Article

Lightning field behavior around grounded airborne systems

Authors:
Article

Lightning field behavior around grounded airborne systems

If you want to read the PDF, try requesting it from the authors.

Abstract

A variety of innovative airborne concepts are being developed to capture the wind energy available at higher altitudes, facilitate wireless communication and provide heavy lift capability. These airborne systems will be in close proximity to cloud cover and exposed to increased risk of lightning strikes. A two-dimensional physics based formulation that was recently developed to investigate the potential field behavior about circular sections was used to develop uniform and tapered cylindrical elements. These elements were then combined to approximate the total charge and lightning behavior about an airborne wind turbine and a heavy lift airship. Surface electrical charge and lightning collection area are developed as a function of elevation, body shape, cloud cover and leader properties. The surface charge density is utilized to compute the degree of field intensification on the body periphery in order to determine the level of susceptibility of the airborne system to lightning strikes. It was observed that as airborne bodies move closer to the thundercloud the ambient potential field becomes more highly perturbed and leads to greater risk of lightning strikes. The lightning collection area was shown to increase with elevation of the airborne body and decrease with increase in the leader propagation angle. Keywords: Lightning strikes, physics based formulation, electric potential field, composite shapes, surface electrical charge, lightning collection area, strike frequency

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Energy related studies have also been developed focusing on solar powered airships [46][47][48][49][50][51][52][53][54], renewable energies powered airships [55][56][57], hydrogen powered airships [50], high altitude wind power generation with airships [58][59][60], solar turbine power stations with floating solar chimneys [61], energy storage alternatives for airships with regenerative fuel cell (RFC) [62,63] and the effect of high-altitude on its energy system performance [64]. Other studies have also looked at the selection of the best airship routes with the intention for reducing fuel consumption assuming previously selected destinations [11,45]. ...
Article
Full-text available
The maritime shipping sector is a major contributor to CO2 emissions and this figure is expected to rise in coming decades. With the intent of reducing emissions from this sector, this research proposes the utilization of the jet stream to transport a combination of cargo and hydrogen, using airships or balloons at altitudes of 10–20 km. The jet streams flow in the mid-latitudes predominantly in a west–east direction, reaching an average wind speed of 165 km/h. Using this combination of high wind speeds and reliable direction, hydrogen-filled airships or balloons could carry hydrogen with a lower fuel requirement and shorter travel time compared to conventional shipping. Jet streams at different altitudes in the atmosphere were used to identify the most appropriate circular routes for global airship travel. Round-the-world trips would take 16 days in the Northern Hemisphere and 14 in the Southern Hemisphere. Hydrogen transport via the jet stream, due to its lower energy consumption and shorter cargo delivery time, access to cities far from the coast, could be a competitive alternative to maritime shipping and liquefied hydrogen tankers in the development of a sustainable future hydrogen economy.
... In Ground-Gen AWE (GG-AWE), the generator is fixed on the ground and electricity is generated in intermittent phases of production and recovery by exploiting the aerodynamic forces of the aircraft. The examples of GG-AWE systems are Buoyant rotating cylinders, Magnus effect-based airborne, high altitude parachute, gliders and kites [7,16,17,23,[27][28][29][30][31][32][33][34]. Whereas in Fly-Gen system (FG-AWE) or on-board generator system, the generator is attached to a wind turbine and production of electrical energy takes place on-board. ...
Article
The manuscript investigates aerodynamic performance of an airborne wind turbine with varying shell configurations in an effort to elaborate the influence of shell aerodynamics on the performance of the buoyant airborne wind turbine for operating conditions at an altitude of 400 m above the sea level. A systematic study has been conducted on the three airborne duct shapes based on the NACA-5415, NACA-9415 and NACA-5425 cambered aerofoils by considering NREL Phase IV rotor and constant airborne shell throat diameter of 4.02 m. Three dimensional steady state simulations have been performed by employing k-ω SST turbulence model for a range of wind speeds10–25 m/s at zero angle of attack (the angle between wind direction and turbine rotational axis). The performance of the studied turbines have been analysed in terms of rotor thrust coefficient, duct thrust coefficient, turbine power coefficient, swallowed mass flow rate and pressure distribution along the shell. Results demonstrate that among all the considered shell configurations, the NACA-9415 shell based turbine demonstrated highest power coefficient. Increment in the both, aerofoil camber (5–9% of chord length) and thickness (15–25% of the chord length) resulted in 2.05 and 1.45 times higher turbine power coefficient respectively in comparison to the reference aerofoil (NACA-5415) shell based turbine.
