轴流泵叶轮出口尾迹区非定常压力和速度场特性

为了分析轴流泵叶轮出口尾迹和势流交替干扰特性,基于RNGk-ε湍流模型和SIMPLE算法,对南水北调工程用轴流泵模型进行了数值计算。通过定常预测的外特性结果与试验值进行比较,验证了计算网格和湍流模型的适用性,并在此基础上计算了轴流泵叶轮出口尾迹区非定常流场特性。研究结果表明,通过轴流泵全流场数值计算结果与试验值对比,在最优工况下计算扬程相对误差为4.56%,效率相对误差为2.78%,较好反映了轴流泵内部流动特性;在小流量工况下,轴流泵叶轮出口圆周方向轴面速度存在与叶片数相同的3个主波峰和3个次波峰;随着流量增大,叶轮出口圆周方向速度分布图中的波峰与导叶叶片数相同。在小流量工况和设计工况下,叶轮出口尾迹区压力脉动时域图出现3个主波峰,随着流量增大,额外产生了3个次波峰。基于FFT变换发现不同流量工况下的压力脉动主频均以叶频为主,其他谐频以叶频为基频,呈倍数出现,且主频的幅值随着流量减小而迅速上升。     

叶轮中心淹没深度对特低扬程下立式泵装置流道水力性能的影响

为提高特低扬程泵站立式轴流泵装置的水力性能,该研究对叶轮直径为3.0、2.5、2.0、1.5 m的立式轴流泵装置在不同叶轮中心淹没深度下的进、出水流道流场分别进行了三维湍流流动数值计算,并对流道流场和水头损失进行了分析比较;对某特低扬程泵站在叶轮中心淹没深度为3.08、2.38、1.68 m下的立式轴流泵装置水力性能分别进行了数值计算及比较,并进行了泵装置模型试验验证。研究结果表明：叶轮中心淹没深度对肘形进水流道的水流流态及水头损失的影响很小,但对虹吸式出水流道的流态和水头损失影响较大;随着叶轮中心淹没深度的增大,虹吸式出水流道内的流态逐渐改善,流道水头损失基本呈下降趋势,泵装置效率逐渐增大,特低扬程工况下泵装置模型试验最优工况点的效率达75.92%,泵装置能量性能数值模拟结果与模型试验结果基本一致。研究结果可为特低扬程泵站采用立式泵装置的设计提供一定参考依据。     

双向潜水贯流泵装置性能试验与数值分析

该文针对城市防洪排涝泵站的特点,研发了2套双向潜水贯流泵装置,并采用CFD(computational fluid dynamics)技术计算了双向潜水贯流泵装置的内流场,分析了灯泡体段对泵装置正反向运行的影响,包括灯泡体段的水力损失、导叶体内部的流态及"S"形叶轮的水力性能,并经试验验证分析了数值计算结果的有效性。计算结果表明,反向运行时导叶体内部流态较好,反向运行工况优于正向运行;正向运行工况流量为4和5m3/s时,导叶体内均出现涡旋;灯泡体支撑件对"S"形叶轮的水力性能影响极小,但对泵装置水力性能影响较大;正向工况时"S"形叶轮所受轴向力小于反向工况。通过泵装置模型性能试验比较了2套泵装置的综合水力特性指标,并给出了供参考的潜水贯流泵装置的结构尺寸,其中导叶体扩散角为3°,灯泡体长度为2.43D、灯泡体直径为0.46D、泵装置总长为13.45D(D为叶轮名义直径),灯泡体采用流线型尾部及5片支撑件。     

