Vortex lattice modelling of winglets on wind turbine blades. 3. ed.

Energy Technology Data Exchange (ETDEWEB)

Doessing, M.

2007-08-15

The power production of wind turbines can be increased by the use of winglets without increasing the swept area. This makes them suitable for sites with restrictions in rotor diameter and in wind farms. The present project aims at understanding how winglets influences the flow and the aerodynamic forces on wind turbine blades. A free wake vortex lattice code and a fast design algorithm for a horizontal axis wind turbine under steady conditions has been developed. 2 winglet designs are treated in detail. (au)

Remote Sensing for Wind Energy

DEFF Research Database (Denmark)

The Remote Sensing in Wind Energy Compendium provides a description of several topics and it is our hope that students and others interested will learn from it. The idea behind this compendium began in year 2008 at Risø DTU during the first PhD Summer School: Remote Sensing in Wind Energy. Thus......-of-the-art compendium available for people involved in Remote Sensing in Wind Energy....

Vortex system studies on small wind turbines

Energy Technology Data Exchange (ETDEWEB)

Montgomerie, Bjoern; Dahlberg, Jan-Aake [Swedish Defence Research Agency, Stockholm (Sweden). Div. of Aeronautics, FFA

2003-10-01

The wind tunnel experiment reported included a small wind turbine setup and smoke to visualize the trailing tip vortices for different wind turbine configurations. Several combinations of tunnel wind speeds and tip speed ratios generated a database where the end result functions were radius and pitch, of the tip vortex spirals, versus the downstream coordinate. The Reynolds number in the experiment was very low compared to that of full size turbines. The results should therefore be seen as valid only for low Reynolds numbers. The models were 18 and 25 cm diameter turbines. This is thought to be complementary to the information obtained in similar wind tunnel investigations for much larger models. The database is meant to be a fundamental tool for the construction of practical aerodynamic induction methods. Such methods typically employ the Biot-Savart law has been shown to lead to a flow field, which deviates considerably from that of reality. E.g. concentration into tip vortices does not happen when the flow is simulated with Biot-Savart law only. Thus, a combination of the induction method and its modification, based on investigations such as the one reported, is foreseen to replace the widely used Blade Element Momentum method for wind turbine loads and performance prediction.

Remote Sensing Wind and Wind Shear System.

Science.gov (United States)

Contents: Remote sensing of wind shear and the theory and development of acoustic doppler; Wind studies; A comparison of methods for the remote detection of winds in the airport environment; Acoustic doppler system development; System calibration; Airport operational tests.

Remote Sensing for Wind Energy

DEFF Research Database (Denmark)

The Remote Sensing in Wind Energy Compendium provides a description of several topics and it is our hope that students and others interested will learn from it. The idea behind this compendium began in year 2008 at Risø DTU during the first PhD Summer School: Remote Sensing in Wind Energy. Thus...... in the Meteorology and Test and Measurements Programs from the Wind Energy Division at Risø DTU in the PhD Summer Schools. We hope to add more topics in future editions and to update as necessary, to provide a truly state-of-the-art compendium available for people involved in Remote Sensing in Wind Energy....

Remote Sensing for Wind Energy

DEFF Research Database (Denmark)

Peña, Alfredo; Hasager, Charlotte Bay; Badger, Merete

The Remote Sensing in Wind Energy report provides a description of several topics and it is our hope that students and others interested will learn from it. The idea behind it began in year 2008 at DTU Wind Energy (formerly Risø) during the first PhD Summer School: Remote Sensing in Wind Energy...... colleagues in the Meteorology and Test and Measurements Sections from DTU Wind Energy in the PhD Summer Schools. We hope to continue adding more topics in future editions and to update and improve as necessary, to provide a truly state-of-the-art ‘guideline’ available for people involved in Remote Sensing...

Full scale wind turbine test of vortex generators mounted on the entire blade

DEFF Research Database (Denmark)

Bak, Christian; Skrzypinski, Witold Robert; Gaunaa, Mac

2016-01-01

Measurements on a heavily instrumented pitch regulated variable speed Vestas V52 850 kW wind turbine situated at the DTU Risø Campus are carried out, where the effect of vortex generators mounted on almost the entire blade is tested with and without leading edge roughness. The measurements...... are compared to the predictions carried out by a developed design tool, where the effect of vortex generators and leading edge roughness is simulated using engineering models. The measurements showed that if vortex generators are mounted there is an increase in flapwise blade moments if the blades are clean...

Numerical study on the impact of ground heating and ambient wind speed on flow fields in street canyons

Science.gov (United States)

Li, Lei; Yang, Lin; Zhang, Li-Jie; Jiang, Yin

2012-11-01

The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors including height-to-width (H/W) ratio, ambient wind speed and ground heating intensity were taken into account. Three types of street canyon with H/W ratios of 0.5, 1.0 and 2.0, respectively, were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s-1 were set for the ambient wind speed. The ground heating intensity, which was defined as the difference between the ground temperature and air temperature, ranged from 10 to 40 K with an increase of 10 K in the tests. The results showed that under calm conditions, ground heating could induce circulation with a wind speed of around 1.0 m s-1, which is enough to disperse pollutants in a street canyon. It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio. When ambient wind speed was lower than the threshold identified in this study, the impact of the thermal effect on the flow field was obvious, and there existed a multi-vortex flow pattern in the street canyon. When the ambient wind speed was higher than the threshold, the circulation pattern was basically determined by dynamic effects. The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon, which would help improve pollutant diffusion capability in street canyons.

Impact of a wind turbine on turbulence: Un-freezing turbulence by means of a simple vortex particle approach

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre; Mercier, P.; Machefaux, Ewan

2016-01-01

by a bound vorticity lifting line while the turbine wake vorticity and the turbulence vorticity are projected onto vortex particles. In the present work the rotor blades are stiff leaving aero-elastic interactions for future work. Inflow turbulence is generated with the model of Mann and converted to vortex......? Is it acceptable to neglect the influence of the wake and the wind turbine on the turbulent inflow? Is there evidence to justify the extra cost of a method capable of including these effects correctly? To this end, a unified vorticity representation of the flow is used: the wind turbine model is represented......A vortex particle representation of turbulent fields is devised in order to address the following questions: Does a wind turbine affect the statistics of the incoming turbulence? Should this imply a change in the way turbulence boxes are used in wind turbine aero-elastic simulations...

Numerical Study of a Long-Lived, Isolated Wake Vortex in Ground Effect

Science.gov (United States)

Proctor, Fred H.

2014-01-01

This paper examines a case observed during the 1990 Idaho Falls Test program, in which a wake vortex having an unusually long lifetime was observed while in ground effect. A numerical simulation is performed with a Large Eddy Simulation model to understand the response of the environment in affecting this event. In the simulation, it was found that one of the vortices decayed quickly, with the remaining vortex persisting beyond the time-bound of typical vortex lifetimes. This unusual behavior was found to be related to the first and second vertical derivatives of the ambient crosswind.

Parametric Adjustments to the Rankine Vortex Wind Model for Gulf of Mexico Hurricanes

Science.gov (United States)

2012-11-01

2012 4. TITLE AND SUBTITLE Parametric Adjustments to the Rankine Vortex Wind Model for Gulf of Mexico Hurricanes 5a. CONTRACT NUMBER 5b. GRANT ...may be used to construct spatially varying wind fields for the GOM region (e.g., Thompson and Cardone [12]), but this requires using a complicated...Storm Damage Reduc- tion, and Dredging Operations and Environmental Research (DOER). The USACE Headquarters granted permission to publish this paper

The Effect of Mounting Vortex Generators on the DTU 10MW Reference Wind Turbine Blade

DEFF Research Database (Denmark)

Skrzypinski, Witold Robert; Gaunaa, Mac; Bak, Christian

2014-01-01

The aim of the current work is to analyze possible advantages of mounting Vortex Generators (VG's) on a wind turbine blade. Specifically, the project aims at investigating at which radial sections of the DTU 10 MW Reference Wind Turbine blade it is most beneficial to mount the VG's in order...

Wind uplift of radioactive dust from the ground

International Nuclear Information System (INIS)

Makhon'ko, K.P.

1992-01-01

Near nuclear power plants the recontamination of the atmosphere near the ground becomes dangerous, if a radioactive zone has formed at the site. Wind can easily carry toxic dust from the polluted territory of neighboring industrial enterprises. Moreover, wind erosion of the soil during the summer or transport of radioactive snow by a snowstorm during the winter can displace the boundaries of the contaminated radioactive zone. In Russia the investigation of wind pickup of radioactive dust from the ground began after a radiation accident occurred at a storage facility in the Southern Urals in 1957, as a result of which a contaminated zone formed in the area. Since the direct mechanism of detachment of dust particles from the ground is not important in studying the results of the raising of radioactive dust into the atmosphere by wind, the authors do not distinguish between wind pickup and wind erosion, and the entire process wind pickup of radioactivity from the ground. After the radiation accident at the Chernobyl nuclear power plant a new generation of investigators began to study wind pickup of radioactive dust from the ground, and the process under consideration was sometimes referred to as wind uplift. The intensity of the process of wind pickup of radioactive dust from the ground is characterized by the wind pickup coefficient α, which is the coefficient of proportionality between the upward flux Q of radioactivity from the ground and the density A of radioactive contamination of the ground: α = Q/A. Physically, the coefficient α is the upward flux of the impurity from the ground with unit contamination density, i.e., the intensity of dust contamination or the fraction of radioactivity picked up by the wind from the ground per unit time. The greatest difficulty in determining α experimentally under dusty conditions is measuring correctly the upward radioactivity flux Q. The author discusses three methods for determining this quantity

A free wake vortex lattice model for vertical axis wind turbines: Modeling, verification and validation

International Nuclear Information System (INIS)

Meng, Fanzhong; Schwarze, Holger; Vorpahl, Fabian; Strobel, Michael

2014-01-01

Since the 1970s several research activities had been carried out on developing aerodynamic models for Vertical Axis Wind Turbines (VAWTs). In order to design large VAWTs of MW scale, more accurate aerodynamic calculation is required to predict their aero-elastic behaviours. In this paper, a 3D free wake vortex lattice model for VAWTs is developed, verified and validated. Comparisons to the experimental results show that the 3D free wake vortex lattice model developed is capable of making an accurate prediction of the general performance and the instantaneous aerodynamic forces on the blades. The comparison between momentum method and the vortex lattice model shows that free wake vortex models are needed for detailed loads calculation and for calculating highly loaded rotors

Remote sensing for wind energy

Energy Technology Data Exchange (ETDEWEB)

Pena, A.; Bay Hasager, C.; Lange, J. [Technical Univ. of Denmark. DTU Wind Energy, DTU Risoe Campus, Roskilde (Denmark) (and others

2013-06-15

The Remote Sensing in Wind Energy report provides a description of several topics and it is our hope that students and others interested will learn from it. The idea behind it began in year 2008 at DTU Wind Energy (formerly Risoe) during the first PhD Summer School: Remote Sensing in Wind Energy. Thus it is closely linked to the PhD Summer Schools where state-of-the-art is presented during the lecture sessions. The advantage of the report is to supplement with in-depth, article style information. Thus we strive to provide link from the lectures, field demonstrations, and hands-on exercises to theory. The report will allow alumni to trace back details after the course and benefit from the collection of information. This is the third edition of the report (first externally available), after very successful and demanded first two, and we warmly acknowledge all the contributing authors for their work in the writing of the chapters, and we also acknowledge all our colleagues in the Meteorology and Test and Measurements Sections from DTU Wind Energy in the PhD Summer Schools. We hope to continue adding more topics in future editions and to update and improve as necessary, to provide a truly state-of-the-art 'guideline' available for people involved in Remote Sensing in Wind Energy. (Author)

UWB Wind Turbine Blade Deflection Sensing for Wind Energy Cost Reduction

DEFF Research Database (Denmark)

Zhang, Shuai; Jensen, Tobias Lindstrøm; Franek, Ondrej

2015-01-01

A new application of utilizing ultra-wideband (UWB) technology to sense wind turbine blade deflections is introduced in this paper for wind energy cost reduction. The lower UWB band of 3.1–5.3 GHz is applied. On each blade, there will be one UWB blade deflection sensing system, which consists...... is always of sufficient quality for accurate estimations under different deflections. The measured results reveal that the blade tip-root distance and blade deflection can be accurately estimated in the complicated and lossy wireless channels around a wind turbine blade. Some future research topics...

Vortex coupling in trailing vortex-wing interactions

Science.gov (United States)

Chen, C.; Wang, Z.; Gursul, I.

2018-03-01

The interaction of trailing vortices of an upstream wing with rigid and flexible downstream wings has been investigated experimentally in a wind tunnel, using particle image velocimetry, hot-wire, force, and deformation measurements. Counter-rotating upstream vortices exhibit increased meandering when they are close to the tip of the downstream wing. The upstream vortex forms a pair with the vortex shed from the downstream wing and then exhibits large displacements around the wing tip. This coupled motion of the pair has been found to cause large lift fluctuations on the downstream wing. The meandering of the vortex pair occurs at the natural meandering frequency of the isolated vortex, with a low Strouhal number, and is not affected by the frequency of the large-amplitude wing oscillations if the downstream wing is flexible. The displacement of the leading vortex is larger than that of the trailing vortex; however, it causes highly correlated variations of the core radius, core vorticity, and circulation of the trailing vortex with the coupled meandering motion. In contrast, co-rotating vortices do not exhibit any increased meandering.

Satellite Remote Sensing in Offshore Wind Energy

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Badger, Merete; Astrup, Poul

2013-01-01

Satellite remote sensing of ocean surface winds are presented with focus on wind energy applications. The history on operational and research-based satellite ocean wind mapping is briefly described for passive microwave, scatterometer and synthetic aperture radar (SAR). Currently 6 GW installed...

Hybrid vortex simulations of wind turbines using a three-dimensional viscous-inviscid panel method

DEFF Research Database (Denmark)

Ramos García, Néstor; Hejlesen, Mads Mølholm; Sørensen, Jens Nørkær

2017-01-01

adirect calculation, whereas the contribution from the large downstream wake is calculated using a mesh-based method. Thehybrid method is first validated in detail against the well-known MEXICO experiment, using the direct filament method asa comparison. The second part of the validation includes a study......A hybrid filament-mesh vortex method is proposed and validated to predict the aerodynamic performance of wind turbinerotors and to simulate the resulting wake. Its novelty consists of using a hybrid method to accurately simulate the wakedownstream of the wind turbine while reducing...

WindScanner.eu - a new Remote Sensing Research Infrastructure for On- and Offshore Wind Energy

DEFF Research Database (Denmark)

Mikkelsen, Torben; Siggaard Knudsen, Søren; Sjöholm, Mikael

2012-01-01

will be disseminated throughout Europe to pilot European wind energy research centers. The new research infrastructure will become an open source infrastructure that also invites collaboration with wind energy related atmospheric scientists and wind energy industry overseas. Recent achievements with 3D Wind......A new remote sensing based research infrastructure for atmospheric boundary-layer wind and turbulence measurements named WindScanner have during the past three years been in its early phase of development at DTU Wind Energy in Denmark. During the forthcoming three years the technology......Scanners and spin-off innovation activity are described. The Danish WindScanner.dk research facility is build from new and fast-scanning remote sensing equipment spurred from achievements within fiber optics and telecommunication technologies. At the same time the wind energy society has demanded excessive 3D wind...

Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

Science.gov (United States)

Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

2013-09-06

Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

Vortex capturing vertical axis wind turbine

International Nuclear Information System (INIS)

Zannetti, L; Gallizio, F; Ottino, G

2007-01-01

An analytical-numerical study is presented for an innovative lift vertical axis turbine whose blades are designed with vortex trapping cavities that act as passive flow control devices. The unsteady flow field past one-bladed and two-bladed turbines is described by a combined analytical and numerical method based on conformal mapping and on a blob vortex method

Aerodynamically shaped vortex generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Velte, Clara Marika; Øye, Stig

2016-01-01

An aerodynamically shaped vortex generator has been proposed, manufactured and tested in a wind tunnel. The effect on the overall performance when applied on a thick airfoil is an increased lift to drag ratio compared with standard vortex generators. Copyright © 2015 John Wiley & Sons, Ltd....

Remote sensing for wind power potential: a prospector's handbook

Energy Technology Data Exchange (ETDEWEB)

Wade, J.E.; Maule, P.A.; Bodvarsson, G.; Rosenfeld, C.L.; Woolley, S.G.; McClenahan, M.R.

1983-02-01

Remote sensing can aid in identifying and locating indicators of wind power potential from the terrestrial, marine, and atmospheric environments (i.e.: wind-deformed trees, white caps, and areas of thermal flux). It is not considered as a tool for determining wind power potential. A wide variety of remotely sensed evidence is described in terms of the scale at which evidence of wind power can be identified, and the appropriate remote sensors for finding such evidence. Remote sensing can be used for regional area prospecting using small-scale imagery. The information from such small-scale imagery is most often qualitative, and if it is transitory, examination of a number of images to verify presistence of the feature may be required. However, this evidence will allow rapid screening of a large area. Medium-scale imagery provides a better picture of the evidence obtained from small-scale imagery. At this level it is best to use existing imagery. Criteria relating to land use, accessibility, and proximity of candidate sites to nearby transmission lines can also be effectively evaluated from medium-scale imagery. Large-scale imagery provides the most quantitative evidence of the strength of wind. Wind-deformed trees can be identified at a large number of sites using only a few hours in locally chartered aircraft. A handheld 35mm camera can adequately document any evidence of wind. Three case studies that employ remote sensing prospecting techniques are described. Based on remotely sensed evidence, the wind power potential in three geographically and climatically diverse areas of the United States is estimated, and the estimates are compared to actual wind data in those regions. In addition, the cost of each survey is discussed. The results indicate that remote sensing for wind power potential is a quick, cost effective, and fairly reliable method for screening large areas for wind power potential.

Cylindrical vortex wake model: right cylinder

DEFF Research Database (Denmark)

Branlard, Emmanuel; Gaunaa, Mac

2015-01-01

The vortex system consisting of a bound vortex disk, a root vortex and a vortex cylinder as introduced by Joukowski in 1912 is further studied in this paper. This system can be used for simple modeling of rotors (e.g. wind turbines) with infinite number of blades and finite tip-speed ratios....... For each vortex element, the velocity components in all directions and in the entire domain are computed analytically in a novel approach. In particular, the velocity field from the vortex actuator disk is derived for the first time. The induction from the entire vortex system is studied and is seen...

On mean wind and turbulence profile measurements from ground-based wind lidars

DEFF Research Database (Denmark)

Mikkelsen, Torben

2009-01-01

Two types of wind lidar?s have become available for ground-based vertical mean wind and turbulence profiling. A continuous wave (CW) wind lidar, and a pulsed wind lidar. Although they both are build upon the same recent 1.55 μ telecom fibre technology, they possess fundamental differences between...... their temporal and spatial resolution capabilities. A literature review of the two lidar systems spatial and temporal resolution characteristics will be presented, and the implication for the two lidar types vertical profile measurements of mean wind and turbulence in the lower atmospheric boundary layer...

UWB Wind Turbine Blade Deflection Sensing for Wind Energy Cost Reduction.

Science.gov (United States)

Zhang, Shuai; Jensen, Tobias Lindstrøm; Franek, Ondrej; Eggers, Patrick C F; Olesen, Kim; Byskov, Claus; Pedersen, Gert Frølund

2015-08-12

A new application of utilizing ultra-wideband (UWB) technology to sense wind turbine blade deflections is introduced in this paper for wind energy cost reduction. The lower UWB band of 3.1-5.3 GHz is applied. On each blade, there will be one UWB blade deflection sensing system, which consists of two UWB antennas at the blade root and one UWB antenna at the blade tip. The detailed topology and challenges of this deflection sensing system are addressed. Due to the complexity of the problem, this paper will first realize the on-blade UWB radio link in the simplest case, where the tip antenna is situated outside (and on the surface of) a blade tip. To investigate this case, full-blade time-domain measurements are designed and conducted under different deflections. The detailed measurement setups and results are provided. If the root and tip antenna locations are properly selected, the first pulse is always of sufficient quality for accurate estimations under different deflections. The measured results reveal that the blade tip-root distance and blade deflection can be accurately estimated in the complicated and lossy wireless channels around a wind turbine blade. Some future research topics on this application are listed finally.

Sensing the wind profile

Energy Technology Data Exchange (ETDEWEB)

Pena, A.

2009-03-15

This thesis consists of two parts. The first is a synopsis of the theoretical progress of the study that is based on a number of journal papers. The papers, which constitute the second part of the report, aim to analyze, measure, and model the wind prole in and beyond the surface layer by combining observations from cup anemometers with lidars. The lidar is necessary to extend the measurements on masts at the Horns Rev offshore wind farm and over at land at Hoevsoere, Denmark. Both sensing techniques show a high degree of agreement for wind speed measurements performed at either sites. The wind speed measurements are averaged for several stability conditions and compare well with the surface-layer wind profile. At Hoevsoere, it is sufficient to scale the wind speed with the surface friction velocity, whereas at Horns Rev a new scaling is added, due to the variant roughness length. This new scaling is coupled to wind prole models derived for flow over the sea and tested against the wind proles up to 160 m at Horns Rev. The models, which account for the boundary-layer height in stable conditions, show better agreement with the measurements than compared to the traditional theory. Mixing-length parameterizations for the neutral wind prole compare well with length-scale measurements up to 300 m at Hoevsoere and 950 m at Leipzig. The mixing-length-derived wind proles strongly deviate from the logarithmic wind prole, but agree better with the wind speed measurements. The length-scale measurements are compared to the length scale derived from a spectral analysis performed up to 160 m at Hoevsoere showing high agreement. Mixing-length parameterizations are corrected to account for stability and used to derive wind prole models. These compared better to wind speed measurements up to 300 m at Hoevsoere than the surface-layer wind prole. The boundary-layer height is derived in nearneutral and stable conditions based on turbulent momentum uxes only and in unstable conditions

Wind and Wake Sensing with UAV Formation Flight: System Development and Flight Testing

Science.gov (United States)

Larrabee, Trenton Jameson

sensing data using UAVs in formation flight. This has been achieved and well documented before in manned aircraft but very little work has been done on UAV wake sensing especially during flight testing. This document describes the development and flight testing of small unmanned aerial system (UAS) for wind and wake sensing purpose including a Ground Control Station (GCS) and UAVs. This research can be stated in four major components. Firstly, formation flight was obtained by integrating a formation flight controller on the WVU Phastball Research UAV aircraft platform from the Flight Control Systems Laboratory (FCSL) at West Virginia University (WVU). Second, a new approach to wind estimation using an Unscented Kalman filter (UKF) is discussed along with results from flight data. Third, wake modeling within a simulator and wake sensing during formation flight is shown. Finally, experimental results are used to discuss the "sweet spot" for energy harvesting in formation flight, a novel approach to cooperative wind estimation, and gust suppression control for a follower aircraft in formation flight.

Phenomenological Model of Vortex Generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Westergaard, C.

1995-01-01

For some time attempts have been made to improve the power curve of stall regulated wind turbines by using devices like vortex generators VG and Gurney flaps. The vortex produces an additional mixing of the boundary layer and the free stream and thereby increasing the momentum close to the wall......, which again delays separation in adverse pressure gradient regions. A model is needed to include the effect of vortex generators in numerical computations of the viscous flow past rotors. In this paper a simple model is proposed....

Double helix vortex breakdown in a turbulent swirling annular jet flow

Science.gov (United States)

Vanierschot, M.; Percin, M.; van Oudheusden, B. W.

2018-03-01

In this paper, we report on the structure and dynamics of double helix vortex breakdown in a turbulent annular swirling jet. Double helix breakdown has been reported previously for the laminar flow regime, but this structure has rarely been observed in turbulent flow. The flow field is investigated experimentally by means of time-resolved tomographic particle image velocimetry. Notwithstanding the axisymmetric nature of the time-averaged flow, analysis of the instantaneous three-dimensional (3D) vortical structures shows the existence of a vortex core along the central axis which breaks up into a double helix downstream. The winding sense of this double helix is opposite to the swirl direction (m =-2 ) and it is wrapped around a central vortex breakdown bubble. This structure is quite different from double helix breakdown found in laminar flows where the helix is formed in the wake of the bubble and not upstream. The double helix precesses around the central axis of the jet with a precessing frequency corresponding to a Strouhal number of 0.27.

Stable dissipative optical vortex clusters by inhomogeneous effective diffusion.

Science.gov (United States)

Li, Huishan; Lai, Shiquan; Qui, Yunli; Zhu, Xing; Xie, Jianing; Mihalache, Dumitru; He, Yingji

2017-10-30

We numerically show the generation of robust vortex clusters embedded in a two-dimensional beam propagating in a dissipative medium described by the generic cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion term, which is asymmetrical in the two transverse directions and periodically modulated in the longitudinal direction. We show the generation of stable optical vortex clusters for different values of the winding number (topological charge) of the input optical beam. We have found that the number of individual vortex solitons that form the robust vortex cluster is equal to the winding number of the input beam. We have obtained the relationships between the amplitudes and oscillation periods of the inhomogeneous effective diffusion and the cubic gain and diffusion (viscosity) parameters, which depict the regions of existence and stability of vortex clusters. The obtained results offer a method to form robust vortex clusters embedded in two-dimensional optical beams, and we envisage potential applications in the area of structured light.

Sphagnum moss disperses spores with vortex rings.

Science.gov (United States)

Whitaker, Dwight L; Edwards, Joan

2010-07-23

Sphagnum spores, which have low terminal velocities, are carried by turbulent wind currents to establish colonies many kilometers away. However, spores that are easily kept aloft are also rapidly decelerated in still air; thus, dispersal range depends strongly on release height. Vascular plants grow tall to lift spores into sufficient wind currents for dispersal, but nonvascular plants such as Sphagnum cannot grow sufficiently high. High-speed videos show that exploding capsules of Sphagnum generate vortex rings to efficiently carry spores high enough to be dispersed by turbulent air currents. Spores launched ballistically at similar speeds through still air would travel a few millimeters and not easily reach turbulent air. Vortex rings are used by animals; here, we report vortex rings generated by plants.

Counter-rotating vortex pairs in the wake of a vertical axis wind turbine

Science.gov (United States)

Rolin, Vincent; Porté-Agel, Fernando

2017-04-01

Despite the rising popularity of vertical axis wind turbines, or VAWTs, the wakes behind these machines is much less well understood than those behind horizontal axis wind turbines, or HAWTs. A thorough understanding of wakes is important as they can cause turbines in wind farms to produce less power than anticipated and increase the fatigue loading on turbines due to vibrations. In order to gain a deeper understanding of the wake behind a vertical axis wind turbine in atmospheric flow stereo-PIV is implemented in a boundary-layer wind tunnel to produce snapshots of the 3-component velocity field in the wake at various downstream positions. The boundaries of the wake are readily observed due to the high velocity gradients and turbulence present here. Two pairs of counter-rotating vortices similar to those in the wake of yawed HAWTs are also observed. An examination of the momentum fluxes behind the turbine demonstrates that the mean flow induced by these vortices entrains a large quantity of momentum from the unperturbed boundary layer flow above the wake. This effect proves to play an even more significant role than turbulence in reintroducing momentum into the wake. In order to comprehend why the VAWT produces these vortices we modify the double-multiple stream-tube model typically used to predict VAWT performance to incorporate crosswind forces. The similarity between VAWT and yawed HAWT wakes is found not to be coincidental as both cases feature rotors which exert a lateral thrust on the incoming wind which leads to the creation of counter-rotating vortex pairs.

Comparison of the near-wake between actuator-line simulations and a simplified vortex model of a horizontal-axis wind turbine

DEFF Research Database (Denmark)

Sarmast, Sasan; Segalini, Antonio; Mikkelsen, Robert Flemming

2016-01-01

). The vortex model matched the numerical simulation of the turbine with constant blade circulation in terms of the near-wake structure and local forces along the blade. The results from the Tjæreborg turbine case showed some discrepancies between the two approaches, but overall, the agreement is qualitatively...... good, validating the analytical method for more general conditions. The present results show that a simple vortex code is able to provide an estimation of the flow around the wind turbine similar to the actuator-line approach but with a negligible computational effort. Copyright © 2015 John Wiley...

Comparison of the lifting-line free vortex wake method and the blade-element-momentum theory regarding the simulated loads of multi-MW wind turbines

International Nuclear Information System (INIS)

Hauptmann, S; Bülk, M; Cheng, P W; Schön, L; Erbslöh, S; Boorsma, K; Grasso, F; Kühn, M

2014-01-01

Design load simulations for wind turbines are traditionally based on the blade- element-momentum theory (BEM). The BEM approach is derived from a simplified representation of the rotor aerodynamics and several semi-empirical correction models. A more sophisticated approach to account for the complex flow phenomena on wind turbine rotors can be found in the lifting-line free vortex wake method. This approach is based on a more physics based representation, especially for global flow effects. This theory relies on empirical correction models only for the local flow effects, which are associated with the boundary layer of the rotor blades. In this paper the lifting-line free vortex wake method is compared to a state- of-the-art BEM formulation with regard to aerodynamic and aeroelastic load simulations of the 5MW UpWind reference wind turbine. Different aerodynamic load situations as well as standardised design load cases that are sensitive to the aeroelastic modelling are evaluated in detail. This benchmark makes use of the AeroModule developed by ECN, which has been coupled to the multibody simulation code SIMPACK

Comparison of the lifting-line free vortex wake method and the blade-element-momentum theory regarding the simulated loads of multi-MW wind turbines

Science.gov (United States)

Hauptmann, S.; Bülk, M.; Schön, L.; Erbslöh, S.; Boorsma, K.; Grasso, F.; Kühn, M.; Cheng, P. W.

2014-12-01

Design load simulations for wind turbines are traditionally based on the blade- element-momentum theory (BEM). The BEM approach is derived from a simplified representation of the rotor aerodynamics and several semi-empirical correction models. A more sophisticated approach to account for the complex flow phenomena on wind turbine rotors can be found in the lifting-line free vortex wake method. This approach is based on a more physics based representation, especially for global flow effects. This theory relies on empirical correction models only for the local flow effects, which are associated with the boundary layer of the rotor blades. In this paper the lifting-line free vortex wake method is compared to a state- of-the-art BEM formulation with regard to aerodynamic and aeroelastic load simulations of the 5MW UpWind reference wind turbine. Different aerodynamic load situations as well as standardised design load cases that are sensitive to the aeroelastic modelling are evaluated in detail. This benchmark makes use of the AeroModule developed by ECN, which has been coupled to the multibody simulation code SIMPACK.

Ground-level climate at a peatland wind farm in Scotland is affected by wind turbine operation

Science.gov (United States)

Armstrong, Alona; Burton, Ralph R.; Lee, Susan E.; Mobbs, Stephen; Ostle, Nicholas; Smith, Victoria; Waldron, Susan; Whitaker, Jeanette

2016-04-01

The global drive to produce low-carbon energy has resulted in an unprecedented deployment of onshore wind turbines, representing a significant land use change for wind energy generation with uncertain consequences for local climatic conditions and the regulation of ecosystem processes. Here, we present high-resolution data from a wind farm collected during operational and idle periods that shows the wind farm affected several measures of ground-level climate. Specifically, we discovered that operational wind turbines raised air temperature by 0.18 °C and absolute humidity (AH) by 0.03 g m-3 during the night, and increased the variability in air, surface and soil temperature throughout the diurnal cycle. Further, the microclimatic influence of turbines on air temperature and AH decreased logarithmically with distance from the nearest turbine. These effects on ground-level microclimate, including soil temperature, have uncertain implications for biogeochemical processes and ecosystem carbon cycling, including soil carbon stocks. Consequently, understanding needs to be improved to determine the overall carbon balance of wind energy.

High-charge and multiple-star vortex coronagraphy from stacked vector vortex phase masks.

Science.gov (United States)

Aleksanyan, Artur; Brasselet, Etienne

2018-02-01

Optical vortex phase masks are now installed at many ground-based large telescopes for high-contrast astronomical imaging. To date, such instrumental advances have been restricted to the use of helical phase masks of the lowest even order, while future giant telescopes will require high-order masks. Here we propose a single-stage on-axis scheme to create high-order vortex coronagraphs based on second-order vortex phase masks. By extending our approach to an off-axis design, we also explore the implementation of multiple-star vortex coronagraphy. An experimental laboratory demonstration is reported and supported by numerical simulations. These results offer a practical roadmap to the development of future coronagraphic tools with enhanced performances.

Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines

DEFF Research Database (Denmark)

Vaal, J.B., de; Hansen, Martin Otto Laver; Moan, T.

2014-01-01

In order to evaluate aerodynamic loads on floating oshore wind turbines, advanced dynamic analysis tools are required. As a unied model that can represent both dynamic in ow and skewed in ow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a model...... presents a good intermediate solution between computationally efficient but simple momentum balance methods and computationally expensive but complete computational fluid dynamics models. The model introduced is shown to be capable of modelling typical steady and unsteady test cases with reasonable...

Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines

International Nuclear Information System (INIS)

Vaal, J B de; Moan, T; Hansen, M O L

2014-01-01

In order to evaluate aerodynamic loads on floating offshore wind turbines, advanced dynamic analysis tools are required. As a unified model that can represent both dynamic inflow and skewed inflow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a model presents a good intermediate solution between computationally efficient but simple momentum balance methods and computationally expensive but complete computational fluid dynamics models. The model introduced is shown to be capable of modelling typical steady and unsteady test cases with reasonable accuracy

Vortex-Induced Vibration of an Airfoil Used in Vertical-Axis Wind Turbines

Science.gov (United States)

Benner, Bridget; Carlson, Daniel; Seyed-Aghazadeh, Banafsheh; Modarres-Sadeghi, Yahya

2017-11-01

In Vertical-axis wind turbines (VAWTs), when the blades are placed at high angles of attack with respect to the incoming flow, they could experience flow-induced oscillations. A series of experiments in a re-circulating water tunnel was conducted to study the possible Vortex-Induced Vibration (VIV) of a fully-submerged, flexibly-mounted NACA 0021 airfoil, which is used in some designs of VAWTs. The airfoil was free to oscillate in the crossflow direction, and the tests were conducted in a Reynolds number range of 600vortex shedding patterns. This research is supported in part by the National Science Foundation under NSF Award Numbers 1460461 and CBET-1437988.

Atmospheric Boundary Layer Wind Data During the Period January 1, 1998 Through January 21, 1999 at the Dallas-Fort Worth Airport. Volume 2; Data and Processing

Science.gov (United States)

Zak, J. Allen; Rodgers, William G., Jr.

2000-01-01

The NASA Langley Research Center's Aircraft Vortex Spacing System (AVOSS) requires accurate winds and turbulence to determine aircraft wake vortex behavior near the ground. Volume 1 described the wind input and quality analysis process. This volume documents the data available during the period January 1998 through January 1999 and the partitioning and concatenation of files for time of day, turbulence, non duplication, cross wind profile quality and ceiling and visibility. It provides the resultant filtered files for the first three partitions as well as identification of ceiling/visibility conditions when they were below 5000 feet and 5 miles respectively. It also includes the wind profile quality flags to permit automatic selection of files for AVOSS application using selected ceiling/visibility and wind profile quality values and flags (or no flags).

Highly reliable wind-rolling triboelectric nanogenerator operating in a wide wind speed range

Science.gov (United States)

Yong, Hyungseok; Chung, Jihoon; Choi, Dukhyun; Jung, Daewoong; Cho, Minhaeng; Lee, Sangmin

2016-01-01

Triboelectric nanogenerators are aspiring energy harvesting methods that generate electricity from the triboelectric effect and electrostatic induction. This study demonstrates the harvesting of wind energy by a wind-rolling triboelectric nanogenerator (WR-TENG). The WR-TENG generates electricity from wind as a lightweight dielectric sphere rotates along the vortex whistle substrate. Increasing the kinetic energy of a dielectric converted from the wind energy is a key factor in fabricating an efficient WR-TENG. Computation fluid dynamics (CFD) analysis is introduced to estimate the precise movements of wind flow and to create a vortex flow by adjusting the parameters of the vortex whistle shape to optimize the design parameters to increase the kinetic energy conversion rate. WR-TENG can be utilized as both a self-powered wind velocity sensor and a wind energy harvester. A single unit of WR-TENG produces open-circuit voltage of 11.2 V and closed-circuit current of 1.86 μA. Additionally, findings reveal that the electrical power is enhanced through multiple electrode patterns in a single device and by increasing the number of dielectric spheres inside WR-TENG. The wind-rolling TENG is a novel approach for a sustainable wind-driven TENG that is sensitive and reliable to wind flows to harvest wasted wind energy in the near future. PMID:27653976

Vortex-Peierls States in Optical Lattices

International Nuclear Information System (INIS)

Burkov, A.A.; Demler, Eugene

2006-01-01

We show that vortices, induced in cold atom superfluids in optical lattices, may order in a novel vortex-Peierls ground state. In such a state vortices do not form a simple lattice but arrange themselves in clusters, within which the vortices are partially delocalized, tunneling between classically degenerate configurations. We demonstrate that this exotic quantum many-body state is selected by an order-from-disorder mechanism for a special combination of the vortex filling and lattice geometry that has a macroscopic number of classically degenerate ground states

Effect of Neutral Grounding Protection Methods for Compensated Wind/PV Grid-Connected Hybrid Power Systems

Directory of Open Access Journals (Sweden)

Nurettin Çetinkaya

2017-01-01

Full Text Available The effects of the wind/PV grid-connected system (GCS can be categorized as technical, environmental, and economic impacts. It has a vital impact for improving the voltage in the power systems; however, it has some negative effects such as interfacing and fault clearing. This paper discusses different grounding methods for fault protection of High-voltage (HV power systems. Influences of these grounding methods for various fault characteristics on wind/PV GCSs are discussed. Simulation models are implemented in the Alternative Transient Program (ATP version of the Electromagnetic Transient Program (EMTP. The models allow for different fault factors and grounding methods. Results are obtained to evaluate the impact of each grounding method on the 3-phase short-circuit fault (SCF, double-line-to-ground (DLG fault, and single-line-to-ground (SLG fault features. Solid, resistance, and Petersen coil grounding are compared for different faults on wind/PV GCSs. Transient overcurrent and overvoltage waveforms are used to describe the fault case. This paper is intended as a guide to engineers in selecting adequate grounding and ground fault protection schemes for HV, for evaluating existing wind/PV GCSs to minimize the damage of the system components from faults. This research presents the contribution of wind/PV generators and their comparison with the conventional system alone.

Bluff body flow and vortex—its application to wind turbines

Energy Technology Data Exchange (ETDEWEB)

Ohya, Yuji, E-mail: ohya@riam.kyushu-u.ac.jp [Research Institute for Applied Mechanics, Kyushu University, Kasuga (Japan)

2014-12-01

Some interesting phenomena of vortex flows we have found in past experimental research are described. For a given flow configuration, multiple flow patterns can exist and a sudden change from one flow pattern to another can occur. We observed the alternate switching of the flow patterns with irregular periods around a bluff body. The change of vortex flow pattern around a bluff body with geometrical parameters or stratification is not always continuous but often shows a sudden change in the whole flow pattern. Based on our research on vortex flows, an innovative application of the vortex flow to a shrouded wind turbine is made in which the power output of a wind turbine is remarkably enhanced. Unlike the majority of conventional aerodynamic machinery, which tends to minimize vortex shedding, the vortex formation of our ‘brimmed’ shroud plays an important role in capturing and concentrating wind energy. Furthermore, aerodynamic noise is reduced in this design. The blade tip vortex is weakened by a counter-rotating vortex generated along the inner side of the shroud as they travel downstream, making the shrouded wind turbine much quieter than conventional turbines. (paper)

Bluff body flow and vortex—its application to wind turbines

International Nuclear Information System (INIS)

Ohya, Yuji

2014-01-01

Some interesting phenomena of vortex flows we have found in past experimental research are described. For a given flow configuration, multiple flow patterns can exist and a sudden change from one flow pattern to another can occur. We observed the alternate switching of the flow patterns with irregular periods around a bluff body. The change of vortex flow pattern around a bluff body with geometrical parameters or stratification is not always continuous but often shows a sudden change in the whole flow pattern. Based on our research on vortex flows, an innovative application of the vortex flow to a shrouded wind turbine is made in which the power output of a wind turbine is remarkably enhanced. Unlike the majority of conventional aerodynamic machinery, which tends to minimize vortex shedding, the vortex formation of our ‘brimmed’ shroud plays an important role in capturing and concentrating wind energy. Furthermore, aerodynamic noise is reduced in this design. The blade tip vortex is weakened by a counter-rotating vortex generated along the inner side of the shroud as they travel downstream, making the shrouded wind turbine much quieter than conventional turbines. (paper)

Vortex Particle-Mesh simulations of Vertical Axis Wind Turbine flows: from the blade aerodynamics to the very far wake

Science.gov (United States)

Chatelain, P.; Duponcheel, M.; Caprace, D.-G.; Marichal, Y.; Winckelmans, G.

2016-09-01

A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. LES of Vertical Axis Wind Turbine (VAWT) flows are performed. The complex wake development is captured in details and over very long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters). The statistics and topology of the mean flow are studied. The computational sizes also allow insights into the detailed unsteady vortex dynamics, including some unexpected topological flow features.

Vortex Particle-Mesh simulations of Vertical Axis Wind Turbine flows: from the blade aerodynamics to the very far wake

International Nuclear Information System (INIS)

Chatelain, P; Duponcheel, M; Caprace, D-G; Winckelmans, G; Marichal, Y

2016-01-01

A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. LES of Vertical Axis Wind Turbine (VAWT) flows are performed. The complex wake development is captured in details and over very long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters). The statistics and topology of the mean flow are studied. The computational sizes also allow insights into the detailed unsteady vortex dynamics, including some unexpected topological flow features. (paper)

Aircraft Vortex Wake Decay Near the Ground

Science.gov (United States)

1977-05-01

A multi-faceted experimental and analytical research program was carried out to explore the details of aircraft wake vortex breakdown under conditions representative of those which prevail at low altitudes in the vicinity of airports. Three separate ...

Wakes behind wind turbines. Studies on tip vortex evolution and stability

Energy Technology Data Exchange (ETDEWEB)

Odemark, Ylva

2012-07-01

The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind power farms. In order to better estimate the total power output of a wind power farm, knowledge about the development and stability of wind turbine wakes is crucial. In the present thesis, the wake behind a small-scale model turbine was investigated experimentally in a wind tunnel. The velocity in the wake was measured with hot-wire anemometry, for different free stream velocities and tip speed ratios. To characterize the behaviour of the model turbine, the power output, thrust force and rotational frequency of the model were also measured. These results were then compared to calculations using the Blade Element Momentum (BEM) method. New turbine blades for the model was constructed using the same method, in order to get an estimate of the distribution of the lift and drag forces along the blades. This information is needed for comparisons with certain numerical simulations, which however remains to be performed.By placing the turbine at different heights in a turbulent boundary layer, the effects of forest turbulence on wind turbine outputs (power and thrust) could also be investigated.The evolution of the tip vortices shed from the turbine blades was studied by performing velocity measurements around the location of the tip vortex breakdown. The vortices' receptivity to disturbances was then studied by introducing a disturbance in the form of two pulsed jets, located in the rear part of the nacelle. In order to introduce a well-defined disturbance and perform phase-locked measurements, a new experimental setup was constructed and successfully tested for two different disturbance frequencies. The mean stream wise velocity and the stream wise turbulence intensity was found to scale well with the free stream velocity and the spreading of the wake was found to be proportional to the square root of the

Development of new tip-loss corrections based on vortex theory and vortex methods

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre; Gaunaa, Mac

2014-01-01

A new analytical formulation of the tip-loss factor is established based on helical vortex lament solutions. The derived tip-loss factor can be applied to wind-turbines, propellers or other rotary wings. Similar numerical formulations are used to assess the influence of wake expansion on tip...

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

Science.gov (United States)

Rorke, J. B.; Moffett, R. C.

1977-01-01

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable.

Development of semiconductor laser based Doppler lidars for wind-sensing applications

DEFF Research Database (Denmark)

Rodrigo, Peter John; Hu, Qi; Pedersen, Christian

2015-01-01

We summarize the progress we have made in the development of semiconductor laser (SL) based Doppler lidar systems for remote wind speed and direction measurements. The SL emitter used in our wind-sensing lidar is an integrated diode laser with a tapered (semiconductor) amplifier. The laser source...

What information do Karman streets offer to flow sensing?

Energy Technology Data Exchange (ETDEWEB)

Akanyeti, Otar; Venturelli, Roberto; Visentin, Francesco; Fiorini, Paolo [Department of Computer Science, University of Verona, 37134 Verona (Italy); Chambers, Lily; Megill, William M, E-mail: otarakanyeti@yahoo.com [Department of Mechanical Engineering, University of Bath, Bath BA2 7AY (United Kingdom)

2011-09-15

In this work, we focus on biomimetic lateral line sensing in Karman vortex streets. After generating a Karman street in a controlled environment, we examine the hydrodynamic images obtained with digital particle image velocimetry (DPIV). On the grounds that positioning in the flow and interaction with the vortices govern bio-inspired underwater locomotion, we inspect the fluid in the swimming robot frame of reference. We spatially subsample the flow field obtained using DPIV to emulate the local flow around the body. In particular, we look at various sensor configurations in order to reliably identify the vortex shedding frequency, wake wavelength and downstream flow speed. Moreover, we propose methods that differentiate between being in and out of the Karman street with >70% accuracy, distinguish right from left with respect to Karman vortex street centreline (>80%) and highlight when the sensor system enters the vortex formation zone (>75%). Finally, we present a method that estimates the relative position of a sensor array with respect to the vortex formation point within 15% error margin.

Short term prediction of the horizontal wind vector within a wake vortex warning system

Energy Technology Data Exchange (ETDEWEB)

Frech, M.; Holzaepfel, F.; Gerz, T. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Wessling (Germany). Inst. fuer Physik der Atmosphaere; Konopka, J. [Deutsche Flugsicherung (DFS) GmbH, Langen (Germany)

2000-07-14

A wake vortex warning system (WVWS) has been developed for Frankfurt airport. This airport has two parallel runways which are separated by 518 m, a distance too short to operate them independently because wake vortices may be advected to the adjacent runway. The objective of the WVWS is to enable operation with reduced separation between two aircraft approaching the parallel runways at appropriate wind conditions. The WVWS applies a statistical persistence model to predict the crosswind within a 20 minute period. One of the main problems identified in the old WVWS are discontinuities between successive forecasts. These forecast breakdowns were not acceptable to airtraffic controllers. At least part of the problem was related to the fact that the forecast was solely based on the prediction of crosswind. A new method is developed on the basis of 523 days of sonic anemometer measurements at Frankfurt airport. It is demonstrated that the prediction of the horizontal wind vector avoids these difficulties and significantly improves the system's performance. (orig.)

