涡轮叶片三维气动分析方法研究

精确的涡轮叶片气动性能计算是对其进行设计优化的重要基础。基于PRO/E软件建立了某涡轮流场叶片三维参数化实体模型,采用SST(shear stress transport)湍流模型对建立的涡轮流场叶片进行了三维气动分析,得到了流场及叶片表面的温度、压力、流速以及能量损失等气动参数分布,并对它们的变化规律进行了分析;基于叶片气动效率计算公式,给出了叶片平均气动效率的计算方法并分析了叶片气动效率沿叶高的变化规律,为涡轮叶片的气动设计优化奠定了较好的基础。     

进口温度不均匀对涡轮叶片热应力的影响

针对航空涡轮叶片的温度场预测问题,采用CFD(computational fluid dynamics)软件和有限元计算理论与方法,以对流冷却叶片的温度场与热应力求解为例,分别计算了涡轮进口温度均匀和不均匀时叶片的温度场和热应力,分析了涡轮进口温度不均匀对叶片热应力的影响,其中叶片温度场的求解采用气热耦合的方法即直接应用CFD软件计算叶片温度场,再依据温度场进行了有限元热应力分析.结果表明,进口温度不均匀时比进口温度均匀时叶片的热应力增大10%左右.     

某涡轮增压器涡轮叶片断裂故障分析及改进

针对某涡轮增压器涡轮叶片断裂问题,基于ANSYS有限元软件对该涡轮进行强度分析和振动特性分析.结果 表明:该涡轮一阶自振频率较低,一阶倍频比不满足设计要求,共振导致涡轮叶片断裂.在此基础上对涡轮整体结构进行了优化,优化后涡轮叶片一阶自振频率得到提升,叶片断裂问题得到解决.     

双层涡轮叶片应力计算与分析

为了对可倒车燃气轮机中双层涡轮叶片应力进行分析,以双层涡轮叶片为研究对象进行反转状态下叶片的换热分析,并基于ANSYS Workbench软件在正车额定工况及倒车额定工况下完成了双层涡轮叶片的应力计算。结果表明：叶片在反转状态下会不断与周围空气产生摩擦,使得叶片温度大幅升高,降低了叶片应力;对叶片采取冷却措施后,双层涡轮叶片的大应力位置主要位于过渡段,通过随形加强筋及空心倒车叶片的优化方案,可使得正车额定工况下的叶片强度储备系数由1.1增加至1.65,满足了叶片强度设计要求。     

叶型变化对叶片表面压力场的影响

使用NUMECA软件的FINE／Design3D模块对某型跨音速涡轮叶栅改型前后的导叶进行了单列三维流场计算，并分析了原型与改型叶栅沿叶片型面压力的分布以及叶片吸力面上的静压等值线分布。结果表明，叶片的改型改变了叶片表面的压力场，改善了叶栅内气体的流动。     

传热对增压器径流涡轮叶片温度分布的影响

采用共轭传热计算方法,对某柴油发动机废气涡轮增压器径流涡轮流场进行了数值模拟,对比了叶轮在绝热和传热条件下温度分布的差别,研究了传热边界对叶轮温度分布的影响。结果表明,绝热条件下,叶片两侧的温度存在显著的温差,并且从叶轮进口到出口也有明显的温降;而传热条件下,相同叶高下的叶片表面温度分布近乎于一条直线,压力面和吸力面的温度几乎相同;在热平衡条件下,叶轮实体内的温度范围很小,不超过10 K,温度梯度较小表明由温差引起的热应力很小。     

涡轮盘-片结构的接触分析

建立某涡轮第五级盘-片的三维有限元模型,对紧急启动过程进行瞬态热弹塑性分析,计算中综合考虑了多种复杂载荷和接触非线性,获得紧急启动过程中轮盘及叶片危险部位的温度、应力时间历程,分析了温度场和应力场特点,提出了运行管理和改进设计的建议.结果可为涡轮结构疲劳寿命预测提供依据.     

