Performance Improvements for a Vertical Axis Wind Turbine by Means of Gurney Flap

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Yan Yan ◽  
Eldad Avital ◽  
John Williams ◽  
Jiahuan Cui
Keyword(s):  
Wind Turbine ◽  
Stokes Equations ◽  
Numerical Study ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Performance Improvements ◽  
Gurney Flap

Abstract A numerical study was carried out to investigate the effects of a Gurney flap (GF) on the aerodynamics performance of the NACA 00 aerofoil and an associated three-blade rotor of a H-type Darrieus wind turbine. The flow fields around a single aerofoil and the vertical axis wind turbine (VAWT) rotor are studied using unsteady Reynolds-averaged Navier–Stokes equations (URANS). The height of GF ranges from 1% to 5% of the aerofoil chord length. The results show that the GF can increase the lift and lift-to-drag ratio of the aerofoil as associated with the generation of additional vortices near the aerofoil trailing edge. As a result, adding a GF can significantly improve the power coefficient of the VAWT at low tip speed ratio (TSR), where it typically gives low power production. The causing mechanism is discussed in detail, pointing to flow separation and dynamic stall delay.

A Numerical Study on the Effects of Unsteady Wind on Vertical Axis Wind Turbine Performance

2013 ◽  
Author(s):  
Louis Angelo Danao ◽  
Jonathan Edwards ◽  
Okeoghene Eboibi ◽  
Robert Howell
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Peak Performance ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio

Numerical simulations using RANS–based CFD have been utilised to carry out investigations on the effects of unsteady wind in the performance of a wind tunnel vertical axis wind turbine. Using a validated CFD model, unsteady wind simulations revealed a fundamental relationship between instantaneous VAWT CP and wind speed. CFD data shows a CP variation in unsteady wind that cuts across the steady CP curve as wind speed fluctuates. A reference case with mean wind speed of 7m/s, wind speed amplitude of ±12%, fluctuating frequency of 0.5Hz and mean tip speed ratio of 4.4 has shown a wind cycle mean power coefficient of 0.33 that equals the steady wind maximum. Increasing wind speed causes the instantaneous tip speed ratio to fall which leads to higher effective angle of attack and deeper stalling on the blades. Stalled flow and rapid changes in angle of attack of the blade induce hysteresis loops in both lift and drag. Decreasing wind speeds limit the perceived angle of attack seen by the blades to near static stall thus reducing the positive effect of dynamic stall on lift generation. Three mean tip speed ratio cases were tested to study the effects of varying conditions of VAWT operation on the overall performance. As the mean tip speed ratio increases, the peak performance also increases.

Aerodynamic Design Optimization of Elliptical-Bladed Savonius-Style Wind Turbine by Numerical Simulations

2016 ◽  
Author(s):  
Nur Alom ◽  
Satish Chandra Kolaparthi ◽  
Sarath Chandra Gadde ◽  
Ujjwal K. Saha
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Wind Turbine ◽  
Numerical Study ◽  
Low Cost ◽  
Vertical Axis ◽  
3D Simulation ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine

Savonius-style wind turbine (SSWT), a class of vertical-axis wind turbine, appears to be promising for off-shore applications because of its design simplicity, good starting ability, insensitivity to wind direction, relatively low operating speed, low cost and easy installation. Various blade shapes have been used over the years to improve the performance of this class of turbine. In the recent past, an elliptic-bladed profile with sectional cut angle of 50° has shown its potential to harness the wind energy more efficiently. The present study aims to optimize this profile by numerical simulations. In view of this, the elliptical-bladed profiles are tested at different sectional cut angles of θ = 45°, 47.5°, 50° and 55°. The shear stress transport (SST) k-ω turbulence model is used to simulate the flow field, and thereafter, the torque and power coefficients are obtained at the rotating conditions. From 2D simulation, pressure and velocity contours are generated and analyzed. 2D simulations are also carried out for a semi-circular bladed profile in order to have a direct comparison. The numerical study demonstrates an improved flow characteristics, and hence the power coefficient of the elliptical-bladed profile at = 47.5°. Finally, 3D simulation is carried out to visualize and analyze the flow field around the optimum elliptical-bladed rotor at a tip speed ratio of 0.8. The aspect ratio of the rotor for the 3D simulation is kept at 0.7.

