H-Darrieus Vertical Axis Wind Turbine Research Articles

Numerical investigation on the spanwise chord distribution effects on the performance of an H-darrieus vertical axis wind turbines

The efficiency of Darrieus wind turbines has increased significantly due to developments in blade design, albeit at the expense of the simplicity provided by simple straight blades. The purpose of this research is to gain insight into the influence of various curvatures embedded in the plan of the blade while maintaining its simple straight shape. A variation in chord length along the span defines the curvature. To assess their effect on performance and efficiency, concave, and convex Leading-Trailing Edged Blades (LTEB) are investigated and evaluated in comparison to straight blades. That is viable to gain valuable insight about these blade designs' potential advantages in various applications by studying their aerodynamic characteristics and flow characteristics. The Q-blade tool is used to simulate 3D unsteady Nonlinear Lifting Lines Free Vortex Wake (3D-NLLFVW). The virtual camber effect brought on by flow curvatures is implemented to improve the results' accuracy. According to the findings, H-Darrieus' aerodynamic efficiency climbed by 16% and 9.5% at high TSR. For the concave and convex LTEBs, the torque ripple is smoothed by 37% and 19%, respectively. Additionally, compared to the straight-bladed rotor, the chosen variations enable volume reductions of 53% and 28%.

CFD comparison of 2D and 3D aerodynamics in H-Darrieus prototype wake

In the present study, a comparative assessment is conducted to evaluate the outcomes derived from two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics (CFD) models utilizing the unsteady Reynolds-averaged Navier–Stokes (URANS) approach. The focus lies on the aerodynamic performance of the H-Darrieus vertical axis wind turbine, which has been the subject of numerous numerical investigations since 2010. The k−ω shear stress transport (SST) turbulence model is employed to replicate the flow structures evolving in the turbine wake.The maximum power coefficients attained through 2D and 3D modeling are reported as Cp=0.4016 and Cp=0.5734, respectively, at a tip speed ratio (λ) of 3.0976. The maximum 2D and 3D absolute errors, corresponding to the evaluation of the power coefficients, are determined to be 14.9714% and 29.1582%, respectively. These errors are calculated at λ=2.5183 and λ=3.0976. The parametric study conducted herein reveals that the range of the power coefficient enhancement, considering 3D aerodynamic effects, surpasses that obtained from 2D calculations. In 3D modeling, this range is delineated between λ=1.85 and λ=3.10, whereas, in 2D modeling, it is defined by the interval bounded by λ=2.05 and λ=3.10. The essential contours for comparing the 2D and 3D approaches and for characterizing the flow structures developing around the H-Darrieus turbine are generated and analyzed.

Numerical analysis of H-Darrieus vertical axis wind turbines with varying aspect ratios for exhaust energy extractions

In this paper, a three-dimensional numerical study has been conducted by solving the unsteady Reynolds Averaged Navier Stokes equations with shear stress transport (SST) k-omega turbulence model to investigate the power production efficiency of a three-bladed H-Darrieus vertical axis wind turbines (HDWT) using S-1046 airfoil under accelerated wind conditions of the cooling tower exhaust system. Aiming to extract the waste energy from the exhaust air, four HDWTs having different aspect ratios were tested by varying the turbine diameter; and the moment and power coefficient values were calculated at tip speed ratios (TSR) in the range of 1.5–3.5. The results showed that the HDWT with a smaller aspect ratio (AR) of 0.44 gives a better power coefficient of 0.294 at TSR 2.5 as compared to other testing conditions. Further, a detailed flow field analysis around the HDWT for different ARs and TSRs has been provided in this paper to discuss the turbine's performance. Finally, a comparative study with the free-stream flow condition showed that HDWT provides 58.5% lower performance than the flow in the exhaust system at lower AR, indicating a positive guided flow effect on the turbine performance under exhaust flow systems.

