Wind-Tunnel Tests of Vertical-Axis Wind Turbine Blades

2011 ◽  
Author(s):  
B. D. Plourde ◽  
J. P. Abraham ◽  
G. S. Mowry ◽  
W. J. Minkowycz
Keyword(s):  
Power Generation ◽  
Wind Tunnel ◽  
Turbine Blade ◽  
Vertical Axis ◽  
Cellular Communication ◽  
Wing Design ◽  
Ongoing Research ◽  
Wind Speeds ◽  
Wide Range ◽  
Communication Towers

An ongoing research project is investigating the potential of locating vertical-axis wind turbines (WT) on remote, off-grid cellular communication towers. The goal of the WT is to provide local power generation to meet the electrical needs of the tower. While vertical-axis devices are less efficient than their more traditional horizontal-axis counterparts, they provide a number of practical advantages which make them a suitable choice for the present situation. First, the direction of their axis is aligned with the existing tower and its rotation does not interfere with the tower structure. Second, vertical-axis devices are much less susceptible to the direction of wind and they do not require control-systems to ensure they are oriented correctly. Third, vertical-axis turbines have very low start-up wind speeds so that they generate power over a wide range of speeds. Fourth, since vertical-axis turbines rotate at a slower speed compared with horizontal counterparts, they impart a lessened vibration load to the tower. These facts, collectively, make the vertical-axis turbine suitable for the proposed application. The design process involved a detailed initial design of the turbine blade using computational methods. Next, a trio of designs was evaluated experimentally in a large, low-speed wind tunnel. The wind tunnel is operated by the University of Minnesota’s St. Anthony Falls Fluid Laboratory. The tunnel possesses two testing sections. The larger section was sufficient to test a full-size turbine blade. Accounting was taken of the blockage effect following the tests. The experiments were completed on (1) a solid-wing design (unvented), (2) a slotted-wing design (vented), and (3) a capped-and-slotted design (capped). Conditions spanned a wide range of wind speeds (4.5–11.5 m/s). The turbines were connected to electronics which simulated a range of electrical loads. The tested range was selected to span the expected range of resistances which will be found in practice. It was discovered that over a range of these wind speeds and electrical resistances, slots located on the wings result in a slight improvement in power generation. On the other hand, the slotted-and-capped design provided very large increases in performance (approximately 200–300% compared with the unvented version). This large improvement has justified commercialization of the product for use in powering remote, off-grid cellular communication towers.

Circulation Controlled Airfoil Analysis Through 360 Degrees Angle of Attack

2009 ◽  
Author(s):  
Henry Z. Graham ◽  
Meagan Hubbell ◽  
Chad Panther ◽  
Jay Wilhelm ◽  
Gerald M. Angle ◽  
...  
Keyword(s):  
Power Generation ◽  
Wind Turbines ◽  
Electrical Power ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Circulation Control ◽  
Wind Speeds ◽  
Wide Range ◽  
Turbine Shaft

Wind turbines are a source of renewable energy with an endless supply. The most efficient types of wind turbines operate by utilizing the lift force of its blades to create a rotational force. The power capabilities of a wind turbine are tied to the blades’ ability to convert the aerodynamic forces into rotational energy. Vertical axis wind turbines (VAWT), unlike the more common horizontal axis (HAWT) type, do not need to be directed into the wind and can place the transmission and electrical power generation components at the bottom of the turbine shaft, near the ground. Currently VAWTs cannot feather or pitch the blades, in the same fashion as a HAWT, for a lift change to control power generation and/or rotational speed at different or changing wind speeds. A method of increasing the lift of a blade without physically moving the blade is to use circulation control (CC), via a blowing slot over a rounded trailing edge. The CC air flow entrains the air around the blade to create more lift. Adding an actuated valve for the blowing slot allows a CC-VAWT to control the amount of lift generated, as well as the location of the augmentation relative to the wind direction, resulting in augmented power generation. In order to study the performance capabilities of a CC-VAWT, a NACA0018 blade was modified to incorporate circulation control. This modified shape was analyzed using computational fluid dynamics at two Reynolds numbers and a wide range of angles of attack. The lift to drag ratio of the CC-VAWT blade shows benefits at low Reynolds numbers over a NACA0018 blade for post stall angles of attack, but there is a decrease in the lift to drag before stall due to a significant increase in drag of the circulation control models. Further CFD refinement and experimental investigations are recommended to validate the predicted effects circulation control will have on the performance of a VAWT.

