基于粒子图像测速的离心泵叶轮内流动分离测试与分析

离心泵在小流量工况下运行极易产生流动分离,严重影响泵的运行稳定性。为了揭示离心泵小流量工况下叶轮内流动分离的变化规律,对一比转数为73的离心泵小流量工况下叶轮内部流动进行了PIV测试和分析,并以流动偏移角和回流强度为参数对测试结果做了量化分析。不同工况的测试结果表明,0.6Qd工况下叶轮内开始出现流动分离,到0.2Qd工况下流动分离已发展充分;随着流量的降低分离泡向流道中部和出口方向移动发展。0.2Qd工况下不同相位的试验结果显示叶轮流道接近隔舌时会出现分离泡,经过隔舌后分离泡迅速发展,远离隔舌后分离泡逐渐消失。流动偏移角的量化分析能够准确反映出叶轮流道内分离泡的数目;回流强度的量化分析表明叶片旋转过隔舌135°后,动静干涉对流动分离的作用明显减弱。     

半开式离心泵变工况叶顶间隙的流动特性

为研究不同工况下,叶顶间隙对半开式叶轮离心泵内部流场及外特性的影响,该文对某半开式叶轮离心泵内部三维湍流流场进行数值模拟。揭示了离心泵内不同工况下叶轮流道和叶顶间隙层内的流动规律,对比分析了4种不同流量工况下叶顶间隙泄漏涡的流动特性、叶顶间隙层总压与相对速度分布,以及流量的变化对离心泵外特性的影响。结果表明:在小流量(设计流量为1.5 m3/h)时,间隙层内充满了泄漏涡,随着流量的增加涡核逐渐减少;大流量时涡核几乎消失,但此时流体速度激增,流动冲击损失变大在叶轮出口与间隙层附近存在着大面积回流,小流量时回流几乎占据了整个出口。通过模型泵外特性试验,验证了数值计算的准确性。该文为离心泵叶顶间隙设计及水力优化提供了参考。     

离心泵压水室内部定常和非定常流动PIV测量

为研究离心泵压水室内的流动特性,利用PIV技术在内同步和外同步模式下分别测量了其内部的定常和非定常流场,详细分析了压水室内部流动现象和流动规律。结果表明,压水室内速度沿轴向分布均匀,随圆周角增大而减小;在叶轮和压水室的交界处,存在清晰的速度分界线;受蜗舌的分流作用,部分流体回流入叶轮流道,扩散管入口处速度显著降低;压水室内部周期性非定常流动规律明显,第VIII断面上,速度的大小和波动幅度沿径向均呈减小趋势,周向速度的波动与叶轮流道内部高速流区的位置有关,而径向速度的波动主要受叶片干扰和哥氏力的影响。研究结果为压水室设计以及离心泵内部流动的试验研究提供了借鉴。     

离心泵叶轮内的网格生成与计算流体力学分析

根据离心泵叶轮通道的几何和流场特点，探讨了离心泵叶轮通道结构化多块网格划分中的一些处理方法。同时应用标准k-ε紊流模型加壁面函数法对离心水泵叶轮内部的三维紊流流动进行了雷诺平均N-S方程的数值计算与分析。分析了离心泵叶轮叶型对流速分布、压力分布和泵性能的影响，研究了离心泵叶轮通道内流动规律，并以计算流体力学(CFD)分析结果为依据，对离心泵叶轮进行了叶型优化设计。结果表明进行离心泵叶轮内三维紊流数值计算可为离心泵叶轮叶型优化提供详细的数据，应用CFD分析技术可提高离心泵叶轮的设计水平。     

半开式叶轮离心泵气液两相条件下内部流动特性分析

半开式叶轮离心泵输送气液两相流时,其性能经常随入流含气率（α）的增加而下降,主要由内部的气液两相不稳定流动造成。为解决传统欧拉双流体模型不能考虑气泡直径变化及气泡形变的问题,采用一种群体平衡模型（Musig模型）数值计算了某设计比转速为88.6的半开式叶轮离心泵在不同入流含气率下的内部流场,并进行了试验验证。研究结果表明：模型泵在1 000 r/min可输送液体的最大入流含气率为4.6%;α>3%以后,Musig模型由于能表征气泡形态及破碎与聚合过程等气液两相流演化规律,其外特性计算结果比欧拉-欧拉双流体模型准确,且与可视化试验流型测试结果较为吻合;α=4%时扬程系数和效率与试验结果的最大误差分别为1.6%和5%;随着入流含气率的增加,叶轮和蜗壳流道内逐步出现均匀泡状流、聚合泡状流、气穴流和分离流等流型分布,设计流量下α≤1%时以均匀泡状流为主,α=3%时以聚合泡状流为主,α=4%时以气穴流为主,α≥4.2%时出现分离流并逐渐堵塞流道;叶顶间隙是影响泵内气液两相流型分布的重要原因,叶轮流道中存在大尺度漩涡和出口回流现象,且随着含气率的增大越发明显,进而在高含气率区域引发较大的湍动能分布,加剧了泵内部的不稳定流动,最终导致α≥4.6%后的泵空转。该研究可为综合分析离心泵内部不稳定流动规律提供一定参考。     

