Design analysis of vertical wind turbine with airfoil variation

Science.gov (United States)

Maulana, Muhammad Ilham; Qaedy, T. Masykur Al; Nawawi, Muhammad

2016-03-01

With an ever increasing electrical energy crisis occurring in the Banda Aceh City, it will be important to investigate alternative methods of generating power in ways different than fossil fuels. In fact, one of the biggest sources of energy in Aceh is wind energy. It can be harnessed not only by big corporations but also by individuals using Vertical Axis Wind Turbines (VAWT). This paper presents a three-dimensional CFD analysis of the influence of airfoil design on performance of a Darrieus-type vertical-axis wind turbine (VAWT). The main objective of this paper is to develop an airfoil design for NACA 63-series vertical axis wind turbine, for average wind velocity 2,5 m/s. To utilize both lift and drag force, some of designs of airfoil are analyzed using a commercial computational fluid dynamics solver such us Fluent. Simulation is performed for this airfoil at different angles of attach rearranging from -12°, -8°, -4°, 0°, 4°, 8°, and 12°. The analysis showed that the significant enhancement in value of lift coefficient for airfoil NACA 63-series is occurred for NACA 63-412.

Wind-induced flow velocity effects on nutrient concentrations at Eastern Bay of Lake Taihu, China.

Science.gov (United States)

Jalil, Abdul; Li, Yiping; Du, Wei; Wang, Jianwei; Gao, Xiaomeng; Wang, Wencai; Acharya, Kumud

2017-07-01

Shallow lakes are highly sensitive to respond internal nutrient loading due to wind-induced flow velocity effects. Wind-induced flow velocity effects on nutrient suspension were investigated at a long narrow bay of large shallow Lake Taihu, the third largest freshwater lake in China. Wind-induced reverse/compensation flow and consistent flow field probabilities at vertical column of the water were measured. The probabilities between the wind field and the flow velocities provided a strong correlation at the surface (80.6%) and the bottom (65.1%) layers of water profile. Vertical flow velocity profile analysis provided the evidence of delay response time to wind field at the bottom layer of lake water. Strong wind field generated by the west (W) and west-north-west (WNW) winds produced displaced water movements in opposite directions to the prevailing flow field. An exponential correlation was observed between the current velocities of the surface and the bottom layers while considering wind speed as a control factor. A linear model was developed to correlate the wind field-induced flow velocity impacts on nutrient concentration at the surface and bottom layers. Results showed that dominant wind directions (ENE, E, and ESE) had a maximum nutrient resuspension contribution (nutrient resuspension potential) of 34.7 and 43.6% at the surface and the bottom profile layers, respectively. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) average concentrations were 6.38, 1.5, and 0.03 mg/L during our field experiment at Eastern Bay of Lake Taihu. Overall, wind-induced low-to-moderate hydrodynamic disturbances contributed more in nutrient resuspension at Eastern Bay of Lake Taihu. The present study can be used to understand the linkage between wind-induced flow velocities and nutrient concentrations for shallow lakes (with uniform morphology and deep margins) water quality management and to develop further models.

Vertical axis wind turbine wake in boundary layer flow in a wind tunnel

Science.gov (United States)

Rolin, Vincent; Porté-Agel, Fernando

2016-04-01

A vertical axis wind turbine is placed in a boundary layer flow in a wind tunnel, and its wake is investigated. Measurements are performed using an x-wire to measure two components of velocity and turbulence statistics in the wake of the wind turbine. The study is performed at various heights and crosswind positions in order to investigate the full volume of the wake for a range of tip speed ratios. The velocity deficit and levels of turbulence in the wake are related to the performance of the turbine. The asymmetric incoming boundary layer flow causes the rate of recovery in the wake to change as a function of height. Higher shear between the wake and unperturbed flow occurs at the top edge of the wake, inducing stronger turbulence and mixing in this region. The difference in flow relative to the blades causes the velocity deficit and turbulence level to change as a function of crosswind position behind the rotor. The relative difference diminishes with increasing tip speed ratio. Therefore, the wake becomes more homogeneous as tip speed ratio increases.

Characterization of wind velocities in the upstream induction zone of a wind turbine using scanning continuous-wave lidars

DEFF Research Database (Denmark)

Simley, Eric; Angelou, Nikolas; Mikkelsen, Torben Krogh

2016-01-01

As a wind turbine generates power, induced velocities, lower than the freestream velocity, will be present upstream of the turbine due to perturbation of the flow by the rotor. In this study, the upstream induction zone of a 225kW horizontal axis Vestas V27 wind turbine located at the Danish...... Technical University’s Risø campus is investigated using a scanning Light Detection and Ranging (lidar) system. Three short-range continuous-wave “WindScanner” lidars are positioned in the field around the V27 turbine allowing detection of all three components of the wind velocity vectors within...... the induction zone. The time-averaged mean wind speeds at different locations in the upstream induction zone are measured by scanning a horizontal plane at hub height and a vertical plane centered at the middle of the rotor extending roughly 1.5 rotor diameters (D) upstream of the rotor. Turbulence statistics...

DESIGN AND DEVELOPMENT OF A 1/3 SCALE VERTICAL AXIS WIND TURBINE FOR ELECTRICAL POWER GENERATION

Directory of Open Access Journals (Sweden)

Altab Md. Hossain

2007-12-01

Full Text Available This research describes the electrical power generation in Malaysia by the measurement of wind velocity acting on the wind turbine technology. The primary purpose of the measurement over the 1/3 scaled prototype vertical axis wind turbine for the wind velocity is to predict the performance of full scaled H-type vertical axis wind turbine. The electrical power produced by the wind turbine is influenced by its two major part, wind power and belt power transmission system. The blade and the drag area system are used to determine the powers of the wind that can be converted into electric power as well as the belt power transmission system. In this study both wind power and belt power transmission system has been considered. A set of blade and drag devices have been designed for the 1/3 scaled wind turbine at the Thermal Laboratory of Faculty of Engineering, Universiti Industri Selangor (UNISEL. Test has been carried out on the wind turbine with the different wind velocities of 5.89 m/s, 6.08 m/s and 7.02 m/s. From the experiment, the wind power has been calculated as 132.19 W, 145.40 W and 223.80 W. The maximum wind power is considered in the present study.

DESIGN AND DEVELOPMENT OF A 1/3 SCALE VERTICAL AXIS WIND TURBINE FOR ELECTRICAL POWER GENERATION

Directory of Open Access Journals (Sweden)

Altab Hossain

2007-01-01

Full Text Available This research describes the electrical power generation in Malaysia by the measurement of wind velocity acting on the wind turbine technology. The primary purpose of the measurement over the 1/3 scaled prototype vertical axis wind turbine for the wind velocity is to predict the performance of full scaled H-type vertical axis wind turbine. The electrical power produced by the wind turbine is influenced by its two major part, wind power and belt power transmission system. The blade and the drag area system are used to determine the powers of the wind that can be converted into electric power as well as the belt power transmission system. In this study both wind power and belt power transmission system has been considered. A set of blade and drag devices have been designed for the 1/3 scaled wind turbine at the Thermal Laboratory of Faculty of Engineering, Universiti Industri Selangor (UNISEL. Test has been carried out on the wind turbine with the different wind velocities of 5.89 m/s, 6.08 m/s and 7.02 m/s. From the experiment, the wind power has been calculated as 132.19 W, 145.40 W and 223.80 W. The maximum wind power is considered in the present study.

Estimation of power in low velocity vertical axis wind turbine

Science.gov (United States)

Sampath, S. S.; Shetty, Sawan; Chithirai Pon Selvan, M.

2015-06-01

The present work involves in the construction of a vertical axis wind turbine and the determination of power. Various different types of turbine blades are considered and the optimum blade is selected. Mechanical components of the entire setup are built to obtain maximum rotation per minute. The mechanical energy is converted into the electrical energy by coupling coaxially between the shaft and the generator. This setup produces sufficient power for consumption of household purposes which is economic and easily available.

Magnetic Geared Radial Axis Vertical Wind Turbine for Low Velocity Regimes

Directory of Open Access Journals (Sweden)

Wei Wei Teow

2018-01-01

Full Text Available In the 21st century, every country is seeking an alternative source of energy especially the renewable sources. There are considerable developments in the wind energy technology in recent years and in more particular on the vertical axis wind turbine (VAWT as they are modular, less installation cost and portable in comparison with that of the horizontal axis wind turbine (HAWT systems. The cut-in speed of a conventional wind turbine is 3.5 m/s to 5 m/s. Mechanical geared generators are commonly found in wind technology to step up power conversion to accommodate the needs of the generator. Wind turbine gearboxes suffer from overload problem and frequent maintenance in spite of the high torque density produced. However, an emerging alternative to gearing system is Magnetic Gear (MG as it offers significant advantages such as free from maintenance and inherent overload protection. In this project, numerical analysis is done on designed magnetic gear greatly affects the performance of the generator in terms of voltage generation. Magnetic flux density is distributed evenly across the generator as seen from the uniform sinusoidal output waveform. Consequently, the interaction of the magnetic flux of the permanent magnets has shown no disturbance to the output of the generator as the voltage generated shows uniform waveform despite the rotational speed of the gears. The simulation is run at low wind speed and the results show that the generator starts generating a voltage of 240 V at a wind speed of 1.04 m/s. This shows great improvement in the operating capability of the wind turbine.

Wind tunnel study of helical and straight-bladed vertical-axis wind turbine wakes

Science.gov (United States)

Bagheri, Maryam; Araya, Daniel

2017-11-01

It is hypothesized that blade curvature can serve as a passive means to control fluid entrainment and wake recovery in vertical-axis wind turbine (VAWT) arrays. We test this experimentally in a wind tunnel using two different VAWT configurations, one with straight blades and another with helical blades, keeping all other experimental parameters fixed. A small-scale, commercially available VAWT (15W max power) is used as the baseline wind tunnel model in each case. The commercial VAWT blades are replaced with either straight or helical blades that are 3D-printed extrusions of the same airfoil cross-section. Results from smoke flow visualization, three-component wake velocity measurements, and turbine power data are presented. These results give insight into the potential use of VAWTs with curved blades in utility-scale wind farms.

Numerical simulations of thermospheric dynamics: divergence as a proxy for vertical winds

Directory of Open Access Journals (Sweden)

S. L. Cooper

2009-06-01

Full Text Available A local scale, time dependent three-dimensional model of the neutral thermosphere was used to test the applicability of two previously published empirical relations between thermospheric vertical wind and velocity divergence, i.e., those due to Burnside et al. (1981 and Brekke (1997. The model self-consistently solves for vertical winds driven by heat and momentum deposited into the neutral atmosphere by high latitude ion convection. The Brekke condition accurately mimicked the overall "shape" of the three-dimensional model vertical wind field although, as written, it consistently overestimated the vertical wind magnitude by a factor of approximately 5/3, for the heating scenarios that we considered. This same general behavior was observed regardless of whether the forcing was static or rapidly changing with time. We discuss the likely reason for the Brekke condition overestimating the magnitude of our vertical winds, and suggest an alternative condition that should better describe vertical winds that are driven by local heating. The applicability of the Burnside condition was, by contrast, quite variable. During static heating, both the magnitude and the sign of the model vertical winds were predicted reliably at heights above those of maximum energy and momentum deposition per unit mass. However, below the thermal forcing, the Burnside condition predicted vertical winds of the wrong sign. It also introduced significant artefacts into the predicted vertical wind field when the forcing changed suddenly with time. If these results are of general applicability (which seems likely, given the way these relations are derived then the Burnside condition could usually be used safely at altitudes above h_mF₂. But it should be avoided below this height at all times, and even at high altitudes during periods of dynamic forcing. While the Brekke condition (or our modified version of it could likely be used in all circumstances

Vertical axis wind turbine airfoil

Science.gov (United States)

Krivcov, Vladimir; Krivospitski, Vladimir; Maksimov, Vasili; Halstead, Richard; Grahov, Jurij Vasiljevich

2012-12-18

A vertical axis wind turbine airfoil is described. The wind turbine airfoil can include a leading edge, a trailing edge, an upper curved surface, a lower curved surface, and a centerline running between the upper surface and the lower surface and from the leading edge to the trailing edge. The airfoil can be configured so that the distance between the centerline and the upper surface is the same as the distance between the centerline and the lower surface at all points along the length of the airfoil. A plurality of such airfoils can be included in a vertical axis wind turbine. These airfoils can be vertically disposed and can rotate about a vertical axis.

Orographic precipitation and vertical velocity characteristics from drop size and fall velocity spectra observed by disdrometers

Science.gov (United States)

Lee, Dong-In; Kim, Dong-Kyun; Kim, Ji-Hyeon; Kang, Yunhee; Kim, Hyeonjoon

2017-04-01

During a summer monsoon season each year, severe weather phenomena caused by front, mesoscale convective systems, or typhoons often occur in the southern Korean Peninsula where is mostly comprised of complex high mountains. These areas play an important role in controlling formation, amount, and distribution of rainfall. As precipitation systems move over the mountains, they can develop rapidly and produce localized heavy rainfall. Thus observational analysis in the mountainous areas is required for studying terrain effects on the rapid rainfall development and its microphysics. We performed intensive field observations using two s-band operational weather radars around Mt. Jiri (1950 m ASL) during summertime on June and July in 2015-2016. Observation data of DSD (Drop Size Distribution) from Parsivel disdrometer and (w component) vertical velocity data from ultrasonic anemometers were analyzed for Typhoon Chanhom on 12 July 2015 and the heavy rain event on 1 July 2016. During the heavy rain event, a dual-Doppler radar analysis using Jindo radar and Gunsan radar was also conducted to examine 3-D wind fields and vertical structure of reflectivity in these areas. For examining up-/downdrafts in the windward or leeward side of Mt. Jiri, we developed a new scheme technique to estimate vertical velocities (w) from drop size and fall velocity spectra of Parsivel disdrometers at different stations. Their comparison with the w values observed by the 3D anemometer showed quite good agreement each other. The Z histogram with regard to the estimated w was similar to that with regard to R, indicating that Parsivel-estimated w is quite reasonable for classifying strong and weak rain, corresponding to updraft and downdraft, respectively. Mostly, positive w values (upward) were estimated in heavy rainfall at the windward side (D1 and D2). Negative w values (downward) were dominant even during large rainfall at the leeward side (D4). For D1 and D2, the upward w percentages were

Estimation of mesospheric vertical winds from a VHF meteor radar at King Sejong Station, Antarctica (62.2S, 58.8W)

Science.gov (United States)

Kim, Y.; Lee, C.; Kim, J.; Jee, G.

2013-12-01

For the first time, vertical winds near the mesopause region were estimated from radial velocities of meteor echoes detected by a VHF meteor radar at King Sejong Station (KSS) in 2011 and 2012. Since the radar usually detects more than a hundred echoes every hour in an altitude bin of 88 - 92 km, much larger than other radars, we were able to fit measured radial velocities of these echoes with a 6 component model that consists of horizontal winds, spatial gradients of horizontal winds and vertical wind. The conventional method of deriving horizontal winds from meteor echoes utilizes a 2 component model, assuming that vertical winds and spatial gradients of horizontal winds are negligible. We analyzed the radar data obtained for 8400 hours in 2012 and 8100 hours in 2011. We found that daily mean values of vertical winds are mostly within +/- 1 m/s, whereas those of zonal winds are a few tens m/s mostly eastward. The daily mean vertical winds sometimes stay positive or negative for more than 20 days, implying that the atmosphere near the mesopause experiences episodically a large scale low and high pressure environments, respectively, like the tropospheric weather system. By conducting Lomb-normalized periodogram analysis, we also found that the vertical winds have diurnal, semidiurnal and terdiurnal tidal components with about equal significance, in contrast to horizontal winds that show a dominant semidiurnal one. We will discuss about uncertainties of the estimated vertical wind and possible reasons of its tidal and daily variations.

Doppler Lidar Vertical Velocity Statistics Value-Added Product

Energy Technology Data Exchange (ETDEWEB)

Newsom, R. K. [DOE ARM Climate Research Facility, Washington, DC (United States); Sivaraman, C. [DOE ARM Climate Research Facility, Washington, DC (United States); Shippert, T. R. [DOE ARM Climate Research Facility, Washington, DC (United States); Riihimaki, L. D. [DOE ARM Climate Research Facility, Washington, DC (United States)

2015-07-01

Accurate height-resolved measurements of higher-order statistical moments of vertical velocity fluctuations are crucial for improved understanding of turbulent mixing and diffusion, convective initiation, and cloud life cycles. The Atmospheric Radiation Measurement (ARM) Climate Research Facility operates coherent Doppler lidar systems at several sites around the globe. These instruments provide measurements of clear-air vertical velocity profiles in the lower troposphere with a nominal temporal resolution of 1 sec and height resolution of 30 m. The purpose of the Doppler lidar vertical velocity statistics (DLWSTATS) value-added product (VAP) is to produce height- and time-resolved estimates of vertical velocity variance, skewness, and kurtosis from these raw measurements. The VAP also produces estimates of cloud properties, including cloud-base height (CBH), cloud frequency, cloud-base vertical velocity, and cloud-base updraft fraction.

Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities

Directory of Open Access Journals (Sweden)

L. Patara

2009-03-01

Full Text Available This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999–May 2001. A tight coupling is observed between the upper and deep traps and the estimated particle sinking rates are more than 200 m day⁻¹. The current vertical velocity field is computed from a 1/16°×1/16° Ocean General Circulation Model simulation and from the wind stress curl. Current vertical velocities are larger and more variable than Ekman vertical velocities, yet the general patterns are alike. Current vertical velocities are generally smaller than 1 m day⁻¹: we therefore exclude a direct effect of downward velocities in determining high sedimentation rates. However we find that upward velocities in the subsurface layers of the water column are positively correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels – thus stimulating primary production and grazing – a few weeks before an enhanced vertical flux is found in the sediment traps. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton. Other sedimentation mechanisms, such as dust deposition, are also considered in explaining large pulses of deep particle fluxes. The fast sinking rates estimated in this study might be an evidence of the efficiency of the biological pump in sequestering organic carbon from the surface layers of the deep Eastern Mediterranean basins.

Numerical Analysis of a Small-Size Vertical-Axis Wind Turbine Performance and Averaged Flow Parameters Around the Rotor

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Rogowski Krzysztof

2017-06-01

Full Text Available Small-scale vertical-axis wind turbines can be used as a source of electricity in rural and urban environments. According to the authors’ knowledge, there are no validated simplified aerodynamic models of these wind turbines, therefore the use of more advanced techniques, such as for example the computational methods for fluid dynamics is justified. The paper contains performance analysis of the small-scale vertical-axis wind turbine with a large solidity. The averaged velocity field and the averaged static pressure distribution around the rotor have been also analyzed. All numerical results presented in this paper are obtained using the SST k-ω turbulence model. Computed power coeffcients are in good agreement with the experimental results. A small change in the tip speed ratio significantly affects the velocity field. Obtained velocity fields can be further used as a base for simplified aerodynamic methods.

Numerical Investigation of the Tip Vortex of a Straight-Bladed Vertical Axis Wind Turbine with Double-Blades

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Yanzhao Yang

2017-10-01

Full Text Available Wind velocity distribution and the vortex around the wind turbine present a significant challenge in the development of straight-bladed vertical axis wind turbines (VAWTs. This paper is intended to investigate influence of tip vortex on wind turbine wake by Computational Fluid Dynamics (CFD simulations. In this study, the number of blades is two and the airfoil is a NACA0021 with chord length of c = 0.265 m. To capture the tip vortex characteristics, the velocity fields are investigated by the Q-criterion iso-surface (Q = 100 with shear-stress transport (SST k-ω turbulence model at different tip speed ratios (TSRs. Then, mean velocity, velocity deficit and torque coefficient acting on the blade in the different spanwise positions are compared. The wind velocities obtained by CFD simulations are also compared with the experimental data from wind tunnel experiments. As a result, we can state that the wind velocity curves calculated by CFD simulations are consistent with Laser Doppler Velocity (LDV measurements. The distribution of the vortex structure along the spanwise direction is more complex at a lower TSR and the tip vortex has a longer dissipation distance at a high TSR. In addition, the mean wind velocity shows a large value near the blade tip and a small value near the blade due to the vortex effect.

Improved double-multiple streamtube model for the Darrieus-type vertical axis wind turbine

Science.gov (United States)

Berg, D. E.

Double streamtube codes model the curved blade (Darrieus-type) vertical axis wind turbine (VAWT) as a double actuator fish arrangement (one half) and use conservation of momentum principles to determine the forces acting on the turbine blades and the turbine performance. Sandia National Laboratories developed a double multiple streamtube model for the VAWT which incorporates the effects of the incident wind boundary layer, nonuniform velocity between the upwind and downwind sections of the rotor, dynamic stall effects and local blade Reynolds number variations. The theory underlying this VAWT model is described, as well as the code capabilities. Code results are compared with experimental data from two VAWT's and with the results from another double multiple streamtube and a vortex filament code. The effects of neglecting dynamic stall and horizontal wind velocity distribution are also illustrated.

Vertical axis wind turbine

International Nuclear Information System (INIS)

Obretenov, V.; Tsalov, T.; Chakarov, T.

2012-01-01

In recent years, the interest in wind turbines with vertical axis noticeably increased. They have some important advantages: low cost, relatively simple structure, reliable packaging system of wind aggregate long period during which require no maintenance, low noise, independence of wind direction, etc.. The relatively low efficiency, however, makes them applicable mainly for small facilities. The work presents a methodology and software for approximately aerodynamic design of wind turbines of this type, and also analyzed the possibility of improving the efficiency of their workflow

Field investigation of a wake structure downwind of a VANT (Vertical-Axis Wind Turbine) in a wind farm array

Science.gov (United States)

Liu, H. T.; Buck, J. W.; Germain, A. C.; Hinchee, M. E.; Solt, T. S.; Leroy, G. M.; Srnsky, R. A.

1988-09-01

The effects of upwind turbine wakes on the performance of a FloWind 17-m vertical-axis wind turbine (VAWT) were investigated through a series of field experiments conducted at the FloWind wind farm on Cameron Ridge, Tehachapi, California. From the field measurements, we derived the velocity and power/energy deficits under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. A method to estimate the energy deficit was developed based on the measured power deficit and the wind speed distributions. This method may be adopted for other turbine types and sites. Recommendations are made for optimizing wind farm design and operations, as well as for wind energy management.

Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear

Science.gov (United States)

Mendoza, Victor; Goude, Anders

2017-05-01

The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

Climatology of tropospheric vertical velocity spectra

Science.gov (United States)

Ecklund, W. L.; Gage, K. S.; Balsley, B. B.; Carter, D. A.

1986-01-01

Vertical velocity power spectra obtained from Poker Flat, Alaska; Platteville, Colorado; Rhone Delta, France; and Ponape, East Caroline Islands using 50-MHz clear-air radars with vertical beams are given. The spectra were obtained by analyzing the quietest periods from the one-minute-resolution time series for each site. The lengths of available vertical records ranged from as long as 6 months at Poker Flat to about 1 month at Platteville. The quiet-time vertical velocity spectra are shown. Spectral period ranging from 2 minutes to 4 hours is shown on the abscissa and power spectral density is given on the ordinate. The Brunt-Vaisala (B-V) periods (determined from nearby sounding balloons) are indicated. All spectra (except the one from Platteville) exhibit a peak at periods slightly longer than the B-V period, are flat at longer periods, and fall rapidly at periods less than the B-V period. This behavior is expected for a spectrum of internal waves and is very similar to what is observed in the ocean (Eriksen, 1978). The spectral amplitudes vary by only a factor of 2 or 3 about the mean, and show that under quiet conditions vertical velocity spectra from the troposphere are very similar at widely different locations.

Analysis and design of a vertical axis wind turbine

OpenAIRE

Goyena Iriso, Joseba

2011-01-01

The main objective of this project is to design a new vertical axis wind turbine, specifically one Giromill wind turbine. The project development requires performing a previous study of the vertical axis wind turbines currently development. This study has to be performed before starting to design the wind turbine. Other very important aim is the development of a new vertical axis wind turbine. The after analyses that will result in the final design of the wind turbine will b...

Self-starting aerodynamics analysis of vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Jianyang Zhu

2015-12-01

Full Text Available Vertical axis wind turbine is a special type of wind-force electric generator which is capable of working in the complicated wind environment. The self-starting aerodynamics is one of the most important considerations for this kind of turbine. This article aims at providing a systematic synthesis on the self-starting aerodynamic characteristics of vertical axis wind turbine based on the numerical analysis approach. First, the physical model of vertical axis wind turbine and its parameter definitions are presented. Secondary, the interaction model between the vertical axis wind turbine and fluid is developed by using the weak coupling approach; the numerical data of this model are then compared with the wind tunnel experimental data to show its feasibility. Third, the effects of solidity and fixed pitch angle on the self-starting aerodynamic characteristics of the vertical axis wind turbine are analyzed systematically. Finally, the quantification effects of the solidity and fixed pitch angle on the self-starting performance of the turbine can be obtained. The analysis in this study will provide straightforward physical insight into the self-starting aerodynamic characteristics of vertical axis wind turbine.

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.

Results of verification and investigation of wind velocity field forecast. Verification of wind velocity field forecast model

International Nuclear Information System (INIS)

Ogawa, Takeshi; Kayano, Mitsunaga; Kikuchi, Hideo; Abe, Takeo; Saga, Kyoji

1995-01-01

In Environmental Radioactivity Research Institute, the verification and investigation of the wind velocity field forecast model 'EXPRESS-1' have been carried out since 1991. In fiscal year 1994, as the general analysis, the validity of weather observation data, the local features of wind field, and the validity of the positions of monitoring stations were investigated. The EXPRESS which adopted 500 m mesh so far was improved to 250 m mesh, and the heightening of forecast accuracy was examined, and the comparison with another wind velocity field forecast model 'SPEEDI' was carried out. As the results, there are the places where the correlation with other points of measurement is high and low, and it was found that for the forecast of wind velocity field, by excluding the data of the points with low correlation or installing simplified observation stations to take their data in, the forecast accuracy is improved. The outline of the investigation, the general analysis of weather observation data and the improvements of wind velocity field forecast model and forecast accuracy are reported. (K.I.)

Horizontal and vertical winds and temperatures in the equatorial thermosphere: measurements from Natal, Brazil during August-September 1982

International Nuclear Information System (INIS)

Biondi, M.A.

1985-01-01

Fabry-Perot interferometer measurements of Doppler shifts and widths of the 630.0 nm nightglow line have been used to determine the neutral winds and temperatures in the equatorial thermosphere over Natal, Brazil during August-September 1982. During this period, in the early night (2130 U.T.) the average value of the horizontal wind vector was 95 m s -1 at 100 0 azimuth, and the temperature varied from a low of 950 K during geomagnetically quiet conditions to a high of approx. 1400 K during a storm (6 September). The meridional winds were small, -1 , and the eastward zonal winds reached a maximum value 1-3 h after sunset, in qualitative agreement with TGCM predictions. On 26 August, an observed persistent convergence in the horizontal meridional flow was accompanied by a downward vertical velocity and an increase in the thermospheric temperature measured overhead. Oscillations with periods of 40-45 min in both the zonal and vertical wind velocities were observed during the geomagnetic storm of 6 September, suggesting gravity wave modulation of the equatorial thermospheric flow. (author)

Design of h-Darrieus vertical axis wind turbine

Science.gov (United States)

Parra, Teresa; Vega, Carmen; Gallegos, A.; Uzarraga, N. C.; Castro, F.

2015-05-01

Numerical simulation is used to predict the performance of a Vertical Axis Wind Turbine (VAWT) H-Darrieus. The rotor consists of three straight blades with shape of aerofoil of the NACA family attached to a rotating vertical shaft. The influence of the solidity is tested to get design tendencies. The mesh has two fluid volumes: one sliding mesh for the rotor where the rotation velocity is established while the other is the environment of the rotor. Bearing in mind the overall flow is characterized by important secondary flows, the turbulence model selected was realizable k-epsilon with non-equilibrium wall functions. Conservation equations were solved with a Third-Order Muscl scheme using SIMPLE to couple pressure and velocity. During VAWT operation, the performance depends mainly on the relative motion of the rotating blade and has a fundamental period which depends both on the rate of rotation and the number of blades. The transient study is necessary to characterise the hysteresis phenomenon. Hence, more than six revolutions get the periodic behaviour. Instantaneous flows provide insight about wake structure interaction. Time averaged parameters let obtain the characteristic curves of power coefficient.

Design of h-Darrieus vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Parra Teresa

2015-01-01

Full Text Available Numerical simulation is used to predict the performance of a Vertical Axis Wind Turbine (VAWT H-Darrieus. The rotor consists of three straight blades with shape of aerofoil of the NACA family attached to a rotating vertical shaft. The influence of the solidity is tested to get design tendencies. The mesh has two fluid volumes: one sliding mesh for the rotor where the rotation velocity is established while the other is the environment of the rotor. Bearing in mind the overall flow is characterized by important secondary flows, the turbulence model selected was realizable k-epsilon with non-equilibrium wall functions. Conservation equations were solved with a Third-Order Muscl scheme using SIMPLE to couple pressure and velocity. During VAWT operation, the performance depends mainly on the relative motion of the rotating blade and has a fundamental period which depends both on the rate of rotation and the number of blades. The transient study is necessary to characterise the hysteresis phenomenon. Hence, more than six revolutions get the periodic behaviour. Instantaneous flows provide insight about wake structure interaction. Time averaged parameters let obtain the characteristic curves of power coefficient.

Self-starting aerodynamics analysis of vertical axis wind turbine

OpenAIRE

Jianyang Zhu; Hailin Huang; Hao Shen

2015-01-01

Vertical axis wind turbine is a special type of wind-force electric generator which is capable of working in the complicated wind environment. The self-starting aerodynamics is one of the most important considerations for this kind of turbine. This article aims at providing a systematic synthesis on the self-starting aerodynamic characteristics of vertical axis wind turbine based on the numerical analysis approach. First, the physical model of vertical axis wind turbine and its parameter defi...

Year-Long Vertical Velocity Statistics Derived from Doppler Lidar Data for the Continental Convective Boundary Layer

Energy Technology Data Exchange (ETDEWEB)

Berg, Larry K. [Pacific Northwest National Laboratory, Richland, Washington; Newsom, Rob K. [Pacific Northwest National Laboratory, Richland, Washington; Turner, David D. [Global Systems Division, NOAA/Earth System Research Laboratory, Boulder, Colorado

2017-09-01

One year of Coherent Doppler Lidar (CDL) data collected at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) site in Oklahoma is analyzed to provide profiles of vertical velocity variance, skewness, and kurtosis for cases of cloud-free convective boundary layers. The variance was scaled by the Deardorff convective velocity scale, which was successful when the boundary layer depth was stationary but failed in situations when the layer was changing rapidly. In this study the data are sorted according to time of day, season, wind direction, surface shear stress, degree of instability, and wind shear across the boundary-layer top. The normalized variance was found to have its peak value near a normalized height of 0.25. The magnitude of the variance changes with season, shear stress, and degree of instability, but was not impacted by wind shear across the boundary-layer top. The skewness was largest in the top half of the boundary layer (with the exception of wintertime conditions). The skewness was found to be a function of the season, shear stress, wind shear across the boundary-layer top, with larger amounts of shear leading to smaller values. Like skewness, the vertical profile of kurtosis followed a consistent pattern, with peak values near the boundary-layer top (also with the exception of wintertime data). The altitude of the peak values of kurtosis was found to be lower when there was a large amount of wind shear at the boundary-layer top.

Simulating dynamic stall in a two-dimensional vertical-axis wind turbine: Verification and validation with particle image velocimetry data

NARCIS (Netherlands)

Ferreira, C.J.S.; Zuijlen, van A.H.; Bijl, H.; Bussel, van G.J.W.; Kuik, van G.A.M.

2010-01-01

The implementation of wind energy conversion systems in the built environment has renewed the interest and the research on Vertical Axis Wind Turbines (VAWTs). The VAWT has an inherent unsteady aerodynamic behavior due to the variation of angle of attack and perceived velocity with azimuth angle.

CFD modeling of a vertical-axis wind turbine for efficiency improvement and climate change mitigation

International Nuclear Information System (INIS)

Ajedegba, J.O.; Rosen, M.A.; Naterer, G.F.; Tsang, E.

2009-01-01

Wind power can help mitigate climate change. Computational fluid dynamics (CFD) is used here to simulate and analyze the Zephyr vertical axis wind turbine and to assess how it reduces greenhouse gas emissions. Fluid flow through the turbine is simulated to predict its performance. A multiple reference frame model capability of CFD is used to express the turbine power output as a function of the wind free stream velocity and the rotor rotational speed. The results suggest the wind turbine could significantly reduce energy demand and greenhouse gas emissions in urban and rural settings relative to conventional power systems. (author)

Numerical and Computational Analysis of a New Vertical Axis Wind Turbine, Named KIONAS

Directory of Open Access Journals (Sweden)

Eleni Douvi

2017-01-01

Full Text Available This paper concentrates on a new configuration for a wind turbine, named KIONAS. The main purpose is to determine the performance and aerodynamic behavior of KIONAS, which is a vertical axis wind turbine with a stator over the rotor and a special feature in that it can consist of several stages. Notably, the stator is shaped in such a way that it increases the velocity of the air impacting the rotor blades. Moreover, each stage’s performance can be increased with the increase of the total number of stages. The effects of wind velocity, the various numbers of inclined rotor blades, the rotor diameter, the stator’s shape and the number of stages on the performance of KIONAS were studied. A FORTRAN code was developed in order to predict the power in several cases by solving the equations of continuity and momentum. Subsequently, further knowledge on the flow field was obtained by using a commercial Computational Fluid Dynamics code. Based on the results, it can be concluded that higher wind velocities and a greater number of blades produce more power. Furthermore, higher performance was found for a stator with curved guide vanes and for a KIONAS configuration with more stages.

Variation of the solar wind velocity following solar flares

International Nuclear Information System (INIS)

Huang, Y.; Lee, Y.

1975-01-01

By use of the superposed epoch method, changes in the solar wind velocity following solar flares have been investigated by using the solar wind velocity data obtained by Pioneer 6 and 7 and Vela 3, 4, and 5 satellites. A significant increase of the solar wind velocity has been found on the second day following importance 3 solar flares and on the third day following importance 2 solar flares. No significant increase of the solar wind velocity has been found for limb flares. (auth)

Estimation of sand dune thickness using a vertical velocity profile

International Nuclear Information System (INIS)

Al-Shuhail, Abdullatif A.

2004-01-01

Previous field and mathematical studies have shown that sand dunes may have vertical velocity profiles (i.e. continuous increase of velocity with depth). Therefore, computing the dunes thickness using conventional seismic refraction methods that assume a vertically homogeneous layer will likely produce some errors. The purpose of this study is to quantify the effect of the vertical velocity profile in a sand dune on the process of thickness estimation using seismic refraction data. First, the time distance (T-X) data of the direct wave in the dune is calculated using a vertical velocity profile, V (z), derived from Hertz-Mindlin contact theory. Then the thickness is estimated from the calculated T-X data, intercept time and velocity of the refractor at the dune's base assuming a constant velocity in the dune. The error in the estimated thickness due to the constant-velocity assumption increases with increasing thickness and decreasing porosity of the dune. For sand dunes with porosities greater than 0.2 and thickness less than 200 meter, the error is less than 15%. (author)

Wind speed and direction shears with associated vertical motion during strong surface winds

Science.gov (United States)

Alexander, M. B.; Camp, D. W.

1984-01-01

Strong surface winds recorded at the NASA 150-Meter Ground Winds Tower facility at Kennedy Space Center, Florida, are analyzed to present occurrences representative of wind shear and vertical motion known to be hazardous to the ascent and descent of conventional aircraft and the Space Shuttle. Graphical (percentage frequency distributions) and mathematical (maximum, mean, standard deviation) descriptions of wind speed and direction shears and associated updrafts and downdrafts are included as functions of six vertical layers and one horizontal distance for twenty 5-second intervals of parameters sampled simultaneously at the rate of ten per second during a period of high surface winds.

Vertically and Horizontally Mounted Wind Mills : Wind Energy Production in Tampere University of Applied Sciences

OpenAIRE

Evdokimova, Ekaterina

2013-01-01

The purpose of this thesis was to gather information about vertical and horizontal wind mills and to complete a research on wind power production by wind mills which were installed in Tampere University of Applied Sciences. The horizontally mounted wind mill Windspot 3.5 and vertically mounted wind mill Cypress were installed in summer 2011 but they started functioning and supplying energy only during 2012. In the theoretical part of this thesis wind speed and wind power production is dis...

Effect of moment of inertia to H type vertical axis wind turbine aerodynamic performance

International Nuclear Information System (INIS)

Yang, C X; Li, S T

2013-01-01

The main aerodynamic performances (out power out power coefficient torque torque coefficient and so on) of H type Vertical Axis wind Turbine (H-VAWT) which is rotating machinery will be impacted by moment of inertia. This article will use NACA0018 airfoil profile to analyze that moment of inertia through impact performance of H type VAWT by utilizing program of Matlab and theory of Double-Multiple Streamtube. The results showed that the max out power coefficient was barely impacted when moment of inertia is changed in a small area,but the lesser moment of inertia's VAWT needs a stronger wind velocity to obtain the max out power. The lesser moment of inertia's VAWT has a big out power coefficient, torque coefficient and out power before it gets to the point of max out power coefficient. Out power coefficient, torque and torque coefficient will obviously change with wind velocity increased for VAWT of the lesser moment of inertia

Predicting vertical jump height from bar velocity.

Science.gov (United States)

García-Ramos, Amador; Štirn, Igor; Padial, Paulino; Argüelles-Cienfuegos, Javier; De la Fuente, Blanca; Strojnik, Vojko; Feriche, Belén

2015-06-01

The objective of the study was to assess the use of maximum (Vmax) and final propulsive phase (FPV) bar velocity to predict jump height in the weighted jump squat. FPV was defined as the velocity reached just before bar acceleration was lower than gravity (-9.81 m·s(-2)). Vertical jump height was calculated from the take-off velocity (Vtake-off) provided by a force platform. Thirty swimmers belonging to the National Slovenian swimming team performed a jump squat incremental loading test, lifting 25%, 50%, 75% and 100% of body weight in a Smith machine. Jump performance was simultaneously monitored using an AMTI portable force platform and a linear velocity transducer attached to the barbell. Simple linear regression was used to estimate jump height from the Vmax and FPV recorded by the linear velocity transducer. Vmax (y = 16.577x - 16.384) was able to explain 93% of jump height variance with a standard error of the estimate of 1.47 cm. FPV (y = 12.828x - 6.504) was able to explain 91% of jump height variance with a standard error of the estimate of 1.66 cm. Despite that both variables resulted to be good predictors, heteroscedasticity in the differences between FPV and Vtake-off was observed (r(2) = 0.307), while the differences between Vmax and Vtake-off were homogenously distributed (r(2) = 0.071). These results suggest that Vmax is a valid tool for estimating vertical jump height in a loaded jump squat test performed in a Smith machine. Key pointsVertical jump height in the loaded jump squat can be estimated with acceptable precision from the maximum bar velocity recorded by a linear velocity transducer.The relationship between the point at which bar acceleration is less than -9.81 m·s(-2) and the real take-off is affected by the velocity of movement.Mean propulsive velocity recorded by a linear velocity transducer does not appear to be optimal to monitor ballistic exercise performance.

A Method for Modeling of Floating Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Wang, Kai; Hansen, Martin Otto Laver; Moan, Torgeir

2013-01-01

It is of interest to investigate the potential advantages of floating vertical axis wind turbine (FVAWT) due to its economical installation and maintenance. A novel 5MW vertical axis wind turbine concept with a Darrieus rotor mounted on a semi-submersible support structure is proposed in this paper....... In order to assess the technical and economic feasibility of this novel concept, a comprehensive simulation tool for modeling of the floating vertical axis wind turbine is needed. This work presents the development of a coupled method for modeling of the dynamics of a floating vertical axis wind turbine....... This integrated dynamic model takes into account the wind inflow, aerodynamics, hydrodynamics, structural dynamics (wind turbine, floating platform and the mooring lines) and a generator control. This approach calculates dynamic equilibrium at each time step and takes account of the interaction between the rotor...

Inference and Biogeochemical Response of Vertical Velocities inside a Mode Water Eddy

Science.gov (United States)

Barceló-Llull, B.; Pallas Sanz, E.; Sangrà, P.

2016-02-01

With the aim to study the modulation of the biogeochemical fluxes by the ageostrophic secondary circulation in anticyclonic mesoscale eddies, a typical eddy of the Canary Eddy Corridor was interdisciplinary surveyed on September 2014 in the framework of the PUMP project. The eddy was elliptical shaped, 4 month old, 110 km diameter and 400 m depth. It was an intrathermocline type often also referred as mode water eddy type. We inferred the mesoscale vertical velocity field resolving a generalized omega equation from the 3D density and ADCP velocity fields of a five-day sampled CTD-SeaSoar regular grid centred on the eddy. The grid transects where 10 nautical miles apart. Although complex, in average, the inferred omega velocity field (hereafter w) shows a dipolar structure with downwelling velocities upstream of the propagation path (west) and upwelling velocities downstream. The w at the eddy center was zero and maximum values were located at the periphery attaining ca. 6 m day-1. Coinciding with the occurrence of the vertical velocities cells a noticeable enhancement of phytoplankton biomass was observed at the eddy periphery respect to the far field. A corresponding upward diapycnal flux of nutrients was also observed at the periphery. As minimum velocities where reached at the eddy center, lineal Ekman pumping mechanism was discarded. Minimum values of phytoplankton biomass where also observed at the eddy center. The possible mechanisms for such dipolar w cell are still being investigated, but an analysis of the generalized omega equation forcing terms suggest that it may be a combination of horizontal deformation and advection of vorticity by the ageostrophic current (related to nonlinear Ekman pumping). As expected for Trades, the wind was rather constant and uniform with a speed of ca. 5 m s-1. Diagnosed nonlinear Ekman pumping leaded also to a dipolar cell that mirrors the omega w dipolar cell.