Surrogate-Based Design Optimization of a H-Darrieus Wind Turbine Comparing Classical Response Surface, Artificial Neural Networks, and Kriging

Clean energy sources like wind energy have been receiving much attention, and great emphasis has been given to the design and optimization of horizontal axis wind turbines, but just as important are the vertical axis wind turbines that can be used for generating energy for small businesses, houses, and buildings. This article sought to study the optimal geometrical parameters of a H-Darrieus vertical axis wind turbine using surrogate-based optimization with three different types of surrogate models and compared them. Airfoil chord and thickness were chosen as the design variables and respective ranges set at 0.32-0.6 m and 0.04-0.16 m. All evaluations are carried out for a tip-speed ratio of 1.5. Three different surrogate models were used and compared, namely a quadratic polynomial response surface, an artificial neural network based on radial basis functions called Extreme Learning Machine and a Kriging interpolator. Surrogates were constructed based on an initial sample data distributed according to a full factorial design. A test set was designed to evaluate the accuracy of the surrogates. Both training and testing data sets were generated using 2D CFD modeling to reduce computational cost. From the test set, Extreme Learning Machine surrogate showed the smallest RMSE of 11.24%, followed by Kriging, at 17.64%, and Response Surface of 22.17%. For the optimal designs the same pattern ensued, with optimal power coefficient overestimated by 8.7% for the response surface surrogate, followed by 3.12% and 2.17% for the Kriging interpolator and the Extreme Learning Machine, respectively. Power coefficient curves comparing the three optimal geometries from each surrogate were calculated and plotted. Optimal turbine obtained from Kriging surrogate optimization process resulted in a 7.92% increase in the Cp, whilst Extreme Learning Machine and Response Surface resulted in a 7.86% and 4.29% increase, respectively, all when compared to baseline CFD model. Concluding guidelines are that the quadratic polynomial response surface may not be the best alternative when dealing with complex non-linear relationships as typically present in VAWT simulations. Superior techniques such as Extreme Learning Machine and Kriging could be more suitable for this application.

Experimental analysis of hybrid VAWT and the effect of semi-cylindrical attachment to the trailing edge

Vertical axis wind turbines (VAWTs) work efficiently in low wind speed regions and varying wind directions like urban environments due to their omnidirectional capability. The current study examines experimentally the performance of the H-Darrieus VAWT having NACA 0018 airfoil by use of semi-cylindrical attachments at the trailing edge and hybridization using two bladed S-Savonius rotor with zero overlap conditions. The rotor's static torque and dynamic performances are investigated at a low wind speed of 4 m/s. The results show that the semi-cylindrical attachment increases the range of positive static torque. The static torque of Darrieus with attachment at 90° inside is more consistent, which enhances the starting capability of the Darrieus turbine with a static torque coefficient of 0.031, which is 29.7 % higher than a simple Darrieus turbine. The hybrid configuration shows maximum dynamic torque only at the 90° azimuthal position. The power coefficient of all configurations with attachments is lower than simple Darrieus due to drag created by attachments. The power coefficient value of 0.03 for hybrid configuration is the highest, with a wide range of tip speed ratio (TSR).

Numerical investigation of h-Darrieus wind turbine aerodynamics at different tip speed ratios

