Blockage corrections for the experimental results obtained for a small-scale wind turbine in a wind tunnel are required in order to estimate how the same turbine would perform in real conditions. The ...tunnel blockage is defined as the ratio of the wind turbine swept area to the wind tunnel cross-section area. Experimental measurements of the power coefficient were performed on a horizontal-axis wind turbine with two rotors of diameter equal to 2 m and different numbers of blades, namely three and five. Measurements were carried out for different tip speed ratios in the closed circuit open test section wind tunnel of the University of Perugia (Italy). The obtained experimental results were compared with the numerical ones carried out in free conditions by using a CFD approach based on the steady-RANS method with the SST k-ω turbulence model, adopting the multiple reference frame (MRF) strategy to reduce the computational effort. The comparison showed that the maximum value of blockage, which is reached in the asymptotic limit at very large tip speed ratio (TSR) values, does not depend appreciably on the number of blades. A higher number of blades, however, makes the occurrence of the maximum blockage come earlier at lower TSRs.
The present paper applies Synthetic Aperture Radar (SAR) based on Local Gradient-Modified (LG-Mod) algorithm to retrieve wind directions from Sentinel-1 data in the Camargue and the Wadden Sea ...protected coastal areas. Wind speeds are estimated through the inversion of the C-band MODel 5.N (CMOD5.N) backscattering model. Both Interferometric Wide Swath (IW) and Extra Wide Swath (EW) Level 1 products were evaluated for wind fields retrieval at high (5 km) and medium (12.5 km) output spatial resolutions. SSW fields from Sentinel-1 were compared with Numerical Weather Prediction (NWP) models and in situ data. Exploitation of the LG-Mod provided wind direction with a related marginal error parameter (i.e., MEαROI) which proved useful for selecting the optimal input pixel size of SAR data processing. When compared to in situ data, the selection of the optimal pixel size reduced the Root Mean Squared Error (RMSE) values of LG-Mod wind directions up to 7° and about 45° for Wadden Sea and the Camargue site, respectively. In turn, such reduction provided a decrease of the wind speed RMSE values up to 0.7 m/s and 2.1 m/s, for Wadden Sea and the Camargue site, respectively. In addition, the LG-Mod gave better performance than the global NWP model European Centre for Medium-Range Weather Forecasts (ECMWF) in estimation of wind direction, at 12.5 km output spatial resolution, for both sites. The MEαROI exploitation in the directional analysis of IW and EW products evidenced that at high resolution (5 km) the percentage of reliable wind directions from IW images (84.5%) resulted much larger than that obtained from EW images (30.1%). At medium resolution (12.5 km) instead, the percentage values resulted quite close to each other (99.2% and 86.3%, respectively). IW images proved optimal for high resolution SSW retrieval, whereas EW images suitable for medium resolution. With respect to NWP models, the spectral analysis confirmed the suitability of Sentinel-1 to represent the local wind fields spatial variability in coastal areas, at both high and medium output resolution. Our findings suggest that the combination of the LG-Mod algorithm with NWP models could better resolve spatially wind patterns in complex coastal areas.
•Effectiveness of Sentinel-1 wind direction retrieval in coastal areas investigated•Different image mode and resolution class products (IW and EW) analyzed by LG-Mod•At both high and medium resolution, IW images provide reliable directional results.•Validation of LG-Mod wind estimation through in situ measurements•Comparison of LG-Mod wind estimation with regional and global NWP models and in situ data
•Techno-economic analysis of a real wind farm repowering project.•A comparative assessment of the wind energy production is carried out.•Results show the feasibility and profitability of the ...repowering project.•The sensitivity analysis shows the uncertainties affecting key parameters.•Model could be applied to other repowering projects and other geographical areas.
The wind industry is currently facing a major challenge due to the ageing of the wind turbines that were first commissioned. Recent wind turbine designs present higher power performance and lower maintenance requirements than older wind turbines. Furthermore, most of the old wind turbines are installed in the best sites for wind resource exploitation. Under this framework, the repowering of wind farms with the replacement of the old machines by new designs is recognised as a focus area for the wind industry. This paper performs a techno-economic analysis of a real wind farm repowering experience at the Malpica wind farm, located in the Northwest of Spain. Results show the annual energy production of the repowered wind farm increases up to twofold that of the old wind farm with the same rated power. Moreover, the economic analysis reveals the project yields satisfactory profitability, even without reliance on public subsidies as currently happens in Spain. In addition, a sensitivity analysis allows us to understand the effects of the uncertainties over the lifetime of the wind farm, and how they affect the projects performance and profitability.