An LES study of vertical-axis wind turbine wakes aerodynamics

Science.gov (United States)

Abkar, Mahdi; Dabiri, John O.

2016-11-01

In this study, large-eddy simulation (LES) combined with a turbine model is used to investigate the structure of the wake behind a vertical-axis wind turbine (VAWT). In the simulations, a recently developed minimum dissipation model is used to parameterize the subgrid-scale stress tensor, while the turbine-induced forces are modeled with an actuator-line technique. The LES framework is first tested in the simulation of the wake behind a model straight-bladed VAWT placed in the water channel, and then used to study the wake structure downwind of a full-scale VAWT sited in the atmospheric boundary layer. In particular, the self-similarity of the wake is examined, and it is found that the wake velocity deficit is well characterized by a two-dimensional elliptical Gaussian distribution. By assuming a self-similar Gaussian distribution of the velocity deficit, and applying mass and momentum conservation, an analytical model is developed and tested to predict the maximum velocity deficit downwind of the turbine.

THE CHARACTERISTICS OF THE OPERATING PARAMETERS OF THE VERTICAL AXIS WIND TURBINE FOR THE SELECTED WIND SPEED

Directory of Open Access Journals (Sweden)

Zbigniew Czyż

2017-03-01

Full Text Available The article presents the results of examining a wind turbine on the vertical axis of rotation. The study was conducted in an open circuit wind tunnel Gunt HM 170 in the laboratory of the Department of Thermodynamics, Fluid Mechanics and Aviation Propulsion Systems in Lublin University of Technology. The subject of research was a rotor based on the patent PL 219985. The research object in the form of rotor consists of blades capable of altering the surface of the active area (receiving kinetic energy of the wind. The study was performed on appropriately scaled and geometrically similar models with maintaining, relevant to the type of research, the criterion numbers. Research objects in the form of rotors with different angles of divergence of blades were made using a 3D powder printer ZPrinter® 450. The results of the research conducted were carried out at the selected flow velocity of 6.5 m/s for three angles of divergence, ie. 30°, 60°, and 90° at variable rotational speed. The applied research station allows braking of the turbine to the required speed, recording velocity and torque, which allows to obtain characteristics of torque and power as a function of rotor speed.

Shaping the distribution of vertical velocities of antihydrogen in GBAR

Energy Technology Data Exchange (ETDEWEB)

Dufour, G.; Lambrecht, A.; Reynaud, S. [CNRS, ENS, UPMC, Laboratoire Kastler-Brossel, Paris (France); Debu, P. [CEA-Saclay, Institut de Recherche sur les lois Fondamentales de l' Univers, Gif-sur-Yvette (France); Nesvizhevsky, V.V. [Institut Max von Laue-Paul Langevin, Grenoble (France); Voronin, A.Yu. [P.N. Lebedev Physical Institute, Moscow (Russian Federation)

2014-01-15

GBAR is a project aiming at measuring the freefall acceleration of gravity for antimatter, namely antihydrogen atoms (H). The precision of this timing experiment depends crucially on the dispersion of initial vertical velocities of the atoms as well as on the reliable control of their distribution.We propose to use a new method for shaping the distribution of the vertical velocities of H, which improves these factors simultaneously. The method is based on quantum reflection of elastically and specularly bouncing H with small initial vertical velocity on a bottom mirror disk, and absorption of atoms with large initial vertical velocities on a top rough disk.We estimate statistical and systematic uncertainties, and we show that the accuracy for measuring the free fall acceleration g of H could be pushed below 10{sup -3} under realistic experimental conditions. (orig.)

Shaping the distribution of vertical velocities of antihydrogen in GBAR

CERN Document Server

Dufour, G.; Lambrecht, A.; Nesvizhevsky, V.V.; Reynaud, S.; Voronin, A.Yu.

2014-01-30

GBAR is a project aiming at measuring the free fall acceleration of gravity for antimatter, namely antihydrogen atoms ($\\overline{\\mathrm{H}}$). Precision of this timing experiment depends crucially on the dispersion of initial vertical velocities of the atoms as well as on the reliable control of their distribution. We propose to use a new method for shaping the distribution of vertical velocities of $\\overline{\\mathrm{H}}$, which improves these factors simultaneously. The method is based on quantum reflection of elastically and specularly bouncing $\\overline{\\mathrm{H}}$ with small initial vertical velocity on a bottom mirror disk, and absorption of atoms with large initial vertical velocities on a top rough disk. We estimate statistical and systematic uncertainties, and show that the accuracy for measuring the free fall acceleration $\\overline{g}$ of $\\overline{\\mathrm{H}}$ could be pushed below $10^{-3}$ under realistic experimental conditions.

Vertical velocity variances and Reynold stresses at Brookhaven

DEFF Research Database (Denmark)

Busch, Niels E.; Brown, R.M.; Frizzola, J.A.

1970-01-01

Results of wind tunnel tests of the Brookhaven annular bivane are presented. The energy transfer functions describing the instrument response and the numerical filter employed in the data reduction process have been used to obtain corrected values of the normalized variance of the vertical wind v...

A Unified Geodetic Vertical Velocity Field (UGVVF), Version 1.0

Science.gov (United States)

Schmalzle, G.; Wdowinski, S.

2014-12-01

Tectonic motion, volcanic inflation or deflation, as well as oil, gas and water pumping can induce vertical motion. In southern California these signals are inter-mingled. In tectonics, properly identifying regions that are contaminated by other signals can be important when estimating fault slip rates. Until recently vertical deformation rates determined by high precision Global Positioning Systems (GPS) had large uncertainties compared to horizontal components and were rarely used to constrain tectonic models of fault motion. However, many continuously occupied GPS stations have been operating for ten or more years, often delivering uncertainties of ~1 mm/yr or less, providing better constraints for tectonic modeling. Various processing centers produced GPS time series and estimated vertical velocity fields, each with their own set of processing techniques and assumptions. We compare vertical velocity solutions estimated by seven data processing groups as well as two combined solutions (Figure 1). These groups include: Central Washington University (CWU) and New Mexico Institute of Technology (NMT), and their combined solution provided by the Plate Boundary Observatory (PBO) through the UNAVCO website. Also compared are the Jet Propulsion Laboratory (JPL) and Scripps Orbit and Permanent Array Center (SOPAC) and their combined solution provided as part of the NASA MEaSUREs project. Smaller velocity fields included are from Amos et al., 2014, processed at the Nevada Geodetic Laboratory, Shen et al., 2011, processed by UCLA and called the Crustal Motion Map 4.0 (CMM4) dataset, and a new velocity field provided by the University of Miami (UM). Our analysis includes estimating and correcting for systematic vertical velocity and uncertainty differences between groups. Our final product is a unified velocity field that contains the median values of the adjusted velocity fields and their uncertainties. This product will be periodically updated when new velocity fields

Wave Tank Studies of Phase Velocities of Short Wind Waves

Science.gov (United States)

Ermakov, S.; Sergievskaya, I.; Shchegolkov, Yu.

Wave tank studies of phase velocities of short wind waves have been carried out using Ka-band radar and an Optical Spectrum Analyser. The phase velocities were retrieved from measured radar and optical Doppler shifts, taking into account measurements of surface drift velocities. The dispersion relationship was studied in centimetre (cm)- and millimetre(mm)-scale wavelength ranges at different fetches and wind speeds, both for a clean water surface and for water covered with surfactant films. It is ob- tained that the phase velocities do not follow the dispersion relation of linear capillary- gravity waves, increasing with fetch and, therefore, depending on phase velocities of dominant decimetre (dm)-centimetre-scale wind waves. One thus can conclude that nonlinear cm-mm-scale harmonics bound to the dominant wind waves and propagat- ing with the phase velocities of the decimetric waves are present in the wind wave spectrum. The resulting phase velocities of short wind waves are determined by re- lation between free and bound waves. The relative intensity of the bound waves in the spectrum of short wind waves is estimated. It is shown that this relation depends strongly on the surfactant concentration, because the damping effect due to films is different for free and bound waves; this results to changes of phase velocities of wind waves in the presence of surfactant films. This work was supported by MOD, UK via DERA Winfrith (Project ISTC 1774P) and by RFBR (Project 02-05-65102).

A search for thermospheric composition perturbations due to vertical winds

Science.gov (United States)

Krynicki, Matthew P.

The thermosphere is generally in hydrostatic equilibrium, with winds blowing horizontally along stratified constant-pressure surfaces, driven by the dayside-to-nightside pressure gradient. A marked change in this paradigm resulted after Spencer et al. [1976] reported vertical wind measurements of 80 m·s-1 from analyses of AE-C satellite data. It is now established that the thermosphere routinely supports large-magnitude (˜30-150 m·s-1) vertical winds at auroral latitudes. These vertical winds represent significant departure from hydrostatic and diffusive equilibrium, altering locally---and potentially globally---the thermosphere's and ionosphere's composition, chemistry, thermodynamics and energy budget. Because of their localized nature, large-magnitude vertical wind effects are not entirely known. This thesis presents ground-based Fabry-Perot Spectrometer OI(630.0)-nm observations of upper-thermospheric vertical winds obtained at Inuvik, NT, Canada and Poker Flat, AK. The wind measurements are compared with vertical displacement estimates at ˜104 km2 horizontal spatial scales determined from a new modification to the electron transport code of Lummerzheim and Lilensten [1994] as applied to FUV-wavelength observations by POLAR spacecraft's Ultraviolet Imager [Torr et al. , 1995]. The modification, referred to as the column shift, simulates vertical wind effects such as neutral transport and disruption of diffusive equilibrium by vertically displacing the Hedin [1991] MSIS-90 [O2]/[N2] and [O]/([N2]+[O2]) mixing ratios and subsequently redistributing the O, O2, and N 2 densities used in the transport code. Column shift estimates are inferred from comparisons of UVI OI(135.6)-nm auroral observations to their corresponding modeled emission. The modeled OI(135.6)-nm brightness is determined from the modeled thermospheric response to electron precipitation and estimations of the energy flux and characteristic energy of the precipitation, which are inferred from UVI

Modal Parameter Identification of New Design of Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Chougule, Prasad; Nielsen, Søren R.K.

2013-01-01

Vertical axis wind turbines have lower power efficiency than the horizontal axis wind turbines. However vertical axis wind turbines are proven to be economical and noise free on smaller scale. A new design of three bladed vertical axis wind turbine by using two airfoils in construction of each...... blade has been proposed to improve power efficiency. The purpose of two airfoils in blade design of vertical axis wind turbine is to create high lift which in turns gives higher power output. In such case the structural parameter identification is important to understand the system behavior due to its...... first kind of design before experimental analysis. Therefore a study is carried out to determine the natural frequency to avoid unstable state of the system due to rotational frequency of rotor. The present paper outlines a conceptual design of vertical axis wind turbine and a modal analysis by using...

Dynamics of the standard deviations of three wind velocity components from the data of acoustic sounding

Science.gov (United States)

Krasnenko, N. P.; Kapegesheva, O. F.; Shamanaeva, L. G.

2017-11-01

Spatiotemporal dynamics of the standard deviations of three wind velocity components measured with a mini-sodar in the atmospheric boundary layer is analyzed. During the day on September 16 and at night on September 12 values of the standard deviation changed for the x- and y-components from 0.5 to 4 m/s, and for the z-component from 0.2 to 1.2 m/s. An analysis of the vertical profiles of the standard deviations of three wind velocity components for a 6-day measurement period has shown that the increase of σx and σy with altitude is well described by a power law dependence with exponent changing from 0.22 to 1.3 depending on the time of day, and σz depends linearly on the altitude. The approximation constants have been found and their errors have been estimated. The established physical regularities and the approximation constants allow the spatiotemporal dynamics of the standard deviation of three wind velocity components in the atmospheric boundary layer to be described and can be recommended for application in ABL models.

Aerodynamic Interactions between Pairs of Vertical-Axis Wind Turbines

Science.gov (United States)

Brownstein, Ian; Dabiri, John

2017-11-01

Increased power production has been observed in downstream vertical-axis wind turbines (VAWTs) when positioned offset from the wake of upstream turbines. This effect was found to exist in both laboratory and field environments with pairs of co- and counter-rotating turbines. It is hypothesized that the observed power production enhancement is due to flow acceleration adjacent to the upstream turbine caused by bluff body blockage, which increases the incident freestream velocity on appropriately positioned downstream turbines. This type of flow acceleration has been observed in computational and laboratory studies of VAWTs and will be further investigated here using 3D-PTV measurements around pairs of laboratory-scale VAWTs. These measurements will be used to understand the mechanisms behind the performance enhancement effect and seek to determine optimal separation distances and angles between turbines based on turbine design parameters. These results will lead to recommendations for optimizing the power production of VAWT wind farms which utilize this effect.

Vertical axis wind turbines: a survey and bibliography

Energy Technology Data Exchange (ETDEWEB)

Abramovich, H

1987-01-01

The stimulus for the development of modern, big wind turbines has been the world-wide oil crisis during the seventies. Although the horizontal axis wind turbines (HAWT) was the most popular type of wind turbine the Darrieus vertical axis wind turbine (VAWT) has been recognized as a machine with competitive economic potential. The state of the art of the VAWT is reviewed. The wind turbine carrying the name of Darrieus was first proposed by the French inventor in 1925. His original patent covered a range of vertical-axis configurations but the term 'Darrieus' is now generally associated with the curved-blade geometry. In 1966 two researchers at the Canadian NRC again raised the idea of both the straight and curved-blade versions of the Darrieus VAWT.

3D CFD Analysis of a Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Andrea Alaimo

2015-04-01

Full Text Available To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

Characteristics for wind energy and wind turbines by considering vertical wind shear

Institute of Scientific and Technical Information of China (English)

郑玉巧; 赵荣珍

2015-01-01

The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm, the power-law process was used to simulate the wind speeds at a hub height of 60 m. The Weibull and Rayleigh distributions were chosen to express the wind speeds at two different heights. The parameters in the model were estimated via the least square (LS) method and the maximum likelihood estimation (MLE) method, respectively. An adjusted MLE approach was also presented for parameter estimation. The main indices of wind energy characteristics were calculated based on observational wind speed data. A case study based on the data of Hexi area, Gansu Province of China was given. The results show that MLE method generally outperforms LS method for parameter estimation, and Weibull distribution is more appropriate to describe the wind speed at the hub height.

Characteristics of Wind Velocity and Temperature Change Near an Escarpment-Shaped Road Embankment

Directory of Open Access Journals (Sweden)

Young-Moon Kim

2014-01-01

Full Text Available Artificial structures such as embankments built during the construction of highways influence the surrounding airflow. Various types of damage can occur due to changes in the wind velocity and temperature around highway embankments. However, no study has accurately measured micrometeorological changes (wind velocity and temperature due to embankments. This study conducted a wind tunnel test and field measurement to identify changes in wind velocity and temperature before and after the construction of embankments around roads. Changes in wind velocity around an embankment after its construction were found to be influenced by the surrounding wind velocity, wind angle, and the level difference and distance from the embankment. When the level difference from the embankment was large and the distance was up to 3H, the degree of wind velocity declines was found to be large. In changes in reference wind velocities around the embankment, wind velocity increases were not proportional to the rate at which wind velocities declined. The construction of the embankment influenced surrounding temperatures. The degree of temperature change was large in locations with large level differences from the embankment at daybreak and during evening hours when wind velocity changes were small.

Vertical gust response prediction of cable-stayed bridges in yawed wind; Shachokyo no shafu ni yoru enchoku gust oto no yosoku

Energy Technology Data Exchange (ETDEWEB)

Nakamura, S.; Nagamachi, K.; Kawai, Y. [Kawasaki Steel Corp., Tokyo (Japan); Kimura, K.; Fujino, Y. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Tanaka, H.

1996-03-01

This paper outlines the vertical gust response analysis method in a yawed wind, gives an analytic example, and compares the experimental result with the analytic result to investigate the application of an analysis method and the validity of assumption and approximation. The vertical gust response to two cable-stayed bridges under construction in a yawed wind was predicted by applying assumption and approximation to the gust response prediction method in a yawed wind with the cantilever model having a plate cross-section manipulated. In this case, the wind velocity component perpendicular to the leading edge was defined as an effective wind velocity, and a bridge axis and the component perpendicular to a bridge axis were separately calculated in response. Moreover, some aerodynamic coefficients of a bridge girder cross-section were approximately obtained from the characteristics of the flat blades with same aspect ratio. The obtained analytic result was compared with the wind tunnel test result based on all bridge models. The result showed that the former almost coincides with the latter, the assumption and approximation of this time are verified in validity, and this analysis method can be used for cable-stayed bridges under construction. 10 refs., 7 figs., 2 tabs.

Generalized multidemensional propagation velocity equations for pool-boiling superconducting windings

International Nuclear Information System (INIS)

Christensen, E.H.; O'Loughlin, J.M.

1984-09-01

Several finite difference, finite element detailed analyses of propagation velocities in up to three dimensions in pool-boiling windings have been conducted for different electromagnetic and cryogenic environments. Likewise, a few full scale simulated winding and magnet tests have measured propagation velocities. These velocity data have been correlated in terms of winding thermophysical parameters. This analysis expresses longitudinal and transverse propagation velocities in the form of power function regression equations for a wide variety of windings and electromagnetic and thermohydraulic environments. The generalized velocity equations are considered applicable to well-ventilated, monolithic conductor windings. These design equations are used piecewise in a gross finite difference mode as functions of field to predict the rate of normal zone growth during quench conditions. A further check of the validity of these predictions is available through total predicted quench durations correlated with actual quench durations of large magnets

New Urban Vertical Axis Wind Turbine Design

Directory of Open Access Journals (Sweden)

Alexandru-Mihai CISMILIANU

2015-12-01

Full Text Available This paper develops a different approach for enhancing the performance of Vertical Axis Wind Turbines for the use in the urban or rural environment and remote isolated residential areas. Recently the vertical axis wind turbines (VAWT have become more attractive due to the major advantages of this type of turbines in comparison to the horizontal axis wind turbines. We aim to enhance the overall performance of the VAWT by adding a second set of blades (3 x 2=6 blades following the rules of biplane airplanes. The model has been made to operate at a maximum power in the range of the TSR between 2 to 2.5. The performances of the VAWT were investigated numerically and experimentally and justify the new proposed design.

Results from a three-month intercomparison of boundary-layer wind profiler and sodar wind measurements at Lindenberg, Germany

Energy Technology Data Exchange (ETDEWEB)

Beyrich, F.; Goersdorf, U.; Neisser, J.; Steinhagen, H.; Weisensee, U. [Deutscher Wetterdienst, Lindenberg (Germany). Meteorologisches Observatorium

1998-10-01

Intercomparison experiments with a wind profiler and a Doppler sodar have been performed at the meteorological observatory Lindenberg of the German weather service in summer, 1994, and in autumn, 1995, over a total period of about three months. The paper presents selected results of the wind measurements performed with the two systems. Sodar and wind profiler are shown to complement each other quite well. Therefore, a combination of both is a promising tool for continuous, high-resolution measurements of the wind profile. A problem to be solved is the construction of composite wind profiles when the measurements with the two systems disagree in the height range of overlapping. Measurements of the vertical velocity are difficult to assess due to their small absolute values. Long-term averages of the vertical velocity show slightly negative values, especially for the wind profiler. However, similar signatures have been found in the vertical velocity time series during frontal passages or during well-developed convection. (orig.) 7 refs.

Velocity spectrum and blade’s deformation of horizontal axis wind turbines

Directory of Open Access Journals (Sweden)

Sanda BUDEA

2014-04-01

Full Text Available The paper presents the velocity distribution calculated by numerical method in axial relative motion of a viscous and incompressible fluid into the impeller of a horizontal axis wind turbine. Simulations are made for different airflow speeds: 0.5,1, 3, 4, 5 m/s. The relative vortex on the backside of the blade to the trailing edge, and the vortices increase with the wind speed can be observed from the numerical analysis. Also the translational deformation-the deflection of the wind turbine blades for different values of the wind velocities has been established in this paper. The numerical simulations are made for the following speed values:5 m/s, 10m/s and 20 m/s. ANSYS CFD – Fluent was used both to calculate the velocities spectrum and to establish the translational blades deformations. The analyzed wind impeller has small dimensions, a diameter of 2 m and four profiled blades. For this small impeller the translational deformation increases with the wind velocity from 83 to 142 mm. For high wind velocities and large–scale wind turbine impellers, these translational deformations are about several meters, reason to /shut-down the impellers to wind velocities exceeding 25 m/s.

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.

Wind tunnel study of a vertical axis wind turbine in a turbulent boundary layer flow

Science.gov (United States)

Rolin, Vincent; Porté-Agel, Fernando

2015-04-01

Vertical axis wind turbines (VAWTs) are in a relatively infant state of development when compared to their cousins the horizontal axis wind turbines. Very few studies have been carried out to characterize the wake flow behind VAWTs, and virtually none to observe the influence of the atmospheric boundary layer. Here we present results from an experiment carried out at the EPFL-WIRE boundary-layer wind tunnel and designed to study the interaction between a turbulent boundary layer flow and a VAWT. Specifically we use stereoscopic particle image velocimetry to observe and quantify the influence of the boundary layer flow on the wake generated by a VAWT, as well as the effect the VAWT has on the boundary layer flow profile downstream. We find that the wake behind the VAWT is strongly asymmetric, due to the varying aerodynamic forces on the blades as they change their position around the rotor. We also find that the wake adds strong turbulence levels to the flow, particularly on the periphery of the wake where vortices and strong velocity gradients are present. The boundary layer is also shown to cause greater momentum to be entrained downwards rather than upwards into the wake.

Use of acoustic backscatter and vertical velocity to estimate concentration and dynamics of suspended solids in Upper Klamath Lake, south-central Oregon: Implications for Aphanizomenon flos-aquae

Science.gov (United States)

Wood, Tamara M.; Gartner, Jeffrey W.

2010-01-01

Vertical velocity and acoustic backscatter measurements by acoustic Doppler current profilers were used to determine seasonal, subseasonal (days to weeks), and diel variation in suspended solids in a freshwater lake where massive cyanobacterial blooms occur annually. During the growing season, the suspended material in the lake is dominated by the buoyancy-regulating cyanobacteria, Aphanizomenon flos-aquae. Measured variables (water velocity, relative backscatter [RB], wind speed, and air and water temperatures) were averaged over the deployment season at each sample time of day to determine average diel cycles. Phase shifts between diel cycles in RB and diel cycles in wind speed, vertical water temperature differences (delta T(degree)), and horizontal current speeds were found by determining the lead or lag that maximized the linear correlation between the respective diel cycles. Diel cycles in RB were more in phase with delta T(degree) cycles, and, to a lesser extent, wind cycles, than to water current cycles but were out of phase with the cycle that would be expected if the vertical movement of buoyant cyanobacteria colonies was controlled primarily by light. Clear evidence of a diel cycle in vertical velocity was found only at the two deepest sites in the lake. Cycles of vertical velocity, where present, were out of phase with expected vertical motion of cyanobacterial colonies based on the theoretical cycle for light-driven vertical movement. This suggests that water column stability and turbulence were more important factors in controlling vertical distribution of colonies than light. Variations at subseasonal time scales were determined by filtering data to pass periods between 1.2 and 15 days. At subseasonal time scales, correlations between RB and currents or air temperature were consistent with increased concentration of cyanobacterial colonies near the surface when water column stability increased (higher air temperatures or weaker currents) and

Offshore vertical wind shear: Final report on NORSEWInD’s work task 3.1

DEFF Research Database (Denmark)

Pena Diaz, Alfredo; Mikkelsen, Torben; Gryning, Sven-Erik

of power outputs. Background related to the parametrization of the vertical wind speed profile and the behavior of the vertical wind shear in and beyond the atmospheric surface layer is presented together with the application of the long-term atmospheric stability parameters for the analysis of the long......This document reports on the analysis performed by the work task 3.1 of the EU NORSEWInD project and includes the following deliverables: 3.2 Calculated vertical wind shears 3.3 Multi-variational correlation analysis 3.4 NWP data for wind shear model 3.5 Vertical extrapolation methodology 3.......6 Results input into satellite maps The nature of the offshore vertical wind shear is investigated using acquired data from the NORSEWInD network of mast and wind lidar stations. The importance of the knowledge of the vertical wind speed profile and wind shear is first illustrated for the evaluation...

Wind Velocity and Position Sensor-less Operation for PMSG Wind Generator

Science.gov (United States)

Senjyu, Tomonobu; Tamaki, Satoshi; Urasaki, Naomitsu; Uezato, Katsumi; Funabashi, Toshihisa; Fujita, Hideki

Electric power generation using non-conventional sources is receiving considerable attention throughout the world. Wind energy is one of the available non-conventional energy sources. Electrical power generation using wind energy is possible in two ways, viz. constant speed operation and variable speed operation using power electronic converters. Variable speed power generation is attractive, because maximum electric power can be generated at all wind velocities. However, this system requires a rotor speed sensor, for vector control purpose, which increases the cost of the system. To alleviate the need of rotor speed sensor in vector control, we propose a new sensor-less control of PMSG (Permanent Magnet Synchronous Generator) based on the flux linkage. We can estimate the rotor position using the estimated flux linkage. We use a first-order lag compensator to obtain the flux linkage. Furthermore‚we estimate wind velocity and rotation speed using a observer. The effectiveness of the proposed method is demonstrated thorough simulation results.

The system design and performance test of hybrid vertical axis wind turbine

Science.gov (United States)

Dwiyantoro, Bambang Arip; Suphandani, Vivien

2017-04-01

Vertical axis wind turbine is a tool that is being developed to generate energy from wind. One cause is still little use of wind energy is the design of wind turbines that are less precise. Therefore in this study will be developed the system design of hybrid vertical axis wind turbine and tested performance with experimental methods. The design of hybrid turbine based on a straight bladed Darrieus turbine along with a double step Savonius turbine. The method used to design wind turbines is by studying literature, analyzing the critical parts of a wind turbine and the structure of the optimal design. Wind turbine prototype of the optimal design characteristic tests in the wind tunnel experimentally by varying the speed of the wind. From the experimental results show that the greater the wind speed, the greater the wind turbine rotation and torque is raised. The hybrid vertical axis wind turbine has much better self-starting and better conversion efficiency.

The influence of turbulence and vertical wind profile in wind turbine power curve

Energy Technology Data Exchange (ETDEWEB)

Honrubia, A.; Gomez-Lazaro, E. [Castilla-La Mancha Univ., Albacete (Spain). Renewable Energy Research Inst.; Vigueras-Rodriguez, A. [Albacete Science and Technolgy Park, Albacete (Spain)

2012-07-01

To identify the influence of turbulence and vertical wind profile in wind turbine performance, wind speed measurements at different heights have been performed. Measurements have been developed using a cup anemometer and a LIDAR equipment, specifically a pulsed wave one. The wind profile has been recorded to study the effect of the atmospheric conditions over the energy generated by a wind turbine located close to the LIDAR system. The changes in the power production of the wind turbine are relevant. (orig.)

Experimental data on load test and performance parameters of a LENZ type vertical axis wind turbine in open environment condition

Directory of Open Access Journals (Sweden)

Seralathan Sivamani

2017-12-01

Full Text Available Performance and load testing data of a three bladed two stage LENZ type vertical axis wind turbine from the experiments conducted in an open environment condition at Hindustan Institute of Technology and Science, Chennai (location 23.2167°N, 72.6833°E are presented here. Low-wind velocity ranging from 2 to 11 m/s is available everywhere irrespective of climatic seasons and this data provides the support to the researchers using numerical tool to validate and develop an enhanced Lenz type design. Raw data obtained during the measurements are processed and presented in the form so as to compare with other typical outputs. The data is measured at different wind speeds prevalent in the open field condition ranging from 3 m/s to 9 m/s. Keywords: Vertical axis wind turbine, Lenz type, Performance, Two-stage, Open environment measurement

Small Vertical Axis Wind Turbines: aerodynamics and starting behavior

Directory of Open Access Journals (Sweden)

Horia DUMITRESCU

2013-12-01

Full Text Available In urban areas the wind is very turbulent and unstable with fast changes in direction andvelocity. In these environments, the use of small vertical axis wind turbines (VAWT becomesincreasingly attractive due to several advantages over horizontal axis wind turbines (HAWT.However, such designs have received much less attention than the more common propeller-typedesigns and the understanding of same aspects of their operation remains, to this day, incomplete.This is particularly true of their starting characteristics. Indeed, same authors heuristically maintainthat they cannot start without external assistance. This paper reviews the cause of the inability of thelow solidity fixed pitch vertical axis wind turbines to self-start, and investigates the way ofovercoming this draw back.

Relationship between velocity gradients and magnetic turbulence in the solar wind

International Nuclear Information System (INIS)

Garrett, H.B.

1974-01-01

The correlations among the time derivative of the solar-wind velocity, the magnitude of the interplanetary magnetic field (IMF), and the IMF turbulence level are examined to test the idea that interaction between two colliding solar-wind streams can generate turbulence in the solar wind and the IMF. Data obtained by Explorer 33 on the solar wind and IMF are described, and the analysis techniques are outlined. The results indicate that the IMF turbulence level, as measured by the variance, is correlated with the existence of positive velocity gradients in the solar wind. It is noted that while the variance is an increasing function of the field magnitude, it is also independently correlated with the solar-wind velocity gradient

Combined Structural Optimization and Aeroelastic Analysis of a Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Roscher, Björn; Ferreira, Carlos Simao; Bernhammer, Lars O.

2015-01-01

Floating offshore wind energy poses challenges on the turbine design. A possible solution is vertical axis wind turbines, which are possibly easier to scale-up and require less components (lower maintenance) and a smaller floating structure than horizontal axis wind turbines. This paper presents...... a structural optimization and aeroelastic analysis of an optimized Troposkein vertical axis wind turbine to minimize the relation between the rotor mass and the swept area. The aeroelastic behavior of the different designs has been analyzed using a modified version of the HAWC2 code with the Actuator Cylinder...... model to compute the aerodynamics of the vertical axis wind turbine. The combined shape and topology optimization of a vertical axis wind turbine show a minimum mass to area ratio of 1.82 kg/m2 for blades with varying blade sections from a NACA 0040 at the attachment points to a NACA 0015...

On the vertical structure of wind gusts

DEFF Research Database (Denmark)

Suomi, I.; Gryning, Sven-Erik; Floors, Rogier Ralph

2015-01-01

The increasing size of wind turbines, their height and the area swept by their blades have revised the need for understanding the vertical structure of wind gusts. Information is needed for the whole profile. In this study, we analyzed turbulence measurements from a 100m high meteorological mast...... and the turbulence intensity, of which the turbulence intensity was found to dominate over the peak factor in determining the effects of stability and height above the surface on the gust factor. The peak factor only explained 15% or less of the vertical decrease of the gust factor, but determined the effect of gust...... duration on the gust factor. The statistical method to estimate the peak factor did not reproduce the observed vertical decrease in near-neutral and stable conditions and near-constant situation in unstable conditions. Despite this inconsistency, the theoretical method provides estimates for the peak...

Research on the aerodynamic characteristics of a lift drag hybrid vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Xiaojing Sun

2016-01-01

Full Text Available Compared with a drag-type vertical axis wind turbines, one of the greatest advantages for a lift-type vertical axis wind turbines is its higher power coefficient (Cp. However, the lift-type vertical axis wind turbines is not a self-starting turbine as its starting torque is very low. In order to combine the advantage of both the drag-type and the lift-type vertical axis wind turbines, a lift drag hybrid vertical axis wind turbines was designed in this article and its aerodynamics and starting performance was studied in detail with the aid of computational fluid dynamics simulations. Numerical results indicate that the power coefficient of this lift drag hybrid vertical axis wind turbines declines when the distance between its drag-type blades and the center of rotation of the turbine rotor increases, whereas its starting torque can be significantly improved. Studies also show that unlike the lift-type vertical axis wind turbines, this lift drag hybrid-type vertical axis wind turbines could be able to solve the problem of low start-up torque. However, the installation position of the drag blade is very important. If the drag blade is mounted very close to the spindle, the starting torque of the lift drag hybrid-type vertical axis wind turbines may not be improved at all. In addition, it has been found that the power coefficient of the studied vertical axis wind turbines is not as good as expected and possible reasons have been provided in this article after the pressure distribution along the surfaces of the airfoil-shaped blades of the hybrid turbine was analyzed.

Electric power from vertical-axis wind turbines

Science.gov (United States)

Touryan, K. J.; Strickland, J. H.; Berg, D. E.

1987-12-01

Significant advancements have occurred in vertical axis wind turbine (VAWT) technology for electrical power generation over the last decade; in particular, well-proven aerodynamic and structural analysis codes have been developed for Darrieus-principle wind turbines. Machines of this type have been built by at least three companies, and about 550 units of various designs are currently in service in California wind farms. Attention is presently given to the aerodynamic characteristics, structural dynamics, systems engineering, and energy market-penetration aspects of VAWTs.

Wind tower with vertical rotors

Energy Technology Data Exchange (ETDEWEB)

Dietz, A

1978-08-03

The invention concerns a wind tower with vertical rotors. A characteristic is that the useful output of the rotors is increased by the wind pressure, which is guided to the rotors at the central opening and over the whole height of the structure by duct slots in the inner cells. These duct slots start behind the front nose of the inner cell and lead via the transverse axis of the pillar at an angle into the space between the inner cells and the cell body. This measure appreciably increases the useful output of the rotors, as the rotors do not have to provide any displacement work from their output, but receive additional thrust. The wind pressure pressing from inside the rotor and accelerating from the outside produces a better outflow of the wind from the power plant pillar with only small tendency to turbulence, which appreciably improves the effect of the adjustable turbulence smoothers, which are situated below the rotors over the whole height.

Integrated simulation challenges with the DeepWind floating vertical axis wind turbine concept

DEFF Research Database (Denmark)

Verelst, David; Aagaard Madsen, Helge; Borg, Michael

2015-01-01

This paper presents the experiences and challenges with concurrently carrying out numerical model development, integrated simulations and design of a novel floating vertical axis wind turbine, the DeepWind concept. The floating VAWT modelling capabilities of the aero-hydro-elastic HAWC2 simulation...

Development of a 5.5 m diameter vertical axis wind turbine, phase 3

Science.gov (United States)

Dekitsch, A.; Etzler, C. C.; Fritzsche, A.; Lorch, G.; Mueller, W.; Rogalla, K.; Schmelzle, J.; Schuhwerk, W.; Vollan, A.; Welte, D.

1982-06-01

In continuation of development of a 5.5 m diameter vertical axis windmill that consists in conception, building, and wind tunnel testing, a Darrieus rotor windpowered generator feeding an isolated network under different wind velocity conditions and with optimal energy conversion efficiency was designed built, and field tested. The three-bladed Darrieus rotor tested in the wind tunnel was equiped with two variable pitch Savonius rotors 2 m in diameter. By means of separate measures of the aerodynamic factors and the energy consumption, effect of revisions and optimizations on different elements was assessed. Pitch adjustement of the Savonius blades, lubrication of speed reducer, rotor speed at cut-in of generator field excitation, time constant of field excitation, stability conditions, switch points of ohmic resistors which combined with a small electric battery simulated a larger isolated network connected with a large storage battery, were investigated. Fundamentals for the economic series production of windpowered generators with Darrieus rotors for the control and the electric conversion system are presented.

Design of a wind turbine-generator system considering the conformability to wind velocity fluctuations

Energy Technology Data Exchange (ETDEWEB)

Wakui, Tetsuya; Hashizume, Takumi; Outa, Eisuke

1999-07-01

The conformability of the rated power output of the wind turbine-generator system and of the wind turbine type to wind velocity fluctuations are investigated with a simulation model. The authors examine three types of wind turbines: the Darrieus-Savonius hybrid, the Darrieus proper and the Propeller. These systems are mainly operated at a constant tip speed ratio, which refers to a maximum power coefficient points. As a computed result of the net extracting power, the Darrieus turbine proper has little conformability to wind velocity fluctuations because of its output characteristics. As for the other turbines, large-scale systems do not always have an advantage over small-scale systems as the effect of its dynamic characteristics. Furthermore, it is confirmed that the net extracting power of the Propeller turbine, under wind direction fluctuation, is much reduced when compared with the hybrid wind turbine. Thus, the authors conclude that the appropriate rated power output of the system exists with relation to the wind turbine type for each wind condition.

Ten years statistics of wind direction and wind velocity measurements performed at the Karlsruhe Nuclear Research Center

International Nuclear Information System (INIS)

Becker, M.; Dilger, H.

1979-06-01

The measurements of wind direction and wind velocity performed at 60 m and 200 m height were evaluated for one year each and frequency distributions of the measured values were established. The velocity was divided into 1 m/s steps and the direction into 10 0 sectors. The frequency distribution of the wind direction reveals three maxima located in the southwest, northeast and north, respectively. The maximum of the frequency distribution of the wind velocity occurs between 4 and 5 m/s at 200 m height and between 3 and 4 m/s at 60 m height. (orig.) [de

Design Of Rotor Blade For Vertical Axis Wind Turbine Using Double Aerofoil

DEFF Research Database (Denmark)

Chougule, Prasad; Ratkovich, Nicolas Rios; Kirkegaard, Poul Henning

Nowadays, small vertical axis wind turbines are receiving more attention compared to horizontal wind turbines due to their suitability in urban use because they generate less noise, have bird free turbines and lower cost. There is few vertical axis wind turbines design with good power curve....... However, the efficiency of power extraction has not been improved. Therefore, an attempt has been made to utilize high lift technology in practice for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double aerofoil elements mainly used in aeroplane wing design....... In this current work two aerofoils are used to design a rotor blade for a vertical axis wind turbine to improve the power efficiency on the rotor. Double aerofoil blade design consists of a main aerofoil and a slat aerofoil. The parameters related to position and orientation of the slat aerofoil with respect...

The Effect of Wind Velocity on the Cooling Rate of Water

OpenAIRE

Shrey Aryan

2016-01-01

The effect of wind velocity on the cooling rate of water was investigated by blowing air horizontally over the surface of water contained in a plastic water-bottle cap. The time taken for the temperature to fall to the average of the surrounding and initial temperatures was recorded at different values of wind velocity. It was observed that on increasing the wind velocity, the time taken to achieve average temperature not only decreased but also remained the same after a certain point.

Investigation of the effect of inflow turbulence on vertical axis wind turbine wakes

International Nuclear Information System (INIS)

Chatelain, P; Duponcheel, M; Buffin, S; Caprace, D-G; Winckelmans, G; Bricteux, L; Zeoli, S

2017-01-01

The aerodynamics of Vertical Axis Wind Turbines (VAWTs) is inherently unsteady, which leads to vorticity shedding mechanisms due to both the lift distribution along the blade and its time evolution. In this paper, we perform large-scale, fine-resolution Large Eddy Simulations of the flow past Vertical Axis Wind Turbines by means of a state-of-the-art Vortex Particle-Mesh (VPM) method combined with immersed lifting lines. Inflow turbulence with a prescribed turbulence intensity (TI) is injected at the inlet of the simulation either from a precomputed synthetic turbulence field obtained using the Mann algorithm [1] or generated on the-fly using time-correlated synthetic velocity planes. The wake of a standard, medium-solidity, H-shaped machine is simulated for several TI levels. The complex wake development is captured in details and over long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake. Mean flow and turbulence statistics are computed over more than 10 diameters downstream of the machine. The sensitivity of the wake topology and decay to the TI and to the operating conditions is then assessed. (paper)

Investigation of the effect of inflow turbulence on vertical axis wind turbine wakes

Science.gov (United States)

Chatelain, P.; Duponcheel, M.; Zeoli, S.; Buffin, S.; Caprace, D.-G.; Winckelmans, G.; Bricteux, L.

2017-05-01

The aerodynamics of Vertical Axis Wind Turbines (VAWTs) is inherently unsteady, which leads to vorticity shedding mechanisms due to both the lift distribution along the blade and its time evolution. In this paper, we perform large-scale, fine-resolution Large Eddy Simulations of the flow past Vertical Axis Wind Turbines by means of a state-of-the-art Vortex Particle-Mesh (VPM) method combined with immersed lifting lines. Inflow turbulence with a prescribed turbulence intensity (TI) is injected at the inlet of the simulation either from a precomputed synthetic turbulence field obtained using the Mann algorithm [1] or generated on the-fly using time-correlated synthetic velocity planes. The wake of a standard, medium-solidity, H-shaped machine is simulated for several TI levels. The complex wake development is captured in details and over long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake. Mean flow and turbulence statistics are computed over more than 10 diameters downstream of the machine. The sensitivity of the wake topology and decay to the TI and to the operating conditions is then assessed.

Determination of performance parameters of vertical axis wind turbines in wind tunnel

Directory of Open Access Journals (Sweden)

Nguyen Van Bang

2017-01-01

Full Text Available The paper deals with the determination of the performance parameters of a small vertical axis wind turbines (VAWT, which operate by the utilization of drag forces acting on the blades of the turbine. The performance was evaluated by investigating the electrical power output and torque moment of the wind machine. Measurements were performed on the full-scale model and the experimental data are assessed and compared to other types of wind turbines, with respect to its purpose.

Parameters determining maximum wind velocity in a tropical cyclone

International Nuclear Information System (INIS)

Choudhury, A.M.

1984-09-01

The spiral structure of a tropical cyclone was earlier explained by a tangential velocity distribution which varies inversely as the distance from the cyclone centre outside the circle of maximum wind speed. The case has been extended in the present paper by adding a radial velocity. It has been found that a suitable combination of radial and tangential velocities can account for the spiral structure of a cyclone. This enables parametrization of the cyclone. Finally a formula has been derived relating maximum velocity in a tropical cyclone with angular momentum, radius of maximum wind speed and the spiral angle. The shapes of the spirals have been computed for various spiral angles. (author)

The Effect of Wind Velocity on the Cooling Rate of Water

Directory of Open Access Journals (Sweden)

Shrey Aryan

2016-01-01

Full Text Available The effect of wind velocity on the cooling rate of water was investigated by blowing air horizontally over the surface of water contained in a plastic water-bottle cap. The time taken for the temperature to fall to the average of the surrounding and initial temperatures was recorded at different values of wind velocity. It was observed that on increasing the wind velocity, the time taken to achieve average temperature not only decreased but also remained the same after a certain point.

