小型离心压气机径向扩压器复杂涡系结构分析

对某小型离心压气机进行详细数值模拟,构建径向扩压器复杂涡系结构模型,重点分析设计、堵塞、失速工况下径向扩压器内部复杂涡系结构。研究表明：径向扩压器内部涡系结构主要包括前缘涡、两个通道涡（压力面侧通道涡与吸力面侧通道涡）以及喉部涡;主叶片吸力面的前缘涡是机匣侧低能流体在展向与流向压力梯度作用下形成的,喉部涡是吸力面侧通道涡沿分流叶片前缘的回流与前缘涡构成的;喉部涡在喉部的堆积是导致径向扩压器失速的原因,径向扩压器喉部的激波则是堵塞的原因;随流量的减小,前缘涡的涡核越向相邻主叶片压力面迁移。     

排汽缸导流内环子午型线改型设计的数值研究

为了降低某汽轮机低压排汽缸的流动损失,对占流动损失比例较高的环形扩压器进行了改型设计,改变扩压器内导流环子午型线圆弧段半径,数值研究其大小变化对排汽缸气动性能的影响。结果表明,扩压器内导流环圆弧段半径增大,提高了汽流在环形扩压器中的增压程度,降低了汽流由扩压器出口进入排汽蜗壳时的压力突升,改善了排汽缸的气动性能。     

扇形喷孔气膜冷却流场的大涡模拟

对锥形角γ=30°扇形喷孔横向紊动射流进行了大涡模拟,在吹风比M=1.0工况下模拟了不同截面上涡量随时间变化的过程,并对各种涡的流动机理进行了分析.结果表明:对称面的正、反向旋转涡、垂直截面的马蹄形涡的两翼周期性地交替脱落成新的涡,对称面涡的周期为0.024 s,马蹄形涡的周期为0.032 s;反向旋涡对气膜冷却流场有重要影响,沿主气流流动方向的无量纲长度X/D在1～2时,反向旋涡的涡量值逐渐衰减;当X/D＞4时,反向旋涡开始逐渐消失,导致壁面附近的能量交换快,对底面的冷却效果好;由于在射流上游和下游的压力梯度不等,造成射流两侧的脉动速度变化不一致,导致了反向旋涡的不对称分布.     

两种透平叶栅流场二次流特性及其涡系结构的可视化实验研究

本文应用 Ｔｉ Ｃｌ４ 烟迹法和表面油膜法对两种透平叶栅二次流特性及其涡系结构进行了流场可视化研究,深入地分析了叶栅端壁及叶栅型面的流动,揭示了叶栅二次流涡系的结构与叶型形状的关系以及马蹄涡吸力面分支和吸力面角涡的发生演变情况。     

圆柱表面沟槽减阻的大涡模拟研究

为了降低钝体绕流的阻力,以圆柱为研究对象,考虑在圆柱表面布置沟槽来实现减阻。研究采用大涡模拟(Large Eddy Simulation, LES)方法对雷诺数Re为3 900的圆柱绕流进行数值模拟,通过表面沟槽影响近壁区流动来达到流动控制的效果。分析了V型和L型两种沟槽分别以横向和纵向形式布置时对圆柱阻力系数的影响,通过对比粗糙圆柱与光滑圆柱的壁面摩擦力系数、流动分离点及近壁区流场结构,研究了表面沟槽对于钝体流动的减阻机理。数值模拟结果表明：表面布置特定深度与间距的沟槽后,粗糙圆柱的阻力系数与光滑圆柱相比最多可降低12.5%,边界层分离点也更延后;流体在流经沟槽表面时,会在沟槽底部形成稳定的旋转小涡,减少了壁面摩擦阻力。     

翼型表面随行波结构流动控制的数值研究

针对翼型表面的流动分离,采用数值模拟方法研究随行波结构流动控制的机制。为了验证计算方法的可靠性,将翼型表面静压曲线与实验测试结果进行对比,发现两者吻合程度较好。数值计算结果表明,适当增加随行波的相对弦长长度,有助于改善翼型的气动性能。当攻角小于3°时,随行波位于分离点之前,沟槽内形成顺时针旋转的二次涡,有助于加速边界层低速条带;在大攻角下,随行波位于分离点之后,顺时针卷起的分离涡在沟槽内形成逆时针旋转的二次涡,与分离涡互为反向涡对,减小了尾缘分离区范围。翼型表面随行波能有效地控制边界层流动。     

自由活塞发动机电动压气机优化及熵产分析

为了使设计工况下匹配的增压器性能更优从而提高系统能量利用率,针对自由活塞发动机匹配的电动压气机,采用遗传算法对原压气机进行了优化,研究了优化前、后压气机内部流场特性,以熵产分析的方法量化了3种不可逆因素导致的流动损失,并将优化前、后压气机熵产和涡度分布对比分析,进一步明确了压气机的优化策略．结果表明：叶轮和扩压器中湍流耗散、传热耗散和黏性耗散的比例近乎为6∶3∶1．不可逆损失主要集中在叶顶间隙和叶片压力面,损失来源为间隙泄漏流与部分主流掺混形成的反向涡团．压壳中湍流耗散占比超过85%,具体表现为局部损失和沿程损失．优化后压气机等熵效率提高了6%,流道内涡团的范围、幅值大幅减小,不可逆流动损失降低．上述工作揭示了压气机流场中不同耗散机制的不可逆因素对能量损失的影响机理,为压气机气动优化设计提供指导．     

两种透平叶栅流场二流特性及其涡系结构的可视化实验研究

本语文应用ＴｉＣｌ４烟这法和表面油膜法对两种透平叶栅二次流特性及其涡系结构进行了注场可视化研究,入地分析了叶栅端壁及叶栅型面的流动,揭示了叶栅二次流涡系的结构与叶型形状的关系以及马蹄涡吸力面分支和吸力面角涡的发生演变情况。     

非轴对称端壁控制高负荷叶片端区流动的数值研究

用数值模拟的方法研究了非轴对称端壁对端部流动的机理,分析了非轴对称端壁对横截面涡量和总压损失的影响。研究表明:在亚音速流动条件下,流道后半部分端壁区流动参数变化较小,降低后半端壁的翘曲幅度,均能进一步提高翘曲端壁对端壁流动的控制效果;端壁翘曲通过延长端壁附面层流动、形成扩散性流道等途径降低了端壁横向压力梯度,减少了进入吸力侧壁角的端壁横流及其与吸力面相互作用产生的通道涡量,有效降低了端壁流动的总压损失。     

叶片弯曲对跨音速涡轮叶栅流场的影响

对均匀加载叶型所构成的直叶栅及不同弯角所构成的弯叶栅流场进行了数值模拟。研究了弯叶片作用下型面压力分布、马赫数等值线及叶片表面压力分布的改变,同时考察了叶片弯曲对马蹄涡及通道涡生成位置的影响。叶片正变后有助于减少端壁处的横向压力梯度,削弱端壁二次流动;另外叶片正弯后会使马蹄涡起始分离点位置向流道中间偏移,促使通道涡提早发生。本文所选用的差分格式为具有ＴＶＤ性质的三阶精度的Ｇｏｄｕｎｏｖ格式,湍流模型为修正后的Ｂ－Ｌ代数模型。     

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.     

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。     

Contents in Volume 23,2014

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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.