Initial Analysis on the Effect of High-low Altitude Jet Stream on Heavy Precipitation in Guangxi

By using the routine observation data,a heavy precipitation process which happened in Guangxi on May 27,2006 was analyzed.The results that this heavy precipitation occurred in the common coordination weather system which included the high-altitude trough,the shear line and the ground cold front.The ascent branch of subtropical longitude circle circulation and the polar front jet stream longitude circle circulation had the important role for the formation of rainstorm area.The coupling effect of southerly jet,low-altitude westerly jet and high-altitude westerly jet in the boundary layer was the important reason of rainstorm occurrence.

Analysis on the Forecast Characteristics of K Index and Low-altitude Jet Stream in the Rainstorm Process

By using the durative rainstorm data in South China during May-early June in 2010,the forecast characteristics of K index and low level jet were analyzed.The results found that K2 had the good indication,advancement and relativity on the intensity and falling zone forecast of regional rainstorm in future 24 h,and the positive relative coefficient reached 0.987.The low level jet also had the same advancement and indication significance on the intensity and influence scope of regional rainstorm in 24 h in the future,and the relative coefficient reached above 0.8.K2 and the low level jet were selected as the main factors,and the basic conceptual model of rainstorm falling zone was established.The model has passed the computer program and realized the business automation.K2 provided the important basis for the forecast of rainstorm intensity and falling zone.

Change of Low-level Jet in a Heavy Rainstorm Process of Xiangtan in July 2016

Based on the previous research on the model of rainstorm weather with low-level jet in Xiangtan,using the classification result of radar echo characteristics,the wind profile data provided by new generation of weather radar in Changsha and hourly rainfall data,a thorough study of the heavy rainfall from 2 to 5 July 2016 in Xiangtan was conducted. It was concluded that heavy precipitation had the characteristics of the WPSH pattern of rainstorm with low-level jet at early stage,and then it converted to cold shear jet pattern in latter stage. When low-level southwest jet began to have momentum download,that is to say,there was more than 12 m/s of southwest jet below 1 km,and it rapidly strengthened and expanded downward,it was conducive to the occurrence of short-term rainstorm. The low-level jet would not immediately cause a strong precipitation when it reached the station,with a certain lag. A positive correlation existed between the increase of low-level jet index and precipitation intensity,and low-level jet index could predict the occurrence of heavy rainfall and rain intensity.

Numerical Investigation on a Dual-jet Consisting of a Plane Wall Jet and a Parallel Offset Jet at Low-Reynolds Number

A dual-jet consisting of a wall jet and an offset jet has been numerically simulated using lattice Boltzmann method to examine the effects of jet spacing between two jet centerlines,defined as s.The Reynolds number based on jet-exit-width dis set to be Re = 56 and the jet spacing is set to be less than or equal 10 times the jet-exitwidth.Computational results reveal that the flow field displays periodic vortex shedding when the jet spacing is in the range of 9≤s/d ≤ 10,while it remains steady with two counter-rotating vortices in the converging region when s/d ≤ 8.When s/d = 9,the power spectral analyses indicate that the vortex shedding phenomenon has specific frequency.The significant oscillation stresses induced by the periodic components of velocities are found to mainly exist in the inner shear layer regions,implying stronger momentum transfer occuring in these regions.

OSCILLATION PHENOMENA IN FAR FIELD REGION OF PLANE JETS AT LOW REYNOLDS NUMBERS

Oscillation phenomena in far field region of plane jets are studied by lattice Boltzmann method over a range of Reynolds numbers （Re） from 16 to 65. Numerical results show that the instantaneous centerline velocities show periodic oscillation behavior in far field region when Re〉38. In contrast, the periodic behavior is invisible in corresponding flow field when Re≤38. For the cases of Re≤38, the exchange of momentum due to straining mo- tion gradually dominates the downstream flow filed, which qualitatively suggests the possibility of iet instability.

