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Recent studies have revealed the large potential of vertical‐axis wind turbines (VAWTs) for high‐energy‐density wind farms due to their favorable wake recovery characteristics. The present study provides an experimental demonstration and proof‐of‐concept for the wake recovery mechanism of the novel X‐Rotor VAWT. The phase‐locked flowfield is measured at several streamwise locations along the X‐Rotor's wake using stereoscopic particle image velocimetry (PIV) with fixed‐pitch offsets applied to the blades. The streamwise vortex system of the upper half of the X‐Rotor is first hypothesized and then experimentally verified. The induced wake deformations of the vortex systems are discussed in comparison with previous studies concerning traditional H‐type VAWTs. The results suggest that positive blade pitch is more favorable for accelerated wake recovery due to the dominant tip‐vortex generated on the upwind windward quadrant of the cycle. Utilizing theoretical blade load variations along the span explains distinct unsteady flow features in the near wake generated at select quadrants of the rotor rotation, shedding light on the potential of the two pitch schemes. [ABSTRACT FROM AUTHOR]

ABSTRACT Recent studies have revealed the large potential of vertical‐axis wind turbines (VAWTs) for high‐energy‐density wind farms due to their favorable wake recovery characteristics. The present study provides an experimental demonstration and proof‐of‐concept for the wake recovery mechanism of the novel X‐Rotor VAWT. The phase‐locked flowfield is measured at several streamwise locations along the X‐Rotor's wake using stereoscopic particle image velocimetry (PIV) with fixed‐pitch offsets applied to the blades. The streamwise vortex system of the upper half of the X‐Rotor is first hypothesized and then experimentally verified. The induced wake deformations of the vortex systems are discussed in comparison with previous studies concerning traditional H‐type VAWTs. The results suggest that positive blade pitch is more favorable for accelerated wake recovery due to the dominant tip‐vortex generated on the upwind windward quadrant of the cycle. Utilizing theoretical blade load variations along the span explains distinct unsteady flow features in the near wake generated at select quadrants of the rotor rotation, shedding light on the potential of the two pitch schemes.

For both conventional and renewable energy conversion processes, computational fluid dynamics (CFD) has been used to address more energy-related challenges in recent decades. Using CFD to investigate vertical-axis wind turbines has become more common in recent years. The main goals of this application have been to more accurately predict the turbine's performance and to comprehend the complicated nature of the complex turbulent flow. The vertical-axis wind turbine (VAWT) simulation for energy-generating applications has several intricate components. One of them is the study of the chaotic flow that occurs during the first stages of the starting process, and which greatly influences overall effectiveness. In this article, the performance of the wind turbine was increased using a passive flow control approach. The numerical research was carried out using Large Eddy Simulation for four alternative tip speed ratios in both cases, the classic and the optimized case, equipped with a vortex trap on the extrados of the blades. The power and torque coefficient variations, as well as the velocity magnitude contours, show that the starting process may begin with a significant improvement in efficiency when flow control is used. [ABSTRACT FROM AUTHOR]

Analytical wake models are widely used to predict wind turbine wakes. While these models are well-established for horizontal-axis wind turbines (HAWTs), the analytical wake models for vertical-axis wind turbines (VAWTs) remain under-explored in the wind energy community. In this study, the accuracy of two wake scaling techniques is evaluated to predict the change in the normalized maximum wake velocity deficit behind VAWTs by re-scaling the maximum wake velocity deficit behind an actuator disk with the same thrust coefficient. The wake scaling is defined in terms of equivalent diameter, considering the geometrical properties of the wake-generating object. Two different equivalent diameters are compared, namely the momentum diameter and hydraulic diameter. Different approaches are used to calculate the change in the normalized wake velocity deficit behind a disk with the same thrust coefficient as the VAWT. The streamwise distance is scaled with the equivalent diameter to predict the normalized maximum wake velocity deficit behind the desired VAWT. The performance of the proposed framework is assessed using large-eddy simulation data of VAWTs operating in a turbulent boundary layer with varying operating conditions and aspect ratios. For all of the cases, the momentum diameter scaling provides reasonable predictions of the VAWT normalized maximum wake velocity deficit. [ABSTRACT FROM AUTHOR]

Vertical-axis wind turbines (VAWT) with Darrieus and Savonius rotors were studied based on the developed specialized package of computational aerodynamics. The flow structure around the Savonius and Darrieus rotors was numerically reconstructed, considering the mutual influence. From this reconstruction, the main stages of the vortex structure formation during the flow of the turbulent wind around the rotors were identified. Qualitative and quantitative assessments of the influence of the Savonius rotor on the total aerodynamic and energy characteristics of a VAWT were carried out. It is shown that the main contribution to the torque of the VAWT is due to the Darrieus rotor, mainly in the windward section of the trajectory. The Savonius rotor accounts for only a few percent of the total torque produced by the installation. The interaction of the Darrieus rotor blades with macrovortices from the Savonius rotor in the leeward part of the trajectory leads to a sharp drop in the torque coefficient. In the absence of a Savonius rotor, the vortices separated from supported tower are much smaller both in size and intensity. Therefore, their interaction with the blades of the Darrieus rotor does not lead to a significant change in the aerodynamic characteristics. A power characteristics comparison of two VAWTs showed that the torque coefficient is higher for wind turbines with only single Darrieus rotor. The developed approaches and techniques make it possible to reproduce real aerodynamic processes of flow most reliably around bodies of arbitrary shape and calculate their aerodynamic characteristics.

