Due to the importance and advantages of Vertical-axis wind turbines (VAWTs) over traditional horizontal-axis wind turbines (HAWTs), this paper is implemented. Savonius turbines with drag-based rotors are adopted from the two more extensive arrangements of vertical wind turbines because of their advantages. In this paper, six diverse rotor plans with measure up to cleared regions are analyzed with exploratory wind burrow testing and numerical reenactments. These proposed models incorporate a conventional Savonius with two different edges criteria and 90 degree helical bend models with two, three and four sharp edges. The models were designed using SolidWorks software then the physical models were 3D printed for testing. A subsonic open-sort wind burrow was utilized for Revolution per Minute (RPM) and torque estimation over a scope of wind speeds. ANSYS Fluent reenactments were utilized for dissecting streamlined execution by using moving reference outline and sliding lattice display methods. A 3-dimensional and transient strategy was utilized for precisely tackling torque and power coefficients. The five new rotor geometries have important advantages such as making a focal point of weight advance from the hub of revolution and causing more noteworthy torque on the turbine shaft contrasted with the customary Savonius turbine. Our new models with the names of CC model and QM model display cross-areas lessen the aggregate scope of negative torque on the edges by 20 degrees, contrasted with the customary Savonius demonstrate. Helical plans are better spread the connected torque over a total transformation resulting in positive torque over every single operational point. Moreover, helical models with 2 and 3 cutting edges have the best self-starting ability in low wind speeds. Helical VAWT with 3 edges starts revolution of 35 RPM at only 1.4 m/s wind speed under no generator stacking. The most noteworthy power coefficient is accomplished, both tentatively and numerically, by the helical VAWT with 2 sharp edges.
Wind energy is one of the most viable renewable sources today due to its year-round availability, and pollution-free nature. According to the Wind Vision Report, published by the U.S. Department of Energy, wind energy is the largest source of added renewable energy generation in the United States since 2000. Experts predict that, with proper development, 20% of the nation’s electricity can be supplied by wind by the year 2030, and 35% by 2050. The report states that a key to achieving this goal is to improve the potential of low-wind-speed locales [
Horizontal-axis wind turbines (HAWTs) have been in practice for some time and are heavily favored over Vertical-axis wind turbines (VAWTs) for large-scale power generation; however, research of VAWTs has gained growing interest in recent years because of the opportunities available for small-scale and off-grid power generation which favors the use of VAWTs. VAWTs have many advantages for small scale wind energy applications. Interest in VAWT technology has recently grown due to potential for off-grid power supply in several different applications. One of the greatest advantages for VAWTs over traditional HAWTs is the ability to self-start in some designs. Under low wind speed conditions, many VAWTs begin to rotate without the added expense of actuators or controls. For VAWTs the generator may be located on the ground rather than high in the air. This provides much more convenient and cost efficient installation and maintenance than that of HAWTs. Another advantageous feature of VAWTs is the fact that they can accept wind from all directions. Regardless of where the wind is coming from, the turbines generally perform equally as well. For this reason, VAWTs are preferred over HAWTs where unsteady and low speed wind conditions exist.
There are three important non-dimensional coefficients that characterize turbine performance. Tip-speed ratio (TSR) is the ratio of blade tip speed to the free-stream wind velocity. It is the product of angular velocity and overall radius, divided by the wind velocity. The moment coefficient (Cm), also known as the torque coefficient, characterizes the amount of torque generated by the blade geometry. It is the measured torque divided by the theoretical torque value available in the wind. Power coefficient is the product of tip-speed ratio and moment coefficient. The power coefficient is the efficiency of the turbine useful way for comparing the efficiencies of different wind turbine designs is plotting the power coefficient vs. tip-speed ratio. Savonius VAWTs operate in a tip-speed ratio range of 0 to 1.2 and have a maximum efficiency of 20%. Darrieus rotors operate in higher wind speeds and achieve a maximum efficiency of 35 percent, while HAWTs enjoy the highest power coefficients of any turbine type.