PurposeThe purpose of the paper is to predict the aerodynamic performance of a complete scale model H-Darrieus vertical axis wind turbine (VAWT) with end plates at different operating conditions. This paper aims at understanding the flow physics around a model VAWT for three different tip speed ratios corresponding to three different flow regimes.Design/methodology/approachThis study achieves a first three-dimensional hybrid lattice Boltzmann method/very large eddy simulation (LBM-VLES) model for a complete scaled model VAWT with end plates and mast using the solver PowerFLOW. The power curve predicted from the numerical simulations is compared with the experimental data collected at Erlangen University. This study highlights the complexity of the turbulent flow features that are seen at three different operational regimes of the turbine using instantaneous flow structures, mean velocity, pressure iso-contours, blade loading and skin friction plots.FindingsThe power curve predicted using the LBM-VLES approach and setup provides a good overall match with the experimental power curve, with the peak and drop after the operational point being captured. Variable turbulent flow structures are seen over the azimuthal revolution that depends on the tip speed ratio (TSR). Significant dynamic stall structures are seen in the upwind phase and at the end of the downwind phase of rotation in the deep stall regime. Strong blade wake interactions and turbulent flow structures are seen inside the rotor at higher TSRs.Research limitations/implicationsThe computational cost and time for such high-fidelity simulations using the LBM-VLES remains expensive. Each simulation requires around a week using supercomputing facilities. Further studies need to be performed to improve analytical VAWT models using inputs/calibration from high fidelity simulation databases. As a future work, the impact of turbulent and nonuniform inflow conditions that are more representative of a typical urban environment also needs to be investigated.Practical implicationsThe LBM methodology is shown to be a reliable approach for VAWT power prediction. Dynamic stall and blade wake interactions reduce the aerodynamic performance of a VAWT. An ideal operation close to the peak of the power curve should be favored based on the local wind resource, as this point exhibits a smoother variation of forces improving operational performance. The 3D flow features also exhibit a significant wake asymmetry that could impact the optimal layout of VAWT clusters to increase their power density. The present work also highlights the importance of 3D simulations of the complete model including the support structures such as end plates and mast.Social implicationsAccurate predictions of power performance for Darrieus VAWTs could help in better siting of wind turbines thus improving return of investment and reducing levelized cost of energy. It could promote the development of onsite electricity generation, especially for industrial sites/urban areas and renew interest for VAWT wind farms.Originality/valueA first high-fidelity simulation of a complete VAWT with end plates and supporting structures has been performed using the LBM approach and compared with experimental data. The 3D flow physics has been analyzed at different operating regimes of the turbine. These physical insights and prediction capabilities of this approach could be useful for commercial VAWT manufacturers.

Effect of Macroscopic Turbulent Gust on the Aerodynamic Performance of Vertical Axis Wind Turbine

Vertical Axis Wind Turbines (VAWTs) have proven to be suitable for changing wind conditions, particularly in urban settings. In this paper, a 2D URANS (Unsteady Reynolds-Averaged Navier Stokes) numerical analysis is employed for an H-Darrieus VAWT. A turbulent domain is created through systemically randomising the inlet velocity to create macro-turbulence in front of the VAWT. The parameters for spatial and temporal randomisation of velocity and its effects on the turbine performance are studied for a mean free stream velocity, U∞ = 10 m/s, and a tip speed ratio (TSR) of 4.1. The mean Coefficient of power (Cp) for randomised fluctuation of 2 m/s and half-cycle randomisation update frequency is 0.411 and for uniform inlet velocity is 0.400. The Cp vs. Tip Speed ratio plot suggests that the optimal tip speed ratio for operation is around 4.1 for this particular wind turbine of diameter 1 m, chord 0.06 m, and NACA 0018 airfoils. The effect of randomisation for tip speed ratio λ = 2.5, 3.3, 4.1, and 5.3 on the performance of the turbine is studied. Turbine wake recovers at a faster rate for macro-turbulent conditions and is symmetric when compared to wake generated by uniform velocity inlet. The maximum velocity deficit for a distance behind the turbine, x/d = 8 at TSR (λ) = 4.1 is 46% for randomised inlet and 64% for uniform inlet. The effect of randomisation for λ = 2.5 to 5.3 on the performance of the turbine is analysed. A time-varying gust based on International Electrotechnical Commission (IEC) Extreme Operating Gust is used to study the effect of fluctuating wind conditions in a turbulent environment. Since real-time conditions often exceed gust factors mentioned by IEC, winds with large gust factors such as 1.50, 1.64, and 1.80 are analysed. With an increase in gust amplitude, Ugust = 6 m/s to Ugust = 12 m/s on a free stream velocity of U∞ = 10 m/s, the mean Cp decreases from 0.41 to 0.35 since the wind turbine operates under tip speed ratios outside optimal range due to large fluctuations in incoming velocity.