Numerical Analysis of Airfoils Used for Vertical Axis Wind Turbine

2012 ◽  
Author(s):  
N. C. Uzarraga-Rodriguez ◽  
A. Gallegos-Muñoz ◽  
Maria T. Parra-Santos ◽  
Juan M. Belman-Flores
Keyword(s):  
Numerical Analysis ◽  
Wind Turbine ◽  
Stokes Equations ◽  
Numerical Study ◽  
Twist Angle ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Angle Variation ◽  
Straight Blade

A numerical analysis of a three-bladed straight vertical axis wind turbine with NACA0015 airfoils-shaped is presented. The effect generated on the moment coefficient and power coefficient of the wind turbine rotor by the twist angle variation at the chord ends was analyzed. The configurations included the variation of blade twist angle of 15° and 30° located at 70%, 80% and 90% of chord length from leading end of the straight blade. The numerical study was developed in a commercial Computational Fluid Dynamics (CFD) using FLUENT®. This code allows to solve the Reynolds averaged Navier-Stokes equations and the transport equations of the turbulence quantities. The results show the aerodynamic performance for each configuration of the blade twist angle in the wind turbine, and are compared with data obtained from straight blade without twist angle. The wind turbine performance decrease about 67% as the blade twist angle increases, due to an increment in the drag force causing a negative moment against the rotation of vertical axis wind turbine. Also, the surface pressure distribution in a VAWT’s is presented.

scholarly journals Assessment of stress-blended eddy simulation model for accurate performance prediction of vertical axis wind turbine

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Taurista Perdana Syawitri ◽  
Yufeng Yao ◽  
Jun Yao ◽  
Budi Chandra
Keyword(s):  
Wind Turbine ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Content Type ◽  
Eddy Simulation

Purpose The aim of this paper is to assess the ability of a stress-blended eddy simulation (SBES) turbulence model to predict the performance of a three-straight-bladed vertical axis wind turbine (VAWT). The grid sensitivity study is conducted to evaluate the simulation accuracy. Design/methodology/approach The unsteady Reynolds-averaged Navier–Stokes equations are solved using the computational fluid dynamics (CFD) technique. Two types of grid topology around the blades, namely, O-grid (OG) and C-grid (CG) types, are considered for grid sensitivity studies. Findings With regard to the power coefficient (Cp), simulation results have shown significant improvements of predictions using compared to other turbulence models such as the k-e model. The Cp distributions predicted by applying the CG mesh are in good agreement with the experimental data than that by the OG mesh. Research limitations/implications The current study provides some new insights of the use of SBES turbulence model in VAWT CFD simulations. Practical implications The SBES turbulence model can significantly improve the numerical accuracy on predicting the VAWT performance at a lower tip speed ratio (TSR), which other turbulence models cannot achieve. Furthermore, it has less computational demand for the finer grid resolution used in the RANS-Large Eddy Simulation (LES) “transition” zone compared to other hybrid RANS-LES models. Originality/value To authors’ knowledge, this is the first attempt to apply SBES turbulence model to predict VAWT performance resulting for accurate CFD results. The better prediction can increase the credibility of computational evaluation of a new or an improved configuration of VAWT.