Savonius wind turbines are drag-type VAWTs with negligible lift forces. The traditional Savonius rotor is made up of two opposite-facing semicircular buckets. Rotation is caused due to a difference in pressure between the advancing and retreating blades. When wind strikes the blades of the turbine, two components of drag force are generated on each blade surface. Normal drag force (Fn) acts perpendicular to the blade wall and tangential drag force (Ft) acts along the tangential direction of each blade [
Rather than conventional Savonius types, some have investigated alternative drag-based designs. Ghatage et al. [
Lift-based VAWTs is a popular research area because of the higher power coefficient potential. Typically Darrieus rotors consist of straight, vertical airfoils. The most prevalent work in this area is the optimization of airfoil shape. This is done by testing different designs by the use of two-dimensional Computational Fluid Dynamics. Aerodynamic investigations are performed numerically in order to improve maximum output torque and power coefficients [
Work by Kou et al. [
Cambered S818 airfoil blades display better self-starting characteristics at most azimuthal angles, and Savonius rotors provide the best start-up performance. In order to achieve completely self-starting rotor at all azimuthal positions, a hybrid system was modeled by Bhuyan and Biswas [
Recently, Alaimo et al. [
Based on the literature review, some gaps in the VAWT research are identified. First, only semi-circle geometries are used for Savonius blades. Second, there is no available data for helical models with 90 degree twist angle, even though positive results are seen with higher twist angles in low TSR ranges. Also, there is plenty of research involving changing the number of blades for standard Savonius turbines but none for varying blade number of helical models. Lastly, very few researchers have developed three-dimensional and transient flow simulations for the study of aerodynamic behavior of vertical-axis wind turbines. With these opportunities for advancing the body of knowledge in mind, the following goals are outlined for this study:
・ Model 3 Savonius blade geometries in SolidWorks with different cross-section geometries
・ Validate increased performance of new designs with numerical simulations
・ Complete CAD models of helical designs with 2-4 blades
・ 3D print 6 models for experimental testing
・ Experimentally determine the self-starting capabilities and power coefficients of the 6 VAWT models (wind velocity, RPM, torque)
・ Investigate performance of helical models with ANSYS Fluent simulation and plot power coefficient vs. tip-speed ratio
In the present study, six different rotor designs are analyzed. Wind tunnel experiments are conducted to find reactional torque and rotations per minute (RPM) from which turbine efficiencies are calculated. Computational Fluid Dynamic (CFD) simulations are performed with ANSYS Fluent to study aerodynamic characteristics of the models. The objectives of the research are as follows:
・ Increase power coefficient of Savonius turbines by creating new blade geometries
・ Determine the self-starting capabilities of the new models
・ Develop a three-dimensional and transient model for VAWT simulation
It is hypothesized that the new “CC” and “QM” models will achieve higher maximum torque and power coefficients than the conventional Savonius model. Also, the helical models will create positive torque on the turbine shaft over all operational angles of rotation and possess the ability to self-start in lower wind speeds, increasing overall performance.
This section covers procedures for the experimental and numerical studies. An open-type, subsonic wind tunnel is used for the experimental portion of this study. At each wind speed tested, reactional torque, wind velocity, and RPM data are collected. Reactional (static) torque is measured for every 10 degrees of turbine rotation. ANSYS Fluent software is used for computational fluid dynamics simulations. The simulations are performed in three dimensions to gather moment coefficient data over time for one rotation.
