This issue is a continuation of the previous successful Special Issue “Wind Turbines 2013”. Similarly, this issue also focuses on recent advances in the wind energy sector on a wide range of topics, ...including: wind resource mapping, wind intermittency issues, aerodynamics, foundations, aeroelasticity, wind turbine technologies, control of wind turbines, diagnostics, generator concepts including gearless concepts, power electronic converters, grid interconnection, ride-through operation, protection, wind farm layouts - optimization and control, reliability, operations and maintenance, effects of wind farms on local and global climate, wind power stations, smart-grid and micro-grid related to wind turbine operation.
Wind turbine aerodynamics is one of the central subjects of wind turbine technology. To reduce the levelized cost of energy (LCOE), the size of a single wind turbine has been increased to 12 MW at ...present, with further increases expected in the near future. Big wind turbines and their associated wind farms have many advantages but also challenges. The typical effects are mainly related to the increase in Reynolds number and blade flexibility. This Special Issue is a collection of 21 important research works addressing the aerodynamic challenges appearing in such developments. The 21 research papers cover a wide range of problems related to wind turbine aerodynamics, which includes atmospheric turbulent flow modeling, wind turbine flow modeling, wind turbine design, wind turbine control, wind farm flow modeling in complex terrain, wind turbine noise modeling, vertical axis wind turbine, and offshore wind energy. Readers from all over the globe are expected to greatly benefit from this Special Issue collection regarding their own work and the goal of enabling the technological development of new environmentally friendly and cost-effective wind energy systems in order to reach the target of 100% energy use from renewable sources, worldwide, by 2050
The current study systematically analyzes the impact of solidity (σ) and number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines ...(VAWTs). Solidity varies within the wide range of 0.09–0.36. A large number of operational parameters, i.e., tip speed ratio (λ), Reynolds number (Re), turbulence intensity and reduced frequency (K) are investigated to provide a deeper insight into the impact of σ and n on the dynamic loads on blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that the turbine optimal tip speed ratio (λopt) is invariant to a newly-introduced parameter ‘σλ3’, regardless of the turbine geometrical and operational characteristics. In addition, a new correlation is derived to estimate λopt as a function of σ, which can also be employed to predict the optimal σ for a turbine with a given λ. It is also found that: (i) for constant-speed urban VAWTs, which due to the low mean wind speed in the urban environment, frequently operate at moderate to high λ, a relatively-low σ is optimal; (ii) an optimal VAWT is a moderately-high-solidity variable-speed rotor maintaining a relatively-low λ, where due to the large blade chord length the resulting Re and K are favorably high; (iii) within the turbine optimal operational range, turbine power coefficient (CP) is almost independent of n. The present findings support the optimal aerodynamic design of small-to large-scale VAWTs.
•New insights on the impact of solidity σ and number of blades for VAWTs.•A new correlation for optimal tip speed ratio λopt and σ.•λopt is found to be invariant to ‘σλ3’ for different conditions.•In the optimal regime, power coefficient is almost independent of number of blades.•Reduced frequency is shown as a critical parameter on turbine power performance.
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Review of propulsion systems on LNG carriers Fernández, Ignacio Arias; Gómez, Manuel Romero; Gómez, Javier Romero ...
Renewable & sustainable energy reviews,
January 2017, 2017-01-00, Volume:
67
Journal Article
Peer reviewed
Vessel ozone depleting emission regulations are regulated in Annex VI of the MARPOL Convention, wherein the maximum levels of NOx, SOx and suspended particles are established. These increasingly ...strict regulations, together with the increase in natural gas consumption and its price, have conditioned propulsion systems implemented on board vessels.
This article reviews the different propulsion systems used on board vessels for the transport of Liquefied Natural Gas (LNG). The study describes the main characteristics of the propulsion systems, and the advantages and drawbacks that come along with these, from its very beginnings up to the systems installed to date. The described propulsion systems include both gas and steam turbines, combined cycles, 2 and 4 stroke internal combustion engines, as well as reliquefaction plants, while encompassing mechanical, electric and Dual Fuel (DF) technology systems.
