The Effect of the Configuration of the Amplification Device on the Power Output of a Piezoelectric Strip

2012 ◽  
Author(s):  
Jesse M. McCarthy ◽  
Arvind Deivasigamani ◽  
Sabu J. John ◽  
Simon Watkins ◽  
Floreana Coman
Keyword(s):  
Aspect Ratio ◽  
Power Output ◽  
Polyvinylidene Fluoride ◽  
Leading Edge ◽  
Wind Speeds ◽  
Start Up ◽  
Piezoelectric Strip ◽  
Power Measurements ◽  
System 1 ◽  
Leaf Parameters

We investigated the behaviour of a polyvinylidene-fluoride piezoelectric strip (‘stalk’) clamped at the leading edge, and hinged to an amplification device (‘leaf’) at the trailing edge. Flutter of this cantilevered system was induced within smooth, parallel flow, and an AC voltage was generated from the PVDF strip. A polypropylene, triangle comprised the leaf. Two leaf parameters were varied so as to quantify their effect on the power output of the system: 1) the area, and 2) the aspect ratio. It was found that the highest power output was realised with the 2nd-largest leaf across a range of wind speeds, but the variation in power measurements was large. Thus, the 3rd-largest leaf was found to give the highest power output with the lowest power variation. This leaf area was then fixed and the aspect ratio varied. It was found that the largest aspect ratio-leaf rendered the highest power output, but had a relatively high start-up wind speed.

Small-Scale Power Generation and Storage Using Piezoelectric Films

2011 ◽  
Author(s):  
Theodore Hatch ◽  
John Styrvoky ◽  
Jared Barton ◽  
Hualiang Zhang ◽  
Gayatri Mehta ◽  
...  
Keyword(s):  
Power Output ◽  
Polyvinylidene Fluoride ◽  
Bluff Body ◽  
Piezoelectric Materials ◽  
Buck Converter ◽  
Small Scale ◽  
Super Capacitor ◽  
Wind Speeds ◽  
Silver Ink ◽  
Piezoelectric Films

Piezoelectric materials have many applications including sensors, actuators, and motors. However, the ability of piezoelectric films to generate electricity from wind power has only recently been advanced. Piezoelectric films harvest wind energy by means of a layer of polyvinylidene fluoride (PVDF) that upon deformation generates an internal electrical voltage across two silver-ink electrodes. These films are allowed to freely flap in an airflow to cause deformation and thus electricity generation. A single small film (4.14 cm (1.63 in) × 1.63 cm (0.64 in) × 0.15 cm (0.06 in)) is tested at various wind speeds. The output of the film may be enhanced with the addition of a bluff body (in this case, a cylinder) upstream from the film. The vortex shedding from the cylinder produces a wake that can enhance the vibrations of the piezoelectric device, which in turn optimize voltage and/or power output. Voltage and power output is recorded across varying load resistances. The method of storing useful energy from the piezoelectric films is also of particular interest. Preliminary experiments using a LTC3588-1 energy harvester to various configurations of supercapacitors and Li-ion batteries are conducted. The LTC3588-1 is comprised of an efficient rectifier with a buck converter to allow the chip to efficiently charge the super capacitor while only requiring a small input to begin charging.

Study of Aerodynamic Performance and Power Output for Residential-Scale Wind Turbines

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Alaa S. Hasan ◽  
Mohammed Abousabae ◽  
Abdel Rahman Salem ◽  
Ryoichi S. Amano
Keyword(s):  
Wind Turbines ◽  
Power Output ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Speed Ratio ◽  
Computational Domain ◽  
Horizontal Axis Wind Turbine ◽  
Layer Transition ◽  
Baseline Design ◽  
Wind Speeds

Abstract This study presents the rotor blade airfoil analysis of residential-scale wind turbines. On this track, four new airfoils (GOE 447, GOE 446, NACA 6412, and NACA 64(3)-618) characterized by their high lift-to-drag ratios (161.3, 148.7, 142.7, and 136.3, respectively). These new airfoils are used to generate an entire 7 m long blades for three-bladed rotor horizontal axis wind turbine models tested numerically at low, medium, and rated wind speeds of 7.5, 10, and 12.5 m/s, respectively, with a design tip speed ratio of 7. The criterion to judge each model’s performance is power output. Thus, the blades of the model that produce the highest power are selected to undergo a tip modification (winglet) and leading-edge modification (tubercles), seeking power improvement. It is found that the GOE 447 airfoil outperformed the other three airfoils at all tested wind speeds. Thus, it is opted for adding winglets and tubercles. At 12.5 m/s, winglet design produced 5% more power, while tubercles produced 5.5% more power than the GOE 447 baseline design. Furthermore, the computational domain is divided into two regions: rotating (the disc that encloses the rotor) and stationary (the rest of the flow domain). Meanwhile, the numerical model is validated against the experimental velocity measurements. Since Reynolds-averaged Navier–Stokes with k–ω shear stress transport turbulence model can capture the laminar-to-turbulent boundary layer transition, it is used in the 18 simulations of the current work. However, large eddy simulation (LES) can deal successfully with the various scale eddies resulting from the rotor blades and its interactions with the surrounding flow. Thus, the LES was used in the six simulations done at the rated wind speed. LES power output calculation is 7.9% to 11.9% higher than the RANS power output calculation.

