燃烧加热污染空气对超燃冲压发动机性能影响研究

针对燃烧加热地面试验设备存在的工质污染问题,采用数值模拟方法研究了燃烧加热污染空气对氢燃料超燃冲压发动机性能的影响。以飞行马赫数Ma=6.5,当量油气比ER=0.6为计算基准状态,分别对纯净空气和污染空气来流下氢燃料超燃冲压发动机的整机流场和性能进行了对比计算分析。燃烧化学反应模拟采用了改进的H₂/O₂七组分八方程模型,湍流模型为标准的 k-ε模型,并采用直连式燃烧室试验数据进行了数值方法的验证。研究结果表明:(1)相对于纯净空气来流,污染空气来流下的超燃冲压发动机推力和比冲均有所下降。(2)采用酒精燃烧加热器的前提下,来流参数匹配静温、静压、马赫数时,发动机性能与纯净空气来流下的结果最为接近,而匹配总温、总压、马赫数时相差最大。(3)来流参数匹配总焓、静压、马赫数的前提下,采用氢燃烧加热器时发动机性能与纯净空气来流下的结果最为接近,而采用甲烷燃烧加热器时相差最大。      

高超声速风洞进气道流量系数测量精度影响因素研究

进气道是飞行器动力装置的重要组成部分,准确测量进气道流量系数是进气道风洞试验的重要内容。对来流马赫数Ma=4.5,5.0和6.0状态下皮托管进气道开展流量系数测量研究,通过对比理论值和实测值,获取各状态流量系数修正系数。试验结果表明,随着来流马赫数增加,进气道流量系数与理论值偏差较明显,并逐渐增大。超声速风洞试验通常认为测量截面总温与来流总温相等,通过对测量截面总温与来流总温偏差以及测量截面流场畸变情况的分析,判断测量偏差主要是由测量截面总温等于来流总温的假设导致的。在高超声速风洞试验中,由于模型壁面热交换的存在,测量截面总温低于来流总温,进气道流量系数测量时需要进行总温修正,以提高流量测量精度。      

弯度对风力机翼型气动噪声特性的影响

指出了陆上风电装机向着低风速区和分散式发展,风力机距离居民区越来越近,风力机的噪声问题日趋严重,需要在风力机的设计阶段对气动噪声进行研究与控制。翼型是风力机叶片的基本元素,是风力机功率及噪声性能的基石。弯度对翼型的气动性能有显著影响,因而也必然影响气动噪声源。选取NACA系列翼型作为研究对象,翼型的最大厚度及最大厚度的弦向位置、最大弯度的弦向位置相同,而最大弯度不同。采用经典的翼型分析软件XFOIL计算了上述翼型的升阻力系数、半经验模型计算气动噪声源水平,以研究最大相对弯度对气动和噪声性能的影响。结果表明:在小攻角范围内,翼型的升力系数、升阻比随着最大相对弯度的增加而增加,大攻角时升阻比随着最大弯度的增大而减小。翼型最大弯度增加会使得压力面尾缘噪声在低频段内减小;在整个频率段内,边界层分离噪声随着最大弯度的增加向低频区移动。     

常温下树种及厚度对胶合板吸声性能影响的研究

采用驻波管法对胶合板的吸声性能进行研究,通过对泡桐、杨木、桦木、桉木以及竹胶合板的吸声系数进行测量,探了树种、厚度对胶合板吸声系数的影响。实验结果表明：胶合板成板树种、胶合板厚度对材料的声学性能影响显著,随着厚度的增加其吸声系数有所改善,在一定范围内,树种对胶合板吸声系数影响显著。     

壁面马赫数分布规律可控的新型内收缩基准流场设计方法

根据有旋特征线理论,设计出了沿程马赫数下降规律可控的轴对称基准流场,分析了基准流场的几何参数(前缘压缩角及中心体半径)的影响规律,发现选取较小的前缘压缩角和中心体半径有利于得到性能优良的基准流场；然后在设计状态Ma=6时研究了三种典型的马赫数下降规律对这种轴对称流场性能的影响。最后考虑了粘性的影响,并进行了粘性修正探索,结果表明,采用附面层位移厚度修正方法后,基准流场的壁面压力分布和无粘情况吻合良好。      

山东省2012年航空护林航线规划探析

航空护林航线是飞机在执行森林消防作业任务时所飞行的空中路线。航线要依据区域森林资源分布情况和执行飞行巡护任务的飞机性能科学规划,确保飞机在巡护时最大限度的将重点林区、重点火险区以及自然保护区等涵盖在内。2012年,山东省首次在全省范围内进行了航空护林消防作业,并根     

浅谈通用汽油机排气系统降低成本的一种方法

通过对通用汽油机排气系统进行分析,在不影响其排放性能的前提下,通过合理的改变排气系统的内部结构,可有效地降低通用发动机的生产成本,并在实践中得到了验证。     

汽车车轮的防抱死装置

汽车的制动性是汽车的主要性能之一。汽车车轮安装防抱死装置就是为使制动性能更完善,行驶更为安全所采用的一项新措施。一、设置防抱死装置的理论基础如图1所示,目前一般汽车前后轮制动力比值有固定关系的β曲线及理想制动力矩曲线。图中 Fu_1、Fu_2—前后车轮的制动器制动力,(?)—附着系数;(?)_o—同步附着系数;β线—制动器制动力分配系数线,一般两轴汽车的前后制动器制动力之比为一固定值。β=Fu_1/Fu_1;Fu—汽车总制动器制动力;Ⅰ曲线—满载汽车理想的前后     