Model Design and FabricationIn total, six different VAWT models are tested in the study. Each model is developed using Solid Works commercial CAD software. Due to some complex and twisted geometries, the models are 3D printed using fused deposition modeling (FDM) and stereo lithography (SLA) methods. The models are named SAV, CC, QM, Helical 2, Helical 3, and Helical 4 for reference. The traditional Savonius model with straight blades, SAV, is used for benchmarking and comparing results of the new designs. The SAV cross-section can be seen in
Each model in the study is designed with a 4.2 inch blade diameter (D) and blade height (H) of 4 inches; therefore, the swept area (A) is kept consistent across all models. Cross-sectional views of the new Savonius designs, “CC” model and “QM” model, are displayed in
CC is modeled with slightly smaller diameter buckets of 1.5 inches, connected
with a tangent line. The QM model has the same dimensions with a curved line connecting the 2 blades. The SLA 3D printed models are presented in
The other three VAWT models in the study are constructed with a helical twist of 90 degrees. Helical 2, Helical 3, and Helical 4 have similar cross-sections to that of the traditional Savonius with varying number of blades from 2 to 4. Details of the blade-tip helix for each of these models may be seen in
Completed CAD models of the VAWTs with 90 degree helical twist may be seen in
These physical models are then created from PLA plastic with a FDM 3D printer for experimental testing, shown in
The Georgia Southern wind energy laboratory is equipped with a subsonic open-type wind tunnel for experimental testing. The existing wind tunnel and
test section are shown in
Free stream velocity through the test section is easily controlled with the variable
frequency drive (VFD) operator interface. Consistent and maintainable RPMs of the motor depend on the frequency, measured and displayed in Hertz, transmitted from the VFD. The internal fan produces wind speeds of 0 to 13 m/s through the outlet.
A hand held anemometer is used to measure wind velocity for each test. Wind speed is measured about 6 inches in front of the model and centered on the axis of rotation. The instrument is capable of measuring current, maximum, or average wind speed. Each time the VFD is used to alter wind conditions, current wind speed is measured in time intervals of 2 - 10 seconds. For each experiment at a given wind speed, 5 separate readings of current wind velocity are taken to ensure consistent wind conditions. The anemometer has a range of 0.2 to 30 m/s and is accurate to 0.1 m/s.
A small circular base with 2.5 in. vertical shaft is used for RPM measurement. Two sealed stainless steel ball bearings are fitted inside the models to allow for free rotation on the fixed shaft. A laser tachometer is used to measure RPM of the models under varying wind conditions, seen in
A reactional torque meter with error of no more than ±0.1% of 1000 Nm, or ±1 Nm is used for each model under increasing wind speeds. For each wind condition, torque is measured at every 10 degrees of turbine rotation. The torque meter and experimental setup is displayed in
The base plate of the torque measurement fixture is marked for every 10 degrees of rotation. It is important to define the turbine angle relative to incoming wind velocity. The CC and Helical 2 models are positioned on the fixture at an angle of zero degrees relative to incoming wind in
Once torque data is calculated, analysis must be done to compare the performance of the models to other research. Non-dimensional coefficients are used for comparison to other similar research and validation of the experiment. Three
of these universally used non-dimensional entities are considered for this study. The power coefficient describes the energy conversion efficiency of the turbine. Torque coefficient is a non-dimensional representation of rotor torque, which is proportional to power produced.
Using the following equations, tip-speed ratio and moment coefficient data are used to calculate the power coefficient over a range of wind velocities for each helical rotor design. In order to find the moment coefficient for each turbine, the rotor swept area must first be calculated using Equation (1),
A = D H (1)
where H is rotor height in m and D is overall diameter in m.
The swept area is kept consistent across all three models and used as a reference value in ANSYS Fluent for solving moment coefficients. The non-dimensional moment coefficient is calculated using Equation (2),
C m = T 1 4 ρ A D V 2 (2)
where T is torque in N∙m, is air density in kg/m3, A is rotor area in m2, and V is air velocity in m/s. The non-dimensional term for comparing efficiency of VAWTs is the power coefficient. First the angular velocity of the rotor must be calculated by Equation (3),
ω = 2 π N 60 (3)
where N is the measured revolutions per minute. Once the angular velocity is determined, the tip-speed ratio of the rotor is solved from Equation (4).