This paper explores an interesting approach to wind energy technology, focusing on a novel type of drag-driven vertical-axis wind turbines (VAWTs). Studied geometries employ rotor-shaped cross-sections, presenting a distinctive approach to harnessing wind energy efficiently. The rotor-shaped cross-section geometries are examined for their aerodynamic efficiency, showcasing the meticulous engineering behind this innovation. The drag-driven turbine shapes are analyzed for their ability to maximize energy extraction in a variety of wind conditions. A significant aspect of these turbines is their adaptability for diverse applications. This article discusses the feasibility and advantages of utilizing these VAWTs in fence configurations, offering an innovative integration of renewable energy generation with physical infrastructure. The scalability of the turbines is highlighted, enabling their deployment as a fence around residential properties or as separators between highway lanes and as energy-generating structures atop buildings. The scientific findings presented in this article contribute valuable insights into the technological advancements of rotor-shaped VAWTs and their potential impact on decentralized wind energy generation. The scalable and versatile nature of these turbines opens up new possibilities for sustainable energy solutions in both urban and residential settings, marking a significant step forward in the field of renewable energy research and technology. In particular, it was shown that among the proposed rotor geometries, the five-blade rotor was characterized by the highest efficiency and, working in a palisade configuration with a spacing of 10 mm to 20 mm, produced higher average values of the torque coefficient than the corresponding Savonius turbine. [ABSTRACT FROM AUTHOR]

Türkiye's earthquake zone, primarily located along the North Anatolian Fault, is one of the world's most seismically active regions, frequently experiencing devastating earthquakes, such as the one in Hatay in 2023. Therefore, reconstructing energy-efficient buildings after major earthquakes enhances disaster resilience and promotes energy efficiency through retrofitting, renovation, or demolition and reconstruction. To this end, this study proposes implementing energy-efficient design solutions in dwelling units to minimize energy consumption in new buildings in Hatay, Southern Turkiye, an area affected by the 2023 earthquake. This research focused on a five-story residential building in the district of Kurtlusarımazı, incorporating small-scale Vertical-Axis Wind Turbines (VAWTs) with thin-film photovoltaic (PV) panels, along with the application of a green wall surrounding the building. ANSYS Fluent v.R2 Software was used for a numerical investigation of the small-scale IceWind turbine, and DesignBuilder Software v.6.1.0.006 was employed to simulate the baseline model and three energy-efficient design strategies. The results demonstrated that small-scale VAWTs, PV panels, and the application of a green wall reduced overall energy use by 8.5%, 18%, and 4.1%, respectively. When all strategies were combined, total energy consumption was reduced by up to 28.5%. The results of this study could guide designers in constructing innovative energy-efficient buildings following extensive demolition such as during the 2023 earthquake in Hatay, Türkiye. [ABSTRACT FROM AUTHOR]

The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that for 0°. The NACA0018 airfoil turbines with pitch angles of 0° and 5° fail to complete selfstarting. The airfoil type also plays a crucial role, with the NACA2418 airfoil demonstrating superior self-starting performance and power performance. Furthermore, the minimum self-starting wind speed of the NACA0018 airfoil turbine was explored and determined be between 5.5 m/s and 6 m/s. The utilization of this novel self-starting evaluation method addresses the limitations of traditional approaches, providing a more universally applicable interpretation of the characteristics of turbine self-starting behavior. [ABSTRACT FROM AUTHOR]

The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that for 0°. The NACA0018 airfoil turbines with pitch angles of 0° and 5° fail to complete self-starting. The airfoil type also plays a crucial role, with the NACA2418 airfoil demonstrating superior self-starting performance and power performance. Furthermore, the minimum self-starting wind speed of the NACA0018 airfoil turbine was explored and determined be between 5.5 m/s and 6 m/s. The utilization of this novel self-starting evaluation method addresses the limitations of traditional approaches, providing a more universally applicable interpretation of the characteristics of turbine self-starting behavior.

The constant need for fuel to meet the commercial sector's ever-increasing demand has driven researchers to discover and optimize renewable energy resources, paving the way for sustainable production of reliable and clean energy resources. The goal of the current work is to close the gap in process parameter optimization needed to convert wind energy wake from traffic on highways into electrical energy utilizing vertical-axis wind turbines (VAWTs). The energy output from the VAWT is analyzed to investigate how it is impacted by the variations in multiple parameter settings. Using the central composite design (CCD), a threelevel four-factor array was used to investigate the following parameters: VAWT vertical distance (VD) and horizontal distance (HD) as continuous parameters, while road side (S) and location (L) of VAWT as categorical parameters. To find the most important parameter, response surface methodology (RSM) optimization and an analysis of variance (ANOVA) test are performed. L accounts for 66.67% of the total variable, with S coming in second with 51.80%. Using the best results from RSM and ANOVA, a confirmation test is run, and the results show yields of 88.75% ±0.05% and 87.5% ±0.05%, respectively. Therefore, RSM and ANOVA can be utilized equally for optimization at the same VAWT design. Lastly, the findings of the economic and environmental evaluation demonstrate that, in comparison to the basic settings, VAWT operating at optimal settings can save up to 180% and 200% more energy and reduce carbon emissions, respectively. [ABSTRACT FROM AUTHOR]

