Including Swirl in the Actuator Disk Analysis of Wind Turbines

2007 ◽  
Vol 31 (5) ◽  
pp. 317-323 ◽  
Author(s):  
D.H. Wood
Keyword(s):  
Wind Turbine ◽  
Vortex Structure ◽  
General Model ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Core Radius ◽  
Simple Analysis ◽  
Tip Speed Ratio ◽  
Vortex Model ◽  
Actuator Disk

It is shown that the presence of swirl in the wake of a wind turbine complicates the simple actuator disk analysis that provides such basic results as the Lanchester-Betz limit on the power coefficient. The simple analysis remains valid at high tip speed ratio for a sufficiently small core radius of the hub vortex. As the tip speed ratio decreases, the present analysis eventually becomes invalid. It is, however, reasonable to conclude that including the effects of the hub vortex causes the maximum power coefficient to increase above the Lanchester-Betz limit with decreasing tip speed ratio. The extent to which this conclusion depends on the assumed vortex model was investigated briefly by considering a more general model for the hub vortex. The results strongly imply that some account of the vortex structure of the wake will be required to resolve fully the effects of swirl. Unfortunately there are no measurements currently available for the hub vortex.

scholarly journals Performance assessment and optimization of a helical Savonius wind turbine by modifying the Bach’s section

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
M. Niyat Zadeh ◽  
M. Pourfallah ◽  
S. Safari Sabet ◽  
M. Gholinia ◽  
S. Mouloodi ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Performance Assessment ◽  
Turbulent Flows ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Basic Model ◽  
Turbine Performance ◽  
Primary Model ◽  
Savonius Wind Turbine

AbstractIn this paper, we attempted to measure the effect of Bach’s section, which presents a high-power coefficient in the standard Savonius model, on the performance of the helical Savonius wind turbine, by observing the parameters affecting turbine performance. Assessment methods based on the tip speed ratio, torque variation, flow field characterizations, and the power coefficient are performed. The present issue was stimulated using the turbulence model SST (k- ω) at 6, 8, and 10 m/s wind flow velocities via COMSOL software. Numerical simulation was validated employing previous articles. Outputs demonstrate that Bach-primary and Bach-developed wind turbine models have less flow separation at the spoke-end than the simple helical Savonius model, ultimately improving wind turbines’ total performance and reducing spoke-dynamic loads. Compared with the basic model, the Bach-developed model shows an 18.3% performance improvement in the maximum power coefficient. Bach’s primary model also offers a 12.4% increase in power production than the initial model’s best performance. Furthermore, the results indicate that changing the geometric parameters of the Bach model at high velocities (in turbulent flows) does not significantly affect improving performance.

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.

Study on Performance and Flow Condition of a Cross-Flow Wind Turbine With a Symmetrical Casing

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Junichiro Fukutomi ◽  
Toru Shigemitsu ◽  
Hiroki Daito
Keyword(s):  
Wind Turbine ◽  
Rotational Speed ◽  
Flow Condition ◽  
Cross Flow ◽  
Low Noise ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
The Cross

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio. Therefore, it is a good candidate for use as a self-starting turbine. Furthermore, it has low noise and excellent stability; therefore, it has attracted attention from the viewpoint of applications as a small wind turbine for an urban district. However, its maximum power coefficient is extremely low (10%) as compared to that of other small wind turbines. Prevailing winds in two directions often blow in urban and coastal regions. Therefore, in order to improve the performance and the flow condition of the cross-flow rotor, a casing suitable for this sort of prevailing wind conditions is designed in this research and the effect of the casing is investigated by experimental and numerical analysis. In the experiment, a wind tunnel with a square discharge is used and main flow velocity is set as 20 m/s. A torque meter, a rotational speed pickup, and a motor are assembled with the same axis as the test wind turbine and the tip speed ratio is changeable by a rotational speed controller. The casing is set around the cross-flow rotor and flow distribution at the rotor inlet and the outlet is measured by a one-hole pitot tube. The maximum power coefficient is obtained as Cpmax = 0.19 with the casing, however Cpmax = 0.098 without the casing. It is clear that the inlet and the outlet flow condition is improved by the casing. In the present paper, in order to improve the performance of a cross-flow wind turbine, a symmetrical casing suitable for prevailing winds in two directions is proposed. Then, the performance and the internal flow condition of the cross-flow wind turbine with the casing are clarified. Furthermore, the influence of the symmetrical casing on performance is discussed and the relation between the flow condition and performance is considered.