CFD Modeling of an H-Type Darrieus VAWT under High Winds: The Vorticity Index and the Imminent Vortex Separation Condition

This study introduces a Vorticity Index (VI) and an Imminent Vortex Separation Condition (IVSC), which are considered valuable indicators to quantify the vorticity impact on vertical axis wind turbines (VAWTs) operation. The VI and IVSC are specifically applied to a H-Darrieus vertical axis wind turbine (VAWT). Findings show that these two parameters display a direct relationship with the aerodynamic forces that govern the performance of this type of VAWT. This analysis is accomplished via 2D-CFD simulations of a H-Darrieus with a symmetrical NACA 0018, powered by high winds (8 and 20 m/s), by using a Shear Stress Transport SST k-ω model. The 2D model used is validated for Class II winds (8 m/s), for tip speed ratios (λ) ranging from 0.4 to 0.9. Power coefficients (Cp) predictions are close to those obtained with both 3D simulations and with experimental data, reported in the technical literature. It is found with the numerical simulations developed, that despite the significant increase of the average rotor overall torque values, when the wind speed is augmented from 8 m/s to 20 m/s, the energy extracted by the rotor seems to be moderately lessened by the amplified turbulence and vorticity.

Performance Enhancement of VAWT using Diffuser for Energy Extraction from Cooling Tower Exhaust Air

Renewable energy generation need to be accelerated to battle climate change and depletion of fossil fuel resources. Innovation to design wind recovery system which are efficient is vital to contribute green energy production. Many advancements in vertical axis wind turbines (VAWT) were made over the years however, it is still not as efficient as conventional turbines, and some countries does not have the luxury of strong consistent wind throughout the year. Therefore, this study focuses on extracting wind energy from unnatural sources, specifically for cooling tower exhaust air energy recovery. In this study, cycloidal diffuser with different shroud lengths was used to study the performance of a 3-bladed H-Darrieus VAWT (HDWT) with S-1046 airfoils under accelerated wind conditions in a 3-dimensional numerical study using shear stress transport k-ω turbulence model. The cycloidal diffuser with shroud length of 0.48D increased the HDWT power coefficient by 26.66% compared to the bare HDWT at tip speed ratio of 2.0. Aerodynamics around the energy extractor system was also discussed and this investigation has provided good understanding of the flow behaviour of the wind augmented HDWT under cooling tower exhaust air.

Unscented Kalman filter-based blade-effective wind speed estimation for a vertical-axis wind turbine

On-shore horizontal-axis wind turbines (HAWTs) provide a cost-effective solution for low carbon electricity generation. However, public acceptance is still a problem. A possible alternative to a HAWT is a vertical-axis wind turbine (VAWT), which is more visually appealing and less noisy. Furthermore, the inherent omni-directionality of VAWTs makes them suitable for installation in urban environments where the turbulence levels are high, and the wind direction variations are significant. However, the variation with the azimuth angle of the blade-effective wind speed and the angle of attack makes VAWT performance difficult to predict. This study proposes a wind speed estimator for a VAWT to address this challenge and to exploit knowledge of the blade-effective wind speed for load reduction control strategies. An Unscented Kalman Filter is used to solve the blade-effective wind speed estimation problem and is applied to a realistic 1.5 m two-bladed H-Darrieus VAWT model, for which the aerodynamic characteristics are determined using an actuator cylinder model. The system performance is evaluated using different wind speed variation scenarios. Overall, good agreement between the reference and estimated blade-effective wind speed is found both in terms of trend and absolute values.