The performance of a new vertical-axis wind turbine rotor based on the mathematical equation of the cycloid is analyzed and compared through simulation and experimental testing against a semicircular or S-type rotor, which is widely used. The study examines three cases: equalizing the diameter, chord length and the area under the curve. Computational Fluid Dynamics (CFD) was used to simulate these cases and evaluate moment, angular velocity and power. Experimental validation was carried out in a wind tunnel that was designed and optimized with the support of CFD. The rotors for all three cases were 3D printed in resin to analyze their experimental performance as a function of wind speed. The moment and Maximum Power Point (MPP) were determined in each case. The simulation results indicate that the cycloid-type rotor outperforms the semicircular or S-type rotor by 15%. Additionally, experimental evidence confirms that the cycloid-type rotor performs better in all three cases. In the MPP analysis, the cycloid-type rotor achieved an efficiency of 10.8% which was 38% better than the S-type rotor. [ABSTRACT FROM AUTHOR]

In this article, a modified immersed boundary method (IBM) with a ghost-cells strategy is introduced to study a kind of vertical-axis wind turbine (VAWT). In order to improve the accuracy of the numerical calculation and enhance its adaptability, some treatments on the IBM for the VAWT especially are carried out. The method is testified by the numerical simulation of an Eppler387 airfoil. With the help of the method, some flowing characteristics of the wind turbine have been thoroughly observed and understood. Furthermore, the effects of blade shape, tip vortex and secondary flowing on the turbine performance are discussed in detail based on the numerical results. [ABSTRACT FROM AUTHOR]

The popularity of small wind turbines intended for domestic use has significantly increased during the recent years, and it is reasonable to assume that this trend will continue given the present political and economic environment. There is a greater need for clean, pollution-free energy due to worries about climate change. In this study, a 1.5 KW vertical-axis Darrieus helix wind turbine for residential use was designed and its performance was mathematically evaluated under typical wind speed circumstances of 12 m/s. The study is split into two sections: In the first, we examined a standard wind turbine design with three identical blades, whereas in the second, the blades were different, each with a unique airfoil with a varying chord, even though they shared the same rotor diameter. For each case, 5 CFD simulations were performed in order to determine the power characteristics of the wind turbines. To correctly set up the computational domain, the number of elements and the minimum element size were taken into account whereas mesh dependency analysis was performed. In order to compare the results, the vorticity magnitude was measured at 4 different blade locations in each boundary condition. The results showed that when the power coefficient of the turbines is considered, such geometry adjustments are possible. Furthermore, the evolution of the torque coefficient over a full 360-degree rotation was studied. A summary of the improvements in performance resulting from the geometry adjustment is provided. [ABSTRACT FROM AUTHOR]

A numerical simulation study on the combination of a Darrieus and a Savonius wind turbine is conducted. Hybrid T-II, T-III, and T-IV turbines are suggested with the same Darrieus turbine T-I. In the T-II and T-III, the Savonius turbine is at the center of the Darrieus turbine, whereas in the T-IV, the Savonius turbine is above the Darrieus turbine. The T-III Savonius turbine has half the radius of that of the T-II turbine. Results reveal that variations of the power coefficients, Cp with the tip speed ratio, TSR for the hybrid turbines have different slopes. It is observed that Cp increases with increasing TSR for the T-II and T-IV and does not decrease for the range of TSRs considered, in contrast with the Cp behavior of the T-I. The proposed hybrid T-IV turbine has also a larger Cp than the T-I turbine at the highest TSR. [ABSTRACT FROM AUTHOR]

Noise pollution is one of the biggest problems of wind turbines, especially when these turbines are located near residential areas. In this article, the effect of blade thickness is numerically investigated on the noise pollution of an H-type Darrieus wind turbine. The flow is first simulated using the unsteady Reynolds averaged Navier-Stokes equations and the SST-kω model at the tip speed ratio of 2.64. Then, the noise is calculated using Ffowcs Williams-Hawkings equations. Blade thickness is changed using NACA airfoils from NACA 0008 up to NACA 0024. It is concluded that noise calculation at only one point, known as a routine method in noise investigation of wind turbines, is insufficient to investigate the noise of this turbine. Here, maximum noise in directivity is defined as the criterion of noise pollution. The results show that changing the blade profile of the benchmark turbine from NACA 0021 to NACA 0015 increases the power coefficient from 0.318 to 0.371 and reduces the maximum noise from 95.67 dB (76.35 dB) to 90.19 dB (71.01 dB) at R = 2 m (8m). For NACA 0018, the power coefficient is 0.353, and the maximum noise is 89.78 dB (70.47 dB) at R = 2 m (8m). Overall, the highest output power is for NACA 0015, and the lowest noise pollution is for NACA 0018.

