result, it was confirmed that the casing could improve the output performance of the cross-flow wind turbine by approximately 60% at the maximum performance point and could also maintain the output performance about 50% higher compared to the bare cross-flow wind turbine without the casing within a deviation angle of ±10 degrees, even when the casing direction was inclined against the wind direction due to changes in wind direction. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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29 pages, 10570 KiB

Open AccessArticle

Method to Predict Outputs of Two-Dimensional VAWT Rotors by Using Wake Model Mimicking the CFD-Created Flow Field

by Jirarote Buranarote, Yutaka Hara, Masaru Furukawa and Yoshifumi Jodai

Energies 2022, 15(14), 5200; https://doi.org/10.3390/en15145200 - 18 Jul 2022

Cited by 1 | Viewed by 1284

Abstract

Recently, wind farms consisting of clusters of closely spaced vertical-axis wind turbines (VAWTs) have attracted the interest of many people. In this study, a method using a wake model to predict the flow field and the output power of each rotor in a VAWT cluster is proposed. The method uses the information obtained by the preliminary computational fluid dynamics (CFD) targeting an isolated single two-dimensional (2D) VAWT rotor and a few layouts of the paired 2D rotors. In the method, the resultant rotor and flow conditions are determined so as to satisfy the momentum balance in the main wind direction. The pressure loss of the control volume (CV) is given by an interaction model which modifies the prepared information on a single rotor case and assumes the dependence on the inter-rotor distance and the induced velocity. The interaction model consists of four equations depending on the typical four-type layouts of selected two rotors. To obtain the appropriate circulation of each rotor, the searching range of the circulation is limited according to the distribution of other rotors around the rotor at issue. The method can predict the rotor powers in a 2D-VAWT cluster including a few rotors in an incomparably shorter time than the CFD analysis using a dynamic model. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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19 pages, 7020 KiB

Open AccessArticle

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

by Masaru Furukawa, Yutaka Hara and Yoshifumi Jodai

Energies 2022, 15(11), 4130; https://doi.org/10.3390/en15114130 - 4 Jun 2022

Cited by 2 | Viewed by 1499

Abstract

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. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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21 pages, 1966 KiB

Open AccessArticle

Integrated Surrogate Optimization of a Vertical Axis Wind Turbine

by Marco A. Moreno-Armendáriz, Eddy Ibarra-Ontiveros, Hiram Calvo and Carlos A. Duchanoy

Energies 2022, 15(1), 233; https://doi.org/10.3390/en15010233 - 30 Dec 2021

Cited by 5 | Viewed by 2399

Abstract

In this work, a 3D computational model based on computational fluid dynamics (CFD) is built to simulate the aerodynamic behavior of a Savonius-type vertical axis wind turbine with a semi-elliptical profile. This computational model is used to evaluate the performance of the wind turbine in terms of its power coefficient (Cp). Subsequently, a full factorial design of experiments (DOE) is defined to obtain a representative sample of the search space on the geometry of the wind turbine. A dataset is built on the performance of each geometry proposed in the DOE. This process is carried out in an automated way through a scheme of integrated computational platforms. Later, a surrogate model of the wind turbine is fitted to estimate its performance using machine learning algorithms. Finally, a process of optimization of the geometry of the wind turbine is carried out employing metaheuristic optimization algorithms to maximize its Cp; the final optimized designs are evaluated using the computational model for validating their performance. Full article

(This article belongs to the Special Issue Vertical-Axis Wind Turbine)

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