scholarly journals Numerical simulation and experimental study of blade pitch effect on Darrieus straight-bladed wind turbine with high solidity: A case study under realistic conditions

2020 ◽  
Author(s):  
Milad Babadi Soultanzadeh ◽  
Alireza Moradi
Keyword(s):  
Wind Turbine ◽  
Numerical Method ◽  
Pitch Angle ◽  
Numerical Results ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Regulation System ◽  
Lower Velocity ◽  
Realistic Condition ◽  
Tip Speed Ratio

Abstract Numerical and experimental studies were performed to examined the influence of pitch angle on the aerodynamic performance of a small Darrieus straight blade vertical axis wind turbine with high solidity and pitch regulation system under a realistic condition. By comparing experimental and numerical results, numerical results were validated. The power coefficient was measured and calculated at different tip speed ratios and for two pitch angles 0 and 5. The results revealed that 5 degrees increase in the pitch angle led to 25% elevation in the maximum value of the power coefficient (performance coefficient). Also, the numerical results showed higher accuracy at lower tip speed ratios for both pitch angles. After numerical method validation, numerical method employed to calculate the coefficient of performance and coefficient of torque function of Azimuth position as well as the flow field in the rotor affected zone and lateral distance. According to the numerical results, vorticity generation increased by the rise in the pitch angle at a constant tip speed ratio; the maximum performance coefficient occurred at a lower tip speed ratio with elevation in the pitch angle; finally, the increment in the pitch angle led to lower velocity profile in lateral distances of the rotor.

Experimental Study of a Pinwheel-Type Wind Turbine

2003 ◽  
Vol 27 (3) ◽  
pp. 227-236 ◽  
Author(s):  
Yasuyuki Nemoto ◽  
Izumi Ushiyama
Keyword(s):  
Experimental Study ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Optimum Design ◽  
Architectural Design ◽  
Frontal Area ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Torque Coefficient

Pinwheels have been familiar as toys for hundreds of years. Not only do they have an attractive appearance, they can also be fabricated from just one piece of plate. Application is possible, e.g. for education and architectural design. The purpose of this paper is to clarify the characteristics and to determine the optimum design configuration of pinwheel type wind turbines. The authors fabricated the test rotors with various shapes and carried out the experiment in a wind tunnel. As a result, the following facts were obtained: (1) Power coefficient with the traditional 4 blades has, CPmax = 0.17 at λ = 2. (2) High tip speed is obtained by cutting the frontal area of pinwheel. Tip speed ratio at no load can be easily changed from λ = 3 to 6 by changing the cutting area. Maximum power coefficient CPmax = 0.22 was obtained at tip speed ratio λ = 3.5. (3) Increased torque is obtained by cutting the edge area of the pinwheel. Tip speed ratio at no load can be easily changed from λ = 2 to 3, and torque coefficient can be easily changed from CQmax = 0.15 to 0.25, by changing the cut area.

Aerodynamic Performance Analysis of a Large Scale Wind Turbine Blade under Variable Condition

2013 ◽  
Vol 291-294 ◽  
pp. 527-530
Author(s):  
Peng Zhan Zhou ◽  
Fang Sheng Tan
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Wind Power ◽  
Turbine Blade ◽  
Large Scale ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Variable Condition

Based on BLADED software, the aerodynamic performance of a large scale wind turbine blade was analyzed under variable condition. The results show that the rated power of the blade under variable condition is increased 10%, when the rated wind speed is changed from 10.5m/s to 11.0 m/s. The blade’s wind power coefficient is above 0.46, and its tip speed ratio is between 7.8 and 11.4. When its tip speed ratio is 9.5, the blade’s maximum wind power coefficient is 0.486. It is indicated that the blade has good aerodynamic performance and wide scope of wind speed adaptive capacity. The blade root’s equivalent fatigue load is 2.11 MN•m, and its extreme flapwise load is 4.61 MN•m. The loads under variable condition are both less than that of the designed condition, so the blade’s application under variable condition is safe.