An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines: Part 2 — Post-Stall Data Extrapolation Methods

2015 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
John M. Rainbird ◽  
Joaquim Peiro ◽  
J. Michael R. Graham ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Full Range ◽  
Vertical Axis ◽  
Wind Tunnel Tests ◽  
Numerical Assessment ◽  
Wide Range ◽  
Naca0018 Airfoil ◽  
Lift And Drag ◽  
Data Extrapolation

Accurate post-stall airfoil data extending to a full range of incidences between −180° to +180° is important to the analysis of Darrieus vertical-axis wind turbines (VAWTs) since the blades experience a wide range of angles of attack, particularly at the low tip-speed ratios encountered during startup. Due to the scarcity of existing data extending much past stall, and the difficulties associated with obtaining post-stall data by experimental or numerical means, wide use is made of simple models of post-stall lift and drag coefficients in wind turbine modeling (through, for example, BEM codes). Most of these models assume post-stall performance to be virtually independent of profile shape. In this study, wind tunnel tests were carried out on a standard NACA0018 airfoil and a NACA 0018 conformally transformed to mimic the “virtual camber” effect imparted on a blade in a VAWT with a chord-to-radius ratio c/R of 0.25. Unsteady CFD results were taken for the same airfoils both at stationary angles of attack and at angles of attack resulting from a slow VAWT-like motion in an oncoming flow, the latter to better replicate the transient conditions experienced by VAWT blades. Excellent agreement was obtained between the wind tunnel tests and the CFD computations for both the symmetrical and cambered airfoils. Results for both airfoils also compare favorably to earlier studies of similar profiles. Finally, the suitability of different models for post-stall airfoil performance extrapolation, including those of Viterna-Corrigan, Montgomerie and Kirke, was analyzed and discussed.

Design and Analysis of Wind Turbine Blades: Winglet, Tubercle, and Slotted

2013 ◽  
Author(s):  
Alka Gupta ◽  
Abdulrahman Alsultan ◽  
R. S. Amano ◽  
Sourabh Kumar ◽  
Andrew D. Welsh
Keyword(s):  
Power Generation ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Alternative Energy ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Wind Turbine Blade ◽  
Wind Turbine Blades ◽  
Wind Speeds ◽  
Governing Factor

Energy is the heart of today’s civilization and the demand seems to be increasing with our growing population. Alternative energy solutions are the future of energy, whereas the fossil-based fuels are finite and deemed to become extinct. The design of the wind turbine blade is the main governing factor that affects power generation from the wind turbine. Different airfoils, angle of twist and blade dimensions are the parameters that control the efficiency of the wind turbine. This study is aimed at investigating the aerodynamic performance of the wind turbine blade. In the present paper, we discuss innovative blade designs using the NACA 4412 airfoil, comparing them with a straight swept blade. The wake region was measured in the lab with a straight blade. All the results with different designs of blades were compared for their performance. A complete three-dimensional computational analysis was carried out to compare the power generation in each case for different wind speeds. It was found from the numerical analysis that the slotted blade yielded the most power generation among the other blade designs.

Novel Controlled-Velocity Wind Turbine Testing Apparatus to Simulate Turbulent, Non-Return Flow

2014 ◽  
Author(s):  
Corey P. Ressler ◽  
James Hilbish ◽  
Jesse J. French
Keyword(s):  
Wind Tunnel ◽  
Vertical Axis ◽  
Test Method ◽  
Return Flow ◽  
Test Apparatus ◽  
Number Range ◽  
Wind Speeds ◽  
Valid Test ◽  
Flow Interference ◽  
Work Done

This paper presents the work done by the authors to analyze the method of performance characterization of a 100W scale vertical axis wind turbines using a controlled-velocity test apparatus. The design of the power transfer system containing a gearbox and generator requires test data to determine the peak and operating range of wind speed, corresponding to RPM and torque. Multiple methods of turbine testing were considered, including in situ, wind tunnel, and control-velocity. Controlled-velocity, a method where the turbine is moved through a fluid, was selected based on lack of test location wind speeds or access to a wind tunnel of sufficient size. The test apparatus is designed to be effective for VAWT turbines of a diameter range from 1.45 to 4.2 meters in a wind velocity range of 1 to 17 m/s. This covers a Reynolds number range between (2.5 × 10^5 < Re < 4.2 × 10^6). A change from previous control-velocity test apparatus is the use of a separate truck and trailer compared to a flatbed truck, which allows greater distance between the truck cab and the turbine, to decrease any flow interference of the cab. This previous work and testing has shown to be a valid test method in that the turbine is in similar turbulent conditions as near the ground and buildings which the turbine is designed for. The main advantage of this test apparatus is the ability to test turbines in a region with low average wind speeds and minimum infrastructure.

