Average Power Coefficient Research Articles

Experimental and Simulation Investigation of J-shaped and Kammtail Virtual Airfoils in Small-Scale Horizontal Axis Wind Turbines

Abstract In this work, the performance of new wind blade designs for small-scale horizontal axis wind turbines (HAWTs) was studied and compared with the performance of a baseline design. The studied designs were J-shaped and Kammtail Virtual Foil profiles. Three J-shaped pressure-side truncation ratios and two KVF truncation ratios were studied. All proposed cases were first investigated in a two-dimensional simulation study to get the lift-to-drag ratio by applying different wind speeds and angles of attack. The baseline design was experimentally investigated. Output power was measured using a digital rotary torque sensor at three wind speeds. The tip speed ratio was calculated after measuring each wind speed's free rotating revolutions. Three wind speeds and experimental TSRs were used in three-dimensional simulations to capture the performances of the proposed cases and compare them with the baseline. The simulation investigation was carried out for lab-scale and scaled cases. The three-dimensional study found that the J-shaped blades enhanced the performance of the HAWTs for both lab-scale and scaled cases. J-shaped blades with a 1/3 opening ratio yielded an average power coefficient enhancement of around 1.56% and 4.16% for lab-scale and scaled cases, respectively. J-shaped blades with a 2/3 opening ratio enhanced the average power coefficient for lab-scale and scaled cases. Furthermore, it was found that the KVF blades diminished the performance for both lab-scale and scaled cases.

Novel passive flow control method using leading-edge prism-shaped cylinder: Performance enhancement of vertical-axis wind turbines

Due to periodic dynamic stall at low tip speed ratios (TSRs), vertical-axis wind turbines (VAWTs) experience notable performance challenges during rotation, which leads to fluctuations in torque and a decrease in energy capture. This research aims to boost the aerodynamic performance of Darrieus VAWTs by employing a leading-edge (LE) prism cylinder (PC) to enhance energy extraction. This novel small-scale device functions as a passive method for controlling flow separation, aiming to energize the boundary layer and adjust the pressure distribution on the blades. Its effectiveness depends on factors such as size, shape, and placement, necessitating careful optimization. A three-dimensional (3D) computational fluid dynamics (CFD) analysis, combined with Taguchi optimization and analysis of variance, is conducted to determine the optimal design parameters for the LE PC tool. This 3D CFD method captures the full complexity of flow dynamics, including vortex structures and wake behavior, leading to more accurate wind turbine performance predictions than two-dimensional (2D) CFD models. The results highlight the crucial role of PC size (Factor A), which contributes nearly 85% to the total contribution factor, while the angle of PC influence is minimal. The optimized rotor demonstrates a 36% increase in maximum average power coefficient (CP) compared to an uncontrolled rotor at TSR = 1.5. However, the effectiveness of this control method diminishes at higher TSRs because the blades encounter angles of attack below the critical stall angle throughout the rotation cycle, naturally preventing flow separation and making the flow separation control method unnecessary. The PC installed on the optimized blade delays flow separation to 55% of the blade chord length, compared to 40% for the base blade. Consequently, the rotor operates efficiently, ensuring consistent, and reliable power generation without flow separation issues.

Simulation of a Tidal Current-Powered Freshwater and Energy Supply System for Sustainable Island Development

Sustainable development of islands cannot be achieved without the use of renewable energy to address energy and freshwater supply issues. Utilizing the widely distributed tidal current energy in island regions can enhance local energy and water supply security. To achieve economic and operational efficiency, it is crucial to fully account for the unique periodicity and intermittency of tidal current energy. In this study, a tidal current-powered freshwater and energy supply system is proposed. The marine current turbine adopts a direct-drive configuration and will be able to directly transfer the power of the turbine rotation to the seawater pump to improve the energy efficiency. Additionally, the system incorporates batteries for short-term energy storage, aimed at increasing the capacity factor of the electrolyzer. A simulation is conducted using measured inflow velocity data from a full 12 h tidal cycle. The results show that the turbine’s average power coefficient reaches 0.434, the electrolyzer’s average energy efficiency is 60.9%, the capacity factor is 70.1%, and the desalination system’s average specific energy consumption is 6.175 kWh/m3. The feasibility of the system design has been validated.

