The world's focus is shifting towards solar and wind energies which are primarily contributing to renewable energy. Wind turbines are subdivided into horizontal axis wind turbines (HAWTs) and ...vertical axis wind turbines (VAWTs). Savonius turbine is a VAWT that works mainly on the drag force. Despite its low efficiency, a Savonius turbine is quite useful due to its operational independence on wind direction, its advantage as a stand-alone turbine, and its low-cost power production. Savonius turbine performance depends mainly on the overlap ratio, aspect ratio, number of blades, and blade design. Various researchers have focused on modifying these parameters to improve the efficiency of Savonius turbines using CFD studies. One key challenge encountered in such studies is the selection of an appropriate turbulence model to predict the flow characteristics and performance parameters accurately. Due to small computational time and cost associated with the RANS-based turbulence models, various researchers have focused mainly on using these models. This article presents a review of various turbulence models employed in different CFD studies on Savonius turbines. Further, various computational approaches used in CFD simulations of Savonius wind and hydro turbines and key findings of such studies are also presented along with future directions.
•Steps for CFD simulations of Savonius wind turbines presented.•Effects of turbulence models on Savonius turbine characteristics are explored.•Grid requirements, computing costs, and accuracies of turbulence models are shown.•Use of different turbulence models for various blade shapes is reviewed.•Future scope of CFD studies presented.
This study aims to enhance the hydrodynamic efficiency of the fairing system and increase the power coefficient Cp of a three-bladed H-Darrieus turbine by investigating various geometries and ...configurations in comparison to the reference model. 2D CFD modeling and URANS calculations along with the k-ω SST turbulence model are employed for conducting parametric studies. The analysis focuses on assessing the geometric parameters of the fairing system that affect its behavior, such as the angle of incidence α and the chord length C of the fairing profile. It was found that at x/C=0.39934, the normalized power coefficient Cp/Cp,max of H-Darrieus equipped with the fairing amounts to 0.967581, whereas at x/C=0.750825, it attains Cp=0.486284. A power coefficient of Cp=0.621315 is achieved when an angle of attack α=10∘ and a tip speed ratio λ=2 are combined. In addition, the optimal operating point Cp for both fairing profiles is λ=2. In addition, maximum performance is reached at α=18∘ for the Eppler-420 profile, with a peak Cp=0.662, whereas the S1223-RTL profile demonstrates optimal performance at α=30∘ , with a peak Cp=0.728. Differences in the maximum and minimum ΔP∗ values between the Eppler-420 and S1223-RTL are also noted. It is observed that the S1223-RTL profile displays lower drag Cd and lift Cl coefficient values than the Eppler-420 profile up to α≈22∘. finally yet importantly, the highest Cp is observed at a chord length of C=4.0R, while the lowest occurs at a chord length of C=2.5R. Both Cd and Cl exhibit relative constancy for chord lengths shorter than C=4.0R.
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•Examining Eppler-420 and S1223-RTL fairing profiles optimizes hydro-turbine design.•2D URANS CFD studies identification of the effects of fairing angle of attack α and chord length C.•Fairings enhance H-Darrieus hydro-turbine efficiency by reducing pressure losses.•Optimize H-Darrieus hydro-turbines for improved efficiency and power output Cp.
In this work, a 370-W small wind turbine was developed which is equipped to a controllable nuzzle-diffuser duct. The developed duct is consisting of a fixed ring and a two-piece diffuser which can ...rotate on each other and so the diffuser wall opening will have altered from 0 to 180°. This mechanism is developed to control speed-up ratio and drag forces acting on the turbine structure in high ranges of wind speeds. The rotor is designed using BEM algorithm and the duct geometry is reached by CFD works considering the atheistic aspect of view. As the turbine is designed for a comprehensive research project, so it contains several asubsystems like an electromagnetic brake, external electric starter motor, electromagnetic flywheel, variable nacelle, etc. The designed mechanism fabricated using several machining processes as turning, milling, boring, drilling, welding and rolling works. The turbine performance implemented in a low-speed wind tunnel. Experimental results show a comprehensive raise in power generation and rotor speed by shrouded wind turbines. In the 180-degree diffuser wall opening, the augmentation ratio in average is 39.75% while the ratio is 28.5% for a complete diffuser augmented wind turbine. The rotor speed-up ratio for them is 53 and 74% respectively.
•The fully closed duct augments the turbine power by 37% compared with the bare one.•The fully closed duct raises the rotor speed by 61% comparing to the bare one.•The half-closed duct augments the turbine power by 37% comparing to the bare one.•The half-closed duct raises the rotor speed by 80% compared with the bare one.•The controlled duct augments the power and rotor speed by 50 and 61% respectively.