Article
The paper presents the effect of fluctuating yaw angle and wind speed on the performance of a horizontal axis airborne wind turbine of three different shell shapes for the high altitude operational conditions. For this purpose, a numerical analysis has been performed by considering the ranges of yaw angle and wind speed of 0°−20° and 10m/s−25m/s, respectively. The turbine shell shapes are based on the three aerofoil profiles of NACA-5415, NACA-9415 and NACA-5425 to investigates the influence of the aerofoil camber and thickness. The turbine has been modelled using a NREL Phase IV rotor with the fixed rotor radius of 2m for all shell configurations. A 3-D numerical analysis has been conducted by implementing k−ω SST turbulence model to solve the Reynolds-averaged Navier-Stokes equations. Numerical results demonstrated that the increment in both the tip speed ratio and yaw angle augmented the rotor thrust coefficient. At the high yaw angles, the buoyant shell is prone to encounter instability due to unbalancing of the aerodynamic forces subjected to the shell body. Among all the studied shell configurations, the NACA-9415 aerofoil based shell displayed the relatively higher turbine power coefficient as well as the stable operation.
Article
Full-text available
This article summarizes the fundamental dynamics and control attributes and challenges faced by stationary and crosswind airborne wind energy (AWE) systems. AWE systems have undergone rapid and steady technological development over the past decade, with several organizations demonstrating basic economic and technical viability of their concepts. The theoretical and numerical analyses performed so far indicate that crosswind systems have the potential to achieve a power curve similar in shape to that of current commercial wind turbines, with rated power of 2–5 MW. The ongoing development activities are increasing the viability of the concept; yet, several technical issues remain and need to be addressed, to definitively show that this technology can be scaled up to industrial size. The expert analysis suggests that AWE technologies are at the dawn of their development, and there is significant untapped potential for the use of innovative solutions in multiple fields such as materials, power electronics, and aerodynamics, to tackle problems. These challenges present a wealth of opportunities for future, multidisciplinary research and development activities.
Article
Full-text available
From the analysis of digital high-speed videos and electric field records of two flashes, some relationships are presented between the channel luminosity preceding the occurrence of the luminosity pulse and the characteristics of the related electric field signature. Some M components may produce E-field signatures very similar to those produced by subsequent return strokes if the preceding luminosity of channel flash is very faint. These M components may be detected by LLS. If the channel luminosity is high, that is, if the continuing current flowing through it is high, then the E-field signature is different from the signature of a subsequent return stroke. The luminosity intensity preceding each M component along with its 10-90% risetime, estimated peak current and peak E-field are presented.
Article
Full-text available
Cloud-to-ground (CG) lightning data have been analyzed for the years 2001-09 for North America, which includes Alaska, Canada, and the lower 48 U.S. states. Flashes recorded within the North American Lightning Detection Network (NALDN) are examined. No corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising North America. There were network changes in the NALDN during the 9 yr, but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 kA have been deleted. Thus, the reader should be aware that secular changes are not just climatological in nature. All data were analyzed with a spatial resolution of 20 km. The analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in North America, including the impacts of physical changes in the network during the 9 yr of study. These data complement and extend previous analyses that evaluate the U.S. NLDN during periods of upgrade. The total (negative and positive) flashes for ground flash density, the percentage of positive lightning, and the positive flash density have been analyzed. Furthermore, the negative and positive first stroke peak currents and theflash multiplicity have been examined. The highest flash densities in Canada are along the U.S.