Analysis of the Effect of a Slotted Flap Mechanism on the Performance of an H-Darrieus Turbine Using CFD

2014 ◽  
Author(s):  
László Daróczy ◽  
Mohamed H. Mohamed ◽  
Gábor Janiga ◽  
Dominique Thévenin
Keyword(s):  
Three Dimensional ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Horizontal Axis ◽  
Pollutant Emissions ◽  
Power Coefficient ◽  
Major Drawback ◽  
Systematic Analysis ◽  
Low Wind Speed ◽  
Low Efficiency

Wind energy represents nowadays a very important source of energy for many countries. It provides an efficient and effective solution to reduce fuel consumption as well as pollutant emissions. VAWTs (vertical axis wind turbines) were originally considered as very promising, before being superseded by the present, horizontal axis turbines. There is now a resurgence of interests for VAWTs, in particular Darrieus turbines. VAWTs like the H-rotor Darrieus turbine appear to be particularly promising for low wind speed conditions, but suffer from a low efficiency compared to horizontal axis turbines. Additionally, Darrieus turbines are not self-starting, which is a major drawback. The present paper introduces a new idea to improve the global performance of Darrieus rotors, relying on a slotted flap. Due to its low manufacturing costs and size, a two-bladed H-rotor with a radius of 2 meters was retained as a first application example. The blade airfoil relies on the S1046 profile, which was shown in previous studies to be superior under relevant operating conditions [1]. The solidity (Nc/R) of the rotor is kept at 0.25 for all the computations. In the first step a parametric geometry is created, where the end of the blade is converted into a slotted flap (with appropriate rounding). The main parameters are the distance between the main part of the blade and the flap (width of gap), the angle of the slot and the angle of the flap. In the second step a systematic analysis of the effect of those variables on the force and power coefficient is carried out using three-dimensional full factorial Design-of-Experiment with an in-house parameterization and optimization software. For each configuration, force and power coefficients are calculated for four different tip-speed ratios (including the value, where the S1046 profile without flap shows its maximal power coefficient). The evaluation of each configuration is performed using a commercial CFD software. The flow is assumed in this first study to be two-dimensional and unsteady. Turbulence intensities follow the relevant norms (DIN EN 61400). Finally the results are compared to each other and to the reference design (S1046 without flap) and conclusions are given regarding power coefficient and flap load.

scholarly journals CFD Investigation of A New Elliptical-Bladed Multistage Savonius Rotors

2020 ◽  
Vol 9 (3) ◽  
pp. 383-392
Author(s):  
Khalid Mrigua ◽  
Abdelghani Toumi ◽  
Mounia Zemamou ◽  
Bader Ouhmmou ◽  
Yahya Lahlou ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Low Wind Speed ◽  
Coefficient Increase ◽  
Savonius Wind Turbine ◽  
Low Efficiency ◽  
Two Stages

The Savonius-conventional wind turbine is a class of wind turbines designed with a vertical axis. It has a good starting capacity and   an insensitivity to wind direction. It works relatively at low wind speed in an easy installation. Savonius wind turbine faces major drawbacks, including some of the low efficiency and high negative torque created by the returning blade. Many attempts have been undertaken to optimize the blade’s shape to increase the performance of these wind turbines. The vertical axis is still under development. The elliptical-blades with a cut angle equal 47.50° have recently shown enhanced performance. In this study, we investigate the effect of Elliptical-bladed multistage Savonius Rotors (rotor aspect ratio, stage aspect ratio) on the performance by means of numerical simulation. The results obtained by comparison of one, two, and three-stage rotors indicate that the maximum power coefficient increase with a number of the stages (for the rotors with similar RAR of 0.7). Moreover, for the rotors with similar SAR of 0.7, the two stages have the highest performance than others.©2020. CBIORE-IJRED. All rights reserved

scholarly journals Preliminary Performance Tests and Simulation of a V-Shape Roof Guide Vane Mounted on an Eco-Roof System

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2846 ◽  
Author(s):  
Xiaohang Wang ◽  
Wentong Chong ◽  
Kokhoe Wong ◽  
Liphuat Saw ◽  
Sinchew Poh ◽  
...  
Keyword(s):  
Power Generation ◽  
Guide Vane ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Roof System ◽  
Low Wind Speed ◽  
Computational Fluid Dynamics Cfd ◽  
Power Generation System ◽  
Low Efficiency