Numerical Study of Pitch Angle on H-Type Vertical Axis Wind Turbine

2012 ◽  
Vol 499 ◽  
pp. 259-264
Author(s):  
Qi Yao ◽  
Ying Xue Yao ◽  
Liang Zhou ◽  
S.Y. Zheng
Keyword(s):  
Wind Turbine ◽  
Pitch Angle ◽  
Numerical Study ◽  
Vertical Axis ◽  
Azimuth Angle ◽  
Power Coefficient ◽  
Cfd Model ◽  
Vertical Axis Wind Turbine ◽  
Sliding Mesh ◽  
Mesh Technique

This paper presents a simulation study of an H-type vertical axis wind turbine. Two dimensional CFD model using sliding mesh technique was generated to help understand aerodynamics performance of this wind turbine. The effect of the pith angle on H-type vertical axis wind turbine was studied based on the computational model. As a result, this wind turbine could get the maximum power coefficient when pitch angle adjusted to a suited angle, furthermore, the effects of pitch angle and azimuth angle on single blade were investigated. The results will provide theoretical supports on study of variable pitch of wind turbine.

Numerical Research on the Characteristics of Lift-Drag Type Vertical Axis Wind Turbine

2012 ◽  
Vol 189 ◽  
pp. 448-452
Author(s):  
Yan Jun Chen ◽  
Guo Qing Wu ◽  
Yang Cao ◽  
Dian Gui Huang ◽  
Qin Wang ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Chord Length ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Middle Range ◽  
Parabolic Form ◽  
Cfd Method

Numerical studies are conducted to research the performance of a kind of lift-drag type vertical axis wind turbine (VAWT) affected by solidity with the CFD method. Moving mesh technique is used to construct the model. The Spalart-Allmaras one equation turbulent model and the implicit coupled algorithm based on pressure are selected to solve the transient equations. In this research, how the tip speed ratio and the solidity of blade affect the power coefficient (Cp) of the small H-VAWT is analyzed. The results indicate that Cp curves exhibit approximate parabolic form with its maximum in the middle range of tip speed ratio. The two-blade wind turbine has the lowest Cp while the three-blade one is more powerful and the four-blade one brings the highest power. With the certain number of blades, there is a best chord length, and too long or too short chord length may reduce the Cp.

Experimental Study of Vertical Axis Wind Turbine with Wind Speed Self-Adapting

2012 ◽  
Vol 215-216 ◽  
pp. 1323-1326
Author(s):  
Ming Wei Xu ◽  
Jian Jun Qu ◽  
Han Zhang
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Wind Velocity ◽  
Vertical Axis ◽  
Maximum Power ◽  
The Self ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Opening And Closing

A small vertical axis wind turbine with wind speed self-adapting was designed. The diameter and height of the turbine were both 0.7m. It featured that the blades were composed of movable and fixed blades, and the opening and closing of the movable blades realized the wind speed self-adapting. Aerodynamic performance of this new kind turbine was tested in a simple wind tunnel. Then the self-starting and power coefficient of the turbine were studied. The turbine with load could reliably self-start and operate stably even when the wind velocity was only 3.6 m/s. When the wind velocity was 8 m/s and the load torque was 0.1Nm, the movable blades no longer opened and the wind turbine realized the conversion from drag mode to lift mode. With the increase of wind speed, the maximum power coefficient of the turbine also improves gradually. Under 8 m/s wind speed, the maximum power coefficient of the turbine reaches to 12.26%. The experimental results showed that the new turbine not only improved the self-starting ability of the lift-style turbine, but also had a higher power coefficient in low tip speed ratio.

scholarly journals A Dynamic Rotor Vertical-Axis Wind Turbine with a Blade Transitioning Capability

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1446 ◽  
Author(s):  
Elie Antar ◽  
Amne El Cheikh ◽  
Michel Elkhoury
Keyword(s):  
Wind Turbine ◽  
Average Power ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Optimized Design ◽  
Detached Eddy Simulation ◽  
Vertical Axis Wind Turbine ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

