Savonius-type Vertical Axis Wind Turbines Research Articles

Wind Velocity Effect on the Aerodynamic and Acoustic Behavior of a Vertical Axis Wind Turbine

In this work we present a numerical study on the effect of wind velocity on the aerodynamic and acoustic behavior of a Savonius-type vertical axis wind turbine (VAWT). The study focuses on the prediction of the torque coefficient for different flow velocities and rotational velocities of the wind turbine. We also present the triggering of the wake zone near the wind turbine blades to see the dynamic effect on the behavior of the wind turbine. The study of the numerical simulation is carried out using a fluent CFD calculation code using the finite volume method for the discretization of the differential equations. The equations governing the flow are solved by the SIMPLE algorithm using two K-epsilon turbulence models.

Optimizing Vertical-Axis Wind Turbine Performance and Determining Optimal Velocity and Deflector Configuration Based on Wind Speed

In the realm of wind energy harnessing, Vertical-axis Wind Turbines (VAWTs) have emerged as promising alternatives. However, they face persistent challenges due to their low efficiency and poor self-starting properties. This study addresses these limitations and aims to unlock the full potential of VAWTs by conducting a comprehensive investigation. The focus of this research lies in determining the optimal operating velocities to enhance the performance of Savonius-type VAWTs, leveraging advanced deflectors. The study delves into an in-depth analysis of the optimal deflector distances and angles for the turbine, taking into account different geographical areas with varying wind velocities. To achieve this, a Savonius-type VAWT equipped with advanced wind deflectors was meticulously designed and tested. Utilizing SOLIDWORKS software, sophisticated turbine models were crafted, which were then subjected to rigorous analysis using ANSYS Fluent, Computational Fluid Dynamics (CFD) software. The research methodology involved conducting simulations across a range of wind velocities, spanning from 1 ms-1 to 8 ms-1, and changing the deflector distance from 100 cm to 150 cm from the centre of the turbine, and the deflector angle from 12 to 45 degrees. During the simulations, critical indicators of turbine performance, including moment coefficient, moment, force coefficient, and force acting on the blade, were closely examined. The study uncovered significant variations in the power output of the Savonius-type vertical-axis wind turbine (VAWT) fitted with an advanced deflector system, especially at lower wind speeds. Notably, the study revealed that at different wind velocities, the optimum deflector configuration changed, with the highest energy-generating capacity observed at 1 m/s for the wind turbine equipped with advanced deflectors. Outperforming the turbine lacking a deflector system, this inventive method demonstrates the capacity to notably boost energy generation. This novel method underscores the capacity for substantial improvements in energy production. Additionally, the research offers valuable insights into customized deflector distance and angle combinations, optimizing turbine performance for specific wind velocity ranges. By strategically positioning the deflectors, higher energy output can be achieved, making the VAWT system more adaptable and efficient across diverse wind conditions
 
 Keywords: Vertical-axis wind turbine, Wind deflectors, Computational Fluid Dynamics, SOLIDWORKS, ANSYS Fluent

Robust optimization of Savonius-type wind turbine deflector blades considering wind direction sensitivity and production material decrease

Savonius-type vertical axis wind turbine (SWT) has several characteristics appropriate for urban usage: low rotational speed, low noise, easy self-starting; but also has a low power coefficient. One of the methods to improve the SWT efficiency is to use fixed deflector blades, but this makes the SWT performance sensitive to wind direction. This paper performs a robust optimization of deflector blade shape, considering the whole range of wind directions. The objectives are to reduce the required production material and to maximize the annual energy production (which is related to the average power coefficient cPave). Each design efficiency is estimated using 2D CFD transient simulation with GEKO turbulence model. The results show that cPave is increased to cPave = 0.35 using an 8-blade optimized deflector (46% improvement compared to no-deflector) coupled with classical SWT rotor. The 4-blade deflector is inferior with 33% improvement (cPave = 0.32) but with 60% material reduction compared to the previous design. Application of the novel Scooplet-based design achieves a further improvement of cPave = 0.43 and cP,ave = 0.385 for 4-blade and 8-blade deflectors, respectively. A selected optimized design was evaluated using 3D CFD for various aspect ratios (Ar).