Effect of Leading Edge Blowing Slots on Stall Angles of a 10:1 Elliptical Airfoil

2010 ◽  
Author(s):  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Aspect Ratio ◽  
Closed Loop ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Circulation Control ◽  
West Virginia University ◽  
Trailing Edge ◽  
Wind Speeds ◽  
Stall Angle

Traditional uses of circulation control have been studied since the early 1960’s and have been developed primarily using trailing edge slots over a rounded trailing edge in order to take advantage of the Coanda˘ effect. The leading edge activated slots allow jets of air to enter the freestream flowing around the airfoil thus enhancing the energy of the lift force. The main purpose of circulation control for fixed wing aircraft is to increase the lifting force when large lifting forces and/or slow speeds are required, such as at take-off and landing. While there is a significant increase in the lifting forces achievable through the use of circulation control, there is also an inherent increase in the drag force on the airfoil (Abramson, 2004, Loth, 1976, 1984). Current effects of circulation control on stall angles of airfoils are not well documented and thus needs to be studied. Stall occurs when a sudden reduction in lift occurs caused by a flow separation between the incoming air flow and the lifting surface. The angle at which this happens is commonly called the critical angle of attack, and is typically between eight and twenty degrees depending on the wing profile, aspect ratio, camber, and planform area. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on internal plenum pressure. By comparing the non-circulation controlled wing with the active leading edge slot circulation control data, a trend was found as to the influence of the circulation control exit jet on the stall characteristics of the wing. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreases, from eight degrees to six degrees, while providing up to a 46% increase in lift coefficient.

Geometric and Material Optimization of Vortex-Induced Vibration Micro Energy Harvesters for Localized Wind Environments

2012 ◽  
Author(s):  
Jesse J. French ◽  
Colton T. Sheets
Keyword(s):  
Energy Harvesting ◽  
Power Output ◽  
Fluid Velocity ◽  
Frequency Variation ◽  
Vortex Induced Vibration ◽  
Energy Harvesters ◽  
Wind Speeds ◽  
Material Optimization ◽  
Piezoelectric Energy ◽  
Wind Velocities

Wind energy capture in today’s environment is often focused on producing large amounts of power through massive turbines operating at high wind speeds. The device presented by the authors performs on the extreme opposite scale of these large wind turbines. Utilizing vortex induced vibration combined with developed and demonstrated piezoelectric energy harvesting techniques, the device produces power consistent with peer technologies in the rapidly growing field of micro-energy harvesting. Vortex-induced vibrations in the Karman vortex street are the catalyst for energy production of the device. To optimize power output, resonant frequency of the harvester is matched to vortex shedding frequency at a given wind speed, producing a lock-on effect that results in the greatest amplitude of oscillation. The frequency of oscillation is varied by altering the effective spring constant of the device, thereby allowing for “tuning” of the device to specific wind environments. While localized wind conditions are never able to be predicted with absolute certainty, patterns can be established through thorough data collection. Sampling of local wind conditions led to the design and testing of harvesters operating within a range of wind velocities between approximately 4 mph and 25 mph. For the extremities of this range, devices were constructed with resonant frequencies of approximately 17 and 163 Hz. Frequency variation was achieved through altering the material composition and geometry of the energy harvester. Experimentation was performed on harvesters to determine power output at optimized fluid velocity, as well as above and below. Analysis was also conducted on shedding characteristics of the device over the tested range of wind velocities. Computational modeling of the device is performed and compared to experimentally produced data.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Study on the Relation Between Side Ratios of Rectangular Cross Sections and Secondary Vortices at Trailing Edge in Motion-Induced Vortex Excitation

2017 ◽  
Author(s):  
Kazutoshi Matsuda ◽  
Kusuo Kato ◽  
Kouki Arise ◽  
Hajime Ishii
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Cross Sections ◽  
Leading Edge ◽  
Trailing Edge ◽  
Wind Speeds ◽  
Smoke Flow ◽  
Flow Visualizations ◽  
Institute Of Technology ◽  
Secondary Vortices

