安装高程对潮流能水轮机尾迹特性影响试验研究

为探究安装高程对潮流能水轮机尾迹特性的影响,以模型潮流能水轮机为研究对象,采用ADV采集尾流场速度数据,对比分析不同高程下的尾流场特性,揭示安装高程对潮流能水轮机尾迹特性的影响规律.结果表明:随着安装高程的增加,转轮后方尾流速恢复速度逐渐加快,而湍流强度和雷诺切应力恢复速度有逐渐减小的趋势;横向尾流场水动力特性沿转轮中...     

偏流条件下水平轴水轮机水动力学性能与尾流场研究

针对水平轴水轮机在偏流条件下的复杂水动力学问题,借助计算流体力学(CFD)数值模拟方法,建立了水轮机的计算模型并通过试验数据验证了模型及方法的可靠性,之后对不同偏流角下的水平轴水轮机的水动力学性能及尾流场进行了研究。结果表明,随着偏流角的增大,水轮机的平均功率系数和推力系数逐渐下降,而瞬时功率系数、推力系数和压力脉动系数的波动幅值逐渐增大。此外,水轮机的尾流场将变得十分复杂和不稳定,并在下游相应位置处出现反向漩涡,但尾流速度恢复明显加快。     

不同交错排布对潮流能垂直轴水轮机性能的影响

为了优化潮流能垂直轴水轮机排布方案,采用计算流体动力学(CFD)方法得到双水轮机在不同轴间距H、不同相对位置角(RPA)β及前后排水轮机不同尖速比λ下平均功率系数CP变化规律,分析流场的速度和涡量云图,解释变化机理.同时,对比单、双水轮机尾流速度分布情况,探究双水轮机尾流特性.结果表明:后排水轮机处于前排水轮机尾流区内...     

阻塞比对潮流能水轮机尾流特性影响数值模拟研究

首先通过对比分析数值模拟结果与水槽实验尾流场速度数据,验证数值模拟的准确性。通过在软件STAR-CCM+中改变水槽宽度的模型,使水轮机阻塞比分别在9.8%、14.7%和29.5%的情况下进行模拟计算,分析潮流能水轮机尾流特性的变化。结果显示,阻塞比的变化不仅会改变水轮机扫略区域外流体速度,影响远尾流恢复速度,还会对尾流的旋转和湍动能分布造成影响;但随着槽宽增加阻塞比减小,其对尾流特性影响逐渐减弱。     

多工况条件下变叶片数潮流能水轮机能量及流动特性研究

文章建立了潮流能水轮机水动力性能数值计算模型,通过实验验证了利用该模型预测水轮机尾流的准确性,并利用该模型研究了潮流能水轮机在不同叶片数和不同叶尖速比条件下的能量和流动特性。研究结果表明:该数值计算模型在预测尾流速度亏损和湍流强度方面具有较好的精度,尤其在远尾流区,数值计算结果与实验结果保持一致;当叶尖速比(TSR)为4.5左右时,3叶片和4叶片的潮流能水轮机具有相对较高的获能系数,此结果对于水平轴潮流能水轮机的设计具有一定的指导意义。     

基于致动盘的潮流能水轮机尾流场研究

相比于三维CFD叶片真实模拟,致动盘方法将水轮机简化为流场中分布有作用力的核心区域,所需网格大大降低,节省了计算资源和计算时间。文章介绍了一种精度适中、计算成本较低的潮流能水轮机CFD致动盘数值模拟模型,将动量理论与CFD方法相结合,通过致动盘来模拟水轮机对流场的作用,通过求解Navier-Stokes方程获得尾流场。对比基于致动盘理论的数值模拟结果与真实水轮机的水槽实验数据,结果表明,致动盘数值模拟在远尾流处的结果比近尾流处更加接近实验值,致动盘方法很容易捕捉到远尾流的流场情况。研究结果可为潮流能大规模利用的数值模拟提供依据和参考。     

真实地形条件下潮流场及水轮机的数值模拟与研究

为了考察实际潮流场地形因素对实尺度水轮机影响,用数值模拟方法研究潮流场内部流动在海底地形作用下的变化规律,并探讨其对水平轴潮流能水轮机水动力学性能的影响。对安放水轮机位置处流速随水深的变化规律进行分析,讨论上游来流在底部地形和水轮机双重因素作用下的变化趋势;着重对比在不同工况下海底地形条件对水轮机水动力学性能的影响,并进一步分析真实潮流场中水轮机尾流的分布特性,为未来大尺度潮流能水轮机的设计优化及性能预测提供依据,并为复杂海况下潮流能水轮机水动力学研究提供一种思路和方法。     

横向布置单桩潮流能水轮机的数值模拟研究

文章以单桩潮流能水轮机为研究对象,通过数值计算的方法对横向布置下两台单桩潮流能水轮机的尾流场及机组性能进行研究。通过对比不同横向间距下单桩潮流能水轮机的尾流场,获得了横向间距对潮流能水轮机尾流场的影响规律。数值计算结果表明:单桩结构会改变水轮机的纵向尾流场,但对横向尾流场的影响较小;随着横向间距的改变,机组的功率系数和推力系数的变化幅值不超过0.01;横向间距对机组的横向尾流场也造成了影响,导致各个机组的尾流中心偏向两个机组的中间位置,且随着横向间距的增大,机组u/U0低于0.9的范围随之增大,幅值可达0.26D。     

偏流角对潮流能水轮机水动力影响研究

基于三维CFD数值模拟方法对潮流能水平轴水轮机进行分析研究,并与试验结果比较,验证该方法的有效性。通过改变迎流式和背流式偏流角的大小,研究不同偏流角对水平轴水轮机水动力特性的影响规律。结果表明:偏流使水轮机效率及轴向载荷的平均值下降,偏流20°时,迎流式和背流式效率最大下降分别约为5%和6%,轴向载荷系数最大下降分别为5.5%和7.0%;使瞬时值波动幅值增加,偏流角越大,波动幅值越大。     

海浪条件下水平轴叶片式潮流能水轮机流动特性的数值模拟

为了研究自由海浪条件下的高潮汐流速对水平轴潮流能水轮机的动态特性影响，基于STAR-CCM+建立了海浪条件下潮流能水轮机水动力特性的数值模拟方法，得到了海浪对潮流能水轮机转动影响规律及转动过程中产生的尾流特征。结果表明，潮流能水轮机角加速度的幅度与频率受海浪影响，但波动幅度小于海浪波动幅度、变化频率高于海浪波动频率；水轮机转动产生的尾流会使下一个水轮机的周围流场更紊乱，对叶片转动的影响、水轮机轴负载和能量利用率等方面会产生影响；压力脉动变化趋势分析认为，尾流对水轮机疲劳损伤并无太大影响。     

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%.     

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.     

Contents in Volume 23,2014

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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。     

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.     

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.