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。      

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。      

风廓线仪在中尺度试验中的应用

1985年5—6月期间,在堪萨斯和俄克拉何马中心进行了一次研究中尺度对流系统(MCSs)的试验,在试验过程中使用了许多大气科学领域内最新的测量技术。其中有3台50 MHz风廓线仪。通过初夏发生在美国高原上强对流环境下的两次飑线系统描述了廓线仪的性能。6月10—11日的飑线比较强烈和有组织;6月26—27日的飑线系统不太紧密。对于较强的天气,在飑线经过的前后时期,两个廓线仪都提供了很好的时间-高度范围内的水平风,但是当强对流线正在当地上空时不能很好地观测。相比之下,诺曼的廓线仪较好地提供了整个弱系统持续时间内的水平风资料,虽然有几个与廓线仪性能无关的数据失测。由风廓线及无线电测风资料证明两个飑线系统的中尺度结构相同。例如,在飑线后中层后部人流下有强烈的逆转风廓线,在飑线前面低层为顺转风廓线。在两个飑线系统的层状云区廓线仪比无线电探空测风仪探测的范围更完全些。但一个重要的问题是,50MHz廓线仪无法探测到地面以上1.5到2.0km的风。     

712天气雷达故障排除一例

当712天气雷达天线方位转到270°时,天线会发生瞬时的俯仰震动,有时甚至很剧烈,观察高度显示器及俯仰度盘,其扫描线及俯仰指示度盘均有严重抖动。 对这种现象判断的结果是:俯仰“放大指示”氖灯亮,这是俯控系统存在较大误差的信号,而此系统     

701C测风二次雷达的故障检修一例

1　故障现象电源分系统Ｄ1和天控分系统Ｋ1上的电源接通后 ,不用摇动手轮 ,天线仰角即可缓缓驱动 ,俯仰角度显示值逐渐变小 ,测速机和天线系统连续发出驱动时特有的轰鸣声。2　检查与分析2 .1　摇动俯仰手轮 ,天线照常驱动 ,手轮摇得快 ,电机转得快 ,反之则慢 ,手轮正摇 ,电机正转 ,角度显示增大 ,反之则角度减小。等电机停下来不摇时 ,又恢复到故障现象。2 .2　天控分系统从手控切转到外控 ,不让外控盒驱动天线 ,测速机和天线系统会间断发出轰鸣声 ,俯仰角度间断变化。2 .3　当天线仰角降到下限位时 ,角度不再变化 ,轰鸣声也即消失。从以上…     

大规模风电场建成后对风能资源影响的研究

考虑了千万千瓦级风电基地建成后风电机群对近地面层风速的影响,采用Frandsen研究了大规模风电场内部风速损失时所使用的方法,在内边界层已经充分发展成新边界层的区域内,对轮毂高度65m处风速Uh进行了计算。结果表明,风电场建成后研究区内,风速Uh与未建场时的65m风速U0相比变小,存在风速损失,该风速损失随着U0的增大而减小,与风电机的推力系数CT性质有关;大规模风电场建成后,Uh在3～20m.s-1范围内的平均风功率密度与未建场时U0在此范围内的平均风功率密度相比损失约为58.45%,这与建场地区建场前65m处风速值大小以及各风速值出现的概率有关。     

“2.23”昆明长水机场低空风切变分析及可预报时效估计

随着航空事业的发展,飞机性能得到提高,但低空风切变仍然对航空安全构成威胁,为了解其发展规律,就昆明长水机场2017年2月23日发生的四次低空风切变进行了特征分析,揭示了风切变产生的水平及垂直风场的调整过程。分析发现,昆明机场特殊的地理位置造成冷锋推进速度缓慢;冷锋过境时,跑道两端出现风向和风速的不连续,造成跑道两端风向和风速均无法满足运行标准,导致跑道关闭;冷锋过境后,在跑道上60m决断高度附近形成水平风的垂直风切变,造成飞机复飞,对飞行安全造成较大影响。跑道道面上的风切变空间尺度小、存在时间长、而且风切变发生高度较低,并随时间变化,结合自动观测系统及风廓线雷达能更好的了解冷锋型风切变的特征,可以为航空飞行安全提供更精细化的服务。      

基于多套再分析数据的全球山脉力矩计算及比较分析

山脉力矩是地球与大气角动量交换的重要途径之一,为了深刻地理解全球的大气环流变化,比较了NCEP再分析数据、欧洲中心中尺度天气预报的ECMWF再分析数据和NASA的MERRA再分析数据计算的1979-2012年的全球山脉力矩的时、空分布及其年际变化。研究发现三套数据计算的山脉力矩空间分布基本一致,均显示北半球的青藏高原、落基山脉以及南半球的安第斯山脉是对全球山脉力矩贡献最大的三个区域。NCEP再分析数据计算的山脉力矩空间差异和多年变化标准差明显高于其他两套数据,其在纬向上的积分廓线与其他两套数据也差异较大,但是全球积分以后其平均值与标准差与其他两套数据基本一致,而且其在欧亚、南美和北美区域的积分与其他两套数据也没有明显差别,因此,NCEP再分析数据适用于大尺度的山脉力矩模拟。在研究空间尺度较小的山脉力矩变化时,建议优先考虑ECMWF和MERRA再分析数据。三套数据对北美地区山脉力矩计算的一致性较高,其次是欧亚地区,对南美区域山脉力矩计算的一致性则较差,表明北美地区气象数据质量要高于亚洲,南美洲气象数据质量较差。欧亚地球山脉力矩与大西洋-欧洲环流有很强的相关,北美山脉力矩与太平洋区极涡面积关系密切。      

乌鲁木齐地区飞机积冰综合分析

积冰是影响飞机安全航行的重要天气现象之一.在航行中,飞机如遇到积冰,能使飞机的空气动力学性能变差,阻力增大,升力减小,仪表失灵,通讯中断,甚至导致机毁人亡的恶性事故.例如:1986年12月15日,一架安-24,3413号飞机,执行兰州-西安的航班任务时,在3600m高空遇到严重积冰.由于发动机进气口严重积冰,引起进气道气流不畅,使气压机工作不稳定,从而导致发动机喘振、右发停车.飞机速度由338km/h,降到195km/h,飞机高度从3675m,掉到2450m.飞机被迫返航中川,降落阶段,又在积冰单发飞行的情况下进行复飞,结果在中川机场跑道头延长线1345m处,撞断15棵树和一根电线杆后触地失火,造成机上6名乘客不幸身亡.     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on