Performance evaluation of a horizontal axis wind turbine in operation

The operation of modern horizontal axis wind turbine (HAWT) includes a number of important factors, such as wind power (P), power coefficient (C_P), axial flow induction factor (a), rotational speed (Ω), tip speed ratio (λ), and thrust force (T). The aerodynamic qualities of these aspects are evaluated and discussed in this study. For this aim, the measured data are obtained from the Sebenoba Wind Energy Power Plant (WEPP) that is located in the Sebenoba region in Hatay, Turkey, and a wind turbine with a capacity of 2 MW is selected for evaluation. According to the results obtained, the maximum turbine power output, maximum power coefficient, maximum axial flow induction factor, maximum thrust force, optimum rotational speed, probability density of optimum rotational speed, and optimum tip speed ratio are found to be 2 MW, 30%, 0.091, 140 kN, 16.11 rpm, 46.76%, and 7, respectively. This study has revealed that wind turbines must work under optimum conditions in order to extract as much energy as possible for approaching the ideal limit.     

The effects of sinusoidal leading edge of turbine blades on the power coefficient of horizontal-axis wind turbine (HAWT)

In order to improve the aerodynamic performance of horizontal-axis wind turbine (HAWT), a sinusoidal shape is applied to turbine blade. In this study, four types of modified blades were chosen based on variations in amplitude and wavelength of protuberance along the leading edge. Compared with the baseline model, the power coefficients (C_p) of HAWT with modified blades were improved, especially at low tip speed ratios. At low wind speed (V = 6 m/s), blades with short wavelength obtain significant improvement in C_p compared with the baseline model. As wind speed increases, this improvement decreases. In addition, turbine blade with large amplitude and long wavelength obtains better C_p values at higher wind speeds than lower ones, which have a great potential to be more superior at relatively higher wind speeds.     

水电开发对生态环境的影响及防治对策

近年来,水电建设在迅速发展的同时也不断暴露出一些问题。本文结合一些实例,分析了目前水电建设中存在的生态环境问题,并提出了相应的对策。     

Blade thickness effect on the aerodynamic performance of an asymmetric NACA six series blade vertical axis wind turbine in low wind speed

ABSTRACT

Vertical axis wind turbine (VAWT) is an economic and widely used energy converter for converting wind energy into useful form of energy, like mechanical and electrical energy. For efficient energy conversion in low wind speed and to have improved power coefficient of asymmetric blade VAWT, selection of optimum blade thickness is needed thus entailing its detailed investigation with respect to different operating wind speed conditions. Present study methodically explores the impact of thickness to chord (t/c) ratio on aerodynamic performance of a three bladed asymmetrical blade H-Darrieus VAWT at different low wind speed conditions by using 2D unsteady CFD simulations. The optimal t/c is obtained on the basis of maximum power coefficient and average moment coefficient of the turbine. The aerodynamic performance curves are obtained at different operating and t/c conditions and the performance insights are corroborated with the findings from the flow physics study to come to some concrete conclusions on the effects of the thickness to chord ratio. The present study identifies large blade curvature to create a large diverging passage on the blade suction surface as the prominent reason for aerodynamic performance drop at a high t/c ratio.     

Effects of wind‐energy facilities on breeding grassland bird distributions

The contribution of renewable energy to meet worldwide demand continues to grow. Wind energy is one of the fastest growing renewable sectors, but new wind facilities are often placed in prime wildlife habitat. Long‐term studies that incorporate a rigorous statistical design to evaluate the effects of wind facilities on wildlife are rare. We conducted a before‐after‐control‐impact (BACI) assessment to determine if wind facilities placed in native mixed‐grass prairies displaced breeding grassland birds. During 2003–2012, we monitored changes in bird density in 3 study areas in North Dakota and South Dakota (U.S.A.). We examined whether displacement or attraction occurred 1 year after construction (immediate effect) and the average displacement or attraction 2–5 years after construction (delayed effect). We tested for these effects overall and within distance bands of 100, 200, 300, and >300 m from turbines. We observed displacement for 7 of 9 species. One species was unaffected by wind facilities and one species exhibited attraction. Displacement and attraction generally occurred within 100 m and often extended up to 300 m. In a few instances, displacement extended beyond 300 m. Displacement and attraction occurred 1 year after construction and persisted at least 5 years. Our research provides a framework for applying a BACI design to displacement studies and highlights the erroneous conclusions that can be made without the benefit of adopting such a design. More broadly, species‐specific behaviors can be used to inform management decisions about turbine placement and the potential impact to individual species. Additionally, the avoidance distance metrics we estimated can facilitate future development of models evaluating impacts of wind facilities under differing land‐use scenarios.     