Experimental wind tunnel study of a smart sensing skin for condition evaluation of a wind turbine blade

Science.gov (United States)

Downey, Austin; Laflamme, Simon; Ubertini, Filippo

2017-12-01

Condition evaluation of wind turbine blades is difficult due to their large size, complex geometry and lack of economic and scalable sensing technologies capable of detecting, localizing, and quantifying faults over a blade’s global area. A solution is to deploy inexpensive large area electronics over strategic areas of the monitored component, analogous to sensing skin. The authors have previously proposed a large area electronic consisting of a soft elastomeric capacitor (SEC). The SEC is highly scalable due to its low cost and ease of fabrication, and can, therefore, be used for monitoring large-scale components. A single SEC is a strain sensor that measures the additive strain over a surface. Recently, its application in a hybrid dense sensor network (HDSN) configuration has been studied, where a network of SECs is augmented with a few off-the-shelf strain gauges to measure boundary conditions and decompose the additive strain to obtain unidirectional surface strain maps. These maps can be analyzed to detect, localize, and quantify faults. In this work, we study the performance of the proposed sensing skin at conducting condition evaluation of a wind turbine blade model in an operational environment. Damage in the form of changing boundary conditions and cuts in the monitored substrate are induced into the blade. An HDSN is deployed onto the interior surface of the substrate, and the blade excited in a wind tunnel. Results demonstrate the capability of the HDSN and associated algorithms to detect, localize, and quantify damage. These results show promise for the future deployment of fully integrated sensing skins deployed inside wind turbine blades for condition evaluation.

An experimental investigation of wind pressures on square pillars in tornado-like vortices

International Nuclear Information System (INIS)

Iwatani, Yoshiharu; Maruta, Eizou; Kanda, Makoto; Hattori, Yousuke; Hamano, Naoki; Matsuura, Takeshi

1992-01-01

This report describes a laboratory simulation of tornado-like vortices and laboratory measurements of steady wind loads on model structures in tornado-like vortices. The variations of wind direction and wind speed of tornado-like vortices and ground surface pressure under tornado-like vortices with the swirl ratio, Reynolds number and the surface roughness were investigated. Wind pressure distributions on square pillars were measured in tornado-like vortices. It was observed in the experiment that the negative pressures on the roof faces of square pillars were high and distributed rather uniformly but these on the side faces differed greatly from place to place and locally became high. The high pressure regions on the side faces were close to ground surface in the case where the model structures stood in the center of tornado-like vortex, and became higher as the increase of distance between the model structures and the center of tornado-like vortices. (author)

Microwave Remote Sensing Modeling of Ocean Surface Salinity and Winds Using an Empirical Sea Surface Spectrum

Science.gov (United States)

Yueh, Simon H.

2004-01-01

Active and passive microwave remote sensing techniques have been investigated for the remote sensing of ocean surface wind and salinity. We revised an ocean surface spectrum using the CMOD-5 geophysical model function (GMF) for the European Remote Sensing (ERS) C-band scatterometer and the Ku-band GMF for the NASA SeaWinds scatterometer. The predictions of microwave brightness temperatures from this model agree well with satellite, aircraft and tower-based microwave radiometer data. This suggests that the impact of surface roughness on microwave brightness temperatures and radar scattering coefficients of sea surfaces can be consistently characterized by a roughness spectrum, providing physical basis for using combined active and passive remote sensing techniques for ocean surface wind and salinity remote sensing.

Ground-based remote sensing observation of the complex behaviour of the Marseille boundary layer during ESCOMPTE

Science.gov (United States)

Delbarre, H.; Augustin, P.; Saïd, F.; Campistron, B.; Bénech, B.; Lohou, F.; Puygrenier, V.; Moppert, C.; Cousin, F.; Fréville, P.; Fréjafon, E.

2005-03-01

Ground-based remote sensing systems have been used during the ESCOMPTE campaign, to continuously characterize the boundary-layer behaviour through many atmospheric parameters (wind, extinction and ozone concentration distribution, reflectivity, turbulence). This analysis is focused on the comparison of the atmospheric stratification retrieved from a UV angular ozone lidar, an Ultra High Frequency wind profiler and a sodar, above the area of Marseille, on June 26th 2001 (Intensive Observation Period 2b). The atmospheric stratification is shown to be very complex including two superimposed sea breezes, with an important contribution of advection. The temporal and spatial evolution of the stratification observed by the UV lidar and by the UHF radar are in good agreement although the origin of the echoes of these systems is quite different. The complexity of the dynamic situation has only partially been retrieved by a non-hydrostatic mesoscale model used with a 3 km resolution.

Analyzing complex wake-terrain interactions and its implications on wind-farm performance.

Science.gov (United States)

Tabib, Mandar; Rasheed, Adil; Fuchs, Franz

2016-09-01

Rotating wind turbine blades generate complex wakes involving vortices (helical tip-vortex, root-vortex etc.).These wakes are regions of high velocity deficits and high turbulence intensities and they tend to degrade the performance of down-stream turbines. Hence, a conservative inter-turbine distance of up-to 10 times turbine diameter (10D) is sometimes used in wind-farm layout (particularly in cases of flat terrain). This ensures that wake-effects will not reduce the overall wind-farm performance, but this leads to larger land footprint for establishing a wind-farm. In-case of complex-terrain, within a short distance (say 10D) itself, the nearby terrain can rise in altitude and be high enough to influence the wake dynamics. This wake-terrain interaction can happen either (a) indirectly, through an interaction of wake (both near tip vortex and far wake large-scale vortex) with terrain induced turbulence (especially, smaller eddies generated by small ridges within the terrain) or (b) directly, by obstructing the wake-region partially or fully in its flow-path. Hence, enhanced understanding of wake- development due to wake-terrain interaction will help in wind farm design. To this end the current study involves: (1) understanding the numerics for successful simulation of vortices, (2) understanding fundamental vortex-terrain interaction mechanism through studies devoted to interaction of a single vortex with different terrains, (3) relating influence of vortex-terrain interactions to performance of a wind-farm by studying a multi-turbine wind-farm layout under different terrains. The results on interaction of terrain and vortex has shown a much faster decay of vortex for complex terrain compared to a flatter-terrain. The potential reasons identified explaining the observation are (a) formation of secondary vortices in flow and its interaction with the primary vortex and (b) enhanced vorticity diffusion due to increased terrain-induced turbulence. The implications of

Experimental study of improved HAWT performance in simulated natural wind by an active controlled multi-fan wind tunnel

Science.gov (United States)

Toshimitsu, Kazuhiko; Narihara, Takahiko; Kikugawa, Hironori; Akiyoshi, Arata; Kawazu, Yuuya

2017-04-01

The effects of turbulent intensity and vortex scale of simulated natural wind on performance of a horizontal axis wind turbine (HAWT) are mainly investigated in this paper. In particular, the unsteadiness and turbulence of wind in Japan are stronger than ones in Europe and North America in general. Hence, Japanese engineers should take account of the velocity unsteadiness of natural wind at installed open-air location to design a higher performance wind turbine. Using the originally designed five wind turbines on the basis of NACA and MEL blades, the dependencies of the wind frequency and vortex scale of the simulated natural wind are presented. As the results, the power coefficient of the newly designed MEL3-type rotor in the simulated natural wind is 130% larger than one in steady wind.

A New Dark Vortex on Neptune

Science.gov (United States)

Wong, Michael H.; Tollefson, Joshua; Hsu, Andrew I.; de Pater, Imke; Simon, Amy A.; Hueso, Ricardo; Sánchez-Lavega, Agustín; Sromovsky, Lawrence; Fry, Patrick; Luszcz-Cook, Statia; Hammel, Heidi; Delcroix, Marc; de Kleer, Katherine; Orton, Glenn S.; Baranec, Christoph

2018-03-01

An outburst of cloud activity on Neptune in 2015 led to speculation about whether the clouds were convective in nature, a wave phenomenon, or bright companions to an unseen dark vortex (similar to the Great Dark Spot studied in detail by Voyager 2). The Hubble Space Telescope (HST) finally answered this question by discovering a new dark vortex at 45 degrees south planetographic latitude, named SDS-2015 for “southern dark spot discovered in 2015.” SDS-2015 is only the fifth dark vortex ever seen on Neptune. In this paper, we report on imaging of SDS-2015 using HST’s Wide Field Camera 3 across four epochs: 2015 September, 2016 May, 2016 October, and 2017 October. We find that the size of SDS-2015 did not exceed 20 degrees of longitude, more than a factor of two smaller than the Voyager dark spots, but only slightly smaller than previous northern-hemisphere dark spots. A slow (1.7–2.5 deg/year) poleward drift was observed for the vortex. Properties of SDS-2015 and its surroundings suggest that the meridional wind shear may be twice as strong at the deep level of the vortex as it is at the level of cloud-tracked winds. Over the 2015–2017 period, the dark spot’s contrast weakened from about -7 % to about -3 % , while companion clouds shifted from offset to centered, a similar evolution to some historical dark spots. The properties and evolution of SDS-2015 highlight the diversity of Neptune’s dark spots and the need for faster cadence dark spot observations in the future.

Simulating Wake Vortex Detection with the Sensivu Doppler Wind Lidar Simulator

Science.gov (United States)

Ramsey, Dan; Nguyen, Chi

2014-01-01

In support of NASA's Atmospheric Environment Safety Technologies NRA research topic on Wake Vortex Hazard Investigation, Aerospace Innovations (AI) investigated a set of techniques for detecting wake vortex hazards from arbitrary viewing angles, including axial perspectives. This technical report describes an approach to this problem and presents results from its implementation in a virtual lidar simulator developed at AI. Threedimensional data volumes from NASA's Terminal Area Simulation System (TASS) containing strong turbulent vortices were used as the atmospheric domain for these studies, in addition to an analytical vortex model in 3-D space. By incorporating a third-party radiative transfer code (BACKSCAT 4), user-defined aerosol layers can be incorporated into atmospheric models, simulating attenuation and backscatter in different environmental conditions and altitudes. A hazard detection algorithm is described that uses a twocomponent spectral model to identify vortex signatures observable from arbitrary angles.

Multiple Lightning Discharges in Wind Turbines Associated with Nearby Cloud-to-Ground Lightning

DEFF Research Database (Denmark)

Candela Garolera, Anna; Cummins, Kenneth L.; Madsen, Søren Find

2015-01-01

This paper presents the analysis of five events where simultaneous lightning currents were registered in different wind turbines of a wind farm with lightning monitoring equipment installed. Measurements from current monitoring devices installed at the wind turbines and observations from auto......-triggering video cameras were correlated with data from the U.S. National Lighting Detection Network. In all five events, the correlation showed that a cloud-to-ground (CG) lightning stroke with high peak current struck the ground within 10 km of the affected turbines at the time of the currents in the wind...... by the nearby CG strokes, involving mechanisms that vary depending on the polarity of the associated CG stroke. The analysis also suggests that the event of upward lightning from wind turbines triggered by nearby lightning activity occurs very often and therefore it should be considered carefully...

Vortex rings from Sphagnum moss capsules

Science.gov (United States)

Whitaker, Dwight; Strassman, Sam; Cha, Jung; Chang, Emily; Guo, Xinyi; Edwards, Joan

2010-11-01

The capsules of Sphagnum moss use vortex rings to disperse spores to suitable habitats many kilometers away. Vortex rings are created by the sudden release of pressurized air when the capsule ruptures, and are an efficient way to carry the small spores with low terminal velocities to heights where they can be carried by turbulent wind currents. We will present our computational model of these explosions, which are carried out using a 2-D large eddy simulation (LES) on FLUENT. Our simulations can reproduce the observed motion of the spore clouds observed from moss capsules with high-speed videos, and we will discuss the roles of bursting pressure, cap mass, and capsule morphology on the formation and quality of vortex rings created by this plant.

Vortex dynamics in coherently coupled Bose-Einstein condensates

Science.gov (United States)

Calderaro, Luca; Fetter, Alexander L.; Massignan, Pietro; Wittek, Peter

2017-02-01

In classical hydrodynamics with uniform density, vortices move with the local fluid velocity. This description is rewritten in terms of forces arising from the interaction with other vortices. Two such positive straight vortices experience a repulsive interaction and precess in a positive (anticlockwise) sense around their common centroid. A similar picture applies to vortices in a two-component, two-dimensional uniform Bose-Einstein condensate (BEC) coherently coupled through rf Rabi fields. Unlike the classical case, however, the rf Rabi coupling induces an attractive interaction and two such vortices with positive signs now rotate in the negative (clockwise) sense. Pairs of counter-rotating vortices are instead found to translate with uniform velocity perpendicular to the line joining their cores. This picture is extended to a single vortex in a two-component trapped BEC. Although two uniform vortex-free components experience familiar Rabi oscillations of particle-number difference, such behavior is absent for a vortex in one component because of the nonuniform vortex phase. Instead the coherent Rabi coupling induces a periodic vorticity transfer between the two components.

Characterization of the wind loads and flow fields around a gable-roof building model in tornado-like winds

Energy Technology Data Exchange (ETDEWEB)

Hu, Hui; Yang, Zifeng; Sarkar, Partha [Iowa State University, Department of Aerospace Engineering, Ames, IA (United States); Haan, Fred [Iowa State University, Department of Aerospace Engineering, Ames, IA (United States); Rose-Hulman Institute of Technology, Department of Mechanical Engineering, Terre Haute, IN (United States)

2011-09-15

An experimental study was conducted to quantify the characteristics of a tornado-like vortex and to reveal the dynamics of the flow-structure interactions between a low-rise, gable-roof building model and swirling, turbulent tornado-like winds. The experimental work was conducted by using a large-scale tornado simulator located in the Aerospace Engineering Department of Iowa State University. In addition to measuring the pressure distributions and resultant wind loads acting on the building model, a digital Particle Image Velocimetry system was used to conduct detailed flow field measurements to quantify the evolution of the unsteady vortices and turbulent flow structures around the gable-roof building model in tornado-like winds. The effects of important parameters, such as the distance between the centers of the tornado-like vortex and the test model and the orientation angles of the building model related to the tornado-like vortex, on the evolutions of the wake vortices and turbulent flow structures around the gable-roof building model as well as the wind loads induced by the tornado-like vortex were assessed quantitatively. The detailed flow field measurements were correlated with the surface pressure and wind load measurements to elucidate the underlying physics to gain further insight into flow-structure interactions between the gable-roof building model and tornado-like winds in order to provide more accurate prediction of wind damage potential to built structures. (orig.)

Modeling Vortex Generators in a Navier-Stokes Code

Science.gov (United States)

Dudek, Julianne C.

2011-01-01

A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.

Aerodynamic forces and flow structures of the leading edge vortex on a flapping wing considering ground effect

International Nuclear Information System (INIS)

Truong, Tien Van; Yoon, Kwang Joon; Byun, Doyoung; Kim, Min Jun; Park, Hoon Cheol

2013-01-01

The aim of this work is to provide an insight into the aerodynamic performance of the beetle during takeoff, which has been estimated in previous investigations. We employed a scaled-up electromechanical model flapping wing to measure the aerodynamic forces and the three-dimensional flow structures on the flapping wing. The ground effect on the unsteady forces and flow structures were also characterized. The dynamically scaled wing model could replicate the general stroke pattern of the beetle's hind wing kinematics during takeoff flight. Two wing kinematic models have been studied to examine the influences of wing kinematics on unsteady aerodynamic forces. In the first model, the angle of attack is asymmetric and varies during the translational motion, which is the flapping motion of the beetle's hind wing. In the second model, the angle of attack is constant during the translational motion. The instantaneous aerodynamic forces were measured for four strokes during the beetle's takeoff by the force sensor attached at the wing base. Flow visualization provided a general picture of the evolution of the three-dimensional leading edge vortex (LEV) on the beetle hind wing model. The LEV is stable during each stroke, and increases radically from the root to the tip, forming a leading-edge spiral vortex. The force measurement results show that the vertical force generated by the hind wing is large enough to lift the beetle. For the beetle hind wing kinematics, the total vertical force production increases 18.4% and 8.6% for the first and second strokes, respectively, due to the ground effect. However, for the model with a constant angle of attack during translation, the vertical force is reduced during the first stroke. During the third and fourth strokes, the ground effect is negligible for both wing kinematic patterns. This finding suggests that the beetle's flapping mechanism induces a ground effect that can efficiently lift its body from the ground during takeoff

Next Generation Fiber Coherent Lidar System for Wake Vortex Detection, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — SibellOptics proposes to develop an eye-safe, long-range, compact, versatile, all-fiber wind LIDAR system for wake vortex measurement and other wind measurement...

Characterisation of vortex flow inside an entrained cavity

Energy Technology Data Exchange (ETDEWEB)

Rambert, A.; Elcafsi, A.; Gougat, P. [Centre National de la Recherche Scientifique, 91 - Orsay (France). Lab. d' Informatique pour la Mecanique et les Sciences de l' Ingenieur

2000-07-01

A number of studies have referred to the existence of a vortex cell within an urban street canyon when ambient winds aloft are perpendicular to the street. The understanding of vortex dynamics or vorticity distribution in a such configuration is of great interest. Vortex structures play an important role in the dynamics of pollutant dispersion. This configuration was simulated by the interaction between a boundary layer and a cavity. Experimental characterisation of the vortex structures evolution was developed by flow velocity measurements inside and out of the cavity. Classical methods like hot wire and laser Doppler velocimetry (LDV) display only local measurements. Particle image velocimetry (PIV) method based on the optical flow technique permitted global velocity measurements. This technique emphasis the vortex structures inside the cavity which present small scales as well as large scales related to the cavity geometry. These vortices are usually non-stationary. (orig.)

Experimental benchmark and code validation for airfoils equipped with passive vortex generators

DEFF Research Database (Denmark)

Baldacchino, D.; Manolesos, M.; Ferreira, Célia Maria Dias

2016-01-01

Experimental results and complimentary computations for airfoils with vortex generators are compared in this paper, as part of an effort within the AVATAR project to develop tools for wind turbine blade control devices. Measurements from two airfoils equipped with passive vortex generators, a 30...

Automatic tracking of wake vortices using ground-wind sensor data

Science.gov (United States)

1977-01-03

Algorithms for automatic tracking of wake vortices using ground-wind anemometer : data are developed. Methods of bad-data suppression, track initiation, and : track termination are included. An effective sensor-failure detection-and identification : ...

Evolution and breakdown of helical vortex wakes behind a wind turbine

International Nuclear Information System (INIS)

Nemes, A; Jacono, D Lo; Sheridan, J; Blackburn, H M; Sherry, M

2014-01-01

The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable

Wind erosion in semiarid landscapes: Predictive models and remote sensing methods for the influence of vegetation

Science.gov (United States)

Musick, H. Brad

1993-01-01

The objectives of this research are: to develop and test predictive relations for the quantitative influence of vegetation canopy structure on wind erosion of semiarid rangeland soils, and to develop remote sensing methods for measuring the canopy structural parameters that determine sheltering against wind erosion. The influence of canopy structure on wind erosion will be investigated by means of wind-tunnel and field experiments using structural variables identified by the wind-tunnel and field experiments using model roughness elements to simulate plant canopies. The canopy structural variables identified by the wind-tunnel and field experiments as important in determining vegetative sheltering against wind erosion will then be measured at a number of naturally vegetated field sites and compared with estimates of these variables derived from analysis of remotely sensed data.

Vortex particle-mesh simulations of vertical axis wind turbine flows: from the airfoil performance to the very far wake

Directory of Open Access Journals (Sweden)

P. Chatelain

2017-06-01

Full Text Available A vortex particle-mesh (VPM method with immersed lifting lines has been developed and validated. Based on the vorticity–velocity formulation of the Navier–Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. Large-eddy simulation (LES of vertical axis wind turbine (VAWT flows is performed. The complex wake development is captured in detail and over up to 15 diameters downstream: from the blades to the near-wake coherent vortices and then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters. The statistics and topology of the mean flow are studied. The computational sizes also allow insights into the detailed unsteady vortex dynamics and topological flow features, such as a recirculation region influenced by the tip speed ratio and the rotor geometry.

An investigation of the vortex method

Energy Technology Data Exchange (ETDEWEB)

Pryor, Jr., Duaine Wright [Univ. of California, Berkeley, CA (United States)

1994-05-01

The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. This is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.

PREFACE: Special section on vortex rings Special section on vortex rings

Science.gov (United States)

Fukumoto, Yasuhide

2009-10-01

This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill

Resonant-spin-ordering of vortex cores in interacting mesomagnets

Science.gov (United States)

Jain, Shikha

2013-03-01

The magnetic system of interacting vortex-state elements have a dynamically reconfigurable ground state characterized by different relative polarities and chiralities of the individual disks; and have a corresponding dynamically controlled spectrum of collective excitation modes that determine the microwave absorption of the crystal. The development of effective methods for dynamic control of the ground state in this vortex-type magnonic crystal is of interest both from fundamental and technological viewpoints. Control of vortex chirality has been demonstrated previously using various techniques; however, control and manipulation of vortex polarities remain challenging. In this work, we present a robust and efficient way of selecting the ground state configuration of interacting magnetic elements using resonant-spin-ordering approach. This is achieved by driving the system from the linear regime of constant vortex gyrations to the non-linear regime of vortex-core reversals at a fixed excitation frequency of one of the coupled modes. Subsequently reducing the excitation field to the linear regime stabilizes the system to a polarity combination whose resonant frequency is decoupled from the initialization frequency. We have utilized the resonant approach to transition between the two polarity combinations (parallel or antiparallel) in a model system of connected dot-pairs which may form the building blocks of vortex-based magnonic crystals. Taking a step further, we have extended the technique by studying many-particle system for its potential as spin-torque oscillators or logic devices. Work at Argonne was supported by the U. S. DOE, Office of BES, under Contract No. DE-AC02-06CH11357. This work was in part supported by grant DMR-1015175 from the U. S. National Science Foundation, by a Contract from the U.S. Army TARDEC and RDECOM.

A SAR Observation and Numerical Study on Ocean Surface Imprints of Atmospheric Vortex Streets

Directory of Open Access Journals (Sweden)

William G. Pichel

2008-05-01

Full Text Available The sea surface imprints of Atmospheric Vortex Street (AVS off Aleutian Volcanic Islands, Alaska were observed in two RADARSAT-1 Synthetic Aperture Radar (SAR images separated by about 11 hours. In both images, three pairs of distinctive vortices shedding in the lee side of two volcanic mountains can be clearly seen. The length and width of the vortex street are about 60-70 km and 20 km, respectively. Although the AVS’s in the two SAR images have similar shapes, the structure of vortices within the AVS is highly asymmetrical. The sea surface wind speed is estimated from the SAR images with wind direction input from Navy NOGAPS model. In this paper we present a complete MM5 model simulation of the observed AVS. The surface wind simulated from the MM5 model is in good agreement with SAR-derived wind. The vortex shedding rate calculated from the model run is about 1 hour and 50 minutes. Other basic characteristics of the AVS including propagation speed of the vortex, Strouhal and Reynolds numbers favorable for AVS generation are also derived. The wind associated with AVS modifies the cloud structure in the marine atmospheric boundary layer. The AVS cloud pattern is also observed on a MODIS visible band image taken between the two RADARSAT SAR images. An ENVISAT advance SAR image taken 4 hours after the second RADARSAT SAR image shows that the AVS has almost vanished.

Vortex dynamics equation in type-II superconductors in a temperature gradient

International Nuclear Information System (INIS)

Vega Monroy, R.; Sarmiento Castillo, J.; Puerta Torres, D.

2010-01-01

In this work we determined a vortex dynamics equation in a temperature gradient in the frame of the time dependent Ginzburg-Landau equation. In this sense, we derived a local solvability condition, which governs the vortex dynamics. Also, we calculated the explicit form for the force coefficients, which are the keys for the understanding of the balance equation due to vortex interactions with the environment. (author)

Vortex dynamics equation in type-II superconductors in a temperature gradient

Energy Technology Data Exchange (ETDEWEB)

Vega Monroy, R.; Sarmiento Castillo, J. [Universidad del Atlantico, Barranquilla (Colombia). Facultad de Ciencias Basicas; Puerta Torres, D. [Universidad de Cartagena (Colombia). Facultad de Ciencias Exactas

2010-12-15

In this work we determined a vortex dynamics equation in a temperature gradient in the frame of the time dependent Ginzburg-Landau equation. In this sense, we derived a local solvability condition, which governs the vortex dynamics. Also, we calculated the explicit form for the force coefficients, which are the keys for the understanding of the balance equation due to vortex interactions with the environment. (author)

Anomalous Josephson effect controlled by an Abrikosov vortex

Science.gov (United States)

Mironov, S.; Goldobin, E.; Koelle, D.; Kleiner, R.; Tamarat, Ph.; Lounis, B.; Buzdin, A.

2017-12-01

The possibility of a fast and precise Abrikosov vortex manipulation by a focused laser beam opens the way to create laser-driven Josephson junctions. We theoretically demonstrate that a vortex pinned in the vicinity of the Josephson junction generates an arbitrary ground state phase which can be equal not only to 0 or π but to any desired φ0 value in between. Such φ0 junctions have many peculiar properties and may be effectively controlled by the optically driven Abrikosov vortex. Also we theoretically show that the Josephson junction with the embedded vortex can serve as an ultrafast memory cell operating at sub THz frequencies.

Giant moving vortex mass in thick magnetic nanodots.

Science.gov (United States)

Guslienko, K Y; Kakazei, G N; Ding, J; Liu, X M; Adeyeye, A O

2015-09-10

Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5-50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50-100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing.

Offshore wind potential evaluation and remote sensing imagery; Evaluation du potentiel eolien offshore et imagerie satellitale

Energy Technology Data Exchange (ETDEWEB)

Fichaux, N.

2003-12-15

Offshore wind energy may help to contribute to the respect of the Kyoto objectives by Europe. It is a key issue to struggle against global change. To sit the future offshore wind parks, it is necessary to accurately evaluate the spatial repartition of the wind potential. We demonstrate that the offshore wind potential shall be represented by maps of wind statistics. As remote sensing is a tool for measuring space physical phenomena, we evaluate its potentialities for mapping wind statistics. Space-borne scatterometers enables the obtention of wind statistics, but far from our areas of interest and at low spatial resolution. Synthetic Aperture Radar (SAR) enables the computation of high resolution wind maps over our areas of interest, but are unsuitable to compute wind statistics. We define the mathematical framework of a statistical method. That method enables to take advantage of both scatterometer and SAR to compute maps of wind statistics at high spatial resolution over the areas of interest. It enables remote sensing to be used operationally to map the offshore wind potential. (author)

Frequency Stepped Pulse Train Modulated Wind Sensing Lidar

DEFF Research Database (Denmark)

Olesen, Anders Sig; Pedersen, Anders Tegtmeier; Rottwitt, Karsten

2011-01-01

of frequency shifts corresponding to a specific distance. The spatial resolution depends on the repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed......In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from the lidar. Theoretically the FSPT lidar continuously produces measurements...... as is the case with a CW lidar, but at the same time with a spatial resolution, and without the range ambiguity originating from e.g. clouds. The FSPT lidar utilizes a frequency sweeping source for generation of the FSPT. The source generates a pulse train where each pulse has an optical carrier frequency...

Forced pitch motion of wind turbines

Science.gov (United States)

Leble, V.; Barakos, G.

2016-09-01

The possibility of a wind turbine entering vortex ring state during pitching oscillations is explored in this paper. The aerodynamic performance of the rotor was computed using the Helicopter Multi-Block flow solver. This code solves the Navier-Stokes equations in integral form using the arbitrary Lagrangian-Eulerian formulation for time-dependent domains with moving boundaries. A 10-MW wind turbine was put to perform yawing and pitching oscillations suggesting the partial vortex ring state during pitching motion. The results also show the strong effect of the frequency and amplitude of oscillations on the wind turbine performance.

Forced pitch motion of wind turbines

International Nuclear Information System (INIS)

Leble, V; Barakos, G

2016-01-01

The possibility of a wind turbine entering vortex ring state during pitching oscillations is explored in this paper. The aerodynamic performance of the rotor was computed using the Helicopter Multi-Block flow solver. This code solves the Navier-Stokes equations in integral form using the arbitrary Lagrangian-Eulerian formulation for time-dependent domains with moving boundaries. A 10-MW wind turbine was put to perform yawing and pitching oscillations suggesting the partial vortex ring state during pitching motion. The results also show the strong effect of the frequency and amplitude of oscillations on the wind turbine performance. (paper)

Testing a ground-based canopy model using the wind river canopy crane

Science.gov (United States)

Robert Van Pelt; Malcolm P. North

1999-01-01

A ground-based canopy model that estimates the volume of occupied space in forest canopies was tested using the Wind River Canopy Crane. A total of 126 trees in a 0.25 ha area were measured from the ground and directly from a gondola suspended from the crane. The trees were located in a low elevation, old-growth forest in the southern Washington Cascades. The ground-...

WindScanner.dk - a new Remote Sensing based Research Infrastructure for on- and offshore Wind Energy Research

DEFF Research Database (Denmark)

Mikkelsen, Torben

obtained in planetary boundary layer turbulent flow have been acquired from both ground-based and wind turbine-integrated space by time and space synchronized scanning lidars. Results to date include: turbulent inflow over complex terrain scanned in a horizontal-vertical 2D scan plane, and 2-dimensional...... and 3-dimensional wind vector scan measurements obtained during various WindScanner boundary-layer field campaigns. A special designed `2D upwind rotor plane scanning SpinnerLidar', mounted in the rotating spinner, and able to provide the wind turbine control systems with detailed upwind feed......-forward inflow information, is also investigated as a provider of rotor plane inflow for accurate power curve measurements. The instrument development involves both a short range (10 -200 m) and a long-range (100 - 6000 m) synchronized 3D scanning wind lidar system....

Vortex structure and characterization of quasiperiodic functions

International Nuclear Information System (INIS)

Dana, Itzhack; Chernov, Vladislav E

2002-01-01

Quasiperiodic functions (QPFs) are characterized by their full vortex structure in one unit cell. This characterization is much finer and more sensitive than the topological one given by the total vorticity per unit cell (the 'Chern index'). It is shown that QPFs with an arbitrarily prescribed vortex structure exist by constructing explicitly such a 'standard' QPF. Two QPFs with the same vortex structure are equivalent, in the sense that their ratio is a function which is strictly periodic, nonvanishing and at least continuous. A general QPF can then be approximately reconstructed from its vortex structure on the basis of the standard QPF and the equivalence concept. As another application of this concept, a simple method is proposed for calculating the quasiperiodic eigenvectors of periodic matrices. Possible applications to the quantum-chaos problem on a phase-space torus are briefly discussed

Wind climate modeling using Weibull and extreme value distribution ...

African Journals Online (AJOL)

It is very much important to fit wind speed data into some suitable statistical model for two aspects. One is fatigue failure due to periodic vortex shedding and the other is to estimate the wind energy potential of a particular location. For the fatigue failure due to periodic vortex shedding, it is important to analyse the load cycle.

Meteorology and Wake Vortex Influence on American Airlines FL-587 Accident

Science.gov (United States)

Proctor, Fred H.; Hamilton, David W.; Rutishauser, David K.; Switzer, George F.

2004-01-01

The atmospheric environment surrounding the crash of American Airlines Flight 587 is investigated. Examined are evidence for any unusual atmospheric conditions and the potential for encounters with aircraft wake vortices. Computer simulations are carried out with two different vortex prediction models and a Large Eddy Simulation model. Wind models are proposed for studying aircraft and pilot response to the wake vortex encounter.

Vortex solutions in a Witten-type model

International Nuclear Information System (INIS)

Itaya, Satoru; Sawado, Nobuyuki; Suzuki, Michitaka

2014-01-01

Straight line vortex solutions in a Witten's superconducting string model are studied. The model has many parameters and this is the main reason of the complexity. We argue the precise conditions of the parameters for finding the solutions of the model. We obtain the rotationally symmetric solutions for the winding numbers m = 1 - 4 with/without the gauge field. For the higher winding numbers, an energy minimization algorithm is used to investigate non-rotational solutions

Mapping wind erosion hazard in Australia using MODIS-derived ground cover, soil moisture and climate data

International Nuclear Information System (INIS)

Yang, X; Leys, J

2014-01-01

This paper describes spatial modeling methods to identify wind erosion hazard (WEH) areas across Australia using the recently available time-series products of satellite-derived ground cover, soil moisture and wind speed. We implemented the approach and data sets in a geographic information system to produce WEH maps for Australia at 500 m ground resolution on a monthly basis for the recent thirteen year period (2000–2012). These maps reveal the significant wind erosion hazard areas and their dynamic tendencies at paddock and regional scales. Dust measurements from the DustWatch network were used to validate the model and interpret the dust source areas. The modeled hazard areas and changes were compared with results from a rule-set approach and the Computational Environmental Management System (CEMSYS) model. The study demonstrates that the time series products of ground cover, soil moisture and wind speed can be jointly used to identify landscape erodibility and to map seasonal changes of wind erosion hazard across Australia. The time series wind erosion hazard maps provide detailed and useful information to assist in better targeting areas for investments and continuous monitoring, evaluation and reporting that will lead to reduced wind erosion and improved soil condition

Measurements of a vortex transitional ndro Josephson memory cell

International Nuclear Information System (INIS)

Tahara, S.; Ishida, I.; Hidaka, M.; Nagasawa, S.; Ajisawa, Y.; Wada, Y.

1988-01-01

A novel vortex transitional NDRO Jospehson memory cell has been successfully fabricated and tested. The memory cell consists of two superconducting loops and a two-junction interferometer gate as a sense gate. The superconducting loop contains one Josephson junction and inductances, and stores single flux quantum. The memory cell employs vortex transitions in the superconducting loops for writing and reading data. The memory cell chips have been fabricated using niobium planarization process. The +-21 percent address signal current margin and the +-33 percent sense gate current margin have been obtained experimentally. The memory operation of the cell driven by the two-junction interferometer gates has been accurately demonstrated

Coastal wind study based on Sentinel-1 and ground-based scanning lidar

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Badger, Merete; Pena Diaz, Alfredo

Winds in the coastal zone have importance for near-shore wind farm planning. Recently the Danish Energy Agency gave new options for placing offshore wind farms much closer to the coastlines than previously. The new tender areas are located from 3 to 8 km from the coast. Ground-based scanning lidar...... located on land can partly cover this area out to around 15 km. In order to improve wind farm planning for near-shore coastal areas, the project‘Reducing the Uncertainty of Near-shore Energy estimates from meso- and micro-scale wind models’ (RUNE) is established. The measurement campaign starts October....... The various observation types have advantages and limitations; one advantage of both the Sentinel-1 and the scanning lidar is that they both observe wind fields covering a large area and so can be combined for studying the spatial variability of winds. Sentinel-1 are being processed near-real-time at DTU Wind...

Use of ground-based wind profiles in mesoscale forecasting

Science.gov (United States)

Schlatter, Thomas W.

1985-01-01

A brief review is presented of recent uses of ground-based wind profile data in mesoscale forecasting. Some of the applications are in real time, and some are after the fact. Not all of the work mentioned here has been published yet, but references are given wherever possible. As Gage and Balsley (1978) point out, sensitive Doppler radars have been used to examine tropospheric wind profiles since the 1970's. It was not until the early 1980's, however, that the potential contribution of these instruments to operational forecasting and numerical weather prediction became apparent. Profiler winds and radiosonde winds compare favorably, usually within a few m/s in speed and 10 degrees in direction (see Hogg et al., 1983), but the obvious advantage of the profiler is its frequent (hourly or more often) sampling of the same volume. The rawinsonde balloon is launched only twice a day and drifts with the wind. In this paper, I will: (1) mention two operational uses of data from a wind profiling system developed jointly by the Wave Propagation and Aeronomy Laboratories of NOAA; (2) describe a number of displays of these same data on a workstation for mesoscale forecasting developed by the Program for Regional Observing and Forecasting Services (PROFS); and (3) explain some interesting diagnostic calculations performed by meteorologists of the Wave Propagation Laboratory.

Potential of Future Hurricane Imaging Radiometer (HIRAD) Ocean Surface Wind Observations for Determining Tropical Storm Vortex Intensity and Structure

Science.gov (United States)

Atlas, Robert; Bailey, M. C.; Black, Peter; James, Mark; Johnson, James; Jones, Linwood; Miller, Timothy; Ruf, Christopher; Uhlhorn, Eric

2008-01-01

The Hurricane Imaging Radiometer (HIRAD) is an innovative technology development, which offers the potential of new and unique remotely sensed observations of both extreme oceanic wind events and strong precipitation from either UAS or satellite platforms. It is based on the airborne Stepped Frequency Microwave Radiometer (SFMR), which is a proven aircraft remote sensing technique for observing tropical cyclone ocean surface wind speeds and rain rates, including those of major hurricane intensity. The proposed HIRAD instrument advances beyond the current nadir viewing SFMR to an equivalent wide-swath SFMR imager using passive microwave synthetic thinned aperture radiometer technology. This sensor will operate over 4-7 GHz (C-band frequencies) where the required tropical cyclone remote sensing physics has been validated by both SFMR and WindSat radiometers. HIRAD incorporates a unique, technologically advanced array antenna and several other technologies successfully demonstrated by the NASA's Instrument Incubator Program. A brassboard version of the instrument is complete and has been successfully tested in an anechoic chamber, and development of the aircraft instrument is well underway. HIRAD will be a compact, lightweight, low-power instrument with no moving parts that will produce wide-swath imagery of ocean vector winds and rain during hurricane conditions when existing microwave sensors (radiometers or scatterometers) are hindered. Preliminary studies show that HIRAD will have a significant positive impact on analyses as either a new aircraft or satellite sensor.

Flow induced by a skewed vortex cylinder

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre

2017-01-01

The velocity field induced by a skewed vortex cylinder of longitudinal and tangential vorticity is derived in this chapter by direct integration of the Biot– Savart law. The derivation steps are provided in details. The results of Castles and Durham for the skewed semi-infinite cylinder....... The content of this chapter is based on the publication of the author entitled "Cylindrical vortex wake model: skewed cylinder, application to yawed or tilted rotors" [1]. Results from this chapter are applied: in Chap. 21 to model a wind turbine (or rotor) in yaw, in Chap. 22 to derive a new yaw...

Aeroelastic simulation of multi-MW wind turbines using a free vortex model coupled to a geometrically exact beam model

International Nuclear Information System (INIS)

Saverin, Joseph; Peukert, Juliane; Marten, David; Pechlivanoglou, George; Paschereit, Christian Oliver; Greenblatt, David

2016-01-01

The current paper investigates the aeroelastic modelling of large, flexible multi- MW wind turbine blades. Most current performance prediction tools make use of the Blade Element Momentum (BEM) model, based upon a number of simplifying assumptions that hold only under steady conditions. This is why a lifting line free vortex wake (LLFVW) algorithm is used here to accurately resolve unsteady wind turbine aerodynamics. A coupling to the structural analysis tool BeamDyn, based on geometrically exact beam theory, allows for time-resolved aeroelastic simulations with highly deflected blades including bend-twist, coupling. Predictions of blade loading and deformation for rigid and flexible blades are analysed with reference to different aerodynamic and structural approaches. The emergency shutdown procedure is chosen as an examplary design load case causing large deflections to place emphasis on the influence of structural coupling and demonstrate the necessity of high fidelity structural models. (paper)

Evaluating the High Frequency Behavior of the Modified Grounding Scheme in Wind Farms

Directory of Open Access Journals (Sweden)

Seyede Fatemeh Hajeforosh

2017-12-01

Full Text Available Wind generators are exposed to numerous destructive forces such as lightning and are therefore vulnerable to these phenomena. To evaluate the transient behavior of a wind power plant during direct and indirect strikes, modeling of all relevant components is required. Among the protective and control components of wind turbines, the grounding system is the most important element for protection against lightning strikes. This paper examines the impact of nonlinear soil ionization behavior and frequency dependency on a wind turbine in order to model a sufficient protection scheme to reduce overvoltage and make the system tolerable against transitions. The high frequency models of other equipment such as transformers, horizontal conductors, vertical rods, surge arresters and underground cables must also be taken into account to design the grounding system. Our Proposed Modified Grounding Scheme (PMGS is to reduce the maximum transient overvoltages. We simulate the model in a restructured version of the Electromagnetic Transient Program (EMTP-RV software to examine the effectiveness of the system. We then apply the simulated results to pair of turbines that are interconnected with a frequency-dependent cable. We carry out the simulation for direct and indirect lightning strikes. The results indicate that the MGS can lead to considerably more than a 50% reduction in transient voltages for lightning and thus leads to more reliable networks.

Breaking down the delta wing vortex: The role of vorticity in the breakdown process. Ph.D. Thesis Final Report

Science.gov (United States)

Nelson, Robert C.; Visser, Kenneth D.

1990-01-01

Experimental x-wire measurements of the flowfield above a 70 and 75 deg flat plate delta wing were performed at a Reynolds number of 250,000. Grids were taken normal to the wing at various chordwise locations for angles of attack of 20 and 30 deg. Axial and azimuthal vorticity distributions were derived from the velocity fields. The dependence of circulation on distance from the vortex core and on chordwise location was also examined. The effects of nondimensionalization in comparison with other experimental data is made. The results indicate that the circulation distribution scales with the local semispan and grows in a nearly linear fashion in the chordwise direction. The spanwise distribution of axial vorticity is severely altered through the breakdown. The axial vorticity components with a negative sense, such as that found in the secondary vortex, seem to remain unaffected by changes in wind sweep or angle of attack, in direct contrast to the positive components. In addition, the inclusion of the local wing geometry into a previously derived correlation parameter allows the circulation of growing leading edge vortex flows to be reduced into a single curve.

Remote Sensing of Complex Flows by Doppler Wind Lidar: Issues and Preliminary Recommendations

Energy Technology Data Exchange (ETDEWEB)

Clifton, Andrew [National Renewable Energy Lab. (NREL), Golden, CO (United States); Boquet, Matthieu [Leosphere, Orsay (France); Burin Des Roziers, Edward [UL International Gmbh, Freemont, CA (United States); Westerhellweg, Annette [UL International Gmbh, Freemont, CA (United States); Hofsass, Martin [Univ. of Stuttgart (Germany). Stuttgart Wind Energy; Klaas, Tobias [Fraunhofer Inst. for Wind Energy and Energy System Technology, Freiburg (Germany); Vogstad, Klaus [Meventus, Hamburg (Germany); Clive, Peter [Sgurr Energy, Glasgow (United Kingdom); Harris, Mike [ZephIR Limited, Kirkcudbrightshire (United Kingdom); Wylie, Scott [ZephIR Limited, Kirkcudbrightshire (United Kingdom); Osler, Evan [Renewable NRG Systems, Hinesburg, VT (United States); Banta, Bob [National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States); Choukulkar, Aditya [National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States); Lundquist, Julie [Univ. of Colorado, Boulder, CO (United States); Aitken, Matthew [Univ. of Colorado, Boulder, CO (United States)

2015-12-01

Remote sensing of winds using lidar has become popular and useful in the wind energy industry. Extensive experience has been gained with using lidar for applications including land-based and offshore resource assessment, plant operations, and turbine control. Prepared by members of International Energy Agency Task 32, this report describes the state of the art in the use of Doppler wind lidar for resource assessment in complex flows. The report will be used as input for future recommended practices on this topic.

Evaluation of Aircraft Wing-Tip Vortex Using PIV

Science.gov (United States)

Alsayed, Omer A.; Asrar, Waqar; Omar, Ashraf A.

2010-06-01

The formation and development of a wing-tip vortex in a near and extended near filed were studied experimentally. Particle image velocimetry was used in a wind tunnel to measure the tip vortex velocity field and hence investigate the flow structure in a wake of aircraft half-wing model. The purpose of this investigation is to evaluate the main features of the lift generated vortices in order to find ways to alleviate hazardous wake vortex encounters for follower airplanes during start and approach such that the increase in airport capacity can be achieved. First the wake structure at successive downstream planes crosswise to the axis of the wake vortices was investigated by measuring parameters such as core radius, maximum tangential velocities, vorticities and circulation distributions. The effect of different angles of attack setting on vortex parameters was examined at one downstream location. In very early stages the vortex sheet evolution makes the tip vortex to move inward and to the suction side of the wing. While the core radius and circulation distributions hardly vary with the downstream distance, noticeable differences for the same vortex parameters at different angles of attack settings were observed. The center of the wing tip vortices scatter in a circle of radius nearly equal to 1% of the mean wing chord and wandering amplitudes shows no direct dependence on the vortex strength but linearly increase with the downstream distance.

The regional ground-based wind energy scheme of Pays-de-la-Loire: project, Assessment of the consultation on the regional wind energy project, final version, Prefect decree bearing approval of the regional ground-based wind energy scheme of Pays-de-la-Loire

International Nuclear Information System (INIS)

2012-08-01

This document first presents the regional wind energy scheme (SRE) as a framework for ground-based wind energy development, and as the wind energy component of the regional climate air energy scheme (SRCAE), briefly presents the elaboration approach, and indicates the legal scope of this scheme. The next part outlines the high rate development of wind energy in the Pays-de-la-Loire region. The third part reports the identification, analysis and assessment of areas of interest for the development of wind energy. Finally, the objective of this development by 2020 is estimated

Study of vortex breakdown of F-106B by Euler code

Science.gov (United States)

Pao, Jenn Louh

1990-01-01

The 'Three-dimensional Euler Aerodynamic Method' (TEAM) is presently applied to the F-106B at subsonic speed, in order to examine the relationship between off- and on-surface flow features at angles-of-attack sufficiently great for the occurrence of vortex breakdown. Although TEAM's flow separation is triggered by numerical dissipation, the general trend of vortex-breakdown effect on computed lift characteristics is similar to extant wind tunnel results.

Antenna Gain Impact on UWB Wind Turbine Blade Deflection Sensing

DEFF Research Database (Denmark)

Zhang, Shuai; Franek, Ondrej; Byskov, Claus

2018-01-01

Antenna gain impact on UWB wind turbine blade deflection sensing is studied in this paper. Simulations are applied with a 4.5-meter blade tip. The antennas with high gain (HG) and low gain (LG) in free space are simulated inside a blade. It is interesting to find that tip antennas with HG and LG...

Vortex, ULF wave and Aurora Observation after Solar Wind Dynamic Pressure Change

Science.gov (United States)

Shi, Q.