Data-driven multi-objective optimization of aerodynamics and aeroacoustics in dual Savonius wind turbines using large eddy simulation and machine learning

Savonius rotor is a popular form of vertical-axis wind turbine (VAWT) for small-scale and urban applications because of its straightforward design and self-starting ability. Dual VAWTs present challenges in terms of wake interactions and noise, particularly in urban areas. Optimizing these parameters is essential for future wind energy adoption. This research is the first to analyze how the interaction of wakes from adjacent rotors, combined with a deflector, affects both the aerodynamic performance and noise levels of dual Savonius rotors. Large Eddy Simulation is applied, as it effectively captures detailed turbulent wind flows and their interactions with wind turbines. A multi-objective optimization method combining Machine Learning and Computational Fluid Dynamics (CFD) is developed to optimize rotors for maximum power efficiency and minimum noise, considering their wake interactions with a unique deflector system. First, the influence of geometric parameters on aerodynamics and aeroacoustics characteristics of rotors is analyzed, and the database is generated using Design of Experiment approach. Next, the CFD model is replaced by Artificial Neural Network (ANN) model established for predicting rotor performances. A Multi-Objective Genetic Algorithm method is used to optimize aerodynamics and aeroacoustics characteristics of rotors. Finally, optimal design parameters are identified from the Pareto front using the technique for order of preference by similarity to ideal solution decision-making method. The ANN model demonstrated high accuracy with an RANN2 of 0.995 and 0.971 for the average power coefficient (CP) and overall sound pressure level (OSPL) predictions, respectively. Multi-objective optimization revealed the best configuration of the deflector with bleed jets, improving the average CP up to 57.5% and reducing OSPL to an almost 5.2% compared to the dual rotor case at TSR = 0.8.

Optimizing a vertical axis wind turbine with helical blades: Application of 3D CFD and Taguchi method

Vertical axis wind turbines (VAWT) with helical blades are being interested in urban areas due to the low dependency on the wind direction and also due to low noise production. In spite of good self-starting and smooth operation as the advantages of this type of turbine, its optimizing has not been reported in literature yet and is the subject of this research. A primary investigation by 3D computational fluid dynamics (CFD) to simulate the air flow about the above type of VAWT in the first step showed the importance of three design variables of tip speed ratio, helical angle, and airfoil chord length. However, in the second step, CFD runs were very time consuming and costly. For considering five values for each design variable, 53=125 cases had to be simulated by 3D CFD. Thus, by the use of Taguchi method and with definition of an orthogonal array named L-25, the number of required 3D CFD simulations reduced from 125 to 25. Then, the optimum values of variables were obtained as 1.33 for the tip speed ratio, 30 degrees for the helical angle, and 0.4 m for the airfoil chord length. At the optimum point, the average power coefficient increased to 0.17542. The presented research is novel for optimizing VAWT with helical blades.

Green Electromagnetic Interference Shielding Material Based on Thermally Expandable Microspheres.

With the aggravation of electromagnetic pollution, electromagnetic interference (EMI) shielding materials have received enormous attention. However, most of the current EMI shielding materials only focus on the shielding effectiveness (SE), neglecting the electromagnetic pollution brought by secondary reflection. In this work, a method of preparing absorption-dominated EMI shielding materials, which are also called green EMI materials, using thermally expandable microspheres (TEMs) and expanded graphite (EG), is proposed. The expansion of TEMs in the EG/waterborne polyurethane mixture can improve the impedance matching between the composite and air. When the content of TEMs is 5 wt % and the content of EG is 15 wt %, the EMI SE of the sample reaches 38.4 dB, and the average reflection power coefficient of this composite is 0.27, indicating that the material mainly shields electromagnetic waves through absorption. Meanwhile, the prepared material also exhibits good stability, maintaining outstanding EMI SE and low value of reflection power coefficient even after the compression-recovery test.

Study on the Influence of Protuberance Amplitude on the Performance of Vertical Axis Wind Turbines

Abstract The performance of vertical axis wind turbine (VAWT) is mainly affected by the dynamic stall process of the blade. Inspired by the anti-stall performance of the humpback whale flipper, leading edge protuberances (LEPs) are applied to 2-blade VAWT. Based on computational fluid dynamics simulation method, the effects of LEPs amplitude on VAWT performance are investigated when blade tip speed ratio is 2.19. The results show that the larger the amplitude of the LEP, the lower the average power coefficient. When the number of protuberances is 3, the average power coefficient of the VAWT with a protuberance amplitude of 6.625mm is 1.8% higher than prototype blade. Considering the impact of increasing the chord length of biomimetic blades, the average tangential force coefficient of all biomimetic VAWTs decreases. The peak section performance of the bionic blade decreases significantly while the trough section performance increases significantly. The difference between the peak section and trough section of the LEPS plays an important role in improving the performance. This study provides a reference for the application of bionic protuberances in VAWTs.