Theoretical Calculation and Economic Assessment of the Integrated Solar Combined Cycle Power Plants

The ISCC technology representing an integrated solar combined cycle and the economic assessment of ISCC are investigated. Comparisons conducted by theoretical calculation method among two cases, that is, an integrated solar combined cycle system (ISCCS) and a combined cycle gas turbine system (CCGTS) show that ISCCS provides the best solution with the highest efficiency of heat to electricity among them. The results reflected by theoretical calculation also reveal that ISCCS is beneficial to energy saving and emission reduction. Due to the great advantages of ISCC, comprehensive analysis on the basic conditions for building ISCC power plants is analyzed in detail.     

Use of fertilization and grazing exclusion in mitigating lost meadow production in the Sierra Nevada,California, USA

The effects of a single fertilizer treatment (ammonium phosphate at 841 kg/ha, plus dolomite at 336 kg/ha) and cattle exclusion were studied in two meadows in the Sierra Nevada of California in the USA. Grazing exclusion had no effects on soil bulk density during the three years of the study. Fertilization had no effect on total soil nitrogen, soil pH, or crude protein concentrations in graminoids or forbs. Saturated soils and the development of anaerobic conditions close to the surface may have led to denitrification and the loss of usable nitrogen. Fertilization did result in short-term (one- to two-year) increases in available soild phosphorus in the drier of the two meadows, and in total phosphorus concentrations in graminoids and forbs, which were otherwise generally deficient in phosphorus. Few changes in plant species composition or production were detected, although a combination of fertilization and grazing exclusion increased forb production in the drier meadow. Based on our initial results, fertilization with phosphorus was the recommended treatment for meadow improvement projects in the central Sierra Nevada.     

Sustainable gas turbine power generation by adopting green control technologies

Performance analysis of a gas turbine with two configurations (a parallel and series free turbine) is presented and analysed. A simple configuration is analysed here for comparison. The performance parameters are work output, specific fuel consumption (SFC) and efficiency. Off-design characteristics are based on two methods of control, the first (A) is fixing the compressor–turbine inlet temperature (TIT) and varying the power TIT, whereas the second (B) method is by varying the two turbine-inlet temperatures while keeping them equal. Conclusively the series configuration has higher work output (11%), whereas the parallel arrangement has higher efficiency and lower SFC (9%). Hence, as a compromise, it is more efficient and work-productive to use method A (TIT = const.) to control both series and parallel arrangements than using method B (TIT = T₅).     

Environmental Impacts of Brazil's Tucuruí Dam: Unlearned Lessons for Hydroelectric Development in Amazonia

Brazil's Tucuruí Dam provides valuable lessons for improving decision-making on major public works in Amazonia and elsewhere. Together with social impacts, which were reviewed in a companion paper, the project's environmental costs are substantial. Monetary costs include costs of construction and maintenance and opportunity costs of natural resources (such as timber) and of the money invested by the Brazilian government. Environmental costs include forest loss, leading to both loss of natural ecosystems and to greenhouse gas emissions. Aquatic ecosystems are heavily affected by the blockage of fish migration and by creation of anoxic environments. Decay of vegetation left in the reservoir creates anoxic water that can corrode turbines, as well as producing methane and providing conditions for methylation of mercury. Defoliants were considered for removing forest in the submergence area but plans were aborted amid a public controversy. Another controversy surrounded impacts of defoliants used to prevent regrowth along the transmission line. Mitigation measures included archaeological and faunal salvage and creation of a “gene bank” on an island in the reservoir. Decision-making in the case of Tucuruí was virtually uninfluenced by environmental studies, which were done concurrently with construction. The dam predates Brazil's 1986 requirement of an Environmental Impact Assessment. Despite limitations, research results provide valuable information for future dams. Extensive public-relations use of the research effort and of mitigation measures such as faunal salvage were evident. Decision-making was closely linked to the influence of construction firms, the military, and foreign financial interests in both the construction project and the use of the resulting electrical power (most of which is used for aluminum smelting). Social and environmental costs received virtually no consideration when decisions were made, an outcome facilitated by a curtain of secrecy surrounding many aspects of the project. Despite improvements in Brazil's system of environmental impact assessment since the Tucuruí reservoir was filled in 1984, many essential features of the decision-making system remain unchanged.     

涡流技术的试验研究与工程应用

本文介绍了一种新型涡流烟气净化装置,并通过模拟试验及工程应用研究了涡流装置、中心力场等有关参数及除尘脱硫的技术经济综合指标。