Integrated Surrogate Optimization of a Vertical Axis Wind Turbine

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

Global optimization of Savonius-type vertical axis wind turbine with multiple circular-arc blades using validated 3D CFD model

Vertical-axis wind turbines, such as Savonius-type wind turbines (SWT) are an attractive choice for small-scale electricity generation. Recent SWT research is mostly targeted at improving the SWT power coefficient, which is also the topic of this paper. The power coefficient was improved by optimization of a multi-blade SWT (2, 4 and 6), with blades based on circular arc segments. Additional optimization variables were the tip-speed ratio and the aspect ratio. The main novelty of this paper is the global optimization using genetic algorithm, which involved analysis of many different designs (∼105) using a validated 3D CFD model with a 4eq SST turbulence model. Since many designs were investigated, the optimization result is considered as the global optimal solution. In the 4 and 6-blade cases, the global optimal solution was similar to the previously proposed Scooplet-based design. The design was improved to achieve power coefficient cP = 0.32 with aspect ratio 1.5, and additionally cP = 0.34 with an increased aspect ratio of 2.5. Optimized designs were compared with a similar multiple quarter-blade design known from previous research (which was outperformed by 60%). For the 2-blade case a novel design was reached, which operates at TSR = 1.2, and achieves a 12% improvement over the classical SWT.

Optimal Design of Novel Blade Profile for Savonius Wind Turbines

Since the affirming of global warming, most wind energy projects have focused on the large-scale Horizontal Axis Wind Turbines (HAWTs). In recent years, the fast-growing wind energy sector and the demand for smarter grids have led to the use of Vertical Axis Wind Turbines (VAWTs) for decentralized energy generation systems, both in urban and remote rural areas. The goals of this study are to improve the Savonius-type VAWT’s efficiency and oscillation. The main concept is to redesign a Novel Blade profile using the Taguchi Robust Design Method and the ANSYS-Fluent simulation package. The convex contour of the blade faces against the wind, creating sufficient lift force and minimizing drag force; the concave contour faces up to the wind, improving or maintaining the drag force. The result is that the Novel Blade improves blade performance by 65% over the Savonius type at the best angular position. In addition, it decreases the oscillation and noise accordingly. This study achieved its two goals.

Global Optimization of Savonius-Type Vertical Axis Wind Turbine with Multiple Circular-Arc Blades Using Validated 3D CFD Model

Global Optimization of Savonius-Type Vertical Axis Wind Turbine with Multiple Circular-Arc Blades Using Validated 3D CFD Model

An experimental investigation into performance characteristics of H-shaped and Savonius-type VAWT rotors

The effects of flow regime and rotor configuration strongly influence the power performance of vertical axis wind turbines (VAWTs). Yet, there exits few experimental investigations from literature that have been carried to explain this effect. This could be attributable to huge wind tunneling cost requirement and an array of design skills required including time constrains. The balance between cost and power performance has limited development of VAWTs towards utility scale type. In this paper therefore, we seek to investigate in detail the performance characteristics of vertical axis wind rotors in a wind tunnel environment. The H-Darrieus and Savonius-type VAWT configurations have been utilized to carry out the investigation. A systematic analysis of effect of blade number, rotor configuration, and flow regime including comparison of the two configurations was presented to predict the power performance using a rotary sensor. Results revealed a significant impact of flow field regime on power performance of the VAWT models, with the Savonius-type rotor attaining lower power coefficient (CP) than the Darrieus-type rotor across all the tested wind speeds. In addition, increase in number of blades for Darrieus-type rotor revealed narrower negative CP band that decreased with increase in wind speeds. In both configurations, the CP decreased at low tip speed ratios while an increase in CP was revealed at high tip speed ratios. The understanding gained from the results could be useful to the VAWT research community, and the findings can be extended to the design of wind turbines for mini-grid and utility scale applications.

Fluid structure interaction analysis of the operating Savonius wind turbine

In the last few decades vertical axis wind turbines (VAWTs) have gained increased interest among researchers worldwide. This paper aims to present full two-way Fluid Structure Interaction (FSI) approach to model operation of the Savonius-type VAWT. The developed methodology couples the set of Unsteady Reynolds Averaged Navier-Stokes Equations (URANS) with the unsteady linear elasticity equations and dynamic mesh approach to comprehensively describe the deformations of the turbine rotor. The obtained results provide detailed information on the unsteady flow fields around the operating wind turbine as well as deformations of a turbine rotor caused by an interaction between solid and flowing air. This allowed us to determine the influence of the unsteady deformations of a turbine rotor on the instantaneous and average performance of a wind turbine. Computations were carried out for the wind speed equal to 15 m/s and the tip speed ratio equal to 0.8. The simulations were performed using the commercial ANSYS software. The obtained results showed that deformation of the turbine rotor increases the wind turbine power coefficient by around 5%. Moreover, it was shown that the centrifugal force has a significant effect on the rotor deformation and turbine operation, hence it cannot be neglected.