The increasing attention of stakeholders to extreme winds impacting the built environment is driving towards the adoption of probabilistic risk assessment methods, which aim at the stochastic ...modelling of three main risk components: hazard, vulnerability (or fragility), and exposure. Taking from seismic risk assessment, the hazard is typically expressed in terms of exceedance rate of an intensity measure of the natural event, usually related to wind speed, and the risk metric is the expected annual loss or the exceedance rate of the loss. On these premises the extreme wind risk assessment software, ERMESS, has been developed for risk assessment for portfolios of buildings. It integrates recent global- and regional-scale hazard maps for extreme wind events, that is, cyclones and tornadoes, and a database of more than five-thousand building- and component-level wind vulnerability and fragility functions from the literature. A procedure to develop building-level fragility models, based on existing component-level fragility functions, was also developed and embedded in ERMESS. Finally, the exposure (i.e. consequence) models are based on information provided by the insurance industry. The paper illustrates the software by means of proof-of-concept applications that show how ERMESS can be effective in wind risk assessment.
Abstract
The Great Plains (GP) low-level jet (GPLLJ) contributes to GP warm season water resources (precipitation), wind resources, and severe weather outbreaks. Past research has shown that synoptic ...and local mesoscale physical mechanisms (Holton and Blackadar mechanisms) are required to explain GPLLJ variability. Although soil moisture–PBL interactions are central to local mechanistic theories, the diurnal effect of regional soil moisture anomalies on GPLLJ speed, northward penetration, and propensity for severe weather is not well known. In this study, two 31-member WRF-ARW stochastic kinetic energy backscatter scheme ensembles simulate a typical warm season GPLLJ case under CONUS-wide wet and dry soil moisture scenarios. In the GP (24°–48°N, 103°–90°W), ensemble mean differences in sensible heating and PBL height of 25–150 W m−2 and 100–700 m, respectively, at 2100 UTC (afternoon) culminate in GPLLJ 850-hPa wind speed differences of 1–4 m s−1 12 hours later (0900 UTC; early morning). Greater heat accumulation in the daytime PBL over dry soil impacts the east–west geopotential height gradient in the GP (synoptic conditions and Holton mechanism) resulting in a deeper thermal low in the northern GP, causing increases in the geostrophic wind. Enhanced daytime turbulent mixing over dry soil impacts the PBL structure (Blackadar mechanism), leading to increased ageostrophic wind. Overnight geostrophic and ageostrophic winds constructively interact, leading to a faster nocturnal GPLLJ over dry soil. Ensemble differences in CIN (~50–150 J kg−1) and CAPE (~500–1000 J kg−1) have implications for severe weather predictability.
Small horizontal axis wind turbines operating at low wind speeds face the issue of low performance compared to large wind turbines. A high amount of torque is required to start producing power at low ...wind speed to overtake friction of mechanical parts. A low design tip-speed ratio (λ) is suitable for low power applications. The relevance of the classical blade-element/ momentum theory, traditionally used for the design of large wind turbines operating at high tip-speed ratio, is controversial at low tip-speed ratio. This paper presents a new design methodology for a 300 mm horizontal axis wind turbine operating at very low tip-speed ratio. Chord and blade angle distributions were computed by applying the Euler’s turbomachinery theorem. The new wind turbine has multiple fan-type blades and a high solidity. The rotor was tested in wind tunnel. The power and torque coefficients have been measured, and the velocities in the wake have been explored by stereoscopic particle image velocimetry. The results are compared to a conventional 3-bladed horizontal axis wind turbine operating at higher tip-speed ratio λ=3. The new wind turbine achieves a maximum power coefficient of 0.31 for λ=1. The conventional wind turbine achieves similar performance. At low tip-speed ratio, the torque coefficient (Cτ) is higher for the new wind turbine than for the conventional one and decreases linearly with the tip-speed ratio. The high magnitude of torque at low tip-speed ratio allows it to have lower instantaneous cut-in wind speed (2.4 m.s−1) than the conventional wind turbine (7.9 m.s−1). The order of magnitude of the axial and tangential velocities in the near wake are closed to the design requirements. The current method could still be improved in order to better predict the profiles. The analysis of the wake shows that the new wind turbine induces a highly stable and rotating wake, with lower wake expansion and deceleration than the conventional one. This could be useful to drive a contra-rotating rotor.
•A 30 cm wind turbine operating at very low tip-speed ratio has been developed.•Its maximum power coefficient is 0.31 reached for the tip-speed ratio equal to 1.•It generates high torque at low tip-speed ratio and has very low cut-in wind speed.•Its torque coefficient decreases linearly with the tip-speed ratio.•It has a stable and highly rotating wake compared to conventional wind turbines.