进口管壁面轴向开槽消除轴流泵特性曲线驼峰

当轴流泵在小流量工况下运行时,由于叶轮进口的冲角增大,导致在叶轮内产生脱流等不稳定流动结构,降低泵的水力性能。该文采用计算流体动力学分析方法对轴流泵内部流场进行了研究,结果表明:该轴流泵的特性曲线存在明显的驼峰区域,在0.3到0.61倍最优流量工况区间,轴流泵的扬程和效率明显下降。在临界失速工况下(0.61倍最优流量工况),叶片吸力面前缘靠近轮缘处及叶片尾缘靠近轮毂处均出现了脱流;在深度失速工况下(0.45倍最优流量工况),脱流进一步发展,并与来流共同作用形成稳定的涡旋结构,阻塞整个流道。为了提高轴流泵在小流量工况下的水力性能,引入一种轴流泵进口管开槽技术,分析其对轴流泵内部流场的影响及驼峰的改善作用。结果表明:在小流量工况下,轴向开槽可以减小叶轮进口环量和冲角,可以减小叶片背部的脱流,轴流泵的驼峰得到明显的改善。开槽深度是改善轴流泵小流量工况下驼峰的重要因素之一,当槽深与叶轮直径比为0.02时,叶轮内的通道涡几乎完全消除,轴流泵深度失速工况点的扬程、效率分别提高了66%和32%,极大地改善了轴流泵的水力性能。沟槽数目越多,槽长越长,消除驼峰的能力越好,60个沟槽与2/3倍叶轮直径的槽长在其他参数相同的条件下消除驼峰的能力更强。该文可为避免轴流泵内部的失速流动以及消除水力性能曲线上的驼峰相关研究提供参考。     

采用熵产理论的离心泵断电过渡过程特性

该文对商业软件ANSYS CFX进行二次开发,通过自定义函数求解角动量方程获取实时转速,建立了模拟离心泵事故断电过渡过程的三维瞬态数值计算方法,获得了离心泵外特性参数瞬变规律以及内部流场的动态特性。进一步采用熵产理论获得了离心泵事故断电停机飞逸过程中过流部件流场能量损失分布情况,并对流场内随时间变化的能量损失进行定量评估。结果表明:在整个事故断电飞逸过程中,熵产与离心泵外特性之间存在着明显的相关性,能量损失的产生与流场内部的流动分离、回流、漩涡等不良流动现象相关;叶轮、导叶与引水管的主要损失均是由湍流耗散引起的,其壁面熵产占总熵产的10%~15%左右,不可以忽略,而蜗壳区的损失则主要是由近壁面处的强壁面效应引起的;通过分析各部件流场局部熵产率分布随时间的变化情况,可以得出在制动工况中内流场的高损失区域最大。     

采用熵产理论的离心泵断电过渡过程特性

该文对商业软件ANSYS CFX进行二次开发,通过自定义函数求解角动量方程获取实时转速,建立了模拟离心泵事故断电过渡过程的三维瞬态数值计算方法,获得了离心泵外特性参数瞬变规律以及内部流场的动态特性。进一步采用熵产理论获得了离心泵事故断电停机飞逸过程中过流部件流场能量损失分布情况,并对流场内随时间变化的能量损失进行定量评估。结果表明:在整个事故断电飞逸过程中,熵产与离心泵外特性之间存在着明显的相关性,能量损失的产生与流场内部的流动分离、回流、漩涡等不良流动现象相关;叶轮、导叶与引水管的主要损失均是由湍流耗散引起的,其壁面熵产占总熵产的10%～15%左右,不可以忽略,而蜗壳区的损失则主要是由近壁面处的强壁面效应引起的;通过分析各部件流场局部熵产率分布随时间的变化情况,可以得出在制动工况中内流场的高损失区域最大。     

轴流泵多工况优化设计及效果分析

为了提高轴流泵非设计工况的运行效率,拓宽轴流泵高效区范围,对轴流泵进行多工况优化设计。结合轴流泵段的模型试验,采用数值模拟手段和数值优化技术,改变叶轮的几何设计参数。对轴流泵叶片进行参数化建模,再对轴流泵叶轮结果进行泵段数值模拟。最后以轴流泵段3个流量工况点的加权平均效率最高,扬程为约束条件,改变轴流泵叶轮的设计参数,对轴流泵段进行多工况优化设计。研究结果表明:优化后轴流泵段效率曲线较初始泵段明显变宽,其中小流量工况点效率提高约2.6%,设计工况点效率提高约0.5%,大流量工况点效率提高最多,约7.4%,而对于扬程变化范围较小,各工况点扬程均能满足运行要求,大大降低了运行成本,缩短了优化设计的周期。同时采用CFD计算的学科分析方式,结合试验研究的手段取代人工凭经验的优化方式,证实了轴流泵段多工况优化设计的可靠性、高效性。该研究将为泵站的高效运行和轴流泵的多工况优化设计提供参考。     