不同混合式吸附剂导热性能实验研究

通过将吸附剂活性炭与多种金属以不同的比例混合,配置成混合式吸附剂,并分别测试了其导热系数,试图发现一种合适的金属及比例,使其既能提高吸附剂的传热性能而又不严重影响吸附剂的传质性能。结果表明:随着活性炭与金属混合比例增加,各混合式吸附剂导热系数随之增大,并且在混合比例为10:8时达到最大值;对于3种混合式吸附剂(活性炭-铁屑、活性炭-铝屑、活性炭-铜屑),活性炭-铝屑混合式吸附剂在比例为10:3便达到很高的值,此后随着比例增加,导热系数变化不大,而另外两种混合式吸附剂随着比例增加导热系数均变化很大。     

新型木丝板吸声性能的试验分析

采用驻波管法测量木丝板的吸声系数,分析板材厚度、密度、后背空腔深度、组合方式等因素对木丝板吸声性能的影响。结果表明:木丝板的吸声性能符合多孔材料吸声机理;在0~2 000Hz的声频范围内,木丝板的吸声性能随着声波频率和板材密度的增大而提高,增加背面空腔深度能够提高材料的吸声系数;厚度10mm、密度0.50g/cm3木丝板的吸音效果较理想,不同密度的木丝板组合使用,亦可提高其吸声性能。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Natural Regeneration in Clear-cuts: Effects of Scarification,Slash Removal and Clear-cut Age

The effects of soil scarification (mounding), slash removal and clear-cut age on the natural regeneration in clear-cuts was evaluated using data from four sites in southern Sweden. The treatments were carried out during a good seed and establishment year for birch ( Betula pubescens Ehrh. and B. pendula Roth). Scarification had the strongest positive effect on the density of naturally regenerated seedlings, especially in birch, but also in pine ( Pinus sylvestris L.) and spruce [ Picea abies (L.) Karst]. Slash removal had a positive effect on birch density. No statistically significant effect of clear-cut age was found. In addition, no statistically significant interactions between clear-cut age and scarification or slash removal were found. The ingrowth of field vegetation was the fastest in areas that were not scarified, less rapid in areas scarified on old clear-cuts, and the slowest after scarification in fresh clear-cuts. In conclusion, it may be possible to control the density of birch during a good establishment year for birch. If birch is desired, the best combination of treatments is to remove the slash and scarify; otherwise, these treatments should be avoided.     

Risk Perception Among Non-industrial Private Forest Owners

Based on an enquiry, risk perception among non-industrial private forest owners is described in relation to climate change and forestry hazards. Of the respondents, 11% took action to remedy the effects of climate change. Out of a given set, hazards were ranked according to each respondent's experience of recent substantial financial loss to the estate and in relation to his or her willingness to make investments aimed at risk reduction. For each hazard, the respondent assessed the risk in four classes ranging from very high to negligible risk. Six hazards were considered most problematic in all three aspects: browsing damage, falling timber prices, damage by wind, spruce bark beetle, root rot and pine weevil. A majority of the respondents claimed to take action to reduce the risk associated with at least one hazard, while 35% did not know whether they did. Excluding climate change, the need for decision support was the largest in relation to damage by wind owing to a combination of perceived high risk and a high level of ignorance in relation to whether risk-reducing measures were taken.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Pasture production and tree growth in a young pine plantation fertilized with inorganic fertilizers and milk sewage in northwestern Spain

The use of organic waste materials such as milk sewage as an organic fertilizer could have the dual advantages of organic-waste disposal and reduced dependence on inorganic fertilizers. The effects of fertilization with (1) conventional mineral fertilization, (2) milk sewage sludge at 40 kg N ha⁻¹ target rate and (3) no fertilization on pasture production and tree growth were examined in an experiment consisting of two pasture mixtures under a one-year-old Pinus radiata plantation with a density of 2500 trees ha⁻¹. The two pasture mixtures were: (1) Dactylis glomerata L. var. saborto (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹); (2) Lolium perenne L. var. Tove (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹). The experiment began in the spring of 1995 using a randomized block design with three replicates in Castro Riberas de Lea (Lugo, Galicia, north-western Spain). Plot size was 12 × 8 m², with a 1 m buffer strip between plots. Two-year data showed that fertilization with either material had a positive effect on pasture production, with no significant difference between the two fertilization treatments. Tree growth in the milk sewage sludge plot was significantly higher than in the control plots. Inorganic fertilization increased pasture production, but affected tree growth negatively. The results show that milk sewage sludge could be used as a fertilizer in silvo-pastoral systems. This revised version was published online in June 2006 with corrections to the Cover Date.