Determination of the number of Vertical Axis Wind Turbine blades based on power spectrum

Directory of Open Access Journals (Sweden)

Fedak Waldemar

2017-01-01

Full Text Available Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allows the reduction of costs. The maximum power of the rotor is selected as the performance target. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. The major result of this research is the Vertical Axis Wind Turbine power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.

Determination of the number of Vertical Axis Wind Turbine blades based on power spectrum

Science.gov (United States)

Fedak, Waldemar; Anweiler, Stanisław; Gancarski, Wojciech; Ulbrich, Roman

2017-10-01

Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the Vertical Axis Wind Turbine allows the reduction of costs. The maximum power of the rotor is selected as the performance target. The optimum number of Vertical Axis Wind Turbine blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the Vertical Axis Wind Turbine rotor. The major result of this research is the Vertical Axis Wind Turbine power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, and can be used regarding investment outlays and power output of the Vertical Axis Wind Turbine.

ALADIN: an atmospheric laser Doppler wind lidar instrument for wind velocity measurements from space

Science.gov (United States)

Krawczyk, R.; Ghibaudo, JB.; Labandibar, JY.; Willetts, D.; Vaughan, M.; Pearson, G.; Harris, M.; Flamant, P. H.; Salamitou, P.; Dabas, A.; Charasse, R.; Midavaine, T.; Royer, M.; Heimel, H.

2018-04-01

This paper, "ALADIN: an atmospheric laser Doppler wind lidar instrument for wind velocity measurements from space," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.

Solar wind velocity and geomagnetic moment variations

International Nuclear Information System (INIS)

Kalinin, Yu.D.; Rozanova, T.S.

1982-01-01

The mean year values of the solar wind velocity have been calculated from the mean-year values of a geomagnetic activity index am according to the Svalgard equation of regression for the pe-- riod from 1930 to 1960. For the same years the values of the geomagnetic moment M and separately of its ''inner'' (causes of which'' are inside the Earth) and ''external'' (causes of which are outside the Earth) parts have been calculated from the mean year data of 12 magnetic observatories. The proof of the presence of the 11-year variation in the moment M has been obtained. It is concluded that the 11-year variations in M result from the variations of the solar wind velocity

A parabolic velocity-decomposition method for wind turbines

Science.gov (United States)

Mittal, Anshul; Briley, W. Roger; Sreenivas, Kidambi; Taylor, Lafayette K.

2017-02-01

An economical parabolized Navier-Stokes approximation for steady incompressible flow is combined with a compatible wind turbine model to simulate wind turbine flows, both upstream of the turbine and in downstream wake regions. The inviscid parabolizing approximation is based on a Helmholtz decomposition of the secondary velocity vector and physical order-of-magnitude estimates, rather than an axial pressure gradient approximation. The wind turbine is modeled by distributed source-term forces incorporating time-averaged aerodynamic forces generated by a blade-element momentum turbine model. A solution algorithm is given whose dependent variables are streamwise velocity, streamwise vorticity, and pressure, with secondary velocity determined by two-dimensional scalar and vector potentials. In addition to laminar and turbulent boundary-layer test cases, solutions for a streamwise vortex-convection test problem are assessed by mesh refinement and comparison with Navier-Stokes solutions using the same grid. Computed results for a single turbine and a three-turbine array are presented using the NREL offshore 5-MW baseline wind turbine. These are also compared with an unsteady Reynolds-averaged Navier-Stokes solution computed with full rotor resolution. On balance, the agreement in turbine wake predictions for these test cases is very encouraging given the substantial differences in physical modeling fidelity and computer resources required.

Velocity fluctuations in polar solar wind: a comparison between different solar cycles

Directory of Open Access Journals (Sweden)

B. Bavassano

2009-02-01

Full Text Available The polar solar wind is a fast, tenuous and steady flow that, with the exception of a relatively short phase around the Sun's activity maximum, fills the high-latitude heliosphere. The polar wind properties have been extensively investigated by Ulysses, the first spacecraft able to perform in-situ measurements in the high-latitude heliosphere. The out-of-ecliptic phases of Ulysses cover about seventeen years. This makes possible to study heliospheric properties at high latitudes in different solar cycles. In the present investigation we focus on hourly- to daily-scale fluctuations of the polar wind velocity. Though the polar wind is a quite uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize wind velocity variations is that of performing a multi-scale statistical analysis of the wind velocity differences. Our analysis is based on the computation of velocity differences at different time lags and the evaluation of statistical quantities (mean, standard deviation, skewness, and kurtosis for the different ensembles. The results clearly show that, though differences exist in the three-dimensional structure of the heliosphere between the investigated solar cycles, the velocity fluctuations in the core of polar coronal holes exhibit essentially unchanged statistical properties.

Velocity fluctuations in polar solar wind: a comparison between different solar cycles

Directory of Open Access Journals (Sweden)

B. Bavassano

2009-02-01

Full Text Available The polar solar wind is a fast, tenuous and steady flow that, with the exception of a relatively short phase around the Sun's activity maximum, fills the high-latitude heliosphere. The polar wind properties have been extensively investigated by Ulysses, the first spacecraft able to perform in-situ measurements in the high-latitude heliosphere. The out-of-ecliptic phases of Ulysses cover about seventeen years. This makes possible to study heliospheric properties at high latitudes in different solar cycles. In the present investigation we focus on hourly- to daily-scale fluctuations of the polar wind velocity. Though the polar wind is a quite uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize wind velocity variations is that of performing a multi-scale statistical analysis of the wind velocity differences. Our analysis is based on the computation of velocity differences at different time lags and the evaluation of statistical quantities (mean, standard deviation, skewness, and kurtosis for the different ensembles. The results clearly show that, though differences exist in the three-dimensional structure of the heliosphere between the investigated solar cycles, the velocity fluctuations in the core of polar coronal holes exhibit essentially unchanged statistical properties.

Small-Scale vertical axis wind turbine design

OpenAIRE

Castillo Tudela, Javier

2011-01-01

The thesis focuses on the design of a small vertical axis wind turbine rotor with solid wood as a construction material. The aerodynamic analysis is performed implementing a momentum based model on a mathematical computer program. A three bladed wind turbine is proposed as candidate for further prototype testing after evaluating the effect of several parameters in turbine efficiency, torque and acceleration. The results obtained indicate that wood is a suitable material for rotor cons...

Vega-1 and Vega-2: vertical profiles of wind velocity according to Doppler measurements data at landing spacecrafts

International Nuclear Information System (INIS)

Kerzhanovich, V.V.; Antsibor, N.M.; Bakit'ko, R.V.

1987-01-01

Results of the measurements of the Venus atmosphere vertical motion using the ''Vega'' landing spacecrafts are presented. Signal emitted by the landing spacecraft transmitter was received by flying apparatus and retranslated to the Earth. The difference between the measured frequency of the retranslated signal and reference one (Doppler's shift) permitted to determine the velocity of the landing spacecraft with the accuracy of 2 cm/s with the pitch of 1 s

Using Smartphone Pressure Sensors to Measure Vertical Velocities of Elevators, Stairways, and Drones

Science.gov (United States)

Monteiro, Martín; Martí, Arturo C.

2017-01-01

We measure the vertical velocities of elevators, pedestrians climbing stairs, and drones (flying unmanned aerial vehicles), by means of smartphone pressure sensors. The barometric pressure obtained with the smartphone is related to the altitude of the device via the hydrostatic approximation. From the altitude values, vertical velocities are…

Aerodynamic Analysis of a Vertical Axis Wind Turbine in a Diffuser

NARCIS (Netherlands)

Geurts, B.M.; Simao Ferreira, C.; Van Bussel, G.J.W.

Wind energy in the urban environment faces complex and often unfavorable wind conditions. High turbulence, lower average wind velocities and rapid changes in the wind direction are common phenomena in the complex built environments. A possible way to improve the cost-efficiency of urban wind

Retrieving 3D Wind Field from Phased Array Radar Rapid Scans

Directory of Open Access Journals (Sweden)

Xiaobin Qiu

2013-01-01

Full Text Available The previous two-dimensional simple adjoint method for retrieving horizontal wind field from a time sequence of single-Doppler scans of reflectivity and/or radial velocity is further developed into a new method to retrieve both horizontal and vertical winds at high temporal and spatial resolutions. This new method performs two steps. First, the horizontal wind field is retrieved on the conical surface at each tilt (elevation angle of radar scan. Second, the vertical velocity field is retrieved in a vertical cross-section along the radar beam with the horizontal velocity given from the first step. The method is applied to phased array radar (PAR rapid scans of the storm winds and reflectivity in a strong microburst event and is shown to be able to retrieve the three-dimensional wind field around a targeted downdraft within the storm that subsequently produced a damaging microburst. The method is computationally very efficient and can be used for real-time applications with PAR rapid scans.

Design optimization and analysis of vertical axis wind turbine blade

International Nuclear Information System (INIS)

Jarral, A.; Ali, M.; Sahir, M.H.

2013-01-01

Wind energy is clean and renwable source of energy and is also the world's fastest growing energy resource. Keeping in view power shortages and growing cost of energy, the low cost wind energy has become a primary solution. It is imperative that economies and individuals begin to conserve energy and focus on the production of energy from renewable sources. Present study describes a wind turbine blade designed with enhanced aerodynamic properties. Vertical axis turbine is chosen because of its easy installment, less noisy and having environmental friendly characteristics. Vertical axis wind turbines are thought to be ideal for installations where wind conditions are not consistent. The presented turbine blade is best suitable for roadsides where the rated speed due to vehicles is most /sup -1/ often 8 ms .To get an optimal shape design symmetrical profile NACA0025 has been considered which is then analyzed for stability and aerodynamic characteristics at optimal conditions using analysis tools ANSYS and CFD tools. (author)

Experimental characterization of vertical-axis wind turbine noise.

Science.gov (United States)

Pearson, C E; Graham, W R

2015-01-01

Vertical-axis wind turbines are wind-energy generators suitable for use in urban environments. Their associated noise thus needs to be characterized and understood. As a first step, this work investigates the relative importance of harmonic and broadband contributions via model-scale wind-tunnel experiments. Cross-spectra from a pair of flush-mounted wall microphones exhibit both components, but further analysis shows that the broadband dominates at frequencies corresponding to the audible range in full-scale operation. This observation has detrimental implications for noise-prediction reliability and hence also for acoustic design optimization.

Multi-component wind measurements of wind turbine wakes performed with three LiDARs

Science.gov (United States)

Iungo, G. V.; Wu, Y.-T.; Porté-Agel, F.

2012-04-01

Field measurements of the wake flow produced from the interaction between atmospheric boundary layer and a wind turbine are performed with three wind LiDARs. The tested wind turbine is a 2 MW Enercon E-70 located in Collonges, Switzerland. First, accuracy of mean values and frequency resolution of the wind measurements are surveyed as a function of the number of laser rays emitted for each measurement. Indeed, measurements performed with one single ray allow maximizing sampling frequency, thus characterizing wake turbulence. On the other hand, if the number of emitted rays is increased accuracy of mean wind is increased due to the longer sampling period. Subsequently, two-dimensional measurements with a single LiDAR are carried out over vertical sections of the wind turbine wake and mean wake flow is obtained by averaging 2D measurements consecutively performed. The high spatial resolution of the used LiDAR allows characterizing in details velocity defect present in the central part of the wake and its downstream recovery. Single LiDAR measurements are also performed by staring the laser beam at fixed directions for a sampling period of about ten minutes and maximizing the sampling frequency in order to characterize wake turbulence. From these tests wind fluctuation peaks are detected in the wind turbine wake at blade top-tip height for different downstream locations. The magnitude of these turbulence peaks is generally reduced by moving downstream. This increased turbulence level at blade top-tip height observed for a real wind turbine has been already detected from previous wind tunnel tests and Large Eddy simulations, thus confirming the presence of a source of dangerous fatigue loads for following wind turbines within a wind farm. Furthermore, the proper characterization of wind fluctuations through LiDAR measurements is proved by the detection of the inertial subrange from spectral analysis of these velocity signals. Finally, simultaneous measurements with two

Self-similarity and flow characteristics of vertical-axis wind turbine wakes: an LES study

Science.gov (United States)

Abkar, Mahdi; Dabiri, John O.

2017-04-01

Large eddy simulation (LES) is coupled with a turbine model to study the structure of the wake behind a vertical-axis wind turbine (VAWT). In the simulations, a tuning-free anisotropic minimum dissipation model is used to parameterise the subfilter stress tensor, while the turbine-induced forces are modelled with an actuator line technique. The LES framework is first validated in the simulation of the wake behind a model straight-bladed VAWT placed in the water channel and then used to study the wake structure downwind of a full-scale VAWT sited in the atmospheric boundary layer. In particular, the self-similarity of the wake is examined, and it is found that the wake velocity deficit can be well characterised by a two-dimensional multivariate Gaussian distribution. By assuming a self-similar Gaussian distribution of the velocity deficit, and applying mass and momentum conservation, an analytical model is developed and tested to predict the maximum velocity deficit downwind of the turbine. Also, a simple parameterisation of VAWTs for LES with very coarse grid resolutions is proposed, in which the turbine is modelled as a rectangular porous plate with the same thrust coefficient. The simulation results show that, after some downwind distance (x/D ≈ 6), both actuator line and rectangular porous plate models have similar predictions for the mean velocity deficit. These results are of particular importance in simulations of large wind farms where, due to the coarse spatial resolution, the flow around individual VAWTs is not resolved.

Wind Predictions Upstream Wind Turbines from a LiDAR Database

Directory of Open Access Journals (Sweden)

Soledad Le Clainche

2018-03-01

Full Text Available This article presents a new method to predict the wind velocity upstream a horizontal axis wind turbine from a set of light detection and ranging (LiDAR measurements. The method uses higher order dynamic mode decomposition (HODMD to construct a reduced order model (ROM that can be extrapolated in space. LiDAR measurements have been carried out upstream a wind turbine at six different planes perpendicular to the wind turbine axis. This new HODMD-based ROM predicts with high accuracy the wind velocity during a timespan of 24 h in a plane of measurements that is more than 225 m far away from the wind turbine. Moreover, the technique introduced is general and obtained with an almost negligible computational cost. This fact makes it possible to extend its application to both vertical axis wind turbines and real-time operation.

Overview and Design of self-acting pitch control mechanism for vertical axis wind turbine using multi body simulation approach

DEFF Research Database (Denmark)

Chougule, Prasad; Nielsen, Søren R.K.

2014-01-01

Awareness about wind energy is constantly growing in the world. Especially a demand for small scale wind turbine is increasing and various products are available in market. There are mainly two types of wind turbines, horizontal axis wind turbine and vertical axis wind turbines. Horizontal axis...... wind turbines are suitable for high wind speed whereas vertical axis wind turbines operate relatively low wind speed area. Vertical axis wind turbines are cost effective and simple in construction as compared to the horizontal axis wind turbine. However, vertical axis wind turbines have inherent...

Simulation of flow over double-element airfoil and wind tunnel test for use in vertical axis wind turbine

International Nuclear Information System (INIS)

Chougule, Prasad; Nielsen, Søren R K

2014-01-01

Nowadays, small vertical axis wind turbines are receiving more attention due to their suitability in micro-electricity generation. There are few vertical axis wind turbine designs with good power curve. However, the efficiency of power extraction has not been improved. Therefore, an attempt has been made to utilize high lift technology for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double-element airfoil mainly used in aeroplane wing design. In this current work a low Reynolds number airfoil is selected to design a double-element airfoil blade for use in vertical axis wind turbine to improve the power efficiency. Double-element airfoil blade design consists of a main airfoil and a slat airfoil. Orientation of slat airfoil is a parameter of investigation in this paper and air flow simulation over double-element airfoil. With primary wind tunnel test an orientation parameter for the slat airfoil is initially obtained. Further a computational fluid dynamics (CFD) has been used to obtain the aerodynamic characteristics of double-element airfoil. The CFD simulations were carried out using ANSYS CFX software. It is observed that there is an increase in the lift coefficient by 26% for single-element airfoil at analysed conditions. The CFD simulation results were validated with wind tunnel tests. It is also observe that by selecting proper airfoil configuration and blade sizes an increase in lift coefficient can further be achieved

Design of rotor blade for vertical axis wind turbine using double aerofoil

Energy Technology Data Exchange (ETDEWEB)

Chougule, P.D.; Ratkovich, N.; Kirkegaard, P.H.; Nielsen, Soeren R.K. [Aalborg Univ.. Dept. of Civil Engineering, Aalborg (Denmark)

2012-07-01

Nowadays, small vertical axis wind turbines are receiving more attention compared to horizontal wind turbines due to their suitability in urban use,because they generate less noise, have bird free turbines and lower cost. There are few vertical axis wind turbines design with good power curve. However, the efficiency of power extraction has not been improved. Therefore, an attempt has been made to utilize high lift technology in practice for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double aerofoil elements mainly used in aeroplane wing design. In this current work, two aerofoils are used to design a rotor blade for a vertical axis wind turbine to improve the power efficiency on the rotor. Double aerofoil blade design consists of a main aerofoil and a slat aerofoil. The parameters related to position and orientation of the slat aerofoil with respect to the main aerofoil defines the high lift. Orientation of slat aerofoil is a parameter of investigation in this paper. Computational fluid dynamics (CFD) have been used to obtain the aerodynamic characteristics of double aerofoil. The CFD simulations were carried out using Star CCM+ v7.04 (CD-adapco, UK) software. Aerofoils used in this work are selected from standard aerofoil shapes. (Author)

Method for Estimating Evaporative Potential (IM/CLO) from ASTM Standard Single Wind Velocity Measures

Science.gov (United States)

2016-08-10

IM/CLO) FROM ASTM STANDARD SINGLE WIND VELOCITY MEASURES DISCLAIMER The opinions or assertions contained herein are the private views of the...USARIEM TECHNICAL REPORT T16-14 METHOD FOR ESTIMATING EVAPORATIVE POTENTIAL (IM/CLO) FROM ASTM STANDARD SINGLE WIND VELOCITY... ASTM STANDARD SINGLE WIND VELOCITY MEASURES Adam W. Potter Biophysics and Biomedical Modeling Division U.S. Army Research Institute of Environmental

A Straight-bladed Vertical Axis Wind Turbine with a Directed Guide Vane Row-Effect of Guide Vane Geometry on the Performance-

Institute of Scientific and Technical Information of China (English)

Manabu TAKAO; Hideki KUMA; Takao MAEDA; Yasunari KAMADA; Michiaki OKI; Atsushi MINODA

2009-01-01

The objective of this study is to show the effect of guide vane geometry on the performance. In order to over-come the disadvantages of vertical axis wind turbine, a straight-bladed vertical axis wind turbine (S-VAWT) with a directed guide vane row has been proposed and tested by the authors. According to previous studies, it was clarified that the performance of the turbine can be improved by means of the directed guide vane row. However, the guide vane geometry of S-VAWT has not been optimized so far. In order to clarify the effect of guide vane geometry, the effects of setting angle and gap between rotor blade and guide vane on power coefficient and start-ing characteristic were investigated in the experiments. The experimental study of the proposed wind turbine was carded out by a wind tunnel. The wind tunnel with a diameter of 1.8m is open jet type. The wind velocity is 8 m/s in the experiments. The rotor has three straight blades with a profile of NACA0018 and a chord length of 100 mm, a diameter of 0.6 m and a blade height of 0.7 m. The guide vane row consists of 3 arc plates.

Post-midnight equatorial irregularity distributions and vertical drift velocity variations during solstices

Science.gov (United States)

Su, S.-Y.; Liu, C. H.; Chao, C.-K.

2018-04-01

Longitudinal distributions of post-midnight equatorial ionospheric irregularity occurrences observed by ROCSAT-1 (1st satellite of the Republic of China) during moderate to high solar activity years in two solstices are studied with respect to the vertical drift velocity and density variations. The post-midnight irregularity distributions are found to be similar to the well-documented pre-midnight ones, but are different from some published distributions taken during solar minimum years. Even though the post-midnight ionosphere is sinking in general, longitudes of frequent positive vertical drift and high density seems to coincide with the longitudes of high irregularity occurrences. Large scatters found in the vertical drift velocity and density around the dip equator in different ROCSAT-1 orbits indicate the existence of large and frequent variations in the vertical drift velocity and density that seem to be able to provide sufficient perturbations for the Rayleigh-Taylor (RT) instability to cause the irregularity occurrences. The need of seeding agents such as gravity waves from atmospheric convective clouds to initiate the Rayleigh-Taylor instability may not be necessary.

Addressing Spatial Variability of Surface-Layer Wind with Long-Range WindScanners

DEFF Research Database (Denmark)

Berg, Jacob; Vasiljevic, Nikola; Kelly, Mark C.

2015-01-01

of the WindScanner data is high, although the fidelity of the estimated vertical velocity component is significantly limited by the elevation angles of the scanner heads. The system of long-range WindScanners presented in this paper is close to being fully operational, with the pilot study herein serving...

Artificial neural network approach to spatial estimation of wind velocity data

International Nuclear Information System (INIS)

Oztopal, Ahmet

2006-01-01

In any regional wind energy assessment, equal wind velocity or energy lines provide a common basis for meaningful interpretations that furnish essential information for proper design purposes. In order to achieve regional variation descriptions, there are methods of optimum interpolation with classical weighting functions or variogram methods in Kriging methodology. Generally, the weighting functions are logically and geometrically deduced in a deterministic manner, and hence, they are imaginary first approximations for regional variability assessments, such as wind velocity. Geometrical weighting functions are necessary for regional estimation of the regional variable at a location with no measurement, which is referred to as the pivot station from the measurements of a set of surrounding stations. In this paper, weighting factors of surrounding stations necessary for the prediction of a pivot station are presented by an artificial neural network (ANN) technique. The wind speed prediction results are compared with measured values at a pivot station. Daily wind velocity measurements in the Marmara region from 1993 to 1997 are considered for application of the ANN methodology. The model is more appropriate for winter period daily wind velocities, which are significant for energy generation in the study area. Trigonometric point cumulative semivariogram (TPCSV) approach results are compared with the ANN estimations for the same set of data by considering the correlation coefficient (R). Under and over estimation problems in objective analysis can be avoided by the ANN approach

A Vertical-Axis Off-Grid Squirrel-Cage Induction Generator Wind Power System

Directory of Open Access Journals (Sweden)

Peifeng Xu

2016-10-01

Full Text Available In order to broaden the limited utilization range of wind power and improve the charging and discharging control performance of the storage battery in traditional small wind power generation systems, a wind power system based on a vertical-axis off-grid induction generator is proposed in this paper. The induction generator not only can run in a wide wind speed range but can also assist the vertical-axis wind turbine to realize self-starting at low wind speed. Combined with the maximum power point tracking method, the slip frequency control strategy is employed to regulate the pulse width modulation (PWM converter to control the output power of the proposed system when the wind speed and load change. The charge and discharge of the storage battery is realized by the segmented current-limiting control strategy by means of an electric power unloader device connected to the DC bus. All these implement a balanced and stable operation of the proposed power generation system. The experimental research on the 5.5 kW prototype system is developed, and the corresponding results verify the correctness and feasibility of the system design and control strategy. Some comparison experiments with a magnetic suspension permanent magnet synchronous generator (PMSG demonstrate the application prospect of the proposed vertical-axis off-grid induction generator wind power system.

Wind direction dependent vertical wind shear and surface roughness parameter in two different coastal environments

International Nuclear Information System (INIS)

Bagavathsingh, A.; Srinivas, C.V.; Baskaran, R.; Venkatraman, B.; Sardar Maran, P.

2016-01-01

Atmospheric boundary layer parameters and surface layer parameterizations are important prerequisites for air pollution dispersion analysis. The turbulent flow characteristics vary at coastal and inland sites where the nuclear facilities are situated. Many pollution sources and their dispersion occur within the roughness sub layer in the lower atmosphere. In this study analysis of wind direction dependence vertical wind shear, surface roughness lengths and surface layer wind condition has been carried out at a coastal and the urban coastal site for the different wind flow regime. The differential response of the near coastal and inland urban site SBL parameters (wind shear, roughness length, etc) was examined as a function of wind direction

Design and analysis of a semi-submersible vertical axis wind turbine

OpenAIRE

Siddique, Muhammad Abu Zafar

2017-01-01

Wind energy are deployed by two types of wind turbines. They are Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT), classified according to their axis of rotation. In recent years, offshore wind energy playing a vital role in the wind turbine industry due to high intensity of air, less turbulent and comparatively clean and easily employed in large area which is difficult to manage for onshore or near-shore. The advantages of HAWTs are now facing different challenge in ...

The role of wind field induced flow velocities in destratification and hypoxia reduction at Meiling Bay of large shallow Lake Taihu, China.

Science.gov (United States)

Jalil, Abdul; Li, Yiping; Du, Wei; Wang, Wencai; Wang, Jianwei; Gao, Xiaomeng; Khan, Hafiz Osama Sarwar; Pan, Baozhu; Acharya, Kumud

2018-01-01

Wind induced flow velocity patterns and associated thermal destratification can drive to hypoxia reduction in large shallow lakes. The effects of wind induced hydrodynamic changes on destratification and hypoxia reduction were investigated at the Meiling bay (N 31° 22' 56.4″, E 120° 9' 38.3″) of Lake Taihu, China. Vertical flow velocity profile analysis showed surface flow velocities consistency with the wind field and lower flow velocity profiles were also consistent (but with delay response time) when the wind speed was higher than 6.2 m/s. Wind field and temperature found the control parameters for hypoxia reduction and for water quality conditions at the surface and bottom profiles of lake. The critical temperature for hypoxia reduction at the surface and the bottom profile was ≤24.1C° (below which hypoxic conditions were found reduced). Strong prevailing wind field (onshore wind directions ESE, SE, SSE and E, wind speed ranges of 2.4-9.1 m/s) reduced the temperature (22C° to 24.1C°) caused reduction of hypoxia at the near surface with a rise in water levels whereas, low to medium prevailing wind field did not supported destratification which increased temperature resulting in increased hypoxia. Non-prevailing wind directions (offshore) were not found supportive for the reduction of hypoxia in study area due to less variable wind field. Daytime wind field found more variable (as compared to night time) which increased the thermal destratification during daytime and found supportive for destratification and hypoxia reduction. The second order exponential correlation found between surface temperature and Chlorophyll-a (R 2 : 0.2858, Adjusted R-square: 0.2144 RMSE: 4.395), Dissolved Oxygen (R 2 : 0.596, Adjusted R-square: 0.5942, RMSE: 0.3042) concentrations. The findings of the present study reveal the driving mechanism of wind induced thermal destratification and hypoxic conditions, which may further help to evaluate the wind role in eutrophication

Characterization of a new open jet wind tunnel to optimize and test vertical axis wind turbines

DEFF Research Database (Denmark)

Tourn, Silvana; Pallarès, Jordi; Cuesta, Ildefonso

2017-01-01

Based on the increasing interest in urban environmental technologies, the study of small scale vertical axis wind turbines shows motivating challenges. In this paper, we present the characteristics and potentials of a new open jet wind tunnel. It has a nozzle exit area of 1.5 × 1.5 m2, and it can......%. The detailed characterization of the flow carried out indicates that the wind tunnel can be used to test small scale models of wind turbines....

Experimental characterization of individual pitch controlled vertical axis wind turbine

NARCIS (Netherlands)

Leblanc, B.P.; Simao Ferreira, C.

2017-01-01

Research into the Vertical Axis Wind Turbine (VAWT) has been progressing over the last few years due to
the large shift in design constraints for large floating offshore wind turbines by leveraging tools and experience
from research beginning in the 1970s and lasting until the HAWT

A relaxed eddy accumulation system for measuring vertical fluxes of nitrous acid

Directory of Open Access Journals (Sweden)

X. Ren

2011-10-01

Full Text Available A relaxed eddy accumulation (REA system combined with a nitrous acid (HONO analyzer was developed to measure atmospheric HONO vertical fluxes. The system consists of three major components: (1 a fast-response sonic anemometer measuring both vertical wind velocity and air temperature, (2 a fast-response controlling unit separating air motions into updraft and downdraft samplers by the sign of vertical wind velocity, and (3 a highly sensitive HONO analyzer based on aqueous long path absorption photometry that measures HONO concentrations in the updrafts and downdrafts. A dynamic velocity threshold (±0.5σ_w, where σ_w is a standard deviation of the vertical wind velocity was used for valve switching determined by the running means and standard deviations of the vertical wind velocity. Using measured temperature as a tracer and the average values from two field deployments, the flux proportionality coefficient, β, was determined to be 0.42 ± 0.02, in good agreement with the theoretical estimation. The REA system was deployed in two ground-based field studies. In the California Research at the Nexus of Air Quality and Climate Change (CalNex study in Bakersfield, California in summer 2010, measured HONO fluxes appeared to be upward during the day and were close to zero at night. The upward HONO flux was highly correlated to the product of NO₂ and solar radiation. During the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX 2009 at Blodgett Forest, California in July 2009, the overall HONO fluxes were small in magnitude and were close to zero. Causes for the different HONO fluxes in the two different environments are briefly discussed.

Dynamic Analysis of a Floating Vertical Axis Wind Turbine Under Emergency Shutdown Using Hydrodynamic Brake

DEFF Research Database (Denmark)

Wang, K.; Hansen, Martin Otto Laver; Moan, T.

2014-01-01

Emergency shutdown is always a challenge for an operating vertical axis wind turbine. A 5-MW vertical axis wind turbine with a Darrieus rotor mounted on a semi-submersible support structure was examined in this study. Coupled non-linear aero-hydro-servo-elastic simulations of the floating vertical...... axis wind turbine were carried out for emergency shutdown cases over a range of environmental conditions based on correlated wind and wave data. When generator failure happens, a brake should be applied to stop the acceleration of the rotor to prevent the rotor from overspeeding and subsequent disaster...

Aeroelastically coupled blades for vertical axis wind turbines

Science.gov (United States)

Paquette, Joshua; Barone, Matthew F.

2016-02-23

Various technologies described herein pertain to a vertical axis wind turbine blade configured to rotate about a rotation axis. The vertical axis wind turbine blade includes at least an attachment segment, a rear swept segment, and optionally, a forward swept segment. The attachment segment is contiguous with the forward swept segment, and the forward swept segment is contiguous with the rear swept segment. The attachment segment includes a first portion of a centroid axis, the forward swept segment includes a second portion of the centroid axis, and the rear swept segment includes a third portion of the centroid axis. The second portion of the centroid axis is angularly displaced ahead of the first portion of the centroid axis and the third portion of the centroid axis is angularly displaced behind the first portion of the centroid axis in the direction of rotation about the rotation axis.

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.

Downstream wind flow path diversion and its effects on the performance of vertical axis wind turbine

International Nuclear Information System (INIS)

Maganhar, A.L.

2015-01-01

In the present experimental study efforts have been made to analysis path diversion effect of downstream wind flow on performance of vertical axis wind turbine (VAWT). For the blockage of downstream wind flow path at various linear displaced positions, a normal erected flat wall, semi-circular and cylindrical shapes were tested for path diverting geometries. Performance of VAWT in terms of improved rotor speed up to 45% was achieved. (author)

Brief communication: On the influence of vertical wind shear on the combined power output of two model wind turbines in yaw

Directory of Open Access Journals (Sweden)

J. Schottler

2017-08-01

Full Text Available The effect of vertical wind shear on the total power output of two aligned model wind turbines as a function of yaw misalignment of the upstream turbine is studied experimentally. It is shown that asymmetries of the power output of the downstream turbine and the combined power of both with respect to the upstream turbine's yaw misalignment angle can be linked to the vertical wind shear of the inflow.

Analytical Aerodynamic Simulation Tools for Vertical Axis Wind Turbines

International Nuclear Information System (INIS)

Deglaire, Paul

2010-01-01

Wind power is a renewable energy source that is today the fastest growing solution to reduce CO 2 emissions in the electric energy mix. Upwind horizontal axis wind turbine with three blades has been the preferred technical choice for more than two decades. This horizontal axis concept is today widely leading the market. The current PhD thesis will cover an alternative type of wind turbine with straight blades and rotating along the vertical axis. A brief overview of the main differences between the horizontal and vertical axis concept has been made. However the main focus of this thesis is the aerodynamics of the wind turbine blades. Making aerodynamically efficient turbines starts with efficient blades. Making efficient blades requires a good understanding of the physical phenomena and effective simulations tools to model them. The specific aerodynamics for straight bladed vertical axis turbine flow are reviewed together with the standard aerodynamic simulations tools that have been used in the past by blade and rotor designer. A reasonably fast (regarding computer power) and accurate (regarding comparison with experimental results) simulation method was still lacking in the field prior to the current work. This thesis aims at designing such a method. Analytical methods can be used to model complex flow if the geometry is simple. Therefore, a conformal mapping method is derived to transform any set of section into a set of standard circles. Then analytical procedures are generalized to simulate moving multibody sections in the complex vertical flows and forces experienced by the blades. Finally the fast semi analytical aerodynamic algorithm boosted by fast multipole methods to handle high number of vortices is coupled with a simple structural model of the rotor to investigate potential aeroelastic instabilities. Together with these advanced simulation tools, a standard double multiple streamtube model has been developed and used to design several straight bladed

Overview and Design of self-acting pitch control mechanism for vertical axis wind turbine using multi body simulation approach

International Nuclear Information System (INIS)

Chougule, Prasad; Nielsen, Søren

2014-01-01

Awareness about wind energy is constantly growing in the world. Especially a demand for small scale wind turbine is increasing and various products are available in market. There are mainly two types of wind turbines, horizontal axis wind turbine and vertical axis wind turbines. Horizontal axis wind turbines are suitable for high wind speed whereas vertical axis wind turbines operate relatively low wind speed area. Vertical axis wind turbines are cost effective and simple in construction as compared to the horizontal axis wind turbine. However, vertical axis wind turbines have inherent problem of self-start inability and has low power coefficient as compare to the horizontal axis wind turbine. These two problems can be eliminated by incorporating the blade pitching mechanism. So, in this paper overview of various pitch control systems is discussed and design of self-acting pitch mechanism is given. A pitch control linkage mechanism for vertical axis wind turbine is modeled by multi-body approach using MSC Software. Aerodynamic loads are predicted from a mathematical model based on double multiple stream tube method. An appropriate airfoil which works at low Reynolds number is selected for blade design. It is also focused on commercialization of the vertical axis wind turbine which incorporates the self-acting pitch control system. These aerodynamic load model will be coupled with the multi-body model in future work for optimization of the pitch control linkage mechanism. A 500 Watt vertical axis wind turbine is designed and it is planned to implement the self-acting pitch control mechanism in real model

Experimental data on load test and performance parameters of a LENZ type vertical axis wind turbine in open environment condition.

Science.gov (United States)

Sivamani, Seralathan; T, Micha Premkumar; Sohail, Mohammed; T, Mohan; V, Hariram

2017-12-01

Performance and load testing data of a three bladed two stage LENZ type vertical axis wind turbine from the experiments conducted in an open environment condition at Hindustan Institute of Technology and Science, Chennai (location 23.2167°N, 72.6833°E) are presented here. Low-wind velocity ranging from 2 to 11 m/s is available everywhere irrespective of climatic seasons and this data provides the support to the researchers using numerical tool to validate and develop an enhanced Lenz type design. Raw data obtained during the measurements are processed and presented in the form so as to compare with other typical outputs. The data is measured at different wind speeds prevalent in the open field condition ranging from 3 m/s to 9 m/s.

The Parameters Affect on Power Coefficient Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Ahmed Y. Qasim

2012-04-01

Full Text Available ABSTRACT: This study describes the design of a special type of vertical axis rotor wind turbine with moveable vertically positioned vanes. The novel design increases the torque in the left side of the wind turbine by increasing the drag coefficient. It also reduces the negative torque of the frame which rotates contrary to the wind in the other side. Two different types of models, having different vane shapes (flat vane and cavity shaped vane, were fabricated. Each type consisted of two models with varying number of frames (three and four frames. The models were tested in a wind tunnel with variable wind speed in order to understand the effect of shape, weight, and number of frames on the power coefficient of the wind turbine. ABSTRAK: Di dalam kajian ini, rotor turbin angin berpaksi vertikel sebagai rangka khusus telah direkabentuk dengan lokasi vertikel mudahalih oleh bilah kipas. Rekabentuk ini meningkatkan tork di bahagian kiri turbin angin dengan meningkatkan pekali seretan dan mengurangkan tork negatif rangka yang berputar berlawanan dengan angin pada bahagian lain. Dua jenis model berbentuk berlainan telah difabrikasi (bilah kipas rata dan bilah kipas berbentuk kaviti, dengan setiap jenis mempunyai dua model dengan bilangan rangka yang berlainan (berangka tiga dan berangka empat. Model-model telah diuji di dalam terowong angin dengan kelajuan angin yang berbeza bagi mendapatkan kesan rekabentuk, berat dan bilangan rangka ke atas pekali kuasa.KEYWORDS: design; wind turbine; drag coefficient; vane

Mitigating the negative impacts of tall wind turbines on bats: Vertical activity profiles and relationships to wind speed.

Science.gov (United States)

Wellig, Sascha D; Nusslé, Sébastien; Miltner, Daniela; Kohle, Oliver; Glaizot, Olivier; Braunisch, Veronika; Obrist, Martin K; Arlettaz, Raphaël

2018-01-01

Wind turbines represent a source of hazard for bats, especially through collision with rotor blades. With increasing technical development, tall turbines (rotor-swept zone 50-150 m above ground level) are becoming widespread, yet we lack quantitative information about species active at these heights, which impedes proposing targeted mitigation recommendations for bat-friendly turbine operation. We investigated vertical activity profiles of a bat assemblage, and their relationships to wind speed, within a major valley of the European Alps where tall wind turbines are being deployed. To monitor bat activity we installed automatic recorders at sequentially increasing heights from ground level up to 65 m, with the goal to determine species-specific vertical activity profiles and to link them to wind speed. Bat call sequences were analysed with an automatic algorithm, paying particular attention to mouse-eared bats (Myotis myotis and Myotis blythii) and the European free-tailed bat (Tadarida teniotis), three locally rare species. The most often recorded bats were the Common pipistrelle (Pipistrellus pipistrellus) and Savi's pipistrelle (Hypsugo savii). Mouse-eared bats were rarely recorded, and mostly just above ground, appearing out of risk of collision. T. teniotis had a more evenly distributed vertical activity profile, often being active at rotor level, but its activity at that height ceased above 5 ms-1 wind speed. Overall bat activity in the rotor-swept zone declined with increasing wind speed, dropping below 5% above 5.4 ms-1. Collision risk could be drastically reduced if nocturnal operation of tall wind turbines would be restricted to wind speeds above 5 ms-1. Such measure should be implemented year-round because T. teniotis remains active in winter. This operational restriction is likely to cause only small energy production losses at these tall wind turbines, although further analyses are needed to assess these losses precisely.

Effective solidity in vertical axis wind turbines

Science.gov (United States)

Parker, Colin M.; Leftwich, Megan C.

2016-11-01

The flow surrounding vertical axis wind turbines (VAWTs) is investigated using particle imaging velocimetry (PIV). This is done in a low-speed wind tunnel with a scale model that closely matches geometric and dynamic properties tip-speed ratio and Reynolds number of a full size turbine. Previous results have shown a strong dependance on the tip-speed ratio on the wake structure of the spinning turbine. However, it is not clear whether this is a speed or solidity effect. To determine this, we have measured the wakes of three turbines with different chord-to-diameter ratios, and a solid cylinder. The flow is visualized at the horizontal mid-plane as well as the vertical mid-plane behind the turbine. The results are both ensemble averaged and phase averaged by syncing the PIV system with the rotation of the turbine. By keeping the Reynolds number constant with both chord and diameter, we can determine how each effects the wake structure. As these parameters are varied there are distinct changes in the mean flow of the wake. Additionally, by looking at the vorticity in the phase averaged profiles we can see structural changes to the overall wake pattern.

75 FR 27583 - Job Corps: Final Finding of No Significant Impact (FONSI) for Small Vertical Wind Turbine and...

Science.gov (United States)

2010-05-17

... CFR 11.11(d), gives final notice of the proposed construction of a small vertical axis wind turbine... (FONSI) for Small Vertical Wind Turbine and Solar Installation at the Paul Simon Job Corps Center Located... impact. This notice serves as the Final Finding of No Significant Impact (FONSI) for Small Vertical Wind...

Quantifying error of lidar and sodar Doppler beam swinging measurements of wind turbine wakes using computational fluid dynamics

Science.gov (United States)

Lundquist, J. K.; Churchfield, M. J.; Lee, S.; Clifton, A.

2015-02-01

Wind-profiling lidars are now regularly used in boundary-layer meteorology and in applications such as wind energy and air quality. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler beam swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Using such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in errors. To quantify the errors expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably stratified flow past a wind turbine, with a mean wind speed of 6.5 m s-1 at the turbine hub-height of 80 m. This slightly stable case results in 15° of wind direction change across the turbine rotor disk. The resulting flow field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, including the lidar range weighting function, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small errors, which are ameliorated with time averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow approach 30% of the hub-height inflow wind speed close to the rotor disk. Errors in the cross-stream and vertical velocity components are also significant: cross-stream component errors are on the order of 15% of the hub-height inflow wind speed (1.0 m s-1) and errors in the vertical velocity measurement exceed the actual vertical velocity

Simulation of flow over double-element airfoil and wind tunnel test for use in vertical axis wind turbine

DEFF Research Database (Denmark)

Chougule, Prasad; Nielsen, Søren R.K.

2014-01-01

been made to utilize high lift technology for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double-element airfoil mainly used in aeroplane wing design. In this current work a low Reynolds number airfoil is selected to design a double-element airfoil blade...... for use in vertical axis wind turbine to improve the power efficiency. Double-element airfoil blade design consists of a main airfoil and a slat airfoil. Orientation of slat airfoil is a parameter of investigation in this paper and air flow simulation over double-element airfoil. With primary wind tunnel...... that there is an increase in the lift coefficient by 26% for single-element airfoil at analysed conditions. The CFD simulation results were validated with wind tunnel tests. It is also observe that by selecting proper airfoil configuration and blade sizes an increase in lift coefficient can further be achieved....