Effect of upstream deflector utilization on H-Darrieus wind turbine performance: An optimization study

This paper aims to enhance the performance of H-Darrieus Vertical Axis Wind Turbine (VAWT) via introducing upstream deflectors. The impact of this addition has been investigated and discussed through different deflector configurations. The turbine performance before and after adding different wind rotor barriers was compared. A two dimensional, incompressible, transient, and turbulent flow model was built up in order to simulate the air flow around the turbine blades. Model verification and validation were performed through comparing the model solutions using different mesh sizes, time steps, turbulent models, and discretization schemes. Computational Fluid Dynamics (CFD) models were validated to provide novel insights on the effect of the deflectors on the aerodynamic characteristics of a VAWT blades. Results showed that the presence of a single deflector increases the highest value of the moment coefficient of the bare configuration by 24%, either increases the negative torque values, while two defectors increase the maximum value by 22% and the overall average value of the moment coefficient over the optimal range for the tip speed ratio.

Passive control of dynamic stall in a H-Darrieus Vertical Axis Wind Turbine using blade leading-edge protuberances

Dynamic stall flow conditions affect the performance of most Vertical Axis Wind Turbine (VAWT) designs; however, the associated losses are especially relevant in smaller turbines, such as those typically used in urban environment applications. The work described in this paper experimentally evaluated the effectiveness of leading-edge protuberances in controlling the aforementioned stall behavior. A numerical study was first performed to define the leading-edge geometry to be subsequently tested in the wind tunnel. A custom experimental setup was also developed for this purpose. The wind tunnel measurements of the modified turbine showed significant performance gains over the baseline and a considerably improved self-starting behavior. The power coefficient increase was between 46% and 20% for wind velocities ranging from 5.5 m/s to 9 m/s, respectively. Nevertheless, the tip-speed ratio characteristics of the studied turbine were not meaningfully affected by the use of leading-edge protuberances.

Optimisation of H-Darrieus VAWT Solidity for Energy Extraction in Cooling Tower Exhaust Systems

The technologies surrounding renewable energy have been receiving surmountable attention to producing clean energy and reducing the dependency on depleting fossil fuel sources. In this context, research investigations on vertical axis wind turbines (VAWT) in free stream flow condition has been extensively conducted to improve the energy extraction efficiency from the wind. VAWTs are particularly advantageous in locations not suitable for conventional horizontal axis wind turbines (HAWT). However, the applications of VAWTs are still limited due to their lower performances compared to their counterparts. Furthermore, the wind energy extraction problem is more prominent in urban areas with unpredictable and inadequate wind speed conditions. The present study focuses on an alternative way to harness wind energy from unnatural sources such as cooling tower exhaust systems with the reliable and consistent exhaust air. A three-dimensional numerical study has been conducted to investigate the performance of a 3-bladed H-Darrieus wind turbine (HDWT) using S-1046 airfoils of four different solidities under accelerated wind conditions of a cooling tower. The HDWT model is positioned at the cooling tower outlet, where it rotates using sliding mesh to measure the power output. Shear stress transport (SST) k- turbulence model solver was used to solve the implicit unsteady Reynolds-Averaged Navier-Stokes equations. It is observed that the higher solidity HDWT reached peak power coefficient at a lower tip speed ratio (TSR). In contrast, lower solidity HDWT achieved peak power coefficient at higher TSR. The higher solidity 0.375 and 0.450 produced a maximum power coefficient of 0.233 at TSR of 2.0.

Design and multiperspectivity-based performance investigations of H-Darrieus vertical axis wind turbine through computational fluid dynamics adopted with moving reference frame approaches

Abstract The power output of a straight-bladed H-rotor Darrieus vertical axis wind turbine (HDVAWT) is explored in this article. The comparisons are performed between the NACA0018 airfoil and a series of Kline Fogelman modified NACA0018 airfoils. The computational fluid dynamics findings are first cross-checked with the experimental data, and the computational processes are validated as a consequence. Then, in CATIA, 12 airfoils were constructed by modifying the step thickness, step placement and trailing edge form to get an efficient model for the wind turbine. The approved computational processes are applied to all 13 models, and the results are obtained. In comparison to the NACA 0018 airfoil, the KFm3 airfoil with 12% step thickness and a rectangular trailing edge demonstrated a 47% efficiency under 6.65 m/s wind velocity and a rotational velocity of 120 RPM. The KFm3 airfoil also performed better when tested at 80 and 162 RPMs. Thus, the final HDVAWT has been presented for real-time applications, which is the primary goal of this work; also, the proposed HDVAWT outperforms all existing vertical axis wind turbines.