2017-12-01

Here we will summarize our recent study and show some new results on the Magnetosphere and Ionosphere Response to Dynamic Pressure Change/disturbances in the Solar Wind and foreshock regions. We study the step function type solar wind dynamic pressure change (increase/decrease) interaction with the magnetosphere using THEMIS satellites at both dayside and nightside in different geocentric distances. Vortices generated by the dynamic pressure change passing along the magnetopause are found and compared with model predictions. ULF waves and vortices are excited in the dayside and nightside plasma sheet when dynamic pressure change hit the magnetotail. The related ionospheric responses, such as aurora and TCVs, are also investigated. We compare Global MHD simulations with the observations. We will also show some new results that dayside magnetospheric FLRs might be caused by foreshock structures.Shi, Q. Q. et al. (2013), THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events, J. Geophys. Res. Space Physics, 118, doi:10.1029/2012JA017984. Shi, Q. Q. et al. (2014), Solar wind pressure pulse-driven magnetospheric vortices and their global consequences, J. Geophys. Res. Space Physics, 119, doi:10.1002/2013JA019551. Tian, A.M. et al.(2016), Dayside magnetospheric and ionospheric responses to solar wind pressure increase: Multispacecraft and ground observations, J. Geophys. Res., 121, doi:10.1002/2016JA022459. Shen, X.C. et al.(2015), Magnetospheric ULF waves with increasing amplitude related to solar wind dynamic pressure changes: THEMIS observations, J. Geophys. Res., 120, doi:10.1002/2014JA020913Zhao, H. Y. et al. (2016), Magnetospheric vortices and their global effect after a solar wind dynamic pressure decrease, J. Geophys. Res. Space Physics, 121, doi:10.1002/2015JA021646. Shen, X. C., et al. (2017), Dayside magnetospheric ULF wave frequency modulated by a solar wind dynamic pressure negative impulse, J. Geophys. Res

Wind energy conversion. Volume II. Aerodynamics of horizontal axis wind turbines

Energy Technology Data Exchange (ETDEWEB)

Miller, R.H.; Dugundji, J.; Martinez-Sanchez, M.; Gohard, J.; Chung, S.; Humes, T.

1978-09-01

The basic aerodynamic theory of the wind turbine is presented, starting with the simple momentum theory based on uniform inflow and an infinite number of blades. The basic vortex theory is then developed. Following these basics, the more complete momentum theory, including swirl, non-uniform inflow, the effect of a finite number of blades, and empirical correction for the vortex ring condition is presented. The more complete vortex theory is presented which includes unsteady aerodynamic effects but based on a semi-rigid wake. Methods of applying this theory for performance estimation are discussed as well as for the purpose of computing time varying airloads due to windshear and tower interference.

The energy balance of wind waves and the remote sensing problem

Science.gov (United States)

Hasselmann, K.

1972-01-01

Measurements of wave growth indicate an energy balance of the wave spectrum governed primarily by input from the atmosphere, nonlinear transfer to shorter and longer waves, and advection. The pronounced spectral peak and sharp low frequency cut-off characteristic of fetch-limited spectra are explained as a self-stabilizing feature of the nonlinear wave-wave interactions. The momentum transferred from the atmosphere to the wind waves accounts for a large part of the wind drag. These findings are relevant for remote microwave sensing of the sea surface by backscatter and passive radiometry methods.

An Improved Wake Vortex Tracking Algorithm for Multiple Aircraft

Science.gov (United States)

Switzer, George F.; Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.

2010-01-01

The accurate tracking of vortex evolution from Large Eddy Simulation (LES) data is a complex and computationally intensive problem. The vortex tracking requires the analysis of very large three-dimensional and time-varying datasets. The complexity of the problem is further compounded by the fact that these vortices are embedded in a background turbulence field, and they may interact with the ground surface. Another level of complication can arise, if vortices from multiple aircrafts are simulated. This paper presents a new technique for post-processing LES data to obtain wake vortex tracks and wake intensities. The new approach isolates vortices by defining "regions of interest" (ROI) around each vortex and has the ability to identify vortex pairs from multiple aircraft. The paper describes the new methodology for tracking wake vortices and presents application of the technique for single and multiple aircraft.

An Empirical Model for Vane-Type Vortex Generators in a Navier-Stokes Code

Science.gov (United States)

Dudek, Julianne C.

2005-01-01

An empirical model which simulates the effects of vane-type vortex generators in ducts was incorporated into the Wind-US Navier-Stokes computational fluid dynamics code. The model enables the effects of the vortex generators to be simulated without defining the details of the geometry within the grid, and makes it practical for researchers to evaluate multiple combinations of vortex generator arrangements. The model determines the strength of each vortex based on the generator geometry and the local flow conditions. Validation results are presented for flow in a straight pipe with a counter-rotating vortex generator arrangement, and the results are compared with experimental data and computational simulations using a gridded vane generator. Results are also presented for vortex generator arrays in two S-duct diffusers, along with accompanying experimental data. The effects of grid resolution and turbulence model are also examined.

Numerical Validation of a Vortex Model against ExperimentalData on a Straight-Bladed Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Eduard Dyachuk

2015-10-01

Full Text Available Cyclic blade motion during operation of vertical axis wind turbines (VAWTs imposes challenges on the simulations models of the aerodynamics of VAWTs. A two-dimensional vortex model is validated against the new experimental data on a 12-kW straight-bladed VAWT, which is operated at an open site. The results on the normal force on one blade are analyzed. The model is assessed against the measured data in the wide range of tip speed ratios: from 1.8 to 4.6. The predicted results within one revolution have a similar shape and magnitude as the measured data, though the model does not reproduce every detail of the experimental data. The present model can be used when dimensioning the turbine for maximum loads.

Vortex transmutation.

Science.gov (United States)

Ferrando, Albert; Zacarés, Mario; García-March, Miguel-Angel; Monsoriu, Juan A; de Córdoba, Pedro Fernández

2005-09-16

Using group theory arguments and numerical simulations, we demonstrate the possibility of changing the vorticity or topological charge of an individual vortex by means of the action of a system possessing a discrete rotational symmetry of finite order. We establish on theoretical grounds a "transmutation pass" determining the conditions for this phenomenon to occur and numerically analyze it in the context of two-dimensional optical lattices. An analogous approach is applicable to the problems of Bose-Einstein condensates in periodic potentials.

Vortex Transmutation

International Nuclear Information System (INIS)

Ferrando, Albert; Garcia-March, Miguel-Angel; Zacares, Mario; Monsoriu, Juan A.; Cordoba, Pedro Fernandez de

2005-01-01

Using group theory arguments and numerical simulations, we demonstrate the possibility of changing the vorticity or topological charge of an individual vortex by means of the action of a system possessing a discrete rotational symmetry of finite order. We establish on theoretical grounds a 'transmutation pass rule' determining the conditions for this phenomenon to occur and numerically analyze it in the context of two-dimensional optical lattices. An analogous approach is applicable to the problems of Bose-Einstein condensates in periodic potentials

Some observations concerning blade-element-momentum (BEM) methods and vortex wake methods, including numerical experiments with a simple vortex model

Energy Technology Data Exchange (ETDEWEB)

Snel, H. [Netherlands Energy Research Foundation ECN, Renewable Energy, Wind Energy (Netherlands)

1997-08-01

Recently the Blade Element Momentum (BEM) method has been made more versatile. Inclusion of rotational effects on time averaged profile coefficients have improved its achievements for performance calculations in stalled flow. Time dependence as a result of turbulent inflow, pitching actions and yawed operation is now treated more correctly (although more improvement is needed) than before. It is of interest to note that adaptations in modelling of unsteady or periodic induction stem from qualitative and quantitative insights obtained from free vortex models. Free vortex methods and further into the future Navier Stokes (NS) calculations, together with wind tunnel and field experiments, can be very useful in enhancing the potential of BEM for aero-elastic response calculations. It must be kept in mind however that extreme caution must be used with free vortex methods, as will be discussed in the following chapters. A discussion of the shortcomings and the strength of BEM and of vortex wake models is given. Some ideas are presented on how BEM might be improved without too much loss of efficiency. (EG)

A wind tunnel investigation of the effects of micro-vortex generators and Gurney flaps on the high-lift characteristics of a business jet wing. M.S. Thesis

Science.gov (United States)

Martuccio, Michelle Therese

1994-01-01

A study of a full-scale, semi-span business jet wing has been conducted to investigate the potential of two types of high-lift devices for improving aircraft high-lift performance. The research effort involved low-speed wind-tunnel tests of micro-vortex generators and Gurney flaps applied to the flap system of the business jet wing and included force and moment measurements, surface pressure surveys and flow visualization on the wing and flap. Results showed that the micro-vortex generators tested had no beneficial effects on the longitudinal force characteristics in this particular application, while the Gurney flaps were an effective means of increasing lift. However, the Gurney flaps also caused an increase in drag in most circumstances.

A Ground Systems Template for Remote Sensing Systems

Science.gov (United States)

McClanahan, Timothy P.; Trombka, Jacob I.; Floyd, Samuel R.; Truskowski, Walter; Starr, Richard D.; Clark, Pamela E.; Evans, Larry G.

2002-10-01

Spaceborne remote sensing using gamma and X-ray spectrometers requires particular attention to the design and development of reliable systems. These systems must ensure the scientific requirements of the mission within the challenging technical constraints of operating instrumentation in space. The Near Earth Asteroid Rendezvous (NEAR) spacecraft included X-ray and gamma-ray spectrometers (XGRS), whose mission was to map the elemental chemistry of the 433 Eros asteroid. A remote sensing system template, similar to a blackboard systems approach used in artificial intelligence, was identified in which the spacecraft, instrument, and ground system was designed and developed to monitor and adapt to evolving mission requirements in a complicated operational setting. Systems were developed for ground tracking of instrument calibration, instrument health, data quality, orbital geometry, solar flux as well as models of the asteroid's surface characteristics, requiring an intensive human effort. In the future, missions such as the Autonomous Nano-Technology Swarm (ANTS) program will have to rely heavily on automation to collectively encounter and sample asteroids in the outer asteroid belt. Using similar instrumentation, ANTS will require information similar to data collected by the NEAR X-ray/Gamma-Ray Spectrometer (XGRS) ground system for science and operations management. The NEAR XGRS systems will be studied to identify the equivalent subsystems that may be automated for ANTS. The effort will also investigate the possibility of applying blackboard style approaches to automated decision making required for ANTS.

A ground systems template for remote sensing systems

International Nuclear Information System (INIS)

McClanahan, Timothy P.; Trombka, Jacob I.; Floyd, Samuel R.; Truskowski, Walter; Starr, Richard D.; Clark, Pamela E.; Evans, Larry G.

2002-01-01

Spaceborne remote sensing using gamma and X-ray spectrometers requires particular attention to the design and development of reliable systems. These systems must ensure the scientific requirements of the mission within the challenging technical constraints of operating instrumentation in space. The Near Earth Asteroid Rendezvous (NEAR) spacecraft included X-ray and gamma-ray spectrometers (XGRS), whose mission was to map the elemental chemistry of the 433 Eros asteroid. A remote sensing system template, similar to a blackboard systems approach used in artificial intelligence, was identified in which the spacecraft, instrument, and ground system was designed and developed to monitor and adapt to evolving mission requirements in a complicated operational setting. Systems were developed for ground tracking of instrument calibration, instrument health, data quality, orbital geometry, solar flux as well as models of the asteroid's surface characteristics, requiring an intensive human effort. In the future, missions such as the Autonomous Nano-Technology Swarm (ANTS) program will have to rely heavily on automation to collectively encounter and sample asteroids in the outer asteroid belt. Using similar instrumentation, ANTS will require information similar to data collected by the NEAR X-ray/Gamma-Ray Spectrometer (XGRS) ground system for science and operations management. The NEAR XGRS systems will be studied to identify the equivalent subsystems that may be automated for ANTS. The effort will also investigate the possibility of applying blackboard style approaches to automated decision making required for ANTS

Progress in wind tunnel experimental techniques for wind turbine?

Institute of Scientific and Technical Information of China (English)

Jingping XIAO; Li CHEN; Qiang WANG; Qiao WANG

2016-01-01

Based on the unsteady aerodynamics experiment (UAE) phase VI and the model experiment in controlled conditions (MEXICO) projects and the related research carried out in China Aerodynamic Research and Development Center (CARDC), the recent progress in the wind tunnel experimental techniques for the wind turbine is sum-marized. Measurement techniques commonly used for di?erent types of wind tunnel ex-periments for wind turbine are reviewed. Important research achievements are discussed, such as the wind tunnel disturbance, the equivalence of the airfoil in?ow condition, the three-dimensional (3D) e?ect, the dynamic in?ow in?uence, the ?ow ?eld structure, and the vortex induction. The corresponding research at CARDC and some ideas on the large wind turbine are also introduced.

City of Flagstaff Project: Ground Water Resource Evaluation, Remote Sensing Component

Science.gov (United States)

Chavez, Pat S.; Velasco, Miguel G.; Bowell, Jo-Ann; Sides, Stuart C.; Gonzalez, Rosendo R.; Soltesz, Deborah L.

1996-01-01

Many regions, cities, and towns in the Western United States need new or expanded water resources because of both population growth and increased development. Any tools or data that can help in the evaluation of an area's potential water resources must be considered for this increasingly critical need. Remotely sensed satellite images and subsequent digital image processing have been under-utilized in ground water resource evaluation and exploration. Satellite images can be helpful in detecting and mapping an area's regional structural patterns, including major fracture and fault systems, two important geologic settings for an area's surface to ground water relations. Within the United States Geological Survey's (USGS) Flagstaff Field Center, expertise and capabilities in remote sensing and digital image processing have been developed over the past 25 years through various programs. For the City of Flagstaff project, this expertise and these capabilities were combined with traditional geologic field mapping to help evaluate ground water resources in the Flagstaff area. Various enhancement and manipulation procedures were applied to the digital satellite images; the results, in both digital and hardcopy format, were used for field mapping and analyzing the regional structure. Relative to surface sampling, remotely sensed satellite and airborne images have improved spatial coverage that can help study, map, and monitor the earth surface at local and/or regional scales. Advantages offered by remotely sensed satellite image data include: 1. a synoptic/regional view compared to both aerial photographs and ground sampling, 2. cost effectiveness, 3. high spatial resolution and coverage compared to ground sampling, and 4. relatively high temporal coverage on a long term basis. Remotely sensed images contain both spectral and spatial information. The spectral information provides various properties and characteristics about the surface cover at a given location or pixel

Review of commonly used remote sensing and ground-based ...

African Journals Online (AJOL)

This review provides an overview of the use of remote sensing data, the development of spectral reflectance indices for detecting plant water stress, and the usefulness of field measurements for ground-truthing purposes. Reliable measurements of plant water stress over large areas are often required for management ...

Theoretical tornado vortex model for nuclear plant design

International Nuclear Information System (INIS)

Sun, C.N.; Barnett, R.O.; Burdette, E.G.

1977-01-01

A simplified tornado vortex model is defined using fluid dynamics theory. Beginning with the Navier-Stokes equations of motion for an incompressible fluid and simpifying in a way consistent with a tornado wind field, develops the well-known cyclostrophic wind equation referred to by Hoecker and another equation which defines the tangential velocity profile. Together, they define a simplified tornado vertex model of which the Rankine and Hoecker vortices are special cases. Practical implications of the results obtained are discussed. (Auth.)

Aeroelastic analysis of large horizontal wind turbine baldes?

Institute of Scientific and Technical Information of China (English)

Di TANG; Zhiliang LU; Tongqing GUO

2016-01-01

A nonlinear aeroelastic analysis method for large horizontal wind turbines is described. A vortex wake method and a nonlinear ?nite element method (FEM) are coupled in the approach. The vortex wake method is used to predict wind turbine aero-dynamic loads of a wind turbine, and a three-dimensional (3D) shell model is built for the rotor. Average aerodynamic forces along the azimuth are applied to the structural model, and the nonlinear static aeroelastic behaviors are computed. The wind rotor modes are obtained at the static aeroelastic status by linearizing the coupled equations. The static aeroelastic performance and dynamic aeroelastic responses are calculated for the NH1500 wind turbine. The results show that structural geometrical nonlinearities signi?cantly reduce displacements and vibration amplitudes of the wind turbine blades. Therefore, structural geometrical nonlinearities cannot be neglected both in the static aeroelastic analysis and dynamic aeroelastic analysis.

An experimental study of the effect of external turbulence on the decay of a single vortex and a vortex pair

NARCIS (Netherlands)

van Jaarsveld, J.P.J.; Holten, A.P.C.; Elsenaar, A.; Trieling, R.R.; Heijst, van G.J.F.

2011-01-01

This study is concerned with the effect of external turbulence on the decay of vortices. Single vortices and vortex pairs were generated with wing(s) mounted in the sidewalls of a wind tunnel. The distance between the two vortices could be adjusted such that they just touched each other or

Velocity measurement by vortex shedding. Contribution to the mass-flow measurement

International Nuclear Information System (INIS)

Martinez Piquer, T.

1988-01-01

The phenomenon of vortex shedding has been known for centuries and has been the subject of scientific studies for about one hundred years. It is only in the ten last years that is has been applied to the measurement of fluids velocity. In 1878 F. Strouhal observed the vortex shedding phenomenon and shown that the shedding frequency of a wire vibrating in the wind was related to the wire diameter and the wind velocity. Rayleigh, who introduced the non-dimensional Strouhal number, von Karman and Rohsko, carried out extensive work or the subject which indicated that vortex shedding could form the basis for a new type of flowmeter. The thesis describes two parallel lines of investigation which study in depth the practical applications of vortex shedding. The first one deals with the measure of velocity and it presents the novelty of a bluff body with a cross-section which has not been used until this day. This body is a circular cylinder with a two-dimensional slit along the diameter and situated in crossdirection to the fluid's stream. It possesses excellent characteristics and it is the most stable as a vortex shedder, which gives it great advantage to the rest of the shapes used until now. The detection of the vortex has been performed by measuring the pressure changes generated by the vortex on two posts situated just beside the slit. To calculate the frequency of the vortex shedding, we obtain the difference of the mentioned signals, which are the same and 180 out of phase. Finding out the period of the autocorrelation function of this signal we can estimate the velocity of the fluid. A logical equipment based on a microprocessor has been designed for the calculation using a zero-crossing time algorithm implemented in assembler language. The second line of research refers to a new method of measure mass flow. The pressure signal generated by the vortex has an intensity which is proportional to the density and to the square of the velocity. Since we have already

Wind Loads on Structures

DEFF Research Database (Denmark)

Dyrbye, Claes; Hansen, Svend Ole

Wind loads have to be taken into account when designing civil engineering structures. The wind load on structures can be systematised by means of the wind load chain: wind climate (global), terrain (wind at low height), aerodynamic response (wind load to pressure), mechanical response (wind...... pressure to structural response) and design criteria. Starting with an introduction of the wind load chain, the book moves on to meteorological considerations, atmospheric boundary layer, static wind load, dynamic wind load and scaling laws used in wind-tunnel tests. The dynamic wind load covers vibrations...... induced by wind turbulence, vortex shedding, flutter and galloping. The book gives a comprehensive treatment of wind effects on structures and it will be useful for consulting engineers designing wind-sensitive structures. It will also be valuable for students of civil engineering as textbook...

Mesoscale spiral vortex embedded within a Lake Michigan snow squall band - High resolution satellite observations and numerical model simulations

Science.gov (United States)

Lyons, Walter A.; Keen, Cecil S.; Hjelmfelt, Mark; Pease, Steven R.

1988-01-01

It is known that Great Lakes snow squall convection occurs in a variety of different modes depending on various factors such as air-water temperature contrast, boundary-layer wind shear, and geostrophic wind direction. An exceptional and often neglected source of data for mesoscale cloud studies is the ultrahigh resolution multispectral data produced by Landsat satellites. On October 19, 1972, a clearly defined spiral vortex was noted in a Landsat-1 image near the southern end of Lake Michigan during an exceptionally early cold air outbreak over a still very warm lake. In a numerical simulation using a three-dimensional Eulerian hydrostatic primitive equation mesoscale model with an initially uniform wind field, a definite analog to the observed vortex was generated. This suggests that intense surface heating can be a principal cause in the development of a low-level mesoscale vortex.

Simulation of a MW rotor equipped with vortex generators using CFD and an actuator shape model

DEFF Research Database (Denmark)

Troldborg, Niels; Zahle, Frederik; Sørensen, Niels N.

2015-01-01

This article presents a comparison of CFD simulations of the DTU 10 MW reference wind turbine with and without vortex generators installed on the inboard part of the blades. The vortex generators are modelled by introducing body forces determined using a modified version of the so-called BAY mode...

A Parrinello-Rahman approach to vortex lattices

International Nuclear Information System (INIS)

Carretero-Gonzalez, R.; Kevrekidis, P.G.; Kevrekidis, I.G.; Maroudas, D.; Frantzeskakis, D.J.

2005-01-01

We present a framework for studying vortex lattice patterns and their structural transitions, using the Parrinello-Rahman (PR) method for molecular-dynamics (MD) simulations. Assuming an interaction between vortices derived from a Ginzburg-Landau field-theoretic context, we extract the ground-state of a 'vortex gas' using the PR-MD technique and find it to be a triangular pattern. Other patterns are also obtained for special initial conditions. Generalizations of the technique, such as the inclusion of external potentials or excitation of quadrupolar modes, are also commented upon

Three-Phased Wake Vortex Decay

Science.gov (United States)

Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.

2010-01-01

A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.

Ground-Based Remote or In Situ Measurement of Vertical Profiles of Wind in the Lower Troposphere

Energy Technology Data Exchange (ETDEWEB)

Clifton, Andrew; Newman, Jennifer

2017-02-24

Knowledge of winds in the lower troposphere is essential for a range of applications, including weather forecasting, transportation, natural hazards, and wind energy. This presentation focuses on the measurement of vertical profiles of wind in the lower troposphere for wind energy applications. This presentation introduces the information that wind energy site development and operations require, how it used, and the benefits and problems of current measurements from in-situ measurements and remote sensing. The development of commercial Doppler wind lidar systems over the last 10 years are shown, along with the lessons learned from this experience. Finally, potential developments in wind profiling aimed at reducing uncertainty and increasing data availability are introduced.

Vortex line topology during vortex tube reconnection

Science.gov (United States)

McGavin, P.; Pontin, D. I.

2018-05-01

This paper addresses reconnection of vortex tubes, with particular focus on the topology of the vortex lines (field lines of the vorticity). This analysis of vortex line topology reveals key features of the reconnection process, such as the generation of many small flux rings, formed when reconnection occurs in multiple locations in the vortex sheet between the tubes. Consideration of three-dimensional reconnection principles leads to a robust measurement of the reconnection rate, even once instabilities break the symmetry. It also allows us to identify internal reconnection of vortex lines within the individual vortex tubes. Finally, the introduction of a third vortex tube is shown to render the vortex reconnection process fully three-dimensional, leading to a fundamental change in the topological structure of the process. An additional interesting feature is the generation of vorticity null points.

Vortex Shedding from Tapered Cylinders at high Reynolds Numbers

DEFF Research Database (Denmark)

Johansson, Jens; Andersen, Michael Styrk; Christensen, Silas Sverre

2015-01-01

percent for strakes of circular cross section. The present paper argues that this height can be reduced for structures where the critical wind velocity for vortex shedding is in the Supercritical Reynolds number regime. The present investigations are aimed for suppressing VIV on offshore wind turbine......^5 (Supercritical). Results indicate that circular strakes with a diameter corresponding to 3 percent of the structures mean diameter can be used to efficiently reduce VIV in the Supercritical Reynolds number regime....

Dynamics of a vortex ring moving perpendicularly to the axis of a rotating fluid

NARCIS (Netherlands)

Eisenga, A.H.M.; Verzicco, R.; Heijst, van G.J.F.

1998-01-01

The dynamics of a vortex ring moving orthogonally to the rotation vector of a uniformly rotating fluid is analysed by laboratory experiments and numerical simulations. In the rotating system the vortex ring describes a curved trajectory, turning in the opposite sense to the system's anti-clockwise

Wind Tunnel Investigation of Passive Vortex Control and Vortex-Tail Interactions on a Slender Wing at Subsonic and Transonic Speeds

Science.gov (United States)

Erickson, Gary E.

2013-01-01

A wind tunnel experiment was conducted in the NASA Langley 8-Foot Transonic Pressure Tunnel to determine the effects of passive porosity on vortex flow interactions about a slender wing configuration at subsonic and transonic speeds. Flow-through porosity was applied in several arrangements to a leading-edge extension, or LEX, mounted to a 65-degree cropped delta wing as a longitudinal instability mitigation technique. Test data were obtained with LEX on and off in the presence of a centerline vertical tail and twin, wing-mounted vertical fins to quantify the sensitivity of the aerodynamics to tail placement and orientation. A close-coupled canard was tested as an alternative to the LEX as a passive flow control device. Wing upper surface static pressure distributions and six-component forces and moments were obtained at Mach numbers of 0.50, 0.85, and 1.20, unit Reynolds number of 2.5 million, angles of attack up to approximately 30 degrees, and angles of sideslip to +/-8 degrees. The off-surface flow field was visualized in cross planes on selected configurations using a laser vapor screen flow visualization technique. Tunnel-to-tunnel data comparisons and a Reynolds number sensitivity assessment were also performed. 15.

A numerical study of the stabilitiy of helical vortices using vortex methods

International Nuclear Information System (INIS)

Walther, J H; Guenot, M; Machefaux, E; Rasmussen, J T; Chatelain, P; Okulov, V L; Soerensen, J N; Bergdorf, M; Koumoutsakos, P

2007-01-01

We present large-scale parallel direct numerical simulations using particle vortex methods of the instability of the helical vortices. We study the instability of a single helical vortex and find good agreement with inviscid theory. We outline equilibrium configurations for three double helical vortices-similar to those produced by three blade wind turbines. The simulations confirm the stability of the inviscid model, but predict a breakdown of the vortical system due to viscosity

A numerical study of the stabilitiy of helical vortices using vortex methods

Energy Technology Data Exchange (ETDEWEB)

Walther, J H [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Guenot, M [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Machefaux, E [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Rasmussen, J T [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Chatelain, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Okulov, V L [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Soerensen, J N [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Bergdorf, M [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Koumoutsakos, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland)

2007-07-15

We present large-scale parallel direct numerical simulations using particle vortex methods of the instability of the helical vortices. We study the instability of a single helical vortex and find good agreement with inviscid theory. We outline equilibrium configurations for three double helical vortices-similar to those produced by three blade wind turbines. The simulations confirm the stability of the inviscid model, but predict a breakdown of the vortical system due to viscosity.

Numerical Simulation of the Aircraft Wake Vortex Flowfield

Science.gov (United States)

Ahmad, Nashat N.; Proctor, Fred H.; Perry, R. Brad

2013-01-01

The near wake vortex flowfield from a NACA0012 half-wing was simulated using a fully unstructured Navier-Stokes flow solver in three dimensions at a chord Reynolds number of 4.6 million and a Mach number of approximately 0.15. Several simulations were performed to examine the effect of boundary conditions, mesh resolution and turbulence scheme on the formation of wingtip vortex and its downstream propagation. The standard Spalart-Allmaras turbulence model was compared with the Dacles-Mariani and Spalart-Shur corrections for rotation and curvature effects. The simulation results were evaluated using the data from experiment performed at NASA Ames' 32in x 48in low speed wind tunnel.

Flight test operations using an F-106B research airplane modified with a wing leading-edge vortex flap

Science.gov (United States)

Dicarlo, Daniel J.; Brown, Philip W.; Hallissy, James B.

1992-01-01

Flight tests of an F-106B aircraft equipped with a leading-edge vortex flap, which represented the culmination of a research effort to examine the effectiveness of the flap, were conducted at the NASA Langley Research Center. The purpose of the flight tests was to establish a data base on the use of a wing leading-edge vortex flap as a means to validate the design and analysis methods associated with the development of such a vortical flow-control concept. The overall experiment included: refinements of the design codes for vortex flaps; numerous wind tunnel entries to aid in verifying design codes and determining basic aerodynamic characteristics; design and fabrication of the flaps, structural modifications to the wing tip and leading edges of the test aircraft; development and installation of an aircraft research instrumentation system, including wing and flap surface pressure measurements and selected structural loads measurements; ground-based simulation to assess flying qualities; and finally, flight testing. This paper reviews the operational aspects associated with the flight experiment, which includes a description of modifications to the research airplane, the overall flight test procedures, and problems encountered. Selected research results are also presented to illustrate the accomplishments of the research effort.

Vortex lattices in different configurations of periodic pinning line-arrays

International Nuclear Information System (INIS)

Lima, Clessio Leao S.; Cabral, Leonardo R.E.; Souza Silva, Clecio C. de; Aguiar, J. Albino

2006-01-01

The vortex lattice (VL) ground-state configurations are found using Monte Carlo (MC) simulated annealing with a local molecular dynamics (MD) in the London limit. We study the field dependence of the melting temperature for commensurate and incommensurate vortex lattices interacting with different periodic arrays of pinning. We also investigated the proliferation of topological defects and its dependence on the periodic pinning array symmetry and temperature

Adaptive computations of flow around a delta wing with vortex breakdown

Science.gov (United States)

Modiano, David L.; Murman, Earll M.

1993-01-01

An adaptive unstructured mesh solution method for the three-dimensional Euler equations was used to simulate the flow around a sharp edged delta wing. Emphasis was on the breakdown of the leading edge vortex at high angle of attack. Large values of entropy, which indicate vortical regions of the flow, specified the region in which adaptation was performed. The aerodynamic normal force coefficients show excellent agreement with wind tunnel data measured by Jarrah, and demonstrate the importance of adaptation in obtaining an accurate solution. The pitching moment coefficient and the location of vortex breakdown are compared with experimental data measured by Hummel and Srinivasan, showing good agreement in cases in which vortex breakdown is located over the wing.

Propagation of stochastic electromagnetic vortex beams through the turbulent biological tissues

Energy Technology Data Exchange (ETDEWEB)

Luo, Meilan; Chen, Qi; Hua, Limin; Zhao, Daomu, E-mail: zhaodaomu@yahoo.com

2014-01-10

The general analytical expression of the stochastic electromagnetic vortex beams through turbulent biological tissues is derived based on the fractal model. The statistical properties, including the spectral density, the spectral degree of coherence and the spectral degree of polarization are investigated in detail. It can be found that the normalized spectral density of the stochastic electromagnetic vortex beams with higher topological charge is less influenced by turbulence than that with lower topological charge. In addition, the change of the degree of polarization versus propagation distance of the anisotropic vortex beams in biological tissues differs from that of the isotropic vortex beams. The findings might be useful in the investigation of the structures of biological tissues and operation of communication and sensing systems involving biological tissues turbulence channels.

Vortex profiles and vortex interactions at the electroweak crossover

OpenAIRE

Chernodub, M. N.; Ilgenfritz, E. -M.; Schiller, A.

1999-01-01

Local correlations of Z-vortex operators with gauge and Higgs fields (lattice quantum vortex profiles) as well as vortex two-point functions are studied in the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs model. The vortex profiles resemble certain features of the classical vortex solutions in the continuum. The vortex-vortex interactions are analogous to the interactions of Abrikosov vortices in a type-I superconductor.

Magnetization reversal in circular vortex dots of small radius.

Science.gov (United States)

Goiriena-Goikoetxea, M; Guslienko, K Y; Rouco, M; Orue, I; Berganza, E; Jaafar, M; Asenjo, A; Fernández-Gubieda, M L; Fernández Barquín, L; García-Arribas, A

2017-08-10

We present a detailed study of the magnetic behavior of Permalloy (Ni 80 Fe 20 alloy) circular nanodots with small radii (30 nm and 70 nm) and different thicknesses (30 nm or 50 nm). Despite the small size of the dots, the measured hysteresis loops manifestly display the features of classical vortex behavior with zero remanence and lobes at high magnetic fields. This is remarkable because the size of the magnetic vortex core is comparable to the dot diameter, as revealed by magnetic force microscopy and micromagnetic simulations. The dot ground states are close to the border of the vortex stability and, depending on the dot size, the magnetization distribution combines attributes of the typical vortex, single domain states or even presents features resembling magnetic skyrmions. An analytical model of the dot magnetization reversal, accounting for the large vortex core size, is developed to explain the observed behavior, providing a rather good agreement with the experimental results. The study extends the understanding of magnetic nanodots beyond the classical vortex concept (where the vortex core spins have a negligible influence on the magnetic behavior) and can therefore be useful for improving emerging spintronic applications, such as spin-torque nano-oscillators. It also delimits the feasibility of producing a well-defined vortex configuration in sub-100 nm dots, enabling the intracellular magneto-mechanical actuation for biomedical applications.

Estimating cotton canopy ground cover from remotely sensed scene reflectance

International Nuclear Information System (INIS)

Maas, S.J.

1998-01-01

Many agricultural applications require spatially distributed information on growth-related crop characteristics that could be supplied through aircraft or satellite remote sensing. A study was conducted to develop and test a methodology for estimating plant canopy ground cover for cotton (Gossypium hirsutum L.) from scene reflectance. Previous studies indicated that a relatively simple relationship between ground cover and scene reflectance could be developed based on linear mixture modeling. Theoretical analysis indicated that the effects of shadows in the scene could be compensated for by averaging the results obtained using scene reflectance in the red and near-infrared wavelengths. The methodology was tested using field data collected over several years from cotton test plots in Texas and California. Results of the study appear to verify the utility of this approach. Since the methodology relies on information that can be obtained solely through remote sensing, it would be particularly useful in applications where other field information, such as plant size, row spacing, and row orientation, is unavailable

A Free Wake Numerical Simulation for Darrieus Vertical Axis Wind Turbine Performance Prediction

Science.gov (United States)

Belu, Radian

2010-11-01

In the last four decades, several aerodynamic prediction models have been formulated for the Darrieus wind turbine performances and characteristics. We can identified two families: stream-tube and vortex. The paper presents a simplified numerical techniques for simulating vertical axis wind turbine flow, based on the lifting line theory and a free vortex wake model, including dynamic stall effects for predicting the performances of a 3-D vertical axis wind turbine. A vortex model is used in which the wake is composed of trailing stream-wise and shedding span-wise vortices, whose strengths are equal to the change in the bound vortex strength as required by the Helmholz and Kelvin theorems. Performance parameters are computed by application of the Biot-Savart law along with the Kutta-Jukowski theorem and a semi-empirical stall model. We tested the developed model with an adaptation of the earlier multiple stream-tube performance prediction model for the Darrieus turbines. Predictions by using our method are shown to compare favorably with existing experimental data and the outputs of other numerical models. The method can predict accurately the local and global performances of a vertical axis wind turbine, and can be used in the design and optimization of wind turbines for built environment applications.

Inclined Jet in Crossflow Interacting with a Vortex Generator

Science.gov (United States)

Zaman, K. B. M. Q.; Rigby, D .L.; Heidmann, J. D.

2011-01-01

An experiment is conducted on the effectiveness of a vortex generator in preventing liftoff of a jet in crossflow, with possible relevance to film-cooling applications. The jet issues into the boundary layer at an angle of 20 degreees to the freestream. The effect of a triangular ramp-shaped vortex generator is studied while varying its geometry and location. Detailed flowfield properties are obtained for a case in which the height of the vortex generator and the diameter of the orifice are comparable with the approach boundary-layer thickness. The vortex generator produces a streamwise vortex pair with a vorticity magnitude 3 times larger (and of opposite sense) than that found in the jet in crossflow alone. Such a vortex generator appears to be most effective in keeping the jet attached to the wall. The effect of parametric variation is studied mostly from surveys 10 diameters downstream from the orifice. Results over a range of jet-to-freestream momentum flux ratio (1 vortex generator has a significant effect even at the highest J covered in the experiment. When the vortex generator height is halved, there is a liftoff of the jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensity. Varying the location of the vortex generator, over a distance of three diameters from the orifice, is found to have little impact. Rounding off the edges of the vortex generator with the increasing radius of curvature progressively diminishes its effect. However, allowing for a small radius of curvature may be quite tolerable in practice.

Vortex ring state by full-field actuator disc model

Energy Technology Data Exchange (ETDEWEB)

Soerensen, J.N.; Shen, W.Z.; Munduate, X. [DTU, Dept. of Energy Engineering, Lyngby (Denmark)

1997-08-01

One-dimensional momentum theory provides a simple analytical tool for analysing the gross flow behavior of lifting propellers and rotors. Combined with a blade-element strip-theory approach, it has for many years been the most popular model for load and performance predictions of wind turbines. The model works well at moderate and high wind velocities, but is not reliable at small wind velocities, where the expansion of the wake is large and the flow field behind the rotor dominated by turbulent mixing. This is normally referred to as the turbulent wake state or the vortex ring state. In the vortex ring state, momentum theory predicts a decrease of thrust whereas the opposite is found from experiments. The reason for the disagreement is that recirculation takes place behind the rotor with the consequence that the stream tubes past the rotor becomes effectively chocked. This represents a condition at which streamlines no longer carry fluid elements from far upstream to far downstream, hence one-dimensional momentum theory is invalid and empirical corrections have to be introduced. More sophisticated analytical or semi-analytical rotor models have been used to describe stationary flow fields for heavily loaded propellers. In recent years generalized actuator disc models have been developed, but up to now no detailed computations of the turbulent wake state or the vortex ring state have been performed. In the present work the phenomenon is simulated by direct simulation of the Navier-Stokes equations, where the influence of the rotor on the flow field is modelled simply by replacing the blades by an actuator disc with a constant normal load. (EG) 13 refs.

Wind measurements with SODAR during strong temperature inversions near the ground

International Nuclear Information System (INIS)

Thomas, P.; Vogt, S.

1989-08-01

SODAR (Sound Detection and Ranging) equipment has been increasingly used to measure vertical wind profiles with little expenditure in terms of staff, continuously over time and with a good spatial resolution. These informations serve as input variables for atmospheric transport and dispersion models, environmental monitoring of industrial facilities and, generally, for investigating a broad spectrum of meteorological phenomena. The SODAR principle has proved its suitability since long provided that the data recorded with SODAR have served to establish wind statistics valid for extended periods of time. At industrial sites potentially releasing substances prejudicial to health, e.g., chemical plants, nuclear power plants, etc., a SODAR must, moreover, be capable of measuring reliable the wind conditions also during short periods of release. This would, e.g., be important during accidental releases. Especially interesting situations for pollutant dispersion are distinct temperature inversions. It will be examined in this paper whether a SODAR is capable of measuring reliably the wind conditions also during those inversions. The selection of the situations of inversion as well as the direct intercomparison of data supplied by SODAR and conventional wind measuring instruments (anemometer and wind vane) are possible at the 200 m meteorological tower erected at the Karlsruhe Nuclear Research Center. The comparison between SODAR and the meteorological tower has shown that a SODAR is able to measure reliably the wind data also in situations characterized by strong ground-based and elevated inversions, respectively. (orig./KW) [de

On the effects of leading edge vortex generators on an OA209 airfoil

OpenAIRE

Heine, Benjamin; Mulleners, Karen; Gardner, Anthony; Mai, Holger

2009-01-01

Leading edge vortex generators have been found to significantly increase the aerodynamic performance of an airfoil under dynamic stall conditions. However, the principle of operation of these devices is still unclear. Therefore static wind and water tunnel experiments as well as CFD simulations have been conducted on a rotary aircraft wing profile OA209. A POD analysis applied to the vector fields generated by PIV measurements showed that the vortex generators break larger flow structures...

Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation

Science.gov (United States)

Saini, Aditya

The identification of inflow air data quantities such as airspeed, angle of attack, and local lift coefficient on various sections of a wing or rotor blade provides the capability for load monitoring, aerodynamic diagnostics, and control on devices ranging from air vehicles to wind turbines. Real-time measurement of aerodynamic parameters during flight provides the ability to enhance aircraft operating capabilities while preventing dangerous stall situations. This thesis presents a novel Leading-Edge Flow Sensing (LEFS) algorithm for the determination of the air -data parameters using discrete surface pressures measured at a few ports in the vicinity of the leading edge of a wing or blade section. The approach approximates the leading-edge region of the airfoil as a parabola and uses pressure distribution from the exact potential-ow solution for the parabola to _t the pressures measured from the ports. Pressures sensed at five discrete locations near the leading edge of an airfoil are given as input to the algorithm to solve the model using a simple nonlinear regression. The algorithm directly computes the inflow velocity, the stagnation-point location, section angle of attack and lift coefficient. The performance of the algorithm is assessed using computational and experimental data in the literature for airfoils under different ow conditions. The results show good correlation between the actual and predicted aerodynamic quantities within the pre-stall regime, even for a rotating blade section. Sensing the deviation of the aerodynamic behavior from the linear regime requires additional information on the location of ow separation on the airfoil surface. Bio-inspired artificial hair sensors were explored as a part of the current research for stall detection. The response of such artificial micro-structures can identify critical ow characteristics, which relate directly to the stall behavior. The response of the microfences was recorded via an optical microscope for

CFD Studies on Triangular Micro-Vortex Generators in Flow Control

Science.gov (United States)

Yashodhar, V.; Humrutha, G.; Kaushik, M.; Khan, S. A.

2017-03-01

In the present study, the flow characteristics of the commercially used S809 wind turbine airfoil controlled with triangular counter-rotating micro-vortex generators at stall angle of attack of 15 degrees and 10 m/s, 15 m/s and 20 m/s (speed range used in the wind turbine applications) had been computationally investigated. In addition to the controlled airfoil, an uncontrolled airfoil was also studied for the comparison. The modelling and analysis had been carried out using incompressible, Reynolds Averaged Navier Stokes equation using Spalart-Allmaras one equation turbulence model. The numerical computations were performed with SIMPLE algorithm. The velocity profiles at different locations on the suction surface were plotted for both uncontrolled and controlled airfoils. The shear stresses exerted on the upper surface of the airfoil in both the configurations were also compared. It is found that the controlled airfoil, the shear stress distribution was greatly increased near to trailing edge of the airfoil revealing the superiority of vortex generators in increasing the efficiency of wind turbine by delaying boundary layer separation. The qualitative results of flow visualization in the spanwise direction also support the quantitative findings of velocity profiles and shear stress distribution.

Prediction of the Effect of Vortex Generators on Airfoil Performance

DEFF Research Database (Denmark)

Sørensen, Niels N.; Zahle, Frederik; Bak, Christian

2014-01-01

Vortex Generators (VGs) are widely used by the wind turbine industry, to control the flow over blade sections. The present work describes a computational fluid dynamic procedure that can handle a geometrical resolved VG on an airfoil section. After describing the method, it is applied to two...... different airfoils at a Reynolds number of 3 million, the FFA- W3-301 and FFA-W3-360, respectively. The computations are compared with wind tunnel measurements from the Stuttgart Laminar Wind Tunnel with respect to lift and drag variation as function of angle of attack. Even though the method does...

Targets Mask U-Net for Wind Turbines Detection in Remote Sensing Images

Science.gov (United States)

Han, M.; Wang, H.; Wang, G.; Liu, Y.

2018-04-01

To detect wind turbines precisely and quickly in very high resolution remote sensing images (VHRRSI) we propose target mask U-Net. This convolution neural network (CNN), which is carefully designed to be a wide-field detector, models the pixel class assignment to wind turbines and their context information. The shadow, which is the context information of the target in this study, has been regarded as part of a wind turbine instance. We have trained the target mask U-Net on training dataset, which is composed of down sampled image blocks and instance mask blocks. Some post-processes have been integrated to eliminate wrong spots and produce bounding boxes of wind turbine instances. The evaluation metrics prove the reliability and effectiveness of our method for the average F1-score of our detection method is up to 0.97. The comparison of detection accuracy and time consuming with the weakly supervised targets detection method based on CNN illustrates the superiority of our method.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Galvis, J.A. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá (Colombia); National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States); Herrera, E.; Guillamón, I.; Vieira, S. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain); Suderow, H., E-mail: hermann.suderow@uam.es [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain)

2017-02-15

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

International Nuclear Information System (INIS)

Galvis, J.A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

2017-01-01

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

IEA Task 32: Wind Lidar Systems for Wind Energy Deployment (LIDAR)

Energy Technology Data Exchange (ETDEWEB)

Kuhn, Martin; Trabucchi, Davide; Clifton, Andrew; Courtney, Mike; Rettenmeier, Andreas

2016-05-25

Under the International Energy Agency Wind Implementing Agreement (IEA Wind) Task 11, researchers started examining novel applications for remote sensing and the issues around them during the 51st topical expert meeting about remote sensing in January 2007. The 59th topical expert meeting organized by Task 11 in October 2009 was also dedicated to remote sensing, and the first draft of the Task's recommended practices on remote sensing was published in January 2013. The results of the Task 11 topical expert meetings provided solid groundwork for a new IEA Wind Task 32 on wind lidar technologies. Members of the wind community identified the need to consolidate the knowledge about wind lidar systems to facilitate their use, and to investigate how to exploit the advantages offered by this technology. This was the motivation that led to the start of IEA Wind Task 32 'Lidar Application for Wind Energy Deployment' in November 2011. The kick-off was meeting was held in May 2012.

Vortex methods and vortex statistics

International Nuclear Information System (INIS)

Chorin, A.J.

1993-05-01

Vortex methods originated from the observation that in incompressible, inviscid, isentropic flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus if the vorticity is known at time t = 0, one can deduce the flow at a later time by simply following it around. In this narrow context, a vortex method is a numerical method that makes use of this observation. Even more generally, the analysis of vortex methods leads, to problems that are closely related to problems in quantum physics and field theory, as well as in harmonic analysis. A broad enough definition of vortex methods ends up by encompassing much of science. Even the purely computational aspects of vortex methods encompass a range of ideas for which vorticity may not be the best unifying theme. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (''blobs'') and those whose understanding contributes to the understanding of blob methods. Vortex methods for inviscid flow lead to systems of ordinary differential equations that can be readily clothed in Hamiltonian form, both in three and two space dimensions, and they can preserve exactly a number of invariants of the Euler equations, including topological invariants. Their viscous versions resemble Langevin equations. As a result, they provide a very useful cartoon of statistical hydrodynamics, i.e., of turbulence, one that can to some extent be analyzed analytically and more importantly, explored numerically, with important implications also for superfluids, superconductors, and even polymers. In the authors view, vortex ''blob'' methods provide the most promising path to the understanding of these phenomena

Dynamics of Venus' Southern hemisphere and South Polar Vortex from VIRTIS data obtained during the Venus Expres Mission

Science.gov (United States)

Hueso, R.; Garate-Lopez, I.; Sanchez-Lavega, A.