λ = ω D 2 V (4)
The power coefficient is then calculated. As can be seen by Equation (5), the power coefficient is found from the product of tip-speed ratio and moment coefficient.
C p = P 1 2 ρ A V 3 = T ω 1 2 ρ A V 3 = λ C m (5)
In order to understand the pressure distributions and aerodynamic characteristics of the various blades in the study, numerical simulations are performed using commercial CFD software ANSYS Fluent. The CAD models are imported into ANSYS Design Modeler, and fluid regions are added to the geometry. For transient three-dimensional analysis of VAWTs, two separate fluid domains are needed for simulation [
The fluid domains are discretized using ANSYS Meshing. Each mesh consists of around 500,000 tetrahedral elements since the maximum allowable number of cells for ANSYS Fluent Academic is 512,000. The number of elements and nodes for each mesh are given in
Savonius | CC | QM | Helical 2 | Helical 3 | Helical 4 | |
---|---|---|---|---|---|---|
Elements | 503,727 | 453,849 | 495,219 | 501,394 | 502,216 | 506,989 |
Nodes | 92,986 | 85,320 | 88,663 | 89,656 | 89,754 | 90,557 |
An example mesh is displayed in
The realizable k-epsilon turbulence model with standard wall functions is used for each solution. The realizable model is comparable to the RNG model with more accurate solutions [
The computational domain consists of a rotating zone surrounding the blades and a stationary far-field zone. A mesh interface is created between the two zones. The interface is necessary because the nodes on the boundaries of the far-field and rotational zones are intentionally non-conformal. The interface pairs these so that interpolation can occur, and fluid may pass into and out of the rotating region. For each case, a static simulation with moving reference frame (MRF) and a dynamic sliding mesh model (SMM) are completed. The rotation is first defined using the steady-state solver with MRF, and the simulation is then solved in a transient manner using a sliding mesh motion. The converged static result from the MRF simulation is used to initialize the transient SMM solver. Convergence criteria are kept consistent throughout the study requiring all 5 residuals to decrease to a value of 1e-03. For the transient solver; coefficients of moment (Cm) are monitored over time with accurate reference values. Time step size is dependent on the RPM value for each case. Time steps are calculated to account for every 10 degrees of model rotation. For 2 full rotations, 72 time steps per simulation are run with 20 iterations per time step.
Boundary conditions for the simulations are taken from experimental data. These include air velocity inlet speed and corresponding rotational speed of the blades. The pressure outlet is kept at constant atmospheric pressure. The blade walls are given a no slip condition and zero rotational velocity relative to the sliding mesh zone (equal to the rotating fluid domain).
The realizable k-epsilon model is used with the SIMPLE segregated algorithm [
∂ ∂ t ( ρ k ) + ∂ ∂ x j ( ρ k u j ) = ∂ ∂ x j [ ( u + μ t σ k ) ∂ k ∂ x j ] + P k + P b − ρ ϵ − Y m + S k
and
∂ ∂ t ( ρ ϵ ) + ∂ ∂ x j ( ρ ϵ u j ) = ∂ ∂ x j [ ( u + μ t σ ϵ ) ∂ ϵ ∂ x j ] + ρ C 1 S ϵ − ρ C 2 ϵ 2 k + ν ϵ + C 1 ϵ ϵ k C 3 ϵ P b + S ϵ
where
C 1 = max [ 0.43 , η η + 5 ] , η = S k ϵ , S = 2 S i j S i j
In these equations, P K represents generation of turbulence kinetic energy due to mean velocity gradients, and P b is generation of turbulence kinetic energy due to buoyancy [
A 3D CFD analysis is conducted for the SAV, CC, and QM models to study the effects of the different geometries on the amount of torque generated. Rotational speed of the models is kept constant at 275 RPM for all models and all tip-speed ratios (TSRs) in this part of the study. Only inlet velocity is varied with speeds of 3, 5, and 7 m/s. The increasing wind speeds resulted in tip-speed ratios of 0.51, 0.31, and 0.22. The following results contain the transient moment coefficient monitors for the simulations with constant rotational speed.
