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Aerodynamics of a rigid curved kite wing  [PDF]
Gianmauro Maneia,Caterina Tribuzi,Daniela Tordella,Michele Iovieno
Physics , 2013,
Abstract: A preliminary numerical study on the aerodynamics of a kite wing for high altitude wind power generators is proposed. Tethered kites are a key element of an innovative wind energy technology, which aims to capture energy from the wind at higher altitudes than conventional wind towers. We present the results obtained from three-dimensional finite volume numerical simulations of the steady air flow past a three-dimensional curved rectangular kite wing (aspect ratio equal to 3.2, Reynolds number equal to 3x10^6). Two angles of incidence -- a standard incidence for the flight of a tethered airfoil (6{\deg}) and an incidence close to the stall (18{\deg}) -- were considered. The simulations were performed by solving the Reynolds Averaged Navier-Stokes flow model using the industrial STAR-CCM+ code. The overall aerodynamic characteristics of the kite wing were determined and compared to the aerodynamic characteristics of the flat rectangular non twisted wing with an identical aspect ratio and section (Clark Y profile). The boundary layer of both the curved and the flat wings was considered to be turbulent throughout. It was observed that the curvature induces only a mild deterioration of the aerodynamics properties. Pressure distributions around different sections along the span are also presented, together with isolines of the average pressure and kinetic energy fields at a few sections across the wing and the wake. Our results indicate that the curvature induces a slower spatial decay of the vorticity in the wake, and in particular, inside the wing tip vortices.
Utilization of Wind Energy at High Altitude  [PDF]
Alexander Bolonkin
Physics , 2007,
Abstract: Ground based, wind energy extraction systems have reached their maximum capability. The limitations of current designs are: wind instability, high cost of installations, and small power output of a single unit. The wind energy industry needs of revolutionary ideas to increase the capabilities of wind installations. This article suggests a revolutionary innovation which produces a dramatic increase in power per unit and is independent of prevailing weather and at a lower cost per unit of energy extracted. The main innovation consists of large free-flying air rotors positioned at high altitude for power and air stream stability, and an energy cable transmission system between the air rotor and a ground based electric generator. The air rotor system flies at high altitude up to 14 km. A stability and control is provided and systems enable the changing of altitude. This article includes six examples having a high unit power output (up to 100 MW). The proposed examples provide the following main advantages: 1. Large power production capacity per unit - up to 5,000-10,000 times more than conventional ground-based rotor designs; 2. The rotor operates at high altitude of 1-14 km, where the wind flow is strong and steady; 3. Installation cost per unit energy is low. 4. The installation is environmentally friendly (no propeller noise). -- * Presented in International Energy Conversion Engineering Conference at Providence., RI, Aug. 16-19. 2004. AIAA-2004-5705. USA. Keyword: wind energy, cable energy transmission, utilization of wind energy at high altitude, air rotor, windmills, Bolonkin.
Using of High Altitude Wind Energy  [PDF]
Alexander Bolonkin
Smart Grid and Renewable Energy (SGRE) , 2011, DOI: 10.4236/sgre.2011.22010
Abstract: Ground based, wind energy extraction systems have reached their maximum capability. The limitations of current de-signs are: wind instability, high cost of installations, and small power output of a single unit. The wind energy industry needs of revolutionary ideas to increase the capabilities of wind installations. This article suggests a revolutionary innovation which produces a dramatic increase in power per unit and is independent of prevailing weather and at a lower cost per unit of energy extracted. The main innovation consists of large free-flying air rotors positioned at high altitude for power and air stream stability, and an energy cable transmission system between the air rotor and a ground based electric generator. The air rotor system flies at high altitude up to 14 km. A stability and control is provided and systems enable the changing of altitude. This article includes six examples having a high unit power output (up to 100 MW). The proposed examples provide the following main advantages: 1) Large power production capacity per unit—up to 5,000 - 10,000 times more than conventional ground-based rotor designs; 2) The rotor operates at high altitude of 1 - 14 km, where the wind flow is strong and steady; 3) Installation cost per unit energy is low; 4) The installation is environmentally friendly (no propeller noise).