2011-12-01

The VIRTIS instrument onboard Venus Express observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet. The images have been used to trace the motions of the atmosphere at different layers of clouds [1-3]. We review the VIRTIS cloud image data and wind results obtained by different groups [1-3] and we present new results concerning the morphology and evolution of the South Polar Vortex at the upper and lower cloud levels with data covering the first 900 days of the mission. We present wind measurements of the South hemisphere obtained by cloud tracking individual cloud features and higher-resolution wind results of the polar region covering the evolution of the South polar vortex. The later were obtained by an image correlation algorithm run under human supervision to validate the data. We present day-side data of the upper clouds obtained at 380 and 980 nm sensitive to altitudes of 66-70 km, night-side data in the near infrared at 1.74 microns of the lower cloud (45-50 km) and day and night-side data obtained in the thermal infrared (wavelengths of 3.8 and 5.1 microns) which covers the dynamical evolution of Venus South Polar vortex at the cloud tops (66-70 km). We explore the different dynamics associated to the varying morphology of the vortex, its dynamical structure at different altitudes, the variability of the global wind data of the southern hemisphere and the interrelation of the polar vortex dynamics with the wind dynamics at subpolar and mid-latitudes. Acknowledgements: Work funded by Spanish MICIIN AYA2009-10701 with FEDER support and Grupos Gobierno Vasco IT-464-07. References [1] A. Sánchez-Lavega et al., Geophys. Res. Lett. 35, L13204, (2008). [2] D. Luz et al., Science, 332, 577-580 (2011). [3] R. Hueso, et al., Icarus doi:10.1016/j.icarus.2011.04.020 (2011)

Remote sensing of temperature and wind using acoustic travel-time measurements

Energy Technology Data Exchange (ETDEWEB)

Barth, Manuela; Fischer, Gabi; Raabe, Armin; Weisse, Frank [Leipzig Univ. (Germany). Inst. fuer Meteorologie; Ziemann, Astrid [Technische Univ. Dresden (Germany). Professur fuer Meteorologie

2013-04-15

A remote sensing technique to detect area-averaged temperature and flow properties within an area under investigation, utilizing acoustic travel-time measurements, is introduced. This technique uses the dependency of the speed of acoustic signals on the meteorological parameters temperature and wind along the propagation path. The method itself is scalable: It is applicable for investigation areas with an extent of some hundred square metres as well as for small-scale areas in the range of one square metre. Moreover, an arrangement of the acoustic transducers at several height levels makes it possible to determine profiles and gradients of the meteorological quantities. With the help of two examples the potential of this remote sensing technique for simultaneously measuring averaged temperature and flow fields is demonstrated. A comparison of time histories of temperature and wind values derived from acoustic travel-time measurements with point measurements shows a qualitative agreement whereas calculated root-mean-square errors differ for the two example applications. They amount to 1.4 K and 0.3 m/s for transducer distances of 60 m and 0.4 K and 0.2 m/s for transducer distances in the range of one metre. (orig.)

Vortex-vortex interactions in toroidally trapped Bose-Einstein condensates

OpenAIRE

Schulte, T.; Santos, L.; Sanpera, A.; Lewenstein, M.

2002-01-01

We analyze the vortex dynamics and vortex-vortex interactions in Bose-Einstein condensates confined in toroidal traps. We show that this particular geometry strongly distorts the vortex dynamics. The numerically calculated vortex trajectories are well explained by an analytical calculation based on image method and conformal mapping. Finally, the dissipation effects are discussed.

The use of ground reflecting boards in measuring wind turbine noise

International Nuclear Information System (INIS)

Henderson, A.R.; Mackinnon, A.; Benson, I.M.

1992-01-01

This paper gives an account of an experimental programme to assess the ground microphone measurement technique which can potentially increase the accuracy, reliability and confidence in wind turbine noise emission measurements. It shows that a 1 m diameter circular board can achieve acceptable accuracy and, since it is significantly more practical to use, could readily be adopted for international standards. (author)

Wind Streaks on Earth; Exploration and Interpretation

Science.gov (United States)

Cohen-Zada, Aviv Lee; Blumberg, Dan G.; Maman, Shimrit

2015-04-01

Wind streaks, one of the most common aeolian features on planetary surfaces, are observable on the surface of the planets Earth, Mars and Venus. Due to their reflectance properties, wind streaks are distinguishable from their surroundings, and they have thus been widely studied by remote sensing since the early 1970s, particularly on Mars. In imagery, these streaks are interpreted as the presence - or lack thereof - of small loose particles on the surface deposited or eroded by wind. The existence of wind streaks serves as evidence for past or present active aeolian processes. Therefore, wind streaks are thought to represent integrative climate processes. As opposed to the comprehensive and global studies of wind streaks on Mars and Venus, wind streaks on Earth are understudied and poorly investigated, both geomorphologically and by remote sensing. The aim of this study is, thus, to fill the knowledge gap about the wind streaks on Earth by: generating a global map of Earth wind streaks from modern high-resolution remotely sensed imagery; incorporating the streaks in a geographic information system (GIS); and overlaying the GIS layers with boundary layer wind data from general circulation models (GCMs) and data from the ECMWF Reanalysis Interim project. The study defines wind streaks (and thereby distinguishes them from other aeolian features) based not only on their appearance in imagery but more importantly on their surface appearance. This effort is complemented by a focused field investigation to study wind streaks on the ground and from a variety of remotely sensed images (both optical and radar). In this way, we provide a better definition of the physical and geomorphic characteristics of wind streaks and acquire a deeper knowledge of terrestrial wind streaks as a means to better understand global and planetary climate and climate change. In a preliminary study, we detected and mapped over 2,900 wind streaks in the desert regions of Earth distributed in

Sea Ice Thickness Measurement by Ground Penetrating Radar for Ground Truth of Microwave Remote Sensing Data

Science.gov (United States)

Matsumoto, M.; Yoshimura, M.; Naoki, K.; Cho, K.; Wakabayashi, H.

2018-04-01

Observation of sea ice thickness is one of key issues to understand regional effect of global warming. One of approaches to monitor sea ice in large area is microwave remote sensing data analysis. However, ground truth must be necessary to discuss the effectivity of this kind of approach. The conventional method to acquire ground truth of ice thickness is drilling ice layer and directly measuring the thickness by a ruler. However, this method is destructive, time-consuming and limited spatial resolution. Although there are several methods to acquire ice thickness in non-destructive way, ground penetrating radar (GPR) can be effective solution because it can discriminate snow-ice and ice-sea water interface. In this paper, we carried out GPR measurement in Lake Saroma for relatively large area (200 m by 300 m, approximately) aiming to obtain grand truth for remote sensing data. GPR survey was conducted at 5 locations in the area. The direct measurement was also conducted simultaneously in order to calibrate GPR data for thickness estimation and to validate the result. Although GPR Bscan image obtained from 600MHz contains the reflection which may come from a structure under snow, the origin of the reflection is not obvious. Therefore, further analysis and interpretation of the GPR image, such as numerical simulation, additional signal processing and use of 200 MHz antenna, are required to move on thickness estimation.

A concentrated outbreak of tornadoes, downbursts and microbursts, and implications regarding vortex classification

Science.gov (United States)

Forbes, G. S.; Wakimoto, R. M.

1983-01-01

A remarkable case of severe weather occurred near Springfield, Illinois on 6 August 1977. Aerial and ground surveys revealed that 17 cyclonic vortices, an anticyclonic vortex, 10 downbursts and 19 microbursts occurred in a limited (20 km x 40 km) area, associated with a bow-shaped radar echo. About half of the vortices appeared to have occurred along a gust front. Some of the others appear to have occurred within the circulation of a mesocyclone accompanying the bow echo, but these vortices seem to have developed specifically in response to localized boundary-layer vorticity generation associated with horizontal and vertical wind shears on the periphery of microbursts. Some of these vortices, and other destructive vortices in the literature, do not qualify as tornadoes as defined in the Glossary of Meteorology. A more pragmatic definition of a tornado is suggested.

Multi-site testing and evaluation of remote sensing instruments for wind energy applications

DEFF Research Database (Denmark)

Sanz Rodrigo, J.; Borbon Guillen, F.; Gomez Arranz, P.

2013-01-01

A procedure for testing and evaluation of remote sensing instruments that makes use of two test sites in flat and complex terrain is presented. To illustrate the method, a system intercomparison experiment is presented involving one sodar and two lidars (pulsed and continuous-wave). The wind...

Wind energy harvesting with a piezoelectric harvester

International Nuclear Information System (INIS)

Wu, Nan; Wang, Quan; Xie, Xiangdong

2013-01-01

An energy harvester comprising a cantilever attached to piezoelectric patches and a proof mass is developed for wind energy harvesting, from a cross wind-induced vibration of the cantilever, by the electromechanical coupling effect of piezoelectric materials. The vibration of the cantilever under the cross wind is induced by the air pressure owing to a vortex shedding phenomenon that occurs on the leeward side of the cantilever. To describe the energy harvesting process, a theoretical model considering the cross wind-induced vibration on the piezoelectric coupled cantilever energy harvester is developed, to calculate the charge and the voltage from the harvester. The influences of the length and location of the piezoelectric patches as well as the proof mass on the generated electric power are investigated. Results show that the total generated electric power can be as high as 2 W when the resonant frequency of the cantilever harvester is close to the vortex shedding frequency. Moreover, a value of total generated electric power up to 1.02 W can be practically realized for a cross wind with a variable wind velocity of 9–10 m s −1 by a harvester with a length of 1.2 m. This research facilitates an effective and compact wind energy harvesting device. (paper)

Wind turbine extraction from high spatial resolution remote sensing images based on saliency detection

Science.gov (United States)

Chen, Jingbo; Yue, Anzhi; Wang, Chengyi; Huang, Qingqing; Chen, Jiansheng; Meng, Yu; He, Dongxu

2018-01-01

The wind turbine is a device that converts the wind's kinetic energy into electrical power. Accurate and automatic extraction of wind turbine is instructive for government departments to plan wind power plant projects. A hybrid and practical framework based on saliency detection for wind turbine extraction, using Google Earth image at spatial resolution of 1 m, is proposed. It can be viewed as a two-phase procedure: coarsely detection and fine extraction. In the first stage, we introduced a frequency-tuned saliency detection approach for initially detecting the area of interest of the wind turbines. This method exploited features of color and luminance, was simple to implement, and was computationally efficient. Taking into account the complexity of remote sensing images, in the second stage, we proposed a fast method for fine-tuning results in frequency domain and then extracted wind turbines from these salient objects by removing the irrelevant salient areas according to the special properties of the wind turbines. Experiments demonstrated that our approach consistently obtains higher precision and better recall rates. Our method was also compared with other techniques from the literature and proves that it is more applicable and robust.

Application of Distributed Optical Fiber Sensing Technique in Monitoring the Ground Deformation

Directory of Open Access Journals (Sweden)

Jin Liu

2017-01-01

Full Text Available The monitoring of ground deformation is important for the prevention and control of geological disaster including land subsidence, ground fissure, surface collapse, and landslides. In this study, a distributed optical fiber sensing technique based on Brillouin Optical Time-Domain Analysis (BOTDA was used to monitor the ground deformation. The principle behind the BOTDA is first introduced, and then laboratory calibration test and physical model test were carried out. Finally, BOTDA-based monitoring of ground fissure was carried out in a test site. Experimental results show that the distributed optical fiber can measure the soil strain during ground deformation process, and the strain curve responded to the soil compression and tension region clearly. During field test in Wuxi City, China, the ground fissures deformation area was monitored accurately and the trend of deformation can also be achieved to forecast and warn against the ground fissure hazards.

The AMPTE program's contribution to studies of the solar wind-magnetosphere-ionosphere interaction

International Nuclear Information System (INIS)

Sibeck, D.G.

1990-01-01

The Active Magnetospheric Particle Tracer Explorers (AMPTE) program provided important information on the behavior of clouds of plasma artificially injected into the solar wind and the earth's magnetosphere. Now that the releases are over, data from the satellites are being analyzed to investigate the processes by which the ambient solar wind mass, momentum, and energy are transferred to the magnetosphere. Work in progress at APL indicates that the solar wind is much more inhomogeneous than previously believed, that the solar wind constantly buffets the magnetosphere, and that ground observers may remotely sense these interactions as geomagnetic pulsations. 8 refs

Unsteady aerodynamic analysis for offshore floating wind turbines under different wind conditions.

Science.gov (United States)

Xu, B F; Wang, T G; Yuan, Y; Cao, J F

2015-02-28

A free-vortex wake (FVW) model is developed in this paper to analyse the unsteady aerodynamic performance of offshore floating wind turbines. A time-marching algorithm of third-order accuracy is applied in the FVW model. Owing to the complex floating platform motions, the blade inflow conditions and the positions of initial points of vortex filaments, which are different from the fixed wind turbine, are modified in the implemented model. A three-dimensional rotational effect model and a dynamic stall model are coupled into the FVW model to improve the aerodynamic performance prediction in the unsteady conditions. The effects of floating platform motions in the simulation model are validated by comparison between calculation and experiment for a small-scale rigid test wind turbine coupled with a floating tension leg platform (TLP). The dynamic inflow effect carried by the FVW method itself is confirmed and the results agree well with the experimental data of a pitching transient on another test turbine. Also, the flapping moment at the blade root in yaw on the same test turbine is calculated and compares well with the experimental data. Then, the aerodynamic performance is simulated in a yawed condition of steady wind and in an unyawed condition of turbulent wind, respectively, for a large-scale wind turbine coupled with the floating TLP motions, demonstrating obvious differences in rotor performance and blade loading from the fixed wind turbine. The non-dimensional magnitudes of loading changes due to the floating platform motions decrease from the blade root to the blade tip. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Experimental parameter study for passive vortex generators on a 30% thick airfoil

NARCIS (Netherlands)

Baldacchino, D.; Simao Ferreira, C.; De Tavernier, D.A.M.; Timmer, W.A.; van Bussel, G.J.W.

2018-01-01

Passive vane-type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach

Remotely sensed data fusion for offshore wind energy resource mapping; Fusion de donnees satellitaires pour la cartographie du potentiel eolien offshore

Energy Technology Data Exchange (ETDEWEB)

Ben Ticha, M.B

2007-11-15

Wind energy is a component of an energy policy contributing to a sustainable development. Last years, offshore wind parks have been installed offshore. These parks benefit from higher wind speeds and lower turbulence than onshore. To sit a wind park, it is necessary to have a mapping of wind resource. These maps are needed at high spatial resolution to show wind energy resource variations at the scale of a wind park. Wind resource mapping is achieved through the description of the spatial variations of statistical parameters characterizing wind climatology. For a precise estimation of these statistical parameters, high temporal resolution wind speed and direction measurements are needed. However, presently, there is no data source allying high spatial resolution and high temporal resolution. We propose a data fusion method taking advantage of the high spatial resolution of some remote sensing instruments (synthetic aperture radars) and the high temporal resolution of other remote sensing instruments (scatterometers). The data fusion method is applied to a case study and the results quality is assessed. The results show the pertinence of data fusion for the mapping of wind energy resource offshore. (author)

Vortex-induced dynamic loads on a non-spinning volleyball

Science.gov (United States)

Qing-ding, Wei; Rong-sheng, Lin; Zhi-jie, Liu

1988-09-01

An experiment on vortex-induced dynamic loads on a non-spinning Volleyball was conducted in a wind tunnel. The flow past the Volleyball was visualized, and the aerodynamic load was measured by use of a strain gauge balance. The separation on the Volleyball was measured with hot-film. The experimental results suggest that under the action of an unstable tail vortex system the separation region is changeable, and that the fluctuation of drag and lateral forces is the same order of magnitude as the mean drag, no matter whether the seam of the Volleyball is symmetric or asymmetric, with regard to the flow. Based on the experimental data a numerical simulation of Volleyball swerve motion was made.

Boundary Layer Flow Control by an Array of Ramp-Shaped Vortex Generators

Science.gov (United States)

Zaman, K. B. M. Q.; Hirt, S. M.; Bencic, T. J.

2012-01-01

Flow field survey results for the effect of ramp-shaped vortex generators (VG) on a turbulent boundary layer are presented. The experiments are carried out in a low-speed wind tunnel and the data are acquired primarily by hot-wire anemometry. Distributions of mean velocity and turbulent stresses as well as streamwise vorticity, on cross-sectional planes at various downstream locations, are obtained. These detailed flow field properties, including the boundary layer characteristics, are documented with the primary objective of aiding possible computational investigations. The results show that VG orientation with apex upstream, that produces a downwash directly behind it, yields a stronger pair of streamwise vortices. This is in contrast to the case with apex downstream that produces a pair of vortices of opposite sense. Thus, an array of VG s with the former orientation, usually considered for film-cooling application, may also be superior for mixing enhancement and boundary layer separation control. The data files can be found on a supplemental CD.

Estimates of the effectiveness of automatic control in alleviating wake vortex induced roll excursions

Science.gov (United States)

Tinling, B. E.

1977-01-01

Estimates of the effectiveness of a model following type control system in reducing the roll excursion due to a wake vortex encounter were obtained from single degree of freedom computations with inputs derived from the results of wind tunnel, flight, and simulation experiments. The analysis indicates that the control power commanded by the automatic system must be roughly equal to the vortex induced roll acceleration if effective limiting of the maximum bank angle is to be achieved.

Regimes of Vorticity in the Wake of a Rectangular Vortex Generator

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver

2011-01-01

This paper concerns the study of the secondary structures generated in the wake of a wall mounted rectangular vane, commonly referred to as a vortex generator. The study has been conducted by Stereoscopic PIV measurements in a wind tunnel and supplementary flow visualizations in a water channel...

Experimental benchmark and code validation for airfoils equipped with passive vortex generators

International Nuclear Information System (INIS)

Baldacchino, D; Ferreira, C; Florentie, L; Timmer, N; Van Zuijlen, A; Manolesos, M; Chaviaropoulos, T; Diakakis, K; Papadakis, G; Voutsinas, S; González Salcedo, Á; Aparicio, M; García, N R.; Sørensen, N N.; Troldborg, N

2016-01-01

Experimental results and complimentary computations for airfoils with vortex generators are compared in this paper, as part of an effort within the AVATAR project to develop tools for wind turbine blade control devices. Measurements from two airfoils equipped with passive vortex generators, a 30% thick DU97W300 and an 18% thick NTUA T18 have been used for benchmarking several simulation tools. These tools span low-to-high complexity, ranging from engineering-level integral boundary layer tools to fully-resolved computational fluid dynamics codes. Results indicate that with appropriate calibration, engineering-type tools can capture the effects of vortex generators and outperform more complex tools. Fully resolved CFD comes at a much higher computational cost and does not necessarily capture the increased lift due to the VGs. However, in lieu of the limited experimental data available for calibration, high fidelity tools are still required for assessing the effect of vortex generators on airfoil performance. (paper)

SEA ICE THICKNESS MEASUREMENT BY GROUND PENETRATING RADAR FOR GROUND TRUTH OF MICROWAVE REMOTE SENSING DATA

Directory of Open Access Journals (Sweden)

M. Matsumoto

2018-04-01

Full Text Available Observation of sea ice thickness is one of key issues to understand regional effect of global warming. One of approaches to monitor sea ice in large area is microwave remote sensing data analysis. However, ground truth must be necessary to discuss the effectivity of this kind of approach. The conventional method to acquire ground truth of ice thickness is drilling ice layer and directly measuring the thickness by a ruler. However, this method is destructive, time-consuming and limited spatial resolution. Although there are several methods to acquire ice thickness in non-destructive way, ground penetrating radar (GPR can be effective solution because it can discriminate snow-ice and ice-sea water interface. In this paper, we carried out GPR measurement in Lake Saroma for relatively large area (200 m by 300 m, approximately aiming to obtain grand truth for remote sensing data. GPR survey was conducted at 5 locations in the area. The direct measurement was also conducted simultaneously in order to calibrate GPR data for thickness estimation and to validate the result. Although GPR Bscan image obtained from 600MHz contains the reflection which may come from a structure under snow, the origin of the reflection is not obvious. Therefore, further analysis and interpretation of the GPR image, such as numerical simulation, additional signal processing and use of 200 MHz antenna, are required to move on thickness estimation.

Analysis and model-tests on vortex-induced oscillation of bridges; Kyoryo no uzu reishin ni kansuru sanjigen oto kaiseki to fudo jikken

Energy Technology Data Exchange (ETDEWEB)

Yamamura, N. [Hitachi Zosen Corp., Osaka (Japan); Ogasawara, M. [Kansai Electric Power Co. Inc., Osaka (Japan); Shiraishi, N. [Maizuru College of Technology, Kyoto (Japan); Nanjo, M.

1996-07-21

In order to predict the three-dimensional response to vortex-induced oscillation of bridges, a model was investigated using the aerodynamic force coefficient including vortex-induced and self-excited forces, and the nonlinear response coefficient expressing constancy of response to vortex-induced oscillation. In the analysis, change of frequency in wind by the self-excited force, aerodynamic damping term, effect of the mode, and correlation of the vortex-induced force along member axis were taken into account. The aerodynamic force and nonlinear response coefficients were identified from the homogeneous and turbulent flow results of wind tunnel tests using a two-dimensional spring support rigid body model with varied damping factor. The aerodynamic damping term can be estimated from the nonlinear aerodynamic force coefficient, but it was enough to calculate it from the quasi-stationary coefficient in general bridge profiles. The correlation of the vortex-induced force was obtained from measurements of the vertical variation components of trailing flow under the resonance state, or the pressure distribution of the member surface. When comparing to the wind tunnel test of three-dimensional model of cable-stayed bridge, the response amplitude by the present analysis method was consistent well with the test results rather than by the method in which the amplitude of two-dimensional model was corrected. 10 refs., 4 figs., 3 tabs.

The Energy Budget of a Southwest Vortex With Heavy Rainfall over South China

Institute of Scientific and Technical Information of China (English)

FU Shenming; SUN Jianhua; ZHAO Sixiong; LI Wanli

2011-01-01

Energy budgets were analyzed to study the development of an eastward propagating southwest vortex (SWV) associated with heavy rainfall over southern China (11-13 June 2008). The results show that kinetic energy (KE) generation and a dvection were the most important KE sources, while friction and sub-grid processes were the main KE sinks. There was downward conversion from divergent to rotational wind KE consistent with the downward stretching of SWVs. The Coriolis force was important for the formation and maintenance of the SWV. Convergence was also an important factor for maintenance, as was vertical motion during the mature stage of the SWV and the formation stage of a newly formed vortex (vortex B). The conversion from available potential energy (APE) to KE of divergent wind can lead to strong convection. Vertical motion influenced APE by dynamical and thermal processes which had opposite effects.The variation of APE was related to the heavy rainfall and convection; in this case, vertical motion with direct thermal circulation was the most important way in which APE was released, while latent heat release and vertical temperature advection were important for APE generation.

Remote Sensing Marine Ecology: Wind-driven algal blooms in the open oceans and their ecological impacts

Science.gov (United States)

Tang, DanLing

2016-07-01

Algal bloom not only can increase the primary production but also could result in negative ecological consequence, e.g., Harmful Algal Blooms (HABs). According to the classic theory for the formation of algal blooms "critical depth" and "eutrophication", oligotrophic sea area is usually difficult to form a large area of algal blooms, and actually the traditional observation is only sporadic capture to the existence of algal blooms. Taking full advantage of multiple data of satellite remote sensing, this study: 1), introduces "Wind-driven algal blooms in open oceans: observation and mechanisms" It explained except classic coastal Ekman transport, the wind through a variety of mechanisms affecting the formation of algal blooms. Proposed a conceptual model of "Strong wind -upwelling-nutrient-phytoplankton blooms" in Western South China Sea (SCS) to assess role of wind-induced advection transport in phytoplankton bloom formation. It illustrates the nutrient resources that support long-term offshore phytoplankton blooms in the western SCS; 2), Proposal of the theory that "typhoons cause vertical mixing, induce phytoplankton blooms", and quantify their important contribution to marine primary production; Proposal a new ecological index for typhoon. Proposed remote sensing inversion models. 3), Finding of the spatial and temporaldistributions pattern of harmful algal bloom (HAB)and species variations of HAB in the South Yellow Sea and East China Sea, and in the Pearl River estuary, and their oceanic dynamic mechanisms related with monsoon; The project developed new techniques and generated new knowledge, which significantly improved understanding of the formation mechanisms of algal blooms. 1), It proposed "wind-pump" mechanism integrates theoretical system combing "ocean dynamics, development of algal blooms, and impact on primary production", which will benefit fisheries management. 2), A new interdisciplinary subject "Remote Sensing Marine Ecology"(RSME) has been

Computing the flow past Vortex Generators : Comparison between RANS Simulations and Experiments

NARCIS (Netherlands)

Manolesos, M.; Sorensen, NN; Troldborg, N.; Florentie, L.; Papadakis, G; Voutsinas, S.

2016-01-01

The flow around a wind turbine airfoil equipped with Vortex Generators (VGs) is examined. Predictions from three different Reynolds Averaged Navier Stokes (RANS) solvers with two different turbulence models and two different VG modelling approaches are compared between them and with experimental

Mapping degenerate vortex states in a kagome lattice of elongated antidots via scanning Hall probe microscopy

Science.gov (United States)

Xue, C.; Ge, J.-Y.; He, A.; Zharinov, V. S.; Moshchalkov, V. V.; Zhou, Y. H.; Silhanek, A. V.; Van de Vondel, J.

2017-07-01

We investigate the degeneracy of the superconducting vortex matter ground state by directly visualizing the vortex configurations in a kagome lattice of elongated antidots via scanning Hall probe microscopy. The observed vortex patterns, at specific applied magnetic fields, are in good agreement with the configurations obtained using time-dependent Ginzburg-Landau simulations. Both results indicate that the long-range interaction in this nanostructured superconductor is unable to lift the degeneracy between different vortex states and the pattern formation is mainly ruled by the nearest-neighbor interaction. This simplification makes it possible to identify a set of simple rules characterizing the vortex configurations. We demonstrate that these rules can explain both the observed vortex distributions and the magnetic-field-dependent degree of degeneracy.

Retrieval of liquid water cloud properties from ground-based remote sensing observations

NARCIS (Netherlands)

Knist, C.L.

2014-01-01

Accurate ground-based remotely sensed microphysical and optical properties of liquid water clouds are essential references to validate satellite-observed cloud properties and to improve cloud parameterizations in weather and climate models. This requires the evaluation of algorithms for retrieval of

Copepod behavior response to Burgers' vortex treatments mimicking turbulent eddies

Science.gov (United States)

Elmi, D.; Webster, D. R.; Fields, D. M.

2017-11-01

Copepods detect hydrodynamic cues in the water by their mechanosensory setae. We expect that copepods sense the flow structure of turbulent eddies in order to evoke behavioral responses that lead to population-scale distribution patterns. In this study, the copepods' response to the Burgers' vortex is examined. The Burgers' vortex is a steady-state solution of three-dimensional Navier-Stokes equations that allows us to mimic turbulent vortices at the appropriate scale and eliminate the stochastic nature of turbulence. We generate vortices in the laboratory oriented in the horizontal and vertical directions each with four intensity levels. The objective of including vortex orientation as a parameter in the study is to quantify directional responses that lead to vertical population distribution patterns. The four intensity levels correspond to target vortex characteristics of eddies corresponding to the typical dissipative vortices in isotropic turbulence with mean turbulent dissipation rates in the range of 0.002 to 0.25 cm2/s3. These vortices mimic the characteristics of eddies that copepods most likely encounter in coastal zones. We hypothesize that the response of copepods to hydrodynamic features depends on their sensory architecture and relative orientation with respect to gravity. Tomo-PIV is used to quantify the vortex circulation and axial strain rate for each vortex treatment. Three-dimensional trajectories of the copepod species Calanus finmarchicus are analyzed to examine their swimming kinematics in and around the vortex to quantify the hydrodynamic cues that trigger their behavior.

Regional stratospheric warmings in the Pacific-Western Canada (PWC sector during winter 2004/2005: implications for temperatures, winds, chemical constituents and the characterization of the Polar vortex

Directory of Open Access Journals (Sweden)

A. H. Manson

2008-11-01

Full Text Available The vortex during winter 2004/2005 was interesting for several reasons. It has been described as "cold" stratospherically, with relatively strong westerly winds. Losses of ozone until the final warming in March were considerable, and comparable to the cold 1999–2000 winter. There were also modest warming events, indicated by peaks in 10 hPa zonal mean temperatures at high latitudes, near 1 January and 1 February. Events associated with a significant regional stratospheric warming in the Pacific-Western Canada (PWC sector then began and peaked toward the end of February, providing strong longitudinal variations in dynamical characteristics (Chshyolkova et al., 2007; hereafter C07. The associated disturbed vortex of 25 February was displaced from the pole and either elongated (upper or split into two cyclonic centres (lower. Observations from Microwave Limb Sounder (MLS on Aura are used here to study the thermal characteristics of the stratosphere in the Canadian-US (253° E and Scandinavian-Europe (16° E sectors. Undisturbed high latitude stratopause (55 km zonal mean temperatures during the mid-winter (December–February reached 270 K, warmer than empirical-models such as CIRA-86, suggesting that seasonal polar warming due to dynamical influences affects the high altitude stratosphere as well as the mesosphere. There were also significant stratopause differences between Scandinavia and Canada during the warming events of 1 January and 1 February, with higher temperatures near 275 K at 16° E. During the 25 February "PWC" event a warming occurred at low and middle stratospheric heights (10–30 km: 220 K at 253° E and the stratopause cooled; while over Scandinavia-Europe the stratosphere below ~30 km was relatively cold at 195 K and the stratopause became even warmer (>295 K and lower (~45 km. The zonal winds followed the associated temperature gradients so that the vertical and latitudinal gradients of the winds differed strongly between

Piezoelectric Wind Energy Harvesting from Self-Excited Vibration of Square Cylinder

Directory of Open Access Journals (Sweden)

Junlei Wang

2016-01-01

Full Text Available Self-excited vibration of a square cylinder has been considered as an effective way in harvesting piezoelectric wind energy. In present work, both of the vortex-induced vibration and unstable galloping phenomenon process are investigated in a reduced velocity (Ur=U/ωn·D range of 4≤Ur≤20 with load resistance ranging in 100 Ω≤R≤1 MΩ. The vortex-induced vibration covers presynchronization, synchronization, and postsynchronization branches. An aeroelectromechanical model is given to describe the coupling of the dynamic equation of the fluid-structure interaction and the equation of Gauss law. The effects of load resistance are investigated in both the open-circuit and close-circuit system by a linear analysis, which covers the parameters of the transverse displacement, aerodynamic force, output voltage, and harvested power utilized to measure the efficiency of the system. The highest level of the transverse displacement and the maximum value of harvested power of synchronization branch during the vortex-induced vibration and galloping are obtained. The results show that the large-amplitude galloping at high wind speeds can generate energy. Additionally, energy can be harvested by utilization of the lock-in phenomenon of vortex-induced vibration under low wind speed.

Cascade Analysis of a Floating Wind Turbine Rotor

International Nuclear Information System (INIS)

Eliassen, Lene; Jakobsen, Jasna B; Knauer, Andreas; Nielsen, Finn Gunnar

2014-01-01

Mounting a wind turbine on a floating foundation introduces more complexity to the aerodynamic loading. The floater motion contains a wide range of frequencies. To study some of the basic dynamic load effect on the blades due to these motions, a two-dimensional cascade approach, combined with a potential vortex method, is used. This is an alternative method to study the aeroelastic behavior of wind turbines that is different from the traditional blade element momentum method. The analysis tool demands little computational power relative to a full three dimensional vortex method, and can handle unsteady flows. When using the cascade plane, a ''cut'' is made at a section of the wind turbine blade. The flow is viewed parallel to the blade axis at this cut. The cascade model is commonly used for analysis of turbo machineries. Due to the simplicity of the code it requires little computational resources, however it has limitations in its validity. It can only handle two-dimensional potential flow, i.e. including neither three-dimensional effects, such as the tip loss effect, nor boundary layers and stall effects are modeled. The computational tool can however be valuable in the overall analysis of floating wind turbines, and evaluation of the rotor control system. A check of the validity of the vortex panel code using an airfoil profile is performed, comparing the variation of the lift force, to the theoretically derived Wagner function. To analyse the floating wind turbine, a floating structure with hub height 90 m is chosen. An axial motion of the rotor is considered

Review of Methodologies for Offshore Wind Resource Assessment in European Seas

DEFF Research Database (Denmark)

Sempreviva, Anna Maria; Barthelmie, Rebecca Jane; Pryor, Sara

2008-01-01

promising wind farm sites and (ii) a site specific evaluation of wind climatology and vertical profiles of wind and atmospheric turbulence, in addition to an assessment of historical and possibly future changes due to climate non-stationarity. Phase (i) of the process can involve use of in situ observations......The wind resource offshore is generally larger than at geographically nearby onshore sites, which can offset the higher installation, operation and maintenance costs associated with offshore wind parks. Successful offshore wind energy development relies to some extent on accurate prediction of wind......) of the project often still requires in situ observations (which may or may not be supplemented with ground-based remote sensing technologies) and application of tools to provide a climatological context for the resulting measurements. Current methodologies for undertaking these aspects of the resource assessment...

Ground-based transmission line conductor motion sensor

International Nuclear Information System (INIS)

Jacobs, M.L.; Milano, U.

1988-01-01

A ground-based-conductor motion-sensing apparatus is provided for remotely sensing movement of electric-power transmission lines, particularly as would occur during the wind-induced condition known as galloping. The apparatus is comprised of a motion sensor and signal-generating means which are placed underneath a transmission line and will sense changes in the electric field around the line due to excessive line motion. The detector then signals a remote station when a conditioning of galloping is sensed. The apparatus of the present invention is advantageous over the line-mounted sensors of the prior art in that it is easier and less hazardous to install. The system can also be modified so that a signal will only be given when particular conditions, such as specific temperature range, large-amplitude line motion, or excessive duration of the line motion, are occurring

Remotely sensed wind speed predicts soaring behaviour in a wide-ranging pelagic seabird.

Science.gov (United States)

Gibb, Rory; Shoji, Akiko; Fayet, Annette L; Perrins, Chris M; Guilford, Tim; Freeman, Robin

2017-07-01

Global wind patterns affect flight strategies in many birds, including pelagic seabirds, many of which use wind-powered soaring to reduce energy costs during at-sea foraging trips and migration. Such long-distance movement patterns are underpinned by local interactions between wind conditions and flight behaviour, but these fine-scale relationships are far less well understood. Here we show that remotely sensed ocean wind speed and direction are highly significant predictors of soaring behaviour in a migratory pelagic seabird, the Manx shearwater ( Puffinus puffinus ). We used high-frequency GPS tracking data (10 Hz) and statistical behaviour state classification to identify two energetic modes in at-sea flight, corresponding to flap-like and soar-like flight. We show that soaring is significantly more likely to occur in tailwinds and crosswinds above a wind speed threshold of around 8 m s -1 , suggesting that these conditions enable birds to reduce metabolic costs by preferentially soaring over flapping. Our results suggest a behavioural mechanism by which wind conditions may shape foraging and migration ecology in pelagic seabirds, and thus indicate that shifts in wind patterns driven by climate change could impact this and other species. They also emphasize the emerging potential of high-frequency GPS biologgers to provide detailed quantitative insights into fine-scale flight behaviour in free-living animals. © 2017 The Author(s).

Multipath Suppression with an Absorber for UWB Wind Turbine Blade Deflection Sensing Systems

DEFF Research Database (Denmark)

Zhang, Shuai; Franek, Ondrej; Eggers, Patrick Claus F.

2017-01-01

The deflection of a wind turbine blade can be monitored with an ultra-wideband (UWB) deflection sensing system which consists of one transmitting antenna at the blade tip and two receiving antennas at the blade root. The blade deflection is calculated by two estimated tip-root antenna distances...... verifications of the proposed method are carried out with different full-blade measurements. From all the results, it is found that the proposed technique can efficiently suppress multipath for the in-blade tip antenna, and improve the pulse wave front fidelity, so that the UWB sensing system can also...

Questions-answers - Ground-based wind energy

International Nuclear Information System (INIS)

2017-11-01

After a presentation of some key data on wind energy in France, this publication proposes a set of questions and answers to highlight the reasons of the development of wind energy, to show that wind energy is a reliable one, to discuss various issues related to the presence of wind turbines (regulations, information, impact on biodiversity, on health and on dwelling environment, exploitation and control, end of life), and to determine the role of wind energy in the French economy (economic returns, costs, and so on)

MetaSensing's FastGBSAR: ground based radar for deformation monitoring

Science.gov (United States)

Rödelsperger, Sabine; Meta, Adriano

2014-10-01

The continuous monitoring of ground deformation and structural movement has become an important task in engineering. MetaSensing introduces a novel sensor system, the Fast Ground Based Synthetic Aperture Radar (FastGBSAR), based on innovative technologies that have already been successfully applied to airborne SAR applications. The FastGBSAR allows the remote sensing of deformations of a slope or infrastructure from up to a distance of 4 km. The FastGBSAR can be setup in two different configurations: in Real Aperture Radar (RAR) mode it is capable of accurately measuring displacements along a linear range profile, ideal for monitoring vibrations of structures like bridges and towers (displacement accuracy up to 0.01 mm). Modal parameters can be determined within half an hour. Alternatively, in Synthetic Aperture Radar (SAR) configuration it produces two-dimensional displacement images with an acquisition time of less than 5 seconds, ideal for monitoring areal structures like dams, landslides and open pit mines (displacement accuracy up to 0.1 mm). The MetaSensing FastGBSAR is the first ground based SAR instrument on the market able to produce two-dimensional deformation maps with this high acquisition rate. By that, deformation time series with a high temporal and spatial resolution can be generated, giving detailed information useful to determine the deformation mechanisms involved and eventually to predict an incoming failure. The system is fully portable and can be quickly installed on bedrock or a basement. The data acquisition and processing can be fully automated leading to a low effort in instrument operation and maintenance. Due to the short acquisition time of FastGBSAR, the coherence between two acquisitions is very high and the phase unwrapping is simplified enormously. This yields a high density of resolution cells with good quality and high reliability of the acquired deformations. The deformation maps can directly be used as input into an Early

PIV Measurements of Flows around the Wind Turbines with a Flanged-Diffuser Shroud

Institute of Scientific and Technical Information of China (English)

Kazuhiko Toshimitsu; Koutarou Nishikawa; Wataru Haruki; Shinichi Oono; Manabu Takao; Yuji Ohya

2008-01-01

The wind turbines with a flanged-diffuser shroud -so called "wind lens turbine"- are developed as one of high performance wind turbines by Ohya et al. In order to investigate the flow characteristics and flow acceleration, the paper presents the flow velocity measurements of a long-type and a compact-type wind turbines with a flanged-diffuser shroud by particle image velocimetry. In the case of the long type wind turbine, the velocity vec-tors of the inner flow field of the diffuser for turbine blades rotating and no blades rotating are presented at Rey-nolds number, 0.9x105. Furthermore the flow fields between with and without rotating are compared. Through the PIV measurement results, one can realize that the turbine blades rotating affects as suppress the disturbance and the flow separation near the inner wall of the diffuser. The time average velocity vectors are made on the av-erage of the instantaneous velocity data. There are two large vortices in downstream region of the diffuser. One vortex behind the flange acts as suck in wind to the diffuser and raise the inlet flow velocity. Another large vortex appears in downstream. It might be act as blockage vortex of main flow. The large blockage vortex is not clear in the instantaneous velocity vectors, however it exists clearly in the time average flow field. The flow field around the wind turbine with a compact-type flanged-diffuser shroud is also investigated. The flow pattern behind the flange of the compact-type turbine is the same as the long-type one. It means that the effect of flow acceleration is caused by the unsteady vortices behind the flange. The comparison with CFD and PIV results of meridional time-average streamlines after the compact-type diffuser is also presented.

The interaction of counter-rotating strained vortex pairs with a third vortex

International Nuclear Information System (INIS)

Higgins, Keith; Ooi, Andrew; Chong, M S; Ruetten, Markus

2009-01-01

The vortex dynamics caused by the interaction of counter-rotating Burgers vortex pairs with a third Burgers vortex in a straining flow is investigated numerically. These interactions blend vortex merging and cancellation effects, and the aim is to investigate how the third vortex might influence the evolution of the vortex pair. Many different choices of initial conditions for the pair and third vortex exist, so attention is restricted to a class of initial conditions in which the vortex pair initially moves in the general direction of vortex 3, and the distance from vortex 3 to the line of free propagation of the vortex pair is the 'offset' parameter δ. A series of calculations with 0≤δ≤4 reveals three types of intermediate-time vortex dynamics that are called merging, swapping and switching. The evolution of the vortex core separation and core vorticity level diagnostics are used to determine the points of transition from merging to swapping and switching. In the longer term, vortex merging, cancellation and straining reduces the three vortices to a single vortex. Other diagnostics of interest are also monitored, including the spatial distributions of the rate of viscous dissipation and terms contributing to the vorticity transport equation. During the merging phase for the case with δ=0, double-peak and double-trough structures are observed in the dissipation-rate contours. In addition, the diffusion of vorticity dominates the vortex-stretching effect near vortex 1 during its absorbtion by vortex 3. Finally, the dynamics of the three vortices are also examined by computing a co-rotating angular velocity and stream function. A series of peaks in the co-rotating angular velocity is found to be associated with the conservation of angular momentum and interactions with a 'ghost' vortex in the co-rotating stream function.

Protection from ground faults in the stator winding of generators at power plants in the Siberian networks

International Nuclear Information System (INIS)

Vainshtein, R. A.; Lapin, V. I.; Naumov, A. M.; Doronin, A. V.; Yudin, S. M.

2010-01-01

The experience of many years of experience in developing and utilization of ground fault protection in the stator winding of generators in the Siberian networks is generalized. The main method of protection is to apply a direct current or an alternating current with a frequency of 25 Hz to the primary circuits of the stator. A direct current is applied to turbo generators operating in a unit with a transformer without a resistive coupling to the external grid or to other generators. Applying a 25 Hz control current is appropriate for power generation systems with compensation of a capacitive short circuit current to ground. This method forms the basis for protection of generators operating on busbars, hydroelectric generators with a neutral grounded through an arc-suppression reactor, including in consolidated units with generators operating in parallel on a single low-voltage transformer winding.

Compressible Vortex Ring

Science.gov (United States)

Elavarasan, Ramasamy; Arakeri, Jayawant; Krothapalli, Anjaneyulu

1999-11-01

The interaction of a high-speed vortex ring with a shock wave is one of the fundamental issues as it is a source of sound in supersonic jets. The complex flow field induced by the vortex alters the propagation of the shock wave greatly. In order to understand the process, a compressible vortex ring is studied in detail using Particle Image Velocimetry (PIV) and shadowgraphic techniques. The high-speed vortex ring is generated from a shock tube and the shock wave, which precedes the vortex, is reflected back by a plate and made to interact with the vortex. The shadowgraph images indicate that the reflected shock front is influenced by the non-uniform flow induced by the vortex and is decelerated while passing through the vortex. It appears that after the interaction the shock is "split" into two. The PIV measurements provided clear picture about the evolution of the vortex at different time interval. The centerline velocity traces show the maximum velocity to be around 350 m/s. The velocity field, unlike in incompressible rings, contains contributions from both the shock and the vortex ring. The velocity distribution across the vortex core, core diameter and circulation are also calculated from the PIV data.

导叶对涡轮型垂直轴风力机气动性能的影响%Effects of guiding vanes on aerodynamic performance of vortex vertical axis wind turbine

Institute of Scientific and Technical Information of China (English)

原红红; 赵振宙; 郑源; 黄娟

2013-01-01

To overcome the problem of low efficiency of the traditional vertical axis wind turbine, the structural advantages of the wind turbine with guiding vanes are introduced and the effects of guiding vanes on the vortex vertical axis wind turbine are analyzed in detail. Based on computational fluid dynamics theory, the slippage mesh technique and the k-ε model were used to compare the aerodynamic performance of the vortex vertical axis wind turbine with and without guiding vanes at a design velocity of 12 m/s. Studies have shown that the guiding vanes can effectively prevent the direct impact of the coming flow from acting on the suction section of the blade in the upwind area so as to decrease the drag torque, while the guiding vanes also negatively affect the performance of blades in the downwind area, but the positive effect of the former is more significant, so the performance of a wind turbine with guiding vanes greatly improves. The vortex vertical axis wind turbine with arc-type guiding vanes has a wider operating range, higher optimum tip speed ratio, and higher aerodynamic efficiency. The maximum wind power coefficient can reach 0.24 .%针对传统垂直轴风力机效率低的缺陷,阐述带导叶垂直轴风力机的结构优势,并分析导叶对涡轮型垂直轴风力机的作用。应用计算流体力学理论,在设计风速12 m/s下,采用滑移网格技术及k-着模型对有、无导叶两种涡轮型垂直轴风力机的气动性能进行比较。研究表明,导叶可以有效降低由于来流对逆风区叶片吸力面的直接冲击而造成的阻力扭矩,也会负面影响顺风区叶片的性能,但其负作用效果远不及在逆风区挡流降阻的正作用效果,故加导叶后风轮的性能会有很大提高。带弧线形导叶涡轮型垂直轴风力机最大风能利用系数可达0.24,具有工作范围广、最佳尖速比大的特点。

Topological structures of vortex flow on a flying wing aircraft, controlled by a nanosecond pulse discharge plasma actuator

Science.gov (United States)

Du, Hai; Shi, Zhiwei; Cheng, Keming; Wei, Dechen; Li, Zheng; Zhou, Danjie; He, Haibo; Yao, Junkai; He, Chengjun

2016-06-01

Vortex control is a thriving research area, particularly in relation to flying wing or delta wing aircraft. This paper presents the topological structures of vortex flow on a flying wing aircraft controlled by a nanosecond plasma dielectric barrier discharge actuator. Experiments, including oil flow visualization and two-dimensional particle image velocimetry (PIV), were conducted in a wind tunnel with a Reynolds number of 0.5 × 106. Both oil and PIV results show that the vortex can be controlled. Oil topological structures on the aircraft surface coincide with spatial PIV flow structures. Both indicate vortex convergence and enhancement when the plasma discharge is switched on, leading to a reduced region of separated flow.

Wind farm related mortality among avian migrants - a remote sensing study and model analysis

Energy Technology Data Exchange (ETDEWEB)

Desholm, M

2006-11-15

This thesis is the result of a PhD study on bird-wind farm collisions and consists of a synopsis, five published papers, one submitted manuscript and another ready for submission. The papers describe the findings from pre- and post-construction visual, radar and thermal imaging studies (1999-2006) of migrating birds at the Nysted offshore wind farm in the Baltic Sea, Denmark. This thesis poses and answers the following questions: a) what hazard factors do offshore wind farming pose to wild birds, b) how should one choose the key focal species to study, c) how can remote sensing techniques be applied to the study of bird wind farm interactions, and d) specifically, how do water birds react when approaching an offshore wind farm? The main aim of the study was the development of a predictive bird-wind farm collision model that incorporates the avoidance rate of birds at multiple scales. Out of 235,136 migrating sea ducks only 47 individuals were predicted to collide with the wind turbine rotor-blades, equivalent to an overall mean collision risk of c. 0.02%. This thesis shows the added value of modelling in supplementing sound empirical studies in accessing the effects of major human development pressures on migratory bird populations. (au)

Fuzzy logic based variable speed wind generation system

Energy Technology Data Exchange (ETDEWEB)

Simoes, M.G. [Sao Paulo Univ., SP (Brazil). Escola Politecnica. PMC - Mecatronica; Bose, B.K. [Tennessee Univ., Knoxville, TN (United States). Dept. of Electrical Engineering; Spiegel, Ronal J. [Environmental Protection Agency, Research Triangle Park, NC (United States). Air and Energy Engineering Research Lab.