Effects of increasing tip velocity on wind turbine rotor design.

Energy Technology Data Exchange (ETDEWEB)

Resor, Brian Ray [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Maniaci, David Charles [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Berg, Jonathan Charles [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Richards, Phillip William [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2014-05-01

A reduction in cost of energy from wind is anticipated when maximum allowable tip velocity is allowed to increase. Rotor torque decreases as tip velocity increases and rotor size and power rating are held constant. Reduction in rotor torque yields a lighter weight gearbox, a decrease in the turbine cost, and an increase in the capacity for the turbine to deliver cost competitive electricity. The high speed rotor incurs costs attributable to rotor aero-acoustics and system loads. The increased loads of high speed rotors drive the sizing and cost of other components in the system. Rotor, drivetrain, and tower designs at 80 m/s maximum tip velocity and 100 m/s maximum tip velocity are created to quantify these effects. Component costs, annualized energy production, and cost of energy are computed for each design to quantify the change in overall cost of energy resulting from the increase in turbine tip velocity. High fidelity physics based models rather than cost and scaling models are used to perform the work. Results provide a quantitative assessment of anticipated costs and benefits for high speed rotors. Finally, important lessons regarding full system optimization of wind turbines are documented.

Revisiting the radiative vertical velocity paradigm in the TTL

Science.gov (United States)

Bolot, Maximilien; Moyer, Elisabeth

2015-04-01

We demonstrate that uplift rates in the TTL (tropical tropopause layer) may be commonly overestimated. The mass balance of any tracer in the TTL depends on the vertical speed of large-scale uplift and the rate of convective detrainment from overshoots. Generally, uplift velocity is retrieved from the conservation of energy, assuming that the only significant factor is radiative heating.1,2 The detrainment rate is then computed from the convergence of the uplift flux, with the assumption that detrainment dominates over entrainment in the TTL. We show that this commonly calculated 'radiative vertical velocity' and the associated rate of detrainment are necessarily flawed for either of two mutually exclusive reasons. If radiative heating is the sole diabatic term in the energy budget, then significant convective entrainment must occur at TTL levels. If detrainment dominates over entrainment, then the heat budget must include the cooling rate from the export of sensible heat deficit in overshooting convection. We illustrate the calculations using tropical values of radiative heating rates and large-scale divergence fluxes from ERA-Interim reanalysis. For undilute convection, the export of heat deficit in detrained overshoots would substantially offset radiative heating, lowering the resulting assumed vertical velocity at 16 km by a factor of three. The computed detrainment rate at this altitude also increases significantly, by a factor of five. Because these changes would alter interpretation of tracer profiles, it is important to include all terms in the heat budget in tracer studies. Conversely, tracer transport properties can be used to help constrain the impact of convection on the TTL heat budget.3 [1] Folkins, I. et al., J. Geophys. Res., 111, D23304, (2006). [2] Read, W. G. et al., Atmos. Chem. Phys., 8, 6051-6067, (2008). [3] Kuang, Z. and Bretherton, C. S., J. Atmos. Sci., 61, 2919-2927, (2004)

Some design aspects of high-speed vertical-axis wind turbines

National Research Council Canada - National Science Library

Templin, R. J; South, P

1977-01-01

... (rotor height to diameter ratio, solidity, number of blades, etc.) for high-speed vertical-axis wind turbines from kilowatt to megawatt sizes and shows that very large turbines are theoretically feasible...

Efficiency of the DOMUS 750 vertical-axis wind turbine

Science.gov (United States)

Hallock, Kyle; Rasch, Tyler; Ju, Guoqiang; Alonso-Marroquin, Fernando

2017-06-01

The aim of this paper is to present some preliminary results on the efficiency of a wind turbine for an off-grid housing unit. To generate power, the unit uses a photovoltaic solar array and a vertical-axis wind turbine (VAWT). The existing VAWT was analysed to improve efficiency and increase power generation. There were found to be two main sources of inefficiency: 1. the 750W DC epicyclic generator performed poorly in low winds, and 2. the turbine blades wobbled, allowing for energy loss due to off-axis rotation. A 12V DC permanent magnet alternator was chosen that met the power requirements of the housing unit and would generate power at lower wind speeds. A support bracket was designed to prevent the turbine blades from wobbling.

Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

DEFF Research Database (Denmark)

Draxl, Caroline; Hahmann, Andrea N.; Pena Diaz, Alfredo

2014-01-01

with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights. Winds speeds at heights...... regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by theWeather Research and Forecasting model using seven sets of simulations...

Comparison of aerodynamic models for Vertical Axis Wind Turbines

DEFF Research Database (Denmark)

Ferreira, C. Simão; Aagaard Madsen, Helge; Barone, M.

2014-01-01

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple...

Innovative Design of a Darrieus Straight Bladed Vertical Axis Wind Turbine by using Multi Element Airfoil

DEFF Research Database (Denmark)

Chougle, Prasad Devendra

. Mainly, there is the horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT). HAWTs are more popular than VAWTs due to failure of VAWT commercialization during the late of 1980s on a large scale. However, in recent research work it has been documented that VAWTs are more economical......, and the wind tunnel testing of double-element airfoil is performed. It is found that the aerodynamic characteristics of the airfoil increased considerably by delaying the angle of stall. These two facts are very suitable for vertical axis wind turbine since they operate in a larger range of angle of attack......, ±40_, compared to the horizontal axis wind turbines which operate in the range of attack, ±15_. A new design of vertical axis wind turbine is then proposed, and aerodynamic performance is evaluated based on double multiple stream tube methods. The performance parameters are almost doubled compared...

On a relation of geomagnetic activity, solar wind velocity and irregularity of daily rotation of the Earth

International Nuclear Information System (INIS)

Kalinin, Yu.D.; Kiselev, V.M.

1980-01-01

A possibility of the presence of statistic relation between the changes of the Earth rotation regime and the mean velocity of solar wind is discussed. The ratio between the solar wind velocity observed and planetary index of geomagnetic activity am is used to determine the annual average values of solar wind velocity beyond the twentieth cycle of solar activity. The restored changes of solar wind velocity are compared with solar conditioned variations of the Earth day duration and it is shown that the correspondence takes place only at frequencies lower the frequency of 11-year cycle [ru

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.

Energy and exergy efficiency comparison of horizontal and vertical axis wind turbines

Energy Technology Data Exchange (ETDEWEB)

Pope, K.; Dincer, I.; Naterer, G.F. [Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario (Canada)

2010-09-15

In this paper, an energy and exergy analysis is performed on four different wind power systems, including both horizontal and vertical axis wind turbines. Significant variability in turbine designs and operating parameters are encompassed through the selection of systems. In particular, two airfoils (NACA 63(2)-215 and FX 63-137) commonly used in horizontal axis wind turbines are compared with two vertical axis wind turbines (VAWTs). A Savonius design and Zephyr VAWT benefit from operational attributes in wind conditions that are unsuitable for airfoil type designs. This paper analyzes each system with respect to both the first and second laws of thermodynamics. The aerodynamic performance of each system is numerically analyzed by computational fluid dynamics software, FLUENT. A difference in first and second law efficiencies of between 50 and 53% is predicted for the airfoil systems, whereas 44-55% differences are predicted for the VAWT systems. Key design variables are analyzed and the predicted results are discussed. The exergetic efficiency of each wind turbine is studied for different geometries, design parameters and operating conditions. It is shown that the second law provides unique insight beyond a first law analysis, thereby providing a useful design tool for wind power development. (author)

The effect of pitch angle on the performance of a vertical-axis wind turbine

NARCIS (Netherlands)

Rezaeiha, A.; Kalkman, I.M.; Blocken, B.; Borg, R.P.; Gauci, P.; Staines, C.S.

2016-01-01

Wind energy is a highly promising resource to approach a sustainable built environment. Vertical axis wind turbines (VAWT) offer the advantage of omni-directional operation over horizontal axis wind turbines (HAWT). This makes them ideal for utilization in urban environments which are characterized

Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements

Directory of Open Access Journals (Sweden)

A. Canals

2002-09-01

Full Text Available Interplanetary scintillation measurements can yield estimates of a large number of solar wind parameters, including bulk flow speed, variation in bulk velocity along the observing path through the solar wind and random variation in transverse velocity. This last parameter is of particular interest, as it can indicate the flux of low-frequency Alfvén waves, and the dissipation of these waves has been proposed as an acceleration mechanism for the fast solar wind. Analysis of IPS data is, however, a significantly unresolved problem and a variety of a priori assumptions must be made in interpreting the data. Furthermore, the results may be affected by the physical structure of the radio source and by variations in the solar wind along the scintillation ray path. We have used observations of simple point-like radio sources made with EISCAT between 1994 and 1998 to obtain estimates of random transverse velocity in the fast solar wind. The results obtained with various a priori assumptions made in the analysis are compared, and we hope thereby to be able to provide some indication of the reliability of our estimates of random transverse velocity and the variation of this parameter with distance from the Sun.Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma; instruments and techniques

Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements

Directory of Open Access Journals (Sweden)

A. Canals

Full Text Available Interplanetary scintillation measurements can yield estimates of a large number of solar wind parameters, including bulk flow speed, variation in bulk velocity along the observing path through the solar wind and random variation in transverse velocity. This last parameter is of particular interest, as it can indicate the flux of low-frequency Alfvén waves, and the dissipation of these waves has been proposed as an acceleration mechanism for the fast solar wind. Analysis of IPS data is, however, a significantly unresolved problem and a variety of a priori assumptions must be made in interpreting the data. Furthermore, the results may be affected by the physical structure of the radio source and by variations in the solar wind along the scintillation ray path. We have used observations of simple point-like radio sources made with EISCAT between 1994 and 1998 to obtain estimates of random transverse velocity in the fast solar wind. The results obtained with various a priori assumptions made in the analysis are compared, and we hope thereby to be able to provide some indication of the reliability of our estimates of random transverse velocity and the variation of this parameter with distance from the Sun.

Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma; instruments and techniques

Analysis of conditions favourable for small vertical axis wind turbines between building passages in urban areas of Sweden

Science.gov (United States)

Awan, Muhammad Rizwan; Riaz, Fahid; Nabi, Zahid

2017-05-01

This paper presents the analysis of installing the vertical axis wind turbines between the building passages on an island in Stockholm, Sweden. Based on the idea of wind speed amplification due to the venture effect in passages, practical measurements were carried out to study the wind profile for a range of passage widths in parallel building passages. Highest increment in wind speed was observed in building passages located on the periphery of sland as wind enters from free field. Wind mapping was performed in the island to choose the most favourable location to install the vertical axis wind turbines (VAWT). Using the annual wind speed data for location and measured amplification factor, energy potential of the street was calculated. This analysis verified that small vertical axis wind turbines can be installed in the passage centre line provided that enough space is provided for traffic and passengers.

Numerical simulation on a straight-bladed vertical axis wind turbine with auxiliary blade

Science.gov (United States)

Li, Y.; Zheng, Y. F.; Feng, F.; He, Q. B.; Wang, N. X.

2016-08-01

To improve the starting performance of the straight-bladed vertical axis wind turbine (SB-VAWT) at low wind speed, and the output characteristics at high wind speed, a flexible, scalable auxiliary vane mechanism was designed and installed into the rotor of SB-VAWT in this study. This new vertical axis wind turbine is a kind of lift-to-drag combination wind turbine. The flexible blade expanded, and the driving force of the wind turbines comes mainly from drag at low rotational speed. On the other hand, the flexible blade is retracted at higher speed, and the driving force is primarily from a lift. To research the effects of the flexible, scalable auxiliary module on the performance of SB-VAWT and to find its best parameters, the computational fluid dynamics (CFD) numerical calculation was carried out. The calculation result shows that the flexible, scalable blades can automatic expand and retract with the rotational speed. The moment coefficient at low tip speed ratio increased substantially. Meanwhile, the moment coefficient has also been improved at high tip speed ratios in certain ranges.

Determination of the effect of wind velocity and direction changes on turbidity removal in rectangular sedimentation tanks.

Science.gov (United States)

Khezri, Seyed Mostafa; Biati, Aida; Erfani, Zeynab

2012-01-01

In the present study, a pilot-scale sedimentation tank was used to determine the effect of wind velocity and direction on the removal efficiency of particles. For this purpose, a 1:20 scale pilot simulated according to Frude law. First, the actual efficiency of total suspended solids (TSS) removal was calculated in no wind condition. Then, the wind was blown in the same and the opposite directions of water flow. At each direction TSS removal was calculated at three different velocities from 2.5 to 7 m/s. Results showed that when the wind was in the opposite direction of water flow, TSS removal efficiency initially increased with the increase of wind velocity from 0 to 2.5 m/s, then it decreased with the increase of velocity to 5 m/s. This mainly might happen because the opposite direction of wind can increase particles' retention time in the sedimentation tank. However, higher wind velocities (i.e. 3.5 and 5.5 m/s) could not increase TSS removal efficiency. Thus, if sedimentation tanks are appropriately exposed to the wind, TSS removal efficiency increases by approximately 6%. Therefore, energy consumption will be reduced by a proper site selection for sedimentation tank unit in water and waste water treatment plants.

On the aerodynamics of a vertical axis wind turbine wake : An experimental and numerical study

NARCIS (Netherlands)

Tescione, G.

2016-01-01

THE recent trend in wind energy industry, with the increasing deployment of offshore wind farms, has revived the interest in the concept of a vertical axis wind turbine. The scientific, technological and economical challenges of the next generation of wind turbines indicate that a transformative

Vertical characterization of the wind mode and its effect on the wind farm profitability of Sidi Daoud - Tunisia

International Nuclear Information System (INIS)

Elamouri, M.; Ben Amar, F.; Trabelsi, A.

2011-01-01

The choice of a site and the statistical characterization of the wind speed represent the most significant factors in the process of wind park establishment. Indeed, the average value of the wind speed during one year and its temporal variation are the factors which have the greatest impact on the economic wind farm profitability. Thus, this article presents a meteorological and energetic study, in terms of the height of Sidi Daoud wind power station installed in Tunisia. From the meteorological data recorded, during the year 2004, in two places (masts 3 and 4) of the site and with heights 45, 50 and 60 m above ground level, we studied the vertical profile the wind speed both using the logarithmic law and the power law. The Raleigh distribution is selected to determine the annual characteristics of the wind and their influence on the available energy. The obtained results are then extrapolated vertically using the power law making it possible to make a comparative study between the two places in order to know the evolution of the wind speed at altitudes representing an energetic interest. The study also concerns the aerodynamic performances of the three aerogenerators with horizontal axis AE-46, AE-52 and AE-61 installed in site. From their characteristic curves, we have been able to study their energy efficiency in function of the wind speed, their use factors and the availability rate according to the height. All the numerical results illustrated in the article are obtained by a computer code developed by software MATLAB.

A Numerical Study on a Vertical-Axis Wind Turbine with Inclined Arms

Directory of Open Access Journals (Sweden)

Agostino De Marco

2014-01-01

Full Text Available This work focuses on a particular type of vertical-axis wind turbine, in which a number of inclined arms with airfoil-shaped cross-sections are mounted to connect the principal blades to their hub. While the majority of the known studies on vertical-axis turbines is devoted to the role of principal blades, in most of the cases without taking into account other parts of the wind turbine, the objective of this work is to investigate the effect of uncommon arm geometries, such as the inclined arms. The inclined arms are known to have a potentially beneficial role in the power extraction from the wind current but, due to the complexity of the phenomena, the investigation on aerodynamics of this type of turbine is often impossible through analytical models, such as blade-element momentum theory. It turns out that adequate studies can only be carried out by wind tunnel experiments or CFD simulations. This work presents a methodical CFD study on how inclined arms can be used on a selected wind turbine configuration to harvest additional power from the wind. The turbine configuration, geometry, and some fundamental definitions are introduced first. Then an in-depth CFD analysis is presented and discussed.

VLTI-AMBER Velocity-Resolved Aperture-Synthesis Imaging of Eta Carinae with a Spectral Resolution of 12 000: Studies of the Primary Star Wind and Innermost Wind-Wind Collision Zone

Science.gov (United States)

Weigelt, G.; Hofmann, K.-H.; Schertl, D.; Clementel, N.; Corcoran, M. F.; Damineli, A.; de Wit, W.-J.; Grellmann, R.; Groh, J.; Guieu, S.;

Periodic Variations in the Vertical Velocities of Galactic Masers

Directory of Open Access Journals (Sweden)

Bobylev V. V.

2016-03-01

Full Text Available We compiled published data on Galactic masers with VLBI-measured trigonometric parallaxes and determined the residual tangential, ∆Vcirc, and radial, ∆VR, velocities for 120 masers. We used these data to redetermine the parameters of the Galactic spiral density wave using the method of spectral analysis. The most interesting result of this study is the detection of wavelike oscillations of vertical spatial velocities (W versus distance R from the Galactic rotation axis. Spectral analysis allowed us to determine the perturbation wavelength and the amplitude of this wave, which we found to be equal to λW = 3.4 ± 0.7 kpc and fW = 4.9 ± 1.2 km s−1, respectively.

Horizontal and Vertical Velocities Derived from the IDS Contribution to ITRF2014, and Comparisons with Geophysical Models

Science.gov (United States)

Moreaux, G.; Lemoine, F. G.; Argus, D. F.; Santamaria-Gomez, A.; Willis, P.; Soudarin, L.; Gravelle, M.; Ferrage, P.

2016-01-01

In the context of the 2014 realization of the International Terrestrial Reference Frame (ITRF2014), the International DORIS Service (IDS) has delivered to the IERS a set of 1140 weekly SINEX files including station coordinates and Earth orientation parameters, covering the time period from 1993.0 to 2015.0. From this set of weekly SINEX files, the IDS Combination Center estimated a cumulative DORIS position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 DORIS sites. The main objective of this study is to validate the velocities of the DORIS sites by comparison with external models or time series. Horizontal velocities are compared with two recent global plate models (GEODVEL 2010 and NNR-MORVEL56). Prior to the comparisons, DORIS horizontal velocities were corrected for Global Isostatic Adjustment (GIA) from the ICE-6G (VM5a) model. For more than half of the sites, the DORIS horizontal velocities differ from the global plate models by less than 2-3 mm/yr. For five of the sites (Arequipa, Dionysos/Gavdos, Manila, Santiago) with horizontal velocity differences wrt these models larger than 10 mm/yr, comparisons with GNSS estimates show the veracity of the DORIS motions. Vertical motions from the DORIS cumulative solution are compared with the vertical velocities derived from the latest GPS cumulative solution over the time span 1995.0-2014.0 from the University of La Rochelle (ULR6) solution at 31 co-located DORIS-GPS sites. These two sets of vertical velocities show a correlation coefficient of 0.83. Vertical differences are larger than 2 mm/yr at 23 percent of the sites. At Thule the disagreement is explained by fine-tuned DORIS discontinuities in line with the mass variations of outlet glaciers. Furthermore, the time evolution of the vertical time series from the DORIS station in Thule show similar trends to the GRACE equivalent water height.

Horizontal and vertical velocities derived from the IDS contribution to ITRF2014, and comparisons with geophysical models

Science.gov (United States)

Moreaux, G.; Lemoine, F. G.; Argus, D. F.; Santamaría-Gómez, A.; Willis, P.; Soudarin, L.; Gravelle, M.; Ferrage, P.

2016-10-01

In the context of the 2014 realization of the International Terrestrial Reference Frame, the International DORIS (Doppler Orbitography Radiopositioning Integrated by Satellite) Service (IDS) has delivered to the IERS a set of 1140 weekly SINEX files including station coordinates and Earth orientation parameters, covering the time period from 1993.0 to 2015.0. From this set of weekly SINEX files, the IDS combination centre estimated a cumulative DORIS position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 DORIS sites. The main objective of this study is to validate the velocities of the DORIS sites by comparison with external models or time-series. Horizontal velocities are compared with two recent global plate models (GEODVEL 2010 and NNR-MORVEL56). Prior to the comparisons, DORIS horizontal velocities were corrected for Global Isostatic Adjustment from the ICE-6G (VM5a) model. For more than half of the sites, the DORIS horizontal velocities differ from the global plate models by less than 2-3 mm yr-1. For five of the sites (Arequipa, Dionysos/Gavdos, Manila and Santiago) with horizontal velocity differences with respect to these models larger than 10 mm yr-1, comparisons with GNSS estimates show the veracity of the DORIS motions. Vertical motions from the DORIS cumulative solution are compared with the vertical velocities derived from the latest GPS cumulative solution over the time span 1995.0-2014.0 from the University of La Rochelle solution at 31 co-located DORIS-GPS sites. These two sets of vertical velocities show a correlation coefficient of 0.83. Vertical differences are larger than 2 mm yr-1 at 23 percent of the sites. At Thule, the disagreement is explained by fine-tuned DORIS discontinuities in line with the mass variations of outlet glaciers. Furthermore, the time evolution of the vertical time-series from the DORIS station in Thule show similar trends to the GRACE equivalent water height.

A Comparison on the Dynamics of a Floating Vertical Axis Wind Turbine on Three Different Floating Support Structures

OpenAIRE

Borg, Michael; Collu, Maurizio

2014-01-01

To increase the competitiveness of offshore wind energy in the global energy market, it is necessary to identify optimal offshore wind turbine configurations to deliver the lowest cost of energy. For deep waters where floating wind turbines are the feasible support structure option, the vertical axis wind turbine concept might prove to be one of these optimal configurations. This paper carries out a preliminary investigation into the dynamics of a vertical axis wind turbine coupled with three...

Frequency-domain characteristics of aerodynamic loads of offshore floating vertical axis wind turbines

DEFF Research Database (Denmark)

Borg, Michael; Collu, M.

2015-01-01

The re-emerging interest in vertical axis wind turbines for floating offshore applications has led to a need to investigate the relatively complex dynamics of such floating offshore structures. Through the use of a coupled model of dynamics this article investigates the frequency......-domain characteristics of floating vertical axis wind turbine aerodynamic loads. The impact of platform induced motion on aerodynamic loads is discussed in detail, with results indicating an increase in aerodynamic loads of several orders of magnitude over the range of frequencies usually containing significant wave...

Transient Performance of a Vertical Axis Wind Turbine

Science.gov (United States)

Onol, Aykut; Yesilyurt, Serhat

2016-11-01

A coupled CFD/rotor dynamics modeling approach is presented for the analysis of realistic transient behavior of a height-normalized, three-straight-bladed VAWT subject to inertial effects of the rotor and generator load which is manipulated by a feedback control under standardized wind gusts. The model employs the k- ɛ turbulence model to approximate unsteady Reynolds-averaged Navier-Stokes equations and is validated with data from field measurements. As distinct from related studies, here, the angular velocity is calculated from the rotor's equation of motion; thus, the dynamic response of the rotor is taken into account. Results include the following: First, the rotor's inertia filters large amplitude oscillations in the wind torque owing to the first-order dynamics. Second, the generator and wind torques differ especially during wind transients subject to the conservation of angular momentum of the rotor. Third, oscillations of the power coefficient exceed the Betz limit temporarily due to the energy storage in the rotor, which acts as a temporary buffer that stores the kinetic energy like a flywheel in short durations. Last, average of transient power coefficients peaks at a smaller tip-speed ratio for wind gusts than steady winds. This work was supported by the Sabanci University Internal Research Grant Program (SU-IRG-985).

Steady and Unsteady Analysis of NACA 0018 Airfoil in Vertical-Axis Wind Turbine

DEFF Research Database (Denmark)

Rogowski, Krzysztof; Hansen, Martin Otto Laver; Maronski, Ryszard

2018-01-01

Numerical results are presented for aerodynamic unsteady and steady airfoil characteristtcs of the NACA 0018 airfoil of a two-dimensional vertical-axis wind turbine. A geometrical model of the Darrieus-type wind turbine and the rotor operating parameters used for nurnerieal simulation are taken...

Variable speed control for Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Galinos, Christos; Larsen, Torben J.

A robust variable speed control for vertical axis wind turbine applications is implemented. It is a PI rotor speed controller based on an induction generator model operated at variable frequency. The generator dynamics are approximated by a first order differential equation with a prescribed slip....... In order to allow variability in the rotor speed an inverter is assumed which changes the nominal generator speed. Below rated power the optimum tip speed ratio is tracked, while above the power is constrained to rated. The wind speed which is needed in the control it is considered as a known signal...... the Inflow project. The investigation of the VAWT performance under different control parameters such as the PI gains has been performed by Christos Galinos. Deterministic and turbulent wind speed steps of 2 m/s from 6 m/s to 24 m/s and back to 12 m/s are applied. The controller gives smooth transient...

Wake structure of a single vertical axis wind turbine

International Nuclear Information System (INIS)

Posa, Antonio; Parker, Colin M.; Leftwich, Megan C.; Balaras, Elias

2016-01-01

Highlights: • The wake structure of an isolated Vertical Axis Wind Turbine is studied by both Particle Imaging Velocimetry and Large Eddy Simulation. • The wake structure is investigated for two values of tip speed ratio, TSR_1=1.35 and TSR_2=2.21. • A displacement of the momentum deficit towards the windward side is verified in the wake. • Higher turbulence and coherence is observed on the leeward side of the wake, due to the upwind stall of the blades. • Coherence in the wake core, associated to the downwind stall, decays quickly downstream. - Abstract: The wake structure behind a vertical axis wind turbine (VAWT) is both measured in a wind tunnel using particle imaging velocimetry (PIV) and computed with large-eddy simulation (LES). Geometric and dynamic conditions are closely matched to typical applications of VAWTs (Re_D ∼ 1.8 × 10"5). The experiments and computations were highly coordinated with continuous two-way feedback to produce the most insightful results. Good qualitative agreement is seen between the computational and experimental results. The dependence of the wake structure on the tip speed ratio, TSR, is investigated, showing higher asymmetry and larger vortices at the lower rotational speed, due to stronger dynamic stall phenomena. Instantaneous, ensemble-averaged and phase-averaged fields are discussed, as well as the dynamics of coherent structures in the rotor region and downstream wake.

The formation of sporadic E layers by a vortical perturbation excited in a horizontal wind shear flow

Directory of Open Access Journals (Sweden)

G. G. Didebulidze

2008-06-01

Full Text Available The formation of the mid-latitude sporadic E layers (E_s layers by an atmospheric vortical perturbation excited in a horizontal shear flow (horizontal wind with a horizontal linear shear is investigated. A three-dimensional atmospheric vortical perturbation (atmospheric shear waves, whose velocity vector is in the horizontal plane and has a vertical wavenumber k_z≠0, can provide a vertical shear of the horizontal wind. The shear waves influence the vertical transport of heavy metallic ions and their convergence into thin and dense horizontal layers. The proposed mechanism takes into account the dynamical influence of the shear wave velocity in the horizontal wind on the vertical drift velocity of the ions. It also can explain the multi-layer structure of E_s layers. The pattern of the multi-layer structure depends on the value of the shear-wave vertical wavelength, the ion-neutral collision frequency and the direction of the background horizontal wind. The modelling of formation of sporadic E layers with a single and a double peak is presented. Also, the importance of shear wave coupling with short-period atmospheric gravity waves (AGWs on the variations of sporadic E layer ion density is examined and discussed.

EnKF OSSE Experiments Assessing the Impact of HIRAD Wind Speed and HIWRAP Radial Velocity Data on Analysis of Hurricane Karl (2010)

Science.gov (United States)

Albers, Cerese; Sippel, Jason A.; Braun, Scott A.; Miller, Timothy

2012-01-01

Previous studies (e.g., Zhang et al. 2009, Weng et al. 2011) have shown that radial velocity data from airborne and ground-based radars can be assimilated into ensemble Kalman filter (EnKF) systems to produce accurate analyses of tropical cyclone vortices, which can reduce forecast intensity error. Recently, wind speed data from SFMR technology has also been assimilated into the same types of systems and has been shown to improve the forecast intensity of mature tropical cyclones. Two instruments that measure these properties were present during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment in 2010 which sampled Hurricane Karl, and will next be co-located on the same aircraft for the subsequent NASA HS3 experiment. The High Altitude Wind and Rain Profiling Radar (HIWRAP) is a conically scanning Doppler radar mounted upon NASAs Global Hawk unmanned aerial vehicle, and the usefulness of its radial velocity data for assimilation has not been previously examined. Since the radar scans from above with a fairly large fixed elevation angle, it observes a large component of the vertical wind, which could degrade EnKF analyses compared to analyses with data taken from lesser elevation angles. The NASA Hurricane Imaging Radiometer (HIRAD) is a passive microwave radiometer similar to SFMR, and measures emissivity and retrieves hurricane surface wind speeds and rain rates over a much wider swath. Thus, this study examines the impact of assimilating simulated HIWRAP radial velocity data into an EnKF system, simulated HIRAD wind speed, and HIWRAP+HIRAD with the Weather Research and Forecasting (WRF) model and compares the results to no data assimilation and also to the Truth from which the data was simulated for both instruments.

Effect of pitch angle on power performance and aerodynamics of a vertical axis wind turbine

NARCIS (Netherlands)

Rezaeiha, A.; Kalkman, I.; Blocken, B.J.E.

2017-01-01

Due to growing interest in wind energy harvesting offshore as well as in the urban environment, vertical axis wind turbines (VAWTs) have recently received renewed interest. Their omni-directional capability makes them a very interesting option for use with the frequently varying wind directions

Potential of carbon mitigation by vertical axis wind turbines in urban regions

International Nuclear Information System (INIS)

Pope, K.; Naterer, G.F.

2009-01-01

The potential of greenhouse gas reduction with vertical axis wind turbines (VAWTs) in urban centers is examined in this paper. Four different wind turbine designs are compared, in terms of greenhouse gas reduction and specific energy distribution of the wind energy resource. A VAWT can potentially improve power generation capability in turbulent regions, where wind conditions can be represented by an exponential function. Results are presented to demonstrate that a VAWT covering one square metre, installed in 50% of Toronto residential dwellings, could mitigate between 29,193 and 138,741 tonnes of CO 2 per year. (author)

Orthogonal Analysis Based Performance Optimization for Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Lei Song

2016-01-01

Full Text Available Geometrical shape of a vertical axis wind turbine (VAWT is composed of multiple structural parameters. Since there are interactions among the structural parameters, traditional research approaches, which usually focus on one parameter at a time, cannot obtain performance of the wind turbine accurately. In order to exploit overall effect of a novel VAWT, we firstly use a single parameter optimization method to obtain optimal values of the structural parameters, respectively, by Computational Fluid Dynamics (CFD method; based on the results, we then use an orthogonal analysis method to investigate the influence of interactions of the structural parameters on performance of the wind turbine and to obtain optimization combination of the structural parameters considering the interactions. Results of analysis of variance indicate that interactions among the structural parameters have influence on performance of the wind turbine, and optimization results based on orthogonal analysis have higher wind energy utilization than that of traditional research approaches.

Wind stress, curl and vertical velocity in the Bay of Bengal during southwest monsoon, 1984

Digital Repository Service at National Institute of Oceanography (India)

Babu, M.T.; Heblekar, A.K.; Murty, C.S.

Wind distribution observed during southwest monsoon of 1984 has used to derive the mean wind stress for the season at every 1 degree square grid and curl over the Bay of Bengal. Two regions of maximum wind stress are present over the Bay of Bengal...

Numerical modeling and preliminary validation of drag-based vertical axis wind turbine

Directory of Open Access Journals (Sweden)

Krysiński Tomasz

2015-03-01

Full Text Available The main purpose of this article is to verify and validate the mathematical description of the airflow around a wind turbine with vertical axis of rotation, which could be considered as representative for this type of devices. Mathematical modeling of the airflow around wind turbines in particular those with the vertical axis is a problematic matter due to the complex nature of this highly swirled flow. Moreover, it is turbulent flow accompanied by a rotation of the rotor and the dynamic boundary layer separation. In such conditions, the key aspects of the mathematical model are accurate turbulence description, definition of circular motion as well as accompanying effects like centrifugal force or the Coriolis force and parameters of spatial and temporal discretization. The paper presents the impact of the different simulation parameters on the obtained results of the wind turbine simulation. Analysed models have been validated against experimental data published in the literature.

A 34-meter VAWT (Vertical Axis Wind Turbine) point design

Science.gov (United States)

Ashwill, T. D.; Berg, D. E.; Dodd, H. M.; Rumsey, M. A.; Sutherland, H. J.; Veers, P. S.

The Wind Energy Division at Sandia National Laboratories recently completed a point design based on the 34-m Vertical Axis Wind Turbine (VAWT) Test Bed. The 34-m Test Bed research machine incorporates several innovations that improve Darrieus technology, including increased energy production, over previous machines. The point design differs minimally from the Test Bed; but by removing research-related items, its estimated cost is substantially reduced. The point design is a first step towards a Test-Bed-based commercial machine that would be competitive with conventional sources of power in the mid-1990s.

Three-dimensional Improved Delayed Detached Eddy Simulation of a two-bladed vertical axis wind turbine

International Nuclear Information System (INIS)

Lei, Hang; Zhou, Dai; Bao, Yan; Li, Ye; Han, Zhaolong

2017-01-01

Highlights: • The Improved Delayed Detached Eddy Simulation and polyhedral mesh are utilized. • Power coefficient and wake velocity are compared between experiments and simulations. • Improved Delayed Detached Eddy Simulation shows more vortices under dynamic stall. • Different scales of flow separations are distinguished by these two models. - Abstract: The aerodynamic performance of a two-bladed vertical axis wind turbine is investigated using the turbulence model of the Improved Delayed Detached Eddy Simulation and the polyhedral mesh. The sliding mesh technique is used to simulate the rotation of the rotor. Meanwhile, the results obtained by the shear stress transport k-ω model are presented as contrast. Then, the simulated power coefficients at different tip speed ratios and the wake velocity are validated by comparison with the experimental data from available literature. It is shown that the power coefficients and wake velocity predicted by the Improved Delayed Detached Eddy Simulation are closer to the experimental data than those by the shear stress transport k-ω model. The pressure distributions predicted by the two turbulence models show different degrees of discrepancies in different scales of flow separation. By comparing the vorticity magnitude graphs, the Improved Delayed Detached Eddy Simulation is found to be able to capture more exquisite vortices after the flow separations. Limited by its inherent ability, the shear stress transport k-ω model predicts vortices that are less realistic than those of Improved Delayed Detached Eddy Simulation. Hence, it may cause some errors in predicting the pressure distributions, especially when the blades suffer dynamic stall. It is demonstrated that the Improved Delayed Detached Eddy Simulation is regarded as a reliable model to analyze the aerodynamic performance of vertical axis wine turbines.

Effect of flow velocity on the process of air-steam condensation in a vertical tube condenser

Science.gov (United States)

Havlík, Jan; Dlouhý, Tomáš

2018-06-01

This article describes the influence of flow velocity on the condensation process in a vertical tube. For the case of condensation in a vertical tube condenser, both the pure steam condensation process and the air-steam mixture condensation process were theoretically and experimentally analyzed. The influence of steam flow velocity on the value of the heat transfer coefficient during the condensation process was evaluated. For the condensation of pure steam, the influence of flow velocity on the value of the heat transfer coefficient begins to be seen at higher speeds, conversely, this effect is negligible at low values of steam velocity. On the other hand, for the air-steam mixture condensation, the influence of flow velocity must always be taken into account. The flow velocity affects the water vapor diffusion process through non-condensing air. The presence of air significantly reduces the value of the heat transfer coefficient. This drop in the heat transfer coefficient is significant at low velocities; on the contrary, the decrease is relatively small at high values of the velocity.

Estimates of vertical velocities and eddy coefficients in the Bay of Bengal

Digital Repository Service at National Institute of Oceanography (India)

Varkey, M.J.; Sastry, J.S.

Vertical velocities and eddy coefficients in the intermediate depths of the Bay of Bengal are calculated from mean hydrographic data for 300 miles-squares. The linear current density (sigma- O) versus log-depth plots show steady balance between...

Vertical-axis wind turbine development in Canada

Science.gov (United States)

Templin, R. J.; Rangi, R. S.

1983-12-01

Recent Canadian progress in the development of the curved-blade Darrieus vertical-axis wind turbine (VAWT) is described. Cooperation between government, industry and power utilities in the conduct of field trials, over several years, has demonstrated improved performance and reliability of grid-coupled turbines of this type. The rated power of the VAWTs currently under test ranges from 30 kW, in a wind/diesel powerplant, to 230 kW, in an installation on an island in the Gulf of St. Lawrence. Progress has also been made in understanding the basic aerodynamic behavior of the VAWT and theoretical methods for performance and load prediction have correspondingly improved. A brief description is given of 'Project EOLE', a cooperative project between the federal government and the utility Hydro-Quebec to develop and test, during the next two to three years, a 4 MW VAWT prototype, which will be coupled to the power grid at a location on the south shore of the St. Lawrence River.

Wind-break walls with optimized setting angles for natural draft dry cooling tower with vertical radiators

International Nuclear Information System (INIS)

Ma, Huan; Si, Fengqi; Kong, Yu; Zhu, Kangping; Yan, Wensheng

2017-01-01

Highlights: • Aerodynamic field around dry cooling tower is presented with numerical model. • Performances of cooling deltas are figured out by air inflow velocity analysis. • Setting angles of wind-break walls are optimized to improve cooling performance. • Optimized walls can reduce the interference on air inflow at low wind speeds. • Optimized walls create stronger outside secondary flow at high wind speeds. - Abstract: To get larger cooling performance enhancement for natural draft dry cooling tower with vertical cooling deltas under crosswind, setting angles of wind-break walls were optimized. Considering specific structure of each cooling delta, an efficient numerical model was established and validated by some published results. Aerodynamic fields around cooling deltas under various crosswind speeds were presented, and outlet water temperatures of the two columns of cooling delta were exported as well. It was found that for each cooling delta, there was a difference in cooling performance between the two columns, which is closely related to the characteristic of main airflow outside the tower. Using the present model, air inflow deviation angles at cooling deltas’ inlet were calculated, and the effects of air inflow deviation on outlet water temperatures of the two columns for corresponding cooling delta were explained in detail. Subsequently, at cooling deltas’ inlet along radial direction of the tower, setting angles of wind-break walls were optimized equal to air inflow deviation angles when no airflow separation appeared outside the tower, while equal to zero when outside airflow separation occurred. In addition, wind-break walls with optimized setting angles were verified to be extremely effective, compared to the previous radial walls.

Performance characteristics of a Vertical Axis Wind Turbine (VAWT) under transient conditions

OpenAIRE

Colley, Gareth; Mishra, Rakesh

2011-01-01

The present work investigates the performance characteristics of a novel Vertical Axis Wind Turbine (VAWT) for use in the urban environment. Here the performance of the wind turbine has been analyzed experimentally using a full scale prototype measuring 2.0m diameter and 1.0m in height. The turbine was located at the exit of a 0.6m x 0.6m wind tunnel section and was subjected to a jet flow. The performance output from the turbine has been obtained using a torque transducer unit which provides...

Modal analysis of a small vertical axis wind turbine (Type DARRIEUS

Directory of Open Access Journals (Sweden)

Ion NILA

2012-06-01

Full Text Available This paper reports a brief study on free vibration analysis for determining parameters such as natural frequencies and mode shapes for vertical axis wind turbines (VAWT for an urban application. This study is focused on numerical work using available finite element software. For further understanding of the wind turbine dynamic analysis, two vibration parameters of dynamic response have been studied, namely natural frequencies and mode shapes.Block Lanczos method has been used to analyze the natural frequency while wind turbine mode shapes have been utilized because of their accuracy and faster solution. In this problem 12 modes of structure have been extracted.

Vibrational analysis of vertical axis wind turbine blades

Science.gov (United States)

Kapucu, Onur

The goal of this research is to derive a vibration model for a vertical axis wind turbine blade. This model accommodates the affects of varying relative flow angle caused by rotating the blade in the flow field, uses a simple aerodynamic model that assumes constant wind speed and constant rotation rate, and neglects the disturbance of wind due to upstream blade or post. The blade is modeled as elastic Euler-Bernoulli beam under transverse bending and twist deflections. Kinetic and potential energy equations for a rotating blade under deflections are obtained, expressed in terms of assumed modal coordinates and then plugged into Lagrangian equations where the non-conservative forces are the lift and drag forces and moments. An aeroelastic model for lift and drag forces, approximated with third degree polynomials, on the blade are obtained assuming an airfoil under variable angle of attack and airflow magnitudes. A simplified quasi-static airfoil theory is used, in which the lift and drag coefficients are not dependent on the history of the changing angle of attack. Linear terms on the resulting equations of motion will be used to conduct a numerical analysis and simulation, where numeric specifications are modified from the Sandia-17m Darrieus wind turbine by Sandia Laboratories.

A study of rotor and platform design trade-offs for large-scale floating vertical axis wind turbines

Science.gov (United States)

Griffith, D. Todd; Paquette, Joshua; Barone, Matthew; Goupee, Andrew J.; Fowler, Matthew J.; Bull, Diana; Owens, Brian

2016-09-01

Vertical axis wind turbines are receiving significant attention for offshore siting. In general, offshore wind offers proximity to large populations centers, a vast & more consistent wind resource, and a scale-up opportunity, to name a few beneficial characteristics. On the other hand, offshore wind suffers from high levelized cost of energy (LCOE) and in particular high balance of system (BoS) costs owing to accessibility challenges and limited project experience. To address these challenges associated with offshore wind, Sandia National Laboratories is researching large-scale (MW class) offshore floating vertical axis wind turbines (VAWTs). The motivation for this work is that floating VAWTs are a potential transformative technology solution to reduce offshore wind LCOE in deep-water locations. This paper explores performance and cost trade-offs within the design space for floating VAWTs between the configurations for the rotor and platform.

Georges Darrieus, inventor of vertical axis wind-turbines; Georges Darrieus, pere des eoliennes a axe vertical

Energy Technology Data Exchange (ETDEWEB)

Rogier, E.

2000-10-01

This article is a short biography of the French man Georges Darrieus (1888-1979) who invented the vertical wind turbine. G.Darrieus can be considered as the first industrial researcher in France, he was a double authority in sciences and in industry machinery. He presented more than 50 patterns and wrote about 700 scientific and technological articles.