Global Assessment of High-Altitude Wind Power  [PDF]
Cristina L. Archer,Ken Caldeira
Energies , 2009, DOI: 10.3390/en20200307
Abstract: The available wind power resource worldwide at altitudes between 500 and 12,000 m above ground is assessed for the first time. Twenty-eight years of wind data from the reanalyses by the National Centers for Environmental Prediction and the Department of Energy are analyzed and interpolated to study geographical distributions and persistency of winds at all altitudes. Furthermore, intermittency issues and global climate effects of large-scale extraction of energy from high-altitude winds are investigated.
Optimum Operational Parameters for Yawed Wind Turbines  [PDF]
David A. Peters,Xi Rong
International Journal of Aerospace Engineering , 2011, DOI: 10.1155/2011/635750
Abstract: A set of systematical optimum operational parameters for wind turbines under various wind directions is derived by using combined momentum-energy and blade-element-energy concepts. The derivations are solved numerically by fixing some parameters at practical values. Then, the interactions between the produced power and the influential factors of it are generated in the figures. It is shown that the maximum power produced is strongly affected by the wind direction, the tip speed, the pitch angle of the rotor, and the drag coefficient, which are specifically indicated by figures. It also turns out that the maximum power can take place at two different optimum tip speeds in some cases. The equations derived herein can also be used in the modeling of tethered wind turbines which can keep aloft and deliver energy. 1. Introduction Wind turbines have been around for centuries, from the simple water pump in Arabia to the current widely used HAWT (horizontal axis wind turbine). With more and more public attention drawn to wind energy for its ease of development and environmental friendliness, wind farms that consist of hundreds of wind turbines at the same location are now being constructed rapidly all around the world [1]. Some of the wind farms are even built offshore by using large floating platforms due to the stronger and steadier wind at sea. However, the potential impact of wind farms on the biological, physical, and human environments is still under inspection, and the economics of offshore wind farms is still being demonstrated [2, 3]. Recently, much interest has arisen in new types of wind turbines like tethered wind turbines which can fly at high altitudes while delivering energy from wind [4–6]. Since the captured wind energy is proportional to the cube of the wind speed, a tethered wind turbine at high altitude may have 500 times as much available power as a wind turbine on the surface. Although wind turbines vary in configuration, most of them incorporate the same mechanism of extracting wind energy by using rotor blades. To determine the optimum conditions when the maximum power is generated by the individual rotor, CFD (computational fluid dynamics) is a widely used method due to its predictive accuracy. Other methods like FVM (free vortex models) have also been developed. However, these approaches become computationally intensive for the study on wind farms that involve hundreds of individual wind turbines [7], and they are of limited use in the modeling of new types of wind turbines such as tethered wind turbines. Therefore, BEM (blade element
ELECTRICITY GENERATION AND WIND POTENTIAL ASSESSMENT IN REGIONS OF COLOMBIA
REALPE JIMéNEZ,ALVARO; DIAZGRANADOS,JORGE A.; ACEVEDO MORANTES,MARíA TERESA;
DYNA , 2012,
Abstract: in this work, mathematical modeling and simulation of electricity generation from wind was carried out in regions which are not connected to the national electrical system grid, and have an annual mean wind velocity higher than 4 m/s at an altitude of 10 m. seven different types of power turbines between 6 and 2,750 kw were studied in order to analyze their technical and economic feasibility. the gachaneca (boyaca) and the sesquicentenario (san andres island) stations have an energy potential of 5,106 and 3,823 mwh/year, respectively, using a 2,750 kw turbine at an altitude of 70 m. the production cost of kwh for the two regions was found to be less than us$0.10 for turbines with a capacity higher than 1.0 mw. the energy produced can satisfy the electricity needs of colombian islands such as san andres or providencia.