Design and simulation of an off-grid marine current-powered seawater desalination and hydrogen production system

The use of marine current energy to provide a stable supply of energy and fresh water to islands and remote areas is a promising prospect. In this study, an integrated marine current-powered seawater desalination and hydrogen production system was proposed. For higher integration and efficiency, the generator and seawater pump were integrated into the nacelle and mechanically connected to the main shaft. Four operating modes and the corresponding start-stop and maximum power point tracking (MPPT) control strategy were designed to achieve energy distribution between the two loads. Considering the frequent start-stop caused by the sinusoidal characteristic of marine current energy, a soft start-up process was designed for the RO elements, including dual hydraulic accumulators and a smooth transition process to avoid abrupt changes in feed pressure and feed flow rate. Finally, the performance was obtained by simulation. During the 6 h of the ebb tide, the desalination system produced a total of 841.77 L of fresh water, while the electrolyzer produced 1038.5 SL of hydrogen and consumed 0.95 L of water. The average power coefficient of the turbine was 0.434, and the specific energy consumption of the desalination system was 2.03 kWh/m3, indicating good MPPT performance and high efficiency.

Fully passive model-based numerical analysis of the trailing-edge flexibility of hydrofoil on energy harvesting performance

The oscillating hydrofoil, a device used for collecting environmentally friendly tidal energy, is the focus of the study. The flexibility of the hydrofoil's trailing edge can impact its surface pressure distribution, lift, and moment characteristics. To improve the energy harvesting performance of oscillating hydrofoils, it is important to conduct thorough research on their energy harvesting mechanism. Therefore, numerical analysis is employed to develop a numerical model of the fully passive oscillating hydrofoil with the flexible trailing edge. The dynamic development behavior of surface vortices on hydrofoils is analyzed, demonstrating that the fluid–structure interaction between the hydrofoil and the surrounding fluid alters the hydrofoil's motion. The vortex patterns and pressure distribution on the hydrofoil surface are also affected, ultimately influencing the energy harvesting performance. By optimizing the flexibility coefficient of the fully passive oscillating hydrofoil with a flexible trailing edge, the energy harvesting performance of the oscillating hydrofoil is improved. When the maximum chord offset δm= 0.1c and the flexibility coefficient n= 2, the energy harvesting efficiency is 31.37%, and the average power coefficient is 1.17. Therefore, increasing the tail flexibility can be considered to enhance energy harvesting performance when designing the fully passive oscillating hydrofoil. The research provides a comprehensive analysis of energy harvesting performance, addressing the dynamic problem of the fully passive oscillating hydrofoils with flexible trailing edges. The findings of this study may provide guidance for the design and optimization of tidal energy harvesting devices with similar structures.

Effect of Wavelength on Turbine Performances and Vortical Wake Flows for Various Submersion Depths

When tidal turbines are deployed in water areas with significant waves, assessing the surface wave effects becomes imperative. Understanding the dynamic impact of wave–current conditions on the fluid dynamic performance of tidal turbines is crucial. This paper aims to establish a fundamental understanding of the influence of surface waves on tidal turbines. OpenFOAM, an open-source computational fluid dynamics (CFD) library platform, is utilized to predict the performance of current turbine under waves and currents. This research investigates the effects of two critical wave parameters, wave height and wavelength, on the fluid dynamics and wake structures of current turbine. Additionally, this study explores the influence of various submersion depths on turbine performance. The findings indicate that, under various wave conditions, the turbine’s average power coefficient remains constant, but significant fluctuations are shown. Increasing submersion depth can mitigate the impact of waves. However, in regions characterized by longer wavelengths, altering the submersion depth has limited effects on turbine performance.

