兆瓦级水平轴风力机叶片铺层设计参数影响分析

为研究主梁材料及铺层角度对风力机叶片结构特性影响,基于三维建模软件NX二次开发建立风力机叶片几何模型,结合铺层设计并通过CFD方法获取叶片表面压力分布,采用有限元方法对叶片进行结构模态、强度及屈曲分析。结果表明:碳纤维主梁叶片质量较玻璃钢减轻约8.08%,主梁材料对模态振型影响较小,主梁铺层角度对挥舞方向运动影响更大;0°铺层主梁叶片共振破坏风险低且应力应变峰值均最小,碳纤维主梁叶片较玻璃钢应力及应变峰值降幅最大约20.57%、26.51%;主梁0°铺层时叶片屈曲因子最大,而60°铺层时最小,碳纤维主梁叶片较玻璃钢临界屈曲载荷增幅最大约17.84%,有效降低屈曲失稳风险;额定工况下,叶片局部屈曲域在近叶尖处尾缘区和近叶根处最大弦长截面前缘区。     

基于气动弹性剪裁风力机叶片结构稳定性分析

为提升风力机叶片结构稳定性,改善叶片局部屈曲现象,研究铺层参数对叶片结构稳定性的影响。建立1.5 MW风力机叶片的三维模型和铺层结构,并与实验值对比验证模型的质量和固有频率的准确度。借助CFD计算获得叶片表面的分布压力,以此为载荷对不同铺层角度叶片进行稳定性分析。计算结果表明:叶片在额定风速载荷下不会发生屈曲,满足设计要求;叶片后缘区结构设计较薄弱,局部屈曲主要出现在该区域;增加叶片尾缘铺层角度,保持主梁铺层角度不变,能提高叶片整体稳定性。     

大型风力机叶片模态性能及振动分析

为研究大型风力机叶片铺层参数对叶片动态性能的影响、防止叶片发生共振、减小叶片挠度、改善叶片结构力学性能和提高风力机安全性,建立了5 MW风力机叶片的有限元模型,通过改变铺层材料和铺层角度实现不同的叶片结构,并对成型叶片进行了模态分析;采用CFD方法获得叶片表面载荷,分析不同风速下不同铺层结构叶片振动性能,结果表明:复合材料铺层角度能影响叶片固有频率,叶片低阶振型以挥舞和摆振为主,高阶模态出现扭转;增加0°铺层纤维比例可提高低阶固有频率,45°铺层能提高叶片抗扭能力;叶片振动位移沿叶片展向呈非线性增长,风速越大叶片挠度越大;碳纤维可有效提高叶片固有频率,减小叶片挠度。     

基于气动弹性剪裁的大型风力机弯扭耦合叶片力学性能分析

为分析弯扭耦合叶片的力学性能,基于三维建模软件NX二次开发建立NREL 5 MW风力机叶片壳体模型,进一步对叶片进行复合材料铺层设计,通过镜像偏置主梁纤维实现叶片气动弹性剪裁,采用CFD方法计算叶片表面压力分布,结合有限元方法对其进行模态、静力学及屈曲计算,以研究主梁偏置角度对弯扭耦合叶片力学性能的影响.结果 表明:当主梁偏置角度较小时,弯扭耦合叶片表面最大应力小于传统叶片,其中以偏置角度为-15°时效果最佳,表面最大应力降幅最高为14.78％;相比传统叶片,弯扭耦合叶片各阶固有频率及屈曲因子均有所降低,且正向与反向偏置同角度的叶片固有频率和屈曲因子下降量较接近,主梁偏轴镜像铺设对叶片挥舞振动影响较大;主梁偏置角度对叶片抗屈曲能力产生一定影响,叶片临界屈曲载荷最大降幅约为78％;应重点关注弯扭耦合叶片固有频率及屈曲因子,以避免叶片固有频率与激励频率接近而产生共振,必要时可优化铺层结构以提高叶片抗屈曲能力.     