Analytical wake models are widely used to predict wind turbine wakes. While these models are well-established for horizontal-axis wind turbines (HAWTs), the analytical wake models for vertical-axis wind turbines (VAWTs) remain under-explored in the wind energy community. In this study, the accuracy of two wake scaling techniques is evaluated to predict the change in the normalized maximum wake velocity deficit behind VAWTs by re-scaling the maximum wake velocity deficit behind an actuator disk with the same thrust coefficient. The wake scaling is defined in terms of equivalent diameter, considering the geometrical properties of the wake-generating object. Two different equivalent diameters are compared, namely the momentum diameter and hydraulic diameter. Different approaches are used to calculate the change in the normalized wake velocity deficit behind a disk with the same thrust coefficient as the VAWT. The streamwise distance is scaled with the equivalent diameter to predict the normalized maximum wake velocity deficit behind the desired VAWT. The performance of the proposed framework is assessed using large-eddy simulation data of VAWTs operating in a turbulent boundary layer with varying operating conditions and aspect ratios. For all of the cases, the momentum diameter scaling provides reasonable predictions of the VAWT normalized maximum wake velocity deficit.

The constant need for fuel to meet the commercial sector’s ever-increasing demand has driven researchers to discover and optimize renewable energy resources, paving the way for sustainable production of reliable and clean energy resources. The goal of the current work is to close the gap in process parameter optimization needed to convert wind energy wake from traffic on highways into electrical energy utilizing vertical-axis wind turbines (VAWTs). The energy output from the VAWT is analyzed to investigate how it is impacted by the variations in multiple parameter settings. Using the central composite design (CCD), a three-level four-factor array was used to investigate the following parameters: VAWT vertical distance (VD) and horizontal distance (HD) as continuous parameters, while road side (S) and location (L) of VAWT as categorical parameters. To find the most important parameter, response surface methodology (RSM) optimization and an analysis of variance (ANOVA) test are performed. L accounts for 66.67% of the total variable, with S coming in second with 51.80%. Using the best results from RSM and ANOVA, a confirmation test is run, and the results show yields of 88.75% ± 0.05% and 87.5% ± 0.05%, respectively. Therefore, RSM and ANOVA can be utilized equally for optimization at the same VAWT design. Lastly, the findings of the economic and environmental evaluation demonstrate that, in comparison to the basic settings, VAWT operating at optimal settings can save up to 180% and 200% more energy and reduce carbon emissions, respectively.

In light of the escalating demand for renewable energy sources, vertical-axis wind turbines have emerged as a pivotal technical solution for addressing the challenge of clean energy supply in residential and urban areas. As a simple and feasible passive control method, the plain Gurney flap (PGF) is widely applied to improve turbine aerodynamic performance. In this paper, the influence of a novel serrated gurney flap (SGF) with different flap heights is studied on the NACA0021 airfoil by numerical simulations. The findings demonstrate that, compared with the PGF, the SGF reduces the trailing edge reverse vortices from a pair to a single vortex and possesses lower drag. When the flap height reaches 6% of the chord (6%c), the lift-to-drag ratio of SGF surpasses that of PGF. A turbine rotor is equipped with an SGF and a PGF to compare their performances. The result confirms the flap effect depending on the rotor's tip speed. At a low tip speed ratio (TSR), the PGF works better than the SGF. The SGF is preferred over the PGF for a higher tip speed ratio (TSR > 2.5). With the 6%c flap height, the performance of the SGF rotor surpasses the PGF by 13.9% at TSR = 2.62. [ABSTRACT FROM AUTHOR]

Vertical-axis wind turbines (VAWTs) are an innovative solution for energy harvesting, as they harness the power of the wind by enabling rotational motion around a vertical shaft situated on the ground. This paper deals with the design optimisation of VAWT systems for highway energy harvesting. The four design parameters, blade number, blade curvature angle, blade thickness and blade diameter ratio, have been investigated to find their respective optimalities for the enhanced energy efficiency of VAWT systems. Computational fluid dynamics (CFD) simulations are conducted in Ansys Fluent using a Banki turbine model created in Solidworks®, with a constant velocity inlet of 4 m/s and rotational speeds ranging from 0.5 to 3 rad/s. The simulations consider the placement of the turbine in the central reservation of a highway with a windshield for enhanced performance. From the results, it was observed that increasing blade thickness and blade number improve turbine performance, with maximum power coefficients achieved at specific tip speed ratios (TSRs). The optimal blade diameter ratio has been found to be approximately 0.75 for TSR values between 0.1 and 0.5, whilst a ratio of 0.83 gave the best performance at higher TSR values. Also, a blade curvature angle of 60 degrees has been found optimal for slow rotations, while 100 degrees yielded the highest power coefficient for faster rotations. The study could also highlight the significance of blade curvature angle variation, resulting in a notable 14% performance increase compared to the baseline. The geometric changes proposed in the study allow for greater power extraction from the same turbine footprint, leading to increased energy efficiency in VAWT systems. [ABSTRACT FROM AUTHOR]