ENERGETIC DIAGNOSIS FOR TWO KINDS OF LOW LEVEL JETS

On the basis of the budget equations for KR and KD, this paper presents the horizontal pattern of budget terms for two kinds of low level jets (LLJ ) with and without heavy rain. The results show that the mechanisms for generating and maintaining LLJ are different, and especially, the direction of energy conversion is opposite. A positive conversion from KD to KR appears to be a necessary but not sufficient condition in the lower troposphere near the heavy rain area. The intensity and direction of energy conversion depends not only on the relative position of vorticity and divergence field, but also on the vertical profile of the jets directly.

STATISTICAL ANALYSIS OF LOW-LEVEL JET STREAMS IN NANJING AREA BASED ON WIND PROFILER DATA

In order to understand the activity characteristics of low-level jets in the Nanjing area,statistical analysis and comparative study are carried out on their monthly and diurnal variations,characteristics of their cores and accompanying weather conditions using wind profile data in 2005-2008 collected by two wind profilers.The results show that low-level jets have significant monthly and diurnal variations.They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night,with the maximum wind speed usually occurring at midnight.The central part of the low-level jet occurs mainly at the height of less than 1400 meters,and the enhancement of central speed is beneficial to the appearance of precipitation.Meanwhile,when the low-level jet appears in summer,it helps cause heavy rain.The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler.Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

高、低空急流耦合对山东“利奇马”台风暴雨增幅影响的诊断研究

受登陆北上台风“利奇马”等影响,2019年8月9~12日山东省出现连续暴雨,其中10日夜间出现降雨峰值。利用中国气象局上海台风研究所(Shanghai Typhoon Institute of China Meteorological Administration,简称CMA-STI)热带气旋最佳路径数据、山东省自动气象站逐时降雨量、常规观测资料、中国风云二号地球静止气象卫星(FY-2G)0.1°×0.1°逐小时云顶相当黑体亮温和美国环境预报中心(National Center of Environmental Prediction,简称NCEP)1°×1°逐6 h再分析等资料,主要运用纬向风局地变化方程与大气动能方程,诊断分析降雨明显增幅与高、低层风场变化的关系。结果表明:(1)暴雨主要影响系统有高低空急流、500 hPa西风槽、850 hPa台风倒槽及“利奇马”本体环流等。10日200 hPa中纬度大尺度西南风急流东南移影响鲁西北,当天08:00(北京时,下同)850 hPa因双台风活动而形成的大尺度东南风急流突然北伸越过山东省。台风倒槽对流云与本体环流对流云先、后北移经鲁中,累积效应造成该地区10日夜间雨量最大。(2)10日20:00850 hPa章丘站东北侧出现了过程最快东风增幅,纬向运动方程诊断结果表明,东风平流是东风增加最主要原因,地转偏向力项则不利于东风增加。(3)10日20:00章丘站200 hPa西南风风力明显加大形成急流,10日08:00至11日08:00青岛站850 hPa维持东南风低空急流。同时位于高空急流右后侧与低空急流左前方是鲁中附近10日夜间降雨增幅的重要原因。章丘200 hPa与青岛850 hPa都是在最大风力之前12 h动能增加最快。动能方程诊断表明,最有利于鲁西北高空急流形成的是位能平流项,最有利于鲁东南低空急流形成的是动能垂直通量散度项。(4)10日20:00至13日08:00“利奇马”本体环流一直在影响山东,暴雨期间山东中部地形的动力作用也一直存在,而降雨的峰值是出现在10日夜间,说明10日20:00前后高、低空急流的耦合可能是山东暴雨增幅的主要影响因子。其主要作用至少有加强山东中部的垂直运动、整层水汽输送与静力不稳定度等方面。