The technical and economic features of a patented V-shape roof guide vane (VRGV) with a solar and wind power generation system mounted on an eco-roof system are presented in this paper. Moreover, this innovative VRGV was investigated on for the purpose of improving the performance of a vertical axis wind turbine (VAWT), which was installed on an eco-roof system to solve the low-efficiency power generation problem of the wind turbines under the condition of a low wind speed. This paper proposes a preliminary study for the performance of the VAWT with the VRGV on a building. This research used a mock-up building with a double slope roof, where a five straight-bladed VAWT was mounted and tested under two conditions, with and without the VRGV. From the comparative experiments, the self-starting performance and rotational speed of the VAWT mounted above a double slope roof with the VRGV have been significantly improved compared to the VAWT without the VRGV. Further, the power coefficient (Cp) of the VAWT can be augmented to about 71.2% increment due to the VRGV design. In addition, numerical simulations by computational fluid dynamics (CFD) were proposed to verify the augmented effect of the Cp of the VAWT under the influence of the VRGV in the experiment. Besides, economic estimation of the VRGV was conducted.

scholarly journals Numerical evaluation of aerodynamic performances of vertical-axis wind turbine rotor with flow concentrator

2020 ◽  
Author(s):  
Jelena Svorcan ◽  
◽  
Ognjen Peković ◽  
Toni Ivanov ◽  
Miloš Vorkapić ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Turbine Rotor ◽  
Operating Conditions ◽  
Power Coefficient ◽  
Small Scale ◽  
Vertical Axis Wind Turbine ◽  
Flow Simulations ◽  
Wind Speeds

With wind energy extraction constantly increasing, the interest in small-scale urban wind turbines is also expanding. Given that these machines often work in adverse operating conditions (Earth’s boundary layer, vortex trails of surrounding objects, small and changeable wind speeds), additional elements that locally augment wind velocity and facilitate turbine start may be installed. This paper investigates possible benefits of adding an optimized flow concentrator to a vertical-axis wind turbine (VAWT) rotor. Three-dimensional, unsteady, turbulent, incompressible flow simulations of both isolated rotor consisting of three straight blades and a rotor with flow concentrator have been performed in ANSYS FLUENT by finite volume method for several different operational regimes. This type of flow simulations is challenging since flow angles are high, numerous flow phenomena and instabilities are present and the interaction between the blades and detached vortices can be significant. The rotational motion of the blades is solved by the unsteady Sliding Mesh (SM) approach. Flow field is modeled by Unsteady Reynolds Averaged Navier-Stokes (URANS) equations with k-ω SST turbulence model used for closure. Both quantitative and qualitative examinations of the obtained numerical results are presented. In particular, the two computed power coefficient curves are compared and the advantages of installing a flow concentrator are accentuated.

Four Decades of Research Into the Augmentation Techniques of Savonius Wind Turbine Rotor

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha
Keyword(s):  
Wind Turbine ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Major Drawback ◽  
High Rotational Speed ◽  
Savonius Rotor ◽  
Augmentation Techniques ◽  
Savonius Wind Turbine ◽  
Low Efficiency ◽  
Wind Turbine Rotor

The design and development of wind turbines is increasing throughout the world to offer electricity without paying much to the global warming. The Savonius wind turbine rotor, or simply the Savonius rotor, is a drag-based device that has a relatively low efficiency. A high negative torque produced by the returning blade is a major drawback of this rotor. Despite having a low efficiency, its design simplicity, low cost, easy installation, good starting ability, relatively low operating speed, and independency to wind direction are its main rewards. With the goal of improving its power coefficient (CP), a considerable amount of investigation has been reported in the past few decades, where various design modifications are made by altering the influencing parameters. Concurrently, various augmentation techniques have also been used to improve the rotor performance. Such augmenters reduce the negative torque and improve the self-starting capability while maintaining a high rotational speed of the rotor. The CP of the conventional Savonius rotors lie in the range of 0.12–0.18, however, with the use of augmenters, it can reach up to 0.52 with added design complexity. This paper attempts to give an overview of the various augmentation techniques used in Savonius rotor over the last four decades. Some of the key findings with the use of these techniques have been addressed and makes an attempt to highlight the future direction of research.

Measurement of the Shortening Effect on the Perceived Path of Stroboscopic Movement

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 288-288
Author(s):  
S Nozawa
Keyword(s):  
Three Dimensional ◽  
Vertical Axis ◽  
Horizontal Axis ◽  
The Other ◽  
Horizontal Line ◽  
Optimal Frequency ◽  
Stimulus Line ◽  
Factors Influencing ◽  
Parallel Motion ◽  
Axis I