Given the state of the world nowadays, renewable energy is becoming more and more essential rendering wind turbine electricity quite important. Its shape and the fact that the Savonius vertical axis ...wind turbine runs at relatively low wind speeds with high torque values makes it suitable for practical uses such as that of an irrigation system in agriculture industry. This paper utilizes numerical research with Computational Fluid Dynamics (CFD) to investigate the performance of a vertical-axis wind turbine. The ANSYS CFD program was engaged to construct the simulations during the pre- and post-processing stages. Wind speed remained constant while the angular velocity was altered to enable analysis of the flow through the wind turbine. Because of its mechanical simplicity, the primary profile of a semicircle has remained a typical option for turbines that generate high torque based on drag force. The effects of using elliptical curves and the fluctuation in thickness along the profile chord were both examined in this study. Equivalently, an attempt to optimize the rotor's design was made. After the performance of a numerical simulation, a geometry consisting of simple circle arcs was developed, with a 10.9% improvement in the power coefficient, analogous to prior optimizations with more complicated geometries. The numerical results derived include the torque coefficient evolution throughout a full rotation as well as the distribution of vorticity magnitude at different rotor points.
The relatively low power coefficient restricts the wide application of vertical axis wind turbines (VAWTs). An effective solution to this problem is to design specific airfoil profiles which directly ...influence the capture ratio of wind power. The main aim of the present study is to develop an automatic airfoil profile optimization system to improve the power performance of a VAWT. A three-bladed high-solidity VAWT is adopted as the research object with its chord length, blade span and rotor diameter being 0.2 m, 0.8 m and 0.8 m, respectively. The optimization is conducted at a moderate tip speed ratio (TSR) with a value of 1.0 and the method of coupled CFD simulations with genetic algorithms is employed. The following points make this paper different from previous studies: (a) introducing Multi-Island Genetic Algorithm to optimize airfoils for VAWTs; (b) investigating the airfoil as part of the VAWT rather than as a single isolated body with 3D simulations. The results show that the power coefficient of the VAWT equipped with the optimized blades sensibly improves at all TSRs from 0.4 to 1.5 and the maximum growth rate of it occurs at TSR = 0.9 with a value of 26.82%. The integrated optimization system used in this paper provides an effective way to generate suitable airfoil profiles for given VAWTs with the goal to achieve higher power efficiency.
•An automatic airfoil profile optimization system for VAWTs is established.•3D CFD simulation and Multi-Island Genetic Algorithm are used in the optimization.•The optimized airfoil profile becomes non-symmetric with the thickness enlarged.•The power performance of the VAWT with the optimized airfoil sensibly improves.
•Effect of blade profiles on the Savonius rotor performance is studied numerically.•Performance studies are made on the basis of torque and power coefficients.•Flow field studies are made based on ...velocity, total pressure and turbulence intensity contours.•Wind tunnel experiments are conducted to validate the numerical results.
In this work, some notable blade profiles of drag-based vertical axis Savonius wind turbine rotor have been investigated both numerically and experimentally to judge their performances on a common platform. At the outset, 2D unsteady simulation is performed for semicircular, Benesh, modified Bach and elliptical profiles keeping the overall rotor diameter in each case to be constant. The simulation has been carried out using the Shear Stress Transport k-ω turbulence model with the help of the finite volume solver ANSYS Fluent. The torque and power coefficients, in each case, are estimated as a function of tip speed ratio. The total pressure, velocity magnitude, and turbulence intensity contours are obtained and analyzed. Finally, wind tunnel tests are conducted to validate the numerical results. From the numerical simulation, the maximum power coefficients for the semicircular, Benesh, modified Bach and elliptical profiles are found to be 0.272, 0.294, 0.304 and 0.34, respectively. However, the wind tunnel tests with the semicircular, Benesh, modified Bach and elliptical-bladed rotors demonstrated the maximum CP to be 0.158, 0.159, 0.162, and 0.19, respectively.
•Entropy production theory was employed in vertical axial wind turbine simulation.•The runner energy loss was calculated quantitatively by Entropy production theory.•Asymmetric characteristics of ...energy loss in wake region was analyzed.•Blade tip vortex was the dominant inducement on energy loss in wake region.•Energy loss coefficient was defined to represent energy deficit quantitatively.