The propulsion systems implemented have undergone continual alteration in order to adjust to market needs, which were always governed by both efficiency and the possibility of consuming boil-off gas (BOG), always in compliance with the strict antipollution regulations in force.
The current direction of LNG vessel propulsion systems is the installation of 2-stroke DF low pressure engines due to their high efficiency and their possibility of installing a BOG reliquefaction plant. Another great advantage of this propulsion system is its compliance with the IMO TIER III emission regulations, without the need to install any supplementary gas treatment system.
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The subject of this reprint covers the latest research in the field of wind energy methods and technologies. The results of work on modeling and optimization of wind turbines, their location, methods ...of monitoring and diagnostics, and development prospects were presented. Contemporary problems, dangers and risks in the field of wind engineering were also pointed out.
Fish can be injured or killed during turbine passage. This paper reports the first in-situ evaluation of hydraulic conditions that fish experienced during passage through Francis turbines using an ...autonomous sensor device at Arrowrock, Cougar, and Detroit Dams. Among different turbine passage regions, most of the severe events occurred in the stay vane/wicket gate and the runner regions. In the stay vane/wicket gate region, almost all severe events were collisions. In the runner region, both severe collisions and severe shear events occurred. At Cougar Dam, at least 50% fewer releases experienced severe collisions in the runner region operating at peak efficiency than at the minimum and maximum opening, indicating the wicket gate opening could affect hydraulic conditions in the runner region. A higher percentage of releases experienced severe events in the runner region when passing through the Francis turbines than through an advanced hydropower Kaplan turbine (AHT) at Wanapum Dam. The nadir pressures of the three Francis turbines were more than 50% lower than those of the AHT. The three Francis turbines had much higher magnitudes and rates of pressure change than the AHT. This study provides critical information on hydraulic conditions and fish passage information of Francis turbines, which can help guide future laboratory studies of fish passing through Francis turbine, design fish-friendly turbines, and optimize the operation of existing turbines for better fish passage conditions.
•Three Francis turbines were evaluated using an autonomous sensor device.•At Cougar Dam, peak efficiency operation had the fewest severe collisions at runner.•The three Francis turbines had more severe events than an advanced Kaplan turbine.•The Francis turbines had lower nadir pressure than an advanced Kaplan turbine.•The Francis turbines had higher pressure change than an advanced Kaplan turbine.
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One of the most cost-effective and environmentally sound methods of developing hydropower is through the uprating of hydroelectric turbines. In many countries hydroelectric dams have turbines that ...are approaching their expected service life, with plans underway to install replacement turbines that are expected to improve fish passage survival. To validate these improvements, there is a need to develop a baseline hydraulic characterization of existing Kaplan turbines. An autonomous sensor device known as the Sensor Fish was deployed at Ice Harbor Dam to characterize the hydraulics under different operating conditions. Nadir pressures varied by operating condition, with values decreasing with operating power (144–106 kPaA). Pressure changes during turbine passage varied by operating condition, with values increasing with operating power (311–344 kPa). There were slightly more significant events (acceleration ≥95G) in the stay vane/wicket gate region than the runner region. Rotational velocity data were similar between operating conditions. Sensor Fish data amassed during field studies in similar turbines were used for comparison. This study offers critical insights into the biological performance of large Kaplan turbines and provides vital information that can be used to make informed decisions that lead to additional design or operational improvements.
•Sensor Fish data collected in a large Kaplan turbine at Ice Harbor Dam.•Nadir pressure and rotational velocity were lowest among turbines compared.•Severe acceleration events were similar among the turbines compared.•Data provides insight into the biological performance of large Kaplan turbines.•Data provides information that can lead to further design/operational improvements.
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•Guidelines for CFD simulations of VAWTs are developed using systematic analysis.•Minimum azimuthal increment for all tip speed ratios and solidities: 0.1°.•Minimum distance from turbine center to ...domain inlet: 15D (turbine diameter).•Minimum distance from turbine center to domain outlet: 10D (turbine diameter).•Minimum turbine revolutions reach convergence: 20–30 revolutions.