Harvesting energy along muscat expressway using vertical axis wind turbine

The continuous use of fossil fuels as energy source has depleted their level, and if used by the same rate, these forms of energy sources are going to become extinct in a few hundred years. In addition, the emissions generated from the usage of these fuels are adversely affecting the environment. Hence, governments has been forced to find other non-conventional forms of energy, which can be used sustainably. Due to its geographic location, Oman has a very high potential for renewable energies like solar and wind. Oman receives moderate wind speeds both offshore and onshore. On highways, the wind turbulence caused by fast moving cars would add up to the energy that can be obtained from the natural wind. This study focuses on harvesting of electric energy from the highway wind turbulence along with the normal wind breeze, and converting it into useful electrical energy. A comparative study was done between different types of wind turbines. Based on this study, a Savonius-type Vertical Axis Wind Turbine was selected to study and determine the amount of energy that can be generated along Muscat Expressway from the wind energy. The optimum location for the implementation of the designed VAWT was found out to be in the middle of the highways. The total electricity which can be generated was estimated to be around 1.063 kWh in one day using a single VAWT. It was found that the harvested electricity could be used to power the street lights on the highways if multiple VAWTs would be installed at regular intervals.

Analysis of the blade profile of the Savonius wind turbine using computational fluid dynamics

This study characterises the performance of the Savonius type vertical axis wind turbine (VAWT). The performance of the Savonius type VAWT can be characterised by power and coefficient of power. The main parameter considered for analysing the Savonius-type VAWT is the tip speed ratio (TSR). The mesh independency test and time independency test are carried out, in which the medium mesh and three degree of time step for rotation are selected. The Savonius wind turbine is analysed at various TSR ranging from 0.2 to5.0, in which TSR is 4.4, the performance of the turbine is high. Considering 4.4 TSR as the optimum one, the analysis of the Savonius type VAWT is carried out under various wind speed ranging from 1 to 10 m/s. From the analysis, the validation between numerical analysis and theoretical analysis is carried out and the efficiency of the Savonius type VAWT is increased to 50%.

A numerical study on the performance of a Savonius-type vertical-axis wind turbine in a confined long channel

High-rise buildings in urban environments provide tremendous opportunities for harvesting wind energy. For example, a through-building channel is beneficial for wind speed enhancement and thus wind power generation. In this study, we investigate the performance of a Savonius-type vertical-axis wind turbine (VAWT) placed in a confined long channel, based on computational fluid dynamics (CFD) simulations. Two-dimensional (2D) simulations are conducted using ANSYS Fluent, employing the shear-stress transport (SST) k-ω turbulence model. Incoming wind velocity at the channel inlet is Uo = 4.05 m/s, corresponding to a Reynolds number Re = 1.0 × 105, based on Uo and the diameter (D) of the wind turbine. The channel is 45D long. Three different widths, 2D, 3D and 4D, of the channel together with different wind turbine locations in the channel are considered. The performance of the Savonius-type VAWT in the long channel is discussed, taking into account the contribution of pressure drop towards power generation, and is compared with that in open space. Results show that the power output (Pout) of the Savonius-type VAWT placed in the channel can be significantly increased by 200% in the 2D-wide channel compared with that in open space. Furthermore, a higher optimum tip-speed ratio (TSR) is observed for the wind turbine located in the channel than in open space. A comprehensive comparison is made between the wind turbine in the channel and that in open space. Finally, the maximum power coefficient of a Savonius-type VAWT in the channel is predicted based on a correction to that of a propeller-type horizontal-axis wind turbine (HAWT) in a long channel.

Performance-based Optimizations on Savonius-type Vertical-axis Wind Turbines using Genetic Algorithm

Abstract Evolutionary based Genetic Algorithms (GAs) were employed to optimize the blade shape of a Savonius-type vertical-axis wind turbine (S-VAWT) as well as the shape and the location of one doubly-curved deflector placed upstream the returning blade of an S-VAWT. To this end, GAs were incorporated into computational fluid dynamics (CFD) simulations. Significant improvement in performance was observed for the S-VAWT with optimal blades and that with the optimal deflector. The time-averaged power coefficient of the S-VAWT with optimal blades can be increased by up to 34% over that of the S-VAWT with semi-circular blades. For the S-VAWT with the optimal deflector, its time-averaged power coefficient can be boosted by 95%, compared with that without a deflector. The underlying mechanisms responsible for the performance improvement are discussed based on numerical field data from the CFD simulations.