1996-12-31

This work demonstrates the successful application of fuzzy logic to enhance the performance and control of a variable speed wind generation system. A maximum power point tracker control is performed with three fuzzy controllers, without wind velocity measurement, and robust to wind vortex and turbine torque ripple. A squirrel cage induction generator feeds the power to a double-sided PWM converter system which pumps the power to a utility grid or supplies to an autonomous system. The fuzzy logic controller FLC-1 searches on-line the generator speed so that the aerodynamic efficiency of the wind turbine is optimized. A second fuzzy controller FLC-2 programs the machine flux by on-line search so as to optimize the machine-converter system wind vortex. Detailed analysis and simulation studies were performed for development of the control strategy and fuzzy algorithms, and a DSP TMS320C30 based hardware with C control software was built for the performance evaluation of a laboratory experimental set-up. The theoretical development was fully validated and the system is ready to be reproduced in a higher power installation. (author) 7 refs., 3 figs., 1 tab.

An evaluation of the WindEye wind lidar

DEFF Research Database (Denmark)

Dellwik, Ebba; Sjöholm, Mikael; Mann, Jakob

Prevision of the wind field by remote sensing wind lidars has the potential to improve the performance of wind turbines. The functionality of a WindEye lidar developed by Windar Photonics A/S (Denmark) for the wind energy market was tested in a two months long field experiment. The WindEye sensor...... with a high accuracy during the whole campaign....

Wind farm related mortality among avian migrants - a remote sensing study and model analysis

DEFF Research Database (Denmark)

Desholm, M.

,136 migrating sea ducks only 47 individuals were predicted to collide with the wind turbine rotor-blades, equivalent to an overall mean collision risk of c. 0.02%. This thesis shows the added value of modelling in supplementing sound empirical studies in accessing the effects of major human development......This thesis is the result of a PhD study on bird-wind farm collisions and consists of a synopsis, five published papers, one submitted manuscript and another ready for submission. The papers describe the fi ndings from pre- and post-construction visual, radar and thermal imaging studies (1999......-2006) of migrating birds at the Nysted offshore wind farm in the Baltic Sea, Denmark. This thesis poses and answers the following questions: a) what hazard factors do offshore wind farming pose to wild birds, b) how should one choose the key focal species to study, c) how can remote sensing techniques be applied...

A classical model wind turbine wake “blind test” revisited by remote sensing lidars

DEFF Research Database (Denmark)

Sjöholm, Mikael; Angelou, Nikolas; Nielsen, Morten Busk

2017-01-01

One of the classical model wind turbine wake “blind test” experiments1 conducted in the boundary-layer wind tunnel at NTNU in Trondheim and used for benchmarking of numerical flow models has been revisited by remote sensing lidars in a joint experiment called “Lidars For Wind Tunnels” (L4WT) under...... was D=0.894 m and it was designed for a tip speed ratio (TSR) of 6. However, the TSRs used were 3, 6, and 10 at a free-stream velocity of 10 m/s. Due to geometrical constraints imposed by for instance the locations of the wind tunnel windows, all measurements were performed in the very same vertical...... cross-section of the tunnel and the various down-stream distances of the wake, i.e. 1D, 3D, and 5D were achieved by re-positioning the turbine. The approach used allows for unique studies of the influence of the inherent lidar spatial filtering on previously both experimentally and numerically well...

Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors

Directory of Open Access Journals (Sweden)

Shi-Jun Ge

2017-10-01

Full Text Available Liquid crystal (LC is a promising candidate for terahertz (THz devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual component. Thus, a separating process is indispensable. Here, we introduce a gradient blazed phase, and propose a THz LC forked polarization grating that can simultaneously generate and separate pure THz vortices with opposite circular polarization. The specific LC gradient-rotation directors are implemented by a photoalignment technique. The generated THz vortex beams are characterized with a THz imaging system, verifying features of polarization controllability. This work may pave a practical road towards generating, separating and polarizing THz vortex beams, and may prompt applications in THz communications, sensing and imaging.

Technical Evaluation Report, Part A - Vortex Flow and High Angle of Attack

Science.gov (United States)

Luckring, James M.

2003-01-01

A symposium entitled Vortex Flow and High Angle of Attack was held in Loen, Norway, from May 7 through May 11, 2001. The Applied Vehicle Technology (AVT) panel, under the auspices of the Research and Technology Organization (RTO), sponsored this symposium. Forty-eight papers, organized into nine sessions, addressed computational and experimental studies of vortex flows pertinent to both aircraft and maritime applications. The studies also ranged from fundamental fluids investigations to flight test results, and significant results were contributed from a broad range of countries. The principal emphasis of this symposium was on "the understanding and prediction of separation-induced vortex flows and their effects on military vehicle performance, stability, control, and structural design loads." It was further observed by the program committee that "separation- induced vortex flows are an important part of the design and off-design performance of conventional fighter aircraft and new conventional or unconventional manned or unmanned advanced vehicle designs (UAVs, manned aircraft, missiles, space planes, ground-based vehicles, and ships)." The nine sessions addressed the following topics: vortical flows on wings and bodies, experimental techniques for vortical flows, numerical simulations of vortical flows, vortex stability and breakdown, vortex flows in maritime applications, vortex interactions and control, vortex dynamics, flight testing, and vehicle design. The purpose of this paper is to provide brief reviews of these papers along with some synthesizing perspectives toward future vortex flow research opportunities. The paper includes the symposium program. (15 refs.)

Fast vortex oscillations in a ferrimagnetic disk near the angular momentum compensation point

Science.gov (United States)

Kim, Se Kwon; Tserkovnyak, Yaroslav

2017-07-01

We theoretically study the oscillatory dynamics of a vortex core in a ferrimagnetic disk near its angular momentum compensation point, where the spin density vanishes but the magnetization is finite. Due to the finite magnetostatic energy, a ferrimagnetic disk of suitable geometry can support a vortex as a ground state similar to a ferromagnetic disk. In the vicinity of the angular momentum compensation point, the dynamics of the vortex resemble those of an antiferromagnetic vortex, which is described by equations of motion analogous to Newton's second law for the motion of particles. Owing to the antiferromagnetic nature of the dynamics, the vortex oscillation frequency can be an order of magnitude larger than the frequency of a ferromagnetic vortex, amounting to tens of GHz in common transition-metal based alloys. We show that the frequency can be controlled either by applying an external field or by changing the temperature. In particular, the latter property allows us to detect the angular momentum compensation temperature, at which the lowest eigenfrequency attains its maximum, by performing ferromagnetic resonance measurements on the vortex disk. Our work proposes a ferrimagnetic vortex disk as a tunable source of fast magnetic oscillations and a useful platform to study the properties of ferrimagnets.

Hydrodynamic pressure sensing with an artificial lateral line in steady and unsteady flows

International Nuclear Information System (INIS)

Venturelli, Roberto; Akanyeti, Otar; Visentin, Francesco; Fiorini, Paolo; Ježov, Jaas; Toming, Gert; Kruusmaa, Maarja; Chambers, Lily D; Brown, Jennifer; Megill, William M

2012-01-01

With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Kármán vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Kármán vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Kármán vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Kármán vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Kármán vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors. (paper)

Vortex configuration and vortex-vortex interaction in nano-structured superconductors

International Nuclear Information System (INIS)

Kato, Masaru; Niwa, Yuhei; Suematsu, Hisataka; Ishida, Takekazu

2012-01-01

We study the vortex structures and quasi-particle structures in nano-structured superconductors. We used the Bogoliubov-de Gennes equation and the finite element method and obtained stable magnetic flux structures and the quasi-particle states. We found the vortex configurations are affected by the interference of the quasi-particle bound states around the vortices. In order to clarify the interference between the quasi-particle wave-functions around two vortices we have developed a numerical method using the elliptic coordinates and the Mathieu functions. We apply this method to two singly quantized vortex state in a conventional s-wave superconductor and a pair of half-quantum vortices in a chiral p-wave superconductor.

Influences of some parameters on the performance of a small vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Dumitrache Alexandru

2016-01-01

Full Text Available The effects of various parameters on the performance of a straight bladed vertical axis wind turbine, using the vortex model, have been numerically investigated. A vortex model has been used to evaluate the performance of a vertical axis wind turbine, by means of aerodynamic characteristics of different airfoils for Reynolds numbers between 105 and 106. Parameters such as the thickness and the camber of the blade airfoil, the solidity, the type of blade profile, the number of blades and the pitch angle, which influence the power coefficient, CP, and the start-up regime. This study can be used in the designing an optimal vertical axis wind turbine in a specific location, when the prevailed wind regime is known.

Flow analysis of vortex generators on wing sections by stereoscopic particle image velocimetry measurements

DEFF Research Database (Denmark)

Velte, Clara Marika; Hansen, Martin Otto Laver; Cavar, Dalibor

2008-01-01

a wind turbine blade. The low Reynolds number is chosen on the basis that this is a fundamental investigation of the structures of the flow induced by vortex generators and the fact that one obtains a thicker boundary layer and larger structures evoked by the actuating devices, which are easier...... generators are applied. The idea behind the experiments is that the results will be offered for validation of modeling of the effect of vortex generators using various numerical codes. Initial large eddy simulation (LES) computations have been performed that show the same qualitative behaviour...

Advances in High Energy Solid-State 2-micron Laser Transmitter Development for Ground and Airborne Wind and CO2 Measurements

Science.gov (United States)

Singh, Upendra N.; Yu, Jirong; Petros, Mulugeta; Chen, Songsheng; Kavaya, Michael J.; Trieu, Bo; Bai, Yingxin; Petzar, Paul; Modlin, Edward A.; Koch, Grady;

Paleogene Vertebrate Paleontology, Geology and Remote Sensing in the Wind River Basin

Science.gov (United States)

Stucky, R. K.; Krishtalka, L.

1985-01-01

Biostratigraphic and lithostratigraphic studies were used to correlate different events in the geologic evolution of the northeastern part of the Wind River Basin and have suggested several conclusions. Laterally equivalent exposures of the Lysite member from Cedar Ridge to Bridger Creek show a gradation in lithology from interbedded boulder conglomerates and sandstones to interbedded lenticular sandstones and mudstones to interbedded carbonaceous shales, coals and tabular sandstones. This gradation suggests a shift from alluvial fan to braided stream to paludal or lacustrine sedimentary environments during the late early Eocene. The Lysite and Lost Cabin members of the Wind River Formation are in fault contact in the Bridger Creek area and may intertongue to the east along Cedar Ridge. Ways in which remote sensing could be used in these studies are discussed.

Lidar-based Research and Innovation at DTU Wind Energy - a Review

Science.gov (United States)

Mikkelsen, T.

2014-06-01

As wind turbines during the past decade have increased in size so have the challenges met by the atmospheric boundary-layer meteorologists and the wind energy society to measure and characterize the huge-volume wind fields surpassing and driving them. At the DTU Wind Energy test site "Østerild" for huge wind turbines, the hub-height of a recently installed 8 MW Vestas V164 turbine soars 143 meters up above the ground, and its rotor of amazing 164 meters in diameter make the turbine tips flicker 225 meters into the sky. Following the revolution in photonics-based telecommunication at the turn of the Millennium new fibre-based wind lidar technologies emerged and DTU Wind Energy, at that time embedded within Rise National Laboratory, began in collaboration with researchers from wind lidar companies to measure remote sensed wind profiles and turbulence structures within the atmospheric boundary layer with the emerging, at that time new, all-fibre-based 1.55 μ coherent detection wind lidars. Today, ten years later, DTU Wind Energy routinely deploys ground-based vertical profilers instead of met masts for high-precision measurements of mean wind profiles and turbulence profiles. At the departments test site "Høvsøre" DTU Wind Energy also routinely calibrate and accredit wind lidar manufactures wind lidars. Meanwhile however, new methodologies for power curve assessment based on ground-based and nacelle based lidars have also emerged. For improving the turbines power curve assessments and for advancing their control with feed-forward wind measurements experience has also been gained with wind lidars installed on turbine nacelles and integrated into the turbines rotating spinners. A new mobile research infrastructure WindScanner.dk has also emerged at DTU Wind Energy. Wind and turbulence fields are today scanned from sets of three simultaneously in space and time synchronized scanning lidars. One set consists of three fast scanning continuous-wave based wind lidars

A Comparison of Two Above-Ground Biomass Estimation Techniques Integrating Satellite-Based Remotely Sensed Data and Ground Data for Tropical and Semiarid Forests in Puerto Rico

Science.gov (United States)

Two above-ground forest biomass estimation techniques were evaluated for the United States Territory of Puerto Rico using predictor variables acquired from satellite based remotely sensed data and ground data from the U.S. Department of Agriculture Forest Inventory Analysis (FIA)...

A multipole-expanded effective field theory for vortex ring-sound interactions

Science.gov (United States)

Garcia-Saenz, Sebastian; Mitsou, Ermis; Nicolis, Alberto

2018-02-01

The low-energy dynamics of a zero temperature superfluid or of the compressional modes of an ordinary fluid can be described by a simple effective theory for a scalar field — the superfluid `phase'. However, when vortex lines are present, to describe all interactions in a local fashion one has to switch to a magnetic-type dual two-form description, which comes with six degrees of freedom (in place of one) and an associated gauge redundancy, and is thus considerably more complicated. Here we show that, in the case of vortex rings and for bulk modes that are much longer than the typical ring size, one can perform a systematic multipole expansion of the effective action and recast it into the simpler scalar field language. In a sense, in the presence of vortex rings the non-single valuedness of the scalar can be hidden inside the rings, and thus out of the reach of the multipole expansion. As an application of our techniques, we compute by standard effective field theory methods the sound emitted by an oscillating vortex ring.

Wind effects on long-span bridges: Probabilistic wind data format for buffeting and VIV load assessments

Science.gov (United States)

Hoffmann, K.; Srouji, R. G.; Hansen, S. O.

2017-12-01

The technology development within the structural design of long-span bridges in Norwegian fjords has created a need for reformulating the calculation format and the physical quantities used to describe the properties of wind and the associated wind-induced effects on bridge decks. Parts of a new probabilistic format describing the incoming, undisturbed wind is presented. It is expected that a fixed probabilistic format will facilitate a more physically consistent and precise description of the wind conditions, which in turn increase the accuracy and considerably reduce uncertainties in wind load assessments. Because the format is probabilistic, a quantification of the level of safety and uncertainty in predicted wind loads is readily accessible. A simple buffeting response calculation demonstrates the use of probabilistic wind data in the assessment of wind loads and responses. Furthermore, vortex-induced fatigue damage is discussed in relation to probabilistic wind turbulence data and response measurements from wind tunnel tests.

Comparisons of Crosswind Velocity Profile Estimates Used in Fast-Time Wake Vortex Prediction Models

Science.gov (United States)

Pruis, Mathew J.; Delisi, Donald P.; Ahmad, Nashat N.

2011-01-01

Five methods for estimating crosswind profiles used in fast-time wake vortex prediction models are compared in this study. Previous investigations have shown that temporal and spatial variations in the crosswind vertical profile have a large impact on the transport and time evolution of the trailing vortex pair. The most important crosswind parameters are the magnitude of the crosswind and the gradient in the crosswind shear. It is known that pulsed and continuous wave lidar measurements can provide good estimates of the wind profile in the vicinity of airports. In this study comparisons are made between estimates of the crosswind profiles from a priori information on the trajectory of the vortex pair as well as crosswind profiles derived from different sensors and a regional numerical weather prediction model.

Vortex survival in 3D self-gravitating accretion discs

Science.gov (United States)

Lin, Min-Kai; Pierens, Arnaud

2018-04-01

Large-scale, dust-trapping vortices may account for observations of asymmetric protoplanetary discs. Disc vortices are also potential sites for accelerated planetesimal formation by concentrating dust grains. However, in 3D discs vortices are subject to destructive `elliptic instabilities', which reduces their viability as dust traps. The survival of vortices in 3D accretion discs is thus an important issue to address. In this work, we perform shearing box simulations to show that disc self-gravity enhances the survival of 3D vortices, even when self-gravity is weak in the classic sense (e.g. with a Toomre Q ≃ 5). We find a 3D, self-gravitating vortex can grow on secular timescales in spite of the elliptic instability. The vortex aspect-ratio decreases as it strengthens, which feeds the elliptic instability. The result is a 3D vortex with a turbulent core that persists for ˜103 orbits. We find when gravitational and hydrodynamic stresses become comparable, the vortex may undergo episodic bursts, which we interpret as interaction between elliptic and gravitational instabilities. We estimate the distribution of dust particles in self-gravitating, turbulent vortices. Our results suggest large-scale vortices in protoplanetary discs are more easily observed at large radii.

Regional stratospheric warmings in the Pacific-Western Canada (PWC sector during winter 2004/2005: implications for temperatures, winds, chemical constituents and the characterization of the Polar vortex

Directory of Open Access Journals (Sweden)

A. H. Manson

2008-11-01

Full Text Available The vortex during winter 2004/2005 was interesting for several reasons. It has been described as "cold" stratospherically, with relatively strong westerly winds. Losses of ozone until the final warming in March were considerable, and comparable to the cold 1999–2000 winter. There were also modest warming events, indicated by peaks in 10 hPa zonal mean temperatures at high latitudes, near 1 January and 1 February. Events associated with a significant regional stratospheric warming in the Pacific-Western Canada (PWC sector then began and peaked toward the end of February, providing strong longitudinal variations in dynamical characteristics (Chshyolkova et al., 2007; hereafter C07. The associated disturbed vortex of 25 February was displaced from the pole and either elongated (upper or split into two cyclonic centres (lower.

Observations from Microwave Limb Sounder (MLS on Aura are used here to study the thermal characteristics of the stratosphere in the Canadian-US (253° E and Scandinavian-Europe (16° E sectors. Undisturbed high latitude stratopause (55 km zonal mean temperatures during the mid-winter (December–February reached 270 K, warmer than empirical-models such as CIRA-86, suggesting that seasonal polar warming due to dynamical influences affects the high altitude stratosphere as well as the mesosphere. There were also significant stratopause differences between Scandinavia and Canada during the warming events of 1 January and 1 February, with higher temperatures near 275 K at 16° E. During the 25 February "PWC" event a warming occurred at low and middle stratospheric heights (10–30 km: 220 K at 253° E and the stratopause cooled; while over Scandinavia-Europe the stratosphere below ~30 km was relatively cold at 195 K and the stratopause became even warmer (>295 K and lower (~45 km. The zonal winds followed the associated temperature gradients so that the vertical and latitudinal gradients of the winds differed strongly

Dynamics and Instabilities of Vortex Pairs

Science.gov (United States)

Leweke, Thomas; Le Dizès, Stéphane; Williamson, Charles H. K.

2016-01-01

This article reviews the characteristics and behavior of counter-rotating and corotating vortex pairs, which are seemingly simple flow configurations yet immensely rich in phenomena. Since the reviews in this journal by Widnall (1975) and Spalart (1998) , who studied the fundamental structure and dynamics of vortices and airplane trailing vortices, respectively, there have been many analytical, computational, and experimental studies of vortex pair flows. We discuss two-dimensional dynamics, including the merging of same-sign vortices and the interaction with the mutually induced strain, as well as three-dimensional displacement and core instabilities resulting from this interaction. Flows subject to combined instabilities are also considered, in particular the impingement of opposite-sign vortices on a ground plane. We emphasize the physical mechanisms responsible for the flow phenomena and clearly present the key results that are useful to the reader for predicting the dynamics and instabilities of parallel vortices.

Performance augmentation with vortex generators: Design and testing for stall-regulated AWT-26 turbine

Energy Technology Data Exchange (ETDEWEB)

Griffin, D.A. [Advanced Wind Turbines Inc., Seattle, WA (United States)

1996-12-31

A study investigated the use of vortex generators (VGs) for performance augmentation of the stall-regulated AWT-26 wind turbine. Based on wind-tunnel results and analysis, a VG array was designed for and tested on the AWT-26 prototype, designated Pt. Performance and loads data were measured for P1, both with and without VGs installed. The turbine performance with VGs met most of the design requirements; power output was increased at moderate wind speeds with a minimal effect on peak power. However, VG drag penalties caused a loss in power output for low wind speeds, such that performance with VGs resulted in a net decrease in AEP for wind speed sites up to 8.5 m/s. 8 refs., 8 figs., 3 tabs.

A ground temperature map of the North Atlantic permafrost region based on remote sensing and reanalysis data

DEFF Research Database (Denmark)

Westermann, S.; Østby, T. I.; Gisnås, K.

2015-01-01

Permafrost is a key element of the terrestrial cryosphere which makes mapping and monitoring of its state variables an imperative task. We present a modeling scheme based on remotely sensed land surface temperatures and reanalysis products from which mean annual ground temperatures (MAGT) can be ...... with gradually decreasing permafrost probabilities. The study exemplifies the unexploited potential of remotely sensed data sets in permafrost mapping if they are employed in multi-sensor multi-source data fusion approaches.......Permafrost is a key element of the terrestrial cryosphere which makes mapping and monitoring of its state variables an imperative task. We present a modeling scheme based on remotely sensed land surface temperatures and reanalysis products from which mean annual ground temperatures (MAGT) can...

ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

Science.gov (United States)

Shen, Ya; Zhou, Huimin; Coil, Jeffrey M; Aljazaeri, Bassim; Buttar, Rene; Wang, Zhejun; Zheng, Yu-feng; Haapasalo, Markus

2015-06-01

The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Prediction of the Effect of Vortex Generators on Airfoil Performance

International Nuclear Information System (INIS)

Sørensen, Niels N; Zahle, F; Bak, C; Vronsky, T

2014-01-01

Vortex Generators (VGs) are widely used by the wind turbine industry, to control the flow over blade sections. The present work describes a computational fluid dynamic procedure that can handle a geometrical resolved VG on an airfoil section. After describing the method, it is applied to two different airfoils at a Reynolds number of 3 million, the FFA- W3-301 and FFA-W3-360, respectively. The computations are compared with wind tunnel measurements from the Stuttgart Laminar Wind Tunnel with respect to lift and drag variation as function of angle of attack. Even though the method does not exactly capture the measured performance, it can be used to compare different VG setups qualitatively with respect to chord- wise position, inter and intra-spacing and inclination of the VGs already in the design phase

Simulation of Ground Winds Time Series for the NASA Crew Launch Vehicle (CLV)

Science.gov (United States)

Adelfang, Stanley I.

2008-01-01

Simulation of wind time series based on power spectrum density (PSD) and spectral coherence models for ground wind turbulence is described. The wind models, originally developed for the Shuttle program, are based on wind measurements at the NASA 150-m meteorological tower at Cape Canaveral, FL. The current application is for the design and/or protection of the CLV from wind effects during on-pad exposure during periods from as long as days prior to launch, to seconds or minutes just prior to launch and seconds after launch. The evaluation of vehicle response to wind will influence the design and operation of constraint systems for support of the on-pad vehicle. Longitudinal and lateral wind component time series are simulated at critical vehicle locations. The PSD model for wind turbulence is a function of mean wind speed, elevation and temporal frequency. Integration of the PSD equation over a selected frequency range yields the variance of the time series to be simulated. The square root of the PSD defines a low-pass filter that is applied to adjust the components of the Fast Fourier Transform (FFT) of Gaussian white noise. The first simulated time series near the top of the launch vehicle is the inverse transform of the adjusted FFT. Simulation of the wind component time series at the nearest adjacent location (and all other succeeding next nearest locations) is based on a model for the coherence between winds at two locations as a function of frequency and separation distance, where the adjacent locations are separated vertically and/or horizontally. The coherence function is used to calculate a coherence weighted FFT of the wind at the next nearest location, given the FFT of the simulated time series at the previous location and the essentially incoherent FFT of the wind at the selected location derived a priori from the PSD model. The simulated time series at each adjacent location is the inverse Fourier transform of the coherence weighted FFT. For a selected

Heat Transfer Enhancement in Separated and Vortex Flows

Energy Technology Data Exchange (ETDEWEB)

Richard J. Goldstein

2004-05-27

This document summarizes the research performance done at the Heat Transfer Laboratory of the University of Minnesota on heat transfer and energy separation in separated and vortex flow supported by DOE in the period September 1, 1998--August 31, 2003. Unsteady and complicated flow structures in separated or vortex flows are the main reason for a poor understanding of heat transfer under such conditions. The research from the University of Minnesota focused on the following important aspects of understanding such flows: (1) Heat/mass transfer from a circular cylinder; (2) study of energy separation and heat transfer in free jet flows and shear layers; and (3) study of energy separation on the surface and in the wake of a cylinder in crossflow. The current study used three different experimental setups to accomplish these goals. A wind tunnel and a liquid tunnel using water and mixtures of ethylene glycol and water, is used for the study of prandtl number effect with uniform heat flux from the circular cylinder. A high velocity air jet is used to study energy separation in free jets. A high speed wind tunnel, same as used for the first part, is utilized for energy separation effects on the surface and in the wake of the circular cylinder. The final outcome of this study is a substantial advancement in this research area.

Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events

Science.gov (United States)

Kim, Hyomin; Clauer, C. Robert; Gerrard, Andrew J.; Engebretson, Mark J.; Hartinger, Michael D.; Lessard, Marc R.; Matzka, Jürgen; Sibeck, David G.; Singer, Howard J.; Stolle, Claudia; Weimer, Daniel R.; Xu, Zhonghua

2017-07-01

We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (Pd) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground-based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression-associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72°-74° in magnetic latitude, consistent with the TCV center. The confluence of space-borne and ground instruments including the interhemispheric, high-latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system.

Ginzburg-Landau equations for a d-wave superconductor with applications to vortex structure and surface problems

International Nuclear Information System (INIS)

Xu, J.; Ren, Y.; Ting, C.S.

1995-01-01

The properties of a d x 2 -y 2 -wave superconductor in an external magnetic field are investigated on the basis of Gorkov's theory of weakly coupled superconductors. The Ginzburg-Landau (GL) equations, which govern the spatial variations of the order parameter and the supercurrent, are microscopically derived. The single vortex structure and surface problems in such a superconductor are studied using these equations. It is shown that the d-wave vortex structure is very different from the conventional s-wave vortex: the s-wave and d-wave components, with the opposite winding numbers, are found to coexist in the region near the vortex core. The supercurrent and local magnetic field around the vortex are calculated. Far away from the vortex core, both of them exhibit a fourfold symmetry, in contrast to an s-wave superconductor. The surface problem in a d-wave superconductor is also studied by solving the GL equations. The total order parameter near the surface is always a real combination of s- and d-wave components, which means that the proximity effect cannot induce a time-reversal symmetry-breaking state at the surface

Lidar-based Research and Innovation at DTU Wind Energy – a Review

International Nuclear Information System (INIS)

Mikkelsen, T

2014-01-01

As wind turbines during the past decade have increased in size so have the challenges met by the atmospheric boundary-layer meteorologists and the wind energy society to measure and characterize the huge-volume wind fields surpassing and driving them. At the DTU Wind Energy test site ''Østerild'' for huge wind turbines, the hub-height of a recently installed 8 MW Vestas V164 turbine soars 143 meters up above the ground, and its rotor of amazing 164 meters in diameter make the turbine tips flicker 225 meters into the sky. Following the revolution in photonics-based telecommunication at the turn of the Millennium new fibre-based wind lidar technologies emerged and DTU Wind Energy, at that time embedded within Rise National Laboratory, began in collaboration with researchers from wind lidar companies to measure remote sensed wind profiles and turbulence structures within the atmospheric boundary layer with the emerging, at that time new, all-fibre-based 1.55 μ coherent detection wind lidars. Today, ten years later, DTU Wind Energy routinely deploys ground-based vertical profilers instead of met masts for high-precision measurements of mean wind profiles and turbulence profiles. At the departments test site ''Høvsøre'' DTU Wind Energy also routinely calibrate and accredit wind lidar manufactures wind lidars. Meanwhile however, new methodologies for power curve assessment based on ground-based and nacelle based lidars have also emerged. For improving the turbines power curve assessments and for advancing their control with feed-forward wind measurements experience has also been gained with wind lidars installed on turbine nacelles and integrated into the turbines rotating spinners. A new mobile research infrastructure WindScanner.dk has also emerged at DTU Wind Energy. Wind and turbulence fields are today scanned from sets of three simultaneously in space and time synchronized scanning lidars. One set consists of three fast

Development of Ground Coils with Low Eddy Current Loss by Applying the Compression Molding Method after the Coil Winding

Science.gov (United States)

Suzuki, Masao; Aiba, Masayuki; Takahashi, Noriyuki; Ota, Satoru; Okada, Shigenori

In a magnetically levitated transportation (MAGLEV) system, a huge number of ground coils will be required because they must be laid for the whole line. Therefore, stable performance and reduced cost are essential requirements for the ground coil development. On the other hand, because the magnetic field changes when the superconducting magnet passes by, an eddy current will be generated in the conductor of the ground coil and will result in energy loss. The loss not only increases the magnetic resistance for the train running but also brings an increase in the ground coil temperature. Therefore, the reduction of the eddy current loss is extremely important. This study examined ground coils in which both the eddy current loss and temperature increase were small. Furthermore, quantitative comparison for the eddy current loss of various magnet wire samples was performed by bench test. On the basis of the comparison, a round twisted wire having low eddy current loss was selected as an effective ground coil material. In addition, the ground coils were manufactured on trial. A favorable outlook to improve the size accuracy of the winding coil and uneven thickness of molded resin was obtained without reducing the insulation strength between the coil layers by applying a compression molding after winding.

Nonlinear quantum piston for the controlled generation of vortex rings and soliton trains

KAUST Repository

Pinsker, Florian; Berloff, Natalia G.; Pé rez-Garcí a, Ví ctor M.

2013-01-01

We propose a simple way to generate nonlinear excitations in a controllable way by managing interactions in Bose-Einstein condensates. Under the action of a quantum analog of a classical piston, the condensed atoms are pushed through the trap, generating vortex rings infully three-dimensional condensates or soliton trains in quasi-one-dimensional scenarios. The vortex rings form due to transverse instability of the shock-wave train, enhanced and supported by the energy transfer between waves. We elucidate in what sense the self-interactions within the atom cloud define the properties of the generated vortex rings and soliton trains. Based on the quantum-piston scheme we study the behavior of two-component Bose-Einstein condensates and analyze how the presence of an additional superfluid influences the generation of vortex rings or solitons in the other component, and vice versa. Finally, we show the dynamical emergence of skyrmions within two-component systems in the immiscible regime. © 2013 American Physical Society.

Nonlinear quantum piston for the controlled generation of vortex rings and soliton trains

KAUST Repository

Pinsker, Florian

2013-05-29

We propose a simple way to generate nonlinear excitations in a controllable way by managing interactions in Bose-Einstein condensates. Under the action of a quantum analog of a classical piston, the condensed atoms are pushed through the trap, generating vortex rings infully three-dimensional condensates or soliton trains in quasi-one-dimensional scenarios. The vortex rings form due to transverse instability of the shock-wave train, enhanced and supported by the energy transfer between waves. We elucidate in what sense the self-interactions within the atom cloud define the properties of the generated vortex rings and soliton trains. Based on the quantum-piston scheme we study the behavior of two-component Bose-Einstein condensates and analyze how the presence of an additional superfluid influences the generation of vortex rings or solitons in the other component, and vice versa. Finally, we show the dynamical emergence of skyrmions within two-component systems in the immiscible regime. © 2013 American Physical Society.

Evolution of wind towards wind turbine

NARCIS (Netherlands)

Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.

2015-01-01

Remote sensing of the atmospheric variables with the use of LiDAR is a relatively new technology field for wind resource assessment in wind energy. The validation of LiDAR measurements and comparisons is of high importance for further applications of the data.

Effect of Air-Curtain Discharge Speed on the Effectiveness of Vortex-like Air-Curtain Approach for Severe Accident Management

International Nuclear Information System (INIS)

Ullah, Sana; Yim, Man Sung

2017-01-01

The purpose of air-curtain installation is to isolate reactor containment from outside environment, confine the leaking radioactive material in a localized area, and minimize the impact of outside wind. The wind could blow away airborne radioactive material immediately after discharge leaving little room for effective capturing. Therefore, vortex-like air-curtain plays an important role in this process, and its effectiveness could severely influence the performance of overall system. An approach based on vortex-like air-curtain was proposed earlier for preventing spread of radioactive material to the environment and mitigate subsequent radiological consequences. Effect of air-curtain discharge speed, and discharge angle was studied, and a quantitative account of air curtain in terms of effectiveness parameter was performed in this work. It was found that for given wind speed, air-curtain effectiveness would improve with increase in air-curtain discharge speed to an extent, after which any increase in discharge velicity could deteriorate the performance, due to imbalance between discharge and wind speed. Keeping air-curtain discharge at an angle of 15° opposite to the predominant flow direction is devised.

Numerical Study of Thermal and Flow Characteristics of Plate-Fin Heat Sink with Longitudinal Vortex Generator Installed on the Ground

Directory of Open Access Journals (Sweden)

Yen-Tso Chang

2014-01-01

Full Text Available This study applied the commercial software ANSYS CFD (FLUENT, for simulating the transient flow field and investigating the influence of each parameter of longitudinal vortex generators (LVGs on the thermal flux of a plate-fin heat sink. Vortex generator was set in front of plate-fin heat sink and under the channel, which was in common-flow-down (CFD and common-flow-up (CFU conditions, which have the result of vortex generator of delta winglet pair (DWP. In this study the parameters were varied, such as the minimum transverse distance between winglet pair, the attack angle of the vortex generator, fins number, the fin height, and the distance between the vortex generator and plate-fin. The coolant fluid flew into the fin-to-fin channel and pushed the vortex from different geometry toward the bottom. This phenomenon took off the heat from the plate to enhance the heat transfer. The numerical results indicated that the LVGs located close to the plate-fin heat sink are zero with the attack angle being 30°, presenting optimal overall conditions.

Structural damage identification in wind turbine blades using piezoelectric active sensing with ultrasonic validation

Energy Technology Data Exchange (ETDEWEB)

Claytor, Thomas N [Los Alamos National Laboratory; Ammerman, Curtt N [Los Alamos National Laboratory; Park, Gyu Hae [Los Alamos National Laboratory; Farinholt, Kevin M [Los Alamos National Laboratory; Farrar, Charles R [Los Alamos National Laboratory; Atterbury, Marie K [Los Alamos National Laboratory

2010-01-01

This paper gives a brief overview of a new project at LANL in structural damage identification for wind turbines. This project makes use of modeling capabilities and sensing technology to understand realistic blade loading on large turbine blades, with the goal of developing the technology needed to automatically detect early damage. Several structural health monitoring (SHM) techniques using piezoelectric active materials are being investigated for the development of wireless, low power sensors that interrogate sections of the wind turbine blade using Lamb wave propagation data, frequency response functions (FRFs), and time-series analysis methods. The modeling and sensor research will be compared with extensive experimental testing, including wind tunnel experiments, load and fatigue tests, and ultrasonic scans - on small- to mid-scale turbine blades. Furthermore, this study will investigate the effect of local damage on the global response of the blade by monitoring low-frequency response changes.

Remote sensing the plasmasphere, plasmapause, plumes and other features using ground-based magnetometers

Directory of Open Access Journals (Sweden)

Menk Frederick

2014-01-01

Full Text Available The plasmapause is a highly dynamic boundary between different magnetospheric particle populations and convection regimes. Some of the most important space weather processes involve wave-particle interactions in this region, but wave properties may also be used to remote sense the plasmasphere and plasmapause, contributing to plasmasphere models. This paper discusses the use of existing ground magnetometer arrays for such remote sensing. Using case studies we illustrate measurement of plasmapause location, shape and movement during storms; refilling of flux tubes within and outside the plasmasphere; storm-time increase in heavy ion concentration near the plasmapause; and detection and mapping of density irregularities near the plasmapause, including drainage plumes, biteouts and bulges. We also use a 2D MHD model of wave propagation through the magnetosphere, incorporating a realistic ionosphere boundary and Alfvén speed profile, to simulate ground array observations of power and cross-phase spectra, hence confirming the signatures of plumes and other density structures.

Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays

NARCIS (Netherlands)

Baldacchino, D.; Simao Ferreira, C.; Ragni, D.; van Bussel, G.J.W.

2016-01-01

In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the in_nite vortex cascade, a numerical model of four base-vortices is chosen to represent

Vortex lift augmentation by suction on a 60 deg swept Gothic wing

Science.gov (United States)

Taylor, A. H.; Jackson, L. R.; Huffman, J. K.

1982-01-01

An experimental investigation was conducted in the Langley high-speed 7- by 10-foot wind tunnel to determine the aerodynamic performance of suction applied near the wing tips above the trailing edge of a 60 deg swept Gothic wing. Moveable suction inlets were symmetrically mounted in the proximity of the trailing edge, and the amount of suction was varied to maximize wing lift. Tests were conducted at Mach 0.15, 0.30, and 0.45, and the angle of attack was varied from -4 to 50 deg. The suction augmentation increases the lift coefficient over the entire range of angle of attack. The lift improvement exceeds the unaugmented wing lift by over 20%. Moreover, the augmented lift exceeds the lift predicted by vortex lattice theory to 30 deg angle of attack. Suction augmentation is postulated to strengthen the vortex system by increasing its velocity and making it more concentrated. This causes the vortex breakdown to be delayed to a higher angle of attack

Offshore wind resource estimation for wind energy

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Badger, Merete; Mouche, A.

2010-01-01

Satellite remote sensing from active and passive microwave instruments is used to estimate the offshore wind resource in the Northern European Seas in the EU-Norsewind project. The satellite data include 8 years of Envisat ASAR, 10 years of QuikSCAT, and 23 years of SSM/I. The satellite observati......Satellite remote sensing from active and passive microwave instruments is used to estimate the offshore wind resource in the Northern European Seas in the EU-Norsewind project. The satellite data include 8 years of Envisat ASAR, 10 years of QuikSCAT, and 23 years of SSM/I. The satellite...... observations are compared to selected offshore meteorological masts in the Baltic Sea and North Sea. The overall aim of the Norsewind project is a state-of-the-art wind atlas at 100 m height. The satellite winds are all valid at 10 m above sea level. Extrapolation to higher heights is a challenge. Mesoscale...... modeling of the winds at hub height will be compared to data from wind lidars observing at 100 m above sea level. Plans are also to compare mesoscale model results and satellite-based estimates of the offshore wind resource....

The Myres Hill remote sensing intercomparison study: preliminary results

Energy Technology Data Exchange (ETDEWEB)

Clive, P J M; Chindurza, I [SgurrEnergy Ltd, 79 Coplaw Street, Glasgow G42 7JG, Scotland (United Kingdom); Ravey, I; Bass, J [RES Group Ltd, James Blyth House, 7000 Academy Park, Glasgow, Scotland (United Kingdom); Boyle, R J; Jones, P [TUV NEL Ltd, East Kilbride, Glasgow G75 0QF, Scotland (United Kingdom); Lang, S J [Sustainable Energy Research Group, University College Cork (Ireland); Bradley, S [Mighty River Power, Level 14, 23-29 Albert Street, Auckland (New Zealand); Hay, L [Garrad Hassan and Partners Ltd, 2064 Maryhill Road, Glasgow G20 0AB, Scotland (United Kingdom); Oldroyd, A [Oldbaum Services Ltd, Schoolhouse, Brig o' Turk, Callander, Scotland (United Kingdom); Stickland, M [University of Strathclyde, 16 Richmond Street, Glasgow G1 1XQ, Scotland (United Kingdom)], E-mail: peter.clive@sgurrenergy.com

2008-05-01

Two remote sensing techniques (SODAR and LIDAR) have been developed for measuring wind speed and turbulence from ground level up to altitudes of 300 m or higher. Although originally developed in the defence sector, these techniques are now generating considerable interest in the renewable energy and meteorological sectors. Despite the benefits of these instruments they are not yet generally accepted for due diligence measurements by wind energy developers and financial institutions. There is a requirement for a series of independent assessments of these new metrology techniques, comparing their measurements with the approved cup-type anemometer readings. This is being addressed at TUV NEL's Myres Hill wind turbine test site in a measurement programme supported by the DIUS National Measurement Systems Measurement for Innovators scheme and a consortium of 21 industrial collaborators. Data from SODAR and LIDAR systems are being compared with results from cup-type anemometers mounted at different heights on an 80m meteorological mast. An ultrasonic sensor is also mounted on the mast. The objective of the test programme is to assess the effectiveness of SODAR and LIDAR wind speed measurement techniques under different operating regimes and atmospheric conditions. Results from the measurements will provide definitive data on the performance of the remote wind speed sensing techniques under test on complex terrain typical of many wind farm sites. Preliminary measurements based on data acquired during the initial measurement campaign are presented.

Vortex-induced buckling of a viscous drop impacting a pool

KAUST Repository

Li, Erqiang

2017-07-20

We study the intricate buckling patterns which can form when a viscous drop impacts a much lower viscosity miscible pool. The drop enters the pool by its impact inertia, flattens, and sinks by its own weight while stretching into a hemispheric bowl. Upward motion along the outer bottom surface of this bowl produces a vortical boundary layer which separates along its top and rolls up into a vortex ring. The vorticity is therefore produced in a fundamentally different way than for a drop impacting a pool of the same liquid. The vortex ring subsequently advects into the bowl, thereby stretching the drop liquid into ever thinner sheets, reaching the micron level. The rotating motion around the vortex pulls in folds to form multiple windings of double-walled toroidal viscous sheets. The axisymmetric velocity field thereby stretches the drop liquid into progressively finer sheets, which are susceptible to both axial and azimuthal compression-induced buckling. The azimuthal buckling of the sheets tends to occur on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution of the vortex ring. The total interfacial area between the drop and the pool liquid can grow over 40-fold during the first 50 ms after impact. Increasing pool viscosity shows entrapment of a large bubble on top of the drop, while lowering the drop viscosity produces intricate buckled shapes, appearing at the earliest stage and being promoted by the crater motions. We also present an image collage of the most intriguing and convoluted structures observed. Finally, a simple point-vortex model reproduces some features from the experiments and shows variable stretching along the wrapping sheets.

Effect of the Initial Vortex Size on Intensity Change in the WRF-ROMS Coupled Model

Science.gov (United States)

Zhao, Xiaohui; Chan, Johnny C. L.

2017-12-01

Numerous studies have demonstrated that the tropical cyclone (TC) induced sea surface temperature (SST) cooling strongly depends on the preexisting oceanic condition and TC characteristics. However, very few focused on the correlation of SST cooling and the subsequent intensity with TC size. Therefore, a series of idealized numerical experiments are conducted using the Weather Research Forecasting (WRF) model coupled with the Regional Ocean Model System (ROMS) model to understand how the vortex size is related to SST cooling and subsequent intensity changes of a stationary TC-like vortex. In the uncoupled experiments, the radius of maximum wind (RMW) and size (radius of gale-force wind (R17)) both depend on the initial size within the 72 h simulation. The initially small vortex is smaller than the medium and large vortices throughout its life cycle and is the weakest. In other words, thermodynamic processes do not contribute as much to the R17 change as the dynamic processes proposed (e.g., angular momentum transport) in previous studies. In the coupled experiments, the area-averaged SST cooling induced by medium and large TCs within the inner-core region is comparable due to the similar surface winds and thus mixing in the ocean. Although a stronger SST cooling averaged within a larger region outside the inner-core is induced by the larger TC, the intensity of the larger TC is more intense. This is because that the enthalpy flux in the inner-core region is higher in the larger TC than that in the medium and small TCs.

A Coaxial Vortex Ring Model for Vortex Breakdown

OpenAIRE

Blackmore, Denis; Brons, Morten; Goullet, Arnaud

2008-01-01

A simple - yet plausible - model for B-type vortex breakdown flows is postulated; one that is based on the immersion of a pair of slender coaxial vortex rings in a swirling flow of an ideal fluid rotating around the axis of symmetry of the rings. It is shown that this model exhibits in the advection of passive fluid particles (kinematics) just about all of the characteristics that have been observed in what is now a substantial body of published research on the phenomenon of vortex breakdown....

Summer planetary-scale oscillations: aura MLS temperature compared with ground-based radar wind

Directory of Open Access Journals (Sweden)

C. E. Meek

2009-04-01

Full Text Available The advent of satellite based sampling brings with it the opportunity to examine virtually any part of the globe. Aura MLS mesospheric temperature data are analysed in a wavelet format for easy identification of possible planetary waves (PW and aliases masquerading as PW. A calendar year, 2005, of eastward, stationary, and westward waves at a selected latitude is shown in separate panels for wave number range −3 to +3 for period range 8 h to 30 days (d. Such a wavelet analysis is made possible by Aura's continuous sampling at all latitudes 82° S–82° N. The data presentation is suitable for examination of years of data. However this paper focuses on the striking feature of a "dish-shaped" upper limit to periods near 2 d in mid-summer, with longer periods appearing towards spring and fall, a feature also commonly seen in radar winds. The most probable cause is suggested to be filtering by the summer jet at 70–80 km, the latter being available from ground based medium frequency radar (MFR. Classically, the phase velocity of a wave must be greater than that of the jet in order to propagate through it. As an attempt to directly relate satellite and ground based sampling, a PW event of period 8d and wave number 2, which appears to be the original rather than an alias, is compared with ground based radar wind data. An appendix discusses characteristics of satellite data aliases with regard to their periods and amplitudes.

The vortex free energy in the screening phase of the Z(2) Higgs model

International Nuclear Information System (INIS)

Meyer, H.

1983-06-01

The vortex free energy was proposed to distinguish between the confinement - and the Higgs phase (in the sense of 't Hooft) in lattice gauge theory, when matter fields are present that transform according to an arbitrary representation of the gauge group. In this paper I consider the Z(2) Higgs model and calculate the vortex free energy in the screening part of the confining/screening phase of Fradkin and Shenker. The result does not agree with the expected behavior that corresponds to the structure of the phase diagram. Therefore the vortex free energy is no longer a good indicator for confinement when matter fields transform nontrivially under the center of the gauge group (such as Z(2) Higgs scalars). (orig.)

Analysis of Ground Effects on Aerodynamic Characteristics of Aerofoils Using Boundary Layer Approximation

Science.gov (United States)

Takahashi, Yuji; Kikuchi, Masanori; Hirano, Kimitaka

A study of a new high-speed zero-emission transportation “Aerotrain” is being carried out in Tohoku University and the University of Miyazaki. Because the aerotrain utilizes the ground effect, research on the aerofoil section, which can harness the ground effect effectively, is important. The aerotrain moves along a U-shaped guideway, which has a ground and sidewalls, so it has many viscous interference elements. In an analysis of the ground effects on the aerodynamic characteristics of aerofoils, the boundary layers on the aerofoil surface must be considered. At first, velocity distributions on the surfaces of aerofoils in potential flows are computed using the vortex method, then the momentum integration equations of the boundary layer are solved with experimental formulas. This procedure has the following advantages: modifications of the aerofoil section are easy because it is not necessary to make complicated computational grids, boundary layer transition and separation can be predicted using empirical procedures. The aerodynamic characteristics of four types of aerofoil sections are investigated to clarify the relationship between aerofoil sections and ground effects. Computational results are compared with experimental results obtained using a towing wind tunnel to verify computational precisions. In addition, aerofoil characteristics at an actual cruise speed are analyzed.