The SAV model is used for obtaining baseline results, to which the new designs may be compared. At 3 m/s inlet velocity, the maximum Cm is 0.134 with an average of 0.029. At 5 m/s the maximum Cm is 0.560 with an average of 0.145. At 7 m/s the maximum Cm is 1.248 with an average of 0.315. The Cm vs. time graph for SAV is displayed in
The CC rotor experiences higher maximum and average moment coefficients than SAV at all 3 tested tip-speed ratios. The maximum Cm achieved is 1.390 at 7m/s inlet velocity. Results are displayed in
total range of negative torque at 7 m/s wind velocity is 20 degrees more narrow, compared to the SAV model.
The QM model outperforms both the CC and SAV models in terms of maximum moment coefficient at 5 and 7 m/s inlet velocities as shown in
A comparison of Cm data for each design is presented in Figures 17-19 at
inlet velocities of 3, 5, and 7 m/s, respectively.
At highest simulated wind speed, SAV experiences negative torque from 0-55 degrees and 180 - 235 degrees. QM and CC both have negative torque ranges of 5 - 45 degrees and 185 - 235 degrees. As can be seen in the comparison figures, a large difference in moment coefficient between the new designs and the traditional SAV model occurs at about 0.06 seconds (100 degrees) for each tested wind speed. CFD post-processing within the ANSYS Fluent software is used to investigate the aerodynamic characteristics at this time step. Air pressure contours surrounding the blades, air velocity vectors, and blade wall pressures are displayed in Tables 2-5 for the 5 m/s wind velocity simulations.
The SAV model experiences higher pressure at the front of the blades. CC and QM experience more negative pressure on the back side of the blade. These two conditions result in greater torque for the CC and QM models.
The air velocity vectors for each model are shown in
blade for the new designs. This results in a greater pressure difference and larger moment coefficient.
The negative pressures on the reverse side of the retreating blades at 0.06s are presented as 3D pressure contours in
Using calculated tip-speed ratio and moment coefficient data from ANSYS, the power coefficient (Cp) of each case is determined. Maximum and average power coefficients for the 9 dynamic simulations in this study are presented in
A graph of maximum Cp vs. TSR for the 3 models is displayed in
Model | V (m/s) | TSR | Avg Cm | Max Cm | Avg Cp | Max Cp |
---|---|---|---|---|---|---|
SAV | 3 | 0.512 | 0.029 | 0.134 | 0.015 | 0.068 |
SAV | 5 | 0.307 | 0.142 | 0.560 | 0.043 | 0.172 |
SAV | 7 | 0.219 | 0.315 | 1.248 | 0.069 | 0.274 |
CC | 3 | 0.512 | 0.041 | 0.157 | 0.021 | 0.080 |
CC | 5 | 0.307 | 0.203 | 0.594 | 0.062 | 0.182 |
CC | 7 | 0.219 | 0.442 | 1.390 | 0.097 | 0.305 |
QM | 3 | 0.512 | 0.037 | 0.150 | 0.019 | 0.077 |
QM | 5 | 0.307 | 0.214 | 0.664 | 0.066 | 0.204 |
QM | 7 | 0.219 | 0.455 | 1.474 | 0.100 | 0.323 |
in this section are only used to compare the aerodynamic performance of the different blade geometries. Both of the new designs achieve higher power coefficients than the semicircle Savonius blade design. Compared to the SAV model, CC achieves an 11.38% increase in maximum efficiency and a 40.07% increase in average efficiency. The highest efficiency observed in the study of 32.35% was the QM model at TSR 0.219. This was an increase in power coefficient of 18.10%, compared to the standard SAV model.
Both QM and CC model geometries effectively produce a center of pressure on the blades further from the axis of rotation. This change in blade geometry increases the applied torque on the turbine shaft while maintaining the same swept area as the conventional Savonius model.