Türkiye’s earthquake zone, primarily located along the North Anatolian Fault, is one of the world’s most seismically active regions, frequently experiencing devastating earthquakes, such as the one in Hatay in 2023. Therefore, reconstructing energy-efficient buildings after major earthquakes enhances disaster resilience and promotes energy efficiency through retrofitting, renovation, or demolition and reconstruction. To this end, this study proposes implementing energy-efficient design solutions in dwelling units to minimize energy consumption in new buildings in Hatay, Southern Turkiye, an area affected by the 2023 earthquake. This research focused on a five-story residential building in the district of Kurtlusarımazı, incorporating small-scale Vertical-Axis Wind Turbines (VAWTs) with thin-film photovoltaic (PV) panels, along with the application of a green wall surrounding the building. ANSYS Fluent v.R2 Software was used for a numerical investigation of the small-scale IceWind turbine, and DesignBuilder Software v.6.1.0.006 was employed to simulate the baseline model and three energy-efficient design strategies. The results demonstrated that small-scale VAWTs, PV panels, and the application of a green wall reduced overall energy use by 8.5%, 18%, and 4.1%, respectively. When all strategies were combined, total energy consumption was reduced by up to 28.5%. The results of this study could guide designers in constructing innovative energy-efficient buildings following extensive demolition such as during the 2023 earthquake in Hatay, Türkiye.

This paper explores an interesting approach to wind energy technology, focusing on a novel type of drag-driven vertical-axis wind turbines (VAWTs). Studied geometries employ rotor-shaped cross-sections, presenting a distinctive approach to harnessing wind energy efficiently. The rotor-shaped cross-section geometries are examined for their aerodynamic efficiency, showcasing the meticulous engineering behind this innovation. The drag-driven turbine shapes are analyzed for their ability to maximize energy extraction in a variety of wind conditions. A significant aspect of these turbines is their adaptability for diverse applications. This article discusses the feasibility and advantages of utilizing these VAWTs in fence configurations, offering an innovative integration of renewable energy generation with physical infrastructure. The scalability of the turbines is highlighted, enabling their deployment as a fence around residential properties or as separators between highway lanes and as energy-generating structures atop buildings. The scientific findings presented in this article contribute valuable insights into the technological advancements of rotor-shaped VAWTs and their potential impact on decentralized wind energy generation. The scalable and versatile nature of these turbines opens up new possibilities for sustainable energy solutions in both urban and residential settings, marking a significant step forward in the field of renewable energy research and technology. In particular, it was shown that among the proposed rotor geometries, the five-blade rotor was characterized by the highest efficiency and, working in a palisade configuration with a spacing of 10 mm to 20 mm, produced higher average values of the torque coefficient than the corresponding Savonius turbine.

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. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments were conducted by installing wind-acceleration structures on both sides of a straight-bladed vertical-axis wind turbine (VAWT) to improve the output performance of the turbine. In the case of Venturi-shape structures, a curved shape with a large outlet opening produced a higher power output than straight or brimmed Venturi shapes. More importantly, two simple flat plates installed upstream of the wind turbine achieved the highest power enhancement of 2.4 times the power of the bare wind turbine. From the analysis of the flow visualization results, the power enhancement was attributed to the increase in lift force on the blades in the upstream region due to the acceleration of the gap flow between the flat plates, and the decrease in drag force on the blades toward the upstream region due to stagnation of the flow behind the plates. [ABSTRACT FROM AUTHOR]

Noise pollution is a significant challenge in developing the use of wind turbines, especially in residential areas. H-Darrieus turbine is a wind turbine widely used in residential areas, usually exposed to variable wind speeds, and works in a wide range of tip speed ratios. In this article, the importance of tip speed ratio on the output power and noise pollution of an H-Darrieus turbine is numerically investigated using the SST-kω model (for flow simulation at tip speed ratios of 2.04 to 3.3) and the Ffowcs Williams-Hawkings equations (for noise calculation in far-field). The directivity results show that the angle position of maximum noise differs for different tip speed ratios. Therefore, noise calculation only at the angle position of 0o, widely used for wind turbines, is insufficient. The results show that in terms of noise pollution, tip speed ratios of 2.04 and 3.3 have the best and worst performances, with maximum noises of 67.91 dB and 71.85 dB, respectively. On the other hand, the tip speed ratio of 2.64 has the highest power (2.92 times the power of 2.04) with a maximum noise of 68.26 dB, which is negligibly higher than that for the tip speed ratio of 2.04. Overall, it is concluded that in terms of compromise between noise pollution and power generation, the tip speed ratio of 2.64 is the best point for this turbine. [ABSTRACT FROM AUTHOR]

In the current study, effects of a Gurney flap and pitch angle on the aerodynamic performance of a vertical-axis wind turbine are investigated by comparing CFD results of the standard and flap-equipped wind turbines at various pitch angles. Both wind turbines show better performance at the negative pitch angles and the flap-equipped wind turbine shows higher performance than the standard one at most of the pitch angles. The best flap-equipped wind turbine obtained a 7.5 % higher power coefficient than the best standard wind turbine by varying the pitch angle. Flow analysis reveals that wind turbine's pitch angle control and small device attachment should be implemented to make its blades remain in the pre-stall region. For the high-performance wind turbine, positive flow characteristics in terms of no formation of the vortex around the trailing edge and weak traces of the vortex have been identified. [ABSTRACT FROM AUTHOR]