-Canadian border (1-2 flashes per square kilometer) and in the United States along the Gulf of Mexico coast from Texas through Florida (exceeding 14 flashes per square kilometer in Florida). The Gulf Stream is "outlined" by higher flash densities off the east coast of the United States. Maximum annual positive flash densities in Canada range primarily from 0.01 to 0.3 flashes per square kilometer, and in the United States to over 0.5 flashes per square kilometer in the Midwest and in the states of Louisiana and Mississippi. The annual percentage of positive lightning to ground varies from less than 2% over Florida to values exceeding 25% off the West Coast, Alaska, and the Yukon. A localized maximum in the percentage of positive lightning in the NALDN occurs in Manitoba and western Ontario, just north of North Dakota and Minnesota. When averaged over North America, first stroke negative median peak currents range from 19.8 kA in 2001 to 16.0 kA in 2009 and for all years, average 16.1 kA. First stroke positive median peak currents range from a high of 29.0 kA in 2008 and 2009 to a low of 23.3kA in 2003 with a median of 25.7 kA for all years. There is a relatively sharp transition from low to high median negative peak currents along the Gulf and Atlantic coasts of the United States. No sharp transitions are observed for the median positive peak currents. Relatively lower positive peak currents occur throughout the southeastern United States. The highest values of mean negative multiplicity exceed 3.0 strokes per flash in the NALDN with some variation over the 9 yr. Lower values of mean negative multiplicity occur in the western United States. Positive flash mean multiplicity is slightly higher than 1.1, with the highest values of 1.7 observed in the southwestern states. As has been noted in prior research, CG lightning has significant variations from storm to storm as well as between geographical regions and/or seasons and, consequently, a single distribution for any lightning parameter, such as multiplicity or peak current, may not be sufficient to represent or describe the parameter.
Book
Full-text available
This reference offers an overview of the field of airborne wind energy. As the first book of its kind, it provides a consistent compilation of the fundamental theories, a compendium of current research and development activities as well as economic and regulatory aspects. In five parts, the book demonstrates the relevance of Airborne Wind Energy and the role that this emerging field of technology can play for the transition towards a renewable energy economy. Part I on "Fundamentals" contains seven general chapters explaining the principles of airborne wind energy and its different variants, of meteorology, the history of kites, and financing strategies. Part II on "System Modeling, Optimization and Control" contains eight contributions that develop and use detailed dynamic models for simulation, optimization, and control of airborne wind energy systems, while Part III on "Analysis of Flexible Kite Dynamics" collects four chapters that focus on the particularly challenging simulation problems related to flexible kites. Part IV "Implemented Concepts" contains eleven contributions each of which presents developed prototypes together with real-world experimental results obtained with the different concepts. Finally, in Part V on "Component Design", five papers are collected that address in detail the technical challenges for some of the components of airborne wind energy.
Article
Full-text available
The paper presents the innovative technology of high-altitude wind power generation, indicated as Kitenergy, which exploits the automatic flight of tethered airfoils (e.g., power kites) to extract energy from wind blowing between 200 and 800 m above the ground. The key points of this technology are described and the design of large scale plants is investigated, in order to show that it has the potential to overcome the limits of the actual wind turbines and to provide large quantities of renewable energy, with competitive cost with respect to fossil sources. Such claims are supported by the results obtained so far in the Kitenergy project, undergoing at Politecnico di Torino, Italy, including numerical simulations, prototype experiments, and wind data analyses.
Article
Full-text available
Flying electric generators (FEGs) are proposed to harness kinetic energy in the powerful, persistent high-altitude winds. Average power density can be as high as 20 kW/m<sup>2</sup> in an approximately 1000-km-wide band around latitude 30deg in both the hemispheres of the Earth. At 15 000 ft (4600 m) and above, tethered rotorcraft, with four or more rotors mounted on each unit, could give individual rated outputs of up to 40 MW. These aircrafts would be highly controllable and could be flown in arrays, making them a large-scale source of reliable wind power. The aerodynamics, electrics, and control of these craft are described in detail, along with a description of the tether mechanics. A 240 kW craft has been designed to demonstrate the concept at altitude. It is anticipated that large-scale units would make low-cost electricity available for grid supply, for hydrogen production, or for hydro-storage from large-scale generating facilities
Article
