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.

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 Comparative investigations in the effect of angle of attack profile on hydrodynamic performance of bio-inspired foil, (corrected)

2013 ◽  
Vol 10 (2) ◽  
pp. 99-108 ◽  
Author(s):  
J. A. Esfahani ◽  
E. Barati ◽  
Hamid Reza Karbasian
Keyword(s):  
Angle Of Attack ◽  
Underwater Vehicles ◽  
Hydrodynamic Performance ◽  
Profile Function ◽  
Flapping Foil ◽  
Propulsive Performance ◽  
Wide Range ◽  
Effective Angle ◽  
Thrust Production ◽  
Optimum Profile

In flapping underwater vehicles the propulsive performance of harmonically sinusoidal heaving and pitching foil will be degraded by some awkward changes in effective angle of attack profile, as the Strouhal number increases. This paper surveys different angle of attack profiles (Sinusoidal, Square, Sawtooth and Cosine) and considers their thrust production ability. In the wide range of Strouhal numbers, thrust production of Square profile is considerable but it has a discontinuity in heave velocity profile, in which an infinite acceleration exists. This problem poses a significant defect in control of flapping foil. A novel profile function is proposed to omit sharp changes in heave velocity and acceleration. Furthermore, an optimum profile is found for different Strouhal numbers with respect to Square angle of attack profile.DOI: http://dx.doi.org/10.3329/jname.v10i2.14229

Quasi-Steady Effective Angle of Attack and Its Use in Lift-Equivalent Motion Design

AIAA Journal ◽  
2021 ◽  
pp. 1-14
Author(s):  
Xianzhang Xu ◽  
Francis D. Lagor
Keyword(s):  
Angle Of Attack ◽  
Effective Angle ◽  
Motion Design

Modification of effective angle of attack on hydrofoil power extraction

2021 ◽  
Vol 240 ◽  
pp. 109919
Author(s):  
Guanghua He ◽  
Weijie Mo ◽  
Yun Gao ◽  
Zhigang Zhang ◽  
Jiadong Wang ◽  
...  
Keyword(s):  
Angle Of Attack ◽  
Power Extraction ◽  
Effective Angle

scholarly journals CFD investigation on the performance analysis of Tesla turbine

2021 ◽  
Vol 850 (1) ◽  
pp. 012026
Author(s):  
J Kevin Joseph ◽  
R Jeyanthinathan ◽  
R Harish
Keyword(s):  
Power Output ◽  
Cfd Simulation ◽  
Simulation Software ◽  
Working Fluid ◽  
Maintenance Cost ◽  
Ansys Fluent ◽  
Rotating Speed ◽  
Velocity Magnitude ◽  
Turbine Disc ◽  
Improved Performance

Abstract A Tesla turbine is a bladeless turbine in which fluid flows in the direction of the centripetal path. It uses fluid properties such as Boundary layer & adhesion of fluid on a series of discs keyed to a shaft. The initial cost and maintenance cost of the Tesla turbine is very low. Our project’s main motive is to improve the performance of a Tesla turbine by changing various parameters such as disc diameter and disc rotating speed through the CFD simulation software using water as a working fluid. The CAD model is designed using Ansys design modeler, meshing is performed using Ansys meshing and post processing is carried out in Ansys fluent. The numerical simulations were carried out using Ansys Fluent which is based on the finite volume method and the changes that occurred in the pressure and velocities are investigated. The parametric study is performed by varying the turbine disc speed. By performing CFD simulations, total pressure contour and velocity magnitude contours are plotted and it is found that pressure and velocity are maximum when the clearance between disc and turbine casing is lesser and at higher turbine disc speeds. The power output of the Tesla turbine is also plotted for various rpm where higher rpm gives maximum power output. The results from the present study would be useful in designing an efficient Tesla turbine with improved performance.

scholarly journals Investigations: The cost-effective angle

2015 ◽  
Vol 42 (3) ◽  
pp. 213
Author(s):  
ViragG Gokhale
Keyword(s):  
Cost Effective ◽  
Effective Angle ◽  
The Cost

scholarly journals Experimental Investigation of Lift Enhancement and Drag Reduction of Discrete Co-Flow Jet Rotor Airfoil

2021 ◽  
Vol 11 (20) ◽  
pp. 9561
Author(s):  
Shunlei Zhang ◽  
Xudong Yang ◽  
Bifeng Song ◽  
Zhuoyuan Li ◽  
Bo Wang
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Performance Enhancement ◽  
Fundamental Problem ◽  
Unit Length ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Relative Unit ◽  
Lift Enhancement ◽  
Stall Angle