This paper presents results of experimental investigations and numerical simulations of a vertical-axis H-type wind turbine, considering the influence of propeller blade pitch angle on turbine characteristics. An innovative airfoil profile based on a modified symmetric NACA0015 airfoil profile was used as the designed blade profile, which was tested in a wind tunnel over a range of Reynolds numbers from 50,000 to 300,000. The phenomenon of angle-of-attack variation and the resulting forces acting on the blades, particularly in the horizontal configuration and vertical axis of rotation, were discussed. Series of experiments were conducted on a 1:1 scale four-bladed turbine model in the wind tunnel to determine the characteristics, specifically the power coefficient distribution over the tip speed ratio for various Reynolds numbers and blade pitch angles. Subsequently, the turbine was modeled using Qblade software, and a series of calculations were performed under the same conditions. The numerical results were validated with the experimental data. [ABSTRACT FROM AUTHOR]

The nonstationary separated incompressible flows around Darrieus and Savonius rotors of vertical-axis wind turbines were investigated through computational simulation using the Reynolds averaged Navier–Stokes equations and Spalart–Allmaras turbulence model. The implicit finite-volume algorithm, the basis of which was artificial compressibility method, was chosen to obtain the numerical solution. The series of computational and physical experiments for Darrieus rotors with varied numbers and shapes of blades were performed. The detailed visualization of the flow was presented. The turbulent flows surrounding the Darrieus and Savonius rotors were studied, and as a part of these investigations, the major phases of vortex progress were identified. For this purpose, three series of computer tests on the aerodynamic and power properties of Savonius rotors with two and three buckets were performed, and their results are also presented. The influence of tip-speed ratio, solidity, and Reynolds numbers on the power coefficients of the Darrieus and Savonius rotors was investigated. It has been demonstrated that increasing Reynolds number from 104 to 106 causes a rise in Darrieus rotors power coefficient from 0.15 up to 0.5. The maximum values of power coefficient are moved away from higher values of tip-speed ratio from 2 to 5 as a result of a decrease in Darrieus rotor solidity from 1.0 to 0.33. The greatest power coefficient for a Savonius rotor with two blades is 0.23 and for a Savonius rotor with three blades is 0.19. [ABSTRACT FROM AUTHOR]

The performance of a new vertical-axis wind turbine rotor based on the mathematical equation of the cycloid is analyzed and compared through simulation and experimental testing against a semicircular or S-type rotor, which is widely used. The study examines three cases: equalizing the diameter, chord length and the area under the curve. Computational Fluid Dynamics (CFD) was used to simulate these cases and evaluate moment, angular velocity and power. Experimental validation was carried out in a wind tunnel that was designed and optimized with the support of CFD. The rotors for all three cases were 3D printed in resin to analyze their experimental performance as a function of wind speed. The moment and Maximum Power Point (MPP) were determined in each case. The simulation results indicate that the cycloid-type rotor outperforms the semicircular or S-type rotor by 15%. Additionally, experimental evidence confirms that the cycloid-type rotor performs better in all three cases. In the MPP analysis, the cycloid-type rotor achieved an efficiency of 10.8% which was 38% better than the S-type rotor.

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • A curved blade-straight blade hybrid vertical axis wind turbine is proposed. • Aerodynamics of hybrid rotor are quantitatively analyzed. • The influence mechanisms of critical parameters of inner rotor are elucidated. • Hybrid rotor design leads to higher power output than single Φ-shaped rotor. The Φ-shaped Darrieus wind turbines offer promising applications owing to their omnidirectionality and structural advantages. However, their poor performance at low tip-speed ratios remains a challenge. To address this issue, this study proposes a hybrid rotor consisting of a Φ-shaped and straight-bladed Darrieus rotor. The computational fluid dynamics simulation is employed to investigate the effects of diameter ratio, height ratio, chord length ratio, and inner rotor blade pitch angle on the aerodynamic performance of the hybrid rotor. The findings reveal that the power coefficient reaches a maximum of 0.02531 and the lateral force coefficient is minimized at 0.10588 when the diameter ratio is 0.6. With the height ratio of 0.5, the power coefficient peaks, increasing by 77% compared to the single Φ-shaped rotor. The power coefficient is highly sensitive to the chord length ratio, increasing by 114% compared to the single Φ-shaped rotor when chord length ratio is 1.4. The lateral force coefficient increased significantly when the chord length ratio exceeded 1. In addition, changes in the pitch angle have minimal effects on the thrust and lateral force coefficients, which are beneficial for operational stability. This study provides a theoretical basis for the design of efficient and stable double Darrieus vertical-axis wind turbines, which have promising applications in distributed power generation. [ABSTRACT FROM AUTHOR]