Using a Parafoil Kite for Measurement of Variations in Particulate Matter—A Kite-Based Dust Profiling Approach  [PDF]
Matthias Reiche, Roger Funk, Zhuodong Zhang, Carsten Hoffmann, Yong Li, Michael Sommer
Atmospheric and Climate Sciences (ACS) , 2012, DOI: 10.4236/acs.2012.21006
Abstract: This paper reports on the use of a kite-based system for measuring low-altitude particulate matter (PM) concentrations over grassland in Inner Mongolia. The motivation came from PM-concentration measurements at heights below 3 m over non-erodible surfaces which showed constant concentrations and made flux calculations relatively uncertain. One aim was the quantification of wind-driven matter fluxes across ecosystem boundaries, where the relevant layer can be assumed at heights below 100 m. Compared to other measurement techniques (e.g. LIDAR, towers and airborne systems) kite-based systems represent an inexpensive, highly flexible research tool which is well-suited for application in remote sites. The basis of the introduced system is a 4 m2 Parafoil kite which has enough lifting capacity to carry equipment of about 6 kg at wind velocities between 3 ms-1 to nearly 20 ms-1. A self-adjusting platform was constructed to balance moves and to carry a portable Environmental Dust Monitor (EDM), anemometer and a GPS receiver. So, all parameters necessary for a vertical profile of dust fluxes could be measured. In the first flights the applied kite-based dust profiling system (KIDS) was examined according to general technical application problems. Firstly, the influence of diverse surface characteristics, the flying condition and height-stability was tested. The result suggests that surface characteristics in general have a higher influence than the optimal wind velocity, which ranged from 9 ms-1 to 17 ms-1. Secondly, uncertainties in the measured data were quantified and assessed. The uncertainties in wind velocity measurements due to motion in horizontal and vertical direction were not higher than 0.45% - 0.65% and 1.8% - 2.2% during the kite ascent. The outcome of the study illustrates the suitable application of KIDS for low-altitude measurements in remote sites.
The Legality of Wind and Altitude Assisted Performances in the Sprints  [PDF]
J. R. Mureika
Physics , 2001,
Abstract: Based on a mathematical simulation which reproduces accurate split and velocity profiles for the 100 and 200 metre sprints, the magnitudes of altitude and mixed wind/altitude-assisted performances as compared to their sea-level equivalents are presented. It is shown that altitude-assisted times for the 200 metre are significantly higher than for the 100 metre, suggesting that the ``legality'' of such marks perhaps be reconsidered.
Is the Weibull distribution really suited for wind statistics modeling and wind power evaluation?  [PDF]
Philippe Drobinski,Corentin Coulais
Physics , 2012,
Abstract: Wind speed statistics is generally modeled using the Weibull distribution. This distribution is convenient since it fully characterizes analytically with only two parameters (the shape and scale parameters) the shape of distribution and the different moments of the wind speed (mean, standard deviation, skewness and kurtosis). This distribution is broadly used in the wind energy sector to produce maps of wind energy potential. However, the Weibull distribution is based on empirical rather than physical justification and might display strong limitations for its applications. The philosophy of this article is based on the modeling of the wind components instead of the wind speed itself. This provides more physical insights on the validity domain of the Weibull distribution as a possible relevant model for wind statistics and the quantification of the error made by using such a distribution. We thereby propose alternative expressions of more suited wind speed distribution.
Statistical Modeling for Wind-Temperature Meteorological Elements in Troposphere  [PDF]
A. Virtser,Yu. Shtemler,E. Golbraikh
Physics , 2010,
Abstract: A comprehensive statistical model for vertical profiles of the horizontal wind and temperature throughout the troposphere is presented. The model is based on radiosonde measurements of wind and temperature during several years. The profiles measured under quite different atmospheric conditions exhibit qualitative similarity, and a proper choice of the reference scales for the wind, temperature and altitude levels allows to consider the measurement data as realizations of a random process with universal characteristics: means, the basic functions and parameters of standard distributions for transform coefficients of the Principal Component Analysis. The features of the atmospheric conditions are described by statistical characteristics of the wind-temperature ensemble of dimensional reference scales. The high effectiveness of the proposed approach is provided by a similarity of wind - temperature vertical profiles, which allow to carry out the statistical modeling in the low-dimension space of the dimensional reference scales for the wind, temperature and altitude levels. The knowledge of the joint wind-temperature distributions in altitude open wide perspectives for modeling of various physical processes in real atmospheric conditions like the transfer of passive scalars or impurities, the electromagnetic wave penetration, the instability of internal waves, transition to turbulence etc.
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