Variability of the Equatorial Indian Ocean (EIO) winds play crucial roles in driving the upper EIO dynamics and modifying the ocean–atmosphere interactions in the Indian Ocean (IO). This study, using ...a satellite-sensed high-resolution (0.25° × 0.25°) monthly winds, has revealed many salient features of the seasonal and inter-annual variability of winds at various dynamically significant regions of the EIO. Though annual mean wind pattern of the EIO shows westerlies east of 60°E, the different local areas in this ocean exhibit significant seasonal wind variations. Migrations and fluctuations of southerlies and westerlies primarily determine the EIO wind variability. In the western (eastern) EIO, SW and NE monsoon winds are stronger (weaker) and of longer (shorter) duration. Near to the equator (1°S–1°N), in the central EIO, weaker winds occur during SW and NE monsoons, whereas stronger winds during transition periods. Near the equator, meridional winds show a significant annual period, especially in the western EIO. But zonal winds exhibit semi-annual period east of 55°E with a peak in the central ocean associated with the active westerlies during spring and fall, and annual period west of 55°E in the western EIO due to monsoon reversals. Westerlies are stronger during the fall compared to spring. Zonal wind variability in the central EIO is the essential deciding factor for the zonal wind variability occurring in the whole EIO. Both Zonal Sea Level Pressure Gradient (ZSLPG) and Momentum Advection (MA) fields determine the dynamics of zonal winds in the EIO. Zonal winds are weak in the western EIO because of the semi-annual harmonics of both ZSLPG and MA, though with substantial amplitude, exhibiting opposite accelerations there. But stronger zonal winds occur in the central EIO (60°E–80°E) because of the same accelerations set by the relatively weaker ZSLPG and MA fields. The zonal winds show substantial inter-annual variability compared to the meridional winds. The inter-annual variability of zonal winds shows the predominance of two modes, with EOF1 50% and EOF2 20% of the total variance. Zonal wind pattern of EOF1 resembles the monsoon transition seasons, while that of EOF2 describes the SW monsoon. In the EIO, Indian Ocean Dipole (IOD) influences the patterns of winds and SST anomalies better than that of El Niño–Southern Oscillation (ENSO). Spatiotemporal variability of the EIO winds during ENSO and IOD indicates the prevalence of stronger zonal wind anomalies in the eastern and central EIO and weaker anomalies in the western EIO. Although spatial patterns of wind anomalies are similar during El Niño and Positive IOD (PIOD) periods, the monthly variations, spatial extensions, and intensities of anomalies are much different while comparing. Prospectus for understanding the EIO winds variations can help to understand the changes occurring in the wind-driven surface and subsurface zonal currents.
All flights show pronounced meso-gamma (2-20 km) scale variability in the wind, with the largest wind variance (on the order of 2-4 m.sup.2 s.sup.-2) towards cloud base and in the cloud layer on ...flights with large vertical wind shear. The wind and wind variance profiles measured in situ and by lidar compare very well, despite the DWL's coarse (â¼ 8 km) horizontal footprint. This highlights the presence of wind fluctuations on scales larger than a few kilometres and that wind lidars can be used more deliberately in field studies to map (mesoscale) flows.
This paper proposes a new integrated control scheme for large-scale wind turbine generators (WTG) incorporated with a battery energy storage system (BESS). The primary goal is to improve the ...dispatchability of wind power over a wide range. The proposed controller consists of switching feedback controllers for WTG equipped with BESS management and is developed to systematically govern both systems for optimal regulation while ensuring safe operation within defined limits. A scenario-based switching logic is recommended to coordinate the hybrid systems, and a three-layer WTG controller is devised using a gain-scheduled control method. The suggested controller's performance is evaluated through simulation case studies, particularly in dealing with wind forecast errors (WFE) in the short-term dispatch scheme. To assess the proposed controller's effectiveness, a comparison is made against a baseline controller in three criteria: standard deviation (STD), mean (X) and an integral absolute error (IAE). These criteria help to evaluate the energy mismatch concerning the reference power command. The results are presented to elucidate the effectiveness of the proposed controller in regulating WTG-BESS throughout the entire operating region using a real wind profile from a wind farm in Australia. The findings show that the proposed approach has significant potential to enhance performance, leading to vastly improved wind power dispatch compared to the baseline approach.
•A numerical model is developed to predict behavior of wind turbines to tornado loads.•The critical tornado locations leading to peak staining actions were predicted.•Maximum straining actions ...resulting from F2-tornado were compared to IEC 61400 loads.•Pitch angles are proposed to reduce straining actions under the considered tornado.
According to the Global Wind Energy Council, the installation rate for wind turbines is accelerating around the world, leading to the introduction of new wind turbine farms in regions where wind is abundant. As a result, the number of wind turbine towers prone to severe wind loads is increasing, as is the rate of failure due to unexpectedly strong wind loading. Wind turbines are typically designed to resist the synoptic wind loads specified in current International Electrotechnical Commission (IEC) guidelines, but these standards do not account for High-Intensity Wind (HIW) events such as tornadoes or downbursts. Because of the localized nature of HIW events, identifying critical locations that result in peak forces acting on the tower and blades is a challenging task. For this reason, a built-in-house numerical model has been developed in this study for simulating a three-blade horizontal-axis wind turbine tower exposed to 3D tornado wind fields. An extensive study has been conducted with the goal of determining both the critical location of a tornado that will cause peak straining actions on the tower and blades, and the optimal pitch angle that will minimize the effects of that tornado. For the considered wind turbine, the minimum straining actions on the blades were found to occur when the pitch angles are 60°, while the minimum straining actions on the base of the tower takes place when the pitch angles are 15°. A comparison of the simulation results with the extreme wind load scenario, stated in the current IEC guidelines, revealed that the predicted straining actions on the blades arising from the conditions specified in the IEC recommendations are less than the straining actions due to the F2 tornado considered in the study.
PDF