In light of the escalating demand for renewable energy sources, vertical-axis wind turbines have emerged as a pivotal technical solution for addressing the challenge of clean energy supply in residential and urban areas. As a simple and feasible passive control method, the plain Gurney flap (PGF) is widely applied to improve turbine aerodynamic performance. In this paper, the influence of a novel serrated gurney flap (SGF) with different flap heights is studied on the NACA0021 airfoil by numerical simulations. The findings demonstrate that, compared with the PGF, the SGF reduces the trailing edge reverse vortices from a pair to a single vortex and possesses lower drag. When the flap height reaches 6% of the chord (6%c), the lift-to-drag ratio of SGF surpasses that of PGF. A turbine rotor is equipped with an SGF and a PGF to compare their performances. The result confirms the flap effect depending on the rotor’s tip speed. At a low tip speed ratio (TSR), the PGF works better than the SGF. The SGF is preferred over the PGF for a higher tip speed ratio (TSR > 2.5). With the 6%c flap height, the performance of the SGF rotor surpasses the PGF by 13.9% at TSR = 2.62.

A numerical procedure was developed to determine a variable-pitch law that maximized the performance of a vertical-axis wind turbine (VAWT). The methodology was based on the determination, for each blade, of the angle of attack maximizing the stationary aerodynamic efficiency at prescribed azimuthal positions. The angles of attack were determined by means of a panel method with a low computational effort, and the methodology was implemented in Matlab ® software (version R2021a) allowing us to achieve in real time a variable-pitch law suitable for the turbine geometry. The variable pitch law was validated by considering its effect on the torque of a 2D model of an H-Darrieus turbine. U-RANS analyses were carried out with a K − ω S S T model and a sliding-mesh technique was used to prescribe the blade motion around the shaft and pitch motion. Results showed how the variable-pitch law delayed the dynamic stall and improved the aerodynamic performance considerably. [ABSTRACT FROM AUTHOR]

We improve the aerodynamic performance of a simplified vertical-axis wind turbine (VAWT) using a biomimetic flap, inspired by the movement of secondary feathers of a bird's wing at landing (Liebe 1979 Aerokurier 12 54). The VAWT considered has three NACA0018 straight blades at the Reynolds number of80000based on the turbine diameter and free-stream velocity. The biomimetic flap is made of a rigid rectangular curved plate, and its streamwise length is 0.2 c and axial (spanwise) length is the same as that of blade, where c is the blade chord length. This device is installed on the inner surface of each blade. Its one side is attached near the blade leading edge (pivot point), and the other side automatically rotates around the pivot point (without external power input) in response to the surrounding flow field during blade rotation. The flap increases the time-averaged power coefficient by 88% at the tip-speed ratio of 0.8, when its pivot point is at 0.1 c downstream from the blade leading edge. While the torque on the blade itself does not change even in the presence of the flap, the flap itself generates additional torque, thus increasing the overall power coefficient. The phase analysis indicates that the power coefficient of VAWT significantly increases during flap opening to full deployment through the interaction with vortices separated from the blade leading edge. When the pivot point of flap is farther downstream from the leading edge or the flap operates at a high tip-speed ratio, the performance of the flap diminishes due to its weaker interaction with the separating vortices., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Vertical-axis wind turbines (VAWTs) are an innovative solution for energy harvesting, as they harness the power of the wind by enabling rotational motion around a vertical shaft situated on the ground. This paper deals with the design optimisation of VAWT systems for highway energy harvesting. The four design parameters, blade number, blade curvature angle, blade thickness and blade diameter ratio, have been investigated to find their respective optimalities for the enhanced energy efficiency of VAWT systems. Computational fluid dynamics (CFD) simulations are conducted in Ansys Fluent using a Banki turbine model created in Solidworks®, with a constant velocity inlet of 4 m/s and rotational speeds ranging from 0.5 to 3 rad/s. The simulations consider the placement of the turbine in the central reservation of a highway with a windshield for enhanced performance. From the results, it was observed that increasing blade thickness and blade number improve turbine performance, with maximum power coefficients achieved at specific tip speed ratios (TSRs). The optimal blade diameter ratio has been found to be approximately 0.75 for TSR values between 0.1 and 0.5, whilst a ratio of 0.83 gave the best performance at higher TSR values. Also, a blade curvature angle of 60 degrees has been found optimal for slow rotations, while 100 degrees yielded the highest power coefficient for faster rotations. The study could also highlight the significance of blade curvature angle variation, resulting in a notable 14% performance increase compared to the baseline. The geometric changes proposed in the study allow for greater power extraction from the same turbine footprint, leading to increased energy efficiency in VAWT systems.

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.

Wind tunnel experiments were conducted by installing wind-acceleration structures on both sides of a straight-bladed vertical-axis wind turbine (VAWT) to improve the output performance of the turbine. In the case of Venturi-shape structures, a curved shape with a large outlet opening produced a higher power output than straight or brimmed Venturi shapes. More importantly, two simple flat plates installed upstream of the wind turbine achieved the highest power enhancement of 2.4 times the power of the bare wind turbine. From the analysis of the flow visualization results, the power enhancement was attributed to the increase in lift force on the blades in the upstream region due to the acceleration of the gap flow between the flat plates, and the decrease in drag force on the blades toward the upstream region due to stagnation of the flow behind the plates.