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

Aeroelastic Stability Investigations for Large-scale Vertical Axis Wind Turbines

International Nuclear Information System (INIS)

2 P O Box 5800, Albuquerque, NM, 87185 (United States))" data-affiliation=" (Senior Member of Technical Staff, Analytical Structural Dynamics Sandia National Laboratories2 P O Box 5800, Albuquerque, NM, 87185 (United States))" >Owens, B C; 2 P O Box 5800, Albuquerque, NM, 87185 (United States))" data-affiliation=" (Principal Member of Technical Staff, Wind Energy Technologies Sandia National Laboratories2 P O Box 5800, Albuquerque, NM, 87185 (United States))" >Griffith, D T

2014-01-01

The availability of offshore wind resources in coastal regions, along with a high concentration of load centers in these areas, makes offshore wind energy an attractive opportunity for clean renewable electricity production. High infrastructure costs such as the offshore support structure and operation and maintenance costs for offshore wind technology, however, are significant obstacles that need to be overcome to make offshore wind a more cost-effective option. A vertical-axis wind turbine (VAWT) rotor configuration offers a potential transformative technology solution that significantly lowers cost of energy for offshore wind due to its inherent advantages for the offshore market. However, several potential challenges exist for VAWTs and this paper addresses one of them with an initial investigation of dynamic aeroelastic stability for large-scale, multi-megawatt VAWTs. The aeroelastic formulation and solution method from the BLade Aeroelastic STability Tool (BLAST) for HAWT blades was employed to extend the analysis capability of a newly developed structural dynamics design tool for VAWTs. This investigation considers the effect of configuration geometry, material system choice, and number of blades on the aeroelastic stability of a VAWT, and provides an initial scoping for potential aeroelastic instabilities in large-scale VAWT designs

Aeroelastic Stability Investigations for Large-scale Vertical Axis Wind Turbines

Science.gov (United States)

Owens, B. C.; Griffith, D. T.

2014-06-01

The availability of offshore wind resources in coastal regions, along with a high concentration of load centers in these areas, makes offshore wind energy an attractive opportunity for clean renewable electricity production. High infrastructure costs such as the offshore support structure and operation and maintenance costs for offshore wind technology, however, are significant obstacles that need to be overcome to make offshore wind a more cost-effective option. A vertical-axis wind turbine (VAWT) rotor configuration offers a potential transformative technology solution that significantly lowers cost of energy for offshore wind due to its inherent advantages for the offshore market. However, several potential challenges exist for VAWTs and this paper addresses one of them with an initial investigation of dynamic aeroelastic stability for large-scale, multi-megawatt VAWTs. The aeroelastic formulation and solution method from the BLade Aeroelastic STability Tool (BLAST) for HAWT blades was employed to extend the analysis capability of a newly developed structural dynamics design tool for VAWTs. This investigation considers the effect of configuration geometry, material system choice, and number of blades on the aeroelastic stability of a VAWT, and provides an initial scoping for potential aeroelastic instabilities in large-scale VAWT designs.

Inferring regional vertical crustal velocities from averaged relative sea level trends: A proof of concept

Directory of Open Access Journals (Sweden)

Bâki Iz H.

2017-02-01

Full Text Available This study demonstrates that relative sea level trends calculated from long-term tide gauge records can be used to estimate relative vertical crustal velocities in a region with high accuracy. A comparison of the weighted averages of the relative sea level trends estimated at six tide gauge stations in two clusters along the Eastern coast of United States, in Florida and in Maryland, reveals a statistically significant regional vertical crustal motion of Maryland with respect to Florida with a subsidence rate of −1.15±0.15 mm/yr identified predominantly due to the ongoing glacial isostatic adjustment process. The estimate is a consilience value to validate vertical crustal velocities calculated from GPS time series as well as towards constraining predictive GIA models in these regions.

EISCAT measurements of solar wind velocity and the associated level of interplanetary scintillation

Directory of Open Access Journals (Sweden)

R. A. Fallows

2002-09-01

Full Text Available A relative scintillation index can be derived from EISCAT observations of Interplanetary Scintillation (IPS usually used to study the solar wind velocity. This provides an ideal opportunity to compare reliable measurements of the solar wind velocity derived for a number of points along the line-of-sight with measurements of the overall level of scintillation. By selecting those occasions where either slow- or fast-stream scattering was dominant, it is shown that at distances from the Sun greater than 30 RS , in both cases the scintillation index fell with increasing distance as a simple power law, typically as R-1.7. The level of scintillation for slow-stream scattering is found to be 2.3 times the level for fast-stream scattering.Key words. Interplanetary physics (solar wind plasma

Vertical axis wind turbines : past initiatives and future prospects

Energy Technology Data Exchange (ETDEWEB)

Islam, M.; Fartaj, A.; Ting, D. [Windsor Univ., ON (Canada). Dept. of Mechanical, Automotive and Materials Engineering

2003-08-01

Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT) are the two categories of modern wind turbines used for producing electricity and pumping water. While their popularity declined in the 1970s and 1980s to more economical fossil fuel resources, many countries have expressed a renewed interest in wind power in response to environmental concerns and energy security. Renewable energy sources supply more than 14 per cent of the total global energy demand, and wind energy plays the biggest role. In 2002, more than $7 billion was invested in wind technology. Canada has been a leader in VAWT technology. In 1966, Engineers at the Low Speed Aerodynamics Laboratory of the National Research Council devised a VAWT configuration with non-adjustable hoop-shaped airfoils that had greater efficiency that conventional high-solidity VAWT. In the early 1980s, a multi-megawatt VAWT was built in Quebec under the auspices of the EOLE project. The EOLE is the largest VAWT in the world. In 1980, Canada's national Atlantic Wind Test Site was developed for the purpose of testing and developing wind technology. Research at this facility has focused on dynamically soft Darrieus rotors, a concept which can reduce structural loads. Early development has shown that although VAWT is slightly less efficient than HAWT, it can be built larger and more cost effectively. This paper presents the outstanding features of VAWT products including the Solwind SW 10/4800 series VAWT, the Chinook 2000 wind turbine, the Ropatec Windrotor, the Windside Turbine, the VAWTEX, the Windstar VAWT, and Windtec. 19 refs., 13 figs.

Standard deviation of vertical two-point longitudinal velocity differences in the atmospheric boundary layer.

Science.gov (United States)

Fichtl, G. H.

1971-01-01

Statistical estimates of wind shear in the planetary boundary layer are important in the design of V/STOL aircraft, and for the design of the Space Shuttle. The data analyzed in this study consist of eleven sets of longitudinal turbulent velocity fluctuation time histories digitized at 0.2 sec intervals with approximately 18,000 data points per time history. The longitudinal velocity fluctuations were calculated with horizontal wind and direction data collected at the 18-, 30-, 60-, 90-, 120-, and 150-m levels. The data obtained confirm the result that Eulerian time spectra transformed to wave-number spectra with Taylor's frozen eddy hypothesis possess inertial-like behavior at wave-numbers well out of the inertial subrange.

Design of multi-energy Helds coupling testing system of vertical axis wind power system

Science.gov (United States)

Chen, Q.; Yang, Z. X.; Li, G. S.; Song, L.; Ma, C.

2016-08-01

The conversion efficiency of wind energy is the focus of researches and concerns as one of the renewable energy. The present methods of enhancing the conversion efficiency are mostly improving the wind rotor structure, optimizing the generator parameters and energy storage controller and so on. Because the conversion process involves in energy conversion of multi-energy fields such as wind energy, mechanical energy and electrical energy, the coupling effect between them will influence the overall conversion efficiency. In this paper, using system integration analysis technology, a testing system based on multi-energy field coupling (MEFC) of vertical axis wind power system is proposed. When the maximum efficiency of wind rotor is satisfied, it can match to the generator function parameters according to the output performance of wind rotor. The voltage controller can transform the unstable electric power to the battery on the basis of optimizing the parameters such as charging times, charging voltage. Through the communication connection and regulation of the upper computer system (UCS), it can make the coupling parameters configure to an optimal state, and it improves the overall conversion efficiency. This method can test the whole wind turbine (WT) performance systematically and evaluate the design parameters effectively. It not only provides a testing method for system structure design and parameter optimization of wind rotor, generator and voltage controller, but also provides a new testing method for the whole performance optimization of vertical axis wind energy conversion system (WECS).

A model for the response of vertical axis wind turbines to turbulent flow: Parts 1 and 2

Science.gov (United States)

Malcolm, D. R.

1988-07-01

This report describes a project intended to incorporate the effects of atmospheric turbulence into the structural response of Darrieus rotor, vertical axis wind turbines. The basis of the technique is the generation of a suitable time series of wind velocities, which are passed through a double multiple streamtube aerodynamic representation of the rotor. The aerodynamic loads are decomposed into components of the real eigenvectors of the rotor and subsequently into full-power and cross-spectral densities. These modal spectra are submitted as input to a modified NASTRAN random load analysis and the power spectra of selected responses are obtained. This procedure appears to be successful. Results at zero turbulence agree with alternative solutions, and when turbulence is included, the predicted stress spectra for the Indal 6400 rotor are in good agreement with field data. The model predicts that the effect of turbulence on harmonic frequency peaks and on all lead-lag bending will not be great. However, it appears that only 11 percent turbulence intensity can almost double the rms of cyclic flatwise blade bending.

Determination of vertical velocities in the equatorial part of the western Indian Ocean

Digital Repository Service at National Institute of Oceanography (India)

Bahulayan, N.; Varadachari, V.V.R.

Using steady state two-dimensional turbulent diffusion equations of salt and heat some important characteristics of vertical circulation in the equatorial part of the Indian Ocean have been evaluated and discussed. Upwelling and sinking velocities...

Gravity effects on wind-induced flutter of leaves

Science.gov (United States)

Clemmer, Nickalaus; Kopperstad, Karsten; Solano, Tomas; Shoele, Kourosh; Ordonez, Juan

2017-11-01

Wind-Induced flutter of leaves depends on both wind velocity and the gravity. To study the gravitational effects on the oscillatory behavior of leaves in the wind, a wind tunnel that can be tilted about the center of the test section is created. This unique rotation capability allows systematic investigation of gravitational effects on the fluttering response of leaves. The flow-induced vibration will be studied for three different leaves at several different tilting angles including the wind travels horizontally, vertically downward and vertically upward. In each situation, the long axis of a leaf is placed parallel to the wind direction and its response is studied at different flow speed. Oscillation of the leaf is recorded via high-speed camera at each of setup, and the effect of the gravity on stabilizing or destabilizing the fluttering response is investigated. Summer REU student at Florida State University.

Aerodynamic Optimization of Vertical Axis Wind Turbine with Trailing Edge Flap

DEFF Research Database (Denmark)

Ertem, Sercan; Ferreira, Carlos Simao; Gaunaa, Mac

2016-01-01

Vertical Axis Wind Turbines (VAWT) are competitive concepts for very large scale (10-20 MW)floating ofshore applications. Rotor circulation control (loading control) opens a wide design space to enhance the aerodynamic and operational features of VAWT. The modied linear derivation of the Actuator...

Effects of Wind Velocity Driven by Alfven Waves on the Line Profiles for 32 CYG

Directory of Open Access Journals (Sweden)

Kyung-Mee Kim

1996-06-01

Full Text Available We calculate the theoretical line profiles for 32 Cyg in order to investigate the influence of various velocity fields. Line profiles are calculated with wind accelerations driven by Alfven waves and described by velocity parameters. The results for Alfvenic wave model show weakened line profiles. For the orbital phases ¥÷=0.78 and ¥÷=0.06 the Alfvenic models show strong absorption part due to very low densities at the surface of the supergiant. Hence, we conclude the velocity gradient of the wind near the supergiant could influence on the theoretical line formation.

Numerical study on aerodynamic damping of floating vertical axis wind turbines

DEFF Research Database (Denmark)

Cheng, Zhengshun; Aagaard Madsen, Helge; Gao, Zhen

2016-01-01

Harvesting offshore wind energy resources using floating vertical axis wind turbines (VAWTs) has attracted an increasing interest in recent years. Due to its potential impact on fatigue damage, the aerodynamic damping should be considered in the preliminary design of a floating VAWT based...... on the frequency domain method. However, currently the study on aerodynamic damping of floating VAWTs is very limited. Due to the essential difference in aerodynamic load characteristics, the aerodynamic damping of a floating VAWT could be different from that of a floating horizontal axis wind turbine (HAWT...... to four were considered. The aerodynamic damping under steady and turbulent wind conditions were estimated using fully coupled aero-hydro-servo-elastic time domain simulations. It is found that the aerodynamic damping ratio of the considered floating VAWTs ranges from 1.8% to 5.3%. Moreover...

Wind tunnel testing of scaled models of a newly developed Darrieus-style vertical axis wind turbine with auxiliary straight blades

International Nuclear Information System (INIS)

Scungio, M.; Arpino, F.; Focanti, V.; Profili, M.; Rotondi, M.

2016-01-01

Highlights: • Wind tunnel investigations of Darrieus-style VAWT with auxiliary blades have been made. • Results have been compared with those from standard Darrieus VAWT. • Static and dynamic power and torque coefficients were measured and evaluated. • The auxiliary airfoils have demonstrated to give more torque at the lower wind speeds. • The proposed VAWT configuration is able to work in a wide range of wind speeds. - Abstract: Renewable sources of energy, needed because of the increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in wind energy. Among the different typologies, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, wind tunnel investigations about the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds, has been made on scaled models. The micro turbine under investigation consists of three pairs of airfoils. Each pair consists of a main and auxiliary airfoil with different chord lengths. A standard Darrieus configuration, consisting of three single airfoils, was also tested for comparison. The experiments were conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). Measured data were reported in terms of dimensionless power and torque coefficients for dynamic performance analysis and static torque coefficient for static performance analysis. The adoption of auxiliary airfoils has demonstrated to give more dynamic torque at the lower wind speeds with respect to a standard Darrieus rotor, resulting in better performance for all the wind speeds considered. In terms of dynamic power coefficient, the standard Darrieus

The combined effect of wind and rain on interrill erosion processes

International Nuclear Information System (INIS)

Erpul, G.; Gabriels, D.; Norton, L.D.

2004-01-01

Wind-driven rain is described as raindrops falling through a wind field at an angle from vertical under the effects of both gravitational and drag forces. Wind-driven raindrops gain some degree of horizontal velocity and strike the soil surface with an angle deviated from vertical. Additionally, the distribution and intensity of rainfall on sloping surfaces differs depending on wind direction and velocity. The changes in raindrop trajectory and frequency with wind velocity and direction can have significant effects on rain splash detachment process. The resultant impact velocity, impact angle, and impact frequency of raindrops determine the magnitude of rain splash detachment by wind-driven rain. This differs from the detachment process by windless rain, in which a straight-line trajectory of raindrops and accordingly greatest rainfall intensity for a given rain are implicitly assumed. Wind, as well as slope and overland flow, is another possible factor capable of transporting detached particles by raindrop impact. Once soil particles are entrained in the splash droplets that have risen into the air by raindrop impact, wind velocity gradient will transport these particles. Obviously, in addition to its role in the rain splash detachment process, the wind accompanying rain is an important consideration in the rain splash transport process, which can cause a net transportation in wind direction. In wind-driven rains, wind velocity and direction is expected to affect not only rain splash detachment and transport processes but also shallow flow sediment transport induced by raindrop impacts with an angle on flow and the rain splash trajectories of soil particles within flow. Under wind-driven rain, the interrill transport process is a combined work of both rain splash sediment transport and raindrop-impacted shallow flow sediment transport. The rain splash process acts alone until runoff occurs, and net soil transport is caused by wind. As soon as runoff starts, the

Analysis of trends between solar wind velocity and energetic electron fluxes at geostationary orbit using the reverse arrangement test

Science.gov (United States)

Aryan, Homayon; Boynton, Richard J.; Walker, Simon N.

2013-02-01

A correlation between solar wind velocity (VSW) and energetic electron fluxes (EEF) at the geosynchronous orbit was first identified more than 30 years ago. However, recent studies have shown that the relation between VSW and EEF is considerably more complex than was previously suggested. The application of process identification technique to the evolution of electron fluxes in the range 1.8 - 3.5 MeV has also revealed peculiarities in the relation between VSW and EEF at the geosynchronous orbit. It has been revealed that for a constant solar wind density, EEF increase with VSW until a saturation velocity is reached. Beyond the saturation velocity, an increase in VSW is statistically not accompanied with EEF enhancement. The present study is devoted to the investigation of saturation velocity and its dependency upon solar wind density using the reverse arrangement test. In general, the results indicate that saturation velocity increases as solar wind density decreases. This implies that solar wind density plays an important role in defining the relationship between VSW and EEF at the geosynchronous orbit.

Conceptual Design of a Floating Support Structure and Mooring System for a Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Berthelsen, Petter Andreas; Fylling, Ivar; Vita, Luca

2012-01-01

This paper deals with the conceptual design of a floating support structure and mooring system for a 5MW vertical axis offshore wind turbine. The work is carried out as part of the DeepWind project, where the main objective is to investigate the feasibility of a floating vertical axis offshore wind...... turbine. The DeepWind concept consists of a Darrieus rotor mounted on a spar buoy support structure. The conceptual design is carried out in an iterative process, involving the different subcomponents. The present work is part of the first design iteration and the objective is to find a feasible floating...... support structure and mooring system for the DeepWind concept. The conceptual design is formulated as an optimization problem: Starting with an initial configuration, the optimization procedure tries to find a cheaper solution while satisfying a set of design requirements. This approach utilizes available...

Mean vertical wind in the mesosphere-lower thermosphere region (80–120 km deduced from the WINDII observations on board UARS

Directory of Open Access Journals (Sweden)

V. Fauliot

1997-09-01

Full Text Available The WINDII interferometer placed on board the Upper Atmosphere Research Satellite measures temperature and wind from the O(1S green-line emission in the Earth's mesosphere and lower thermosphere. It is a remote-sensing instrument providing the horizontal wind components. In this study, the vertical winds are derived using the continuity equation. Mean wind annually averaged at equinoxes and solstices is shown. Ascendance and subsidence to the order of 1–2 cm s–1 present a seasonal occurrence at the equator and tropics. Zonal Coriolis acceleration and adiabatic heating and cooling rate associated to the mean meridional and vertical circulations are evaluated. The line emission rate measured together with the horizontal wind shows structures in altitude and latitude correlated with the meridional and vertical wind patterns. The effect of wind advection is discussed.

Vertical Descent and Landing Tests of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane in Still Air, TED No. NACA DE 368

Science.gov (United States)

Smith, Charlee C., Jr.; Lovell, Powell M., Jr.

1954-01-01

An investigation is being conducted to determine the dynamic stability and control characteristics of a 0.13-scale flying model of Convair XFY-1 vertically rising airplane. This paper presents the results of flight and force tests to determine the stability and control characteristics of the model in vertical descent and landings in still air. The tests indicated that landings, including vertical descent from altitudes representing up to 400 feet for the full-scale airplane and at rates of descent up to 15 or 20 feet per second (full scale), can be performed satisfactorily. Sustained vertical descent in still air probably will be more difficult to perform because of large random trim changes that become greater as the descent velocity is increased. A slight steady head wind or cross wind might be sufficient to eliminate the random trim changes.

Reliability Estimation of Parameters of Helical Wind Turbine with Vertical Axis

Directory of Open Access Journals (Sweden)

Adela-Eliza Dumitrascu

2015-01-01

Full Text Available Due to the prolonged use of wind turbines they must be characterized by high reliability. This can be achieved through a rigorous design, appropriate simulation and testing, and proper construction. The reliability prediction and analysis of these systems will lead to identifying the critical components, increasing the operating time, minimizing failure rate, and minimizing maintenance costs. To estimate the produced energy by the wind turbine, an evaluation approach based on the Monte Carlo simulation model is developed which enables us to estimate the probability of minimum and maximum parameters. In our simulation process we used triangular distributions. The analysis of simulation results has been focused on the interpretation of the relative frequency histograms and cumulative distribution curve (ogive diagram, which indicates the probability of obtaining the daily or annual energy output depending on wind speed. The experimental researches consist in estimation of the reliability and unreliability functions and hazard rate of the helical vertical axis wind turbine designed and patented to climatic conditions for Romanian regions. Also, the variation of power produced for different wind speeds, the Weibull distribution of wind probability, and the power generated were determined. The analysis of experimental results indicates that this type of wind turbine is efficient at low wind speed.

Reliability Estimation of Parameters of Helical Wind Turbine with Vertical Axis.

Science.gov (United States)

Dumitrascu, Adela-Eliza; Lepadatescu, Badea; Dumitrascu, Dorin-Ion; Nedelcu, Anisor; Ciobanu, Doina Valentina

2015-01-01

Due to the prolonged use of wind turbines they must be characterized by high reliability. This can be achieved through a rigorous design, appropriate simulation and testing, and proper construction. The reliability prediction and analysis of these systems will lead to identifying the critical components, increasing the operating time, minimizing failure rate, and minimizing maintenance costs. To estimate the produced energy by the wind turbine, an evaluation approach based on the Monte Carlo simulation model is developed which enables us to estimate the probability of minimum and maximum parameters. In our simulation process we used triangular distributions. The analysis of simulation results has been focused on the interpretation of the relative frequency histograms and cumulative distribution curve (ogive diagram), which indicates the probability of obtaining the daily or annual energy output depending on wind speed. The experimental researches consist in estimation of the reliability and unreliability functions and hazard rate of the helical vertical axis wind turbine designed and patented to climatic conditions for Romanian regions. Also, the variation of power produced for different wind speeds, the Weibull distribution of wind probability, and the power generated were determined. The analysis of experimental results indicates that this type of wind turbine is efficient at low wind speed.

Satellite based wind resource assessment over the South China Sea

DEFF Research Database (Denmark)

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

2014-01-01

variations are clearly visible across the domain; for instance sheltering effects caused by the land masses. The satellite based wind resource maps have two shortcomings. One is the lack of information at the higher vertical levels where wind turbines operate. The other is the limited number of overlapping...... years of WRF data – specifically the parameters heat flux, air temperature, and friction velocity – are used to calculate a long-term correction for atmospheric stability effects. The stability correction is applied to the satellite based wind resource maps together with a vertical wind profile...... from satellite synthetic aperture radar (SAR) data are particularly suitable for offshore wind energy applications because they offer a spatial resolution up to 500 m and include coastal seas. In this presentation, satellite wind maps are used in combination with mast observations and numerical...

One Year of Vertical Wind Profiles Measurements at a Mediterranean Coastal Site of South Italy

DEFF Research Database (Denmark)

Calidonna, Claudia Roberta; Gullì, Daniel; Avolio, Elenio

2015-01-01

To exploit wind energy both onshore and offshore in coastal area the effect of the coastal discontinuity is important. The shape of the vertical wind profiles and the related c parameter of the Weibull distribution are impacted by the atmospheric internal boundary layers developing from the coast...

Mean vertical wind in the mesosphere-lower thermosphere region (80–120 km deduced from the WINDII observations on board UARS

Directory of Open Access Journals (Sweden)

V. Fauliot

Full Text Available The WINDII interferometer placed on board the Upper Atmosphere Research Satellite measures temperature and wind from the O(¹S green-line emission in the Earth's mesosphere and lower thermosphere. It is a remote-sensing instrument providing the horizontal wind components. In this study, the vertical winds are derived using the continuity equation. Mean wind annually averaged at equinoxes and solstices is shown. Ascendance and subsidence to the order of 1–2 cm s^–1 present a seasonal occurrence at the equator and tropics. Zonal Coriolis acceleration and adiabatic heating and cooling rate associated to the mean meridional and vertical circulations are evaluated. The line emission rate measured together with the horizontal wind shows structures in altitude and latitude correlated with the meridional and vertical wind patterns. The effect of wind advection is discussed.

Computational Fluid Dynamics based Fault Simulations of a Vertical Axis Wind Turbines

International Nuclear Information System (INIS)

Park, Kyoo-seon; Asim, Taimoor; Mishra, Rakesh

2012-01-01

Due to depleting fossil fuels and a rapid increase in the fuel prices globally, the search for alternative energy sources is becoming more and more significant. One of such energy source is the wind energy which can be harnessed with the use of wind turbines. The fundamental principle of wind turbines is to convert the wind energy into first mechanical and then into electrical form. The relatively simple operation of such turbines has stirred the researchers to come up with innovative designs for global acceptance and to make these turbines commercially viable. Furthermore, the maintenance of wind turbines has long been a topic of interest. Condition based monitoring of wind turbines is essential to maintain continuous operation of wind turbines. The present work focuses on the difference in the outputs of a vertical axis wind turbine (VAWT) under different operational conditions. A Computational Fluid Dynamics (CFD) technique has been used for various blade configurations of a VAWT. The results indicate that there is significant degradation in the performance output of wind turbines as the number of blades broken or missing from the VAWT increases. The study predicts the faults in the blades of VAWTs by monitoring its output.

Model improvements for evaluating the effect of tower tilting on the aerodynamics of a vertical axis wind turbine

DEFF Research Database (Denmark)

Wang, K.; Hansen, Martin Otto Laver; Moan, T.

2015-01-01

If a vertical axis wind turbine is mounted offshore on a semi-submersible, the pitch motion of the platform will dominate the static pitch and dynamic motion of the platform and wind turbine such that the effect of tower tilting on the aerodynamics of the vertical axis wind turbine should...... be investigated to more accurately predict the aerodynamic loads. This paper proposes certain modifications to the double multiple-streamtube (DMS) model to include the component of wind speed parallel to the rotating shaft. The model is validated against experimental data collected on an H-Darrieus wind turbine...... in skewed flow conditions. Three different dynamic stall models are also integrated into the DMS model: Gormont's model with the adaptation of Strickland, Gormont's model with the modification of Berg and the Beddoes-Leishman dynamic stall model. Both the small Sandia 17m wind turbine and the large DeepWind...

Performance testing of a small vertical-axis wind turbine

Energy Technology Data Exchange (ETDEWEB)

Bravo, R.; Tullis, S.; Ziada, S. [McMaster Univ., Hamilton, ON (Canada). Dept. of Mechanical Engineering

2007-07-01

Full-scale wind tunnel testing of a prototype 3.5 kW vertical-axis wind turbine (VAWT) was conducted in a low speed wind tunnel in Ottawa. The tests were conducted to determine nominal power curves as well as the system's structural integrity, safety and operational characteristics. Dimensionless power curves were used to assess the relation between the wind turbine's rotary speed and the produced power for various wind speeds. Tests began at the lowest wind speed and revolutions per minute (RPM) and were gradually increased. A proximity sensor was used to determine the passing frequency of spaced bolts. The aerodynamic performance of the turbine was evaluated using a servo-controlled mechanical variable load with a disc brake calliper and electro-hydraulic servo-actuator. A load cell was used to measure torque produced by the turbine. An active closed loop speed control system was used to regulate the rotary speed of the turbine. The system used a high gain proportional control law to guarantee stability. Calculated power was based on the average rotary speed measurement. Results of the study suggested that the dimensional power performance of the turbine could be predicted from the curve for all rotary speeds and for wind speeds between 8 and 16 m/s. The maximum power coefficient of 0.3 occurred at a tip speed ratio of 1.6. Test results demonstrated that the turbine reached its rated power at 14 m/s. However, the range of tip speed ratios for power production were lower than the range for most other small VAWT. 2 refs., 3 figs.

Noise Emission of a 200 kW Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Erik Möllerström

2015-12-01

Full Text Available The noise emission from a vertical axis wind turbine (VAWT has been investigated. A noise measurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result has been compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE noise. The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to 96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimal due to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above ground was measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparison with similar size horizontal axis wind turbines (HAWTs indicates a noise emission at the absolute bottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layer trailing-edge noise, as modeled here, is much lower than the measured levels, which suggests that other mechanisms are likely to be important, such as inflow turbulence.

The boundary condition for vertical velocity and its interdependence with surface gas exchange

Science.gov (United States)

Kowalski, Andrew S.

2017-07-01

The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ. This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface). This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux-gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube - with vapour transport into an overlying, horizontal airstream - was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.

Carbon isotope evidence for the latitudinal distribution and wind speed dependence of the air-sea gas transfer velocity

International Nuclear Information System (INIS)

Krakauer, Nir Y.

2006-01-01

The air-sea gas transfer velocity is an important determinant of the exchange of gases, including CO 2 , between the atmosphere and ocean, but the magnitude of the transfer velocity and what factors control it remains poorly known. Here, we use oceanic and atmospheric observations of 14 C and 13 C to constrain the global mean gas transfer velocity as well as the exponent of its wind speed dependence, utilizing the distinct signatures left by the air-sea exchange of 14 CO 2 and 13 CO 2 . While the atmosphere and ocean inventories of 14 CO 2 and 13 CO 2 constrain the mean gas transfer velocity, the latitudinal pattern in the atmospheric and oceanic 14 C and 13 C distributions contain information about the wind speed dependence. We computed the uptake of bomb 14 C by the ocean for different transfer velocity patterns using pulse response functions from an ocean general circulation model, and evaluated the match between the predicted bomb 14 C concentrations and observationally based estimates for the 1970s-1990s. Using a wind speed climatology based on satellite measurements, we solved either for the best-fit global relationship between gas exchange and mean wind speed or for the mean gas transfer velocity over each of 11 ocean regions. We also compared the predicted consequences of different gas exchange relationships on the rate of change and interhemisphere gradient of 14 C in atmospheric CO 2 with tree-ring and atmospheric measurements. Our results suggest that globally, the dependence of the air-sea gas transfer velocity on wind speed is close to linear, with an exponent of 0.5 ± 0.4, and that the global mean gas transfer velocity at a Schmidt number of 660 is 20 ± 3 cm/hr, similar to the results of previous analyses. We find that the air-sea flux of 13 C estimated from atmosphere and ocean observations also suggests a lower than quadratic dependence of gas exchange on wind speed

Vertical axis wind rotors: Status and potential. [energy conversion efficiency and aerodynamic characteristics

Science.gov (United States)

Vance, W.

1973-01-01

The design and application of a vertical axis wind rotor is reported that operates as a two stage turbine wherein the wind impinging on the concave side is circulated through the center of the rotor to the back of the convex side, thus decreasing what might otherwise be a high negative pressure region. Successful applications of this wind rotor to water pumps, ship propulsion, and building ventilators are reported. Also shown is the feasibility of using the energy in ocean waves to drive the rotor. An analysis of the impact of rotor aspect ratio on rotor acceleration shows that the amount of venting between rotor vanes has a very significant effect on rotor speed for a given wind speed.

Controlled Velocity Testing of an 8-kW Wind Turbine

Energy Technology Data Exchange (ETDEWEB)

Larwood, S.; Sencenbaugh, J.; Acker, B.

2001-07-31

This paper describes a case study of the controlled-velocity test of an 8-kW wind turbine. The turbine was developed in response to the U.S. Department of Energy's small wind turbine program. As background, the prototype development is discussed. The turbine mechanical and electrical components are described. The turbine was tested on a flatbed truck and driven down an airfield runway at constant relative wind speed. Horizontal furling was used to control over-speed. Various parameters were changed to determine their effects on furling. The testing showed that the machine had insufficient rotor offset for adequate furling. Also, a rotor resonance problem was discovered and remedied. Problems associated with taking the measurements made it difficult to determine if the truck test was a suitable method for code validation. However, qualitative observations gleaned from the testing justified the effort.

WIND TURBINE OPERATION PARAMETER CHARACTERISTICS AT A GIVEN WIND SPEED

Directory of Open Access Journals (Sweden)

Zdzisław Kamiński

2014-06-01

Full Text Available This paper discusses the results of the CFD simulation of the flow around Vertical Axis Wind Turbine rotor. The examined rotor was designed following patent application no. 402214. The turbine operation is characterised by parameters, such as opening angle of blades, power, torque, rotational velocity at a given wind velocity. Those parameters have an impact on the performance of entire assembly. The distribution of forces acting on the working surfaces in the turbine can change, depending on the angle of rotor rotation. Moreover, the resultant force derived from the force acting on the oncoming and leaving blades should be as high as possible. Accordingly, those parameters were individually simulated over time for each blade in three complete rotations. The attempts to improve the performance of the entire system resulted in a new research trend to improve the performance of working turbine rotor blades.

Effect of operating methods of wind turbine generator system on net power extraction under wind velocity fluctuations in fields

Energy Technology Data Exchange (ETDEWEB)

Wakui, Tetsuya; Yamaguchi, Kazuya; Hashizume, Takumi [Waseda Univ., Advanced Research Inst. for Science and Engineering, Tokyo (Japan); Outa, Eisuke [Waseda Univ., Mechanical Engineering Dept., Tokyo (Japan); Tanzawa, Yoshiaki [Nippon Inst. of Technology, Mechanical Engineering Dept., Saitama (Japan)

1999-01-01

The effect of how a wind turbine generator system is operated is discussed from the viewpoint of net power extraction with wind velocity fluctuation in relation to the scale and the dynamic behaviour of the system. On a wind turbine generator system consisting of a Darrieus-Savonius hybrid wind turbine, a load generator and a battery, we took up two operating methods: constant tip speed ratio operation for a stand-alone system (Scheme 1) and synchronous operation by connecting a grid (Scheme 2). With our simulation model, using the result of the net extracting power, we clarified that Scheme 1 is more effective than Scheme 2 for small-scale systems. Furthermore, in Scheme 1, the appropriate rated power output of the system under each wind condition can be confirmed. (Author)

Design and Aero-elastic Simulation of a 5MW Floating Vertical Axis Wind Turbine

DEFF Research Database (Denmark)

Vita, Luca; Schmidt Paulsen, Uwe; Aagaard Madsen, Helge

2013-01-01

This paper deals with the design of a 5MW floating offshore Vertical Axis Wind Turbine (VAWT). The design is based on a new offshore wind turbine concept (DeepWind concept), consisting of a Darrieus rotor mounted on a spar buoy support structure, which is anchored to the sea bed with mooring lines......-DTU. The numerical simulations take into account the fully coupled aerodynamic and hydrodynamic loads on the structure, due to wind, waves and currents. The turbine is tested in operative conditions, at different sea states, selected according to the international offshore standards. The research is part...... of the European project DeepWind (2010-2014), which has been financed by the European Union (FP7-Future Emerging Technologies)....

Structural Dynamic Analysis of Semi-Submersible Floating Vertical Axis Wind Turbines

Directory of Open Access Journals (Sweden)

Jeremiah Ishie

2016-12-01

Full Text Available The strong and stable wind at offshore locations and the increasing demand for energy have made the application of wind turbines in deeper water surge. A novel concept of a 5 MW baseline Floating Vertical Axis Wind Turbine (FVAWT and a 5 MW optimised FVAWT with the DeepWind Darrieus rotor and the optimised DeepWind Darrieus rotor, respectively, were studied extensively. The structural responses, fatigue damages, platform global motions and mooring line dynamics of the FVAWTs were investigated comprehensively during normal operating conditions under steady wind and turbulent wind conditions, using a coupled non-linear aero-hydro-servo-elastic code (the Simo-Riflex-DMS code which was developed by Wang et al. for modeling FVAWTs. This coupled code incorporates the models for the turbulent wind field, aerodynamics, hydrodynamics, structural dynamics, and generator controller. The simulation is performed in a fully coupled manner in time domain. The comparison of responses under different wind conditions were used to demonstrate the effect of turbulence on both FVAWTs dynamic responses. The turbulent wind condition has the advantage of reducing the 2P effects. Furthermore, comparative studies of the FVAWTs responses were undertaken to explore the advantages of adopting the optimised 5 MW DeepWind Darrieus rotor over the baseline model. The results identified the 5 MW optimised FVAWT to having: lower Fore-Aft (FA but higher lower Side-Side (SS bending moments of structural components; lower motions amplitude; lower short-term fatigue equivalent loads and a further reduced 2P effects.

Measurements of ammonia concentrations, fluxes and dry deposition velocities to a spruce forest 1991-1995

DEFF Research Database (Denmark)

Andersen, H.V.; Hovmand, M.F.; Hummelshøj, P.

1999-01-01

The dry deposition velocities and fluxes of ammonia have been estimated from measurements of the vertical gradient of ammonia and micrometeorology above a spruce forest in western Jutland, Denmark. Measurements have been made in seven periods, each lasting about one week and covering all seasons...... measuring period characterized by easterly winds with dry conditions and high ammonia concentrations, and the emissions might relate to evaporation from ammonia saturated surfaces or emission from mineralization in the forest soil. In general, relatively high net deposition velocities were observed during...... at conditions with easterly winds, the air have passed central Jutland with large emission areas. Some of the relatively low deposition velocities or emissions were observed during conditions with low ammonia concentration and westerly winds. These observations might relate to a compensation point of the forest...

Numerical results in a vertical wind axis turbine with relative rotating blades

Energy Technology Data Exchange (ETDEWEB)

Bayeul-Laine, Annie-Claude; Dockter, Aurore; Simonet, Sophie; Bois, Gerard [Arts et Metiers PARISTECH (France)

2011-07-01

The use of wind energy to produce electricity through wind turbines has spread world-wide. The quantity of electricity produced is affected by numerous factors such as wind speed and direction and turbine design; the aim of this paper is to assess the influence of different blades on the performance of a turbine. This study was performed on a turbine in which the blades have a rotating movement, each around its own axis and around the turbine's axis. Unsteady simulations were carried out with several blade stagger angles and one wind speed and 2 different blade geometries were used for 4 rotational speeds. Results showed that the studied turbine gave better performance than vertical axis wind turbines and that blade sketch, blade speed ratios, and blade stagger angle were important influences on the performance. This study showed that this kind of turbine has the potential to achieve good performance but that further work needs to be done.

Optimal placement of horizontal - and vertical - axis wind turbines in a wind farm for maximum power generation using a genetic algorithm

Energy Technology Data Exchange (ETDEWEB)

Chen, Xiaomin; Agarwal, Ramesh [Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, Jolley Hall, Campus Box 1185, One Brookings Drive, St. Louis, Missouri, 63130 (United States)

2012-07-01

In this paper, we consider the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal –Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally position the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed.

WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. I. SUPPRESSION OF THE MAGNETOROTATIONAL INSTABILITY AND LAUNCHING OF THE MAGNETOCENTRIFUGAL WIND

International Nuclear Information System (INIS)

Bai Xuening; Stone, James M.

2013-01-01

We perform local, vertically stratified shearing-box MHD simulations of protoplanetary disks (PPDs) at a fiducial radius of 1 AU that take into account the effects of both Ohmic resistivity and ambipolar diffusion (AD). The magnetic diffusion coefficients are evaluated self-consistently from a look-up table based on equilibrium chemistry. We first show that the inclusion of AD dramatically changes the conventional picture of layered accretion. Without net vertical magnetic field, the system evolves into a toroidal field dominated configuration with extremely weak turbulence in the far-UV ionization layer that is far too inefficient to drive rapid accretion. In the presence of a weak net vertical field (plasma β ∼ 10 5 at midplane), we find that the magnetorotational instability (MRI) is completely suppressed, resulting in a fully laminar flow throughout the vertical extent of the disk. A strong magnetocentrifugal wind is launched that efficiently carries away disk angular momentum and easily accounts for the observed accretion rate in PPDs. Moreover, under a physical disk wind geometry, all the accretion flow proceeds through a strong current layer with a thickness of ∼0.3H that is offset from disk midplane with radial velocity of up to 0.4 times the sound speed. Both Ohmic resistivity and AD are essential for the suppression of the MRI and wind launching. The efficiency of wind transport increases with increasing net vertical magnetic flux and the penetration depth of the FUV ionization. Our laminar wind solution has important implications on planet formation and global evolution of PPDs.

Vertical axis wind turbine drive train transient dynamics

Science.gov (United States)

Clauss, D. B.; Carne, T. G.

1982-01-01

Start up of a vertical axis wind turbine causes transient torque oscillations in the drive train with peak torques which may be over two and one half times the rated torque of the turbine. A computer code, based on a lumped parameter model of the drive train, was developed and tested for the low cost 17 meter turbine; the results show excellent agreement with field data. The code was used to predict the effect of a slip clutch on transient torque oscillations. It was demonstrated that a slip clutch located between the motor and brake can reduce peak torques by thirty eight percent.

Measurements in support of wind farm simulations and power forecasts: The Crop/Wind-energy Experiments (CWEX)

International Nuclear Information System (INIS)

Takle, E S; Rajewski, D A; Lundquist, J K; Gallus, W A Jr; Sharma, A

2014-01-01

The Midwest US currently is experiencing a large build-out of wind turbines in areas where the nocturnal low-level jet (NLLJ) is a prominent and frequently occurring feature. We describe shear characteristics of the NLLJ and their influence on wind power production. Reports of individual turbine power production and concurrent measurements of near-surface thermal stratification are used to turbine wake interactions and turbine interaction with the overlying atmosphere. Progress in forecasting conditions such as wind ramps and shear are discussed. Finally, the pressure perturbation introduced by a line of turbines produces surface flow convergence that may create a vertical velocity and hence a mesoscale influence on cloud formation by a wind farm

Double-multiple streamtube model for studying vertical-axis wind turbines

Science.gov (United States)

Paraschivoiu, Ion

1988-08-01

This work describes the present state-of-the-art in double-multiple streamtube method for modeling the Darrieus-type vertical-axis wind turbine (VAWT). Comparisons of the analytical results with the other predictions and available experimental data show a good agreement. This method, which incorporates dynamic-stall and secondary effects, can be used for generating a suitable aerodynamic-load model for structural design analysis of the Darrieus rotor.

Adjoint Airfoil Optimization of Darrieus-Type Vertical Axis Wind Turbine

Science.gov (United States)

Fuchs, Roman; Nordborg, Henrik

2012-11-01

We present the feasibility of using an adjoint solver to optimize the torque of a Darrieus-type vertical axis wind turbine (VAWT). We start with a 2D cross section of a symmetrical airfoil and restrict us to low solidity ratios to minimize blade vortex interactions. The adjoint solver of the ANSYS FLUENT software package computes the sensitivities of airfoil surface forces based on a steady flow field. Hence, we find the torque of a full revolution using a weighted average of the sensitivities at different wind speeds and angles of attack. The weights are computed analytically, and the range of angles of attack is given by the tip speed ratio. Then the airfoil geometry is evolved, and the proposed methodology is evaluated by transient simulations.