Two-stage Taguchi-based optimization on dynamically-vented blade flaps to enhance the rotor performance of a Savonius turbine

Among the vertical-axis turbine groups for small-scale wind and hydrokinetic applications, the Savonius type is considered practical due to its simple construction, easy maintenance, and good self-starting characteristics. Unfortunately, it has a poor efficiency due to the exertion of negative torques during its returning sweeps. Recently, the technique of controlled dynamic venting has been shown to reduce this negative torque on a two-bladed Savonius rotor while preserving its omnidirectional capability. That investigation was extended in this numerical study by refining the controllable flaps of the same rotor to improve its performance using a two-stage optimization procedure. In the first stage, the design parameters of the controllable flaps were optimized using the Taguchi and Analysis of Variance (ANOVA) methods. In this analysis, the flap length was found to be the most significant parameter affecting the rotor performance with a contribution ratio of 79.8%, in contrast to a ratio of only 6.7% by the least effective parameter: the flap opening angle. The first optimization stage produced an improvement of 16.7% on the average power coefficient (CP) of the vented rotor, compared to the unvented one, at the optimal tip-speed ratio (TSR) of 1.0. In the second stage, the flap length was refined further to a shorter flap of 22.5% of the blade length, resulting in an improvement of 21% on the same metric at the same TSR. Crucially, these controllable flaps only used an energy cost of 6.1% of the total energy produced by the rotor, a significant improvement from the 12.2% energy cost obtained in the previous study.

Experimental study of the upstream bathymetry effects on a ducted twin vertical axis turbine

Tidal turbines at sea are subject to complex flow conditions. Among that complexity, wide bathymetry obstacles can generate powerful coherent flow structures whose impact on horizontal axis tidal turbines was proved to be highly detrimental. Consequently, the present paper aims at studying the effects of such coherent flow structures on the response of another tidal turbine geometry, namely a bottom-mounted ducted twin vertical axis tidal turbine (2-VATT). We tested a 1/20 scale model of such a 2-VATT in Ifremer’s flume tank either with a flat bed or downstream of a wide bathymetry obstacle at a constant far upstream velocity and we measured the turbine response simultaneously with the flow velocity. These flow measurements make it possible to compute cross-correlations in order to analyse the influence of the velocity fluctuation on the turbine response. The results reveal a strong drop in the average power and loads coefficients of the 2-VATT combined with significantly larger fluctuation. The velocity deficit and the high level of turbulence in the obstacle wake is responsible for a 40% lower average power coefficient and more than 3 times higher standard deviation compared to the flat bed configuration. The loads standard deviations are multiplied by 2 for the drag and by 10 for the lift when the 2-VATT is downstream of the bathymetry obstacle. This behaviour strongly increases the risks of structural fatigue failure, but the turbine drifting or overturning risks under those conditions remain lower than with the flat bed. The power fluctuation increase appears to be mostly due to the flow shear in the obstacle wake whereas the load fluctuation is mostly due to the periodical passing of the coherent flow structures. Thus, a proper characterisation of the flow at each precise turbine locations prior deployment at sea is highly recommended to design their structure accordingly.

PENGARUH KONTROLER MAXIMUM POWER POINT TRACKING (MPPT) TERHADAP EFISIENSI DAYA VERTICAL AXIS WIND TURBINE (VAWT) TIPE SAVONIUS DUA SUDU

The purpose of this research is to determine the effect of Maximum Power Point Tracking (MPPT) controller on the power efficiency of a two-bladed Savonius vertical axis wind turbine (VAWT) with a dimensional diameter of 0.9 m and a height of 1 meter, using 1 mm thick stainless steel plate blades. The MPPT controller is applied to the two-bladed Savonius wind turbine to maintain its operation at the maximum power point. The Perturb & Observe type MPPT controller is used in the study to compare the power output of the Savonius wind turbine when the MPPT system is inactive and when it is active, with three variations of load using resistors of 470 ohm, 560 ohm, and 1000 ohm. The research is conducted by subjecting the turbine blades to three variations of wind thrust at speeds of 4.9 m/s, 5.8 m/s, and 6.4 m/s. The testing without using MPPT resulted in an average power of 0.199 Watt, while using MPPT resulted in an average power of 0.620 Watt. The research findings indicate an average power difference of 0.421 Watt, representing an increase of 317.713%. The average power efficiency of the turbine increased by 2.331% compared to the calculated maximum power of the two-bladed Savonius wind turbine. The average power coefficient (Cp) of the two-bladed Savonius wind turbine without MPPT and with MPPT is 0.159% and 0.509%, respectively, indicating a positive effect of MPPT as it led to an average increase in power coefficient of 0.350%.