Power Enhancement of a Vertical Axis Wind Turbine Equipped with an Improved Duct

Efforts to increase the power output of wind turbines include Diffuser Augmented Wind Turbines (DAWT) or a shroud for the rotor of a wind turbine. The selected duct has three main components: a nozzle, a diffuser, and a flange. The combined effect of these components results in enriched upstream velocity for the rotor installed in the throat of the duct. To obtain the maximum velocity in the throat of the duct, the optimum angles of the three parts have been analyzed. A code was developed to allow all the numerical steps including changing the geometries, generating the meshes, and setting up the numerical solver simultaneously. Finally, the optimum geometry of the duct has been established that allows a doubling of the flow velocity. The flow characteristics inside the duct have also been analyzed in detail. An H-Darrieus Vertical Axis Wind Turbine (VAWT) has been simulated inside the optimized duct. The results show that the power coefficient of the DAWT can be enhanced up to 2.9 times. Deep dynamic stall phenomena are captured perfectly. The duct advances the leading-edge vortex generation and delays the vortex separation.

Application of Simultaneous Symmetric and Cambered Airfoils in Novel Vertical Axis Wind Turbines

Two novel four-blade H-darrieus vertical axis wind turbines (VAWTs) have been proposed for enhancing self-start capability and power production. The two different airfoil types for the turbines are assessed: a cambered S815 airfoil and a symmetric NACA0018 airfoil. For the first novel wind turbine configuration, the Non-Similar Airfoils 1 (NSA-1), two NACA0018 airfoils, and two S815 airfoils are opposite to each other. For the second novel configuration (NSA-2), each of the S815 airfoils is opposite to one NACA0018 airfoil. Using computational fluid dynamics (CFD) simulations, static and dynamic conditions are evaluated to establish self-starting ability and the power coefficient, respectively. Dynamic stall investigation of each blade of the turbines shows that NACA0018 under dynamic stall impacts the turbine’s performance and the onset of dynamic stall decreases the power coefficient of the turbine significantly. The results show that NSA-2 followed by NSA-1 has good potential to improve the self-starting ability (13.3%) compared to the turbine with symmetric airfoils called HT-NACA0018. In terms of self-starting ability, NSA-2 not only can perform in about 66.67% of 360° similar to the wind turbine with non-symmetric airfoils (named HT-S815) but the power coefficient of NSA-2 at the design tip speed ratio of 2.5 is also 4.5 times more than the power coefficient of HT-S815; the power coefficient difference between HT-NACA0018 and HT-S815 (=0.231) is decreased significantly when HT-S815 is replaced by NSA-2 (=0.076). These novel wind turbines are also simple.

Aerodynamic noise prediction and reduction of H-Darrieus vertical axis wind turbine

ABSTRACT small scale VAWTs are erected in built up areas while in these locations they will be inherently close to people. Therefore, the noise radiated from a VAWT is very significant to make an investigation. In this work we carried out numerical prediction for aerodynamic acoustics of a H-Darrieus VAWT. The URANS equations is conducted to achieve the time-accurate results. The aero-acoustics noise prediction is simulated by using FW-H equation with low-Mach number assumptions. Simulations are performed under different tip speed ratios. In order to verify the accuracy of the numerical results, mean torque coefficient is compared with the experimental data. The tip-speed ratio, wind speed, receiver distance on the OASPL, distance between the source and receivers and blades number effects are investigated in this work. In addition, this work introduced a method of adding V and S tip vanes on the blade tip to reduce the aerodynamic noise of a H-VAWT. The result showed that two types of tip vanes can weaken the tip vortex and reduce the sound pressure level (SPL) of a H-VAWT.