When two vertical short lines are alternately flashed at certain SOAs, a shortening of the apparent path of the stroboscopic movement is perceived. In the experiments reported here, factors influencing the shortening effect were studied with lines created on a CRT display. Experiment 1 was designed to study the effect of SOA. Each stimulus line was always presented for 100 ms, but intervals were varied in the range from 25 to 800 ms. With short and long SOAs almost no shortening illusion was observed, whereas the SOA for optimal stroboscopic motion (200 ms) also produced the largest illusion (ca 16%). This agrees with the classic study by Scholz (1924 Psychologische Forschung5 219 – 272) who found the largest illusion (25%) at the optimal frequency for stroboscopic motion. Experiment 2 dealt with the effect of inversions (I), mirror reflections (M), and rotations (R) of the line during the stroboscopic movement (see Kolars and Pomerantz, 1971 Journal of Experimental Psychology87 99 – 108). The particular movements were signalled by means of a short horizontal line added to one end of each of the two vertical lines of experiment 1. The configurations were (1), signifying parallel motion in one plane; (2), locomotion with rotation around the vertical axis (M); (3), locomotion with rotation around the horizontal axis (I); and (4), locomotion with rotation in the plane of the display (R). In all these conditions, the shortening illusion was significantly larger than in experiment 1. The differences between the four conditions were not statistically significant, but the illusion under condition (1) seemed smaller than in the other three conditions. With SOAs for optimal stroboscopic motion, ‘rotation’ paths tended to appear three-dimensional.

Optimization of a Horizontal Axis Tidal Current Turbine by Multi-Objective Optimization

2019 ◽  
Author(s):  
Takumi Nagataki ◽  
Ko Kurokawa ◽  
Reiko Yamada ◽  
Daisaku Sakaguchi ◽  
Yusaku Kyozuka
Keyword(s):  
Tidal Current ◽  
Swirling Flow ◽  
Operating Conditions ◽  
Horizontal Axis ◽  
Power Coefficient ◽  
Design Parameters ◽  
Navier Stokes Equation ◽  
Baseline Design ◽  
Tidal Current Turbine ◽  
Current Turbine

Abstract A global search optimization system is applied to the design of a horizontal axis tidal current turbine with shroud. 11 design parameters of the turbine blade and 4 design parameters of the shroud casing are considered for the optimization using a genetic algorithm. In order to reduce the simulation cost, a neural network is applied as the meta-model of the RANS (Reynolds-averaged Navier–Stokes) equation solver. Multi-objectives of the power coefficient at different tip speed ratios are applied to cover a wide operating range of the turbine. The CFD (Computational fluid dynamics) for optimization is validated experimentally for the case of a baseline design, and an optimum design is proposed. In this paper, a static structural analysis has been performed, and its robustness is confirmed under several operating conditions. Furthermore, internal flow of the optimized turbine is discussed in detail. It is found that the optimized blade generates a swirling flow and suppresses flow separation at the diffuser wall. The wide angle of the diffuser successfully achieves a high pressure recovery ratio and results in a high level of suction at the inlet of the turbine. It is found that the high-performance tidal turbine is possible to design if both the blade and the shroud diffuser are optimized at the same time.

scholarly journals A Comparative Study on the Performance of a Horizontal Axis Ocean Current Turbine Considering Deflector and Operating Depths

2020 ◽  
Vol 12 (8) ◽  
pp. 3333
Author(s):  
Nauman Riyaz Maldar ◽  
Cheng Yee Ng ◽  
Lee Woen Ean ◽  
Elif Oguz ◽  
Ahmad Fitriadhy ◽  
...  
Keyword(s):  
Fluid Pressure ◽  
Three Dimensional ◽  
Horizontal Axis ◽  
Ocean Current ◽  
Power Coefficient ◽  
Cfd Simulations ◽  
Torque Coefficient ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
Current Turbine

Several different designs and prototypes of ocean current turbines have been tested over recent years. For every design test, emphasis is given to achieving an optimum power output from the flow. In this study, the performance of a Horizontal Axis Ocean Current Turbine (HAOCT) has been investigated using three-dimensional Computational Fluid Dynamics (CFD) simulations for three cases, namely, (1) a turbine without a deflector, (2) a turbine with a deflector, and (3) a turbine with a deflector operating at a higher fluid depth. The turbine design was modeled in DesignModeler software and simulations were carried out in commercial CFD software Flow-3D. The Torque Coefficient (Cm) and Power Coefficient (Cp) for the turbine have been investigated for a certain range of Tip-Speed Ratios (TSRs) in a flow velocity of 0.7 m/s. Furthermore, comparisons have been made to demonstrate the effect of the deflector on the performance of the turbine and the influence of a higher fluid pressure on the same. The results from the simulations indicate that the higher value of Cp was achieved for Case 2 as compared to the other two cases. The findings from the study indicate that the use of the deflector enhances the performance of the turbine. Furthermore, a higher fluid pressure acting on the turbine has a significant effect on its performance.