Positive interactions of two Savonius-type vertical-axis wind turbines for performance improvement

Abstract The performance of multiple vertical-axis wind turbines (VAWTs) can be greatly enhanced when they are placed close in some configurations where positive interaction or coupling occurs. Based on a systematic study using computational fluid dynamics (CFD) simulations, we investigate the positive coupling of two co-rotating Savonius-type VAWTs. A wide range of configurations are covered, i.e., P/D = 1.2−3.0 and α = -90°−90°, where P is the distance between the turbines’ centres, D is the diameter of turbine rotation, and α is the incident angle between the line connecting the turbines’ centres and incoming wind’s direction. It is found that the time-averaged power coefficient of the upstream turbine can be significantly improved by up to 60% at (P/D, α) = (2.2, 80o), compared to that of a single, isolated turbine. For the two-turbine system, the overall power coefficient can be increased by 40% over that of a single, isolated turbine. Typical configurations corresponding to different positive couplings of the two turbines are identified. The behaviour of torque on the individual turbines and the associated flow structures are discussed.

Concept of flexible vertical-axis wind turbine with numerical simulation and shape optimization

Vertical-axis wind turbines (VAWT) are becoming popular solutions for electric power generation. Among them, Savonius-type VAWTs have low rotational speed, reduced noise and ability to self-start, but their disadvantage is the low energy conversion efficiency. This paper investigates a novel VAWT concept and whether it can provide a higher energy conversion efficiency. The novel concept is a Savonius-type VAWT with flexible blades that change their shape passively due to aerodynamic and blade inertial forces during rotation. An initial design was optimized by a customized shape optimization workflow based on genetic algorithms. The blade design evaluation was performed by CFD model with two-way fluid-structure interaction. The optimization objective was to determine the optimal blade shape, thickness distribution and location of the blade support arms by maximizing the power coefficient and keeping structural stresses below the design limit. The results show that 8% improvement of the power coefficient is possible while keeping the structural stress within the design limit. A detailed performance analysis in the paper shows that there is potential for further optimization considering annual energy production for a selected location. For that purpose, the proposed optimization workflow can serve as a tool for development of future designs.

A novel wake energy reuse method to optimize the layout for Savonius-type vertical axis wind turbines

The long wake of a wind turbine has a significant impact on the performance of downstream turbines. Under the inspiration of migrating geese flying in a V or I formation to save energy, a novel wake energy reuse method is proposed to optimize the layout for Savonius-type vertical axis wind turbines (S-VAWT). VAWT wakes include a series of high speed and energy zones. On both sides of the upstream turbine, 7×16 transient two-dimensional numerical simulations are performed with Fluent to investigate wake structure, interaction effect and power coefficients (Cp) of downstream turbines. Based on Kriging Method, a response surface model (Surrogate model) is created to describe the relationship between the optimization objective Cp and layout positions. Finally, particle swarm optimization algorithm is applied to find the optimal relative layout position (5.25 m, −2.18 m) of the downstream turbine. The optimal position is located in the periodic high speed zone of the wake on the advancing blade side. And the optimal position is suitable for multi-turbines in a large wind farm. The optimization results show that Cp of downstream turbines at optimal layout position is significantly increased from 0.2477 to 0.3044 (22.89% higher).

Investigation into the relationship of the overlap ratio and shift angle of double stage three bladed vertical axis wind turbine (VAWT)

This study presents the experimental test results of Savonius-type vertical axis wind turbines (VAWT) with different overlap ratios and shift angles. Each wind turbine was tested under four different wind speeds. The power coefficients (CP) of vertical axis wind turbines are governed by several key factors, e.g. the number of blades, the shape of the blades, the overlap ratio (OL) and the phase shift angle. The overlap ratio and the phase shift angle (PSA) are the most decisive ones since the measured data shows that their power coefficient drops or rises with them significantly. Three turbines with the overlap ratios of 0, 0.16 and 0.32 were designed and constructed. The wind turbines were then adjusted to the phase shift angles (PSA) of 0, 15, 30, 45 and 60 degrees before testing them in an open wind tunnel under the air velocities of 4m/s, 6m/s, 8m/s and 10m/s.The results show that a higher overlap ratio has a higher impact on improving the starting characteristics of the Savonius wind turbine than any phase shift angle changes. This investigation shows that a specific phase shift angle in relation to a specific air velocity will increase the power coefficient significantly.Besides the increase of the power coefficient seen at specific air velocities and phase shift angles, did the recorded data show an unexpected second performance peak which appeared at higher tip speed ratios. This is surprising since the Savonius turbine is considered as being a drag driven turbine, and suggests that the lift characteristics of Savonius turbines might be more significant than commonly considered.