Numerical study of the effect of turbulence intensity on VAWT performance

This paper demonstrates the capability of CFD to accurately simulate the effect of the flow turbulence intensity on the performance of vertical-axis wind turbines (VAWT). This effect is quite important as it increases the performance of small VAWTs. For this study, two and three dimensional CFD analysis has been performed on different straight-bladed Darrieus-type rotors. Both a small and a large H-Darrieus VAWT with diameters of 0.5 m and 35 m respectively are investigated using NACA0018 blades. Computational results based on a commercial CFD code (Star CCM+) are compared with experimental measurements. Several simulations based on full URANS calculations are proposed. Firstly, the sensitivity of time step, the number of iterations by time step, and discretization schemes are studied. Secondly, the effect of turbulence intensity on the VAWT performance is simulated and compared with experimental data. Finally, results reveal that the power coefficient of a small turbine is increasing for higher turbulence intensity, up to 20%, but stops increasing afterward. For a small turbine H-Darrieus turbine, the power coefficient is increased by 22% when the turbulence intensity is changed from 0.7% to 20%, however, there is no increase detected in the case of a large H-Darrieus wind turbine. The impact of the turbulence intensity was assessed and a range of behaviors was identified.

Optimum power generation assessment in an H-Darrieus vertical axis wind turbine via Exergy Destruction Minimization

In recent years, Vertical Axis Wind Turbines have emerged as a viable complement to the ever-expanding worldwide wind power generation. Compared to conventional wind turbines, they are independent of wind direction, emit less noise, and require a smaller installation area, making them attractive for urban and remote implementations. In this work, a Second Law of Thermodynamics approach is utilized to deepen the understanding of the fluid dynamics phenomena that reduce the turbines' power generation. The turbulent unsteady fluid flow around the turbine is computed using a two-dimensional Finite Volume approach via the commercial software ANSYS Fluent, which is validated using experimental data available from the literature. The Exergy Destruction and the Reversible Work grow in direct proportion to the flow speed, although their growth rate depends on the turbine operating regime: attached flow or dynamic stall. The latter explains how the Second Law Efficiency maximizes at an intermediate Tip Speed Ratio, which coincides with a more efficient power generation.

The effect of geometry variants on the performance of VAWT-rotor with incline-straight blades

This study was conducted theoretically with the aim of investigating the effect of the straight blade angle change on the aerodynamic performance of the vertical axis wind rotor (VAWR). The work was done within the blade angle range of 25°–85° with an angular gradient of 20°. A special name has been given to the VAWR concerned in this paper, where it was called Straight Slant Blades (SSBs). The so-called multi-stream tube (MST) model was modified to be suitable for SSBs. MST is an aerodynamic model, which was previously used to work on what is known as Darrieus and H-Darrieus vertical axis wind turbines. A computer program is designed and developed using Microsoft Visual Basic to be consistent with the objectives of this research. As for verifying the effectiveness of this program, its theoretical results were compared with previous laboratory results from other research studies as it proved its effectiveness in achieving satisfactory results commensurate with the objective of this study. This study is applied to four groups of different engineering designs for the SSB rotor, where each group is concerned with one of the geometric variables confined to the rotor height 2H, the rotor radius R, the number of rotor blades N, and the airfoil C. The results obtained are displayed as rotor power coefficient curves as a function of blade tip speed ratio. As it resulted in the ideal range for the angle of the blade between 45° and 65°, according to the rotor in this range, the value of maximum power coefficient CpMAX is at its maximum and the range of tip speed ratios is the highest in addition to the diminution of the problem of self-movement.