Effects of submergence depth on the performance of the savonius hydrokinetic turbine near a free surface

The influence of the submergence depth ratio on the Savonius hydrokinetic turbine and flow characteristics is numerically studied under different tip speed ratios. The tip speed ratio TSR (Ratio of the flow speed to blade speed) changes from 0.4 to 1.2, and the submergence depth ratio H*(Ratio of the depth to the turbine diameter) ranging from 0.22 to 1.1. The main conclusions are: (1) When the submergence depth ratio increases from 0.22 to 0.66, the flow field structure gradually becomes regular, and the power coefficient keeps increasing. (2) When the submergence depth ratio reaches up to 0.88, the curve of the power coefficient is similar to that of H* = 1.1, which means the effect of free surface can be ignored when H*>0.88. (3) According to the pressure distribution around the turbine, the free surface will increase the pressure difference on the blade due to the surface tension and blockage effect, thereby influencing the rotation of the turbine. (4) As the TSR increase, the submergence depth ratios of 0.55 and 0.88 are regarded as two demarcation points of the average power coefficient.

AgNWs/Fe3O4@NC Conductive Network Hierarchical Assembly to Prepare Flexible EMI Shielding Textile.

With the rapid development of high-power electronic instruments and communication technology, efficient electromagnetic shielding materials with strong absorption of electromagnetic waves and low reflection characteristics have become the focus of the world's attention. This study designs and synthesizes N-doped carbon-coated hollow Fe3O4 nanospheres (Fe3O4@NC) by spraying Ag nanowires (AgNWs) on textiles as conductive networks. Because of the high permeability and hollow structure Fe3O4@NC, electromagnetic wave goes through a unique process of "absorption, reflection, and reabsorption" when it passes through the surface of the composite textile. In X-band (≈8.2-12.4GHz), the average electromagnetic interference shielding effectiveness (EMI SE) reaches 50.1dB, while the reflectance shielding efficiency (SER) is only 2.6dB, and the average reflectance power coefficient (R) is as low as 0.45. The composite fabric has excellent properties and provides an effective strategy for electromagnetic interference shielding based on absorption.

Numerical study on aerodynamic performance improvement of the straight-bladed vertical axis wind turbine by using wind concentrators

The present study proposes a new concept of Straight-bladed Vertical Axis Wind Turbines (SB-VAWTs) with convex-shaped wind concentrator. The wind concentrator is installed up and down the rotor, which is designed to capture more airflow and improve the flow characteristics inside the rotor. The profile of the wind concentrator is generated based on the B-spline, the quadratic rotational orthogonal combination design method is used to study the effects of bottom radius R1, top radius R2, inlet angle α1, and outlet angle α2 of the concentrator, and the distance ΔL between the concentrator and the rotor on the aerodynamic performance of the SB-VAWT by numerical simulation. It is found that the installation of the wind concentrator improves the flow characteristics inside the rotor and enhances the aerodynamic performance of the SB-VAWT, particularly at lower wind speeds. Under the condition of this study, the average torque coefficient and maximum power coefficient of the SB-VAWT with the wind concentrator are enhanced by up to 24.7 % and 52.7 %. This study can provide a reference for using a wind concentrator to improve the aerodynamic characteristics of SB-VAWTs and demonstrate the potential of using this kind of SB-VAWT for wind energy utilization systems.

Optimization Layout and Aerodynamic Performance Research on Double Nautilus Vertical-Axis Wind Turbine

The double vertical-axis wind turbine (VAWT) system serves as a high-performance design solution. The Nautilus wind turbine investigated in this research imitated the structure of a Nautilus shell and is a vertical-axis drag-type wind turbine that exhibits relatively low efficiency. Therefore, the improvement of its wind energy efficiency is of paramount importance. This paper utilizes Computational Fluid Dynamics (CFD) software, based on the Reynolds-averaged Navier–Stokes equations and dynamic meshing techniques, to conduct numerical investigations on the aerodynamic performance of the Nautilus wind turbine array layout. The effects of wind direction, spacing ratio, and rotation direction are individually studied, and the interpretations and explanations are provided based on flow field characteristics. The results show that when the wind direction is 90°, i.e., a transverse layout, the closer the spacing between the transverse turbines, the higher the average power coefficient of the entire wind turbine system, with little effect from the three rotation directions. The maximum average power coefficient reached 28.9% and the power gain factor (TPGF) reached 11.1%. The enhancement effect primarily originates from the wake interaction among neighboring turbines. The experimental results showed a deviation of 8.1% compared to the CFD simulation results, thus validating the accuracy of the numerical CFD modeling. Ultimately, several array layouts are proposed, based on the prevalent wind direction and spacing ratio research. The enhancement of the wind turbine array’s situation could significantly increase the average efficiency of the entire wind turbine cluster. Consequently, this study provides a reference for the practical application of biomimetic vertical-axis drag-type wind turbine systems in actual engineering.