箱涵式进水流道的立式轴流泵装置水动力特性分析

为了研究有涡时箱涵式进水流道的立式轴流泵装置水动力性能,该文采用CFD(computational fluid dynamic)和高速摄影技术对箱涵式进水流道的立式轴流泵装置进水流道内部附底涡流动特征及其对泵装置水动力性能的影响进行了分析。数值模拟和试验结果表明,基于CFD数值模拟技术,成功捕捉到各工况时箱涵式进水流道内部附底涡轨迹,与高速摄影捕捉到附底涡的运动轨迹较为一致,且均发生于喇叭管口下方,附底涡对泵装置的安全运行稳定性有直接影响。有、无消涡锥的箱涵式进水流道出口断面的轴向速度分布均匀度与速度加权平均角的差异性较小,但其水力损失值下降较大;叶轮所受轴向力相对比值m1在0～7.0%范围内波动,轴向力随流量系数的增大而减小,附底涡对叶轮所受径向力的影响较大,径向力相对比值m2在5.0%～110.0%范围内波动,涡带对叶轮受力有一定程度的影响,实际工程中应避免箱涵式进水流道内部涡带的出现。     

不同湍流模型在轴流泵叶顶泄漏涡模拟中的应用与验证

为寻求一种经济、适合的湍流模型模拟轴流泵叶顶泄漏涡的结构和运动特性,该文基于ANSYS CFX软件平台,优化了六面体网格拓扑结构,比较了标准k-ε湍流模型（standard k-ε）、重正化群k-ε湍流模型（renormalization group k-ε,RNG）,标准k-ω湍流模型（standard k-ω）和SST k-ω湍流模型（shear stress transport）等4种湍流模型在轴流泵叶顶泄漏涡模拟中的计算精度和叶顶泄漏涡流场特征。数值模拟和试验结果表明,在最优工况下,SST k-ω湍流模型预测外特性曲线与试验曲线吻合较好,扬程误差为4.688%,较其他3种湍流模型准确;4种湍流模型计算的叶顶泄漏涡流线、叶顶区压力场和轴面速度场分布规律相似,但RNG k-ε和SST k-ω湍流模型计算的涡卷吸较强,涡带的旋涡强度相对较大。基于旋涡强度提出了一种对叶顶泄漏涡的涡心进行识别的方法,并与高速摄影拍摄的涡带结果进行了对比,在设计流量工况和大流量工况下,发现SST k-ω湍流模型计算的叶顶泄漏涡运动轨迹与试验结果吻合度较好,验证了SST k-ω湍流模型在轴流泵叶顶泄漏涡模拟具有较好的适用性。     

高比转速斜流泵内部非定常压力脉动特性

为了研究斜流泵叶轮和导叶的动静相干作用引起的内部压力脉动特性,该文基于标准k-ε模型,采用SIMPLEC算法和滑移网格技术,对高比转速斜流泵进行非定常数值模拟,分析了不同工况下的叶轮进出口、导叶中部和导叶出口等位置的压力脉动的时域和频域特性。通过定常计算的扬程、效率值与试验值进行对比,证明该计算方法和网格可以较准确地反映斜流泵内的流动特性。计算结果表明,斜流泵最大压力脉动发生在叶轮进口前,泵运行偏离最优工况越远,叶轮进口处压力系数幅值越大,在0.7Qopt工况时叶轮进口监测点P03的压力系数幅值约为最优工况的1.5倍;压力脉动主频为叶轮叶片通过频率。研究成果为揭示斜流泵内部压力脉动规律提供了一定的理论参考。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.