In vertical axis wind turbine (VAWT) research, amount studies have been conducted about the flow field around the blades, but the effect of blade tip vortex was not revealed clearly. The present study emphasized on the effect of blade tip vortex on energy loss in wake region and employed entropy production theory to determine where and how energy loss generates quantitatively. The numerical simulation was conducted for the VAWTs versus various tip speed ratio (TSR) conditions, and the numerical results were analyzed by entropy production method. The energy loss calculated by entropy production theory in VAWTs flows increases with TSR increasing. The distribution of entropy production rate (EPR) in wake region was asymmetrical due to the influence of blade tip vortex diffusion downstream and two fluctuation peaks appeared on EPR curves. The energy loss coefficient was defined to represent the energy deficit and kinetic energy recovery in wake region quantitatively. Generally, the energy loss coefficient was reduced to 0.1 between 8D to 9D in wake region and was equal to 0.1051 at x = 8D under optimal condition TSR = 2.19. The present study can guide configuration optimization of VAWTs to improve wind energy utilization and revenue of wind farms.
Savonius turbine presents an attractive, environmentally friendly and cost effective electric generation in low velocity regions. However, this turbine has not been fully explored, as researchers are ...still searching for solution for the main problem of low efficiency of Savonius turbine configuration. This research paper proposes a novel system of ducted nozzle configuration around Savonius rotor to increase the efficiency of the turbine. In this study, six different duct nozzle designs had been investigated. A numerical investigation was carried out in this research work using finite volume Reynolds-Averaged Navier-Stokes Equations (RANSE) code ANSYS Fluent with Reynolds numbers of 1.32×105. Consequently, validation was carried out following previous experiments. Flow characteristics through augmented configuration, and performance of the Savonius turbine had been studied, and it was found that the water flow speed had been enhanced by the developed ducted nozzle system. The maximum power coefficient of the ducted nozzle turbine was increased by 78% compared to the conventional modified rotor. The maximum power coefficient was 0.25 at tip speed ratio (TSR) of 0.73. The use of this system is expected to contribute towards a more efficient utilization of flows in rivers and channels for electrical generation in rural areas.
•Savonius turbine suffers low efficiency problem.•This research paper proposes a novel system of ducted nozzle configuration around Savonius rotor.•In this study, six different duct nozzle designs had been investigated numerically.•The ducted nozzle shields the returning blade, thus reducing the reversing torque of the turbine.•The maximum power coefficient of the ducted nozzle turbine was increased by 78% compared to the conventional rotor.
In the present study, a deflector that can passively rotate is designed for use on a hydrokinetic turbine that generates power from tidal currents. This deflector is capable of self-adjusting its ...position with changes in the water flow, so that the hydrokinetic turbine can generate maximum power at both high and low tides. The purpose of this study is to maximize the output power of a hydrokinetic turbine by improving the geometry of the deflector and the diversion tail. The rotation of both the turbine and the deflector are simulated with finite element analysis software. In addition, the accuracy of the simulation results is verified through experimental tests. The improved design of the deflector and the diversion tail is considered in terms of the parameters, including the deflector reduction angle, the gap between the deflector and the turbine, and the height of the diversion tail. The geometrical design of the deflector and the diversion tail is compared to a turbine without the deflector and to another turbine with the original deflector over the entire operating range using CFD simulations. Without the deflector, the maximum power coefficient of the turbine was 0.0979 at a tip-speed ratio of 0.4, whereas the maximum power coefficient of the turbine was 0.306 at a tip speed ratio of 0.57 when using the improved deflector. The results indicate that, after adding the improved deflector, the power coefficient of the turbine was 3.13 times greater compared with the turbine without the deflector and 18% greater compared with the turbine equipped with the original deflector.
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•The development of a deflector with a diversion tail.•The time to steady rotation was reduced.•The direction of water flow has no bearing on torque or power.•The turbine’s performance improved by 3.13 times.
Although several problems related to biofouling of marine current turbines (MCTs) are reported in the literature, the most important one is related to long-term operational performance and ...maintenance costs. Nevertheless, studies related to the impact of biofouling on MCT performance are rather scarce. In this study, the impact of biofilm on MCT performance is investigated using the Computational Fluid Dynamics (CFD) approach. Biofilm is modelled using previously developed roughness functions implemented in a wall function solver. A verification study is performed to determine sufficient grid spacings and to calculate numerical uncertainty. The validation study is conducted by comparing the obtained results with experimental and numerical ones from the literature. Full-scale CFD simulations are performed for six fouling conditions with varying biofilm height and percentage of surface coverage at eight tip speed ratios (TSRs). The obtained results highlight the significant impact of biofilm on MCT performance reflected in a decrease in the power coefficient, which for the optimal TSR is equal to −10.7% for the R1 fouling condition. Finally, a detailed analysis of the flow around MCTs fouled with biofilm is conducted and the reasons for the detrimental impact of biofilm on MCT performance are discussed.