Experimental RPM data is collected for all 6 VAWT models. The models are free to rotate with no applied load in this test. RPM vs. wind velocity data is presented in
From the graph, it can be seen that the Helical 3 and Helical 2 models achieve the best self-starting characteristics in low wind speed conditions. Helical 3 begins rotation at 1.4 m/s with 35 RPM, while Helical 2 starts rotating at 1.5 m/s with 45 RPM. SAV has the worst self-starting capability in the study, beginning rotation at wind velocity of 2.3 m/s. At higher wind speeds, Helical 3 achieves the fastest rotation of all 6 models. Helical 2 and Helical 3 both record significantly higher RPM than the other 4 models over the entire tested range of wind speeds.
Each model is tested under varying wind conditions to determine the torque generated at every 10 degrees of model rotation. The reactional torque meter is used for the collection of experimental torque data. The torque data recorded for all 6 models are contained in Figures 22-27. The straight-bladed models, SAV, CC, and QM, all experience negative torque in 2 ranges of operation.
As can be seen in Figures 25-27, all of the helical models experience positive torque for each angle of rotation. The Helical 2 and Helical 3 models generate significantly more torque than the Helical 4 model at equivalent wind speeds.
The measured wind velocity, RPM, and torque data from the wind tunnel experiments are used to calculate the coefficient of moment and power for each turbine model. Moment coefficient is found from Equation (2), and power coefficient is found from Equation (5) in the methodology. Graphs of experimental moment coefficient vs. angle of rotation are displayed in Figures 28-33.
In order to compare the experimental efficiencies of the models, experimental power coefficient vs. tip-speed ratio for the 6 designs are plotted together in
The Helical 2 model achieves the highest experimental power coefficient of 0.109 at a tip-speed ratio of 0.497. Maximum Cp for Helical 3 is 0.102 at tip-speed ratio 0.623. The 90 degree helical models with 2 and 3 blades perform significantly better than the other four models in the study.
With experimental data for the helical models, numerical simulations with ANSYS Fluent are performed for validation of results. The same numerical methodology is used to obtain the following results; however, the wind velocity and corresponding RPM input boundary conditions are taken from the experimental data. This provides more realistic results for power coefficient vs. tip-speed ratio as the actual rotation of the VAWTs are modeled. Moment coefficient data from Fluent is used for calculating the average power coefficient for one full rotation. The results are plotted against corresponding tip-speed ratio in
Each data set is fitted with a fourth order polynomial trend line to display the power curves for the numerical results of the helical models.
This section contains the pressure contours surrounding the blades of the helical models. The cross-sections vary in the y-direction due to the blade twist, so three planes were created in post-processing for viewing results. The planes are located at the top, middle, and bottom of each model and are shown in
Pressure contours for the helical models at maximum power coefficient are presented in
The Helical 2 model produces the highest power coefficient in the numerical study of 0.140. Seen in
Helical 2 | Helical 3 | Helical 4 | ||
---|---|---|---|---|
Cp | 0.140 | 0.113 | 0.068 | |
TSR | 0.475 | 0.405 | 0.369 | |
Time | 0.103 s | 0.135 s | 0.024 s | |
a | ||||
b | ||||
c |
Model | Helical 2 | Helical 3 | Helical 4 | |
---|---|---|---|---|
Cp | 0.140 | 0.113 | 0.068 | |
TSR | 0.475 | 0.405 | 0.369 | |
Time | 0.103 s | 0.135 s | 0.024 s | |
a | ||||
b | ||||
c |
the retreating blade, and more negative pressure is present on the backside. This results in larger pressure differential on the blade, compared to the other 2 models, allowing for the higher turbine efficiency.
Air velocity contours and vectors are displayed in
In all 3 planes, higher air velocity is present on the backside of the bottom blade for the Helical 2 model. This creates the lower pressure seen in
Vectors are shown along with contour plots to display air flow direction around the models. Air swirling is present behind the helical models with 2 and 3 blades, reinforcing the observations stated before.