The boundary condition for vertical velocity and its interdependence with surface gas exchange

Directory of Open Access Journals (Sweden)

A. S. Kowalski

2017-07-01

Full Text Available The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ. This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface. This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux–gradient relationships (eddy diffusivities requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal airstream – was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.

Numerical calculation of velocity distribution near a vertical flat plate immersed in bubble flow

International Nuclear Information System (INIS)

Matsuura, Akihiro; Nakamura, Hajime; Horihata, Hideyuki; Hiraoka, Setsuro; Aragaki, Tsutomu; Yamada, Ikuho; Isoda, Shinji.

1992-01-01

Liquid and gas velocity distributions for bubble flow near a vertical flat plate were calculated numerically by using the SIMPLER method, where the flow was assumed to be laminar, two-dimensional, and at steady state. The two-fluid flow model was used in the numerical analysis. To calculate the drag force on a small bubble, Stokes' law for a rigid sphere is applicable. The dimensionless velocity distributions which were arranged with characteristic boundary layer thickness and maximum liquid velocity were adjusted with a single line and their forms were similar to that for single-phase wall-jet flow. The average wall shear stress derived from the velocity gradient at the plate wall was strongly affected by bubble diameter but not by inlet liquid velocity. The present dimensionless velocity distributions obtained numerically agreed well with previous experimental results, and the proposed numerical algorithm was validated. (author)

A new vertical axis wind turbine design for urban areas

Science.gov (United States)

Frunzulica, Florin; Cismilianu, Alexandru; Boros, Alexandru; Dumitrache, Alexandru; Suatean, Bogdan

2016-06-01

In this paper we aim at developing the model of a Vertical Axis Wind Turbine (VAWT) with the short-term goal of physically realising this turbine to operate at a maximmum power of 5 kW. The turbine is designed for household users in the urban or rural areas and remote or isolated residential areas (hardly accsessible). The proposed model has a biplane configuration on each arm of the VAWT (3 × 2 = 6 blades), allowing for increased performance of the turbine at TSR between 2 and 2.5 (urban area operation) compared to the classic vertical axis turbines. Results that validate the proposed configuration as well as passive control methods to increase the performance of the classic VAWTs are presented.

Application of wind-profiling radar data to the analysis of dust weather in the Taklimakan Desert.

Science.gov (United States)

Wang, Minzhong; Wei, Wenshou; Ruan, Zheng; He, Qing; Ge, Runsheng

2013-06-01

The Urumqi Institute of Desert Meteorology of the China Meteorological Administration carried out an atmospheric scientific experiment to detect dust weather using a wind-profiling radar in the hinterland of the Taklimakan Desert in April 2010. Based on the wind-profiling data obtained from this experiment, this paper seeks to (a) analyze the characteristics of the horizontal wind field and vertical velocity of a breaking dust weather in a desert hinterland; (b) calculate and give the radar echo intensity and vertical distribution of a dust storm, blowing sand, and floating dust weather; and (c) discuss the atmosphere dust counts/concentration derived from the wind-profiling radar data. Studies show that: (a) A wind-profiling radar is an upper-air atmospheric remote sensing system that effectively detects and monitors dust. It captures the beginning and ending of a dust weather process as well as monitors the sand and dust being transported in the air in terms of height, thickness, and vertical intensity. (b) The echo intensity of a blowing sand and dust storm weather episode in Taklimakan is about -1~10 dBZ while that of floating dust -1~-15 dBZ, indicating that the dust echo intensity is significantly weaker than that of precipitation but stronger than that of clear air. (c) The vertical shear of horizontal wind and the maintenance of low-level east wind are usually dynamic factors causing a dust weather process in Taklimakan. The moment that the low-level horizontal wind field finds a shear over time, it often coincides with the onset of a sand blowing and dust storm weather process. (d) When a blowing sand or dust storm weather event occurs, the atmospheric vertical velocity tends to be of upward motion. This vertical upward movement of the atmosphere supported with a fast horizontal wind and a dry underlying surface carries dust particles from the ground up to the air to form blown sand or a dust storm.

Structure design and experimental appraisal of the drag force type vertical axis wind turbine

International Nuclear Information System (INIS)

Kim, Dong Keon; Keum, Jong Yoon; Yoon, Soon Hyun

2006-01-01

Experiments were conducted to estimate the performance of drag force type vertical axis wind turbine with an opening-shutting rotor. It was operated by the difference in drag force generated on both sides of the blades. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was measured by using a pitot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller. Various design parameters, such as the number of blades(B), blade aspect ratio(W/R), angle of blades(α) and drag coefficient acting on a blade, were considered for optimal conditions. At the experiment of miniature model, maximum efficiency was found at N=15, α=60 .deg. and W/R=0.32. The measured test variables were power, torque, rotational speed, and wind speeds. The data presented are in the form of power and torque coefficients as a function of tip-speed ratio V/U. Maximum power was found in case of Ω=0.33, when the power and torque coefficient were 0.14 and 0.37 respectively. Comparing model test with prototype test, similarity law by advance ratio for vertical axis wind turbine was confirmed

Investigation of the vertical nitrogen dioxide distribution above a frequented street

Energy Technology Data Exchange (ETDEWEB)

Malissa, H; Juette, W; Alidad, I

1975-01-01

Knowledge of the vertical nitrogen dioxide concentration profile in the atmosphere within a street canyon would enable the estimation of pollutant concentrations in street site living or working rooms and furthermore the calculation of pollutant concentrations at ground level from data measured at roof levels by means of long-line remote sensing methods. A formula was therefore derived under simplified conditions and examined by simultaneous measurements of the nitrogen dioxide concentration, wind velocity, and wind direction at roof level and ground level. The data thus obtained were average values for half an hour. The knowledge of the local vertical wind profile and the influence of the traffic density in neighboring urban areas is essential for the calculation. The verification of the derived model shows a correlation coefficient of r equals 0.88 between calculated and measured data.

Magnetometer-inferred, Equatorial, Daytime Vertical ExB Drift Velocities Observed in the African Longitude Sector

Science.gov (United States)

Anderson, D. N.; Yizengaw, E.

2011-12-01

A recent paper has investigated the sharp longitude gradients in the dayside ExB drift velocities associated with the 4-cell, non-migrating structures thought to be connected with the eastward propagating, diurnal, non-migrating (DE3) tides. Observations of vertical ExB drift velocities obtained from the Ion Velocity Meter (IVM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite were obtained in the Western Pacific, Eastern Pacific, Peruvian and Atlantic sectors for a few days during the months of October, March and December, 2009. Respective ExB drift velocity gradients at the cell boundaries for these 4 longitude sectors were a.) -1.3m/sec/degree, b.) 3m/sec/degree, c.) -4m/sec/degree and d.) 1m/sec/degree and were observed on a day-to-day basis. In this talk, we estimate the longitude gradients in the dayside, vertical ExB drift velocities from magnetometer H-component observations in the African sector. We briefly describe the technique for obtaining realistic ExB drift velocities associated with the difference in the H-component values between a magnetometer on the magnetic equator and one off the magnetic equator at 6 to 9 degrees dip latitude (delta H). We present magnetometer-inferred, dayside ExB drift velocities obtained from the AMBER (African Meridian B-field Education and Research) magnetometer chain in the East Africa (Ethiopian) longitude sector and the West African (Nigerian) longitude sector. We compare the longitude gradients in ExB drift velocities in the African sector with the C/NOFS- observed longitude gradients mentioned above. We also discuss the advantages of using ground-based magnetometer observations to infer ExB drift velocities compared with the C/NOFS satellite observations.

Characterization of aerodynamic performance of vertical axis wind turbines : impact of operational parameters

NARCIS (Netherlands)

Rezaeiha, Abdolrahim; Montazeri, Hamid; Blocken, Bert

2018-01-01

Vertical axis wind turbines (VAWTs) have received growing interest for off-shore application and in the urban environments mainly due to their omni-directional capability, scalability, robustness, low noise and costs. However, their aerodynamic performance is still not comparable with their

A case study using kinematic quantities derived from a triangle of VHF Doppler wind profilers

Science.gov (United States)

Carlson, Catherine A.; Forbes, Gregory S.

1989-01-01

Horizontal divergence, relative vorticity, kinematic vertical velocity, and geostrophic and ageostrophic winds are computed from Colorado profiler network data to investigate an upslope snowstorm in northeastern Colorado. Horizontal divergence and relative vorticity are computed using the Gauss and Stokes theorems, respectively. Kinematic vertical velocities are obtained from the surface to 9 km by vertically integrating the continuity equation. The geostrophic and ageostrophic winds are computed by applying a finite differencing technique to evaluate the derivatives in the horizontal equations of motion. Comparison of the synoptic-scale data with the profiler network data reveals that the two datasets are generally consistent. Also, the profiler-derived quantities exhibit coherent vertical and temporal patterns consistent with conceptual and theoretical flow fields of various meteorological phenomena. It is suggested that the profiler-derived quantities are of potential use to weather forecasters in that they enable the dynamic and kinematic interpretation of weather system structure to be made and thus have nowcasting and short-term forecasting value.

Visualization by PIV of dynamic stall on a vertical axis wind turbine

NARCIS (Netherlands)

Ferreira, C.J.S.; Kuik, van G.A.M.; Bussel, van G.J.W.; Scarano, F.

2009-01-01

The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV), focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior due to the variation with the azimuth angle ¿ of the

Computational analysis of vertical axis wind turbine arrays

Science.gov (United States)

Bremseth, J.; Duraisamy, K.

2016-10-01

Canonical problems involving single, pairs, and arrays of vertical axis wind turbines (VAWTs) are investigated numerically with the objective of understanding the underlying flow structures and their implications on energy production. Experimental studies by Dabiri (J Renew Sustain Energy 3, 2011) suggest that VAWTs demand less stringent spacing requirements than their horizontal axis counterparts and additional benefits may be obtained by optimizing the placement and rotational direction of VAWTs. The flowfield of pairs of co-/counter-rotating VAWTs shows some similarities with pairs of cylinders in terms of wake structure and vortex shedding. When multiple VAWTs are placed in a column, the extent of the wake is seen to spread further downstream, irrespective of the direction of rotation of individual turbines. However, the aerodynamic interference between turbines gives rise to regions of excess momentum between the turbines which lead to significant power augmentations. Studies of VAWTs arranged in multiple columns show that the downstream columns can actually be more efficient than the leading column, a proposition that could lead to radical improvements in wind farm productivity.

Wind tunnel testing of the DeepWind demonstrator in design and tilted operating conditions

DEFF Research Database (Denmark)

Battistia, L.; Benini, E.; Brighenti, A.

2016-01-01

The DeepWind Project aims at investigating the feasibility of a new floating vertical-axis wind turbine (VAWT) concept, whose purpose is to exploit wind resources at deep-water offshore sites. The results of an extensive experimental campaign on the DeepWind reduced scale demonstrator are here...... was installed on a high precision test bench, whose axis was suitable to be inclined up to 15° with respect to the design (i.e. upright) operating condition. The experiments were performed at the large scale, high speed wind tunnel of the Politecnico di Milano (Italy), using a “free jet” (open channel...... presented for different wind speeds and rotor angular velocities, including also skewed flow operation due to a tilted rotor arrangement. To accomplish this, after being instrumented to measure aerodynamic power and thrust (both in streamwise and transversal directions), a troposkien three-bladed rotor...

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 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)

Impacts of the Mesoscale Ocean-Atmosphere Coupling on the Peru-Chile Ocean Dynamics: The Current-Induced Wind Stress Modulation

Science.gov (United States)

Oerder, V.; Colas, F.; Echevin, V.; Masson, S.; Lemarié, F.

2018-02-01

The ocean dynamical responses to the surface current-wind stress interaction at the oceanic mesoscale are investigated in the South-East Pacific using a high-resolution regional ocean-atmosphere coupled model. Two simulations are compared: one includes the surface current in the wind stress computation while the other does not. In the coastal region, absolute wind velocities are different between the two simulations but the wind stress remains very similar. As a consequence, the mean regional oceanic circulation is almost unchanged. On the contrary, the mesoscale activity is strongly reduced when taking into account the effect of the surface current on the wind stress. This is caused by a weakening of the eddy kinetic energy generation near the coast by the wind work and to intensified offshore eddy damping. We show that, above coherent eddies, the current-stress interaction generates eddy damping through Ekman pumping and eddy kinetic energy dissipation through wind work. This alters significantly the coherent eddy vertical structures compared with the control simulation, weakening the temperature and vorticity anomalies and increasing strongly the vertical velocity anomalies associated to eddies.

Analysis and forecasting of wind velocity in chetumal, quintana roo, using the single exponential smoothing method

Energy Technology Data Exchange (ETDEWEB)

Cadenas, E. [Facultad de Ingenieria Mecanica, Universidad Michoacana de San Nicolas de Hidalgo, Santiago Tapia No. 403, Centro (Mexico); Jaramillo, O.A.; Rivera, W. [Centro de Ivestigacion en Energia, Universidad Nacional Autonoma de Mexico, Apartado Postal 34, Temixco 62580, Morelos (Mexico)

2010-05-15

In this paper the analysis and forecasting of wind velocities in Chetumal, Quintana Roo, Mexico is presented. Measurements were made by the Instituto de Investigaciones Electricas (IIE) during two years, from 2004 to 2005. This location exemplifies the wind energy generation potential in the Caribbean coast of Mexico that could be employed in the hotel industry in the next decade. The wind speed and wind direction were measured at 10 m above ground level. Sensors with high accuracy and a low starting threshold were used. The wind velocity was recorded using a data acquisition system supplied by a 10 W photovoltaic panel. The wind speed values were measured with a frequency of 1 Hz and the average wind speed was recorded considering regular intervals of 10 min. First a statistical analysis of the time series was made in the first part of the paper through conventional and robust measures. Also the forecasting of the last day of measurements was made utilizing the single exponential smoothing method (SES). The results showed a very good accuracy of the data with this technique for an {alpha} value of 0.9. Finally the SES method was compared with the artificial neural network (ANN) method showing the former better results. (author)

A novel vertical-axis wind turbine for distributed and utility deployment

Energy Technology Data Exchange (ETDEWEB)

Park, J.Y. [Inha Univ., Incheon (Korea, Republic of); Lee, S. [Inha Univ., Incheon (Korea, Republic of)]|[KR Wind Energy Research Inst., Incheon (Korea, Republic of); Sabourin, T.; Park, K. [KR Windpower Inc., (United States)

2008-07-01

The rapid growth in the wind power industry can be attributed to energy cost saving, power reliability, grid support, and environmental concerns. Wind turbines should also comply with community noise and aesthetic requirements as well as meet a strong need for high capacity. Wind Turbine Generator Systems are classified as either horizontal axis wind turbine (HAWT) or vertical axis wind turbine (VAWT) depending on whether their axis of rotation is parallel or perpendicular to the ground. The average electric power produced by the wind turbine is proportional to the efficiency of the rotor, air density, projected area of the turbine, and cube of wind speed. The capacity factor should be increased to guarantee the economics of the turbine via increase in the rotor size or the turbine efficiency. The low rotational speed of VAWT rotors suggests that the machine will be quieter than the high-rotational speed of HAWTs, thereby being potentially suitable for applications closer to population centres. The slow rotating machine may also be considered to be visually more aesthetic. This paper presented the measured performance of a small-scale VAWT rated as 1 kW which has a tail consisting of a stabilizer and a rudder. It was tested for its electric power produced at specified wind conditions in an open-type wind tunnel. In order to eliminate the inevitable blockage effect by the size of turbine, the flow deceleration effect of the incoming air to the turbine was analyzed through model testing and numerical simulation and implemented to the proto-type testing. The turbine and its furling tail was shown to be safe. 9 refs., 1 tab., 10 figs.

Experimental study of the effect of a slat angle on double-element airfoil and application in vertical axis wind turbine

DEFF Research Database (Denmark)

Chougule, Prasad; Rosendahl, Lasse; Nielsen, Søren R.K.

2015-01-01

A design of double-element airfoil is proposed for its use in the vertical axis wind turbine. The double-element airfoil system consists of a main airfoil and a slat airfoil. The design parameters of the double-element airfoil system are given by the position and orientation of the trailing edge......-element airfoil system designed in this paper. Further, the performance of new design of a vertical axis wind turbine shows considerable increase in the power coefficient and the total power output as compared to the reference wind turbine...

Vertical-axis wind turbine experiments at full dynamic similarity

Science.gov (United States)

Duvvuri, Subrahmanyam; Miller, Mark; Brownstein, Ian; Dabiri, John; Hultmark, Marcus

2017-11-01

This study presents results from pressurized (upto 200 atm) wind tunnel tests of a self-spinning 5-blade model Vertical-Axis Wind Turbine (VAWT). The model is geometrically similar (scale ratio 1:22) to a commercially available VAWT, which has a rotor diameter of 2.17 meters and blade span of 3.66 meters, and is used at the Stanford university field lab. The use of pressurized air as working fluid allows for the unique ability to obtain full dynamic similarity with field conditions in terms of matched Reynolds numbers (Re), tip-speed ratios (λ), and Mach number (M). Tests were performed across a wide range of Re and λ, with the highest Re exceeding the maximum operational field Reynolds number (Remax) by a factor of 3. With an extended range of accessible Re conditions, the peak turbine power efficiency was seen to occur roughly at Re = 2 Remax and λ = 1 . Beyond Re > 2 Remax the turbine performance is invariant in Re for all λ. A clear demonstration of Reynolds number invariance for an actual full-scale wind turbine lends novelty to this study, and overall the results show the viability of the present experimental technique in testing turbines at field conditions.

Velocity and phase distribution measurements in vertical air-water annular flows

International Nuclear Information System (INIS)

Vassallo, P.

1997-07-01

Annular flow topology for three air-water conditions in a vertical duct is investigated through the use of a traversing double-sensor hot-film anemometry probe and differential pressure measurements. Near wall measurements of mean and fluctuating velocities, as well as local void fraction, are taken in the liquid film, with the highest turbulent fluctuations occurring for the flow condition with the largest pressure drop. A modified law-of-the-wall formulation for wall shear is presented which, using near wall values of mean velocity and kinetic energy, agrees reasonably well with the average stress obtained from direct pressure drop measurements. The linear profile using wall coordinates in the logarithmic layer is preserved in annular flow; however, the slope and intercept of the profile differ from the single-phase values for the annular flow condition which has a thicker, more turbulent, liquid film

Velocity of large bubble in liquid-solid mixture in a vertical tube

International Nuclear Information System (INIS)

Hamaguchi, H.; Sakaguchi, T.

1995-01-01

The upward movement of a large bubble in a stationary mixture of liquid and solid is one of the most fundamental phenomena of gas-liquid-solid three phase slug flow in a vertical tube. The purpose of this study is to make clear the characteristic of the rising velocity of this fundamental flow experimentally. The rising velocity of a large bubble V in a liquid-solid mixture was measured and compared with the velocity V o in a liquid (without solid). The experimental results were correlated using a non-dimensional velocity V * (=V/V o ), and the following results were obtained. It was found that the characteristic of the rising velocity differs according to the tube diameter and the liquid viscosity, or the Galileo number in the non-dimensional expression. It can be classified into two regimes. (i) When the liquid viscosity is large (or the tube diameter is small), V * decreases linearly against the volumetric solid fraction ε of the mixture. (ii) When the viscosity is small, on the other hand, the relation between V * and ε is not linear. This classification can be explained by the results in the previous papers by the authors dealing with a large bubble in a liquid

Velocity of large bubble in liquid-solid mixture in a vertical tube

Energy Technology Data Exchange (ETDEWEB)

Hamaguchi, H.; Sakaguchi, T. [Kobe Univ., Kobe (Japan)

1995-09-01

The upward movement of a large bubble in a stationary mixture of liquid and solid is one of the most fundamental phenomena of gas-liquid-solid three phase slug flow in a vertical tube. The purpose of this study is to make clear the characteristic of the rising velocity of this fundamental flow experimentally. The rising velocity of a large bubble V in a liquid-solid mixture was measured and compared with the velocity V{sub o} in a liquid (without solid). The experimental results were correlated using a non-dimensional velocity V{sup *}(=V/V{sub o}), and the following results were obtained. It was found that the characteristic of the rising velocity differs according to the tube diameter and the liquid viscosity, or the Galileo number in the non-dimensional expression. It can be classified into two regimes. (i) When the liquid viscosity is large (or the tube diameter is small), V{sup *} decreases linearly against the volumetric solid fraction {epsilon} of the mixture. (ii) When the viscosity is small, on the other hand, the relation between V{sup *} and {epsilon} is not linear. This classification can be explained by the results in the previous papers by the authors dealing with a large bubble in a liquid.

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

Estimation of the variations of ventilation rate and indoor radon concentration using the observed wind velocity and indoor-outdoor temperature difference

International Nuclear Information System (INIS)

Nagano, Katsuhiro; Inose, Yuichi; Kojima, Hiroshi

2006-01-01

The indoor radon concentration in the building depends on the ventilation rate. Measurement results of indoor-outdoor pressure difference showed the ventilation rate correlated closely with the indoor-outdoor pressure difference. The observation results showed that one of factor of indoor-outdoor pressure difference was the wind velocity. When the wind velocity is small, the ventilation rate is affected by the indoor-outdoor temperature difference and the effect depends on the wind velocity. The temporal variation of indoor radon concentration was predicted by the time depending indoor radon balance model and the ventilation rate estimated from the wind velocity and the indoor-outdoor temperature difference. The temporal variations of predicted radon concentration gave good agreement with the experimental values. The measurement method, indoor radon concentration and ventilation rate, factors of temporal variation of ventilation rate, and prediction of indoor radon concentration are reported. (S.Y.)

Study of large-scale vertical axis wind turbine wake through numerical modelling and fullscale experiments

DEFF Research Database (Denmark)

Immas, Alexandre; Kluczewska-Bordier, Joanna; Beneditti, Pascal

Offshore wind capacity is increasing exponentially over the years in Europe, taking advantage of the strong winds available over the ocean and of the political incentives to reduce greenhouse gases. The technology is however not yet competitive when compared to fossil fuels or onshore wind. One k...... horizontal axis wind turbine wind farm....... improvement that could make offshore wind more attractive is the reduction of the wake effect [1]. The latter corresponds to the velocity deficit generated by each wind turbine wake which affects the production of the others. This effect accounts for approximately 10% of the energy losses for a typical......Offshore wind capacity is increasing exponentially over the years in Europe, taking advantage of the strong winds available over the ocean and of the political incentives to reduce greenhouse gases. The technology is however not yet competitive when compared to fossil fuels or onshore wind. One key...

A short review of recent research activities for characterization of aerodynamic optimization of vertical axis wind turbines

NARCIS (Netherlands)

Rezaeiha, A.; Kalkman, I.; Blocken, B.J.E.

2017-01-01

There is a growing interest in wind energy harvesting in the built environment. Vertical axis wind turbines (VAWT) seem to represent an ideal candidate for this purpose due to their omni-directional operation. However, as a result of a comparatively small amount of research on VAWTs during the last

Effect of the number of blades on the dynamics of floating straight-bladed vertical axis wind turbines

DEFF Research Database (Denmark)

Cheng, Zhengshun; Aagaard Madsen, Helge; Gao, Zhen

2017-01-01

Floating vertical axis wind turbines (VAWTs) are promising solutions for exploiting the wind energy resource in deep waters due to their potential cost-of-energy reduction. The number of blades is one of the main concerns when designing a VAWT for offshore application. In this paper, the effect...

Characteristics of low-mass-velocity vertical gas-liquid two-phase flow

International Nuclear Information System (INIS)

Adachi, Hiromichi; Abe, Yutaka; Kimura, Ko-ji

1995-01-01

In the present paper, characteristics of low mass velocity two-phase flow was analyzed based on a concept that pressure energy of two-phase flow is converted into acceleration work, gravitational work and frictional work, and the pressure energy consumption rate should be minimum at the stable two-phase flow condition. Experimental data for vertical upward air-water two-phase flow at atmospheric pressure was used to verify this concept and the turbulent model used in this method is optimized with the data. (author)

Turbulent Flow Inside and Above a Wind Farm: A Wind-Tunnel Study

Directory of Open Access Journals (Sweden)

Leonardo P. Chamorro

2011-11-01

Full Text Available Wind-tunnel experiments were carried out to better understand boundary layer effects on the flow pattern inside and above a model wind farm under thermally neutral conditions. Cross-wire anemometry was used to characterize the turbulent flow structure at different locations around a 10 by 3 array of model wind turbines aligned with the mean flow and arranged in two different layouts (inter-turbine separation of 5 and 7 rotor diameters in the direction of the mean flow by 4 rotor diameters in its span. Results suggest that the turbulent flow can be characterized in two broad regions. The first, located below the turbine top tip height, has a direct effect on the performance of the turbines. In that region, the turbulent flow statistics appear to reach equilibrium as close as the third to fourth row of wind turbines for both layouts. In the second region, located right above the first one, the flow adjusts slowly. There, two layers can be identified: an internal boundary layer where the flow is affected by both the incoming wind and the wind turbines, and an equilibrium layer, where the flow is fully adjusted to the wind farm. An adjusted logarithmic velocity distribution is observed in the equilibrium layer starting from the sixth row of wind turbines. The effective surface roughness length induced by the wind farm is found to be higher than that predicted by some existing models. Momentum recovery and turbulence intensity are shown to be affected by the wind farm layout. Power spectra show that the signature of the tip vortices, in both streamwise and vertical velocity components, is highly affected by both the relative location in the wind farm and the wind farm layout.

Aerodynamic characteristics of an oscillating airfoil. [For Vertical Axis Wind Turbine

Energy Technology Data Exchange (ETDEWEB)

Wickens, R H

1986-03-01

Results are reported from wind tunnel tests to study the effects of dynamic aerodynamics on the efficiency of a NACA 0018 airfoil used on a Darreius vertical axis wind turbine (VAWT). The topic is of interest because of uncontrolled pitching which occurs during operation and which produces stall, turbulence and separation effects that reduce efficiency. Present stream-tube theory and axial momentum models are not applicable in the unstable regimes. The wind tunnel tests were conducted with a 45 m/sec flow with an Re of 1.5 million. The situation mimicked typical wind turbine operational conditions. The airfoil was mounted on a hydraulic actuator to allow it to rotate about its quarter-chord location and to control the extent and frequency of oscillations. Data were also gathered on the performance in a steady flow for comparative purposes. Summary data are provided on the static and total pressures over a complete cycle of oscillation, and related to the angles of attack, time of onset of stall, and the lift and drag coefficients. The limitations of the study with regard to the absence of consideration of the flow acceleration experienced by an advancing blade are noted. 13 references.

On the ideal and real energy conversion in a straight bladed vertical axis wind turbine. The actuator cylinder flow model compared with experiment

Energy Technology Data Exchange (ETDEWEB)

Aaagard Madsen, H.

1983-01-01

The ideal and the real energy conversion in a straight bladed vertical axis wind turbine (VAWT) with variable pitch has been studied on basis of the actuator cylinder flow model and experimental data from free wind tests on a 9 m/sup 2/ turbine. Particularly, the theoretical upper power limit of VAWT's has been focused upon in the light of the already existing theories for horizontal axis wind turbines (HAWT's). A remarkable result, differing from prior theories, has turned out through the computations with the actuator cylinder flow model and that is: The maximum ideal power coefficient for VAWT's seams neither to be bounded by the Lanchester-Betz power coefficient limit of 16/27 (actuator disc concept), nor by Glauert's ideal power coefficient curve (taking into account the tip speed ratio), both limits derived with particular reference to HAWT's. Concerning the agreement between analysis and the measurements of the power coefficient, the rotor drag coefficient and the flow velocity vector adjacent to the swept area, it was in general found to be good. However, there seems still to be need for future research on the influence of turbulence in the free wind and dynamic stall on the real energy conversion in VAWT's.

Investigation of the aerodynamics of an innovative vertical-axis wind turbine

International Nuclear Information System (INIS)

Kludzinska, K; Tesch, K; Doerffer, P

2014-01-01

This paper presents a preliminary three dimensional analysis of the transient aerodynamic phenomena occurring in the innovative modification of classic Savonius wind turbine. An attempt to explain the increased efficiency of the innovative design in comparison with the traditional solution is undertaken. Several vorticity measures such as enstrophy, absolute helicity and the integral of the velocity gradient tensor second invariant are proposed in order to evaluate and compare designs. Discussed criteria are related to the vortex structures and energy dissipation. These structures are generated by the rotor and may affect the efficiency. There are also different vorticity measure taking advantage of eigenvalues of the velocity gradient tensor.

Observation and modeling of tide- and wind-induced surface currents in Galway Bay

Directory of Open Access Journals (Sweden)

Lei REN

2015-10-01

Full Text Available A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers (ADCPs and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code (EFDC, was developed based on a terrain-following vertical (sigma coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models using different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tide- and wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.

A Large-Eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer

Science.gov (United States)

Shamsoddin, Sina; Porté-Agel, Fernando

2017-04-01

In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs) exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs). Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES). To do this, we use a previously-validated LES framework in which an actuator line model (ALM) is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as Nc/R, where N is the number of blades, c is the chord length and R is the rotor radius) and tip-speed ratio is found to be 0.18 and 4.5, respectively. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulence wake flow statistics. It is found that for this case, the maximum velocity deficit at the equator height of the turbine occurs 2.7 rotor diameters downstream of the center of the turbine, and only after that point, the wake starts to recover. Moreover, it is observed that the maximum turbulence intensity (TI) at the equator height of the turbine occurs at a distance of about 3.8 rotor diameters downstream of the turbine. As we move towards the upper and lower edges of the turbine, the maximum TI (at a certain height) increases, and its location moves relatively closer to the turbine. Furthermore, whereas both TI and turbulent momentum flux fields show clear vertical asymmetries (with larger magnitudes at the upper wake edge

A Large-Eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer

Directory of Open Access Journals (Sweden)

Sina Shamsoddin

2016-05-01

Full Text Available In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs. Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES. To do this, we use a previously-validated LES framework in which an actuator line model (ALM is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as N c / R , where N is the number of blades, c is the chord length and R is the rotor radius and tip-speed ratio is found to be 0.18 and 4.5, respectively. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulence wake flow statistics. It is found that for this case, the maximum velocity deficit at the equator height of the turbine occurs 2.7 rotor diameters downstream of the center of the turbine, and only after that point, the wake starts to recover. Moreover, it is observed that the maximum turbulence intensity (TI at the equator height of the turbine occurs at a distance of about 3.8 rotor diameters downstream of the turbine. As we move towards the upper and lower edges of the turbine, the maximum TI (at a certain height increases, and its location moves relatively closer to the turbine. Furthermore, whereas both TI and turbulent momentum flux fields show clear vertical asymmetries (with larger magnitudes at the

Preliminary tests of a high speed vertical axis windmill model

Energy Technology Data Exchange (ETDEWEB)

South, P; Rangi, R S

1971-01-01

This report discusses a fixed-pitch vertical axis windmill that combines the inherent simplicity of this type of machine with a high aerodynamic efficiency and a high relative velocity. A three-bladed rotor was selected as the basic design, having constant chord symmetric airfoil blades configured in a catenary curve such that the rotor diameter is equal to the rotor height. In wind tunnel tests using a 30 inch scale model, it was found that once this rotor was given a very low rotational speed, it picked up speed and ran at a rotor tip velocity/wind speed ratio greater than 1. The number of blades was varied in the testing. A maximum power coefficient of 0.67 was achieved at 17 ft/s wind speed at a tip speed/wind speed ratio of 7.25 for a 2-bladed rotor. Increasing the number of blades above 3 did not result in higher power. The rotor could operate in gusts which double the mean wind velocity. Examination of Reynolds number effects, and taking into account the scale of the model, it was concluded that a full-scale windmill could run at lower velocity ratios than those predicted by the model tests, and that it could self-start under no-load conditions if the cut-in rpm are at least half the rpm for maximum power at the prevailing wind speed. Preliminary estimates show that a 15 ft diameter windmill of this design, designed to operate with a safety factor of 2.5 up to a maximum wind speed of 60 ft/s, would weigh ca 150 lb and could be marketed for ca $60.00, excluding the driven unit, if sufficient quantities were produced to make tooling costs negligible. Similarly, a 30 ft windmill would weigh ca 1000 lb and cost ca $400.00. 2 refs., 6 figs.

Developments in blade shape design for a Darrieus vertical axis wind turbine

Science.gov (United States)

Ashwill, T. D.; Leonard, T. M.

1986-09-01

A new computer program package has been developed that determines the troposkein shape for a Darrieus Vertical Axis Wind Turbine Blade with any geometrical configuration or rotation rate. This package allows users to interact and develop a buildable blade whose shape closely approximates the troposkein. Use of this package can significantly reduce flatwise mean bending stresses in the blade and increase fatigue life.

Recent Darrieus vertical axis wind turbine aerodynamical experiments at Sandia National Laboratories

Science.gov (United States)

Klimas, P. C.

1981-01-01

Experiments contributing to the understanding of the aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment are described. These experiments are ultimately intended to reduce VAWT cost of energy and increase system reliability. They include chordwise pressure surveys, circumferential blade acceleration surveys, effects of blade camber, pitch and offset, blade blowing, and use of sections designed specifically for VAWT application.

Aerodynamic modeling of floating vertical axis wind turbines using the actuator cylinder flow method

DEFF Research Database (Denmark)

Cheng, Zhengshun; Aagaard Madsen, Helge; Gao, Zhen

2016-01-01

Recently the interest in developing vertical axis wind turbines (VAWTs) for offshore application has been increasing. Among the aerodynamic models of VAWTs, double multi-streamtube (DMST) and actuator cylinder (AC) models are two favorable methods for fully coupled modeling and dynamic analysis...

Statistical characterization of high-to-medium frequency mesoscale gravity waves by lidar-measured vertical winds and temperatures in the MLT

Science.gov (United States)

Lu, Xian; Chu, Xinzhao; Li, Haoyu; Chen, Cao; Smith, John A.; Vadas, Sharon L.

2017-09-01

We present the first statistical study of gravity waves with periods of 0.3-2.5 h that are persistent and dominant in the vertical winds measured with the University of Colorado STAR Na Doppler lidar in Boulder, CO (40.1°N, 105.2°W). The probability density functions of the wave amplitudes in temperature and vertical wind, ratios of these two amplitudes, phase differences between them, and vertical wavelengths are derived directly from the observations. The intrinsic period and horizontal wavelength of each wave are inferred from its vertical wavelength, amplitude ratio, and a designated eddy viscosity by applying the gravity wave polarization and dispersion relations. The amplitude ratios are positively correlated with the ground-based periods with a coefficient of 0.76. The phase differences between the vertical winds and temperatures (φW -φT) follow a Gaussian distribution with 84.2±26.7°, which has a much larger standard deviation than that predicted for non-dissipative waves ( 3.3°). The deviations of the observed phase differences from their predicted values for non-dissipative waves may indicate wave dissipation. The shorter-vertical-wavelength waves tend to have larger phase difference deviations, implying that the dissipative effects are more significant for shorter waves. The majority of these waves have the vertical wavelengths ranging from 5 to 40 km with a mean and standard deviation of 18.6 and 7.2 km, respectively. For waves with similar periods, multiple peaks in the vertical wavelengths are identified frequently and the ones peaking in the vertical wind are statistically longer than those peaking in the temperature. The horizontal wavelengths range mostly from 50 to 500 km with a mean and median of 180 and 125 km, respectively. Therefore, these waves are mesoscale waves with high-to-medium frequencies. Since they have recently become resolvable in high-resolution general circulation models (GCMs), this statistical study provides an important

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Directory of Open Access Journals (Sweden)

S. Oyama

2008-06-01

Full Text Available Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT Kiruna-Sodankylä-Tromsø (KST ultrahigh frequency (UHF radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutral-wind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s−1 in association with an ionospheric heating event. Large downward speeds in excess of −30 m s−1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Directory of Open Access Journals (Sweden)

S. Oyama

2008-06-01

Full Text Available Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT Kiruna-Sodankylä-Tromsø (KST ultrahigh frequency (UHF radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutral-wind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s⁻¹ in association with an ionospheric heating event. Large downward speeds in excess of −30 m s⁻¹ were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

Wind direction/velocity and current direction/velocity data from current meter casts in a world wide distribution from 1970-12-06 to 1991-10-01 (NODC Accession 9700218)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Wind direction/velocity and current direction/velocity data were collected using current meter casts in a world wide distribution from December 6, 1970 to October 1,...

Interaction of an Artificially Thickened Boundary Layer with a Vertically Mounted Pitching Airfoil

Science.gov (United States)

Hohman, Tristen; Smits, Alexander; Martinelli, Luigi

2011-11-01

Wind energy represents a large portion of the growing market in alternative energy technologies and the current landscape has been dominated by the more prevalent horizontal axis wind turbine. However, there are several advantages to the vertical axis wind turbine (VAWT) or Darrieus type design and yet there is much to be understood about how the atmospheric boundary layer (ABL) affects their performance. In this study the ABL was simulated in a wind tunnel through the use of elliptical shaped vortex generators, a castellated wall, and floor roughness elements as described in the method of Counihan (1967) and then verified its validity by hot wire measurement of the mean velocity profile as well as the turbulence intensity. The motion of an blade element around a vertical axis is approximated through the use of a pitching airfoil. The wake of the airfoil is investigated through hot wire anemometry in both uniform flow and in the simulated boundary layer both at Re = 1 . 37 ×105 based on the chord of the airfoil. Sponsored by Hopewell Wind Power (Hong Kong) Limited.

INNOVATIVE SOLUTIONS FOR SMALL SCALE VERTICAL AXIS WIND TURBINES USED IN HARBOURS AND SHORE AREAS

Directory of Open Access Journals (Sweden)

IONESCU Raluca Dora

2014-09-01

Full Text Available The paper aims to analyse the wind turbine solutions implemented in harbours and on shore areas. Also a thorough study of the blade design solutions for small power Vertical axis wind turbines (VAWTs has been conducted, with their advantages and disadvantages, in order to find the best solution that minimises the loads and helps with the self-starting capabilities of the wind turbine. First are presented all the solutions, next are discussed several research results for each solution and, in the end, a combination of solutions is chosen for our new small power VAWT with a pre-dimensioning analysis.

A review on computational fluid dynamic simulation techniques for Darrieus vertical axis wind turbines

International Nuclear Information System (INIS)

Ghasemian, Masoud; Ashrafi, Z. Najafian; Sedaghat, Ahmad

2017-01-01

Highlights: • A review on CFD simulation technique for Darrieus wind turbines is provided. • Recommendations and guidelines toward reliable and accurate simulations are presented. • Different progresses in CFD simulation of Darrieus wind turbines are addressed. - Abstract: The global warming threats, the presence of policies on support of renewable energies, and the desire for clean smart cities are the major drives for most recent researches on developing small wind turbines in urban environments. VAWTs (vertical axis wind turbines) are most appealing for energy harvesting in the urban environment. This is attributed due to structural simplicity, wind direction independency, no yaw mechanism required, withstand high turbulence winds, cost effectiveness, easier maintenance, and lower noise emission of VAWTs. This paper reviews recent published works on CFD (computational fluid dynamic) simulations of Darrieus VAWTs. Recommendations and guidelines are presented for turbulence modeling, spatial and temporal discretization, numerical schemes and algorithms, and computational domain size. The operating and geometrical parameters such as tip speed ratio, wind speed, solidity, blade number and blade shapes are fully investigated. The purpose is to address different progresses in simulations areas such as blade profile modification and optimization, wind turbine performance augmentation using guide vanes, wind turbine wake interaction in wind farms, wind turbine aerodynamic noise reduction, dynamic stall control, self-starting characteristics, and effects of unsteady and skewed wind conditions.

Observation and modeling of tide- and wind-induced surface currents in Galway Bay

Directory of Open Access Journals (Sweden)

Lei Ren

2015-10-01

Full Text Available A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers (ADCPs and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code (EFDC, was developed based on a terrain-following vertical (sigma coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tide- and wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.

Vertical axis wind turbine power regulation through centrifugally pumped lift spoiling

Science.gov (United States)

Klimas, P. C.; Sladky, J. F., Jr.

This paper describes an approach for lowering the rated windspeeds of Darrieus-type vertical axis wind turbines (VAWTs) whose blades are hollow aluminum extrusions. The blades, which when rotating act as centrifugal pumps, are fitted with a series of small perforations distributed along a portion of the blades' span. By valving the ends of the hollow blades, flow into the blade ends and out of the perforations may be controlled. This flow can induce premature aerodynamic stall on the blade elements, thereby reducing both the rated power of the turbine and its cost-of-energy. The concept has been proven on the Sandia National Laboratories 5-m diameter research VAWT and force balance and flow visualization wind tunnel tests have been conducted using a blade section designed for the VAWT application.

Structural design of the Sandia 34-M Vertical Axis Wind Turbine

Science.gov (United States)

Berg, D. E.

Sandia National Laboratories, as the lead DOE laboratory for Vertical Axis Wind Turbine (VAWT) development, is currently designing a 34-meter diameter Darrieus-type VAWT. This turbine will be a research test bed which provides a focus for advancing technology and validating design and fabrication techniques in a size range suitable for utility use. Structural data from this machine will allow structural modeling to be refined and verified for a turbine on which the gravity effects and stochastic wind loading are significant. Performance data from it will allow aerodynamic modeling to be refined and verified. The design effort incorporates Sandia's state-of-the-art analysis tools in the design of a complete machine. The analytic tools used in this design are discussed and the conceptual design procedure is described.

Study of Vertical Axis Wind Turbine for Energy Harvester in A Fishing Boat

Science.gov (United States)

Budi, E. M.; Banjarnahor, D. A.; Hanifan, M.