This study investigates the elastic response characteristics of a floating wind turbine (FOWT) with two vertical-axis wind turbines (VAWTs), called double-rotor VAWTs. The model consists of two VAWTs mounted on a single semi-submersible floating structure and employs a single point mooring, which allows the FOWT to always self-align with the wind. Usually, a coupled analysis of the wind turbine and floating structure is used in the design of FOWTs; however, there is no coupled analysis available for VAWTs. In this study, we attempted to combine the wind turbine design software "QBlade" and the coupled wind turbine/floating body analysis code "UTWind" as one of the methods of coupled analysis of a VAWT and a floating body. Numerical simulation results were compared with experimental results using an elastic model scaled down to 1/100 of its actual model to determine the motion response and cross-sectional bending moments. The experimental results showed that the thrust of the VAWT had a particular influence on the cross-sectional forces and motion response between the two VAWTs. For cross-sectional forces, all results showed similar trends. Overall, the results of UTWind for double-rotor VAWTs are reasonable. It was also found that the pitch motion must be accurately reproduced to improve the accuracy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The nonstationary separated incompressible flows around Darrieus and Savonius rotors of vertical-axis wind turbines were investigated through computational simulation using the Reynolds averaged Navier–Stokes equations and Spalart–Allmaras turbulence model. The implicit finite-volume algorithm, the basis of which was artificial compressibility method, was chosen to obtain the numerical solution. The series of computational and physical experiments for Darrieus rotors with varied numbers and shapes of blades were performed. The detailed visualization of the flow was presented. The turbulent flows surrounding the Darrieus and Savonius rotors were studied, and as a part of these investigations, the major phases of vortex progress were identified. For this purpose, three series of computer tests on the aerodynamic and power properties of Savonius rotors with two and three buckets were performed, and their results are also presented. The influence of tip-speed ratio, solidity, and Reynolds numbers on the power coefficients of the Darrieus and Savonius rotors was investigated. It has been demonstrated that increasing Reynolds number from 104 to 106 causes a rise in Darrieus rotors power coefficient from 0.15 up to 0.5. The maximum values of power coefficient are moved away from higher values of tip-speed ratio from 2 to 5 as a result of a decrease in Darrieus rotor solidity from 1.0 to 0.33. The greatest power coefficient for a Savonius rotor with two blades is 0.23 and for a Savonius rotor with three blades is 0.19.

This paper presents results of experimental investigations and numerical simulations of a vertical-axis H-type wind turbine, considering the influence of propeller blade pitch angle on turbine characteristics. An innovative airfoil profile based on a modified symmetric NACA0015 airfoil profile was used as the designed blade profile, which was tested in a wind tunnel over a range of Reynolds numbers from 50,000 to 300,000. The phenomenon of angle-of-attack variation and the resulting forces acting on the blades, particularly in the horizontal configuration and vertical axis of rotation, were discussed. Series of experiments were conducted on a 1:1 scale four-bladed turbine model in the wind tunnel to determine the characteristics, specifically the power coefficient distribution over the tip speed ratio for various Reynolds numbers and blade pitch angles. Subsequently, the turbine was modeled using Qblade software, and a series of calculations were performed under the same conditions. The numerical results were validated with the experimental data.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the influences of the geometric characteristics of a dimple on the aerodynamic properties of a vertical axis wind turbine are investigated, and its configuration optimization that maximizes the wind turbine's performance is carried out. Three parameters that control the position, size and depth of the dimple are used to parameterize the dimple's configuration and to conduct optimization. With these parameters, when the flows around the wind turbines with various dimples are compared, several meaningful physical phenomena are found. First, a strong association between the position of a dimple and the power coefficient is found where the power coefficient increases as the position of the dimple approaches the trailing edge of the wind turbine blade. Second, high-performance enhancement tends to be achieved when a dimple is small, but this attribution becomes weaker as the dimple moves toward the trailing edge. Furthermore, when the flow of the optimal wind turbine is compared with the one without a dimple, a reduction of the blade wake and delay of the flow separation can be identified. Finally, the shed vortices from the optimal wind turbine blade are weaker and decay faster than the ones shed from the wind turbine without a dimple.

In this study, performance of the blade profiles which was developed numerically and parametrically was examined experimentally for vertical axis wind turbine. In the parametric optimization study, angle of attack, mean (camber) line and thickness were taken as parameter, and the profile was optimized by using Ansys/Response Surface Optimization tool. After that, in the numerical optimization study, the lift and drag coefficients were taken as parameters and the profile was optimized and the blade profiles of NACA0012-α and NACA0012-β, which would make the lift-to-drag ratio maximum, were obtained. The developed profiles were produced by 3D printer and the power data was measured experimentally for 3, 4 and 5 bladed turbines. The highest power was obtained in the 4-bladed turbine for all profiles. The power coefficient of 0.19 was obtained from a reference profile, while power coefficient of 0.24 was obtained from NACA0012-α profile and 0.30 from NACA0012-β profile. The blade profile derived by numerical optimization reached 25% higher power coefficient than the blade profile derived by parametric optimization. It is found that lift coefficient on the power coefficient of the vertical axis wind turbine is more dominant than the drag coefficient.

This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier–Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio. [ABSTRACT FROM AUTHOR]