Helical 2 | Helical 3 | Helical 4 | ||
---|---|---|---|---|
Cp | 0.140 | 0.113 | 0.068 | |
TSR | 0.475 | 0.405 | 0.369 | |
Time | 0.103 s | 0.135 s | 0.024 s | |
a | ||||
b | ||||
c |
The experimental and numerical power coefficient results are plotted together with corresponding tip-speed ratios for the helical models in Figures 37-39.
For both numerical study and wind tunnel experimentation, the Helical 2 model produces maximum power coefficient. Experimentally, maximum Cp of 0.109 is observed at TSR 0.497. Maximum Cp achieved for numerical simulation is 0.140 at TSR 0.475.
Helical 3 achieves maximum experimental Cp of 0.102 at TSR 0.623 and maximum numerical Cp of 0.113 at TSR 0.405.
Lowest efficiencies are observed with the Helical 4 model: experimental Cp of 0.067 at TSR 0.486 and numerical Cp of 0.068 at TSR 0.369.
The Helical 2 numerical results are plotted alongside the reported efficiency for traditional Savonius rotors. The comparison can be seen in
In terms of wind turbine efficiency, a performance increase is observed for the Helical 2 model in the tip-speed ratio range of 0.25 to 0.475. At TSR 0.375, the helical turbine achieves just over a 3% increase in efficiency, compared to the traditional Savonius rotor.
To calculate the fluid characteristic parameters in our simulation; The ANSYS software has powerful design exploration and optimization capabilities by varying parameters from CAD, material properties, boundary conditions and simulation results. It can quickly set up and evaluate multiple design variations to drive design of experiments, goal-driven optimization and Six Sigma analysis. ANSYS technology has the required capabilities to make model setup, meshing and physics solution enabling reliable and accurate fluid, structural, thermal, electromagnetic and multiphysics simulations [
The following conclusions are drawn from the study:
・ The new QM and CC cross-section design for Savonius rotors create a center of pressure further from the axis of rotation, increasing power coefficient.
・ Both the QM and CC designs reduce the total range of negative torque on the blades by 20 degrees, compared to the traditional SAV model.
・ 90 degree helical twist models with 2 - 4 blades each experience positive torque for all angles of operation, while Savonius models experience negative torque in 2 regions.
・ Helical 2 and Helical 3 possess the best self-starting capability. Helical 3: 35 RPM at 1.4 m/s wind speed and Helical 2: 45 RPM at 1.5 m/s wind speed.
・ Highest average power coefficient observed in the study (1 complete rotation) is achieved by the Helical 2 model, both numerically and experimentally. Simulation: Cp = 0.140 at tip-speed ratio = 0.475, and Wind tunnel experiment: Cp = 0.109 at tip-speed ratio = 0.497.
・ At TSR 0.375, the Helical 2 turbine achieves just over a 3% increase in efficiency, compared to the reported efficiency of a traditional Savonius rotor. Increased power coefficient is observed for Helical 2 in the tip-speed ratio range of 0.25 to 0.475.
Authors would express the heartiest deep sense of gratitude to Mechanical Engineering Department of Georgia Southern University for financial support, reference papers, and websites as mentioned below which are necessary for the research. Also, authors acknowledge NSF-RET: ENgaging Educators in Renewable EnerGY (ENERGY), Total Award Amount: $524,706, Award #1609524, Total Award Period Covered: June 1, 2016-May 31, 2019.
Rahman, M., Salyers, T.E., El-Shahat, A., Ilie, M., Ahmed, M. and Soloiu, V. (2018) Numerical and Experimental Investigation of Aerodynamic Performance of Vertical-Axis Wind Turbine Models with Various Blade Designs. Journal of Power and Energy Engineering, 6, 26-63. https://doi.org/10.4236/jpee.2018.65003