2017-07-01

The wind speed in the southern beach of West Java Indonesia is quite promising for wind energy harvesting. A field survey reported that the wind speed reached 10 m/s, while the average recorded in a year is about 4.7 m/s. In this study, two vertical axis wind turbines (VAWT) were compared to be used in that area through calculation as well as experiments. The experiments measured that the turbines can produce about 7.82W and 2.33W of electricity respectively. These experiments are compared with theoretical calculation to obtain the performance of both turbines used. The coefficient of performance (cp) experimentally is 0.09 for Turbine 1 (hybrid Savonius-Darrieus rotor) and 0.14 for Turbine 2 (Savonius rotor). While, rotor’s mechanical performance Cpr, obtained theoritically through calculation, is 0.36 for Turbine 1 and 0.12 for Turbine 2. These results are analysed from mechanical and electrical view.

Electromagnetic Calculation of Combined Earthing System with Ring Earth Electrode and Vertical Rods for Wind Turbine

Science.gov (United States)

Fujii, Toshiaki; Yasuda, Yoh; Ueda, Toshiaki

With the worldwide spread of wind turbine installations, various problems such as landscape issues, bird strikes and grid connections have arisen. Protection of wind turbines from lightning is cited as one of the main problems. Wind turbines are often struck by lightning because of their open-air locations, such as in mountainous areas, and their special configuration and very-high construction. Especially, low-voltage and control circuits can fail or suffer burnout while blades can incur serious damage if struck by lightning. Wind turbine failures caused by lightning strikes account for approximately 25% of all failures. The problem is regarded as a global one that needs immediate resolution. It is important to understand the impedance characteristics of wind turbine earthing systems from the viewpoint of lightning protection. A report from IEC TR61400-24 recommends a “ring earth electrode”. This was originally defined in IEC 61024 (currently revised and re-numbered as IEC 62305), where such an electrode is recommended to reduce touch and step voltages in households and buildings. IEC TR61400-24 also recommended additional electrodes of vertical or horizontal rods. However, these concepts have not been fully discussed from the viewpoint of its application to wind turbines. To confirm the effect of a combination of a ring earth electrode and additional vertical rods for protection of a wind turbine, this report uses the Finite Difference Time Domain (FDTD) method to present an electromagnetic transient analysis on such a wind turbine earthing system. The results show that an optimal combination can be arranged from viewpoints of lightning protection and construction cost. Thus, this report discusses how to establish a quantitative design methodology of the wind turbine earthing system to provide effective lightning protection.

PIV technique implementation for wind mapping in complex topographies

International Nuclear Information System (INIS)

Siddiqui, Kamran; Hangan, Horia; Rasouli, Ashkan

2008-01-01

An experimental study was conducted to demonstrate PIV's capability to provide a detailed characterization of the flow field over complex topographic terrain in a large boundary layer wind tunnel setup. Two-dimensional velocity fields were measured in horizontal and vertical planes over a 1:3000 scaled topographic model. The non-uniform seed distribution was found to be a major issue which could affect the PIV velocity vectors. A novel scheme was developed to automatically detect the regions with low seed density and exclude them from further analysis. The mean and turbulent velocities obtained from PIV and previous hotwire measurements are compared and show good agreement. The study shows that PIV can be successfully used to measure flow over complex geometries in large wind tunnel setups, enabling the flow structure to be mapped with a very high spatial resolution

Dynamic Analysis of Darrieus Vertical Axis Wind Turbine Rotors

Science.gov (United States)

Lobitz, D. W.

1981-01-01

The dynamic response characteristics of the vertical axis wind turbine (VAWT) rotor are important factors governing the safety and fatigue life of VAWT systems. The principal problems are the determination of critical rotor speeds (resonances) and the assessment of forced vibration response amplitudes. The solution to these problems is complicated by centrifugal and Coriolis effects which can have substantial influence on rotor resonant frequencies and mode shapes. The primary tools now in use for rotor analysis are described and discussed. These tools include a lumped spring mass model (VAWTDYN) and also finite-element based approaches. The accuracy and completeness of current capabilities are also discussed.

Numerical study on aerodynamic damping of floating vertical axis wind turbines

Science.gov (United States)

Cheng, Zhengshun; Aagaard Madsen, Helge; Gao, Zhen; Moan, Torgeir

2016-09-01

Harvesting offshore wind energy resources using floating vertical axis wind turbines (VAWTs) has attracted an increasing interest in recent years. Due to its potential impact on fatigue damage, the aerodynamic damping should be considered in the preliminary design of a floating VAWT based on the frequency domain method. However, currently the study on aerodynamic damping of floating VAWTs is very limited. Due to the essential difference in aerodynamic load characteristics, the aerodynamic damping of a floating VAWT could be different from that of a floating horizontal axis wind turbine (HAWT). In this study, the aerodynamic damping of floating VAWTs was studied in a fully coupled manner, and its influential factors and its effects on the motions, especially the pitch motion, were demonstrated. Three straight-bladed floating VAWTs with identical solidity and with a blade number varying from two to four were considered. The aerodynamic damping under steady and turbulent wind conditions were estimated using fully coupled aero-hydro-servo-elastic time domain simulations. It is found that the aerodynamic damping ratio of the considered floating VAWTs ranges from 1.8% to 5.3%. Moreover, the aerodynamic damping is almost independent of the rotor azimuth angle, and is to some extent sensitive to the blade number.

The impact of inertial forces on morphing wind turbine blade in vertical axis configuration

International Nuclear Information System (INIS)

Butbul, Jonathan; MacPhee, David; Beyene, Asfaw

2015-01-01

Highlights: • A novel flexible VAWT has been experimentally tested alongside numerically simulations. • Using FEA and CFD, direction of blade bending was predicted from inertial and aerodynamic forces. • High-speed camera footage has been used to validate the model. • The flexible VAWT was found to self-start in the majority of tests, while the rigid one did not. • It is suggested that flexible VAWTs can have improved performance in part-load applications. - Abstract: A novel flexible blade concept with the ability to morph and geometrically adapt to changing flow conditions has been proposed to improve part-load performance of horizontal-axis wind turbines. The extension of these benefits to a vertical axis wind turbine would make wind technology a more competitive player in the energy market. Both flexible and rigid wind turbine rotor blades for vertical axis application were modeled, designed, manufactured and tested. Their performances were tested in a low speed wind tunnel. The predicted magnitude and direction of blade morph was validated using a high speed camera as well as finite element analysis. The comparative results of straight rigid and straight morphing blades show that the coefficient of performance greatly depends on the tip speed ratio. Overall, the morphing blade has better performance at low RPMs, but the rigid blade performed better at high RPMs. It was observed that the flexible blade self-started in the majority of the experiments. At high RPM, the centrifugal force overwhelmed the lift force, bending the flexible blade out of phase in an undesired direction increasing drag and therefore reducing the coefficient of performance

Design and fabrication of a low-cost Darrieus vertical-axis wind-turbine system, volume 2

Science.gov (United States)

1983-03-01

The fabrication, installation, and checkout of 100-kW 17 meter vertical axis wind turbines is described. Turbines are Darrieus-type VAWIs with rotors 17 meters and 25.15 meters in height. They can produce 100 kW of electric power at a cost of energy as low as 3 cents per kWh, in an 18-mph wind regime using 12% annualized costs. Four turbines were produced; three are installed and are operable. Contract results are documented.

Wind energy generation for electric power production, preliminary studies. Part I

Energy Technology Data Exchange (ETDEWEB)

Fischer, A

1976-03-01

Studies of wind power generation done by SAAB-Scania during 1975 are described. The project deals with generation of electricity for delivery to the transmission system. Both plants with horizontal axis and plants with vertical axis have been studied. A projected pilot plant with a rotor of 18 meter and an effect of 50 kW at 10 m/s wind velocity is described. Suggestions are made for a continuation of the project.

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 600velocity range of 0.6< U * <13. The amplitudes of oscillations and flow forces acting on the airfoil were measured at various angles of attack, α, in the range of 0< α<90. The airfoil was observed to oscillate in the range of 60< α<90, where α = 90 exhibited the widest lock-in range (1.67< U * <11.74) and the largest peak amplitude (A * = 1.93 at U * = 5.7). For all cases where oscillations were observed, the oscillation frequency remained close to the structure's natural frequency, defining a lock-in range. Flow visualization tests were also conducted to study the changes in the vortex shedding patterns. This research is supported in part by the National Science Foundation under NSF Award Numbers 1460461 and CBET-1437988.

Wind Characteristics of Coastal and Inland Surface Flows

Science.gov (United States)

Subramanian, Chelakara; Lazarus, Steven; Jin, Tetsuya

2015-11-01

Lidar measurements of the winds in the surface layer (up to 80 m) inland and near the beach are studied to better characterize the velocity profile and the effect of roughness. Mean and root-mean-squared profiles of horizontal and vertical wind components are analyzed. The effects of variable time (18, 60 and 600 seconds) averaging on the above profiles are discussed. The validity of common surface layer wind profile models to estimate skin friction drag is assessed in light of these measurements. Other turbulence statistics such as auto- and cross- correlations in spatial and temporal domains are also presented. The help of FIT DMES field measurement crew is acknowledged.

Report on a wind power development field test project (detailed wind condition investigation) in the city of Choshi; Choshishi ni okeru furyoku kaihatsu field test jigyo (fukyo seisa) hokokusho

Energy Technology Data Exchange (ETDEWEB)

NONE

1998-11-01

This paper describes observation on the annual wind condition at the Yokka-ichibadai in the city of Choshi. The average wind velocities were 4.7 and 3.8 m/s at the ground height of 20 and 10 meters, respectively, not having reached the NEDO's criterion values 5.6 and 5.0 m/s. The annual wind direction emergence rate on the wind axis was 70%, meeting the criterion value of 60% or higher, and the wind direction is stable. The exponent for the vertical wind velocity distribution was 3.3, which is similar to that in the urban area. Disturbance in the wind condition was 0.18, meeting the criterion value of 0.30 or lower. The maximum momentary wind velocity was 31.9 m/s, which is well below the criterion of 60 m/s presenting no problem as a wind mill construction site. The wind energy density was 94 W/m{sup 2}, being only 63% of the criterion value, when all the azimuths were used as the object. The result of the investigation is that the average wind velocity is low and the wind energy density is also low. However, if the size of wind mill to be introduced is set to the class B (300 kW), it is possible to attain an annual operation rate of 58%, an annual energy acquisition amount of 515 MWh, and a facility utilization rate of 19.6%. If set to the class C (750 kW), an operation rate of 78%, an annual energy acquisition of 1296 MWh, and a facility utilization rate of 19.7% can be obtained, meeting the criterion value. (NEDO)

The vertical structure of airflow turbulence characteristics within a boundary layer during wind blown sand transport over a beach

Science.gov (United States)

Lee, Z. S.; Baas, A. C.; Jackson, D.; Cooper, J. A.; Lynch, K.; Delgado-Fernandez, I.; Beyers, M.

2010-12-01

Recent studies have suggested the significant role of boundary layer turbulence and coherent flow structures on sand transport by wind over beaches and desert dunes. Widespread use of sonic anemometry and high-frequency sand transport sensors and traps have facilitated a move beyond the basic monitoring of shear velocities and bulk sediment transport to more detailed measurements at much higher spatio-temporal resolutions. In this paper we present results of a small-scale point-location field study of boundary layer turbulence and shear stresses conducted under obliquely onshore winds over a beach at Magilligan Strand, Northern Ireland. High-frequency (25 Hz) 3D wind vector measurements were collected at five different heights between 0.13 and 1.67 metres above the bed using sonic anemometry for durations of several hours, and the associated sand transport response was measured using an array of Safires. The wind data are used to investigate the vertical structure of Reynolds shear stresses and burst-sweep event characteristics, as well as a comparison with the standard logarithmic (law-of-the-wall) wind profile. The study explores the identification and selection of a characteristic event duration based on integral time-scales as well as spectral analysis, and includes an assessment of the issues involved with data rotations for yaw, pitch, and roll corrections relative to flow streamlines, and the subsequently derived turbulence parameters based on fluctuating vector components (u’, v’, w’). Results show how the contributions to shear stress and the average pitch of bursts and sweeps changes as a function of height above the bed, indicating the transformation of top-down turbulent eddies as they travel toward the surface. A comparison between the turbulence data and the synchronous sand transport events, meanwhile, reveals the potential effects of enhanced saltation layer roughness feedback on eddies close to the bed.

Flow measurement behind a pair of vertical-axis wind turbines

Science.gov (United States)

Parker, Colin M.; Hummels, Raymond; Leftwich, Megan C.

2017-11-01

The wake from a pair of vertical-axis wind turbines (VAWTs) is measured using particle imaging velocimetry (PIV). The VAWT models are mounted in a low-speed wind tunnel and driven using a motor control system. The rotation of the turbines is synced using a proportional controller that allows the turbine's rotational position to be set relative to each other. The rotation of the turbines is also synced with the PIV system for taking phase averaged results. The VAWTs are tested for both co- and counter-rotating cases over a range of relative phase offsets. Time averaged and phase averaged results are measured at the horizontal mid-plane in the near wake. The time-averaged results compare the bulk wake profiles from the pair of turbines. Phase averaged results look at the vortex interactions in the near wake of the turbines. By changing the phase relation between the turbines we can see the impact of the structure interactions in both the phase and time averaged results.

AXAOTHER XL -- A spreadsheet for determining doses for incidents caused by tornadoes or high-velocity straight winds

International Nuclear Information System (INIS)

Simpkins, A.A.

1996-09-01

AXAOTHER XL is an Excel Spreadsheet used to determine dose to the maximally exposed offsite individual during high-velocity straight winds or tornado conditions. Both individual and population doses may be considered. Potential exposure pathways are inhalation and plume shine. For high-velocity straight winds the spreadsheet has the capability to determine the downwind relative air concentration, however for the tornado conditions, the user must enter the relative air concentration. Theoretical models are discussed and hand calculations are performed to ensure proper application of methodologies. A section has also been included that contains user instructions for the spreadsheet

Effect of the shaft on the aerodynamic performance of urban vertical axis wind turbines

NARCIS (Netherlands)

Rezaeiha, A.; Kalkman, I.; Montazeri, H.; Blocken, B.J.E.

2017-01-01

The central shaft is an inseparable part of a vertical axis wind turbine (VAWT). For small turbines such as those typically used in urban environments, the shaft could operate in the subcritical regime, resulting in large drag and considerable aerodynamic power loss. The current study aims to (i)

Computerized system for building 'the rose' of the winds and defining the velocity and the average density of the wind power for a given place

International Nuclear Information System (INIS)

Valkov, I.; Dekova, I.; Arnaudov, A.; Kostadinov, A.

2002-01-01

This paper considers the structure and the working principle of a computerized system for building 'the rose' of the winds. The behaviour of the system has been experimentally investigated and on the basis of the received data 'the rose' of the winds has been built, a diagram of the average wind velocity at a predefined step in the course of time has been made, and the average density of the wind power has been quantitatively defined. The proposed system enables possibilities for creating a data base of wind parameters, their processing and graphical visualizing of the received results. The system allows to improve the work of devices of wild's wind gauge type. (authors)

Speed and Torque Control Strategies for Loss Reduction of Vertical Axis Wind Turbines

Science.gov (United States)

Argent, Michael; McDonald, Alasdair; Leithead, Bill; Giles, Alexander

2016-09-01

This paper builds on the work into modelling the generator losses for Vertical Axis Wind Turbines from their intrinsic torque cycling to investigate the effects of aerodynamic inefficiencies caused by the varying rotational speed resulting from different torque control strategies to the cyclic torque. This is achieved by modelling the wake that builds up from the rotation of the VAWT rotor to investigate how the wake responds to a changing rotor speed and how this in turn affects the torque produced by the blades as well as the corresponding change in generator losses and any changes to the energy extracted by the wind turbine rotor.

Blade Simulation of Small H-Vertical Axis Wind Turbine Based on Optimal Wind Power Coefficient%风能利用系数最优小型H型垂直轴风力机叶片模拟

Institute of Scientific and Technical Information of China (English)

郭兴文; 刘颖波; 邱勇

2012-01-01

A two-dimensional CFD model of the external flow-field for a 1kW H-vertical axis wind turbine is established by using the software of Flunent. The sliding mesh technique and the SST k -to turbulent model are adopted. The model is intended to study the impact of different lengths of chord and different shapes of airfoil on the wind power coefficient for the H-vertical axis wind turbine. By fixing the Gurney flap of different heights on the tail of blade, the efficiency improvement of wind power coefficient is studied, and the curve of wind power coefficient for the H-vertical axis wind turbine with the tip-speed under different situations is derived. The results show that the blade of NACA 0018 with the chord length of 300mm is relatively suitable for an H-vertical axis wind turbine. The H-vertical axis wind turbine works more effectively at a tip-speed ratio from 2.5 to 3.5. The wind power coefficient of H-vertical axis wind turbine is able to be increased 3% by using the Gurney flap with flap height equaled to 1% of chord length and tip-speed ratio of 2.8.%采用移动网格技术,选用SST(剪切力传输)k-ω湍流模型,建立了1kW功率的H型垂直轴风力机风轮外流场CFD模型,研究了不同叶片翼型、不同弦长和翼尾加装Gurney襟翼对风力机风能利用系数的影响.结果表明,300mm弦长的NACA 0018翼型较为适合H型垂直轴风力机；在尖速比为2.5-3.5时,H型垂直轴风力机的工作效率较高；尖速比为2.8时,高度为1％弦长的Gurney襟翼翼型能够提高风能利用系数3％.

The effect of tip speed ratio on a vertical axis wind turbine at high Reynolds numbers

Science.gov (United States)

Parker, Colin M.; Leftwich, Megan C.

2016-05-01

This work visualizes the flow surrounding a scaled model vertical axis wind turbine at realistic operating conditions. The model closely matches geometric and dynamic properties—tip speed ratio and Reynolds number—of a full-size turbine. The flow is visualized using particle imaging velocimetry (PIV) in the midplane upstream, around, and after (up to 4 turbine diameters downstream) the turbine, as well as a vertical plane behind the turbine. Time-averaged results show an asymmetric wake behind the turbine, regardless of tip speed ratio, with a larger velocity deficit for a higher tip speed ratio. For the higher tip speed ratio, an area of averaged flow reversal is present with a maximum reverse flow of -0.04U_∞. Phase-averaged vorticity fields—achieved by syncing the PIV system with the rotation of the turbine—show distinct structures form from each turbine blade. There were distinct differences in results by tip speed ratios of 0.9, 1.3, and 2.2 of when in the cycle structures are shed into the wake—switching from two pairs to a single pair of vortices being shed—and how they convect into the wake—the middle tip speed ratio vortices convect downstream inside the wake, while the high tip speed ratio pair is shed into the shear layer of the wake. Finally, results show that the wake structure is much more sensitive to changes in tip speed ratio than to changes in Reynolds number.

Vertical Rise Velocity of Equatorial Plasma Bubbles Estimated from Equatorial Atmosphere Radar Observations and High-Resolution Bubble Model Simulations

Science.gov (United States)

Yokoyama, T.; Ajith, K. K.; Yamamoto, M.; Niranjan, K.

2017-12-01

Equatorial plasma bubble (EPB) is a well-known phenomenon in the equatorial ionospheric F region. As it causes severe scintillation in the amplitude and phase of radio signals, it is important to understand and forecast the occurrence of EPBs from a space weather point of view. The development of EPBs is presently believed as an evolution of the generalized Rayleigh-Taylor instability. We have already developed a 3D high-resolution bubble (HIRB) model with a grid spacing of as small as 1 km and presented nonlinear growth of EPBs which shows very turbulent internal structures such as bifurcation and pinching. As EPBs have field-aligned structures, the latitude range that is affected by EPBs depends on the apex altitude of EPBs over the dip equator. However, it was not easy to observe the apex altitude and vertical rise velocity of EPBs. Equatorial Atmosphere Radar (EAR) in Indonesia is capable of steering radar beams quickly so that the growth phase of EPBs can be captured clearly. The vertical rise velocities of the EPBs observed around the midnight hours are significantly smaller compared to those observed in postsunset hours. Further, the vertical growth of the EPBs around midnight hours ceases at relatively lower altitudes, whereas the majority of EPBs at postsunset hours found to have grown beyond the maximum detectable altitude of the EAR. The HIRB model with varying background conditions are employed to investigate the possible factors that control the vertical rise velocity and maximum attainable altitudes of EPBs. The estimated rise velocities from EAR observations at both postsunset and midnight hours are, in general, consistent with the nonlinear evolution of EPBs from the HIRB model.

Modification of Turbulent Pipe Flow Equations to Estimate the Vertical Velocity Profiles Under Woody Debris Jams

Science.gov (United States)

Cervania, A.; Knack, I. M. W.

2017-12-01

The presence of woody debris (WD) jams in rivers and streams increases the risk of backwater flooding and reduces the navigability of a channel, but adds fish and macroinvertebrate habitat to the stream. When designing river engineering projects engineers use hydraulic models to predict flow behavior around these obstructions. However, the complexities of flow through and beneath WD jams are still poorly understood. By increasing the ability to predict flow behavior around WD jams, landowners and engineers are empowered to develop sustainable practices regarding the removal or placement of WD in rivers and flood plains to balance the desirable and undesirable effects to society and the environment. The objective of this study is to address some of this knowledge gap by developing a method to estimate the vertical velocity profile of flow under WD jams. When flow passes under WD jams, it becomes affected by roughness elements on all sides, similar to turbulent flows in pipe systems. Therefore, the method was developed using equations that define the velocity profiles of turbulent pipe flows: the law of the wall, the logarithmic law, and the velocity defect law. Flume simulations of WD jams were conducted and the vertical velocity profiles were measured along the centerline. A calculated velocity profile was fit to the measured profile through the calibration of eight parameters. An optimal value or range of values have been determined for several of these parameters using cross-validation techniques. The results indicate there may be some promise to using this method in hydraulic models.

How well can we measure the vertical wind speed? Implications for fluxes of energy and mass

Science.gov (United States)

John Kochendorfer; Tilden P. Meyers; John Frank; William J. Massman; Mark W. Heuer

2012-01-01

Sonic anemometers are capable of measuring the wind speed in all three dimensions at high frequencies (10­50 Hz), and are relied upon to estimate eddy-covariance-based fluxes of mass and energy over a wide variety of surfaces and ecosystems. In this study, wind-velocity measurement errors from a three-dimensional sonic anemometer with a nonorthogonal transducer...

Investigations on self-starting and performance characteristics of simple H and hybrid H-Savonius vertical axis wind rotors

International Nuclear Information System (INIS)

Bhuyan, S.; Biswas, A.

2014-01-01

Highlights: • Hybrid H-Savonius vertical axis wind rotor for built-in environmental wind speeds. • Self-starting characteristics of unsymmetrical H-rotor and Hybrid H-Savonius rotor. • Comparisons between unsymmetrical H-rotor and Hybrid rotor at same experimental conditions. • Insight of the performances of optimum hybrid H-Savonius rotor. • Higher power performance of the optimum rotor compared with some existing VAWT rotors. - Abstract: With recent surge in fossil fuel prices and demands for renewable energy sources, vertical axis wind turbine (VAWT) technologies have emerged out as one of the prime growing sector for small-scale power generation in the built environment. In such an environment, self-starting and high performances are of utmost importance. Amongst all VAWT designs, H-rotor, being a lift-driven device, exhibits a high power coefficient. However, it suffers from poor starting behavior due to its conventional symmetrical NACA airfoil blades. The objective of the present study is to design a VAWT rotor that possesses both self-starting and high power coefficient simultaneously. For this, a three bladed H-rotor with unsymmetrical cambered S818 airfoil blades is investigated, which shows self-starting characteristics at many of the azimuthal angles. However to make the rotor completely self-starting, the same H-rotor is incorporated in a hybrid system with Savonius rotor as its starter. It is found that the hybrid design fully exhibits self-starting capability at all azimuthal positions, signified by the positive static torque coefficient values. For improving power performance of the hybrid rotor, the same is subjected to rigorous experimentations on the wind tunnel at different Reynolds numbers (Re) between 1.44 × 10 5 and 2.31 × 10 5 for five different overlap conditions in the Savonius rotor part. The performance coefficients of the hybrid rotor are compared with the simple H-rotor. Out of all the designs investigated, the maximum Cp

Development and Evaluation of an Aerodynamic Model for a Novel Vertical Axis Wind Turbine Concept

Directory of Open Access Journals (Sweden)

Andrew Shires

2013-05-01

Full Text Available There has been a resurgence of interest in the development of vertical axis wind turbines which have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. This paper describes an aerodynamic performance model for vertical axis wind turbines specifically developed for the design of a novel offshore V-shaped rotor with multiple aerodynamic surfaces. The model is based on the Double-Multiple Streamtube method and includes a number of developments for alternative complex rotor shapes. The paper compares predicted results with measured field data for five different turbines with both curved and straight blades and rated powers in the range 100–500 kW. Based on these comparisons, the paper proposes modifications to the Gormont dynamic stall model that gives improved predictions of rotor power for the turbines considered.

Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations

Directory of Open Access Journals (Sweden)

J. Park

2013-06-01

Full Text Available In this paper we estimate zonal plasma drift in the equatorial ionospheric F region without counting on ion drift meters. From June 2001 to June 2004 zonal plasma drift velocity is estimated from electron, neutral, and magnetic field observations of Challenging Mini-satellite Payload (CHAMP in the 09:00–20:00 LT sector. The estimated velocities are validated against ion drift measurements by the Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics Instrument (ROCSAT-1/IPEI during the same period. The correlation between the CHAMP (altitude ~ 400 km estimates and ROCSAT-1 (altitude ~ 600 km observations is reasonably high (R ≈ 0.8. The slope of the linear regression is close to unity. However, the maximum westward drift and the westward-to-eastward reversal occur earlier for CHAMP estimates than for ROCSAT-1 measurements. In the equatorial F region both zonal wind and plasma drift have the same direction. Both generate vertical currents but with opposite signs. The wind effect (F region wind dynamo is generally larger in magnitude than the plasma drift effect (Pedersen current generated by vertical E field, thus determining the direction of the F region vertical current.

Improvement of vertical velocity statistics measured by a Doppler lidar through comparison with sonic anemometer observations

Science.gov (United States)

Bonin, Timothy A.; Newman, Jennifer F.; Klein, Petra M.; Chilson, Phillip B.; Wharton, Sonia

2016-12-01

Since turbulence measurements from Doppler lidars are being increasingly used within wind energy and boundary-layer meteorology, it is important to assess and improve the accuracy of these observations. While turbulent quantities are measured by Doppler lidars in several different ways, the simplest and most frequently used statistic is vertical velocity variance (w'2) from zenith stares. However, the competing effects of signal noise and resolution volume limitations, which respectively increase and decrease w'2, reduce the accuracy of these measurements. Herein, an established method that utilises the autocovariance of the signal to remove noise is evaluated and its skill in correcting for volume-averaging effects in the calculation of w'2 is also assessed. Additionally, this autocovariance technique is further refined by defining the amount of lag time to use for the most accurate estimates of w'2. Through comparison of observations from two Doppler lidars and sonic anemometers on a 300 m tower, the autocovariance technique is shown to generally improve estimates of w'2. After the autocovariance technique is applied, values of w'2 from the Doppler lidars are generally in close agreement (R2 ≈ 0.95 - 0.98) with those calculated from sonic anemometer measurements.

Proceedings of the Vertical-Axis Wind Turbine Technology Workshop, Albuquerque, New Mexico, May 18--20, 1976

Energy Technology Data Exchange (ETDEWEB)

1976-07-01

Separate abstracts are included for twenty-nine of the thirty papers presented concerning vertical axis wind turbines. One paper has previously been abstracted and included in the ERDA Energy Data Base and Energy Research Abstracts journal.

Prediction of velocity of the wind generation in Kobe City College of Technology; Kobe Kosen ni okeru furyoku hatsuden no yosoku

Energy Technology Data Exchange (ETDEWEB)

Akamatsu, K; Kanemura, M; Amako, K

1997-11-25

Wind conditions, such as average wind velocity for 10 minutes, maximum instantaneous wind velocity and wind directions, are measured by the anemometer and anemoscope installed 3m above the roof of the Kobe City College of Technology`s Information Processing Center building, to collect the data necessary to validate possibility of wind power generation, if the wind system is installed in the college site. Monthly availability of power is estimated from the output power characteristics curve for a generator having a rated capacity of 200W and wind velocity data collected for 9 months. It will generate power of only 144kWh, even when operated to give the rated output, or approximately 8.5kWh at the highest in a month, because of availability of wind power limited to around 30% of the total as estimated from the relative frequency distribution. It is therefore desirable to install a number of units having a rated capacity of 200W or else a smaller number of larger units. Assuming that days that give the highest output for 24 hours last 1 month, a power of 54.3kWh will be generated. It is estimated, based on these results, that a hybrid unit, in which a wind power generator installed at a high place is combined with a solar unit, can provide power required for nighttime lighting, if a wind power unit having a rated capacity of 2kW is field-controlled under an optimum condition. 13 figs., 3 tabs.

Modeling Atmospheric Turbulence via Rapid Distortion Theory: Spectral Tensor of Velocity and Buoyancy

DEFF Research Database (Denmark)

Chougule, Abhijit S.; Mann, Jakob; Kelly, Mark C.

2017-01-01

A spectral tensor model is presented for turbulent fluctuations of wind velocity components and temperature, assuming uniform vertical gradients in mean temperature and mean wind speed. The model is built upon rapid distortion theory (RDT) following studies by Mann and by Hanazaki and Hunt, using...... the eddy lifetime parameterization of Mann to make the model stationary. The buoyant spectral tensor model is driven via five parameters: the viscous dissipation rate epsilon, length scale of energy-containing eddies L, a turbulence anisotropy parameter Gamma, gradient Richardson number (Ri) representing...

Effect of wind waves on air-sea gas exchange: proposal of an overall CO2 transfer velocity formula as a function of breaking-wave parameter

International Nuclear Information System (INIS)

Zhao, D.; Suzuki, Y.; Komori, S.

2003-01-01

A new formula for gas transfer velocity as a function of the breaking-wave parameter is proposed based on correlating gas transfer with whitecap coverage. The new formula for gas transfer across an air-sea interface depends not only on wind speed but also on wind-wave state. At the same wind speed, a higher gas transfer velocity will be obtained for a more developed wind-sea, which is represented by a smaller spectral peak frequency of wind waves. We suggest that the large uncertainties in the traditional relationship of gas transfer velocity with wind speed be ascribed to the neglect of the effect of wind waves. The breaking-wave parameter can be regarded as a Reynolds number that characterizes the intensity of turbulence associated with wind waves in the downward-bursting boundary layer (DBBL). DBBL provides an effective way to exchange gas across the air-sea interface, which might be related to the surface renewal

The influence of the tangential velocity of inner rotating wall on axial velocity profile of flow through vertical annular pipe with rotating inner surface

Directory of Open Access Journals (Sweden)

Sharf Abdusalam M.

2014-03-01

Full Text Available In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig and computational (employing CFD software investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.

Immersion and contact freezing experiments in the Mainz wind tunnel laboratory

Science.gov (United States)

Eppers, Oliver; Mayer, Amelie; Diehl, Karoline; Mitra, Subir; Borrmann, Stephan; Szakáll, Miklós

2016-04-01

Immersion and contact freezing are of outmost important ice nucleation processes in mixed phase clouds. Experimental studies are carried out in the Mainz vertical wind tunnel laboratory in order to characterize these nucleation processes for different ice nucleating particles (INP), such as for mineral dust or biological particles. Immersion freezing is investigated in our laboratory with two different experimental techniques, both attaining contact-free levitation of liquid droplets and cooling of the surrounding air down to about -25 °C. In an acoustic levitator placed in the cold room of our laboratory, drops with diameters of 2 mm are investigated. In the vertical air stream of the wind tunnel droplets with diameter of 700 micron are freely floated at their terminal velocities, simulating the flow conditions of the free atmosphere. Furthermore, the wind tunnel offers a unique platform for contact freezing experiments. Supercooled water droplets are floated in the vertical air stream at their terminal velocities and INP are injected into the tunnel air stream upstream of them. As soon as INP collides with the supercooled droplet the contact freezing is initiated. The first results of immersion and contact freezing experiments with cellulose particles both in the acoustic levitator and in the wind tunnel will be presented. Cellulose is considered as typical INP of biological origin and a macrotracer for plant debris. Nucleating properties of cellulose will be provided, mainly focusing on the temperature, INP concentration, and specific surface area dependences of the freezing processes. Direct comparison between the different experimental techniques (acoustic levitator and wind tunnel), as well as between nucleation modes (immersion and contact freezing) will be presented. The work is carried out within the framework of the German research unit INUIT.

Fatigue influences lower extremity angular velocities during a single-leg drop vertical jump

OpenAIRE

Tamura, Akihiro; Akasaka, Kiyokazu; Otsudo, Takahiro; Shiozawa, Junya; Toda, Yuka; Yamada, Kaori

2017-01-01

[Purpose] Fatigue alters lower extremity landing strategies and decreases the ability to attenuate impact during landing. The purpose of this study was to reveal the influence of fatigue on dynamic alignment and joint angular velocities in the lower extremities during a single leg landing. [Subjects and Methods] The 34 female college students were randomly assigned to either the fatigue or control group. The fatigue group performed single-leg drop vertical jumps before, and after, the fatigue...

Stochastic dynamic response analysis of a floating vertical-axis wind turbine with a semi-submersible floater

DEFF Research Database (Denmark)

Wang, Kai; Moan, Torgeir; Hansen, Martin Otto Laver

2016-01-01

Floating vertical-axis wind turbines (FVAWTs) provide the potential for utilizing offshore wind resources in moderate and deep water because of their economical installation and maintenance. Therefore, it is important to assess the performance of the FVAWT concept. This paper presents a stochastic...... on the response is demonstrated by comparing the floating wind turbine with the equivalent land-based wind turbine. Additionally, by comparing the behaviour of FVAWTs with flexible and rigid rotors, the effect of rotor flexibility is evaluated. Furthermore, the FVAWT is also investigated in the parked condition...... dynamic response analysis of a 5MW FVAWT based on fully coupled nonlinear time domain simulations. The studied FVAWT, which is composed of a Darrieus rotor and a semi-submersible floater, is subjected to various wind and wave conditions. The global motion, structural response and mooring line tension...

CFD ANALYSIS OF THE AIR FLOW AROUND THE BLADES OF THE VERTICAL AXIS WIND TURBINE

Directory of Open Access Journals (Sweden)

Muhammed Musab Gavgali

2017-06-01

Full Text Available The paper presents the results of calculations of flow around the vertical axis wind turbine. Three-dimensional calculations were performed using ANSYS Fluent. They were made at steady-state conditions for a wind speed of 3 m/s for 4 angular settings of the three-bladed rotor. The purpose of the calculations was to determine the values of the aerodynamic forces acting on the individual blades and to present the pressure contours on the surface of turbine rotor blades. The calculations were made for 4 rotor angular settings.

Comparison of vertical E × B drift velocities and ground-based magnetometer observations of DELTA H in the low latitude under geomagnetically disturbed conditions

Science.gov (United States)

Prabhu, M.; Unnikrishnan, K.

2018-04-01

In the present work, we analyzed the daytime vertical E × B drift velocities obtained from Jicamarca Unattended Long-term Ionosphere Atmosphere (JULIA) radar and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca, and Piura in Peru for 22 geomagnetically disturbed events in which either SC has occurred or Dstmax values of daytime vertical E × B drift velocity and peak value of ΔH for the three consecutive days of the events. It was observed that 45% of the events have daytime vertical E × B drift velocity peak in the magnitude range 10-20 m/s and 20-30 m/s and 20% have peak ΔH in the magnitude range 50-60 nT and 80-90 nT. It was observed that the time of occurrence of the peak value of both the vertical E × B drift velocity and the ΔH have a maximum (40%) probability in the same time range 11:00-13:00 LT. We also investigated the correlation between E × B drift velocity and Dst index and the correlation between delta H and Dst index. A strong positive correlation is found between E × B drift and Dst index as well as between delta H and Dst Index. Three different techniques of data analysis - linear, polynomial (order 2), and polynomial (order 3) regression analysis were considered. The regression parameters in all the three cases were calculated using the Least Square Method (LSM), using the daytime vertical E × B drift velocity and ΔH. A formula was developed which indicates the relationship between daytime vertical E × B drift velocity and ΔH, for the disturbed periods. The E × B drift velocity was then evaluated using the formulae thus found for the three regression analysis and validated for the 'disturbed periods' of 3 selected events. The E × B drift velocities estimated by the three regression analysis have a fairly good agreement with JULIA radar observed values under different seasons and solar activity

Using the Vertical Component of the Surface Velocity Field to Map the Locked Zone at Cascadia Subduction Zone

Science.gov (United States)

Moulas, E.; Brandon, M. T.; Podladchikov, Y.; Bennett, R. A.

2014-12-01

At present, our understanding of the locked zone at Cascadia subduction zone is based on thermal modeling and elastic modeling of horizontal GPS velocities. The thermal model by Hyndman and Wang (1995) provided a first-order assessment of where the subduction thrust might be cold enough for stick-slip behavior. The alternative approach by McCaffrey et al. (2007) is to use a Green's function that relates horizontal surface velocities, as recorded by GPS, to interseismic elastic deformation. The thermal modeling approach is limited by a lack of information about the amount of frictional heating occurring on the thrust (Molnar and England, 1990). The GPS approach is limited in that the horizontal velocity component is fairly insensitive to the structure of the locked zone. The vertical velocity component is much more useful for this purpose. We are fortunate in that vertical velocities can now be measured by GPS to a precision of about 0.2 mm/a. The dislocation model predicts that vertical velocities should range up to about 20 percent of the subduction velocity, which means maximum values of ~7 mm/a. The locked zone is generally entirely offshore at Cascadia, except for the Olympic Peninsula region, where the underlying Juan De Fuca plate has an anomalously low dip. Previous thermal and GPS modeling, as well as tide gauge data and episodic tremors indicate the locked zone there extends about 50 to 75 km onland. This situation provides an opportunity to directly study the locked zone. With that objective in mind, we have constructed a full 3D geodynamic model of the Cascadia subduction zone. At present, the model provides a full representation of the interseismic elastic deformation due to variations of slip on the subduction thrust. The model has been benchmarked against the Savage (2D) and Okada (3D) analytical solutions. This model has an important advantage over traditional dislocation modeling in that we include temperature-sensitive viscosity for the upper and

Fish schooling as a basis for vertical axis wind turbine farm design.

Science.gov (United States)

Whittlesey, Robert W; Liska, Sebastian; Dabiri, John O

2010-09-01

Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high power coefficient (mechanical power output divided by the power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighboring turbines, HAWTs suffer from a reduced power coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's power coefficient when placed in close proximity to neighbors, thus yielding much higher power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance coefficient, which compares the expected average power coefficient of turbines in an array to a spatially isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance coefficient based upon an array of 16 x 16 wind turbines. The results suggest increases in power output of over one order of magnitude for a given area of land as compared to HAWTs.

Fish schooling as a basis for vertical axis wind turbine farm design

International Nuclear Information System (INIS)

Whittlesey, Robert W; Liska, Sebastian; Dabiri, John O

2010-01-01

Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the high power coefficient (mechanical power output divided by the power of the free-stream air through the turbine cross-sectional area) of an isolated turbine. However when in close proximity to neighboring turbines, HAWTs suffer from a reduced power coefficient. In contrast, previous research on vertical axis wind turbines (VAWTs) suggests that closely spaced VAWTs may experience only small decreases (or even increases) in an individual turbine's power coefficient when placed in close proximity to neighbors, thus yielding much higher power outputs for a given area of land. A potential flow model of inter-VAWT interactions is developed to investigate the effect of changes in VAWT spatial arrangement on the array performance coefficient, which compares the expected average power coefficient of turbines in an array to a spatially isolated turbine. A geometric arrangement based on the configuration of shed vortices in the wake of schooling fish is shown to significantly increase the array performance coefficient based upon an array of 16 x 16 wind turbines. The results suggest increases in power output of over one order of magnitude for a given area of land as compared to HAWTs.

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.

Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model

Directory of Open Access Journals (Sweden)

Stanislav Rockel

2014-03-01

Full Text Available Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion.

The velocity distribution caused by an airplane at the points of a vertical plane containing the span

Science.gov (United States)

Munk, Max M

1925-01-01

A formula for the computation of the vertical velocity component on all sides of an airplane is deduced and discussed. The formation is of value for the interpretation of such free flight tests where two airplanes fly alongside each other to facilitate observation.

Passive Acoustic Detection of Wind Turbine In-Flow Conditions for Active Control and Optimization

Energy Technology Data Exchange (ETDEWEB)

Murray, Nathan E.

2012-03-12

Wind is a significant source of energy; however, the human capability to produce electrical energy still has many hurdles to overcome. One of these is the unpredictability of the winds in the atmospheric boundary layer (ABL). The ABL is highly turbulent in both stable and unstable conditions (based on the vertical temperature profile) and the resulting fluctuations can have a dramatic impact on wind turbine operation. Any method by which these fluctuations could be observed, estimated, or predicted could provide a benefit to the wind energy industry as a whole. Based on the fundamental coupling of velocity fluctuations to pressure fluctuations in the nearly incompressible flow in the ABL, This work hypothesizes that a ground-based array of infrasonic pressure transducers could be employed to estimate the vertical wind profile over a height relevant for wind turbines. To analyze this hypothesis, experiments and field deployments were conducted. Wind tunnel experiments were performed for a thick turbulent boundary layer over a neutral or heated surface. Surface pressure and velocity probe measurements were acquired simultaneously. Two field deployments yielded surface pressure data from a 49 element array. The second deployment at the Reese Technology Center in Lubbock, TX, also included data from a smaller aperture, 96-element array and a 200-meter tall meteorological tower. Analysis of the data successfully demonstrated the ability to estimate the vertical velocity profile using coherence data from the pressure array. Also, dynamical systems analysis methods were successful in identifying and tracking a gust type event. In addition to the passive acoustic profiling method, this program also investigated a rapid response Doppler SODAR system, the optimization of wind turbine blades for enhanced power with reduced aeroacoustic noise production, and the implementation of a wireless health monitoring system for the wind turbine blades. Each of these other objectives

Creating a benchmark of vertical axis wind turbines in dynamic stall for validating numerical models

DEFF Research Database (Denmark)

Castelein, D.; Ragni, D.; Tescione, G.