The accuracy of CFD simulations of vertical axis wind turbines (VAWTs) is known to be significantly associated with the computational parameters, such as azimuthal increment, domain size and number of turbine revolutions before reaching a statistically steady state condition (convergence). A detailed review of the literature, however, indicates that there is a lack of extensive parametric studies investigating the impact of the computational parameters. The current study, therefore, intends to systematically investigate the impact of these parameters, on the simulation results to guide the execution of accurate CFD simulations of VAWTs at different tip speed ratios (λ) and solidities (σ). The evaluation is based on 110 CFD simulations validated with wind-tunnel measurements for two VAWTs. Instantaneous moment coefficient, Cm, and power coefficient, CP, are studied for each case using unsteady Reynolds-averaged Navier-Stokes (URANS) simulations with the 4-equation transition SST turbulence model. The results show that the azimuthal increment dθ is largely dependent on tip speed ratio. For moderate to high λ, the minimum requirement for dθ is 0.5° while this decreases to 0.1° at low to moderate λ. The need for finer time steps is associated to the flow complexities related to dynamic stall on turbine blades and blade-wake interactions at low λ. In addition, the minimum distance from the turbine center to the domain inlet and outlet is 15 and 10 times the turbine diameter, respectively. It is also shown that 20–30 turbine revolutions are required to ensure statistically converged solutions. The current findings can serve as guidelines towards accurate and reliable CFD simulations of VAWTs at different tip speed ratios and solidities.
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•A novel vertical axis wind turbine with rotatable auxiliary blades is made.•Wind tunnel experiments are carried out for the proposed wind turbine.•The geometric characteristic of the proposed wind ...turbine provides better self-starting performance.•The maximum power coefficient can be reduced by 63.1% at 0° pitch angle.•Constant output power at different wind speeds is realized through pitch control.
Wind, as a renewable, cost-competitive, and no air-pollution energy source, has caught worldwide attention. As a result of defective performance and backwardness in research, vertical axis wind turbines leg behind horizontal axis wind turbines in terms of commercial application, especially for large-scale wind turbines. In the present study, a new type of straight-bladed vertical axis wind turbine consisting of three pairs of blades has been introduced and tested in a wind tunnel to verify the reliability and efficiency of the novel configuration. There is a fixed main blade and a rotatable auxiliary blade (with different chord and span lengths from that in the main blade) in each pair of the blades. The experimental results demonstrate that the static torque coefficient of the proposed rotor is positive at all azimuthal angles and significantly higher than that of the traditional H-type rotor, which shows better self-starting performance. The proposed wind turbine can obtain a higher power coefficient compared to a traditional three-blade H-type rotor under the wind speeds varying from 4.54 m/s to 8.82 m/s. Besides, the power output of the wind turbine can be effectively controlled through the auxiliary blades pitching, and constant power output can be achieved in varying wind speeds.
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In recent years, the energy crisis severally appears due to the enormous human development. The renewable energy is a new source for world energy demand nowadays, especially the wind energy. ...Generally, wind energy is the most promising source for electric power demand in world because of the availability of the high wind speed around the year in several locations. This work investigates the drag type wind turbines, which have strong potential in small electric power generation demands. The scenario of this work is divided into two sections; the first one is the numerical analysis for the conventional Savonius with fully optimizing for the shape of the blade using a genetic algorithm. This optimization is performed to maximize the power coefficient with the same dimension of the conventional Savonius turbine. The second part is conducted experimentally to measure the performance of the conventional Savonius with the two and three blades; in addition, the optimal blade design (S shape) is tested to compare the performance of this new design with the conventional one or standard semi-circular blade. The results indicated that the captured efficiency of the optimal shape blade has the optimum value with 28% in contrasts to 14 and 10% for the two and three blades respectively.
•The present work is to optimize the drag type vertical axis wind turbine.•Different designs of drag turbines are studied numerically and experimentally.•Genetic Algorithm is used as optimizer to improve the turbine performance.•Experimental work is performed to validate the performance of the optimal design.•Optimal shape has Cp value with 28% in contrasts to 14% for the conventional design.
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