大型风力机叶片铺层及模态分析

使用ANSYS软件,自下而上建立风力机叶片的有限元模型,使用单元类型SHELL 99对叶片模型实行铺层。运用有限元方法,对几组铺层方案进行叶片的模态分析,结果显示大型风力机叶片梁帽的铺层对频率及相对位移影响最大,增加梁帽铺层数可更好地提升叶片的结构动力学性能。     

基于响应面法的仿生风力机叶片可靠性分析

根据风力机的基本理论和相似理论在有限元软件ANSYS中建立了一个翼型为SG6050,半径为1m的小型风力机叶片模型,运用结构仿生学原理,对所设计的风力机叶片进行铺层,其角度范围介于5°～90°之间,为体现中轴的对称性,正负铺层同时出现。利用基于响应面法的可靠性理论,比较了不同铺层方式下风力机叶片的可靠性。计算结果表明:可靠指标较高的角度集中在40°～70°之间,而以65°铺层可靠指标最大,即其失效概率最小,而在5°与90°附近的铺层其可靠指标相对较小。     

基于气动弹性剪裁的风力机叶片模态分析

本文为研究叶片铺层参数对叶片动态特性的影响,防止叶片产生共振,改善叶片力学特性,建立了1.5 MW风力机叶片的有限元模型,通过改变铺层角度和铺层纤维比例实现多种不同层合板结构的叶片铺层,并对上述各种铺层叶片结构进行了模态分析,获得了各模型的前六阶固有频率和振型,分析了铺层参数影响叶片动态特性的原因。结果表明:复合材料具有显著各向异性,通过改变铺层角度能影响固有频率大小;叶片低阶振型以挥舞和摆振为主,增加0°铺层比例能提高低阶固有频率;叶片高阶模态出现扭转,45°铺层能提高叶片抗扭能力,有利于增加高阶固有频率。     

铺层参数对风力机叶片静态结构性能的影响分析

复合材料风力机叶片的性能因铺层参数的变化而不同,为了优化铺层方案,探讨了铺层参数对风力机叶片静态结构性能的影响。以某1.5 MW风力机叶片距叶根1/3段为对象,建立其有限元模型,计算叶片在极限工况下各截面的载荷;分析该叶片铺层所采用的单、双、三轴向布的基本力学性能,得出可行替代方案。通过对不同铺层角度、铺层顺序和铺层比例的代表性铺层方案进行分析对比,初步得出叶片具有良好性能的铺放参数。在此基础上,优化原有设计方案,结果表明改进后叶片的失效因子和变形明显降低,验证了所得结论的正确性。     

基于ABAQUS地震激励下风力机结构损伤分析

高耸的风力机塔架结构属于典型的顶部附有大集中质量的细长柔性体的力学结构,相比传统建筑结构差异性较大,极易受到地震载荷影响。基于有限元分析软件ABAQUS建立风力机塔架、基础平台和土体模型,通过FAST导出风轮非定常推力,作用在塔顶机舱,土体底部施加地震加速度时间序列,进行风力机结构模态分析、稳定性分析和动力学响应分析。研究表明：塔架主要的运动形式为摇摆运动和弯曲振动;塔架一阶固有频率为0.290 Hz,大于风轮的额定旋转频率0.202 Hz,因此叶片旋转不会引起风力机塔架发生共振;风载荷作用下,塔架发生横向屈曲,屈曲位置位于塔架底部且随模态阶数增大而逐渐向上发展,屈曲因子较大;地震载荷作用下,塔架发生纵向屈曲,屈曲位置同样位于塔架底部且随模态阶数增大而逐渐向上发展,较风载荷发生屈曲区域相对更大,屈曲因子相对较小。     

大型水平轴风力机塔影效应特性研究

为了研究塔影效应对大型水平轴风力机的影响,选取NREL 5MW风力机作为研究对象,利用Fluent软件对单台风力机的不同工况进行数值模拟。结果表明:塔影效应的影响主要发生在叶片方位角为140°~210°的时域内;当叶片扫掠过塔筒时,其不同周向位置的转矩和轴向推力出现大幅波动,转矩的相对波动幅度随来流风速的减小而减小,叶片所受轴向推力的相对波动幅度随来流风速的减小而增大;由于叶片尖部周向线速度较大,在研究塔影效应时需考虑叶轮旋转效应的影响;对于风力机尾迹流场,旋转半径越大处,塔筒造成的尾迹越明显,其长度约为叶轮直径的2倍。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Contents in Volume 23,2014

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Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.