2015-01-01

An experimental campaign using Particle Image Velocimetry (2C-PIV) technique has been conducted on a H-type Vertical Axis Wind Turbine (VAWT) to create a benchmark for validating and comparing numerical models. The turbine is operated at tip speed ratios (TSR) of 4.5 and 2, at an average chord...

4-D-VAR assimilation of disdrometer data and radar spectral reflectivities for raindrop size distribution and vertical wind retrievals

Science.gov (United States)

Mercier, François; Chazottes, Aymeric; Barthès, Laurent; Mallet, Cécile

2016-07-01

This paper presents a novel framework for retrieving the vertical raindrop size distribution (DSD) and vertical wind profiles during light rain events. This is also intended as a tool to better characterize rainfall microphysical processes. It consists in coupling K band Doppler spectra and ground disdrometer measurements (raindrop fluxes) in a 2-D numerical model propagating the DSD from the clouds to the ground level. The coupling is done via a 4-D-VAR data assimilation algorithm. As a first step, in this paper, the dynamical model and the geometry of the problem are quite simple. They do not allow the complexity implied by all rain microphysical processes to be encompassed (evaporation, coalescence breakup and horizontal air motion are not taken into account). In the end, the model is limited to the fall of droplets under gravity, modulated by the effects of vertical winds. The framework is thus illustrated with light, stratiform rain events. We firstly use simulated data sets (data assimilation twin experiment) to show that the algorithm is able to retrieve the DSD profiles and vertical winds. It also demonstrates the ability of the algorithm to deal with the atmospheric turbulence (broadening of the Doppler spectra) and the instrumental noise. The method is then applied to a real case study which was conducted in the southwest of France during the autumn 2013. The data set collected during a long, quiet event (6 h duration, rain rate between 2 and 7 mm h-1) comes from an optical disdrometer and a 24 GHz vertically pointing Doppler radar. We show that the algorithm is able to reproduce the observations and retrieve realistic DSD and vertical wind profiles, when compared to what could be expected for such a rain event. A goal for this study is to apply it to extended data sets for a validation with independent data, which could not be done with our limited 2013 data. Other data sets would also help to parameterize more processes needed in the model (evaporation

Towards accurate performance prediction of a vertical axis wind turbine operating at different tip speed ratios

NARCIS (Netherlands)

Rezaeiha, A.; Kalkman, I.; Blocken, B.J.E.

2017-01-01

Accurate prediction of the performance of a vertical-axis wind turbine (VAWT) using CFD simulation requires the employment of a sufficiently fine azimuthal increment (dθ) combined with a mesh size at which essential flow characteristics can be accurately resolved. Furthermore, the domain size needs

Tropospheric weather influenced by solar wind through atmospheric vertical coupling downward control

Science.gov (United States)

Prikryl, Paul; Bruntz, Robert; Tsukijihara, Takumi; Iwao, Koki; Muldrew, Donald B.; Rušin, Vojto; Rybanský, Milan; Turňa, Maroš; Šťastný, Pavel

2018-06-01

Occurrence of severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (MIA) system is investigated. It is observed that significant snowfall, wind and heavy rain, particularly if caused by low pressure systems in winter, tend to follow arrivals of high-speed solar wind. Previously published statistical evidence that explosive extratropical cyclones in the northern hemisphere tend to occur within a few days after arrivals of high-speed solar wind streams from coronal holes (Prikryl et al., 2009, 2016) is corroborated for the southern hemisphere. Cases of severe weather events are examined in the context of the magnetosphere-ionosphere-atmosphere (MIA) coupling. Physical mechanism to explain these observations is proposed. The leading edge of high-speed solar wind streams is a locus of large-amplitude magneto-hydrodynamic waves that modulate Joule heating and/or Lorentz forcing of the high-latitude lower thermosphere generating medium-scale atmospheric gravity waves that propagate upward and downward through the atmosphere. Simulations of gravity wave propagation in a model atmosphere using the Transfer Function Model (Mayr et al., 1990) reveal that propagating waves originating in the lower thermosphere can excite a spectrum of gravity waves in the lower atmosphere. In spite of significantly reduced amplitudes but subject to amplification upon reflection in the upper troposphere, these gravity waves can provide a lift of unstable air to release instabilities in the troposphere and initiate convection to form cloud/precipitation bands. It is primarily the energy provided by release of latent heat that leads to intensification of storms. These results indicate that vertical coupling in the atmosphere exerts downward control from solar wind to the lower atmospheric levels influencing tropospheric weather development.

Effects of Velocity Parameters of the Wind on the Line Formation for 32 CYG

Directory of Open Access Journals (Sweden)

Kyung-Mee Kim

1999-12-01

Full Text Available We calculate the theoretical line profiles in order to investigate the influence of various velocity parameters. Line profiles are calculated by using the exponential velocoty law with two acceleration regions for orbital phases 0.70 and 0.06. From this compttation we find that the influence of the wind velocity gradient on a giant star is more important in the region near the star than in the region away from the star. The observed lines show stronger emission than the calculated line profiles and we interpret the difference is caused by the inhomogeniety in the atmosphere of 32 Cyg.

Wind-Wave Effects on Vertical Mixing in Chesapeake Bay, USA: comparing observations to second-moment closure predictions.

Science.gov (United States)

Fisher, A. W.; Sanford, L. P.; Scully, M. E.

2016-12-01

Coherent wave-driven turbulence generated through wave breaking or nonlinear wave-current interactions, e.g. Langmuir turbulence (LT), can significantly enhance the downward transfer of momentum, kinetic energy, and dissolved gases in the oceanic surface layer. There are few observations of these processes in the estuarine or coastal environments, where wind-driven mixing may co-occur with energetic tidal mixing and strong density stratification. This presents a major challenge for evaluating vertical mixing parameterizations used in modeling estuarine and coastal dynamics. We carried out a large, multi-investigator study of wind-driven estuarine dynamics in the middle reaches of Chesapeake Bay, USA, during 2012-2013. The center of the observational array was an instrumented turbulence tower with both atmospheric and marine turbulence sensors as well as rapidly sampled temperature and conductivity sensors. For this paper, we examined the impacts of surface gravity waves on vertical profiles of turbulent mixing and compared our results to second-moment turbulence closure predictions. Wave and turbulence measurements collected from the vertical array of Acoustic Doppler Velocimeters (ADVs) provided direct estimates of the dominant terms in the TKE budget and the surface wave field. Observed dissipation rates, TKE levels, and turbulent length scales are compared to published scaling relations and used in the calculation of second-moment nonequilibrium stability functions. Results indicate that in the surface layer of the estuary, where elevated dissipation is balanced by vertical divergence in TKE flux, existing nonequilibrium stability functions underpredict observed eddy viscosities. The influences of wave breaking and coherent wave-driven turbulence on modeled and observed stability functions will be discussed further in the context of turbulent length scales, TKE and dissipation profiles, and the depth at which the wave-dominated turbulent transport layer

Large Eddy Simulation of Vertical Axis Wind Turbine wakes; Part II: effects of inflow turbulence

Science.gov (United States)

Duponcheel, Matthieu; Chatelain, Philippe; Caprace, Denis-Gabriel; Winckelmans, Gregoire

2017-11-01

The aerodynamics of Vertical Axis Wind Turbines (VAWTs) is inherently unsteady, which leads to vorticity shedding mechanisms due to both the lift distribution along the blade and its time evolution. Large-scale, fine-resolution Large Eddy Simulations of the flow past Vertical Axis Wind Turbines have been performed using a state-of-the-art Vortex Particle-Mesh (VPM) method combined with immersed lifting lines. Inflow turbulence with a prescribed turbulence intensity (TI) is injected at the inlet of the simulation from a precomputed synthetic turbulence field obtained using the Mann algorithm. The wake of a standard, medium-solidity, H-shaped machine is simulated for several TI levels. The complex wake development is captured in details and over long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake. Mean flow and turbulence statistics are computed over more than 10 diameters downstream of the machine. The sensitivity of the wake topology and decay to the TI level is assessed.

Design Loads on Platforms on Offshore wind Turbine Foundations with Respect to Vertical Wave Run-up

DEFF Research Database (Denmark)

Damsgaard, Mathilde L.; Gravesen, Helge; Andersen, Thomas Lykke

2007-01-01

reduction in the loads by up to 75%. Furthermore it is indicated, that the fact that offshore wind turbines often are placed on limited water depths thereby increasing the amount of (nearly) breaking waves, seems to increase the run-up height and thereby the pressures on the structure.......Experiences have shown that the vertical run-up generated by waves meeting the offshore wind turbine foundations, can result in rather vigorous loads on appurtenances and platform structures. This study aims to provide a qualitative method of determining run-up height and the following loads...

Large Eddy Simulation of Vertical Axis Wind Turbine wakes; Part I: from the airfoil performance to the very far wake

Science.gov (United States)

Chatelain, Philippe; Duponcheel, Matthieu; Caprace, Denis-Gabriel; Marichal, Yves; Winckelmans, Gregoire

2017-11-01

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. 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 with respect to the VAWT geometry and its operating point. 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.

Simple passive methods for the assessment of the directional and vertical distributions of wind-blown particulates

International Nuclear Information System (INIS)

Orza, J. A.G.; Cabello, M.; Mateo, J.

2009-01-01

We have designed and tested two types of passive collectors to study aeolian erosion in the field. The first passive sampler is a sticky pad that allows for directional particulate assessment by an automatic particle counting procedure. the second one features an omni-directional capture opening, and mass of retained particles is gravimetric ally quantified. Vertical arrays of these passive collectors have been constructed to obtain vertical profiles of the horizontal particle flux as a function of soil properties, nearby sources and wind speed. We present some first results from field campaigns. (Author) 3 refs.

CFD simulations of power coefficients for an innovative Darrieus style vertical axis wind turbine with auxiliary straight blades

Science.gov (United States)

Arpino, F.; Cortellessa, G.; Dell'Isola, M.; Scungio, M.; Focanti, V.; Profili, M.; Rotondi, M.

2017-11-01

The increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in renewable energy sources such as wind energy. Amongst the different typologies of wind generators, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, Computational Fluid Dynamic (CFD) simulations were performed in order to investigate the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds. The micro turbine under investigation is composed of three pairs of airfoils, consisting of a main and auxiliary blades with different chord lengths. The simulations were made using the open source finite volume based CFD toolbox OpenFOAM, considering different turbulence models and adopting a moving mesh approach for the turbine rotor. The simulated data were reported in terms of dimensionless power coefficients for dynamic performance analysis. The results from the simulations were compared to the data obtained from experiments on a scaled model of the same VAWT configuration, conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). From the proposed analysis, it was observed that the most suitable model for the simulation of the performances of the micro turbine under investigation is the one-equation Spalart-Allmaras, even if under the conditions analysed in the present work and for TSR values higher than 1.1, some discrepancies between numerical and experimental data can be observed.

Mapping the solar wind HI outflow velocity in the inner heliosphere by coronagraphic ultraviolet and visible-light observations

Science.gov (United States)

Dolei, S.; Susino, R.; Sasso, C.; Bemporad, A.; Andretta, V.; Spadaro, D.; Ventura, R.; Antonucci, E.; Abbo, L.; Da Deppo, V.; Fineschi, S.; Focardi, M.; Frassetto, F.; Giordano, S.; Landini, F.; Naletto, G.; Nicolini, G.; Nicolosi, P.; Pancrazzi, M.; Romoli, M.; Telloni, D.

2018-05-01

We investigated the capability of mapping the solar wind outflow velocity of neutral hydrogen atoms by using synergistic visible-light and ultraviolet observations. We used polarised brightness images acquired by the LASCO/SOHO and Mk3/MLSO coronagraphs, and synoptic Lyα line observations of the UVCS/SOHO spectrometer to obtain daily maps of solar wind H I outflow velocity between 1.5 and 4.0 R⊙ on the SOHO plane of the sky during a complete solar rotation (from 1997 June 1 to 1997 June 28). The 28-days data sequence allows us to construct coronal off-limb Carrington maps of the resulting velocities at different heliocentric distances to investigate the space and time evolution of the outflowing solar plasma. In addition, we performed a parameter space exploration in order to study the dependence of the derived outflow velocities on the physical quantities characterising the Lyα emitting process in the corona. Our results are important in anticipation of the future science with the Metis instrument, selected to be part of the Solar Orbiter scientific payload. It was conceived to carry out near-sun coronagraphy, performing for the first time simultaneous imaging in polarised visible-light and ultraviolet H I Lyα line, so providing an unprecedented view of the solar wind acceleration region in the inner corona. The movie (see Sect. 4.2) is available at https://www.aanda.org

Spectral characteristics of aurorae connected with high-velocity flows of the solar wind from coronal holes

International Nuclear Information System (INIS)

Khviyuzova, T.A.; Leont'ev, S.V.

1997-01-01

Bright electron aurorae almost always followed by red lower edge occur when the Earth is being passed by high-velocity flows from coronal holes within the auroral range at the night meridian. In contrast to other types of the solar wind the high-velocity flows from coronal holes do not cause the occurrence of A type red polar aurorae, that is, the spectrum of electrons pouring into the Earth atmosphere in these cases is shifted towards higher energies

Linear wind generator

International Nuclear Information System (INIS)

Kozarov, A.; Petrov, O.; Antonov, J.; Sotirova, S.; Petrova, B.

2006-01-01

The purpose of the linear wind-power generator described in this article is to decrease the following disadvantages of the common wind-powered turbine: 1) large bending and twisting moments to the blades and the shaft, especially when strong winds and turbulence exist; 2) significant values of the natural oscillation period of the construction result in the possibility of occurrence of destroying resonance oscillations; 3) high velocity of the peripheral parts of the rotor creating a danger for birds; 4) difficulties, connected with the installation and the operation on the mountain ridges and passages where the wind energy potential is the largest. The working surfaces of the generator in questions driven by the wind are not connected with a joint shaft but each moves along a railway track with few oscillations. So the sizes of each component are small and their number can be rather large. The mechanical trajectory is not a circle but a closed outline in a vertical plain, which consists of two rectilinear sectors, one above the other, connected in their ends by semi-circumferences. The mechanical energy of each component turns into electrical on the principle of the linear electrical generator. A regulation is provided when the direction of the wind is perpendicular to the route. A possibility of effectiveness is shown through aiming of additional quantities of air to the movable components by static barriers

Added damping of a wind turbine rotor : Two-dimensional discretization expressing the nonlinear wind-force dependency

NARCIS (Netherlands)

Van der Male, P.; Van Dalen, K.N.; Metrikine, A.

2014-01-01

In determining wind forces on wind turbine blades, and subsequently on the tower and the foundation, the blade response velocity cannot be neglected. This velocity alters the wind force, which depends on the wind velocity relative to that of the blades This blade response velocity component of the

Impact of wind velocity on the performance of the RVACS decay heat removal system

International Nuclear Information System (INIS)

Tzanos, C.P.

1997-01-01

The impact of wind velocity on the performance of the reactor vessel auxiliary cooling system (RVACS) of an advanced liquid-metal reactor design is analyzed, and design modifications that mitigate adverse wind effects are investigated. In the reference design, the reactor is served by four communicating RVACS stacks, and each stack has two air inlets. In this two-inlet stack design, winds blowing in a direction 90 deg from the axis formed by the two stack inlets result in pressure distributions around the stacks that drastically change the desired airflow pattern in the RVACS. This leads to significantly elevated RVACS air temperatures and significant azimuthal guard vessel temperature variations. For example, a 27 m/s (60 mph) wind leads to an air temperature at the exit of the RVACS heated section that is ∼115 C higher than that under no-wind conditions. The addition of two more inlets per stack, one inlet per stack side, significantly improves RVACS performance. The air temperature at the exit of the heated RVACS section is significantly reduced below that of the two-inlet design, and this temperature decreases as the wind speed increases. An increase in wind speed from 3 to 27 m/s leads to an air temperature change from 186 to 165 C. The azimuthal temperature variation is also improved. At the top of the guard vessel, this variation is reduced from 62.5 to 8.5 C at the low wind speed of 3 m/s and from 85.0 to 30.5 C at the high wind speed of 27 m/s

Far-Field and Middle-Field Vertical Velocities Associated with Megathrust Earthquakes

Science.gov (United States)

Fleitout, L.; Trubienko, O.; Klein, E.; Vigny, C.; Garaud, J.; Shestakov, N.; Satirapod, C.; Simons, W. J.

2013-12-01

The recent megathrust earthquakes (Sumatra, Chili and Japan) have induced far-field postseismic subsidence with velocities from a few mm/yr to more than 1cm/yr at distances from 500 to 1500km from the earthquake epicentre, for several years following the earthquake. This subsidence is observed in Argentina, China, Korea, far-East Russia and in Malaysia and Thailand as reported by Satirapod et al. ( ASR, 2013). In the middle-field a very pronounced uplift is localized on the flank of the volcanic arc facing the trench. This is observed both over Honshu, in Chile and on the South-West coast of Sumatra. In Japan, the deformations prior to Tohoku earthquake are well measured by the GSI GPS network: While the East coast was slightly subsiding, the West coast was raising. A 3D finite element code (Zebulon-Zset) is used to understand the deformations through the seismic cycle in the areas surrounding the last three large subduction earthquakes. The meshes designed for each region feature a broad spherical shell portion with a viscoelastic asthenosphere. They are refined close to the subduction zones. Using these finite element models, we find that the pattern of the predicted far-field vertical postseismic displacements depends upon the thicknesses of the elastic plate and of the low viscosity asthenosphere. A low viscosity asthenosphere at shallow depth, just below the lithosphere is required to explain the subsidence at distances from 500 to 1500km. A thick (for example 600km) asthenosphere with a uniform viscosity predicts subsidence too far away from the trench. Slip on the subduction interface is unable tot induce the observed far-field subsidence. However, a combination of relaxation in a low viscosity wedge and slip or relaxation on the bottom part of the subduction interface is necessary to explain the observed postseismic uplift in the middle-field (volcanic arc area). The creep laws of the various zones used to explain the postseismic data can be injected in

A comparison between the dynamics of horizontal and vertical axis offshore floating wind turbines.

Science.gov (United States)

Borg, M; Collu, M

2015-02-28

The need to further exploit offshore wind resources in deeper waters has led to a re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications. However, there has been little effort to systematically compare VAWTs to the more conventional horizontal axis wind turbine (HAWT). This article initiates this comparison based on prime principles, focusing on the turbine aerodynamic forces and their impact on the floating wind turbine static and dynamic responses. VAWTs generate substantially different aerodynamic forces on the support structure, in particular, a potentially lower inclining moment and a substantially higher torque than HAWTs. Considering the static stability requirements, the advantages of a lower inclining moment, a lower wind turbine mass and a lower centre of gravity are illustrated, all of which are exploitable to have a less costly support structure. Floating VAWTs experience increased motion in the frequency range surrounding the turbine [number of blades]×[rotational speed] frequency. For very large VAWTs with slower rotational speeds, this frequency range may significantly overlap with the range of wave excitation forces. Quantitative considerations are undertaken comparing the reference NREL 5 MW HAWT with the NOVA 5 MW VAWT. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Rotor instrumentation circuits for the Sandia 34-meter vertical axis wind turbine

Science.gov (United States)

Sutherland, Herbert J.; Stephenson, William A.

1988-07-01

Sandia National Laboratories has erected a research oriented, 34-meter diameter, Darrieus vertical axis wind turbine near Bushland, Texas, which has been designated the Sandia 34-m VAWT Test Bed. To meet present and future research needs, the machine was equipped with a large array of sensors. This manuscript details the sensors initially placed on the rotor, their respective instrumentation circuits, and the provisions incorporated into the design of the rotor instrumentation circuits for future research. This manuscript was written as a reference manual for the rotor instrumentation of the Test Bed.

Kinematics of a vertical axis wind turbine with a variable pitch angle

Science.gov (United States)

Jakubowski, Mateusz; Starosta, Roman; Fritzkowski, Pawel

2018-01-01

A computational model for the kinematics of a vertical axis wind turbine (VAWT) is presented. A H-type rotor turbine with a controlled pitch angle is considered. The aim of this solution is to improve the VAWT productivity. The discussed method is related to a narrow computational branch based on the Blade Element Momentum theory (BEM theory). The paper can be regarded as a theoretical basis and an introduction to further studies with the application of BEM. The obtained torque values show the main advantage of using the variable pitch angle.

Regional Analysis of Long-term Local and Synoptic Effects on Wind Velocity and Energy Patterns in Complex Terrain

Science.gov (United States)

Belu, R.; Koracin, D. R.

2017-12-01

Investments in renewable energy are justified in both environmental and economic terms. Climate change risks call for mitigation strategies aimed to reduce pollutant emissions, while the energy supply is facing high uncertainty by the current or future global economic and political contexts. Wind energy is playing a strategic role in the efforts of any country for sustainable development and energy supply security. Wind energy is a weather and climate-dependent resource, having a natural spatio-temporal variability at time scales ranging from fraction of seconds to seasons and years, while at spatial scales is strongly affected by the topography and vegetation. Main objective of the study is to investigate spatio-temporal characteristics of the wind velocity in the Southwest U.S., that are relevant to wind energy assessment, analysis, development, operation, and grid integration, by using long-term multiple meteorological tower observations. Wind velocity data and other meteorological parameters from five towers, located near Tonopah, Nevada, operated between 2003 to 2008, and from three towers are located in Carson Valley, Nevada, operated between 2006 and 2014 were used in this study. Multi-annual wind speed data collected did not show significant increase trends with increasing elevation; the differences are mainly governed by the topographic complexity, including local atmospheric circulations. Auto- and cross-correlations show a strong coherence between the wind speed and direction with slowly decreasing amplitude of the multi-day periodicity with increasing lag periods. Besides pronounced diurnal periodicity at all locations, detrended fluctuation analysis also showed significant seasonal and annual periodicities, and long-memory persistence with similar characteristics. In spite of significant differences in mean wind speeds among the towers, due to location specifics, the relatively high auto- and cross-correlation coefficients among the towers indicate

Navy-New Hampshire Wind Energy Program.

Science.gov (United States)

1979-11-01

wind use for both the MOD-2 and Darrieus wind turbine -generators when located on these peaks. lIT...Horizontal Axis WECS 10 2-4 Darrieus Vertical Axis Wind Turbine 12 2-5 Alcoa Design for 500 kW Vertical Axis WECS 13 3-1 Fraction of Wind Observations... Turbines In 1925, G.J.M. Darrieus patented the concept of a vertical axis wind turbine . Today, the Darrieus design has evolved to a fixed-pitch

Experimental and Computational Investigations of Vertical Axis Wind Turbine Enclosed with Flanged Diffuser

Science.gov (United States)

Surya Raj, G.; Sangeetha, N.; Prince, M.

2018-02-01

Generation of wind energy is a must to meet out additional demand. To meet out the additional demand several long term plans were considered now being taken up for generation of energy for the fast developing industries. Detailed researches were since taken up to improve the efficiency of such vertical axis wind turbine (VAWT). In this work VAWT with diffuser and without diffuser arrangement are considered for experimental and analysis. Five diffusers were since provided around its blades of VAWT which will be placed inside a pentagon shaped fabricated structure. In this power output of the diffuser based VAWT arrangement were studied in both numerical and experimental methods and related with that of a bared VAWT. Finally, it was found that the output power of diffuser based VAWT generates approximately two times than that of bared VAWT.

THEORETICAL ASPECTS AND NUMERICAL MODELLING FOR LONG TERM PREDICTION OF ABL AND WIND DISTRIBUTION IN POWER FARM

Directory of Open Access Journals (Sweden)

RADULESCU V.

2015-03-01

Full Text Available The paper is structured in seven parts, the last for few conclusions and finally some references. It is based on concrete measurements and observation during around 2 years. First is presented an introduction of the actual situation. In part two are mentioned the methods and hypotheses in evaluation of wind velocity distribution in boundary layers for atmospheric air, taking into account the roughness of ground surfaces. It is mentioned a concrete area, south part of Moldova. In third part is presented a solution for the geodetic model and finally are selected the altimetry solution. In chapter four is determined the influence of air density, temperature and pressure on wind turbine functioning. In the next chapters are presented the numerical model with special boundary conditions, taking into account different value of roughness and finally the obtained results. It is also estimated velocity variation during day-night. Finally is presented the vertical distribution of horizontal wind velocity for a wind farm, obviously important due the power of turbine (around 3 MW each one. Some conclusions and references are also mentioned.

Ice-Tethered Profiler observations: Vertical profiles of temperature, salinity, oxygen, and ocean velocity from an Ice-Tethered Profiler buoy system

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This collection contains repeated vertical profiles of ocean temperature and salinity versus pressure, as well as oxygen and velocity for some instruments. Data were...

Effect of the number of blades and solidity on the performance of a vertical axis wind turbine

Science.gov (United States)

Delafin, PL; Nishino, T.; Wang, L.; Kolios, A.

2016-09-01

Two, three and four bladed ϕ-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.

Diurnal Dynamics of Standard Deviations of Three Wind Velocity Components in the Atmospheric Boundary Layer

Science.gov (United States)

Shamanaeva, L. G.; Krasnenko, N. P.; Kapegesheva, O. F.

2018-04-01

Diurnal dynamics of the standard deviation (SD) of three wind velocity components measured with a minisodar in the atmospheric boundary layer is analyzed. Statistical analysis of measurement data demonstrates that the SDs for x- and y-components σx and σy lie in the range from 0.2 to 4 m/s, and σz = 0.1-1.2 m/s. The increase of σx and σy with the altitude is described sufficiently well by a power law with exponent changing from 0.22 to 1.3 depending on time of day, and σz increases by a linear law. Approximation constants are determined and errors of their application are estimated. It is found that the maximal diurnal spread of SD values is 56% for σx and σy and 94% for σz. The established physical laws and the obtained approximation constants allow the diurnal dynamics of the SDs for three wind velocity components in the atmospheric boundary layer to be determined and can be recommended for application in models of the atmospheric boundary layer.

Application of Circulation Controlled Blades for Vertical Axis Wind Turbines

Directory of Open Access Journals (Sweden)

Velissarios Kourkoulis

2013-07-01

Full Text Available The blades of a vertical axis wind turbine (VAWT rotor see an inconsistent angle of attack through its rotation. Consequently, VAWT blades generally use symmetrical aerofoils with a lower lift-to-drag ratio than cambered aerofoils tailored to maximise horizontal axis wind turbine rotor performance. This paper considers the feasibility of circulation controlled (CC VAWT blades, using a tangential air jet to provide lift and therefore power augmentation. However CC blade sections require a higher trailing-edge thickness than conventional sections giving rise to additional base drag. The choice of design parameters is a compromise between lift augmentation, additional base drag as well as the power required to pump the air jet. Although CC technology has been investigated for many years, particularly for aerospace applications, few researchers have considered VAWT applications. This paper considers the feasibility of the technology, using Computational Fluid Dynamics to evaluate a baseline CC aerofoil with different trailing-edge ellipse shapes. Lift and drag increments due to CC are considered within a momentum based turbine model to determine net power production. The study found that for modest momentum coefficients significant net power augmentation can be achieved with a relatively simple aerofoil geometry if blowing is controlled through the blades rotation.

Integrated roof wind energy system

Directory of Open Access Journals (Sweden)

Moonen S.P.G.

2012-10-01

Full Text Available Wind is an attractive renewable source of energy. Recent innovations in research and design have reduced to a few alternatives with limited impact on residential construction. Cost effective solutions have been found at larger scale, but storage and delivery of energy to the actual location it is used, remain a critical issue. The Integrated Roof Wind Energy System is designed to overcome the current issues of urban and larger scale renewable energy system. The system is built up by an axial array of skewed shaped funnels that make use of the Venturi Effect to accelerate the wind flow. This inventive use of shape and geometry leads to a converging air capturing inlet to create high wind mass flow and velocity toward a vertical-axis wind turbine in the top of the roof for generation of a relatively high amount of energy. The methods used in this overview of studies include an array of tools from analytical modelling, PIV wind tunnel testing, and CFD simulation studies. The results define the main design parameters for an efficient system, and show the potential for the generation of high amounts of renewable energy with a novel and effective system suited for the built environment.

On the Effect of Offshore Wind Parks on Ocean Dynamics

Science.gov (United States)

Ludewig, E.; Pohlmann, T.

2012-12-01

Nowadays renewable energy resources play a key role in the energy supply discussion and especially an increasingly interest in wind energy induces intensified installations of wind parks. At this offshore wind energy gains in popularity in the course of higher and more consistent energy availability than over land. For example Germany's government adopted a national interurban offshore wind energy program comprising the construction of hundreds of wind turbines within Germany's Exclusive Economic Zone to ensure up to 50% of Germany's renewable energy supply. The large number of installation in coastal regions asks for analyzing the impact of offshore wind parks (OWPs) on the atmosphere and the ocean. As known from literature such wind parks excite also-called wake-effect and such an influence on the wind field in turn affects ocean circulation. To cover OWP's impact on ocean dynamics we evaluate model simulations using the Hamburg Shelf-Ocean-Model (HAMSOM). All simulations were driven with a wind forcing produced by the Mesoscale Atmosphere Model of the Hamburg University (METRAS) which has implemented wind turbines. Wind forcing data were generated in collaboration with and by courtesy of the Meteorological Institute of the University of Hamburg, Department Technical Meteorology, Numeric Modeling-METRAS. To evaluate dynamical changes forced by the OWP's wind wake-effect we did a sensitivity study with a theoretical setup of a virtual ocean of 60m depth with a flat bottom and a temperature and salinity stratification according to common North Sea's conditions. Here our results show that already a small OWP of 12 wind turbines, placed in an area of 4 km^2, lead to a complex change in ocean dynamics. Due to the wake-effect zones of upwelling and downwelling are formed within a minute after turning-on wind turbines. The evolving vertical cells have a size of around 15x15 kilometers with a vertical velocity in order of 10^-2 mm/sec influencing the dynamic of an area

A method of calculation on the airloading of vertical axis wind turbine

Science.gov (United States)

Azuma, A.; Kimura, S.

A new method of analyzing the aerodynamic characteristics of the Darrieus Vertical-Axis Wind Turbine (VAWT) by applying the local circulation method is described. The validity of this method is confirmed by analyzing the air load acting on a curved blade. The azimuthwise variation of spanwise airloading, torque, and longitudinal forces are accurately calculated for a variety of operational conditions. The results are found to be in good agreement with experimental ones obtained elsewhere. It is concluded that the present approach can calculate the aerodynamic characteristics of the VAWT with much less computational time than that used by the free vortex model.

Aerodynamics and Motion Performance of the H-Type Floating Vertical Axis Wind Turbine

Directory of Open Access Journals (Sweden)

Ying Guo

2018-02-01

Full Text Available Aerodynamics and motion performance of the floating vertical wind turbine (VAWT were studied in this paper, where the wind turbine was H-type and the floating foundation was truss spar type. Based on the double-multiple-stream-tube theory, the formulae were deduced to calculate the aerodynamic loads acting on the wind turbine considering the motions of the floating foundation. The surge-heave-pitch nonlinear coupling equations of the H-type floating VAWT were established. Aerodynamics and motion performance of a 5 MW H-type floating VAWT was studied, and the effect of the floating foundation motions on the aerodynamic loads was analyzed. It is shown that the motions of the floating foundation on the aerodynamics cannot be ignored. The motion of the H-type floating VAWT was also compared with that of the Φ-type floating VAWT: they have the same floating foundation, rated output power, mooring system and total displacement. The results show that the H-type floating VAWT has better motion performance, and the mean values of surge, heave and pitch of the H-type floating VAWT are much smaller comparing with the Φ-type floating VAWT.

Numerical investigation on aerodynamic performance of a novel vertical axis wind turbine with adaptive blades

International Nuclear Information System (INIS)

Wang, Ying; Sun, Xiaojing; Dong, Xiaohua; Zhu, Bing; Huang, Diangui; Zheng, Zhongquan

2016-01-01

Highlights: • A novel vertical axis wind turbine with deformed blades is designed. • The universal tendency of power characteristics for simulated turbine is found. • The whole flow field of different turbines from the aspect of vortex is analyzed. • The tracking analysis of vortex at different positions for a blade is conducted. • The aerodynamic performance of turbine with three deformed blades is analyzed. - Abstract: In this paper, a novel Darrieus vertical axis wind turbine was designed whose blade can be deformed automatically into a desired geometry and thus achieve a better aerodynamic performance. A series of numerical simulations were conducted by utilizing the United Computational Fluid Dynamics code. Firstly, analysis and comparison of the performance of undeformed and deformed blades for the rotors having different blades were conducted. Then, the power characteristics of each simulated turbine were summarized and a universal tendency was found. Secondly, investigation on the effect of blade number and solidity on the power performance of Darrieus vertical axis wind turbine with deformable and undeformable blades was carried out. The results indicated that compared to conventional turbines with same solidity, the maximum percentage increase in power coefficient that the low solidity turbine with three deformable blades can achieve is about 14.56%. When solidity is high and also turbine operates at low tip speed ratio of less than the optimum value, the maximum power coefficient increase for the turbines with two and four deformable blades are 7.51% and 8.07%, respectively. However, beyond the optimal tip speed ratio, the power improvement of the turbine using the deformable blades seems not significant and even slightly worse than the conventional turbines. The last section studied the transient behavior of vortex and turbulent flow structures around the deformable rotor blade to explore the physical mechanism of improving aerodynamic

Project "Convective Wind Gusts" (ConWinG)

Science.gov (United States)

Mohr, Susanna; Richter, Alexandra; Kunz, Michael; Ruck, Bodo

2017-04-01

Convectively-driven strong winds usually associated with thunderstorms frequently cause substantial damage to buildings and other structures in many parts of the world. Decisive for the high damage potential are the short-term wind speed maxima with duration of a few seconds, termed as gusts. Several studies have shown that convectively-driven gusts can reach even higher wind speeds compared to turbulent gusts associated with synoptic-scale weather systems. Due to the small-scale and non-stationary nature of convective wind gusts, there is a considerable lack of knowledge regarding their characteristics and statistics. Furthermore, their interaction with urban structures and their influence on buildings is not yet fully understood. For these two reasons, convective wind events are not included in the present wind load standards of buildings and structures, which so far have been based solely on the characteristics of synoptically-driven wind gusts in the near-surface boundary layer (e. g., DIN EN 1991-1-4:2010-12; ASCE7). However, convective and turbulent gusts differ considerably, e.g. concerning vertical wind-speed profiles, gust factors (i.e., maximum to mean wind speed), or exceedance probability curves. In an effort to remedy this situation, the overarching objective of the DFG-project "Convective Wind Gusts" (ConWinG) is to investigate the characteristics and statistics of convective gusts as well as their interaction with urban structures. Based on a set of 110 climate stations of the German Weather Service (DWD) between 1992 and 2014, we analyzed the temporal and spatial distribution, intensity, and occurrence probability of convective gusts. Similar to thunderstorm activity, the frequency of convective gusts decreases gradually from South to North Germany. A relation between gust intensity/probability to orography or climate conditions cannot be identified. Rather, high wind speeds, e.g., above 30 m/s, can be expected everywhere in Germany with almost

Guy cable design and damping for vertical axis wind turbines

Science.gov (United States)

Carne, T. G.

1981-01-01

Guy cables are frequently used to support vertical axis wind turbines since guying the turbine reduces some of the structural requirements on the tower. The guys must be designed to provide both the required strength and the required stiffness at the top of the turbine. The axial load which the guys apply to the tower, bearings, and foundations is an undesirable consequence of using guys to support the turbine. Limiting the axial load so that it does not significantly affect the cost of the turbine is an important objective of the cable design. The lateral vibrations of the cables is another feature of the cable design which needs to be considered. These aspects of the cable design are discussed, and a technique for damping cable vibrations was mathematically analyzed and demonstrated with experimental data.

A comparison of two fully coupled codes for integrated dynamic analysis of floating vertical axis wind turbines

NARCIS (Netherlands)

Koppenol, Boy; Cheng, Zhengshun; Gao, Zhen; Simao Ferreira, C.; Moan, T; Tande, John Olav Giæver; Kvamsdal, Trond; Muskulus, Michael

2017-01-01

This paper presents a comparison of two state-of-the-art codes that are capable of modelling floating vertical axis wind turbines (VAWTs) in fully coupled time-domain simulations, being the HAWC2 by DTU and the SIMO-RIFLEX-AC code by NTNU/MARINTEK. The comparative study focusses on the way

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

Directory of Open Access Journals (Sweden)

H. Steinhagen

Full Text Available A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

Directory of Open Access Journals (Sweden)

H. Steinhagen

1994-07-01

Full Text Available A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.

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...

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。

Real-time approaches to the estimation of local wind velocity for a fixed-wing unmanned air vehicle

International Nuclear Information System (INIS)

Chan, W L; Lee, C S; Hsiao, F B

2011-01-01

Three real-time approaches to estimating local wind velocity for a fixed-wing unmanned air vehicle are presented in this study. All three methods work around the navigation equations with added wind components. The first approach calculates the local wind speed by substituting the ground speed and ascent rate data given by the Global Positioning System (GPS) into the navigation equations. The second and third approaches utilize the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), respectively. The results show that, despite the nonlinearity of the navigation equations, the EKF performance is proven to be on a par with the UKF. A time-varying noise estimation method based on the Wiener filter is also discussed. Results are compared with the average wind speed measured on the ground. All three approaches are proven to be reliable with stated advantages and disadvantages

Application of computational fluid dynamics (CFD) simulation in a vertical axis wind turbine (VAWT) system

Science.gov (United States)

Kao, Jui-Hsiang; Tseng, Po-Yuan

2018-01-01

The objective of this paper is to describe the application of CFD (Computational fluid dynamics) technology in the matching of turbine blades and generator to increase the efficiency of a vertical axis wind turbine (VAWT). A VAWT is treated as the study case here. The SST (Shear-Stress Transport) k-ω turbulence model with SIMPLE algorithm method in transient state is applied to solve the T (torque)-N (r/min) curves of the turbine blades at different wind speed. The T-N curves of the generator at different CV (constant voltage) model are measured. Thus, the T-N curves of the turbine blades at different wind speed can be matched by the T-N curves of the generator at different CV model to find the optimal CV model. As the optimal CV mode is selected, the characteristics of the operating points, such as tip speed ratio, revolutions per minute, blade torque, and efficiency, can be identified. The results show that, if the two systems are matched well, the final output power at a high wind speed of 9-10 m/s will be increased by 15%.

Large-Eddy Simulation of Atmospheric Boundary-Layer Flow Through a Wind Farm Sited on Topography

Science.gov (United States)

Shamsoddin, Sina; Porté-Agel, Fernando

2017-04-01

Large-eddy simulation (LES) has recently been well validated and applied in the context of wind turbines over flat terrain; however, to date its accuracy has not been tested systematically in the case of turbine-wake flows over topography. Here, we investigate the wake flow in a wind farm situated on hilly terrain using LES for a case where wind-tunnel experimental data are available. To this end, first boundary-layer flow is simulated over a two-dimensional hill in order to characterize the spatial distribution of the mean velocity and the turbulence statistics. A flow simulation is then performed through a wind farm consisting of five horizontal-axis wind turbines sited over the same hill in an aligned layout. The resulting flow characteristics are compared with the former case, i.e., without wind turbines. To assess the validity of the simulations, the results are compared with the wind-tunnel measurements. It is found that LES can reproduce the flow field effectively, and, specifically, the speed-up over the hilltop and the velocity deficit and turbulence intensity enhancement induced by the turbines are well captured by the simulations. Besides, the vertical profiles of the mean velocity and turbulence intensity at different streamwise positions match well those for the experiment. In addition, another numerical experiment is carried out to show how higher (and more realistic) thrust coefficients of the turbines lead to stronger wakes and, at the same time, higher turbulence intensities.

Analysis of vertical wind direction and speed gradients for data from the met. mast at Høvsøre

DEFF Research Database (Denmark)

Cariou, Nicolas; Wagner, Rozenn; Gottschall, Julia

The task of this project has been to study the vertical gradient of the wind direction from experimental data obtained with different measurement instruments at the Høvsøre test site, located at the west coast of Denmark. The major part of the study was based on data measured by wind vanes mounted...... at a meteorological (met.) mast. These measurements enabled us to make an analysis of the variation of the direction with altitude, i.e. the wind direction shear. For this purpose, four years of wind direction measurements at two heights (60 m and 100 m) were analysed with special respect to the diurnal and seasonal...... variations of the direction gradient. The location of the test site close to the sea allowed for an investigation of specific trends for offshore and onshore winds, dependent on the considered wind direction sector. Furthermore, a comparison to lidar measurements showed the existence of an offset between...

Development, construction and testing of a vertical axis 200 kW wind turbine

Energy Technology Data Exchange (ETDEWEB)

1974-12-20

It is proposed to design and develop a large vertical axis wind turbine that will generate economically 200 kilowatts of power at a wind speed of about 30 miles per hour. The scope of this proposal is to carry out studies, build, erect and test an electrical power generation plant that will feed into existing power grids. Preliminary technical studies indicate that the power of the turbine increases with the third power of the the wind speed. The rotor power loading should be as high as the prevailing winds allow; thus it would always be advisable to let the rotor run at as high an rpm as the economics will allow. For turbines up to about 100 ft in diameter, an extruded blade seems to be the best solution for economic rotor design. A 300 ft/s runaway tip speed seems to be acceptable as an rpm limit. Structurally, it is advantageous to increase the blade airfoil section to 18%. The proposed program has a very high probability of success in that each element of the total system involves a very low technical risk. The manufacturing methods rely on existing technology, and preliminary research indicates that readily available commercial materials can be used. There will be no involvement with highly stressed, fatigue-sensitive components. The total unit energy cost will be about fifty percent less for the proposed 90 ft. turbine than for the 15 ft. turbine produced for the National Research Council. 8 figs., 12 tabs.

The Dermond vertical axis wind turbine : a suitable solution for remote sites; L'eolienne a axe vertical Dermond : une eolienne particulierement bien adaptee aux milieux isoles