某燃气轮机低压涡轮叶片断裂故障分析

低压涡轮叶片作为燃气轮机内流道的热端部件,长时间受到气流冲击,受离心载荷、气动载荷和热载 荷的综合影响,对叶片强度要求较高。某燃气轮机由退役航空发动机改制而成,通过电站长试考核考验燃气 轮机寿命,在考核期间发生低压涡轮叶片断裂故障。针对故障进行分析、试验及计算,确定叶片断裂的主要 原因是叶片共振引发高周疲劳,采取措施是燃气轮机长期工作时迅速通过易发生多阶次共振的危险转速范围。     

利用现代CAD技术和有限元法进行增压器涡轮叶片变结构模态特性的研究

利用现代 Ｃ Ａ Ｄ技术建立了轴向后弯式增压器涡轮的实体模型,并用有限元法对其进行变结构模态特性研究,给出了不同截面叶片的曲面建模方法。针对涡轮叶片设计中常见的用于调频的结构变化类型,重点分析了在其它参数相同的情况下,不同截面形状涡轮叶片的模态特性以及同种截面形状的涡轮叶片在出口端将其沿轴向斜切一部分后模态特性的变化规律。试验表明：本文方法适用于涡轮叶片模态特性的系统研究,文中计算结果对类似涡轮的设计具有参考价值。文中建模和分析采用了美国 Ｓ Ｄ Ｒ Ｃ公司的 Ｉ Ｄ Ｅ Ａ Ｓ Ｔ Ｍ 软件。     

氦氙混合工质轴流涡轮设计与激波控制研究

基于氦氙混合工质特性,利用Axial软件对比了不同载荷系数和流量系数情况下涡轮的效率,在载荷系数和流量系数分别为1.8和0.6的情况下涡轮效率较高。在此条件下利用AxCent软件对轴流涡轮进行了三维叶片造型。在ANSYS CFX软件中选用SST湍流模型,在给定的工况下对设计好的叶片采用数值模拟方法分析尾缘折转角、尾缘楔角及安装角对激波损失的影响。研究表明：尾缘折转角在5.5°~6.5°之间,尾缘楔角在11°~13°范围内激波损失最低;安装角在43°~48°之间,随着安装角的增大会使激波损失降低;同时,对原始叶型的优化表明,吸力面改进为直线型并且增大压力面曲率会降低激波损失。     

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.     

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.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.     

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.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

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.     

The Solar Office in context

The goal of sustainability in buildings can only hope to be realised if buildings are designed to both conserve and generate energy. The Solar Office at Doxford International is designed to minimise the use of energy while its external fabric is designed to replace such energy that is used. The recently completed building is now subject of a comprehensive monitoring programme. The programme covers both the performance of the 73 kW_p photovoltaic installation and the environmental conditions within the building as a whole. Hour by hour findings are posted on a dedicated web site. Photovoltaics could have the same impact on building form and layout as the invention of the passenger lift at the end of the last century.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Hydrogen recovery from the photovoltaic electroflocculation-flotation process for harvesting Chlorella pyrenoidosa microalgae

In this paper, an integrated process using photovoltaic power to harvest microalgae by electro-flocculation (EF) and hydrogen recovery is presented. It is mainly favorable in regions with high solar radiation. The electro-flocculation efficiency (EFE) of Chlorella pyrenoidosa microalgae was investigated using various types of electrodes (aluminum, iron, zinc, copper and a non-sacrificial electrode of carbon). The best results regarding the EFE, and biomass contamination were achieved with aluminum and carbon electrodes where the electrical energy demand of the process for harvesting 1 kg of algae biomass was 0.28 and 0.34 kWh, respectively, while the energy yield of harvested hydrogen was 0.052 and 0.005 kWh kg^?1, respectively. The highest harvesting efficiency of 95.83 ± 0.87% was obtained with the aluminum electrode.The experimental hydrogen yields obtained were comparable with those calculated from theory. With a low net energy demand, microalgae EF may be a useful and low-cost technology.