This work presents an optimized design of a dynamic rotor vertical-axis wind turbine (DR VAWT) which maximizes the operational tip-speed ratio (TSR) range and the average power coefficient (Cp) value while maintaining a low cut-in wind velocity. The DR VAWT is capable of mimicking a Savonius rotor during the start-up phase and transitioning into a Darrieus one with increasing rotor radius at higher TSRs. The design exploits the fact that with increasing rotor radius, the TSR value increases, where the peak power coefficient is attained. A 2.5D improved delayed detached eddy simulation (IDDES) approach was adopted in order to optimize the dynamic rotor design, where results showed that the generated blades’ trajectories can be readily replicated by simple mechanisms in reality. A thorough sensitivity analysis was conducted on the generated optimized blades’ trajectories, where results showed that they were insensitive to values of the Reynolds number. The performance of the DR VAWT turbine with its blades following different trajectories was contrasted with the optimized turbine, where the influence of the blade pitch angle was highlighted. Moreover, a cross comparison between the performance of the proposed design and that of the hybrid Savonius–Darrieus one found in the literature was carefully made. Finally, the effect of airfoil thickness on the performance of the optimized DR VAWT was thoroughly analyzed.

Numerical Analysis of a Rooftop Vertical Axis Wind Turbine

2011 ◽  
Author(s):  
N. Cristobal Uzarraga-Rodriguez ◽  
A. Gallegos-Mun˜oz ◽  
J. Manuel Riesco A´vila
Keyword(s):  
Numerical Analysis ◽  
Wind Turbine ◽  
Numerical Study ◽  
Vertical Axis ◽  
Turbine Rotor ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Vertical Axis Wind Turbine ◽  
Sliding Mesh ◽  
Mesh Model

A numerical analysis of a rooftop vertical axis wind turbine (VAWT) for applications in urban area is presented. The numerical simulations were developed to study the flow field through the turbine rotor to analyze the aerodynamic performance characteristics of the device. Three different blade numbers of wind turbine are studied, 2, 3 and 4, respectively. Each one of the models was built in a 3D computational model. The effects generated in the performance of turbines by the numbers of blades are considered. A Sliding Mesh Model (SMM) capability was used to present the dimensionless form of coefficient power and coefficient moment of the wind turbine as a function of the wind velocity and the rotor rotational speed. The numerical study was developed in CFD using FLUENT®. The results show the aerodynamic performance for each configuration of wind turbine rotor. In the cases of Rooftop rotor the power coefficient increases as the blade number increases, while in the case of Savonius rotor the power coefficient decrease as the blades number increases.

scholarly journals Vertical-axis wind-turbine computations using a 2D hybrid wake actuator-cylinder model

2021 ◽  
Vol 6 (4) ◽  
pp. 1061-1077
Author(s):  
Edgar Martinez-Ojeda ◽  
Francisco Javier Solorio Ordaz ◽  
Mihir Sen
Keyword(s):  
Wind Turbine ◽  
Hollow Cylinder ◽  
Stokes Equations ◽  
Finite Thickness ◽  
Vertical Axis ◽  
Power Coefficient ◽  
Computational Domain ◽  
Source Terms ◽  
Vertical Axis Wind Turbine ◽  
Cylinder Model

Abstract. The actuator-cylinder model was implemented in OpenFOAM by virtue of source terms in the Navier–Stokes equations. Since the stand-alone actuator cylinder is not able to properly model the wake of a vertical-axis wind turbine, the steady incompressible flow solver simpleFoam provided by OpenFOAM was used to resolve the entire flow and wakes of the turbines. The source terms are only applied inside a certain region of the computational domain, namely a finite-thickness cylinder which represents the flight path of the blades. One of the major advantages of this approach is its implicitness – that is, the velocities inside the hollow cylinder region feed the stand-alone actuator-cylinder model (AC); this in turn computes the volumetric forces and passes them to the OpenFOAM solver in order to be applied inside the hollow cylinder region. The process is repeated in each iteration of the solver until convergence is achieved. The model was compared against experimental works; wake deficits and power coefficients are used in order to assess the validity of the model. Overall, there is a good agreement of the pattern of the power coefficients according to the positions of the turbines in the array. The actual accuracy of the power coefficient depends strongly on the solidity of the turbine (actuator cylinder related) and both the inlet boundary turbulence intensity and turbulence length scale (RANS simulation related).

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