The modeling of lightning strike behavior and estimation of the subsequent electric discharge is of great practical importance. In this study, a complete two-dimensional physics-based analytic formulation is presented for elevated grounded systems that can be envisioned to be contained within two non-concentric circular domains. The inner circle encompasses the body or system of interest, and the periphery of the outer circle addresses the cloud coverage. The potential field between the circular domains is modeled as the sum of two separate contributions. The first is formulated in terms of an eigen-function expansion involving simple radial functions and Legendre polynomials, while the second contribution is developed using two different approaches. The first approach utilizes an eigen-function expansion incorporating spherical Bessel functions and Legendre polynomials, while the second approach uses a Green’s function expansion also involving orthogonal polynomial functions. Each of the contributions to the total potential field leads to linear systems of equations that are solved for the unknown series expansion coefficients. The accuracy of the potential field solution is investigated with regard to convergence, stability, and error compared with an exact solution. The potential field solution is then used as the basis to evaluate leader formation, as a function of elevation, extent of cloud coverage, and propagation angle of the downward leader. Regions of high risk to lightning strikes on the grounded structure are developed in terms of joint probability functions. The electric discharge is estimated using electric current and is shown to be in the range of presently available information.
Article
To exploit the high altitude wind energy, a concept of umbrella-ladder combination system, in which the polyethylene polymer transmission tethers play an important role, was proposed by a company. This paper studies the lightning impulse characteristics of polyethylene polymer transmission tethers. First the lightning environment characteristics are summarized, especially the potential of thundercloud can be 100MV and the maximum electric field strength of thundercloud reaches about 1000V/cm. The high altitude wind energy absorber will reach into the small lower positive charge region at the base of the thundercloud. Secondly, experiments are performed to get data of the lightning impulse breakdown voltages of the polyethylene polymer tethers with different pollution degree and different humidity degree, the lightning-withstand strength per unit length tether is tested as 250kV/m. Finally, the possibility the tether to triggers the lightning and causes a flashover along itself is discussed while the system is working.
Article
(Previously cited in issue 03, p. 399, Accession no. A82-14025)
Article
This report, based on the findings of an Austrian feasibility study, describes balloon-borne tethered wind systems. Latest results and the components of the system are discussed and an outline of the available energy potential is compiled. An overview of economic possibilities is also given.
Article
The wind energy existing at high altitude has been investigated as a potential energy resource in the United States. In terms of the average power density, it can be as high as 16 KW/m2 at northeastern U.S. sites such as New York, which can be compared to 0.5 KW/m2, the maximum ground level value at the U.S. sites. For a lifting generation device, a VTOL concept, new to this type of TWES, which combines the fixed wing with helicopter technology was extensively studied. The cost of electricity (COE) with such a system was determined and found to be competitive to that of fossil fuel in the near future.
Article
The feasibility of generating electricity from jet-stream winds has been investigated. Analysis of published meteorological data indicates that annual average power densities approaching 20 kW/sq m are available in the jet-stream altitudes over the complete west-east extent of Australia at a latitude of about 30 deg S. Computer-based optimization studies indicate that a 100-MW power station based on tethered aerodynamic generating platforms located at a jet-stream altitude would generate electricity at capital and operating costs that are competitive with other methods of electricity generation. The design of the tethered aerodynamic generating platform requires a high lift-to-weight ratio platform housing high power-to-weight ratio diffuser-augmented wind turbines and tethered by a high strength-to-weight ratio cable. Key design parameters include the turbine power coefficient and power-drag coefficient, the rated speed, and the stall speed. The required turbine area is determined primarily by the power coefficient and the rated speed. The cable weight depends directly on the drag associated with the maximum (rated) power generation which follows from the choice of rated speed. The wing area of the aerodynamic platform is fixed usually by the stall speed.
Application of US upper wind data in one design of tethered wind energy systems.
  • O'Doherty R.J.
  • Roberts B.W.