scholarly journals Investigation of an Innovative Rotor Modification for a Small-Scale Horizontal Axis Wind Turbine

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2649 ◽  
Author(s):  
Artur Bugała ◽  
Olga Roszyk
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Cfd Simulation ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Horizontal Axis ◽  
Power Coefficient ◽  
Small Scale ◽  
Horizontal Axis Wind Turbine ◽  
Airflow Distribution

This paper presents the results of the computational fluid dynamics (CFD) simulation of the airflow for a 300 W horizontal axis wind turbine, using additional structural elements which modify the original shape of the rotor in the form of multi-shaped bowls which change the airflow distribution. A three-dimensional CAD model of the tested wind turbine was presented, with three variants subjected to simulation: a basic wind turbine without the element that modifies the airflow distribution, a turbine with a plano-convex bowl, and a turbine with a centrally convex bowl, with the hyperbolic disappearance of convexity as the radius of the rotor increases. The momentary value of wind speed, recorded at measuring points located in the plane of wind turbine blades, demonstrated an increase when compared to the base model by 35% for the wind turbine with the plano-convex bowl, for the wind speed of 5 m/s, and 31.3% and 49% for the higher approaching wind speed, for the plano-convex bowl and centrally convex bowl, respectively. The centrally convex bowl seems to be more appropriate for higher approaching wind speeds. An increase in wind turbine efficiency, described by the power coefficient, for solutions with aerodynamic bowls was observed.

Simulation Analysis of Savonius Turbine with Self-Rotating Blades

2012 ◽  
Vol 614-615 ◽  
pp. 480-484
Author(s):  
Zhi Peng Tang ◽  
Ying Xue Yao ◽  
Liang Zhou ◽  
Jin Ming Wu ◽  
Bo Wen Yu
Keyword(s):  
Wind Speed ◽  
Simulation Analysis ◽  
Power Coefficient ◽  
Rotating Blades ◽  
Low Wind Speed ◽  
Separating Flow ◽  
Wide Range ◽  
Low Efficiency ◽  
Driving Torque ◽  
The Impact

This paper analyzed the advantages of traditional Savonius (S-type) turbine and the reasons of its low efficiency, proposed a new type of turbine with self-rotating blades and surrounded by a rectifier, and studied the aerodynamic performance by numerical simulations. The turbine is composed of a rectifier and a rotor, the rectifier consists by straight and arc segments which can accelerate the wind speed and adjust the inflow wind angle. The self-rotating blade can reduce the impacted area acting on the leeward blade by wind and arm of the impact torque, therefore reduces the resistant torque of the blade, and the driving torque acting on the windward blade is almost the same with traditional S-type turbine, which can increase the overall driving torque. The result shows that the new turbine has the advantages as below: wide range of wind speed for effective working, high power coefficient (Cp), suitable for low wind speed aera etc. Although the flow field in S-type turbine is complex separating flow, the performance of the turbine proposed in this paper is improved and is better than traditional S-type turbine in numerical simulation which is worth for spreading.

Chaotic mixing in a bounded three-dimensional flow

2000 ◽  
Vol 417 ◽  
pp. 265-301 ◽  
Author(s):  
G. O. FOUNTAIN ◽  
D. V. KHAKHAR ◽  
I. MEZIĆ ◽  
J. M. OTTINO
Keyword(s):  
Laser Sheet ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Chaotic Advection ◽  
Base Case ◽  
Dimensional System ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Moderate Reynolds Number

Even though the first theoretical example of chaotic advection was a three-dimensional flow (Hénon 1966), the number of theoretical studies addressing chaos and mixing in three-dimensional flows is small. One problem is that an experimentally tractable three-dimensional system that allows detailed experimental and computational investigation had not been available. A prototypical, bounded, three-dimensional, moderate-Reynolds-number flow is presented; this system lends itself to detailed experimental observation and allows high-precision computational inspection of geometrical and dynamical effects. The flow structure, captured by means of cuts with a laser sheet (experimental Poincaré section), is visualized via continuously injected fluorescent dye streams, and reveals detailed chaotic structures and chains of high-period islands. Numerical experiments are performed and compared with particle image velocimetry (PIV) and flow visualization results. Predictions of existing theories for chaotic advection in three-dimensional volume-preserving flows are tested. The ratio of two frequencies of particle motion – the frequency of motion around the vertical axis and the frequency of recirculation in the plane containing the axis – is identified as the crucial parameter. Using this parameter, the number of islands in the chain can be predicted. The same parameter – using as a base-case the integrable motion – allows the identification of operating conditions where small perturbations lead to nearly complete mixing.

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