多级轴流风扇的性能试验与流场分析

针对某型四级轴流风扇改进设计的需要,通过试验详细测量了风扇的总性能特性,并利用三维流体计算软件NUMECA对设计转速下的部分典型工况进行了数值模拟.研究了风扇总性能和级性能的变化,时比分析了设计工况和近失速工况的流场特征.结果表明:风扇呈现出典型跨音速风扇设计的特点,计算结果与试验数据吻合较好,设计转速下,第三级转子通道中的激波被推出通道是导致失速产生的主要原因.本文结果可为该型风扇的改进设计提供参考.     

单级离心压气机气动性能预测与优化设计

为了提升低转速工况下压气机的气动性能,采用人工神经网络与遗传算法相结合的优化方法对某单级离心压气机离心叶轮的弯特性进行优化计算。利用NUMECA软件对该离心压气机进行了不同转速的数值模拟,得到压气机不同工况下的气动性能。通过设置不同控制参数和曲线形式对离心叶轮叶片进行参数化拟合,以8个改变叶片弯特性的参数为自由参数进行了叶型优化设计,最终得到了优化后的叶轮叶片。结果表明:优化后在低转速的设计工况下离心压气机压比增加了4.69%,稳定裕度拓宽了17.41%。     

发动机导叶和涡轮叶片性能衰退的数值研究

针对导致发动机典型部件性能衰退的多个主要因素——导流叶片调整偏差、叶片粗糙度增大、叶型改变和叶顶间隙增加,基于流场仿真技术,建立了风扇和涡轮的计算模型,完善性能衰退表征方法,分析了多种因素对其气流流场的影响以及主要性能参数的变化规律。结果表明:导流叶片角度调整偏差、叶片粗糙度增加、叶型改变等因素影响风扇和涡轮的工作性能,降低其性能参数。所得结果为深入研究制定相应部件性能衰退后的维护调整措施奠定基础。     

高效宽负荷叶型气动性能研究

针对叶片根中顶3个截面不同的安装角,设计了相应的高效宽负荷叶型,并采用数值模拟的方法,分析了叶型对负荷的适应性,重点分析了对攻角和马赫数的适应性。数值计算表明,以变工况性能较好的高效后加载叶型为母型开发的高效宽负荷叶型,可以实现机组变负荷运行时保持较高通流效率的目标,攻角变化范围为±30°、马赫数变化范围为0.2~0.6时叶型损失变化不超过0.5%。     

给水泵汽轮机流场的数值模拟

介绍了采用NUMECA的Fine/Turbo软件对超超临界1000MW机组给水泵汽轮机的三维复杂流动进行了变工况数值模拟,具体分析了3个典型工况下的反动度、攻角以及效率等的变化情况。计算分析表明,进汽参数和转速对流场的气动特性影响较大。同时,3个不同转速及负荷工况下末级叶片的流场数据为进一步的叶型优化提供了依据。     

几种超音速叶型的设计与比较

针对3种超音速叶型,基于遗传算法和人工神经网络,对这3个叶型进行单个工况点的优化设计,并对得到的所有叶型的气动性能进行多个马赫数工况点的数值分析以及综合比较,分析叶片型面的改变对多个工况下叶片气动性能的影响。结果表明,优化设计使2种叶型在超音速工况下的气动性能显著提高,1种叶型在临界及亚临界工况下的气动性能显著提高,从而获得每一工况点下的最优叶型。     

加弯叶型在轴流风机噪声控制中的应用研究

在风机叶轮直径不变的条件下,利用叶型加弯方法对轴流风机进行改型设计,可在较低转速下获得设计全压,从而达到控制风机气动噪声的设计目标。根据轴流风机的设计参数设计了一个基于原始叶型、转速为9 000 r/min的风机模型和一个基于加弯叶型、风机转速为8 000 r/min的风机模型,两者的叶型升力系数分别为0.72和1.02。通过数值模拟和试验对两风机的流场与性能进行研究。结果表明:在设计工况附近,原始叶型风机与加弯叶型风机的性能基本相近,全压误差约为6%。在半转速运行条件下,加弯叶型风机模型的气动噪声比原始叶型风机降低了1.4 d B,而气动性能基本不变。     

汽轮机末级叶片模态振型与变负荷动应力的三维数值模拟

火电机组参与电网深度灵活调峰已成为当代电力发展的新常态,在机组低负荷深调过程中,蒸汽流量较小。本文针对调峰机组汽轮机末级叶片小容积流量问题进行了模态特性及动应力响应进行数值模拟研究,结果表明:末级叶片在2 820～3 090 rpm之间无共振点,而额定温度范围内整圈叶片无共振转速;以模态分析为基础综合考虑变温特性下得出叶片伸长量,可为现场叶片汽封调整作为参考。基于额定工况与2.2 kPa、40 t/h工况下的动应力满足设计要求,而其他非设计工况下的动应力已超出了叶片的耐振强度,全工况动静应力极值均处于叶型根部出汽侧,导致叶片的耐振强度许用值较低。上述数值结果为电厂调试提供了理论支撑,同时也为机组经济性运行作出了技术指导。     

透平叶片在流-热-固耦合场下的变形研究

透平叶片在复杂耦合场下工作会产生形变,与设计流道曲面产生偏差,严重影响涡轮机的工作效率。基于流-热-固耦合有限元模型对复杂工况下叶片的变形进行了研究。采用RNGk-e湍流模型经FLUENT流场仿真实现叶片的三维温度场和压力场模拟,利用ANSYS分析得到叶片在温度、压力、离心力单独作用和耦合作用下对应的变形量,并运用灰色关联度理论分析变形之间的关系。通过分析发现,耦合场下的叶片变形并不是各载荷单独作用下变形的线性叠加,而是复杂地耦合;温度是影响叶片变形的优势子因素,压力和离心力的影响较小。分析结果对叶片形变控制策略、补偿及重构都具有重大指导价值。     

不同转速下某跨音速轴流压气机的性能分析

为了研究某跨音速压气机的流动机理与稳定工作的范围,采用三维雷诺平均Navier-Stokes方程组和Spalart-Allmaras湍流模型进行了定常数值模拟。分别计算了90%、100%和110%设计转速下的全工况,同时着重分析了100%设计转速下的近堵塞点与近失速点和其他转速下的最高效率点。结果表明:设计工况点的等熵效率85.35%、压比1.387、流量4.861 kg/s,与设计指标相比,等熵效率和流量偏差2%以内以及压比偏差5%左右均在允许范围内,说明该计算方法验证压气机的内部流动特性是可靠的;叶片吸力面的低能流体在叶片尾缘汇合形成尾迹、激波造成叶片边界层分离和激波与叶顶间隙的泄露流相互作用形成的二次流是引发流动失稳的主要因素;随着转速的提高,进口马赫数增加,压气机在90%、100%和110%设计转速下最高效率点的等熵效率分别为88.57%、86.76%和82.66%。     

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.     

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%.     

Contents in Volume 23,2014

<正>~~     

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.     

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.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.