scholarly journals Experimental Study of Vertical Axis Wind Turbine Performance under Vibration

2021 ◽  
Vol 1 (2) ◽  
pp. 177-185
Author(s):  
Md Rasel Sarkar ◽  
Sabariah Julai ◽  
Mst Jesmin Nahar ◽  
Moslem Uddin ◽  
Mahmudur Rahman ◽  
...  
Keyword(s):  
Power Generation ◽  
Experimental Study ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Dynamic Characteristics ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
Flow Uniformity ◽  
Aerodynamic Forces ◽  
Turbine Performance

An experimental study was conducted to study the effects of flow uniformity on vibration and power generation of a small vertical axis wind turbine (VAWT). Previous studies have confirmed that one of the sources of vibration in the turbine is due to aerodynamic forces, which are due to incident wind. Firstly, understanding vibration is essential before proceeding to the measurements. In this experiment, further understand the vibrations of the turbine in operation, the operating deflection shape (ODS) technique was used. A wind tunnel and flow conditioner were fabricated. Experimental modal analysis (EMA) was conducted, and the dynamic characteristics are gathered. The ODS was conducted for operating the turbine at different speeds, with and without the flow conditioner. Results from EMA and ODS are correlated to explain the behavior of structures. In conclusion, the flow conditioner tested did have a big impact on the response of the structure in terms of vibration up to 30% indifference, but not so much in power generated about 2% indifference.

scholarly journals Wind tunnel comparison of four VAWT configurations to test load-limiting concept and CFD validation

2021 ◽  
Vol 6 (1) ◽  
pp. 287-294
Author(s):  
Jan Wiśniewski ◽  
Krzysztof Rogowski ◽  
Konrad Gumowski ◽  
Jacek Szumbarski
Keyword(s):  
Wind Tunnel ◽  
Bending Moment ◽  
Vertical Axis ◽  
Turbine Rotor ◽  
Industrial Scale ◽  
Vertical Axis Wind Turbine ◽  
Cfd Validation ◽  
Shaft Length ◽  
Operating Cycle ◽  
Wide Range

Abstract. The article describes results of experimental wind tunnel testing of four different straight-bladed vertical axis wind turbine model configurations. The experiment tested a novel concept of vertically dividing and azimuthally shifting a turbine rotor into two parts with a specific uneven height division in order to limit cycle amplitudes and average cycle values of bending moments at the bottom of the turbine shaft to increase product lifetime, especially for industrial-scale turbines. Testing reduction effects of simultaneously including a vertical gap between turbine rotor levels, increasing shaft length but also reducing aerodynamic interaction between rotor levels, has also been performed. Experiment results have shown very significant decreases of bending moment cycle amplitudes and average cycle values, for a wide range of measured wind speeds, for dual-level turbine configurations as compared to a single-level turbine configuration. The vertical spacing between levels equal to a blade's single chord length has proven to be sufficient, on laboratory scale, to limit interaction between turbine levels in order to achieve optimal reductions of tested parameters through an operating cycle shift between two position-locked rotor levels during a turbine's expected lifetime. CFD validation of maintaining the effect on industrial scale has been conducted, confirming the initial conclusions.

Experimental Study and Optimization of a 2.44 Meter Vertical Axis Wind Turbine

2011 ◽  
Author(s):  
Brad Nichols ◽  
Timothy Dimond ◽  
Josh Storer ◽  
Paul Allaire
Keyword(s):  
Wind Tunnel ◽  
Power Output ◽  
Vertical Axis ◽  
Chord Length ◽  
Small Scale ◽  
Physical Parameters ◽  
Wind Tunnel Testing ◽  
Wind Speeds ◽  
The Given ◽  
Tunnel Testing