According to the results of conventional wind tunnel tests on rectangular cross sections with side ratios of B/D = 2–8 (B: along-wind length (m), D: cross-wind length (m)), motion-induced vortex excitation was confirmed. The generation of motion-induced vortex excitation is considered to be caused by the unification of separated vortices from the leading edge and secondary vortices at the trailing edge [1]. Spring-supported test for B/D = 1.18 was conducted in a closed circuit wind tunnel (cross section: 1.8 m high×0.9 m wide) at Kyushu Institute of Technology. Vibrations were confirmed in the neighborhoods of reduced wind speeds Vr = V/fD = 2 and Vr = 8 (V: wind speed (m/s), f: natural frequency (Hz)). Because the reduced wind speed in motion-induced vortex excitation is calculated as Vr = 1.67×B/D = 1.67×1.18 = 2.0 [1], vibrations around Vr = 2 were considered to be motion-induced vortex excitation. According to the smoke flow visualization result for B/D = 1.18 which was carried out by the authors, no secondary vortices at the trailing edge were formed, although separated vortices from the leading edge were formed at the time of oscillation at the onset wind speed of motion-induced vortex excitation, where aerodynamic vibrations considered to be motion-induced vortex excitation were confirmed. It was suggested that motion-induced vortex excitation might possibly occur in the range of low wind speeds, even in the case of side ratios where secondary vortices at trailing edge were not confirmed. In this study, smoke flow visualizations were performed for ratios of B/D = 0.5–2.0 in order to find out the relation between side ratios of rectangular cross sections and secondary vortices at trailing edge in motion-induced vortex excitation. The smoke flow visualizations around the model during oscillating condition were conducted in a small-sized wind tunnel at Kyushu Institute of Technology. Experimental Reynolds number was Re = VD/v = 1.6×103. For the forced-oscillating amplitude η, the non-dimensional double amplitudes were set as 2η/D = 0.02–0.15. Spring-supported tests were also carried out in order to obtain the response characteristics of the models.

scholarly journals Oscillating foils of high propulsive efficiency

1998 ◽  
Vol 360 ◽  
pp. 41-72 ◽  
Author(s):  
J. M. ANDERSON ◽  
K. STREITLIEN ◽  
D. S. BARRETT ◽  
M. S. TRIANTAFYLLOU
Keyword(s):  
Reynolds Number ◽  
High Efficiency ◽  
Leading Edge ◽  
Half Cycle ◽  
Trailing Edge ◽  
Propulsive Efficiency ◽  
Principal Characteristics ◽  
Theoretical Predictions ◽  
Power Measurements ◽  
Oscillating Foils

Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at Reynolds number 1100, and force and power data are measured at Reynolds number 40 000. The experimental results are compared with theoretical predictions of linear and nonlinear inviscid theory and it is found that agreement between theory and experiment is good over a certain parametric range, when the wake consists of an array of alternating vortices and either very weak or no leading-edge vortices form. High propulsive efficiency, as high as 87%, is measured experimentally under conditions of optimal wake formation. Visualization results elucidate the basic mechanisms involved and show that conditions of high efficiency are associated with the formation on alternating sides of the foil of a moderately strong leading-edge vortex per half-cycle, which is convected downstream and interacts with trailing-edge vorticity, resulting eventually in the formation of a reverse Kármán street. The phase angle between transverse oscillation and angular motion is the critical parameter affecting the interaction of leading-edge and trailing-edge vorticity, as well as the efficiency of propulsion.

A Straight-Bladed Variable-Pitch VAWT Concept for Improved Power Generation

2003 ◽  
Author(s):  
Yann Staelens ◽  
F. Saeed ◽  
I. Paraschivoiu
Keyword(s):  
Power Output ◽  
Angle Of Attack ◽  
Correction Function ◽  
Wind Speeds ◽  
Abrupt Changes ◽  
Effective Angle ◽  
Improved Performance ◽  
Stall Angle ◽  
The Cost ◽  
Local Angle

The paper presents three modifications for an improved performance in terms of increased power output of a straight-bladed VAWT by varying its pitch. Modification I examines the performance of a VAWT when the local angle of attack is kept just below the stall value throughout its rotation cycle. Although this modification results in a very significant increase in the power output for higher wind speeds, it requires abrupt changes in the local angle of attack making it physically and mechanically impossible to realize. Modification II improves upon the first by replacing the local angle of attack by the blade static-stall angle only when the former exceeds the latter. This step eliminates the two jumps in the local effective angle of attack curve but at the cost of a slight decrease in the power output. Moreover, it requires a discontinuous angle of attack correction function which may still be practically difficult to implement and also result in an early fatigue. Modification III overcomes the limitation of the second by ensuring a continuous variation in the local angle of attack correction during the rotation cycle through the use of a sinusoidal function. Although the power output obtained by using this modification is less than the two preceding ones, it has the inherent advantage of being practically feasible.

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