Microscopic analysis of the non-dissipative force on a line vortex in a superconductor

International Nuclear Information System (INIS)

Gaitan, F.

1994-12-01

A microscopic analysis of the non-dissipative force F nd acting on a line vortex in a type-II superconductor at T = 0 is given. All work presented assumes a charged BCS superconductor. We first examine the Berry phase induced in the BCS superconducting ground state by movement of the vortex and show how this phase enters into the hydro-dynamic action S hyd of the superconducting condensate. Appropriate variation of S hyd gives F nd and variation of the Berry phase term is seen to contribute the Magnus or lift force of classical hydrodynamics to F nd . This analysis, based on the BCS ground state of a charged superconductor, confirms in detail the arguments of Ao and Thouless within the context of the BCS model. Our Berry phase, in the limit e → 0, is seen to reproduce the Berry phase determined by these authors for a neutral superfluid. We also provide a second, independent, determination on F nd through a microscopic derivation of the continuity equation for the condensate linear momentum. This equation yields the acceleration equation for the superflow and shows that the vortex acts as a sink for the condensate linear momentum. The rate at which momentum is lost to the vortex determines F nd in this second approach and the result obtained agrees identically with the previous Berry phase calculation. The Magnus force contribution to F nd is seen in both calculations to be a consequence of the vortex topology and motion. (author). 10 refs

Vortex cutting in superconductors

Science.gov (United States)

Vlasko-Vlasov, Vitalii K.; Koshelev, Alexei E.; Glatz, Andreas; Welp, Ulrich; Kwok, Wai-K.

2015-03-01

Unlike illusive magnetic field lines in vacuum, magnetic vortices in superconductors are real physical strings, which interact with the sample surface, crystal structure defects, and with each other. We address the complex and poorly understood process of vortex cutting via a comprehensive set of magneto-optic experiments which allow us to visualize vortex patterns at magnetization of a nearly twin-free YBCO crystal by crossing magnetic fields of different orientations. We observe a pronounced anisotropy in the flux dynamics under crossing fields and the filamentation of induced supercurrents associated with the staircase vortex structure expected in layered cuprates, flux cutting effects, and angular vortex instabilities predicted for anisotropic superconductors. At some field angles, we find formation of the vortex domains following a type-I phase transition in the vortex state accompanied by an abrupt change in the vortex orientation. To clarify the vortex cutting scenario we performed time-dependent Ginzburg-Landau simulations, which confirmed formation of sharp vortex fronts observed in the experiment and revealed a left-handed helical instability responsible for the rotation of vortices. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

A consistent definition of the Arctic polar vortex breakup in both the lower and upper stratosphere

Science.gov (United States)

Choi, W.; Seo, J.

2014-12-01

Breakup of the polar vortex is a dominant feature of the seasonal transition from winter to summer in the stratosphere, which significantly affects stratospheric O3 concentration and tropospheric weather. Previously several criteria for the vortex breakup have been suggested based on the potential vorticity (PV) and wind speed, however, those mainly have focused on the lower stratospheric vortex of which spatiotemporal evolution and decay are more continuous than those of the upper stratospheric vortex. To find a consistent criterion for the vortex breakup in both the lower and upper stratosphere, the present study defined a polar vortex breakup day as when PV gradient at the polar vortex edge becomes lower than that at the subtropical edge on the area equivalent latitude based on PV. With applying the new definition to the UK Met Office reanalysis data, the breakup days of the Arctic polar vortices on 18 isentropic levels from 450 K to 1300 K were calculated for the period of 1993-2005. In comparison with CH4, N2O and O3 measured by the ILAS and POAM II/III satellite instruments, the breakup days are well consistent with changes in the distribution of such tracers as well as their zonal standard deviations associated with the vortex structure breaking and irreversible mixing. The vortex breakup in the upper stratosphere occurs more or less a month prior to that in the middle and lower stratosphere while the stratospheric final warming events occurs simultaneously in the upper and lower stratosphere.

Dynamic Loads and Wake Prediction for Large Wind Turbines Based on Free Wake Method

Institute of Scientific and Technical Information of China (English)

Cao Jiufa; Wang Tongguang; Long Hui; Ke Shitang; Xu Bofeng

2015-01-01

With large scale wind turbines ,the issue of aerodynamic elastic response is even more significant on dy-namic behaviour of the system .Unsteady free vortex wake method is proposed to calculate the shape of wake and aerodynamic load .Considering the effect of aerodynamic load ,inertial load and gravity load ,the decoupling dy-namic equations are established by using finite element method in conjunction of the modal method and equations are solved numerically by Newmark approach .Finally ,the numerical simulation of a large scale wind turbine is performed through coupling the free vortex wake modelling with structural modelling .The results show that this coupling model can predict the flexible wind turbine dynamic characteristics effectively and efficiently .Under the influence of the gravitational force ,the dynamic response of flapwise direction contributes to the dynamic behavior of edgewise direction under the operational condition of steady wind speed .The difference in dynamic response be-tween the flexible and rigid wind turbines manifests when the aerodynamics/structure coupling effect is of signifi-cance in both wind turbine design and performance calculation .

Wavelet based methods for improved wind profiler signal processing

Directory of Open Access Journals (Sweden)

V. Lehmann

2001-08-01

Full Text Available In this paper, we apply wavelet thresholding for removing automatically ground and intermittent clutter (airplane echoes from wind profiler radar data. Using the concept of discrete multi-resolution analysis and non-parametric estimation theory, we develop wavelet domain thresholding rules, which allow us to identify the coefficients relevant for clutter and to suppress them in order to obtain filtered reconstructions.Key words. Meteorology and atmospheric dynamics (instruments and techniques – Radio science (remote sensing; signal processing

Polar vortex evolution during Northern Hemispheric winter 2004/05

Directory of Open Access Journals (Sweden)

T. Chshyolkova

2007-06-01

Full Text Available As a part of the project "Atmospheric Wave Influences upon the Winter Polar Vortices (0–100 km" of the CAWSES program, data from meteor and Medium Frequency radars at 12 locations and MetO (UK Meteorological Office global assimilated fields have been analyzed for the first campaign during the Northern Hemispheric winter of 2004/05. The stratospheric state has been described using the conventional zonal mean parameters as well as Q-diagnostic, which allows consideration of the longitudinal variability. The stratosphere was cold during winter of 2004/05, and the polar vortex was relatively strong during most of the winter with relatively weak disturbances occurring at the end of December and the end of January. For this winter the strongest deformation with the splitting of the polar vortex in the lower stratosphere was observed at the end of February. Here the results show strong latitudinal and longitudinal differences that are evident in the stratospheric and mesospheric data sets at different stations. Eastward winds are weaker and oscillations with planetary wave periods have smaller amplitudes at more poleward stations. Accordingly, the occurrence, time and magnitude of the observed reversal of the zonal mesospheric winds associated with stratospheric disturbances depend on the local stratospheric conditions. In general, compared to previous years, the winter of 2004/05 could be characterized by weak planetary wave activity at stratospheric and mesospheric heights.

Structures of single vortex and vortex lattice in a d-wave superconductor

International Nuclear Information System (INIS)

Xu, J.; Ren, Y.; Ting, C.

1996-01-01

The structures of a single vortex and vortex lattice in a superconductor with d x 2 -y 2 symmetry are studied self-consistently employing a recently developed Ginzburg-Landau theory. Near a single vortex, we found that an s-wave component of the order parameter is always induced, and it causes the local magnetic-field distribution and the d-wave order parameter to have a fourfold anisotropy. It is shown that there is a strong correlation between the structure of a single vortex and the shape of the vortex lattice. Our numerical calculation indicates that the structure of the vortex lattice is always oblique except for temperatures very close to T c where it becomes triangular. The possible connection of the result with experiment is also discussed. copyright 1996 The American Physical Society

Comparison and validation of wake vortex characteristics collected at different airports by different scanning lidar sensors

Science.gov (United States)

Thobois, Ludovic; Cariou, Jean-Pierre; Cappellazzo, Valerio; Musson, Christian; Treve, Vincent

2018-04-01

Today, the demand for increasing airport capacity is high, in particular for increasing runway throughput from an ATM perspective. Runway capacity is often directly linked with the minima longitudinal separation between aircraft on approach phase or between aircraft on departure. The separation minima are based on surveillance capabilities and on wake turbulence (WT) in order to mitigate respectively collision risk and WT-induced accidents, therefore WT hazard becomes a major concern for ATM. For ten years, many research LIDAR systems have been used for better understanding wake vortices behaviors in the operational environment within large range of wind and turbulence conditions. All these studies[1][2] helped to design new concepts of wake separations between aircrafts thanks to the proven capabilities of LIDAR systems to assess the risks of wake vortex (WV) encounters through the circulation retrievals. The re-categorization project, called RECAT [8], has been launched by a joint EUROCONTROL - FAA initiative in order to renew and optimize the out-of-date currently applied ICAO regulations on distance separation. Nowadays, the first phase of regional RECAT projects, which consists in defining new distance separation matrices composed of six/seven static aircraft categories instead of three, entered the operational phase and is deployed in several airports in United States and Europe. In addition, other concepts like Time-Based Separation have also been studied and deployed in London Heathrow. The airports where these solutions have been deployed obtained significant benefits as increased runway throughput and improved resilience to disruptions. For implementing such new WT solutions at an airport, a local safety assessment before the implementation and a risk monitoring after are usually needed. Before implementation, it may be required to determine for the targeted airport the relative variations of risk of wake vortex encounters, given the local ATM rules, the

Comparison and validation of wake vortex characteristics collected at different airports by different scanning lidar sensors

Directory of Open Access Journals (Sweden)

Thobois Ludovic

2018-01-01

Full Text Available Today, the demand for increasing airport capacity is high, in particular for increasing runway throughput from an ATM perspective. Runway capacity is often directly linked with the minima longitudinal separation between aircraft on approach phase or between aircraft on departure. The separation minima are based on surveillance capabilities and on wake turbulence (WT in order to mitigate respectively collision risk and WT-induced accidents, therefore WT hazard becomes a major concern for ATM. For ten years, many research LIDAR systems have been used for better understanding wake vortices behaviors in the operational environment within large range of wind and turbulence conditions. All these studies[1][2] helped to design new concepts of wake separations between aircrafts thanks to the proven capabilities of LIDAR systems to assess the risks of wake vortex (WV encounters through the circulation retrievals. The re-categorization project, called RECAT [8], has been launched by a joint EUROCONTROL – FAA initiative in order to renew and optimize the out-of-date currently applied ICAO regulations on distance separation. Nowadays, the first phase of regional RECAT projects, which consists in defining new distance separation matrices composed of six/seven static aircraft categories instead of three, entered the operational phase and is deployed in several airports in United States and Europe. In addition, other concepts like Time-Based Separation have also been studied and deployed in London Heathrow. The airports where these solutions have been deployed obtained significant benefits as increased runway throughput and improved resilience to disruptions. For implementing such new WT solutions at an airport, a local safety assessment before the implementation and a risk monitoring after are usually needed. Before implementation, it may be required to determine for the targeted airport the relative variations of risk of wake vortex encounters, given the

Tornado type wind turbines

Science.gov (United States)

Hsu, Cheng-Ting

1984-01-01

A tornado type wind turbine has a vertically disposed wind collecting tower with spaced apart inner and outer walls and a central bore. The upper end of the tower is open while the lower end of the structure is in communication with a wind intake chamber. An opening in the wind chamber is positioned over a turbine which is in driving communication with an electrical generator. An opening between the inner and outer walls at the lower end of the tower permits radially flowing air to enter the space between the inner and outer walls while a vertically disposed opening in the wind collecting tower permits tangentially flowing air to enter the central bore. A porous portion of the inner wall permits the radially flowing air to interact with the tangentially flowing air so as to create an intensified vortex flow which exits out of the top opening of the tower so as to create a low pressure core and thus draw air through the opening of the wind intake chamber so as to drive the turbine.

Wind, QuikSCAT SeaWinds, 0.25 degrees, Global, Science Quality, Meridional

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Remote Sensing Inc. distributes science quality wind velocity data from the SeaWinds instrument onboard NASA's QuikSCAT satellite. SeaWinds is a microwave...

Wind, QuikSCAT SeaWinds, 0.25 degrees, Global, Science Quality, Modulus

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Remote Sensing Inc. distributes science quality wind velocity data from the SeaWinds instrument onboard NASA's QuikSCAT satellite. SeaWinds is a microwave...

Model-based observer and feedback control design for a rigid Joukowski foil in a Kármán vortex street.

Science.gov (United States)

Free, Brian A; Paley, Derek A

2018-03-14

Obstacles and swimming fish in flow create a wake with an alternating left/right vortex pattern known as a Kármán vortex street and reverse Kármán vortex street, respectively. An energy-efficient fish behavior resembling slaloming through the vortex street is called Kármán gaiting. This paper describes the use of a bioinspired array of pressure sensors on a Joukowski foil to estimate and control flow-relative position in a Kármán vortex street using potential flow theory, recursive Bayesian filtering, and trajectory-tracking feedback control. The Joukowski foil is fixed in downstream position in a flowing water channel and free to move on air bearings in the cross-stream direction by controlling its angle of attack to generate lift. Inspired by the lateral-line neuromasts found in fish, the sensing and control scheme is validated using off-the-shelf pressure sensors in an experimental testbed that includes a flapping device to create vortices. We derive a potential flow model that describes the flow over a Joukowski foil in a Kármán vortex street and identify an optimal path through a Kármán vortex street using empirical observability. The optimally observable trajectory is one that passes through each vortex in the street. The estimated vorticity and location of the Kármán vortex street are used in a closed-loop control to track either the optimally observable path or the energetically efficient gait exhibited by fish. Results from the closed-loop control experiments in the flow tank show that the artificial lateral line in conjunction with a potential flow model and Bayesian estimator allow the robot to perform fish-like slaloming behavior in a Kármán vortex street. This work is a precursor to an autonomous robotic fish sensing the wake of another fish and/or performing pursuit and schooling behavior.

A modified Gaussian model for the thermal plume from a ground-based heat source in a cross-wind

International Nuclear Information System (INIS)

Selander, W.N.; Barry, P.J.; Robertson, E.

1990-06-01

An array of propane burners operating at ground level in a cross-wind was used as a heat source to establish a blown-over thermal plume. A three-dimensional array of thermocouples was used to continuously measure the plume temperature downwind from the source. The resulting data were used to correlate the parameters of a modified Gaussian model for plume rise and dispersion with source strength, wind speed, and atmospheric dispersion parameters

Vortex rings

CERN Document Server

Akhmetov, D G

2009-01-01

This text on vortex rings covers their theoretical foundation, systematic investigations, and practical applications such as the extinction of fires at gushing oil wells. It pays special attention to the formation and motion of turbulent vortex rings.

KNOW-BLADE task-3.3 report: Rotor blade computations with 3D vortex generators

DEFF Research Database (Denmark)

Johansen, J.; Sørensen, Niels N.; Reck, M.

2005-01-01

The present report describes the work done in work package WP3.3: Aerodynamic Accessories in 3D in the EC project KNOW-BLADE. Vortex generators (VGs) are modelled in 3D Navier-Stokes solvers and applied on the flow around an airfoil and a wind turbineblade. Three test cases have been investigated...

Remote sensing of high-latitude ionization profiles by ground-based and spaceborne instrumentation

International Nuclear Information System (INIS)

Vondrak, R.R.

1981-01-01

Ionospheric specification and modeling are now largely based on data provided by active remote sensing with radiowave techniques (ionosondes, incoherent-scatter radars, and satellite beacons). More recently, passive remote sensing techniques have been developed that can be used to monitor quantitatively the spatial distribution of high-latitude E-region ionization. These passive methods depend on the measurement, or inference, of the energy distribution of precipitating kilovolt electrons, the principal source of the nighttime E-region at high latitudes. To validate these techniques, coordinated measurements of the auroral ionosphere have been made with the Chatanika incoherent-scatter radar and a variety of ground-based and spaceborne sensors

On the sensitivity of numerical weather prediction to remotely sensed marine surface wind data - A simulation study

Science.gov (United States)

Cane, M. A.; Cardone, V. J.; Halem, M.; Halberstam, I.

1981-01-01

The reported investigation has the objective to assess the potential impact on numerical weather prediction (NWP) of remotely sensed surface wind data. Other investigations conducted with similar objectives have not been satisfactory in connection with a use of procedures providing an unrealistic distribution of initial errors. In the current study, care has been taken to duplicate the actual distribution of information in the conventional observing system, thus shifting the emphasis from accuracy of the data to the data coverage. It is pointed out that this is an important consideration in assessing satellite observing systems since experience with sounder data has shown that improvements in forecasts due to satellite-derived information is due less to a general error reduction than to the ability to fill data-sparse regions. The reported study concentrates on the evaluation of the observing system simulation experimental design and on the assessment of the potential of remotely sensed marine surface wind data.

Field measurements of horizontal forward motion velocities of terrestrial dust devils: Towards a proxy for ambient winds on Mars and Earth

Science.gov (United States)

Balme, M. R.; Pathare, A.; Metzger, S. M.; Towner, M. C.; Lewis, S. R.; Spiga, A.; Fenton, L. K.; Renno, N. O.; Elliott, H. M.; Saca, F. A.; Michaels, T. I.; Russell, P.; Verdasca, J.

2012-11-01

Dust devils - convective vortices made visible by the dust and debris they entrain - are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from landing craft and orbiting instruments have allowed the dust devil translational forward motion (ground velocity) to be calculated, but it is unclear how these velocities relate to the local ambient wind conditions, for (i) only model wind speeds are generally available for Mars, and (ii) on Earth only anecdotal evidence exists that compares dust devil ground velocity with ambient wind velocity. If dust devil ground velocity can be reliably correlated to the ambient wind regime, observations of dust devils could provide a proxy for wind speed and direction measurements on Mars. Hence, dust devil ground velocities could be used to probe the circulation of the martian boundary layer and help constrain climate models or assess the safety of future landing sites. We present results from a field study of terrestrial dust devils performed in the southwest USA in which we measured dust devil horizontal velocity as a function of ambient wind velocity. We acquired stereo images of more than a 100 active dust devils and recorded multiple size and position measurements for each dust devil. We used these data to calculate dust devil translational velocity. The dust devils were within a study area bounded by 10 m high meteorology towers such that dust devil speed and direction could be correlated with the local ambient wind speed and direction measurements. Daily (10:00-16:00 local time) and 2-h averaged dust devil ground speeds correlate well with ambient wind speeds averaged over the same period. Unsurprisingly, individual measurements of dust devil ground speed match instantaneous measurements of ambient wind speed more poorly; a 20-min smoothing window applied to

Vortex mass in a superfluid

Science.gov (United States)

Simula, Tapio

2018-02-01

We consider the inertial mass of a vortex in a superfluid. We obtain a vortex mass that is well defined and is determined microscopically and self-consistently by the elementary excitation energy of the kelvon quasiparticle localized within the vortex core. The obtained result for the vortex mass is found to be consistent with experimental observations on superfluid quantum gases and vortex rings in water. We propose a method to measure the inertial rest mass and Berry phase of a vortex in superfluid Bose and Fermi gases.

Wind energy: Overcoming inadequate wind and modeling uncertainties

Energy Technology Data Exchange (ETDEWEB)

Kane, Vivek

2010-09-15

'Green Energy' is the call of the day, and significance of Wind Energy can never be overemphasized. But the key question here is - What if the wind resources are inadequate? Studies reveal that the probability of finding favorable wind at a given place on land is only 15%. Moreover, there are inherent uncertainties associated with wind business. Can we overcome inadequate wind resources? Can we scientifically quantify uncertainty and model it to make business sense? This paper proposes a solution, by way of break-through Wind Technologies, combined with advanced tools for Financial Modeling, enabling vital business decisions.

Intercomparison of Remotely Sensed Vegetation Indices, Ground Spectroscopy, and Foliar Chemistry Data from NEON

Science.gov (United States)

Hulslander, D.; Warren, J. N.; Weintraub, S. R.

2017-12-01

Hyperspectral imaging systems can be used to produce spectral reflectance curves giving rich information about composition, relative abundances of materials, mixes and combinations. Indices based on just a few spectral bands have been used for over 40 years to study vegetation health, mineral abundance, and more. These indices are much simpler to visualize and use than a full hyperspectral data set which may contain over 400 bands. Yet historically, it has been difficult to directly relate remotely sensed spectral indices to quantitative biophysical properties significant to forest ecology such as canopy nitrogen, lignin, and chlorophyll. This linkage is a critical piece in enabling the detection of high value ecological information, usually only available from labor-intensive canopy foliar chemistry sampling, to the geographic and temporal coverage available via remote sensing. Previous studies have shown some promising results linking ground-based data and remotely sensed indices, but are consistently limited in time, geographic extent, and land cover type. Moreover, previous studies are often focused on tuning linkage algorithms for the purpose of achieving good results for only one study site or one type of vegetation, precluding development of more generalized algorithms. The National Ecological Observatory Network (NEON) is a unique system of 47 terrestrial sites covering all of the major eco-climatic domains of the US, including AK, HI, and Puerto Rico. These sites are regularly monitored and sampled using uniform instrumentation and protocols, including both foliar chemistry sampling and remote sensing flights for high resolution hyperspectral, LiDAR, and digital camera data acquisition. In this study we compare the results of foliar chemistry analysis to the remote sensing vegetation indices and investigate possible sources for variance and difference through the use of the larger hyperspectral dataset as well as ground based spectrometer measurements of

Vortex loops and Majoranas

International Nuclear Information System (INIS)

Chesi, Stefano; Jaffe, Arthur; Loss, Daniel; Pedrocchi, Fabio L.

2013-01-01

We investigate the role that vortex loops play in characterizing eigenstates of interacting Majoranas. We give some general results and then focus on ladder Hamiltonian examples as a test of further ideas. Two methods yield exact results: (i) A mapping of certain spin Hamiltonians to quartic interactions of Majoranas shows that the spectra of these two examples coincide. (ii) In cases with reflection-symmetric Hamiltonians, we use reflection positivity for Majoranas to characterize vortices in the ground states. Two additional methods suggest wider applicability of these results: (iii) Numerical evidence suggests similar behavior for certain systems without reflection symmetry. (iv) A perturbative analysis also suggests similar behavior without the assumption of reflection symmetry

CFD Simulation of Turbulent Wind Effect on an Array of Ground-Mounted Solar PV Panels

Science.gov (United States)

Irtaza, Hassan; Agarwal, Ashish

2018-02-01

Aim of the present study is to determine the wind loads on the PV panels in a solar array since panels are vulnerable to high winds. Extensive damages of PV panels, arrays and mounting modules have been reported the world over due to high winds. Solar array of dimension 6 m × 4 m having 12 PV panels of size 1 m × 2 m on 3D 1:50 scaled models have been simulated using unsteady solver with Reynolds-Averaged Navier-Stokes equations of computational fluid dynamics techniques to study the turbulent wind effects on PV panels. A standalone solar array with 30° tilt angle in atmospheric surface layer with the Renormalized Group (RNG) turbulence closure subjected to incident wind varied from - 90° to 90°. The net pressure, drag and lift coefficients are found to be maximum when the wind is flowing normally to the PV panel either 90° or - 90°. The tilt angle of solar arrays the world over not vary on the latitude but also on the seasons. Keeping this in mind the ground mounted PV panels in array with varying tilt angle from 10° to 60° at an interval of 10° have been analyzed for normal wind incident i.e. 90° and - 90° using unsteady RNG turbulence model. Net pressure coefficients have been calculated and found to be increasing with increase in array tilting angle. Maximum net pressure coefficient was observed for the 60° tilted PV array for 90° and - 90° wind incident having value of 0.938 and 0.904 respectively. The results can be concluded that the PV panels are subjected to significant lift and drag forces under wind loading, which needs to be quantified with sufficient factor of safety to avoid damages.

CFD Simulation of Turbulent Wind Effect on an Array of Ground-Mounted Solar PV Panels

Science.gov (United States)

Irtaza, Hassan; Agarwal, Ashish

2018-06-01

Aim of the present study is to determine the wind loads on the PV panels in a solar array since panels are vulnerable to high winds. Extensive damages of PV panels, arrays and mounting modules have been reported the world over due to high winds. Solar array of dimension 6 m × 4 m having 12 PV panels of size 1 m × 2 m on 3D 1:50 scaled models have been simulated using unsteady solver with Reynolds-Averaged Navier-Stokes equations of computational fluid dynamics techniques to study the turbulent wind effects on PV panels. A standalone solar array with 30° tilt angle in atmospheric surface layer with the Renormalized Group (RNG) turbulence closure subjected to incident wind varied from - 90° to 90°. The net pressure, drag and lift coefficients are found to be maximum when the wind is flowing normally to the PV panel either 90° or - 90°. The tilt angle of solar arrays the world over not vary on the latitude but also on the seasons. Keeping this in mind the ground mounted PV panels in array with varying tilt angle from 10° to 60° at an interval of 10° have been analyzed for normal wind incident i.e. 90° and - 90° using unsteady RNG turbulence model. Net pressure coefficients have been calculated and found to be increasing with increase in array tilting angle. Maximum net pressure coefficient was observed for the 60° tilted PV array for 90° and - 90° wind incident having value of 0.938 and 0.904 respectively. The results can be concluded that the PV panels are subjected to significant lift and drag forces under wind loading, which needs to be quantified with sufficient factor of safety to avoid damages.

Vortex lattices in a rotating Fermi superfluid in the BCS–BEC crossover with many Landau levels

International Nuclear Information System (INIS)

Song, Tie-ling; Ma, C.R.; Ma, Yong-li

2012-01-01

We present an explicit analytical analysis of the ground state of vortex lattice structure, based on a minimization of the generalized Gross–Pitaevskii energy functional in a trapped rotating Fermi superfluid gas. By a Bogoliubov-like transformation we find that the coarse-grained average of the atomic density varies as inverted parabola in three dimensional cases; the Fermi superfluid in the BEC regime enters into the lowest Landau level at fast rotation, in which the vortices form an almost regular triangular lattice over a central region and the vortex lattice is expanded along the radial direction in the outer region; the fluid in the unitarity and BCS regimes occupies many low-lying Landau levels, in which a trapped gas with a triangular vortex lattice has a superfluid core surrounded by a normal gas. The calculation is qualitatively consistent with recent numerical and experimental data both in the vortex lattice structure and vortex numbers and in the density profiles versus the stirring frequency in the whole BCS–BEC crossover. - Highlights: ► We present an analysis of vortex lattice in an interacting trapped rotating Fermi superfluid gas. ► Decomposing the vortex from the condensate, we can explain the vortex lattice. ► The calculation is consistent with numerical and experimental data. ► It can characterize experimentally properties in different regimes of the BCS–BEC crossover.

Fractional vortex lattice structures in spin-triplet superconductors

International Nuclear Information System (INIS)

Chung, Suk Bum; Agterberg, Daniel F; Kim, Eun-A

2009-01-01

Motivated by recent interest in spin-triplet superconductors, we investigate the vortex lattice structures for this class of unconventional superconductors. We discuss how the order parameter symmetry can give rise to U(1)xU(1) symmetry in the same sense as in spinor condensates, making half-quantum vortices (HQVs) topologically stable. We then calculate the vortex lattice structure of HQVs, with particular attention on the roles of the crystalline lattice, the Zeeman coupling and Meissner screening, all absent in spinor condensates. Finally, we consider how spin-orbit coupling leads to a breakdown of the U(1)xU(1) symmetry in free energy and whether the HQV lattice survives this symmetry breaking. As examples, we examine simpler spin-triplet models proposed in the context of Na x CoO 2 ·yH 2 O and Bechgaard salts, as well as the better known and more complex model for Sr 2 RuO 4 .

Fatigue damage from random vibration pulse process of tubular structural elements subject to wind

DEFF Research Database (Denmark)

Christensen, Claus F.; Ditlevsen, Ove Dalager

1997-01-01

In a wide range of the Reynolds number an elastically suspended circular cylinder surrounded by a homogeneous wind velocity field will generate vortex shedding of a frequency that by and large is proportional to the far field wind velocity. However, if the cylinder is free to vibrate, resonance w...

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

Science.gov (United States)

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

Statistical Characterization of River and Channel Network Formation in Intermittently Flowing Vortex Systems.

Science.gov (United States)

Olson, C. J.; Reichhardt, C.; Nori, F.

1997-03-01

Vortices moving in dirty superconductors can form intricate flow patterns, resembling fluid rivers, as they interact with the pinning landscape (F. Nori, Science 271), 1373 (1996).. Weaker pinning produces relatively straight nori>vortex channels, while stronger pinning results in the formation of one or more winding channels that carry all flow. This corresponds to a crossover from elastic flow to plastic flow as the pinning strength is increased. For several pinning parameters, we find the fractal dimension of the channels that form, the vortex trail density, the distance travelled by vortices as they pass through the sample, the branching ratio, the sinuosity, and the size distribution of the rivers, and we compare our rivers with physical rivers that follow Horton's laws.

Integrationof Remote Sensing and Geographic information system in Ground Water Quality Assessment and Management

Science.gov (United States)

Shakak, N.

2015-04-01

Spatial variations in ground water quality in the Khartoum state, Sudan, have been studied using geographic information system (GIS) and remote sensing technique. Gegraphical informtion system a tool which is used for storing, analyzing and displaying spatial data is also used for investigating ground water quality information. Khartoum landsat mosac image aquired in 2013was used, Arc/Gis software applied to extract the boundary of the study area, the image was classified to create land use/land cover map. The land use map,geological and soil map are used for correlation between land use , geological formations, and soil types to understand the source of natural pollution that can lower the ground water quality. For this study, the global positioning system (GPS), used in the field to identify the borehole location in a three dimentional coordinate (Latitude, longitude, and altitude), water samples were collected from 156 borehole wells, and analyzed for physico-chemical parameters like electrical conductivity, Total dissolved solid,Chloride, Nitrate, Sodium, Magnisium, Calcium,and Flouride, using standard techniques in the laboratory and compared with the standards.The ground water quality maps of the entire study area have been prepared using spatial interpolation technique for all the above parameters.then the created maps used to visualize, analyze, and understand the relationship among the measured points. Mapping was coded for potable zones, non-potable zones in the study area, in terms of water quality sutability for drinking water and sutability for irrigation. In general satellite remote sensing in conjunction with geographical information system (GIS) offers great potential for water resource development and management.

Formation of quasistationary vortex and transient hole patterns through vortex merger

International Nuclear Information System (INIS)

Ganesh, R.; Lee, J.K.

2002-01-01

Collection of point-like intense vortices arranged symmetrically outside of a uniform circular vortex patch, both enclosed in a free-slip circular boundary, are numerically time evolved for up to 10-15 patch turnover times. These patterns are found to merge with the patch by successively inducing nonlinear dispersive modes (V-states) on the surface of the patch, draw off fingers of vorticity (filamentation), trap the irrotational regions as the fingers symmetrize under the shear flow of the patch and point-like vortices (wave breaking) followed by the vortex-hole capture. While the hole patterns are observed to break up over several turnover periods the vortex patterns appear to evolve into quasistationary patterns for some cases of an initial number of point-like vortices N pv . The bounded V-states, filamentation, and vortex (hole) pattern formation are discussed in some detail and their possible connection to recently observed vortex 'crystals' is pointed out

Plasmonic vortex generator without polarization dependence

Science.gov (United States)

Wang, Han; Liu, Lixia; Liu, Chunxiang; Li, Xing; Wang, Shuyun; Xu, Qing; Teng, Shuyun

2018-03-01

In view of the limitations of vortex generators with polarization dependence at present, we propose a plasmonic vortex generator composed of rectangular holes etched in silver film, in which the optical vortex can be generated under arbitrary linearly polarized light illumination. Two sets of rectangular holes are arranged equidistantly on a circle and rotate in postulate directions. Theoretical analysis provides the design principle for the vortex generator, and numerical simulations give guidance on designating the vortex generator parameters. Experimental measurements verify the performance of the proposed vortex generator. Moreover, two alternative structures for the generation of a plasmonic vortex are also provided in this paper. The resulting perfect vortex, compact structure and flexible illumination conditions will lead to wide applications of this plasmonic vortex generator.

Unsteady flow challenges tracking performance at vortex shedding frequencies without disrupting lift mechanisms

Science.gov (United States)

Matthews, Megan; Sponberg, Simon

2017-11-01

Birds, insects, and many animals use unsteady aerodynamic mechanisms to achieve stable hovering flight. Natural environments are often characterized by unsteady flows causing animals to dynamically respond to perturbations while performing complex tasks, such as foraging. Little is known about how unsteady flow around an animal interacts with already unsteady flow in the environment or how this impacts performance. We study how the environment impacts maneuverability to reveal any coupling between body dynamics and aerodynamics for hawkmoths, Manduca sexta,tracking a 3D-printed robotic flower in a wind tunnel. We also observe the leading-edge vortex (LEV), a known lift-generating mechanism for insect flight with smoke visualization. Moths in still and unsteady air exhibit near perfect tracking at low frequencies, but tracking in the flower wake results in larger overshoot at mid-range. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite the large effect on flight dynamics, the LEV remains bound to the wing and thorax throughout the wingstroke. In general, unsteady wind seems to decrease maneuverability, but LEV stability seems decoupled from changes in flight dynamics.

The Energy Budget of a Southwest Vortex With Heavy Rainfall over South China

Institute of Scientific and Technical Information of China (English)

无

2011-01-01

Energy budgets were analyzed to study the development of an eastward propagating southwest vortex （SWV） associated with heavy rainfall over southern China（11-13 June 2008）.The results show that kinetic energy（KE） generation and advection were the most important KE sources,while friction and sub-grid processes were the main KE sinks.There was downward conversion from divergent to rotational wind KE consistent with the downward stretching of SWVs.The Coriolis force was important for the formation and maintenance of the SWV.Convergence was also an important factor for maintenance,as was vertical motion during the mature stage of the SWV and the formation stage of a newly formed vortex（vortex B）.The conversion from available potential energy（APE） to KE of divergent wind can lead to strong convection.Vertical motion influenced APE by dynamical and thermal processes which had opposite effects. The variation of APE was related to the heavy rainfall and convection;in this case,vertical motion with direct thermal circulation was the most important way in which APE was released,while latent heat release and vertical temperature advection were important for APE generation.

Profile of the horizontal wind variance near the ground in near neutral flow – K-theory and the transport of the turbulent kinetic energy

Directory of Open Access Journals (Sweden)

S. Yahaya

2009-05-01

Full Text Available This paper deals with the characteristics of the atmospheric turbulent flow in the vicinity of the ground, and particularly with the profile of the horizontal wind variance. The study is based on experimental measurements performed with fast cup anemometers located near the ground at 5 different levels (from 0.25 to 4 m and sampled at 1 Hz. The experiment was carried over two agricultural plots with various tillage treatments in a fallow semiarid area (Central Aragon, Spain. The results of this study reveal that near the ground surface and under moderate wind, the horizontal wind variance logarithmically increases with height, in direct relationship with the friction velocity and the roughness length scale. A theoretical development has allowed us to link this behaviour to the modeling of the turbulent kinetic energy (TKE transport through the eddy diffusivity. Thus, the study proposes a formulation of the similarity universal function of the horizontal wind variance. Besides, the formulation offers a new method for the determination of the friction velocity and the roughness length scale and can be used for the evaluation of the TKE transport rate.

The singing vortex

Science.gov (United States)

Arndt, R.; Pennings, P.; Bosschers, J.; van Terwisga, T.

2015-01-01

Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures. PMID:26442147

DNS of droplet-vortex interaction with a Karman vortex street

International Nuclear Information System (INIS)

Burger, M.; Schmehl, R.; Koch, R.; Wittig, S.; Bauer, H.-J.

2006-01-01

Predicting fuel spray interaction with large scale vortex structures still is a major challenge for state-of-the-art CFD codes. In order to elucidate the mechanisms involved, a fundamental study has been carried out in which the interaction of water droplets with a Karman vortex street is investigated. The disperse two-phase flow around a cylinder has been computed taking into account the mass, momentum and heat transfer between both phases. Flow conditions are chosen such that large scale vortices are generated by periodic flow separations of the well known Karman vortex street. A homogeneous distribution of water droplets is injected into the hot air up-stream of the computational domain. The mixing process as well as the impact of the droplets on the gas phase instabilities is analyzed in the downstream region where large scale vortex structures are present

Forest trees filter chronic wind-signals to acclimate to high winds.

Science.gov (United States)

Bonnesoeur, Vivien; Constant, Thiéry; Moulia, Bruno; Fournier, Meriem

2016-05-01

Controlled experiments have shown that trees acclimate thigmomorphogenetically to wind-loads by sensing their deformation (strain). However, the strain regime in nature is exposed to a full spectrum of winds. We hypothesized that trees avoid overreacting by responding only to winds which bring information on local climate and/or wind exposure. Additionally, competition for light dependent on tree social status also likely affects thigmomorphogenesis. We monitored and manipulated quantitatively the strain regimes of 15 pairs of beech (Fagus sylvatica) trees of contrasting social status in an acclimated stand, and quantified the effects of these regimes on the radial growth over a vegetative season. Trees exposed to artificial bending, the intensity of which corresponds to the strongest wind-induced strains, enhanced their secondary growth by at least 80%. Surprisingly, this reaction was even greater - relatively - for suppressed trees than for dominant ones. Acclimated trees did not sense the different types of wind events in the same way. Daily wind speed peaks due to thermal winds were filtered out. Thigmomorphogenesis was therefore driven by intense storms. Thigmomorphogenesis is also likely to be involved in determining social status. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Ground-based Polarization Remote Sensing of Atmospheric Aerosols and the Correlation between Polarization Degree and PM2.5

International Nuclear Information System (INIS)

Cheng, Chen; Zhengqiang, Li; Weizhen, Hou; Yisong, Xie; Donghui, Li; Kaitao, Li; Ying, Zhang

2014-01-01

The ground-based polarization remote sensing adds the polarization dimension information to traditional intensity detection, which provides a new method to detect atmospheric aerosols properties. In this paper, the polarization measurements achieved by a new multi-wavelength sun photometer, CE318-DP, are used for the ground-based remote sensing of atmospheric aerosols. In addition, a polarized vector radiative transfer model is introduced to simulate the DOLP (Degree Of Linear Polarization) under different sky conditions. At last, the correlative analysis between mass density of PM 2.5 and multi-wavelength and multi-angular DOLP is carried out. The result shows that DOLP has a high correlation with mass density of PM 2.5 , R 2 >0.85. As a consequence, this work provides a new method to estimate the mass density of PM 2.5 by using the comprehensive network of ground-based sun photometer

A wind-tunnel investigation of parameters affecting helicopter directional control at low speeds in ground effect

Science.gov (United States)

Yeager, W. T., Jr.; Young, W. H., Jr.; Mantay, W. R.

1974-01-01

An investigation was conducted in the Langley full-scale tunnel to measure the performance of several helicopter tail-rotor/fin configurations with regard to directional control problems encountered at low speeds in ground effect. Tests were conducted at wind azimuths of 0 deg to 360 deg in increments of 30 deg and 60 deg and at wind speeds from 0 to 35 knots. The results indicate that at certain combinations of wind speed and wind azimuth, large increases in adverse fin force require correspondingly large increases in the tail-rotor thrust, collective pitch, and power required to maintain yaw trim. Changing the tail-rotor direction of rotation to top blade aft for either a pusher tail rotor (tail-rotor wake blowing away from fin) or a tractor tail rotor (tail-rotor wake blowing against fin) will alleviate this problem. For a pusher tail rotor at 180 deg wind azimuth, increases in the fin/tail-rotor gap were not found to have any significant influence on the overall vehicle directional control capability. Changing the tail rotor to a higher position was found to improve tail-rotor performance for a fin-off configuration at a wind azimuth of 180 deg. A V-tail configuration with a pusher tail rotor with top blade aft direction of rotation was found to be the best configuration with regard to overall directional control capability.

A differentiated plane wave as an electromagnetic vortex

International Nuclear Information System (INIS)

Hannay, J H; Nye, J F

2015-01-01

Differentiating a complex scalar plane wave with respect to its direction produces an isolated straight vortex line and has a natural extension, described in earlier papers, to the vector waves of electromagnetism—a differentiated plane wave (DPW). It epitomizes destructive interference and will be shown to have the local structure of an electromagnetic vortex. In this paper its polarization structure and Poynting vector field are compared and contrasted with that of the family of linear polynomial waves, of which it is a special member. By definition this wider family has a general linear complex vector function of position multiplying a plane wave, but the function must be such that the combination satisfies Maxwell’s equations. This forces translational invariance of the function along the wavevector direction—in other words the wave is ‘non-diffracting’. In a natural sense all possible polarizations are exhibited once only. But the DPW has a distinctive polarization structure only partly explored previously. Both classes of waves share similar Poynting vector fields, which can be ‘elliptic’ (helix-like flow lines) or ‘hyperbolic’, of a repulsive nature, unexpected for a vortex. Both classes can be considered as a limit in the superposition of three closely parallel ordinary plane waves in destructive interference, and this derivation is supplied in full here. (paper)

Wake meandering of a model wind turbine operating in two different regimes

Science.gov (United States)

Foti, Daniel; Yang, Xiaolei; Campagnolo, Filippo; Maniaci, David; Sotiropoulos, Fotis

2018-05-01

The flow behind a model wind turbine under two different turbine operating regimes (region 2 for turbine operating at optimal condition with the maximum power coefficient and 1.4-deg pitch angle and region 3 for turbine operating at suboptimal condition with a lower power coefficient and 7-deg pitch angle) is investigated using wind tunnel experiments and numerical experiments using large-eddy simulation (LES) with actuator surface models for turbine blades and nacelle. Measurements from the model wind turbine experiment reveal that the power coefficient and turbine wake are affected by the operating regime. Simulations with and without a nacelle model are carried out for each operating condition to study the influence of the operating regime and nacelle on the formation of the hub vortex and wake meandering. Statistics and energy spectra of the simulated wakes are in good agreement with the measurements. For simulations with a nacelle model, the mean flow field is composed of an outer wake, caused by energy extraction by turbine blades, and an inner wake directly behind the nacelle, while for the simulations without a nacelle model, the central region of the wake is occupied by a jet. The simulations with the nacelle model reveal an unstable helical hub vortex expanding outward toward the outer wake, while the simulations without a nacelle model show a stable and columnar hub vortex. Because of the different interactions of the inner region of the wake with the outer region of the wake, a region with higher turbulence intensity is observed in the tip shear layer for the simulation with a nacelle model. The hub vortex for the turbine operating in region 3 remains in a tight helical spiral and intercepts the outer wake a few diameters further downstream than for the turbine operating in region 2. Wake meandering, a low-frequency large-scale motion of the wake, commences in the region of high turbulence intensity for all simulations with and without a nacelle model

A local-circulation model for Darrieus vertical-axis wind turbines

Science.gov (United States)

Masse, B.

1986-04-01

A new computational model for the aerodynamics of the vertical-axis wind turbine is presented. Based on the local-circulation method generalized for curved blades, combined with a wake model for the vertical-axis wind turbine, it differs markedly from current models based on variations in the streamtube momentum and vortex models using the lifting-line theory. A computer code has been developed to calculate the loads and performance of the Darrieus vertical-axis wind turbine. The results show good agreement with experimental data and compare well with other methods.

A vortex ring interacting with a vortex filament and its deformation near the two-dimensional stagnation point

International Nuclear Information System (INIS)

Kiya, M.; Sato, T.

1986-01-01

In this paper the interaction between vortex filaments and vortex rings and the deformation of vortex rings near the two-dimensional stagnation point are simulated by a three-dimensional vortex method. The two problems are respectively concerned with the effect of free-stream turbulence on turbulent plane mixing layers and the production of turbulence by the vortex stretching near saddles associated with large-scale coherent structures. The authors assume that the first step to understand the free-stream turbulence effect is to study the interaction between a vortex ring and a vortex filament and that the process of deformation of a vortex ring gives us a clue to understand physical processes occurring near the saddles

Wind measurement via direct detection lidar

Science.gov (United States)

Afek, I.; Sela, N.; Narkiss, N.; Shamai, G.; Tsadka, S.

2013-10-01

Wind sensing Lidar is considered a promising technology for high quality wind measurements required for various applications such as hub height wind resource assessment, power curve measurements and advanced, real time, forward looking turbine control. Until recently, the only available Lidar technology was based on coherent Doppler shift detection, whose market acceptance has been slow primarily due to its exuberant price. Direct detection Lidar technology provides an alternative to remote sensing of wind by incorporating high precision measurement, a robust design and an affordable price tag.

High Resolution Mapping of Wind Speed Using Active Distributed Temperature Sensing

Science.gov (United States)

Sayde, C.; Thomas, C. K.; Wagner, J.; Selker, J. S.

2013-12-01

We present a novel approach to continuously measure wind speed simultaneously at thousands of locations using actively heated fiber optics with a distributed temperature sensing system (DTS). Analogous to a hot-wire anemometer, this approach is based on the principal of velocity-dependent heat transfer from a heated surface: The temperature difference between the heated surface and ambient air is a function of the convective cooling of the air flowing past the surface. By knowing the thermal properties of the heated surface, the heating input, and ambient temperature, wind speed can be calculated. In our case, the heated surface consists of a thin stainless steel tube that can exceed several km in length. A fiber optic is enclosed within the stainless steel tube to report the heated tube temperature, which in this case was sampled every 0.125 m. Ambient temperature were measured by an independent fiber optic cable located proximally to the stainless steel tube. We will present the theoretical bases of measuring wind speed using heated fiber optic as well as validation of this method in the field. In the field testing, more than 5000 simultaneous wind speed measurements were obtained every 5.5 second at 3 elevations (2m, 1m, and 0.5 m) every 0.125 m along a 230 m transects located across a shallow gulley in Nunn, CO. This method, which provides both air temperature and wind speed spanning four orders of magnitude in spatial scale (0.1 - 1,000m) opens up many important opportunities for testing basic theories in micro-meteorology regarding spatial scales of turbulent length scales as a function of distance from the earth, development of internal boundary layers, applicability of Taylors hypothesis, etc. The equipment employed, including the heating system, which is available to all US scientists, was provided by CTEMPs.org thanks to the generous grant support from the National Science Foundation under Grant Number 1129003. Any opinions, findings, and conclusions or

The Effect of Predicted Vehicle Displacement on Ground Crew Task Performance and Hardware Design

Science.gov (United States)

Atencio, Laura Ashley; Reynolds, David W.