Rotor airfoil design involves multi-point and multi-objective complex constraints. How to significantly improve the maximum lift coefficient and lift-to-drag ratio of rotor airfoil is a fundamental problem, which should be solved urgently in the development of high-performance helicopter rotor blades. To address this, discrete co-flow jet (DCFJ) technology is one methods with the most potential that can be harnessed to improve the performance of the rotor airfoil. In this study, wind tunnel experiments are conducted to study the effect of DCFJ technology on lift enhancement and drag reduction of OA312 airfoil. Furthermore, the performance improvement effects of the open co-flow jet (CFJ) and DCFJ technologies are studied. In addition, the influence of fundamental parameters, such as the obstruction factor and relative unit length, are analyzed. Results demonstrate that DCFJ technology is better than CFJ technology on the performance enhancement of the OA312 airfoil. Moreover, the DCFJ rotor airfoil can significantly reduce the drag coefficient and increase the maximum lift coefficient and the stall angle of attack. The maximum lift coefficient can be increased by nearly 67.3%, and the stall angle of attack can be delayed by about 12°. The DCFJ rotor airfoil can achieve the optimal performance when the obstruction factor is 1/2 and the relative unit length is 0.025.

scholarly journals Decision Support System For Determining Power Loss And Refurbishability Of Failed Automotive Petrol Engine Block And Crankshaft

2021 ◽  
Author(s):  
BASIL OLUFEMI AKINNULI ◽  
OLADELE AWOPETU ◽  
OLUWASEUN OLUWAGBEMIGA OJO
Keyword(s):  
Decision Support ◽  
Power Loss ◽  
Computer Software ◽  
Engine Block ◽  
Measuring Instruments ◽  
Main Bearing ◽  
Test Engine ◽  
Cause Of Failure ◽  
Improved Performance ◽  
The Cost

Abstract The crankshaft and engine block of automobile wear or fail after certain years of usage. The cause of failure is a contributing factor to the power loss of the engine. Power loss reduces the performance of the vehicle. Due to the economic situation in Nigeria, the cost of buying new engines is usually high and some used engines have problems that are latent. Pre-test engine analysis was carried out and torque of each selected engine was measured with a dynamometer to know the speed of the worn engine. Disassembly of four (4) cylinder engines namely; Toyota, Nissan, Mitsubishi, and Mazda were carried out and the affected failed parts, namely; main bearing, crankpin journal, and bore cylinder diameter were determined and the level of their wear as well as power losses ascertained using measuring instruments. For easy computation and analysis, a computer software using C-sharp programming language was developed to determine the power loss and predicting machining level of refurbish-ability and tested for performance evaluation. The model and its developed software are decision support tools for any automotive industry where maintenance and management of engines for improved performance and efficiency of operation is the focus.

Interactions of a streamwise-oriented vortex with a finite wing

2015 ◽  
Vol 767 ◽  
pp. 782-810 ◽  
Author(s):  
D. J. Garmann ◽  
M. R. Visbal
Keyword(s):  
Separation Bubble ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Vortex ◽  
Recirculation Region ◽  
Rolling Moment ◽  
Effective Angle ◽  
Finite Wing ◽  
Modes Of Interaction

AbstractA canonical study is developed to investigate the unsteady interactions of a streamwise-oriented vortex impinging upon a finite surface using high-fidelity simulation. As a model problem, an analytically defined vortex superimposed on a free stream is convected towards an aspect-ratio-six ($\mathit{AR}=6$) plate oriented at an angle of ${\it\alpha}=4^{\circ }$ and Reynolds number of $\mathit{Re}=20\,000$ in order to characterize the unsteady modes of interaction resulting from different spanwise positions of the incoming vortex. Outboard, tip-aligned and inboard positioning are shown to produce three distinct flow regimes: when the vortex is positioned outboard of, but in close proximity to, the wingtip, it pairs with the tip vortex to form a dipole that propels itself away from the plate through mutual induction, and also leads to an enhancement of the tip vortex. When the incoming vortex is aligned with the wingtip, the tip vortex is initially strengthened by the proximity of the incident vortex, but both structures attenuate into the wake as instabilities arise in the pair’s feeding sheets from the entrainment of opposite-signed vorticity into either structure. Finally, when the incident vortex is positioned inboard of the wingtip, the vortex bifurcates in the time-mean sense with portions convecting above and below the wing, and the tip vortex is mostly suppressed. The time-mean bifurcation is actually a result of an unsteady spiralling instability in the vortex core that reorients the vortex as it impacts the leading edge, pinches off, and alternately attaches to either side of the wing. The increased effective angle of attack inboard of impingement enhances the three-dimensional recirculation region created by the separated boundary layer off the leading edge which draws fluid from the incident vortex inboard and diminishes its impact on the outboard section of the wing. The slight but remaining downwash present outboard of impingement reduces the effective angle of attack in that region, resulting in a small separation bubble on either side of the wing in the time-mean solution, effectively unloading the tip outboard of impingement and suppressing the tip vortex. All incident vortex positions provide substantial increases in the wing’s lift-to-drag ratio; however, significant sustained rolling moments also result. As the vortex is brought inboard, the rolling moment diminishes and eventually switches sign as the reduced outboard loading balances the augmented sectional lift inboard of impingement.

Sign in / Sign up

Export Citation Format

Share Document