Vertical axis wind turbines (VAWTs) have long been considered a viable source for alternative energy; however, limited published research has contributed to limited technological advancement in these machines. Slower advancements are due, in part, to their complex aerodynamic models which include wake effects, vortex shedding, and cyclical blade angles of attack and Reynolds numbers. VAWTs are believed to hold several advantages over their more popular and better studied horizontal axis counterparts, including a simpler design and better efficiencies in lower wind speeds. They may have a unique niche in standalone applications at moderate wind speeds such as on an island, a remote military installation, or an inland farm. Currently, no published design standards or criteria exist for optimizing the physical properties of these turbines to maximize power output. A 2.44 m tall VAWT prototype with variable physical parameters was constructed for wind tunnel testing. The purpose of the experiment was to maximize the turbine’s power output by optimizing its physical configuration within the given parameters. These parameters included rotor radius, blade chord length, and pitch offset angle. The prototype was designed as a scaled-down model of a potential future VAWT unit that may be used to sustain a small farm or 2–4 houses. The wind tunnel consisted of a 2.74 m by 1.52 m cross section and could produce maximum wind speeds of 3.56 m/s. The turbine prototype consisted of three sets of interchangeable blades featuring two airfoils of varying chord length. Spokes of varying length allowed for rotor radii of 190.5, 317.5, and 444.5 mm. The pitch offset of the blades was varied from 0°–20° with a focus on the 10°–16° range as preliminary results suggested that this was the optimal range for this turbine. Ramp-up and steady-state rotational speeds were recorded as the blades were interchanged and the turbine radius was varied. A disk brake provided braking torque so that power coefficients could be estimated. This study successfully optimized the turbine’s power output within the given set of test parameters. The importance of finding an appropriate aspect ratio and pitch offset angle are clearly demonstrated in the results. A systematic approach to small scale wind tunnel testing prior to implementation is presented in this paper.

Study of the Flow Over Wind Turbine Blade

2011 ◽  
Author(s):  
R. S. Amano ◽  
Ryan J. Malloy
Keyword(s):  
Power Generation ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Cross Section ◽  
Acoustic Noise ◽  
Turbine Blades ◽  
Straight Edge ◽  
The Other ◽  
Wind Turbine Blades ◽  
Wind Speeds

This paper presents the comparison of the performance between two different designs of wind turbine blades; one is a straight and the other with a backward swept blade. The straight edge blade was constructed so that it is optimal on coming wind and rotation speeds with 7m/s and 20rpm. The blade has a length of 20m and uses a constant airfoil cross section NACA 4412. The swept edge blade has the same characteristics as the straight edge except for the trajectory of the edge. Each cross section has the same dimensions and has at the same distance from the hub as its corresponding section in the straight edge blade. To test this new design the performance of both blades were measured using CFD at a wind speeds ranging 0 to 20m/s. Comparisons were made for power generation and acoustic noise for both designs of the blades.

Numerical Simulations of Vertical-Axis Wind Turbine Blades

2011 ◽  
Author(s):  
B. D. Plourde ◽  
J. P. Abraham ◽  
G. S. Mowry ◽  
W. J. Minkowycz
Keyword(s):  
Wind Tunnel ◽  
Numerical Simulations ◽  
Large Scale ◽  
Turbine Blades ◽  
Vertical Axis ◽  
Test Facility ◽  
Wing Design ◽  
In Situ Tests ◽  
Initial Design

A recent research project has been focused on the design, manufacture, and testing of novel, vertical-axis turbines which can be directly attached to existing structures (such as communication towers) for local power generation, particularly in areas of the world where grid-connected electricity is unavailable. The proposed turbine has undergone a multitude of design stages, including the wing design, prototype fabrication, wind-tunnel testing, and manufacture. This report discusses the initial design process utilized to create the turbine wing. That process relied upon numerical simulations of the unsteady flow patterns which occur when the wing rotates. Results from the simulation were used to modify the wing design and significant improvements in performance were realized. Based on wind-tunnel tests, improvements on the order of 300% were obtained, compared to the initial design. Improvements of this magnitude have allowed the progression from prototype testing to large-scale manufacturing. The simulations allowed the implementation of novel design features such as preferentially deployed vents which allowed an increase of torque and a decrease of transverse loads. Results from the simulation were compared with experimental results obtained from a wind-tunnel test. In addition, data was extracted from an in situ test facility which was installed with wind-speed and data acquisition equipment. It was found that the results of the simulation were in close agreement with both the results from the wind tunnel and the in situ tests. The congruence gave added confidence to the veracity of the simulations.

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