2011-01-01

NASA continues to explore new launch vehicle concepts that will carry astronauts to low- Earth orbit to replace the soon-to-be retired Space Transportation System (STS) shuttle. A tall vertically stacked launch vehicle (> or =300 ft) is exposed to the natural environment while positioned on the launch pad. Varying directional winds and vortex shedding cause the vehicle to sway in an oscillating motion. Ground crews working high on the tower and inside the vehicle during launch preparations will be subjected to this motion while conducting critical closeout tasks such as mating fluid and electrical connectors and carrying heavy objects. NASA has not experienced performing these tasks in such environments since the Saturn V, which was serviced from a movable (but rigid) service structure; commercial launchers are likewise attended by a service structure that moves away from the vehicle for launch. There is concern that vehicle displacement may hinder ground crew operations, impact the ground system designs, and ultimately affect launch availability. The vehicle sway assessment objective is to replicate predicted frequencies and displacements of these tall vehicles, examine typical ground crew tasks, and provide insight into potential vehicle design considerations and ground crew performance guidelines. This paper outlines the methodology, configurations, and motion testing performed while conducting the vehicle displacement assessment that will be used as a Technical Memorandum for future vertically stacked vehicle designs.

Imaging of artificially induced vortex structures

International Nuclear Information System (INIS)

Fasano, Yanina; Menghini, M.; Cruz, F. de la

2004-01-01

The combination of engineered pinning potentials in superconducting crystals, the detection of the liquid-solid vortex transition and the observation of the vortex structure with single vortex sensitivity allow the microscopic analysis of the response of 3D elastic systems to the presence of these potentials. In this work we review recent results obtained by a combination of those techniques studying different vortex structure induced transformations. On the one hand, we have visualized the transformation, along the vortex direction, of a bulk vortex single crystal with hexagonal symmetry into another crystal with square symmetry induced by an engineered Fe-dot lattice deposited on a surface of the vortex single crystal. On the other hand, we found an infrequent first-order phase transition where a vortex liquid under the presence of a random correlated potential (columnar defects) transforms into a vortex solid with no change of topological order

MJO-Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models.

Science.gov (United States)

Garfinkel, C I; Schwartz, C

2017-10-16

The effect of the Madden-Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex in the period preceding stratospheric sudden warmings is evaluated in operational subseasonal forecasting models. Reforecasts which simulate stronger MJO-related convection in the Tropical West Pacific also simulate enhanced heat flux in the lowermost stratosphere and a more realistic vortex evolution. The time scale on which vortex predictability is enhanced lies between 2 and 4 weeks for nearly all cases. Those stratospheric sudden warmings that were preceded by a strong MJO event are more predictable at ∼20 day leads than stratospheric sudden warmings not preceded by a MJO event. Hence, knowledge of the MJO can contribute to enhanced predictability, at least in a probabilistic sense, of the Northern Hemisphere polar stratosphere.

Influence of wind velocity fluctuation on air temperature difference between the fan and ground levels and the effect of frost protective fan operation

International Nuclear Information System (INIS)

Araki, T.; Matsuo, K.; Miyama, D.; Sumikawa, O.; Araki, S.

2008-01-01

We invested the influence of wind velocity fluctuation on air temperature difference between the fan (4.8 m) and ground levels (0.5 m) and the effect of frost protective fan operation in order to develop a new method to reduce electricity consumption due to frost protective fan operation. The results of the investigations are summarized as follows: (1) Air temperature difference between the fan (4.8 m) and ground levels (0.5 m) was decreased following an increase in wind velocity, and the difference was less than 1°C for a wind velocity more than 3.0 m/s at a height of 6.5 m. (2) When the wind velocity was more than 2-3 m/s, there was hardly any increase in the temperature of the leaves. In contrast, when the wind velocity was less than 2-3 m/s, an increase in the temperature of the leaves was observed. Based on these results, it is possible that when the wind velocity is greater than 2-3 m, it prevents thermal inversion. Therefore, there would be no warmer air for the frost protective fan to return to the tea plants and the air turbulence produced by the frost protective fan would not reach the plants under the windy condition

Middle atmospheric water vapour and dynamics in the vicinity of the polar vortex during the Hygrosonde-2 campaign

Directory of Open Access Journals (Sweden)

S. Lossow

2009-07-01

Full Text Available The Hygrosonde-2 campaign took place on 16 December 2001 at Esrange/Sweden (68° N, 21° E with the aim to investigate the small scale distribution of water vapour in the middle atmosphere in the vicinity of the Arctic polar vortex. In situ balloon and rocket-borne measurements of water vapour were performed by means of OH fluorescence hygrometry. The combined measurements yielded a high resolution water vapour profile up to an altitude of 75 km. Using the characteristic of water vapour being a dynamical tracer it was possible to directly relate the water vapour data to the location of the polar vortex edge, which separates air masses of different character inside and outside the polar vortex. The measurements probed extra-vortex air in the altitude range between 45 km and 60 km and vortex air elsewhere. Transitions between vortex and extra-vortex usually coincided with wind shears caused by gravity waves which advect air masses with different water vapour volume mixing ratios.

From the combination of the results from the Hygrosonde-2 campaign and the first flight of the optical hygrometer in 1994 (Hygrosonde-1 a clear picture of the characteristic water vapour distribution inside and outside the polar vortex can be drawn. Systematic differences in the water vapour concentration between the inside and outside of the polar vortex can be observed all the way up into the mesosphere. It is also evident that in situ measurements with high spatial resolution are needed to fully account for the small-scale exchange processes in the polar winter middle atmosphere.

A Comparison of sector-scan and dual Doppler wind measurements at Høvsøre Test Station – one lidar or two?

DEFF Research Database (Denmark)

Simon, Elliot; Courtney, Michael

from the coast). Ground based remote sensing has numerous advantages over traditional in-situ (offshore met mast) and buoy based installations, mainly in terms or cost, complexity, and failure/delay risk. Since each lidar can only measure a portion of the wind vector, it is necessary to either deploy...

Modelling desertification risk in the north-west of Jordan using geospatial and remote sensing techniques

Directory of Open Access Journals (Sweden)

Jawad T. Al-Bakri

2016-03-01

Full Text Available Remote sensing, climate, and ground data were used within a geographic information system (GIS to map desertification risk in the north-west of Jordan. The approach was based on modelling wind and water erosion and incorporating the results with a map representing the severity of drought. Water erosion was modelled by the universal soil loss equation, while wind erosion was modelled by a dust emission model. The extent of drought was mapped using the evapotranspiration water stress index (EWSI which incorporated actual and potential evapotranspiration. Output maps were assessed within GIS in terms of spatial patterns and the degree of correlation with soil surficial properties. Results showed that both topography and soil explained 75% of the variation in water erosion, while soil explained 25% of the variation in wind erosion, which was mainly controlled by natural factors of topography and wind. Analysis of the EWSI map showed that drought risk was dominating most of the rainfed areas. The combined effects of soil erosion and drought were reflected on the desertification risk map. The adoption of these geospatial and remote sensing techniques is, therefore, recommended to map desertification risk in Jordan and in similar arid environments.

Losses Analysis of Different Grounding Schemes for Transformer-less Wind Turbine with Full-Scale Power Converter

DEFF Research Database (Denmark)

Sztykiel, Michal; Teodorescu, Remus; Munk-Nielsen, Stig

2013-01-01

Following work examines IGBT power loss and temperature distribution with regard to specific grounding method for the future concept of transformer-less offshore wind turbine. Analysis is performed via steady-state IGBT power loss estimator, which is made based on averaging of repetitive pulse...... cycles. Obtained results are validated with the experimental test set-up consisting of high power IGBTs....

Evidence of small-scale magnetic concentrations dragged by vortex motion of solar photospheric plasma

Science.gov (United States)

Balmaceda, L.; Vargas Domínguez, S.; Palacios, J.; Cabello, I.; Domingo, V.

2010-04-01

Vortex-type motions have been measured by tracking bright points in high-resolution observations of the solar photosphere. These small-scale motions are thought to be determinant in the evolution of magnetic footpoints and their interaction with plasma and therefore likely to play a role in heating the upper solar atmosphere by twisting magnetic flux tubes. We report the observation of magnetic concentrations being dragged towards the center of a convective vortex motion in the solar photosphere from high-resolution ground-based and space-borne data. We describe this event by analyzing a series of images at different solar atmospheric layers. By computing horizontal proper motions, we detect a vortex whose center appears to be the draining point for the magnetic concentrations detected in magnetograms and well-correlated with the locations of bright points seen in G-band and CN images.

MAP, MAC, and vortex-rings configurations in the Weinberg-Salam model

Science.gov (United States)

Teh, Rosy; Ng, Ban-Loong; Wong, Khai-Ming

2015-11-01

We report on the presence of new axially symmetric monopoles, antimonopoles and vortex-rings solutions of the SU(2)×U(1) Weinberg-Salam model of electromagnetic and weak interactions. When the ϕ-winding number n = 1, and 2, the configurations are monopole-antimonopole pair (MAP) and monopole-antimonopole chain (MAC) with poles of alternating sign magnetic charge arranged along the z-axis. Vortex-rings start to appear from the MAP and MAC configurations when the winding number n = 3. The MAP configurations possess zero net magnetic charge whereas the MAC configurations possess net magnetic charge of 4 πn / e. In the MAP configurations, the monopole-antimonopole pair is bounded by the Z0 field flux string and there is an electromagnetic current loop encircling it. The monopole and antimonopole possess magnetic charges ± 4πn/e sin2θW respectively. In the MAC configurations there is no string connecting the monopole and the adjacent antimonopole and they possess magnetic charges ± 4 πn/e respectively. The MAC configurations possess infinite total energy and zero magnetic dipole moment whereas the MAP configurations which are actually sphalerons possess finite total energy and magnetic dipole moment. The configurations were investigated for varying values of Higgs self-coupling constant 0 ≤ λ ≤ 40 at Weinberg angle θW = π/4.

Relation between current sheets and vortex sheets in stationary incompressible MHD

Directory of Open Access Journals (Sweden)

D. H. Nickeler

2012-03-01

Full Text Available Magnetohydrodynamic configurations with strong localized current concentrations and vortices play an important role in the dissipation of energy in space and astrophysical plasma. Within this work we investigate the relation between current sheets and vortex sheets in incompressible, stationary equilibria. For this approach it is helpful that the similar mathematical structure of magnetohydrostatics and stationary incompressible hydrodynamics allows us to transform static equilibria into stationary ones. The main control function for such a transformation is the profile of the Alfvén-Mach number MA, which is always constant along magnetic field lines, but can change from one field line to another. In the case of a global constant MA, vortices and electric current concentrations are parallel. More interesting is the nonlinear case, where MA varies perpendicular to the field lines. This is a typical situation at boundary layers like the magnetopause, heliopause, the solar wind flowing around helmet streamers and at the boundary of solar coronal holes. The corresponding current and vortex sheets show in some cases also an alignment, but not in every case. For special density distributions in 2-D, it is possible to have current but no vortex sheets. In 2-D, vortex sheets of field aligned-flows can also exist without strong current sheets, taking the limit of small Alfvén Mach numbers into account. The current sheet can vanish if the Alfvén Mach number is (almost constant and the density gradient is large across some boundary layer. It should be emphasized that the used theory is not only valid for small Alfvén Mach numbers MA MA ≲ 1. Connection to other theoretical approaches and observations and physical effects in space plasmas are presented. Differences in the various aspects of theoretical investigations of current sheets and vortex sheets are given.

Investigation and Optimization of Blade Tip Winglets Using an Implicit Free Wake Vortex Method

Science.gov (United States)

Lawton, Stephen; Crawford, Curran

2014-06-01

Novel outer-blade geometries such as tip winglets can increase the aerodynamic power that can be extracted from the wind by tailoring the relative position and strengths of trailed vorticity. This design space is explored using both parameter studies and gradient-based optimization, with the aerodynamic analysis carried out using LibAero, a free wake vortex-based code introduced in previous work. The starting design is the NREL 5MW reference turbine, which allows comparison of the aerodynamic simulation for the unmodified blade with other codes. The code uses a Prandtl-Weissinger lifting line model to represent the blade, and vortex filaments as the flow elements. A fast multipole method is implemented to accelerate the influence calculations and reduce the computational cost. This results in higher fidelity aerodynamic simulations that can capture the effects of novel geometries while maintaining sufficiently fast run-times (on the order of an hour) to allow the use of optimization. Gradients of the objective function with respect to design variables are calculated using the complex step method which is accurate and efficient. Since the vortex structure behind the rotor is being resolved in detail, insight is also gained into the mechanisms by which these new blade designs affect performance. It is found that adding winglets can increase the power extracted from the wind by around 2%, with a similar increase in thrust. It is also possible to create a winglet that slightly lowers the thrust while maintaining very similar power compared to the standard straight blade.

Investigation and Optimization of Blade Tip Winglets Using an Implicit Free Wake Vortex Method

International Nuclear Information System (INIS)

Lawton, Stephen; Crawford, Curran

2014-01-01

Novel outer-blade geometries such as tip winglets can increase the aerodynamic power that can be extracted from the wind by tailoring the relative position and strengths of trailed vorticity. This design space is explored using both parameter studies and gradient-based optimization, with the aerodynamic analysis carried out using LibAero, a free wake vortex-based code introduced in previous work. The starting design is the NREL 5MW reference turbine, which allows comparison of the aerodynamic simulation for the unmodified blade with other codes. The code uses a Prandtl-Weissinger lifting line model to represent the blade, and vortex filaments as the flow elements. A fast multipole method is implemented to accelerate the influence calculations and reduce the computational cost. This results in higher fidelity aerodynamic simulations that can capture the effects of novel geometries while maintaining sufficiently fast run-times (on the order of an hour) to allow the use of optimization. Gradients of the objective function with respect to design variables are calculated using the complex step method which is accurate and efficient. Since the vortex structure behind the rotor is being resolved in detail, insight is also gained into the mechanisms by which these new blade designs affect performance. It is found that adding winglets can increase the power extracted from the wind by around 2%, with a similar increase in thrust. It is also possible to create a winglet that slightly lowers the thrust while maintaining very similar power compared to the standard straight blade

Orientation of bluff body for designing efficient energy harvesters from vortex-induced vibrations

International Nuclear Information System (INIS)

Dai, H. L.; Abdelkefi, A.; Yang, Y.; Wang, L.

2016-01-01

The characteristics and performances of four distinct vortex-induced vibrations (VIVs) piezoelectric energy harvesters are experimentally investigated and compared. The difference between these VIV energy harvesters is the installation of the cylindrical bluff body at the tip of cantilever beam with different orientations (bottom, top, horizontal, and vertical). Experiments show that the synchronization regions of the bottom, top, and horizontal configurations are almost the same at low wind speeds (around 1.5 m/s). The vertical configuration has the highest wind speed for synchronization (around 3.5 m/s) with the largest harvested power, which is explained by its highest natural frequency and the smallest coupled damping. The results lead to the conclusion that to design efficient VIV energy harvesters, the bluff body should be aligned with the beam for low wind speeds (<2 m/s) and perpendicular to the beam at high wind speeds (>2 m/s)

Wind profiler observations on orographic effects of typhoon wind structure modification over Taiwan (120.38 E, 22.6 N)

Energy Technology Data Exchange (ETDEWEB)

Pan, C.J.; Yang, S.S. [National Central Univ., Taiwan (China). Inst. of Space Science; Krishna Reddy, K. [Yogi Vemana Univ., Kadapa (India). Dept. of Physics; Lai, H.C. [Chang Jung Christian Univ., Taiwan (China). Dept. of Engineering and Management Advanced Technology; Wong, C.J. [Universiti Sains Malaysia (Malaysia). School of Physics

2010-07-01

The interaction of the storm circulation with the Central Mountain Range (CMR) of Taiwan is studied with a wind profiler located at the leeside during the invasions of two (Kaemi (200605) and Bopha (200609)) typhoons. The moderate typhoon Kaemi upgraded from a tropical depression on 21 July 2006. It then was made landfall at 15:45 UTC on 24 July 2006 near Cheng-Kung. The weak typhoon Bopha formed at about 12:00 UTC on 5 August 2006 and also landed near Cheng-Kung at around 19:20 UTC on 8 August. A new finding from both typhoons is the vortex splitting into upper and lower parts with the two typhoons that have passed the observation site nearly. For the typhoon Kaemi, demarcation height of the upper-level vortex and lower level is at 2.8 km and passed the site about 3 h earlier than the low-level one. For the typhoon Bopha, the center of the lower-level vortex at 3.5 km locates to the north of the upper-level one at 5.2 km. The re-organization of the split vortexes is found in typhoon Kaemi but not for typhoon Bopha. (orig.)

Propagation of optical vortex beams and nucleation of vortex-antivortex pairs in disordered nonlinear photonic lattices

International Nuclear Information System (INIS)

Cho, Yeong-Kwon; Kim, Ki-Hong

2014-01-01

The propagation of optical vortex beams through disordered nonlinear photonic lattices is numerically studied. The vortex beams are generated by using a superposition of several Gaussian laser beams arranged in a radially-symmetric manner. The paraxial nonlinear Schroedinger equation describing the longitudinal propagation of the beam array through nonlinear triangular photonic lattices with two-dimensional disorder is solved numerically by using the split-step Fourier method. We find that due to the spatial disorder, the vortex beam is destabilized after propagating a finite distance and new vortex-antivortex pairs are nucleated at the positions of perfect destructive interference. We also find that in the presence of a self-focusing nonlinearity, the vortex-antivortex pair nucleation is suppressed and the vortex beam becomes more stable, while a self-defocusing nonlinearity enhances the vortex-antivortex pair nucleation.

On the spatial and temporal resolution of land cover products for applied use in wind resource mapping

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Badger, Merete; Dellwik, Ebba

as input for modelling the wind conditions over a Danish near-coastal region. The flow model results were compared to alternative use of USGS land cover. Significant variations in the wind speed were found between the two atmospheric flow model results. Furthermore the wind speed from the flow model...... was compared to meteorological observations taken in a tall mast and from ground based remote-sensing wind profiling lidars. It is shown that simulations using CORINE provide better wind flow results close to the surface as compared to those using USGS on the investigated site. The next step towards...... improvement of flow model inputs is to investigate in further detail applied use of satellite maps in forested areas. 75% of new land-based wind farms are planned in or near forests in Europe. In forested areas the near surface atmospheric flow is more challenging to calculate than in regions with low...

Sensing the wind profile

DEFF Research Database (Denmark)

Pena Diaz, Alfredo

This thesis consists of two parts. The first is a synopsis of the theoretical progress of the study that is based on a number of journal papers. The papers, which constitute the second part of the report, aim to analyze, measure, and model the wind prole in and beyond the surface layer by combini...

Remote sensing: best practice

Energy Technology Data Exchange (ETDEWEB)

Brown, Gareth [Sgurr Energy (Canada)

2011-07-01

This paper presents remote sensing best practice in the wind industry. Remote sensing is a technique whereby measurements are obtained from the interaction of laser or acoustic pulses with the atmosphere. There is a vast diversity of tools and techniques available and they offer wide scope for reducing project uncertainty and risk but best practice must take into account versatility and flexibility. It should focus on the outcome in terms of results and data. However, traceability of accuracy requires comparison with conventional instruments. The framework for the Boulder protocol is given. Overviews of the guidelines for IEA SODAR and IEA LIDAR are also mentioned. The important elements of IEC 61400-12-1, an international standard for wind turbines, are given. Bankability is defined based on the Boulder protocol and a pie chart is presented that illustrates the uncertainty area covered by remote sensing. In conclusion it can be said that remote sensing is changing perceptions about how wind energy assessments can be made.

Finite Element Based Lagrangian Vortex Dynamics Model for Wind Turbine Aerodynamics

International Nuclear Information System (INIS)

McWilliam, Michael K; Crawford, Curran

2014-01-01

This paper presents a novel aerodynamic model based on Lagrangian Vortex Dynamics (LVD) formulated using a Finite Element (FE) approach. The advantage of LVD is improved fidelity over Blade Element Momentum Theory (BEMT) while being faster than Numerical Navier-Stokes Models (NNSM) in either primitive or velocity-vorticity formulations. The model improves on conventional LVD in three ways. First, the model is based on an error minimization formulation that can be solved with fast root finding algorithms. In addition to improving accuracy, this eliminates the intrinsic numerical instability of conventional relaxed wake simulations. The method has further advantages in optimization and aero-elastic simulations for two reasons. The root finding algorithm can solve the aerodynamic and structural equations simultaneously, avoiding Gauss-Seidel iteration for compatibility constraints. The second is that the formulation allows for an analytical definition for sensitivity calculations. The second improvement comes from a new discretization scheme based on an FE formulation and numerical quadrature that decouples the spatial, influencing and temporal meshes. The shape for each trailing filament uses basis functions (interpolating splines) that allow for both local polynomial order and element size refinement. A completely independent scheme distributes the influencing (vorticity) elements along the basis functions. This allows for concentrated elements in the near wake for accuracy and progressively less in the far-wake for efficiency. Finally the third improvement is the use of a far-wake model based on semi-infinite vortex cylinders where the radius and strength are related to the wake state. The error-based FE formulation allows the transition to the far wake to occur across a fixed plane

Vortex and half-vortex dynamics in a nonlinear spinor quantum fluid.

Science.gov (United States)

Dominici, Lorenzo; Dagvadorj, Galbadrakh; Fellows, Jonathan M; Ballarini, Dario; De Giorgi, Milena; Marchetti, Francesca M; Piccirillo, Bruno; Marrucci, Lorenzo; Bramati, Alberto; Gigli, Giuseppe; Szymańska, Marzena H; Sanvitto, Daniele

2015-12-01

Vortices are archetypal objects that recur in the universe across the scale of complexity, from subatomic particles to galaxies and black holes. Their appearance is connected with spontaneous symmetry breaking and phase transitions. In Bose-Einstein condensates and superfluids, vortices are both point-like and quantized quasiparticles. We use a two-dimensional (2D) fluid of polaritons, bosonic particles constituted by hybrid photonic and electronic oscillations, to study quantum vortex dynamics. Polaritons benefit from easiness of wave function phase detection, a spinor nature sustaining half-integer vorticity, strong nonlinearity, and tuning of the background disorder. We can directly generate by resonant pulsed excitations a polariton condensate carrying either a full or half-integer vortex as initial condition and follow their coherent evolution using ultrafast imaging on the picosecond scale. The observations highlight a rich phenomenology, such as the spiraling of the half-vortex and the joint path of the twin charges of a full vortex, until the moment of their splitting. Furthermore, we observe the ordered branching into newly generated secondary couples, associated with the breaking of radial and azimuthal symmetries. This allows us to devise the interplay of nonlinearity and sample disorder in shaping the fluid and driving the vortex dynamics. In addition, our observations suggest that phase singularities may be seen as fundamental particles whose quantized events span from pair creation and recombination to 2D+t topological vortex strings.

Vortex generation and wave-vortex interaction over a concave plate with roughness and suction

Science.gov (United States)

Bertolotti, Fabio

1993-01-01

The generation and amplification of vortices by surface homogeneities, both in the form of surface waviness and of wall-normal velocity, is investigated using the nonlinear parabolic stability equations. Transients and issues of algebraic growth are avoided through the use of a similarity solution as initial condition for the vortex. In the absence of curvature, the vortex decays as the square root of 1/x when flowing over streamwise aligned riblets of constant height, and grows as the square root of x when flowing over a corresponding streamwise aligned variation of blowing/suction transpiration velocity. However, in the presence of wall inhomogeneities having both streamwise and spanwise periodicity, the growth of the vortex can be much larger. In the presence of curvature, the vortex develops into a Gortler vortex. The 'direct' and 'indirect' interaction mechanisms possible in wave-vortex interaction are presented. The 'direct' interaction does not lead to strong resonance with the flow conditions investigated. The 'indirect' interaction leads to K-type transition.

ON THE RETRIEVAL OF MESOSPHERIC WINDS ON MARS AND VENUS FROM GROUND-BASED OBSERVATIONS AT 10 μm

Energy Technology Data Exchange (ETDEWEB)

Lopez-Valverde, M. A. [Instituto de Astrofisica de Andalucia, IAA/CSIC, Granada (Spain); Montabone, L. [Space Science Institute, Boulder, CO (United States); Sornig, M.; Sonnabend, G., E-mail: valverde@iaa.es [University of Cologne, KOSMA, Köln (Germany)

2016-01-10

A detailed analysis is presented of ground-based observations of atmospheric emissions on Mars and Venus under non-local thermodynamic equilibrium (non-LTE) conditions at high spectral resolution. Our first goal is to comprehend the difficulties behind the derivation of wind speeds from ground-based observations. A second goal is to set a framework to permit comparisons with other observations and with atmospheric models. A forward model including non-LTE radiative transfer is used to evaluate the information content within the telescopic beam, and is later convolved with the beam function and a typical wind field to discern the major contributions to the measured radiance, including limb and nadir views. The emission mostly arises from the non-LTE limb around altitudes of 75 km on Mars and 110 km on Venus. We propose a parameterization of the limb emission using few geophysical parameters which can be extended to other hypothetical CO{sub 2} planetary atmospheres. The tropospheric or LTE component of the emission varies with the temperature and is important at low solar illumination but only for the emerging radiance, not for the wind determinations since these are derived from the Doppler shift at the non-LTE line cores. We evaluated the sources of uncertainty and found that the forward model errors amount to approximately 12% of the measured winds, which is normally smaller than the instrumental errors. We applied this study to revise a set of measurements extending for three Martian years and confirmed previous results suggesting winds that are too large simulated by current Martian circulation models at equatorial latitudes during solstice. We encourage new observational campaigns, particularly for the strong jet at mid–high latitudes on Mars, and propose general guidelines and recommendations for future observations.

ON THE RETRIEVAL OF MESOSPHERIC WINDS ON MARS AND VENUS FROM GROUND-BASED OBSERVATIONS AT 10 μm

International Nuclear Information System (INIS)

Lopez-Valverde, M. A.; Montabone, L.; Sornig, M.; Sonnabend, G.

2016-01-01

A detailed analysis is presented of ground-based observations of atmospheric emissions on Mars and Venus under non-local thermodynamic equilibrium (non-LTE) conditions at high spectral resolution. Our first goal is to comprehend the difficulties behind the derivation of wind speeds from ground-based observations. A second goal is to set a framework to permit comparisons with other observations and with atmospheric models. A forward model including non-LTE radiative transfer is used to evaluate the information content within the telescopic beam, and is later convolved with the beam function and a typical wind field to discern the major contributions to the measured radiance, including limb and nadir views. The emission mostly arises from the non-LTE limb around altitudes of 75 km on Mars and 110 km on Venus. We propose a parameterization of the limb emission using few geophysical parameters which can be extended to other hypothetical CO 2 planetary atmospheres. The tropospheric or LTE component of the emission varies with the temperature and is important at low solar illumination but only for the emerging radiance, not for the wind determinations since these are derived from the Doppler shift at the non-LTE line cores. We evaluated the sources of uncertainty and found that the forward model errors amount to approximately 12% of the measured winds, which is normally smaller than the instrumental errors. We applied this study to revise a set of measurements extending for three Martian years and confirmed previous results suggesting winds that are too large simulated by current Martian circulation models at equatorial latitudes during solstice. We encourage new observational campaigns, particularly for the strong jet at mid–high latitudes on Mars, and propose general guidelines and recommendations for future observations

Blowing snow detection in Antarctica, from space borne and ground-based remote sensing

Science.gov (United States)

Gossart, A.; Souverijns, N.; Lhermitte, S.; Lenaerts, J.; Gorodetskaya, I.; Schween, J. H.; Van Lipzig, N. P. M.

2017-12-01

Surface mass balance (SMB) strongly controls spatial and temporal variations in the Antarctic Ice Sheet (AIS) mass balance and its contribution to sea level rise. Currently, the scarcity of observational data and the challenges of climate modelling over the ice sheet limit our understanding of the processes controlling AIS SMB. Particularly, the impact of blowing snow on local SMB is not yet constrained and is subject to large uncertainties. To assess the impact of blowing snow on local SMB, we investigate the attenuated backscatter profiles from ceilometers at two East Antarctic locations in Dronning Maud Land. Ceilometers are robust ground-based remote sensing instruments that yield information on cloud base height and vertical structure, but also provide information on the particles present in the boundary layer. We developed a new algorithm to detect blowing snow (snow particles lifted by the wind from the surface to substantial height) from the ceilometer attenuated backscatter. The algorithm successfully allows to detect strong blowing snow signal from layers thicker than 15 m at the Princess Elisabeth (PE, (72°S, 23°E)) and Neumayer (70°S, 8° W) stations. Applying the algorithm to PE, we retrieve the frequency and annual cycle of blowing snow as well as discriminate between clear sky and overcast conditions during blowing snow. We further apply the blowing snow algorithm at PE to evaluate the blowing snow events detection by satellite imagery (Palm et al., 2011): the near-surface blowing snow layers are apparent in lidar backscatter profiles and enable snowdrift events detection (spatial and temporal frequency, height and optical depth). These data are processed from CALIPSO, at a high resolution (1x1 km digital elevation model). However, the remote sensing detection of blowing snow events by satellite is limited to layers of a minimal thickness of 20-30 m. In addition, thick clouds, mostly occurring during winter storms, can impede drifting snow

Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw

Directory of Open Access Journals (Sweden)

Moutaz Elgammi

2016-06-01

Full Text Available Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through

Manipulation of vortex rings for flow control

International Nuclear Information System (INIS)

Toyoda, Kuniaki; Hiramoto, Riho

2009-01-01

This paper reviews the dynamics of vortex rings and the control of flow by the manipulation of vortex rings. Vortex rings play key roles in many flows; hence, the understanding of the dynamics of vortex rings is crucial for scientists and engineers dealing with flow phenomena. We describe the structures and motions of vortex rings in circular and noncircular jets, which are typical examples of flows evolving into vortex rings. For circular jets the mechanism of evolving, merging and breakdown of vortex rings is described, and for noncircular jets the dynamics of three-dimensional deformation and interaction of noncircular vortex rings under the effect of self- and mutual induction is discussed. The application of vortex-ring manipulation to the control of various flows is reviewed with successful examples, based on the relationship between the vortex ring dynamics and the flow properties. (invited paper)

Optical vortex scanning inside the Gaussian beam

International Nuclear Information System (INIS)

Masajada, J; Leniec, M; Augustyniak, I

2011-01-01

We discussed a new scanning method for optical vortex-based scanning microscopy. The optical vortex is introduced into the incident Gaussian beam by a vortex lens. Then the beam with the optical vortex is focused by an objective and illuminates the sample. By changing the position of the vortex lens we can shift the optical vortex position at the sample plane. By adjusting system parameters we can get 30 times smaller shift at the sample plane compared to the vortex lens shift. Moreover, if the range of vortex shifts is smaller than 3% of the beam radius in the sample plane the amplitude and phase distribution around the phase dislocation remains practically unchanged. Thus we can scan the sample topography precisely with an optical vortex

Ground Albedo Neutron Sensing (GANS) for Measurement of Integral Soil Water Content at the Small Catchment Scale

Science.gov (United States)

Rivera Villarreyes, C.; Baroni, G.; Oswald, S. E.

2012-12-01

Soil water content at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. One largest initiative to cover the measuring gap of soil moisture between point scale and remote sensing observations is the COSMOS network (Zreda et al., 2012). Here, cosmic-ray neutron sensing, which may be more precisely named ground albedo neutron sensing (GANS), is applied. The measuring principle is based on the crucial role of hydrogen as neutron moderator compared to others landscape materials. Soil water content contained in a footprint of ca. 600 m diameter and a depth ranging down to a few decimeters is inversely correlated to the neutron flux at the air-ground interface. This approach is now implemented, e.g. in USA (Zreda et al., 2012) and Germany (Rivera Villarreyes et al., 2011), based on its simple installation and integral measurement of soil moisture at the small catchment scale. The present study performed Ground Albedo Neutron Sensing on farmland at two locations in Germany under different vegetative situations (cropped and bare field) and different seasonal conditions (summer, autumn and winter). Ground albedo neutrons were measured at (i) a farmland close to Potsdam and Berlin cropped with corn in 2010, sunflower in 2011 and winter rye in 2012, and (ii) a mountainous farmland catchment (Schaefertal, Harz Mountains) since middle 2011. In order to test this methodology, classical soil moisture devices and meteorological data were used for comparison. Moreover, several calibration approaches, role of vegetation cover and transferability of calibration parameters to different times and locations were also evaluated. Observations suggest that GANS can overcome the lack of data for hydrological processes at the intermediate scale. Soil moisture from GANS compared quantitatively with mean values derived from a network of classical devices under vegetated and non- vegetated conditions. The GANS approach responded well

Multiple helical modes of vortex breakdown

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Naumov, I. V.; Okulov, Valery

2011-01-01

Experimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvi......’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets....

Clear air boundary layer spaced antenna wind measurement with the Multiple Antenna Profiler (MAPR

Directory of Open Access Journals (Sweden)

S. A. Cohn

Full Text Available Spaced antenna (SA wind measurement techniques are applied to Multiple Antenna Profiler (MAPR data to evaluate its performance in clear air conditions. MAPR is a multiple antenna 915 MHz wind profiler developed at the National Center for Atmospheric Research (NCAR and described in Cohn et al. (1997, designed to make high resolution wind measurements. Previous reported measurements with MAPR were restricted to precipitation because of low signal to noise (SNR and signal to ground-clutter (SCR ratios. By using a standard pulse-coding technique and upgrading the profiler control software, increases in average power and SNR were achieved, making routine measurements in clear air possible. Comparison of winds measured by MAPR and by a sonic anemometer on a nearby 300 m tower show correlation coefficients in the range of R² = 0.75 – 0.80, and an average absolute error of ~ 1.4 m s - 1 . This compares favorably with the agreement typically found in wind profiler comparisons. We also consider the use of the parameter ah , which is related to the value of the cross-correlation function at its zero crossing. This parameter is a data quality indicator and possibly a key component in a ground clutter removal technique.

Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; instruments and techniques – Radio science (remote sensing

Cryptanalysis of Vortex

DEFF Research Database (Denmark)

Aumasson, Jean-Philippe; Dunkelman, Orr; Mendel, Florian

2009-01-01

Vortex is a hash function that was first presented at ISC'2008, then submitted to the NIST SHA-3 competition after some modifications. This paper describes several attacks on both versions of Vortex, including collisions, second preimages, preimages, and distinguishers. Our attacks exploit flaws...

An Organic Vortex Laser.

Science.gov (United States)

Stellinga, Daan; Pietrzyk, Monika E; Glackin, James M E; Wang, Yue; Bansal, Ashu K; Turnbull, Graham A; Dholakia, Kishan; Samuel, Ifor D W; Krauss, Thomas F

2018-03-27

Optical vortex beams are at the heart of a number of novel research directions, both as carriers of information and for the investigation of optical activity and chiral molecules. Optical vortex beams are beams of light with a helical wavefront and associated orbital angular momentum. They are typically generated using bulk optics methods or by a passive element such as a forked grating or a metasurface to imprint the required phase distribution onto an incident beam. Since many applications benefit from further miniaturization, a more integrated yet scalable method is highly desirable. Here, we demonstrate the generation of an azimuthally polarized vortex beam directly by an organic semiconductor laser that meets these requirements. The organic vortex laser uses a spiral grating as a feedback element that gives control over phase, handedness, and degree of helicity of the emitted beam. We demonstrate vortex beams up to an azimuthal index l = 3 that can be readily multiplexed into an array configuration.

Dynamic signatures of driven vortex motion.

Energy Technology Data Exchange (ETDEWEB)

Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.

1999-09-16

We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.

Vortex Dynamics in Superconductors with Different Types of Pinning Potentials

International Nuclear Information System (INIS)

Laguna, Maria Fabiana

2001-01-01

In this work we study the behavior of the vortex system in the mixed state of a type II superconductor when it interacts with different kinds of pinning potentials. To do this, we perform numerical simulations in the presence of an external magnetic field, by making use of two different approaches.One corresponds to a Langevin simulation of the three dimensional XY model or Josephson-junction network, whereas the other corresponds to a Molecular dynamics simulation of two dimensional point-like vortices.We analyze the transport properties of highly anisotropic superconductors with different kinds of topological disorder in the configuration in which the external field is applied perpendicular to the CuO planes.We found that for systems with point defects the activation energy is the same for the two components of the resistivity, while in systems with columnar defects the activation energies can be different.We also study the structure, phase transitions and transport properties of the vortex system when the external magnetic field lies parallel to the planes in layered superconductors. We analyze the stability of different phases at low temperatures and show under which conditions the smectic phase is stable.Our results indicate the presence of the smectic phase in an intermediate range of temperatures.We have studied a vortex array in a periodic pinning potential with triangular and kagome geometries.We obtain the ground state vortex configurations and calculate some thermodynamic quantities for different magnetic fields.We observe several stages of lattice pinning and melting and we characterize different phases and transitions between them.Finally, simulating the Bitter pinning effect over the vortex system, we study static and dynamic properties of the vortex system in the presence of the surface Bitter pinning and the bulk pinning.We found low temperature structures similar to those obtained experimentally.We analyze the dynamics of the nucleation and growth

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

International Nuclear Information System (INIS)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe; Lykholt-Ustrup, Flemming

2017-01-01

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

Energy Technology Data Exchange (ETDEWEB)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe [Institute of Fluid System Dynamics, Technische Universitaet, Berlin (Germany); Lykholt-Ustrup, Flemming [Grundfos Holding A/S, Bjerringbro (Denmark)

2017-04-15

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation.

Evaluation of the Performance of Vortex Generators on the DU 91-W2-250 Profile using Stereoscopic PIV

DEFF Research Database (Denmark)

Velte, Clara Marika; Hansen, Martin Otto Laver; Meyer, Knud Erik

2009-01-01

Stereoscopic PIV measurements investigating the effect of Vortex Generators on the lift force near stall and on glide ratio at best aerodynamic performance have been carried out in the LM Glasfiber wind tunnel on a DU 91-W2-250 profile. Measurements at two Reynolds numbers were analyzed; Re=0...

Evaluation of the Performance of Vortex Generators on the DU 91-W2-250 Profile using Stereoscopic PIV

DEFF Research Database (Denmark)

Velte, Clara Marika; Hansen, Martin Otto Laver; Meyer, Knud Erik

2008-01-01

Stereoscopic PIV measurements investigating the effect of Vortex Generators on the lift force near stall and on glide ratio at best aerodynamic performance have been carried out in the LM Glasfiber wind tunnel on a DU 91-W2-250 profile. Measurements at two Reynolds numbers were analyzed; Re=0...

Enhancement of Energy Harvesting Performance by a Coupled Bluff Splitter Body and PVEH Plate through Vortex Induced Vibration near Resonance

Directory of Open Access Journals (Sweden)

Wei Ken Chin

2017-09-01

Full Text Available Inspired by vortex induced vibration energy harvesting development as a new source of renewable energy, a T-shaped design vibration energy harvester is introduced with the aim of enhancing its performance through vortex induced vibration at near resonance conditions. The T-shaped structural model designed consists of a fixed boundary aluminum bluff splitter body coupled with a cantilever piezoelectric vibration energy harvesters (PVEH plate model which is a piezoelectric bimorph plate made of a brass plate sandwiched between 2 lead zirconate titanate (PZT plates. A 3-dimensional Fluid-Structure Interaction simulation analysis is carried out with Reynolds Stress Turbulence Model under wind speed of 7, 10, 12, 14, 16, 18, 19, 20, 22.5, and 25 m/s. The results showed that with 19 m/s wind speed, the model generates 75.758 Hz of vortex frequency near to the structural model’s natural frequency of 76.9 Hz. Resonance lock-in therefore occurred, generating a maximum displacement amplitude of 2.09 mm or a 49.76% increment relatively in vibrational amplitude. Under the effect of resonance at the PVEH plate’s fundamental natural frequency, it is able to generate the largest normalized power of 13.44 mW/cm3g2.

On the basically single-type excitation source of resonance in the wind tunnel and in the hydroturbine channel of a hydraulic power plant

Science.gov (United States)

Karavosov, R. K.; Prozorov, A. G.

2012-01-01

We have investigated the spectra of pressure pulsations in the near field of the open working section of the wind tunnel with a vortex flow behind the tunnel blower formed like the flow behind the hydroturbine of a hydraulic power plant. We have made a comparison between the measurement data for pressure pulsations and the air stream velocity in tunnels of the above type and in tunnels in which a large-scale vortex structure behind the blower is not formed. It has been established that the large-scale vortex formation in the incompressible medium behind the blade system in the wind tunnel is a source of narrow-band acoustic radiation capable of exciting resonance self-oscillations in the tunnel channel.

Aircraft Wake Vortex Deformation in Turbulent Atmosphere

OpenAIRE

Hennemann, Ingo; Holzaepfel, Frank

2007-01-01

Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understan...

The nonlinear dirac equation in Bose-Einstein condensates: vortex solutions and spectra in a weak harmonic trap

Science.gov (United States)

Haddad, L. H.; Carr, Lincoln D.

2015-11-01

We analyze the vortex solution space of the (2+1)-dimensional nonlinear Dirac equation for bosons in a honeycomb optical lattice at length scales much larger than the lattice spacing. Dirac point relativistic covariance combined with s-wave scattering for bosons leads to a large number of vortex solutions characterized by different functional forms for the internal spin and overall phase of the order parameter. We present a detailed derivation of these solutions which include skyrmions, half-quantum vortices, Mermin-Ho and Anderson-Toulouse vortices for vortex winding {\\ell }=1. For {\\ell }≥slant 2 we obtain topological as well as non-topological solutions defined by the asymptotic radial dependence. For arbitrary values of ℓ the non-topological solutions include bright ring-vortices which explicitly demonstrate the confining effects of the Dirac operator. We arrive at solutions through an asymptotic Bessel series, algebraic closed-forms, and using standard numerical shooting methods. By including a harmonic potential to simulate a finite trap we compute the discrete spectra associated with radially quantized modes. We demonstrate the continuous spectral mapping between the vortex and free particle limits for all of our solutions.

Wind profiler observations on orographic effects of typhoon wind structure modification over Taiwan (120.38° E, 22.6° N

Directory of Open Access Journals (Sweden)

C. J. Pan

2010-01-01

Full Text Available The interaction of the storm circulation with the Central Mountain Range (CMR of Taiwan is studied with a wind profiler located at the leeside during the invasions of two (Kaemi (200605 and Bopha (200609 typhoons. The moderate typhoon Kaemi upgraded from a tropical depression on 21 July 2006. It then was made landfall at 15:45 UTC on 24 July 2006 near Cheng-Kung. The weak typhoon Bopha formed at about 12:00 UTC on 5 August 2006 and also landed near Cheng-Kung at around 19:20 UTC on 8 August. A new finding from both typhoons is the vortex splitting into upper and lower parts with the two typhoons that have passed the observation site nearly. For the typhoon Kaemi, demarcation height of the upper-level vortex and lower level is at 2.8 km and passed the site about 3 h earlier than the low-level one. For the typhoon Bopha, the center of the lower-level vortex at 3.5 km locates to the north of the upper-level one at 5.2 km. The re-organization of the split vortexes is found in typhoon Kaemi but not for typhoon Bopha.

Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Sarmast, Sasan

2014-01-01

A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equati......A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier...... of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where...

Ground observations and remote sensing data for integrated modelisation of water budget in the Merguellil catchment, Tunisia

Science.gov (United States)

Mougenot, Bernard

2016-04-01

The Mediterranean region is affected by water scarcity. Some countries as Tunisia reached the limit of 550 m3/year/capita due overexploitation of low water resources for irrigation, domestic uses and industry. A lot of programs aim to evaluate strategies to improve water consumption at regional level. In central Tunisia, on the Merguellil catchment, we develop integrated water resources modelisations based on social investigations, ground observations and remote sensing data. The main objective is to close the water budget at regional level and to estimate irrigation and water pumping to test scenarios with endusers. Our works benefit from French, bilateral and European projects (ANR, MISTRALS/SICMed, FP6, FP7…), GMES/GEOLAND-ESA) and also network projects as JECAM and AERONET, where the Merguellil site is a reference. This site has specific characteristics associating irrigated and rainfed crops mixing cereals, market gardening and orchards and will be proposed as a new environmental observing system connected to the OMERE, TENSIFT and OSR systems respectively in Tunisia, Morocco and France. We show here an original and large set of ground and remote sensing data mainly acquired from 2008 to present to be used for calibration/validation of water budget processes and integrated models for present and scenarios: - Ground data: meteorological stations, water budget at local scale: fluxes tower, soil fluxes, soil and surface temperature, soil moisture, drainage, flow, water level in lakes, aquifer, vegetation parameters on selected fieds/month (LAI, height, biomass, yield), land cover: 3 times/year, bare soil roughness, irrigation and pumping estimations, soil texture. - Remote sensing data: remote sensing products from multi-platform (MODIS, SPOT, LANDSAT, ASTER, PLEIADES, ASAR, COSMO-SkyMed, TerraSAR X…), multi-wavelength (solar, micro-wave and thermal) and multi-resolution (0.5 meters to 1 km). Ground observations are used (1) to calibrate soil

Vortex rings in classical and quantum systems

International Nuclear Information System (INIS)

Barenghi, C F; Donnelly, R J

2009-01-01

The study of vortex rings has been pursued for decades and is a particularly difficult subject. However, the discovery of quantized vortex rings in superfluid helium has greatly increased interest in vortex rings with very thin cores. While rapid progress has been made in the simulation of quantized vortex rings, there has not been comparable progress in laboratory studies of vortex rings in a viscous fluid such as water. This article overviews the history and current frontiers of classical and quantum vortex rings. After introducing the classical results, this review discusses thin-cored vortex rings in superfluid helium in section 2, and recent progress in understanding vortex rings of very thin cores propagating in water in section 3. (invited paper)

Development of ground-based wind energy in DOM and Corsica - Joint CGEDD / CGEIET report

International Nuclear Information System (INIS)

Joannis de Verclos, Christian de; Albrecht, Patrick; Iselin, Philippe; Legait, Benoit; Vignolles, Denis

2012-09-01

Addressing the peculiar cases of the French overseas districts (DOM: Guadeloupe, Martinique, Guyana, Mayotte, La Reunion) and Corsica, this report analyzes four main topics: the objectives and challenges of ground-based wind energy (sustainable development, not-interconnected areas, and public service of electricity supply), the local situations and their cartography, the legal issues and the possible evolution options (energy law, environmental law, urban planning law, local community law), and the modalities of devolution of project. The authors highlight the issues which require a new legal framework, notably governance and the devolution procedure

Winds in the high-latitude lower thermosphere: Dependence on the interplanetary magnetic field

DEFF Research Database (Denmark)

Richmond, A.D.; Lathuillere, C.; Vennerstrøm, Susanne

2003-01-01

-side cyclonic vortex that responds more strongly to B-z variations. The dependence of the wind on the IMF is nonlinear, especially with respect to IMF B-z. For positive B-z the difference winds are largely confined to the polar cap, while for negative B-z the difference winds extend to subauroral latitudes...... of similar to20 hours, a B-y-dependent magnetic-zonal-mean zonal wind generally exists, with maximum wind speeds at 80 magnetic latitude, typically 10 m/s at 105 km, increasing to about 60 m/s at 123 km and 80 m/s at 200 km. In the southern hemisphere the wind is cyclonic when the time-averaged B...