Development of an Analytical Unsteady Model for Wind Turbine Aerodynamic Response to Linear Pitch Changes

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Mohamed M. Hammam ◽  
David H. Wood ◽  
Curran Crawford
Keyword(s):  
Wind Turbine ◽  
Pitch Angle ◽  
Turbine Rotor ◽  
Speed Ratio ◽  
Element Analysis ◽  
Tip Speed Ratio ◽  
First Order ◽  
Vortex Model ◽  
Constant Pitch ◽  
Induced Velocity

A simple unsteady blade element analysis is used to account for the effect of the trailing wake on the induced velocity of a wind turbine rotor undergoing fast changes in pitch angle. At sufficiently high tip speed ratio, the equation describing the thrust of the element reduces to a first order, nonlinear Riccti's equation which is solved in a closed form for a ramp change in pitch followed by a constant pitch. Finite tip speed ratio results in a first order, nonlinear Abel's equation. The unsteady aerodynamic forces on the NREL VI wind turbine are analyzed at different pitch rates and tip speed ratio, and it is found that the overshoot in the forces increases as the tip speed ratio and/or the pitch angle increase. The analytical solution of the Riccati's equation and numerical solution of Abel's equation gave very similar results at high tip speed ratio but the solutions differ as the tip speed ratio reduces, partly because the Abel's equation was found to magnify the error of assuming linear lift at low tip speed ratio. The unsteady tangential induction factor is expressed in the form of first order differential equation with the time constant estimated using Jowkowsky's vortex model and it was found that it is negligible for large tip speed ratio operation.

A Study of Electricity Generating from Small Multi-Blade Wind Turbine for a Household

2013 ◽  
Vol 291-294 ◽  
pp. 435-438
Author(s):  
Yuttachai Keawsuntia
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Electric Power ◽  
Wind Velocity ◽  
Simulation Program ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Alternative Technology ◽  
Tip Speed Ratio ◽  
Program Show

A small multi-blade wind turbine is an alternative technology in order to electricity generating for use in a household because of the construction is cheap. From the study, the performance calculations by simulation program show that a number of blade at 12 blades is the optimum value for applying to this wind turbine that give maximum power coefficient of 0.29 at a tip speed ratio of 1.2. The results from the test run of wind rotor connected with generator in the wind tunnel at a wind velocity of 2 m/s, 3 m/s and 4 m/s, the system give the electric power of 2.5 W, 4.25 W and 4.49 W respectively.

Characteristic Analysis of Three-Bladed Darrieus Wind Turbine Based on the Multiple Streamtube Model

2014 ◽  
Vol 651-653 ◽  
pp. 663-667 ◽  
Author(s):  
Jing Ru Chen ◽  
Zhen Zhou Zhao ◽  
Tao Li
Keyword(s):  
Wind Turbine ◽  
Pitch Angle ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Characteristic Analysis ◽  
Negative Power ◽  
Tip Speed Ratio ◽  
Maximum Value ◽  
Blade Pitch Angle ◽  
Ratio Range

The paper analyzes the effect of airfoil thickness, camber and blade pitch angle on the performance of the three-bladed Darrieus wind turbines. The research results show that the increase of airfoil thickness, camber and pitch angle of blade, can improve power coefficient when the wind turbine tip speed ratio between zero and four. The increase of thickness and camber of the airfoil leads to running tip speed ratio range of wind turbine get narrowed, and reduces the power coefficient when wind turbine runs in high tip speed ratio range. When the pitch angle of blade is 1˚, power coefficient reaches the maximum value. Negative pitch angle has a bad impact on power coefficient and even creates negative power coefficients.

scholarly journals Drag coefficient calculation of modified Myring-Savonius wind turbine with numerical simulations

2020 ◽  
Vol 10 (2) ◽  
pp. 73-84
Author(s):  
Mahmoud Saleh ◽  
Endre Kovács
Keyword(s):  
Drag Coefficient ◽  
Wind Turbine ◽  
Primary Objective ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Energy Potential ◽  
Cross Sectional ◽  
Ansys Fluent ◽  
Tip Speed Ratio ◽  
Savonius Wind Turbine

Nowadays the importance of renewable energy is growing, and the utilization of the low wind energy potential is getting crucial. There are turbines with low and high tip speed ratio. Turbines with low tip speed ratio such as the Savonius wind turbine can generate adequate amount of torque at low wind velocities. These types of turbines are also called drag machines. The geometry of the blade can greatly influence the efficiency of the device. With Computational Fluid Dynamics (CFD) method, several optimizations can be done before the production. In our paper the Savonius wind turbine blade geometry was designed based on the so-called Myring equation. The primary objective of this paper was to investigate the drag coefficient of the force acting on the surface of the blade. Also, the Karman vortex was investigated and the space ratio of that vortex in our simulation was compared to a typical one. The power coefficient of a new Savonius turbine was investigated at different values of top speed ratio (TSR). For the sake of simplicity, a 2D cross-sectional area was investigated in the simulation with ANSYS Fluent 19.2.

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