Dynamic Stall Control for a Vertical-Axis Wind Turbine Using Plasma Actuators

Dynamic stall is a major challenge for vertical-axis wind turbines (VAWTs) as it negatively impacts the aerodynamic performance of VAWTs, resulting in a reduction in net power output from the turbines. This study explores the use of alternating current dielectric barrier discharge plasma actuators for controlling dynamic stall on a VAWT. The flow control process is resolved using a two-dimensional unsteady Reynolds-averaged Navier–Stokes equations simulation with a Reynolds stress turbulence model adopted. The macro-effect of the plasma discharge on mean flow is modeled by an empirical body force model. The detailed flow actuation procedure is simulated. Numerical results show that the flow control process is dominated by the spanwise vortices, which result from the interaction between the plasma discharge and separated flow. The spanwise vortices not only prevent the development of a leading-edge separation bubble into a dynamic stall vortex, but also suppress the flow separation at the trailing edge. The application of plasma forcing has been found to greatly enhance the aerodynamic performance of the turbine in terms of the moment coefficient and averaged power coefficient of the turbine blades. Furthermore, we examine how the positioning of the plasma actuators and the freestream wind velocity affect flow control. The optimal actuation location is determined, and the plasma actuators are seen to be able to substantially enhance the net power output of the blades at all freestream speeds.

Hydrodynamics and Wake Flow Analysis of a Floating Twin-Rotor Horizontal Axis Tidal Current Turbine in Roll Motion

The study of hydrodynamic characteristics of floating double-rotor horizontal axis tidal current turbines (FDHATTs) is of great significance for the development of tidal current energy. In this paper, the effect of roll motion on a FDHATT is investigated using the Computational Fluid Dynamics (CFD) method. The analysis was conducted in the CFD software STAR-CCM+ using the Reynolds-averaged Navier–Stokes method. The effects of different roll periods and tip speed ratios on the power coefficient and thrust coefficient of FDHATT were studied, and then the changes in the vorticity field and velocity field of the turbine wake were analyzed by two-dimensional cross-section and Q criterion. The study indicates that roll motion results in a maximum decrease of 30.76% in the average power coefficient and introduces fluctuations in the instantaneous load. Furthermore, roll motion significantly accelerates the recovery of wake velocity. Different combinations of roll periods and tip speed ratios lead to varying degrees of wake velocity recovery. In the optimal combination, at a position 12 times the rotor diameter downstream, roll motion can recover the wake velocity to 92% of the incoming flow velocity. This represents a 23% improvement compared to the case with no roll motion.

Feasibility analysis of aerodynamic characteristics for vertical-axis turbines in offshore: A comprehensive analysis on scale and design of wind system

With the continuously increasing installed capacity of offshore wind turbines, highly adaptable vertical axis wind turbines (VAWTs) are facing new opportunities. Large-scale offshore platforms need a megawatt installed capacity, at least 1∼2 MW, which requires the feasibility analysis of aerodynamic characteristics for large-scale VAWTs. Due to the unsteady aerodynamic phenomenon, i.e. the dynamic stall phenomenon, the power output of VAWTs is very sensitive to the variations of Reynolds number and reduced frequency, which are closely related to the scale of wind turbines. In order to explore the large-scale VAWTs for offshore platforms, three design methods are proposed: Increasing the Reynolds number; Decreasing reduced frequency; Forming an array. Their feasibility and economies are verified by a high-resolution numerical method, and the results show that increasing the Reynolds number could improve their power coefficients to 0.259 for a one-blade VAWT, while an excessive decrease of reduced frequency would lead to power losses. The form of installing one or more levels of VAWT arrays on a single platform is a better design scheme with averaged power coefficient of 0.326 and a blade weighing 2.7 tons per 10 MW, and for large offshore platforms, it could reach the lowest levelized cost of energy.