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1998-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1997-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

Experimental investigation of the wake behind a model of wind turbine in a water flume

International Nuclear Information System (INIS)

Okulov, V L; Mikkelsen, R; Sørensen, J N; Naumov, I N; Kabardin, I

2014-01-01

The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert's optimization. The transitional regime, generally characterized as in between the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities. The near wake characteristics (development of expansion, tip vortex position, deficit velocity and rotation in the wake) have been measured for different tip speed ratio to compare with main assumptions and conclusions of various rotor theories

Experimental investigation of the wake behind a model of wind turbine in a water flume

DEFF Research Database (Denmark)

Okulov, Valery; Naumov, Igor; Kabardin, I.

2014-01-01

The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert’s optimization. The transitional regime, generally characterized as in between...... the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities....... The near wake characteristics (development of expansion, tip vortex position, deficit velocity and rotation in the wake) have been measured for different tip speed ratio to compare with main assumptions and conclusions of various rotor theories....

Study on the wind field and pollutant dispersion in street canyons using a stable numerical method.

Science.gov (United States)

Xia, Ji-Yang; Leung, Dennis Y C

2005-01-01

A stable finite element method for the time dependent Navier-Stokes equations was used for studying the wind flow and pollutant dispersion within street canyons. A three-step fractional method was used to solve the velocity field and the pressure field separately from the governing equations. The Streamline Upwind Petrov-Galerkin (SUPG) method was used to get stable numerical results. Numerical oscillation was minimized and satisfactory results can be obtained for flows at high Reynolds numbers. Simulating the flow over a square cylinder within a wide range of Reynolds numbers validates the wind field model. The Strouhal numbers obtained from the numerical simulation had a good agreement with those obtained from experiment. The wind field model developed in the present study is applied to simulate more complex flow phenomena in street canyons with two different building configurations. The results indicated that the flow at rooftop of buildings might not be assumed parallel to the ground as some numerical modelers did. A counter-clockwise rotating vortex may be found in street canyons with an inflow from the left to right. In addition, increasing building height can increase velocity fluctuations in the street canyon under certain circumstances, which facilitate pollutant dispersion. At high Reynolds numbers, the flow regimes in street canyons do not change with inflow velocity.

Computing the flow past Vortex Generators: Comparison between RANS Simulations and Experiments

DEFF Research Database (Denmark)

Manolesos, M.; Sørensen, Niels N.; Troldborg, Niels

2016-01-01

The flow around a wind turbine airfoil equipped with Vortex Generators (VGs) is examined. Predictions from three different Reynolds Averaged Navier Stokes (RANS) solvers with two different turbulence models and two different VG modelling approaches are compared between them and with experimental ...... data. The best results are obtained with the more expensive fully resolved VG approach. The cost efficient BAY model can also provide acceptable results, if grid related numerical diffusion is minimized and only force coefficient polars are considered....

Lift enhancement by trapped vortex

Science.gov (United States)

Rossow, Vernon J.

1992-01-01

The viewgraphs and discussion of lift enhancement by trapped vortex are provided. Efforts are continuously being made to find simple ways to convert wings of aircraft from an efficient cruise configuration to one that develops the high lift needed during landing and takeoff. The high-lift configurations studied here consist of conventional airfoils with a trapped vortex over the upper surface. The vortex is trapped by one or two vertical fences that serve as barriers to the oncoming stream and as reflection planes for the vortex and the sink that form a separation bubble on top of the airfoil. Since the full three-dimensional unsteady flow problem over the wing of an aircraft is so complicated that it is hard to get an understanding of the principles that govern the vortex trapping process, the analysis is restricted here to the flow field illustrated in the first slide. It is assumed that the flow field between the two end plates approximates a streamwise strip of the flow over a wing. The flow between the endplates and about the airfoil consists of a spanwise vortex located between the suction orifices in the endplates. The spanwise fence or spoiler located near the nose of the airfoil serves to form a separated flow region and a shear layer. The vorticity in the shear layer is concentrated into the vortex by withdrawal of fluid at the suction orifices. As the strength of the vortex increases with time, it eventually dominates the flow in the separated region so that a shear or vertical layer is no longer shed from the tip of the fence. At that point, the vortex strength is fixed and its location is such that all of the velocity contributions at its center sum to zero thereby making it an equilibrium point for the vortex. The results of a theoretical analysis of such an idealized flow field are described.

On the Idea of a New Artificial Intelligence Based Optimization Algorithm Inspired From the Nature of Vortex

Directory of Open Access Journals (Sweden)

Utku Kose

2015-07-01

Full Text Available In this paper, the idea of a new artificial intelligence based optimization algorithm, which is inspired from the nature of vortex, has been provided briefly. As also a bio-inspired computation algorithm, the idea is generally focused on a typical vortex flow / behavior in nature and inspires from some dynamics that are occurred in the sense of vortex nature. Briefly, the algorithm is also a swarm-oriented evolutional problem solution approach; because it includes many methods related to elimination of weak swarm members and trying to improve the solution process by supporting the solution space via new swarm members. In order have better idea about success of the algorithm; it has been tested via some benchmark functions. At this point, the obtained results show that the algorithm can be an alternative to the literature in terms of single-objective optimizationsolution ways. Vortex Optimization Algorithm (VOA is the name suggestion by the authors; for this new idea of intelligent optimization approach.

Vortex Ring Dynamics in Radially Confined Domains

Science.gov (United States)

Stewart, Kelley; Niebel, Casandra; Jung, Sunghwan; Vlachos, Pavlos

2010-11-01

Vortex ring dynamics have been studied extensively in semi-infinite quiescent volumes. However, very little is known about vortex-ring formation in wall-bounded domains where vortex wall interaction will affect both the vortex ring pinch-off and propagation velocity. This study addresses this limitation and studies vortex formation in radially confined domains to analyze the affect of vortex-ring wall interaction on the formation and propagation of the vortex ring. Vortex rings were produced using a pneumatically driven piston cylinder arrangement and were ejected into a long cylindrical tube which defined the confined downstream domain. A range of confinement domains were studied with varying confinement diameters Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV) and were processed using an in-house developed cross-correlation PIV algorithm. The experimental analysis was used to facilitate the development of a theoretical model to predict the variations in vortex ring circulation over time within confined domains.

Effect of Wavy Trailing Edge on 100meter Flatback Wind Turbine Blade

International Nuclear Information System (INIS)

Yang, SJ; Baeder, J D

2016-01-01

The flatback trailing edge design for modern 100meter wind turbine blade has been developed and proposed to make wind turbine blade to be slender and lighter. On the other hand, it will increase aerodynamic drag; consequently the increased drag diminishes turbine power generation. Thus, an aerodynamic drag reducing technique should be accompanied with the flatback trailing edge in order to prevent loss of turbine power generation. In this work, a drag mitigation design, span-wise wavy trailing edge blade, has been applied to a modern 100meter blade. The span-wise trailing edge acts as a vortex generator, and breaks up the strong span-wise coherent trailing edge vortex structure at the flatback airfoil trailing edge which is a major source of large drag. Three-dimensional unsteady Computational Fluid Dynamics (CFD) simulations have been performed for real scale wind turbine blade geometries. Delayed Detached Eddy Simulation (DDES) with the modified laminar-turbulent transition model has been applied to obtain accurate flow field predictions. Graphical Processor Unit (GPU)-accelerated computation has been conducted to reduce computational costs of the real scale wind turbine blade simulations. To verify the structural reliability of the wavy modification of the blade a simple Eigen buckling analysis has been performed in the current study. (paper)

Examples of, reasons for, and consequences of the poor quality of wind data from ships for the marine boundary layer - Implications for remote sensing

Science.gov (United States)

Pierson, Willard J., Jr.

1990-01-01

Wind reports by data buoys are used to demonstrate that these reports have in the past provided useful values for the synoptic scale winds and that at present these reports provide very reliable value for the synoptic scale winds. Past studies of wind reports by ships have revealed that the data are of poor quality, but the causes for this poor quality are not identified. Examples of the poor quality of wind data from ships are obtained by comparing ship reports with buoy reports and comparing reports of different kinds of ships with each other. These comparisons identify many different reasons for the poor quality of wind data from ships. Suggestions are made for improving the quality of ship data. The consequences of the poor quality of ship winds are described in terms of the effects on weather and wave forecasts. The implications for remotely sensed winds are discussed.

A vortex dynamics perspective on stratospheric sudden warmings

OpenAIRE

Matthewman, N. J.

2009-01-01

A vortex dynamics approach is used to study the underlying mechanisms leading to polar vortex breakdown during stratospheric sudden warmings (SSWs). Observational data are used in chapter 2 to construct climatologies of the Arctic polar vortex structure during vortex-splitting and vortex-displacement SSWs occurring between 1958 and 2002. During vortex-splitting SSWs, polar vortex breakdown is shown to be typically independent of height (barotropic), whereas breakdown during vor...

Controlling vortex motion and vortex kinetic friction

International Nuclear Information System (INIS)

Nori, Franco; Savel'ev, Sergey

2006-01-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcia, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves

Controlling vortex motion and vortex kinetic friction

Science.gov (United States)

Nori, Franco; Savel'ev, Sergey

2006-05-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

Vortex formation and instability in the left ventricle

Science.gov (United States)

Le, Trung Bao; Sotiropoulos, Fotis; Coffey, Dane; Keefe, Daniel

2012-09-01

We study the formation of the mitral vortex ring during early diastolic filling in a patient-specific left ventricle (LV) using direct numerical simulation. The geometry of the left ventricle is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy human subject. The left ventricular kinematics is modeled via a cell-based activation methodology, which is inspired by cardiac electro-physiology and yields physiologic LV wall motion. In the fluid dynamics videos, we describe in detail the three-dimensional structure of the mitral vortex ring, which is formed during early diastolic filling. The ring starts to deform as it propagates toward the apex of the heart and becomes inclined. The trailing secondary vortex tubes are formed as the result of interaction between the vortex ring and the LV wall. These vortex tubes wrap around the circumference and begin to interact with and destabilize the mitral vortex ring. At the end of diastole, the vortex ring impinges on the LV wall and the large-scale intraventricular flow rotates in clockwise direction. We show for the first time that the mitral vortex ring evolution is dominated by a number of vortex-vortex and vortex-wall interactions, including lateral straining and deformation of vortex ring, the interaction of two vortex tubes with unequal strengths, helicity polarization of vortex tubes and twisting instabilities of the vortex cores.

Evaluation of a micro-scale wind model's performance over realistic building clusters using wind tunnel experiments

Science.gov (United States)

Zhang, Ning; Du, Yunsong; Miao, Shiguang; Fang, Xiaoyi

2016-08-01

The simulation performance over complex building clusters of a wind simulation model (Wind Information Field Fast Analysis model, WIFFA) in a micro-scale air pollutant dispersion model system (Urban Microscale Air Pollution dispersion Simulation model, UMAPS) is evaluated using various wind tunnel experimental data including the CEDVAL (Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models) wind tunnel experiment data and the NJU-FZ experiment data (Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data). The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier-Stokes equations, and can produce very high-resolution (1-5 m) wind fields of a complex neighborhood scale urban building canopy (~ 1 km ×1 km) in less than 3 min when run on a personal computer.

Interaction of Vortex Ring with Cutting Plate

Science.gov (United States)

Musta, Mustafa

2015-11-01

The interaction of a vortex ring impinging on a thin cutting plate was made experimentally using Volumetric 3-component Velocitmetry (v3v) technique. The vortex rings were generated with piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and Re at 2-3 and 1500 - 3000, respectively. The cutting of vortex rings below center line leads to the formation of secondary vortices on each side of the plate which is look like two vortex rings, and a third vortex ring propagates further downstream in the direction of the initial vortex ring, which is previously showed by flow visualization study of Weigand (1993) and called ``trifurcation''. Trifurcation is very sensitive to the initial Reynolds number and the position of the plate with respect to the vortex ring generator pipe. The present work seeks more detailed investigation on the trifurcation using V3V technique. Conditions for the formation of trifurcation is analyzed and compared with Weigand (1993). The formed secondary vortex rings and the propagation of initial vortex ring in the downstream of the plate are analyzed by calculating their circulation, energy and trajectories.

Electric vortex in MHD flow

International Nuclear Information System (INIS)

Garcia, M.

1995-01-01

An electric vortex is the circulation of electron space charge about a magnetic field line that is transported by ion momentum. In cold, or low β flow the vortex diameter is the minimum length scale of charge neutrality. The distinctive feature of the vortex is its radial electric field which manifests the interplay of electrostatics, magnetism, and motion

Non-coaxial superposition of vector vortex beams.

Science.gov (United States)

Aadhi, A; Vaity, Pravin; Chithrabhanu, P; Reddy, Salla Gangi; Prabakar, Shashi; Singh, R P

2016-02-10

Vector vortex beams are classified into four types depending upon spatial variation in their polarization vector. We have generated all four of these types of vector vortex beams by using a modified polarization Sagnac interferometer with a vortex lens. Further, we have studied the non-coaxial superposition of two vector vortex beams. It is observed that the superposition of two vector vortex beams with same polarization singularity leads to a beam with another kind of polarization singularity in their interaction region. The results may be of importance in ultrahigh security of the polarization-encrypted data that utilizes vector vortex beams and multiple optical trapping with non-coaxial superposition of vector vortex beams. We verified our experimental results with theory.

E region neutral winds in the postmidnight diffuse aurora during the atmospheric response in aurora 1 rocket campaign

International Nuclear Information System (INIS)

Brinkman, D.G.; Walterscheid, R.L.; Lyons, L.R.

1995-01-01

Measured E region neutral winds from the Atmospheric Response in Aurora (ARIA 1) rocket campaign are compared with winds predicted by a high-resolution nonhydrostatic dynamical thermosphere model. The ARIA 1 rockets were launched into the postmidnight diffuse aurora during the recovery phase of a substorm. Simulations have shown that electrodynamical coupling between the auroral ionosphere and the thermosphere was expected to be strong during active diffuse auroral conditions. This is the first time that simulations using the time history of detailed specifications of the magnitude and latitudinal variation of the auroral forcing based on measurements have been compared to simultaneous wind measurements. Model inputs included electron densities derived from ground-based airglow measurements, precipitating electron fluxes measured by the rocket, electron densities measured on the rocket, electric fields derived from magnetometer and satellite ion drift measurements, and large-scale background winds from a thermospheric general circulation model. Our model predicted a strong jet of eastward winds at E region heights. A comparison between model predicted and observed winds showed modest agreement. Above 135 km the model predicted zonal winds with the correct sense, the correct profile shape, and the correct altitude of the peak wind. However, it overpredicted the magnitude of the eastward winds by more than a factor or 2. For the meridional winds the model predicted the general sense of the winds but was unable to predict the structure or strength of the winds seen in the observations. Uncertainties in the magnitude and latitudinal structure of the electric field and in the magnitude of the background winds are the most likely sources of error contributing to the differences between model and observed winds. Between 110 and 135 km the agreement between the model and observations was poor because of a large unmodeled jetlike feature in the observed winds

Field evaluation of remote wind sensing technologies: Shore-based and buoy mounted LIDAR systems

Energy Technology Data Exchange (ETDEWEB)

Herrington, Thomas [Stevens Inst. of Technology, Hoboken, NJ (United States)

2017-11-03

In developing a national energy strategy, the United States has a number of objectives, including increasing economic growth, improving environmental quality, and enhancing national energy security. Wind power contributes to these objectives through the deployment of clean, affordable and reliable domestic energy. To achieve U.S. wind generation objectives, the Wind and Water Power Program within the Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE) instituted the U.S. Offshore Wind: Removing Market Barriers Program in FY 2011. Accurate and comprehensive information on offshore wind resource characteristics across a range of spatial and temporal scales is one market barrier that needs to be addressed through advanced research in remote sensing technologies. There is a pressing need for reliable offshore wind-speed measurements to assess the availability of the potential wind energy resource in terms of power production and to identify any frequently occurring spatial variability in the offshore wind resource that may impact the operational reliability and lifetime of wind turbines and their components and to provide a verification program to validate the “bankability” of the output of these alternative technologies for use by finance institutions for the financing of offshore wind farm construction. The application of emerging remote sensing technologies is viewed as a means to cost-effectively meet the data needs of the offshore wind industry. In particular, scanning and buoy mounted LIDAR have been proposed as a means to obtain accurate offshore wind data at multiple locations without the high cost and regulatory hurdles associated with the construction of offshore meteorological towers. However; before these remote sensing technologies can be accepted the validity of the measured data must be evaluated to ensure their accuracy. The proposed research will establish a unique coastal ocean test-bed in the Mid-Atlantic for

Some observations of tip-vortex cavitation

Science.gov (United States)

Arndt, R. E. A.; Arakeri, V. H.; Higuchi, H.

1991-08-01

Cavitation has been observed in the trailing vortex system of an elliptic platform hydrofoil. A complex dependence on Reynolds number and gas content is noted at inception. Some of the observations can be related to tension effects associated with the lack of sufficiently large-sized nuclei. Inception measurements are compared with estimates of pressure in the vortex obtained from LDV measurements of velocity within the vortex. It is concluded that a complete correlation is not possible without knowledge of the fluctuating levels of pressure in tip-vortex flows. When cavitation is fully developed, the observed tip-vortex trajectory flows. When cavitation is fully developed, the observed tip-vortex trajectory shows a surprising lack of dependence on any of the physical parameters varied, such as angle of attack, Reynolds number, cavitation number, and dissolved gas content.

Winding sense of galaxies around the local supercluster

International Nuclear Information System (INIS)

Aryal, Binil

2011-01-01

We present an analysis of the winding sense (S and Z-shapes) of 1621 field galaxies that have radial velocity between 3000 km s -1 and 5000 km s -1 . The preferred alignments of S- and Z-shaped galaxies are studied using chi-square, autocorrelation and Fourier series tests. We classify all the galaxies into 32 subsamples and notice a good agreement between the position angle (PA) distribution of the S- and Z-shaped galaxies. The homogeneous distribution of the S- and Z-shaped galaxies is more noticeable for the late-type spirals (Sc, Scd, Sd and Sm) than for the early-types (Sa, Sab, Sb and Sbc). A significant dominance of S-mode galaxies is apparent in the barred spirals. A random alignment is evident in the PA-distribution of Z- and S-mode spirals. In addition, a homogeneous distribution of the S- and Z-shaped galaxies is found to be invariant under global expansion. The PA-distribution of the total S-mode galaxies is found to be random, whereas a preferred alignment is clear for all the Z-mode galaxies. It is found that the galactic planes of Z-mode galaxies tend to lie in the equatorial plane.

Study on the Effect and Mechanism of Aerodynamic Measures for the Vortex-Induced Vibration of Separate Pairs of Box Girders in Cable-Stayed Bridges

Directory of Open Access Journals (Sweden)

Han Xin He

2015-01-01

Full Text Available Although not always resulting in catastrophic failures, vortex-induced vibration (VIV response can seriously impact the fatigue life and functionality of bridges, especially for separate pairs of box girders in cable-stayed bridges. This study investigates the effects of three aerodynamic measures: grating, inclined web plate, and the baffles on separated box girders in the cable-stayed bridges. The experimental result indicates that the grating of different opening ratios can control the vortex-induced vibration effectively, and the optimized grating opening ratio set in this paper is 40%. Increasing the angle of inclined web plate has a great control on mitigation of the vortex-induced vibration. However, there is an optimum angle where the amplitude of vortex-induced vibration is the smallest at low wind speed. The amplitude of vortex-induced vibration becomes larger with the increase of the web inclined angle that exceeds the optimum angle. Comparatively, the baffles installed on both sides of the inclined webs are more effective to restrain the vortex-induced resonance. The Computational Fluent Dynamics (CFD software is utilized to investigate the mechanism of the experimental results.

Discrete vortex method simulations of aerodynamic admittance in bridge aerodynamics

DEFF Research Database (Denmark)

Rasmussen, Johannes Tophøj; Hejlesen, Mads Mølholm; Larsen, Allan

, and to determine aerodynamic forces and the corresponding flutter limit. A simulation of the three-dimensional bridge responseto turbulent wind is carried out by quasi steady theory by modelling the bridge girder as a line like structure [2], applying the aerodynamic load coefficients found from the current version......The meshless and remeshed Discrete Vortex Method (DVM) has been widely used in academia and by the industry to model two-dimensional flow around bluff bodies. The implementation “DVMFLOW” [1] is used by the bridge design company COWI to determine and visualise the flow field around bridge sections...

Dynamic wind interference effects between high chimneys

International Nuclear Information System (INIS)

Ruscheweyh, H.; Traetner, A.

2000-01-01

In an extensive wind tunnel study vortex-induced cross-wind vibrations of chimneys in a row and in grouped arrangements have been investigated. Most of the model tests have been executed in the subcritical Reynolds number range. In order to indicate the influence of the Reynolds number, some tests have been executed at simulated transcritical Reynolds number range in the large wind tunnel NKl in Dresden. It could be shown, that the exciting forces at stacks in a row and in grouped arrangements are multiple larger in the subcritical range than in the transcritical range and cannot be transferred to full-scale concrete stacks. On the contrary the variation of the Strouhal number versus distance ratio is less influenced by the Reynolds number. It could be verified, that the diameter ratio d 2 /d 1 of the luff-side stack to the lee-side stack is of major importance. A recommendation for the estimation of vortex-induced vibrations of concrete stacks in a row and in grouped arrangements could be developed from the results with simulated transcritical Reynolds number. Strouhal number factors, ψ s , and exciting force factors, ψ lat , could be evaluated in dependency of the distance ratio a/d 1 of the stacks. A proposal for practical application is given in Fig. 10 and 11. It is compared with the proposal for stacks in a row which is given in the German Standard DIN 4133 for steel stacks. (orig.) [de

Remote Sensing Data in Wind Velocity Field Modelling: a Case Study from the Sudetes (SW Poland)

Science.gov (United States)

Jancewicz, Kacper

2014-06-01

The phenomena of wind-field deformation above complex (mountainous) terrain is a popular subject of research related to numerical modelling using GIS techniques. This type of modelling requires, as input data, information on terrain roughness and a digital terrain/elevation model. This information may be provided by remote sensing data. Consequently, its accuracy and spatial resolution may affect the results of modelling. This paper represents an attempt to conduct wind-field modelling in the area of the Śnieżnik Massif (Eastern Sudetes). The modelling process was conducted in WindStation 2.0.10 software (using the computable fluid dynamics solver Canyon). Two different elevation models were used: the Global Land Survey Digital Elevation Model (GLS DEM) and Digital Terrain Elevation Data (DTED) Level 2. The terrain roughness raster was generated on the basis of Corine Land Cover 2006 (CLC 2006) data. The output data were post-processed in ArcInfo 9.3.1 software to achieve a high-quality cartographic presentation. Experimental modelling was conducted for situations from 26 November 2011, 25 May 2012, and 26 May 2012, based on a limited number of field measurements and using parameters of the atmosphere boundary layer derived from the aerological surveys provided by the closest meteorological stations. The model was run in a 100-m and 250-m spatial resolution. In order to verify the model's performance, leave-one-out cross-validation was used. The calculated indices allowed for a comparison with results of former studies pertaining to WindStation's performance. The experiment demonstrated very subtle differences between results in using DTED or GLS DEM elevation data. Additionally, CLC 2006 roughness data provided more noticeable improvements in the model's performance, but only in the resolution corresponding to the original roughness data. The best input data configuration resulted in the following mean values of error measure: root mean squared error of velocity

Wind Noise Reduction in a Non-Porous Subsurface Windscreen

Science.gov (United States)

Zuckerwar, Allan J.; Shams, Qamar A.; Knight, H. Keith

2012-01-01

Measurements of wind noise reduction were conducted on a box-shaped, subsurface windscreen made of closed cell polyurethane foam. The windscreen was installed in the ground with the lid flush with the ground surface. The wind was generated by means of a fan, situated on the ground, and the wind speed was measured at the center of the windscreen lid with an ultrasonic anemometer. The wind speed was controlled by moving the fan to selected distances from the windscreen. The wind noise was measured on a PCB Piezotronics 3†electret microphone. Wind noise spectra were measured with the microphone exposed directly to the wind (atop the windscreen lid) and with the microphone installed inside the windscreen. The difference between the two spectra comprises the wind noise reduction. At wind speeds of 3, 5, and 7 m/s, the wind noise reduction is typically 15 dB over the frequency range of 0.1-20 Hz.

Regimes of flow past a vortex generator

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, V.L.; Naumov, I.V.

2012-01-01

A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic...... particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator....

Numerical Simulation of Wind Turbine Blade-Tower Interaction

Institute of Scientific and Technical Information of China (English)

Qiang Wang; Hu Zhou; Decheng Wan

2012-01-01

Numerical simulations of wind turbine blade-tower interaction by using the open source OpenFOAM tools coupled with arbitrary mesh interface (AMI) method were presented.The governing equations were the unsteady Reynolds-averaged Navier-Stokes (PANS) which were solved by the pimpleDyMFoam solver,and the AMI method was employed to handle mesh movements.The National Renewable Energy Laboratory (NREL) phase Ⅵ wind turbine in upwind configuration was selected for numerical tests with different incoming wind speeds (5,10,15,and 25 m/s) at a fixed blade pitch and constant rotational speed.Detailed numerical results of vortex structure,time histories of thrust,and pressure distribution on the blade and tower were presented.The findings show that the wind turbine tower has little effect on the whole aerodynamic performance of an upwind wind turbine,while the rotating rotor will induce an obvious cyclic drop in the front pressure of the tower.Also,strong interaction of blade tip vortices with separation from the tower was observed.

High time resolution boundary layer description using combined remote sensing instruments

Directory of Open Access Journals (Sweden)

C. Gaffard

2008-09-01

Full Text Available Ground based remote sensing systems for future observation operations will allow continuous monitoring of the lower troposphere at temporal resolutions much better than every 30 min. Observations which may be considered spurious from an individual instrument can be validated or eliminated when considered in conjunction with measurements from other instruments observing at the same location. Thus, improved quality control of atmospheric profiles from microwave radiometers and wind profilers should be sought by considering the measurements from different systems together rather than individually. In future test bed deployments for future operational observing systems, this should be aided by observations from laser ceilometers and cloud radars. Observations of changes in atmospheric profiles at high temporal resolution in the lower troposphere are presented from a 12 channel microwave radiometer and 1290 MHz UHF wind profiler deployed in southern England during the CSIP field experiment in July/August 2005. The observations chosen were from days when thunderstorms occurred in southern England. Rapid changes near the surface in dry layers are considered, both when rain/hail may be falling from above and where the dry air is associated with cold pools behind organised thunderstorms. Also, short term variations in atmospheric profiles and vertical stability are presented on a day with occasional low cloud, when thunderstorms triggered 50 km down wind of the observing site Improved quality control of the individual remote sensing systems need to be implemented, examining the basic quality of the underlying observations as well as the final outputs, and so for instance eliminating ground clutter as far as possible from the basic Doppler spectra measurements of the wind profiler. In this study, this was performed manually. The potential of incorporating these types of instruments in future upper air observational networks leads to the challenge to

Magnetic ground states in nanocuboids of cubic magnetocrystalline anisotropy

Energy Technology Data Exchange (ETDEWEB)

Bonilla, F.J., E-mail: fbonilla@cicenergigune.com; Lacroix, L.-M.; Blon, T., E-mail: thomas.blon@insa-toulouse.fr

2017-04-15

Flower and easy-axis vortex states are well-known magnetic configurations that can be stabilized in small particles. However, <111> vortex (V<111>), i.e. a vortex state with its core axis along the hard-axis direction, has been recently evidenced as a stable configuration in Fe nanocubes of intermediate sizes in the flower/vortex transition. In this context, we present here extensive micromagnetic simulations to determine the different magnetic ground states in ferromagnetic nanocuboids exhibiting cubic magnetocrystalline anisotropy (MCA). Focusing our study in the single-domain/multidomain size range (10–50 nm), we showed that V<111> is only stable in nanocuboids exhibiting peculiar features, such as a specific size, shape and magnetic environment, contrarily to the classical flower and easy-axis vortex states. Thus, to track experimentally these V<111> states, one should focused on (i) nanocuboids exhibiting a nearly perfect cubic shape (size distorsion <12%) made of (ii) a material which combines a zero or positive MCA and a high saturation magnetization, such as Fe or FeCo; and (iii) a low magnetic field environment, V<111> being only observed in virgin or remanent states. - Highlights: • The <111> vortex is numerically determined in nanocubes of cubic anisotropy. • It constitutes an intermediate state in the single-domain limit. • Such a vortex can only be stabilized in perfect or slightly deformed nanocuboids. • It exists in nanocuboids made of materials with zero or positive cubic anisotropy. • The associated magnetization reversal is described by a rotation of the vortex axis.

Spectral analysis of point-vortex dynamics: first application to vortex polygons in a circular domain

International Nuclear Information System (INIS)

Speetjens, M F M; Meleshko, V V; Van Heijst, G J F

2014-01-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N-point vortices of equal strength arranged in a polygonal configuration (‘N-vortex polygons’). In unbounded domains, such N-vortex polygons are unconditionally stable for N⩽7. Confinement in a circular domain tightens the stability conditions to N⩽6 and a maximum polygon size relative to the domain radius. This work expands on existing studies on stability and integrability by a first giving an exploratory spectral analysis of the dynamics of N vortex polygons in circular domains. Key to this is that the spectral signature of the time evolution of vortex positions reflects their qualitative behaviour. Expressing vortex motion by a generic evolution operator (the so-called Koopman operator) provides a rigorous framework for such spectral analyses. This paves the way to further differentiation and classification of point-vortex behaviour beyond stability and integrability. The concept of Koopman-based spectral analysis is demonstrated for N-vortex polygons. This reveals that conditional stability can be seen as a local form of integrability and confirms an important generic link between spectrum and dynamics: discrete spectra imply regular (quasi-periodic) motion; continuous (sub-)spectra imply chaotic motion. Moreover, this exposes rich nonlinear dynamics as intermittency between regular and chaotic motion and quasi-coherent structures formed by chaotic vortices. (ss 1)

Vortex diode jet

Science.gov (United States)

Houck, Edward D.

1994-01-01

A fluid transfer system that combines a vortex diode with a jet ejector to transfer liquid from one tank to a second tank by a gas pressurization method having no moving mechanical parts in the fluid system. The vortex diode is a device that has a high resistance to flow in one direction and a low resistance to flow in the other.

The Impacts of Satellite Remotely Sensed Winds and Total Precipitable Vapour in WRF Tropical Cyclone Track Forecasts

Directory of Open Access Journals (Sweden)

Diandong Ren

2016-01-01

Full Text Available This study assesses the impact assimilating the scatterometer near-surface wind observations and total precipitable water from the SSMI, into WRF on genesis and track forecasting of four tropical cyclones (TCs. These TCs are selected to be representative of different intensity categories and basins. Impact is via a series of data denial experiments that systematically exclude the remote sensed information. Compared with the control case, in which only the final analysis atmospheric variables are used to initialize and provide the lateral boundary conditions, the data assimilation runs performed consistently better, but with very different skill levels for the different TCs. Eliassen-Palm flux analyses are employed. It is confirmed that if a polar orbital satellite footprint passes over the TC’s critical genesis region, the forecast will profit most from assimilating the remotely sensed information. If the critical genesis region lies within an interorbital gap then, regardless of how strong the TC later becomes (e.g., Katrina 2005, the improvement from assimilating near-surface winds and total precipitable water in the model prediction is severely limited. This underpins the need for a synergy of data from different scatterometers/radiometers. Other approaches are suggested to improve the accuracy in the prediction of TC genesis and tracks.

Decreasing vortex flux in channels

International Nuclear Information System (INIS)

Migaj, V.K.; Nosova, I.S.

1979-01-01

A new method for reducing vortex flow losses in power plant channels is suggested. The method is based on vortex splitting in vortex flow areas with transverse barriers placed on the channel walls. The upper barrier ends are at the level of the upper boundary of the vortex area and don't protrude to the active flow beyond this boundary. The effectiveness of the method suggested is illustrated taking as an example the investigation of square and flat channels with abrupt widening in one plane, diffusers with widening in one plane, or a rectangualr bend. It is shown that splitting the vortex areas with transverse barriers in the channels results in reduction of hydraulic losses by 10-25%. The above method is characteristic of an extreme simplicity, its application doesn't require changes in the channel shape nor installation of any devices in the flow

Inverse design-momentum, a method for the preliminary design of horizontal axis wind turbines

International Nuclear Information System (INIS)

Battisti, L; Soraperra, G; Fedrizzi, R; Zanne, L

2007-01-01

Wind turbine rotor prediction methods based on generalized momentum theory BEM routinely used in industry and vortex wake methods demand the use of airfoil tabulated data and geometrical specifications such as the blade spanwise chord distribution. They belong to the category of 'direct design' methods. When, on the other hand, the geometry is deduced from some design objective, we refer to 'inverse design' methods. This paper presents a method for the preliminary design of wind turbine rotors based on an inverse design approach. For this purpose, a generalized theory was developed without using classical tools such as BEM. Instead, it uses a simplified meridional flow analysis of axial turbomachines and is based on the assumption that knowing the vortex distribution and appropriate boundary conditions is tantamount to knowing the velocity distribution. The simple conservation properties of the vortex components consistently cope with the forces and specific work exchange expressions through the rotor. The method allows for rotor arbitrarily radial load distribution and includes the wake rotation and expansion. Radial pressure gradient is considered in the wake. The capability of the model is demonstrated first by a comparison with the classical actuator disk theory in investigating the consistency of the flow field, then the model is used to predict the blade planform of a commercial wind turbine. Based on these validations, the authors postulate the use of a different vortex distribution (i.e. not-uniform loading) for blade design and discuss the effect of such choices on blade chord and twist, force distribution and power coefficient. In addition to the method's straightforward application to the pre-design phase, the model clearly shows the link between blade geometry and performance allowing quick preliminary evaluation of non uniform loading on blade structural characteristics

Global empirical wind model for the upper mesosphere/lower thermosphere. I. Prevailing wind

Directory of Open Access Journals (Sweden)

Y. I. Portnyagin

Full Text Available An updated empirical climatic zonally averaged prevailing wind model for the upper mesosphere/lower thermosphere (70-110 km, extending from 80°N to 80°S is presented. The model is constructed from the fitting of monthly mean winds from meteor radar and MF radar measurements at more than 40 stations, well distributed over the globe. The height-latitude contour plots of monthly mean zonal and meridional winds for all months of the year, and of annual mean wind, amplitudes and phases of annual and semiannual harmonics of wind variations are analyzed to reveal the main features of the seasonal variation of the global wind structures in the Northern and Southern Hemispheres. Some results of comparison between the ground-based wind models and the space-based models are presented. It is shown that, with the exception of annual mean systematic bias between the zonal winds provided by the ground-based and space-based models, a good agreement between the models is observed. The possible origin of this bias is discussed.

Key words: Meteorology and Atmospheric dynamics (general circulation; middle atmosphere dynamics; thermospheric dynamics

UpWind D1. Uncertainties in wind assessment with LIDAR

Energy Technology Data Exchange (ETDEWEB)

Lindeloew-Marsden, P.

2009-01-15

In this report sources influencing wind assessments with lidars are listed and discussed. Comparisons with mast mounted cup anemometers are presented and the magnitudes of the errors from the listed error sources are estimated. Finally an attempt to define uncertainty windows for the current state of the two commercial wind sensing lidars is presented. The results in this report give important feedback on system improvements to manufacturers and an estimation of the current ability for wind farm developers which are potential users. (author)

Backreaction of excitations on a vortex

OpenAIRE

Arodz, Henryk; Hadasz, Leszek

1996-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their backreaction on the vortex. In the present paper we investigate backreaction of Proca type excitations on a straightlinear vortex in the Abelian Higgs model. We propose exact Ansatz for fields of the excited vortex. From initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the backreaction corrections. Their approximate solutions are found ...

Instability of vortex pair leapfrogging

DEFF Research Database (Denmark)

Tophøj, Laust; Aref, Hassan

2013-01-01

Leapfrogging is a periodic solution of the four-vortex problem with two positive and two negative point vortices all of the same absolute circulation arranged as co-axial vortex pairs. The set of co-axial motions can be parameterized by the ratio 0 vortex pair sizes at the time when one...... pair passes through the other. Leapfrogging occurs for α > σ2, where is the silver ratio. The motion is known in full analytical detail since the 1877 thesis of Gröbli and a well known 1894 paper by Love. Acheson ["Instability of vortex leapfrogging," Eur. J. Phys.21, 269-273 (2000...... pairs fly off to infinity, and a "walkabout" mode, where the vortices depart from leapfrogging but still remain within a finite distance of one another. We show numerically that this transition is more gradual, a result that we relate to earlier investigations of chaotic scattering of vortex pairs [L...

Wind tunnel test of musi VI bridge

Science.gov (United States)

Permata, Robby; Andika, Matza Gusto; Syariefatunnisa, Risdhiawan, Eri; Hermawan, Budi; Noordiana, Indra

2017-11-01

Musi VI Bridge is planned to cross the Musi River in Palembang City, South Sumatera Province, Indonesia. The main span is a steel arch type with 200 m length and side span length is 75 m. Finite element analysis results showed that the bridge has frequency ratio for torsional and heaving mode (torsional frequency/heaving frequency)=1.14. This close to unity value rises concern about aerodynamic behaviour and stability of the bridge deck under wind loading. Sectional static and free vibration wind tunnel test were performed to clarify this phenomena in B2TA3 facility in Serpong, Indonesia. The test followed the draft of Guide of Wind Tunnel Test for Bridges developed by Indonesian Ministry of Public Works. Results from wind tunnel testing show that the bridge is safe from flutter instability and no coupled motion vibration observed. Therefore, low value of frequency ratio has no effect to aerodynamic behaviour of the bridge deck. Vortex-induced vibration in heaving mode occurred in relatively low wind velocity with permissible maximum amplitude value.

Acoustic scattering of a Bessel vortex beam by a rigid fixed spheroid

Science.gov (United States)

Mitri, F. G.

2015-12-01

Partial-wave series representation of the acoustic scattering field of high-order Bessel vortex beams by rigid oblate and prolate spheroids using the modal matching method is developed. The method, which is applicable to slightly elongated objects at low-to-moderate frequencies, requires solving a system of linear equations which depends on the partial-wave index n and the order of the Bessel vortex beam m using truncated partial-wave series expansions (PWSEs), and satisfying the Neumann boundary condition for a rigid immovable surface in the least-squares sense. This original semi-analytical approach developed for Bessel vortex beams is demonstrated for finite oblate and prolate spheroids, where the mathematical functions describing the spheroidal geometry are written in a form involving single angular (polar) integrals that are numerically computed. The transverse (θ = π / 2) and 3D scattering directivity patterns are evaluated in the far-field for both prolate and oblate spheroids, with particular emphasis on the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid) not exceeding 3:1, the half-cone angle β and order m of the Bessel vortex beam, as well as the dimensionless size parameter kr0. Periodic oscillations in the magnitude plots of the far-field scattering form function are observed, which result from the interference of the reflected waves with the circumferential (Franz') waves circumnavigating the surface of the spheroid in the surrounding fluid. Moreover, the 3D directivity patterns illustrate the far-field scattering from the spheroid, that vanishes in the forward (θ = 0) and backward (θ = π) directions. Particular applications in underwater acoustics and scattering, acoustic levitation and the detection of submerged elongated objects using Bessel vortex waves to name a few, would benefit from the results of the present investigation.

Soliton on thin vortex filament

International Nuclear Information System (INIS)

Konno, Kimiaki; Mituhashi, Masahiko; Ichikawa, Y.H.

1990-12-01

Showing that one of the equations found by Wadati, Konno and Ichikawa is equivalent to the equation of motion of a thin vortex filament, we investigate solitons on the vortex filament. N vortex soliton solution is given in terms of the inverse scattering method. We examine two soliton collision processes on the filament. Our analysis provides the theoretical foundation of two soliton collision processes observed numerically by Aref and Flinchem. (author)

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

Directory of Open Access Journals (Sweden)

R. Rüfenacht

2012-11-01

Full Text Available We report on the wind radiometer WIRA, a new ground-based microwave Doppler-spectro-radiometer specifically designed for the measurement of middle-atmospheric horizontal wind by observing ozone emission spectra at 142.17504 GHz. Currently, wind speeds in five levels between 30 and 79 km can be retrieved which makes WIRA the first instrument able to continuously measure horizontal wind in this altitude range. For an integration time of one day the measurement error on each level lies at around 25 m s⁻¹. With a planned upgrade this value is expected to be reduced by a factor of 2 in the near future. On the altitude levels where our measurement can be compared to wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF very good agreement in the long-term statistics as well as in short time structures with a duration of a few days has been found.

WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a wide range of azimuth angles including the directions east, west, north, and south for zonal and meridional wind measurements. The design of the radiometer is fairly compact and its calibration does not rely on liquid nitrogen which makes it transportable and suitable for campaign use. WIRA is conceived in a way that it can be operated remotely and does hardly require any maintenance.

In the present paper, a description of the instrument is given, and the techniques used for the wind retrieval based on the determination of the Doppler shift of the measured atmospheric ozone emission spectra are outlined. Their reliability was tested using Monte Carlo simulations. Finally, a time series of 11

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

Science.gov (United States)

Rüfenacht, R.; Kämpfer, N.; Murk, A.

2012-11-01

We report on the wind radiometer WIRA, a new ground-based microwave Doppler-spectro-radiometer specifically designed for the measurement of middle-atmospheric horizontal wind by observing ozone emission spectra at 142.17504 GHz. Currently, wind speeds in five levels between 30 and 79 km can be retrieved which makes WIRA the first instrument able to continuously measure horizontal wind in this altitude range. For an integration time of one day the measurement error on each level lies at around 25 m s-1. With a planned upgrade this value is expected to be reduced by a factor of 2 in the near future. On the altitude levels where our measurement can be compared to wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) very good agreement in the long-term statistics as well as in short time structures with a duration of a few days has been found. WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a wide range of azimuth angles including the directions east, west, north, and south for zonal and meridional wind measurements. The design of the radiometer is fairly compact and its calibration does not rely on liquid nitrogen which makes it transportable and suitable for campaign use. WIRA is conceived in a way that it can be operated remotely and does hardly require any maintenance. In the present paper, a description of the instrument is given, and the techniques used for the wind retrieval based on the determination of the Doppler shift of the measured atmospheric ozone emission spectra are outlined. Their reliability was tested using Monte Carlo simulations. Finally, a time series of 11 months of zonal wind measurements over Bern (46°57' N

Synthetic Landau Levels and Spinor Vortex Matter on a Haldane Spherical Surface with a Magnetic Monopole.

Science.gov (United States)

Zhou, Xiang-Fa; Wu, Congjun; Guo, Guang-Can; Wang, Ruquan; Pu, Han; Zhou, Zheng-Wei

2018-03-30

We present a flexible scheme to realize exact flat Landau levels on curved spherical geometry in a system of spinful cold atoms. This is achieved by applying the Floquet engineering of a magnetic quadrupole field to create a synthetic monopole field in real space. The system can be exactly mapped to the electron-monopole system on a sphere, thus realizing Haldane's spherical geometry for fractional quantum Hall physics. This method works for either bosons or fermions. We investigate the ground-state vortex pattern for an s-wave interacting atomic condensate by mapping this system to the classical Thompson's problem. The distortion and stability of the vortex pattern are further studied in the presence of dipolar interaction. Our scheme is compatible with the current experimental setup, and may serve as a promising route of investigating quantum Hall physics and exotic spinor vortex matter on curved space.

ASRS Reports on Wake Vortex Encounters

Science.gov (United States)

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

New scanning technique for the optical vortex microscope.

Science.gov (United States)

Augustyniak, Ireneusz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Drobczyński, Sławomir

2012-04-01

In the optical vortex microscopy the focused Gaussian beam with optical vortex scans a sample. An optical vortex can be introduced into a laser beam with the use of a special optical element--a vortex lens. When moving the vortex lens, the optical vortex changes its position inside the spot formed by a focused laser beam. This effect can be used as a new precise scanning technique. In this paper, we study the optical vortex behavior at the sample plane. We also estimate if the new scanning technique results in observable effects that could be used for a phase object detection.

Particle-vortex duality in topological insulators and superconductors

Energy Technology Data Exchange (ETDEWEB)

Murugan, Jeff [The Laboratory for Quantum Gravity & Strings, Department of Mathematics and Applied Mathematics, University of Cape Town,Private Bag, Rondebosch, 7700 (South Africa); School of Natural Sciences, Institute for Advanced Study, Olden Lane, Princeton, NJ 08540 (United States); Nastase, Horatiu [Instituto de Física Teórica, UNESP-Universidade Estadual Paulista,R. Dr. Bento T. Ferraz 271, Bl. II, Sao Paulo 01140-070, SP (Brazil)

2017-05-31

We investigate the origins and implications of the duality between topological insulators and topological superconductors in three and four spacetime dimensions. In the latter, the duality transformation can be made at the level of the path integral in the standard way, while in three dimensions, it takes the form of “self-duality in odd dimensions'. In this sense, it is closely related to the particle-vortex duality of planar systems. In particular, we use this to elaborate on Son’s conjecture that a three dimensional Dirac fermion that can be thought of as the surface mode of a four dimensional topological insulator is dual to a composite fermion.

Moving vortex matter with coexisting vortices and anti-vortices

International Nuclear Information System (INIS)

Carneiro, Gilson

2009-01-01

Moving vortex matter, driven by transport currents independent of time, in which vortices and anti-vortices coexist is investigated theoretically in thin superconducting films with nanostructured defects. A simple London model is proposed for the vortex dynamics in films with periodic arrays of nanomagnets or cylindrical holes (antidots). Common to these films is that vortex anti-vortex pairs may be created in the vicinity of the defects by relatively small transport currents, because it adds to the current generated by the defects - the nanomagnets screening current, or the antidots backflow current - and may exceed locally the critical value for vortex anti-vortex pair creation. The model assumes that vortex matter dynamics is governed by Langevin equations, modified to account for creation and annihilation of vortex anti-vortex pairs. For pair creation, it is assumed that whenever the total current at some location exceeds a critical value, equal to that needed to separate a vortex from an anti-vortex by a vortex core diameter, a pair is created instantaneously around this location. Pair annihilation occurs by vortex anti-vortex collisions. The model is applied to films at zero external magnetic field and low temperatures. It is found that several moving vortex matter steady-states with equal numbers of vortices and anti-vortices are possible.