离心泵内叶轮与蜗壳间耦合流动的三维紊流数值模拟

根据离心泵通道的几何和流场特点,探讨了离心泵叶轮通道结构化多块网格划分中的一些处理方法。同时求解三维时均Ｎ-Ｓ方程,并采用“冻结转子法”处理叶轮与蜗壳间动静耦合流动的参数传递和相互干扰问题,对某一设计工况下离心泵内的全三维紊流场进行了计算,捕捉到了离心泵叶轮内、叶轮与蜗壳间及蜗壳内的压力分布、速度分布和旋涡的结构与演化特征等重要流动信息。结果表明,该方法能够较为准确地预测出离心泵叶轮与蜗壳间及内部的流动特性,所得结果对进行离心泵的水力设计或改型优化设计等研究具有重要的指导意义。     

前伸式双叶片污水泵内部流场PIV试验

以一台比转速为70的前伸式扭曲双叶片污水泵为研究对象,采用PIV(particle image velocimetry)技术对双叶片污水泵进行内部流场测量,分析了该泵在不同流量工况下(Q/Qdes=0.4、0.6、0.8、1、1.2、1.4)叶轮内部流场的相对速度分布,研究了轴向旋涡和低速区随流量变化的形态特性,发现在流道中部靠近叶片工作面上存在低速区及与叶轮旋转方向相反的轴向旋涡,且随着流量的增大,低速区与轴向旋涡逐渐减小;引入少叶片数离心泵内部流动理论,揭示了低速区和轴向旋涡存在和发展的内在机理。分析了在流量Q/Qdes=0.6时叶轮和蜗壳不同相对位置的相对速度场分布,研究了叶轮和蜗壳之间动静干涉作用对轴向旋涡的影响,发现当轴向旋涡经过蜗壳隔舌时,其与叶轮之间的干涉作用使得轴向旋涡向下游偏移。研究结果对前伸式扭曲双叶片污水泵的内部流动规律研究具有重要参考价值。     

液力偶合器气液两相流动的数值模拟与粒子图像测速

为了更加真实地反映偶合器内部的气液两相流动机理,该文应用计算流体力学（computational fluid dynamics,CFD）对其内部流动的速度和压力等流场特征进行数值模拟,并应用粒子图像测速（particle image velocimetry,PIV）技术对其流场进行了测试,试验结果表明：泵轮内的气泡小而均匀,速度分布较规律,由内环向外环递增;涡轮内气泡较多,并出现了涡流、回流、二次流等不规则流动现象。PIV测试的流场流动趋势与数值模拟的流场流动趋势基本一致。CFD数值模拟方法和PIV技术为揭示液力偶合器内部流场的复杂流动提供有效的解决途径。     

立式管道泵进水弯管和叶轮的参数化分析与验证

管道泵的肘形弯曲进口结构影响了叶轮的入流,导致管道泵内部流动特性复杂,整体性能下降。为了探究管道泵不同设计参数对内部流动的影响,该研究基于三维非定常雷诺时均Navier-Stokes方程,结合剪切应力传输模型对管道泵入流畸变特性展开了数值模拟,并进行了试验验证。同时,选取了进水弯管和叶轮的40个设计参数,使用拉丁超立方设计方法创建了300组设计样本,通过Pearson相关性分析,数值研究了进水弯管和叶轮的设计参数对管道泵效率、扬程及入流不均匀度的影响。结果表明:数值计算结果与试验结果的吻合良好,模拟方法具有较好的预测精度;进口流道内发现了伴有二次流涡对的流动分离区,且其内部流动分布不对称,在设计流量和小流量工况下,进口流道内部流动分别以反向涡对和回流旋涡为主;管道泵的性能与叶片安放角及叶片数显著相关。研究表明具有40°～50°进口安放角、20°～40°出口安放角及较大进水弯管长度的管道泵具有更好的性能和稳定性,此区间内的样本相较于原始模型效率平均提高了5%。研究结果可为管道泵的设计优化提供参考。     

离心泵快速变工况瞬态过程特性模拟

为研究离心泵在不同工况点快速切换过程中的瞬态特性,该文以一台低比转速离心泵为研究对象,对其工况流量突然减小的瞬态过程,分别采用理论分析和数值计算的方式进行了外特性预测和内流场仿真研究。首先基于叶轮机械广义欧拉方程式,对离心泵模型在流量突然减小瞬态过程中的附加理论扬程进行了定量计算与分析。结果表明,同等条件下,变工况过程结束后的稳定流量越小,附加理论扬程越大,瞬态效应愈发明显;同时该瞬态过程后期的瞬态效应比前期更为明显。动静干涉效应对泵出口流动参数产生显著影响,而对泵进口流动参数的影响并不明显;动静干涉效应对小流量工况时各个流动参数的影响将尤为显著。叶片与隔舌相对位置最近时,计算扬程最小;当隔舌位于叶轮流道中间位置稍后时,计算扬程最大。同一个转动周期(T)内,选取叶片转过隔舌后的0.225 T和0.825 T位置进行单次定常计算可取得较高精度的数值预测结果。动静过流部件和粘性效应使得叶轮和蜗壳内的轴向速度分布规律完全相反。瞬态过程中流体加速效应使得瞬态流场演化整体上滞后于准稳态流场。     

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。     

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.     

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.     

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,     

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,     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

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.