毫米级低速圆管自由射流的空中形态分析

自由射流是各类机械设备和管路设施中的常见现象,对毫米级圆管低速射流空中形态的研究,可以为射流距离、水流入水姿态和相应消能及噪声的分析提供依据。为探索毫米级圆管低速射流空中形态,分别以4,5,6 mm圆管射流为对象,研究不同低速、圆管直径对射流连续及破碎的影响。采用高速摄像机捕捉射流碎破点和破碎水滴变化,测量并分析流速、连续长度和破碎水滴直径的特征以及与无量纲雷诺数Re和韦伯数We的关系。结果表明:在管径相同时,射流连续长度随出口流速的增大而增长;随着管径变大,连续长度增加的幅度变小;在流速相同时,连续长度随着喷嘴内径增大而减小。射流连续长度随雷诺数Re、韦伯数We的增大而减小,在We=3 000~3 500附近由曲线关系变为直线关系,拟合出射流连续长度与We的关系式。具体描述破碎水滴的聚合过程,分析破碎后的主水滴与卫星水滴的大小、聚合方式及振动特点,其中,水滴大小与喷嘴内径存在线性关系,均随着喷嘴内径的增加而增大,卫星水滴的大小基本符合Rayleigh线性不稳定理论预测产生液滴尺寸,不同的聚合方式会导致射流掺气量的不同,为不同条件下的水流入水姿态及相应消能与降噪提供参考,并得到水滴平均振动周期为25.67 ms。

Design and Numerical Simulation of Low-Fiber Hollow Spindle in Air-Jet Vortex Spinning

Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is simulated numerically. The negative pressure effect is much bigger at the top of low-fiber hollow spindle than that in Murata No.861,which is more conducive for single fiber to get into the channel of hollow spindle. The tangential velocity in 0-3 mm at the top of hollow spindle increases and the fluctuation of radial velocity is much stronger,which enhance the wrapping effect. In the addition,the distribution of axial velocity remains the same.

东南风低空急流影响“21·7”郑州市极端暴雨分析

利用中国气象局上海台风研究所热带气旋(Tropical Cyclone,TC)最佳路径数据、美国环境预报中心(National Center of Environmental Prediction,NCEP)最终分析格点资料(Final Analysis,FNL)及常规观测数据等,分析了2021年7月郑州极端暴雨过程的特征机理。结果表明:(1)两个TC同时远距离输送大量水汽,东南风低空急流与强降水关系密切。当东南风急流北上到太原、邢台等站后郑州市暴雨减弱。郑州市6 h降水超过62.5 mm站点数目增减与850 hPa地转偏差数值变化趋势一致。(2) 20日白天郑州站极端降水发生前,从850 hPa经500 hPa至200 hPa风向从东南风顺转为西南风。200 hPa与850 hPa水平风的垂直切变(Vertical Wind Shear,VWS)从最大值开始减小、可降水量(Precipitable Water Vapor,PWV)明显加大、不稳定程度减小,这些都是极端暴雨发生的有利条件。极端暴雨具有明显的湿对流特点。(3)纬、经向风变率诊断表明,最有利于郑州市850 hPa东风维持的因子是地转偏差,最有利于南风加大的因子是动量平流。动量对流促使郑州市暴雨过程850 hPa南风减小,故动量上、下传递并非850 hPa南风加大原因。

基于气泡雾化喷嘴的低能耗含油污水处理实验研究

微气泡气浮技术在低能耗下对含油污水的高效处理是目前的研究热点。利用气泡雾化喷嘴作为微气泡发生器,搭建了低能耗微气泡射流气浮处理含油污水的实验系统,系统研究了气液质量流量比(ALR)和工作压力(p)对微气泡群尺度分布特征和除油效果的影响,并计算了气泡雾化喷嘴的能耗。实验结果表明,利用气泡雾化喷嘴形成液下射流可以产生大量微气泡,其中尺度小于150μm的气泡数量占比在55%以上、小于600μm的气泡数量占比在98%以上;随着ALR的增加,微气泡数量整体呈现先增后减的变化趋势,最佳ALR=0.15;当p=0.2 MPa、ALR=0.15时,微气泡群的索特尔平均直径可降低至238μm,出水含油质量浓度为29.73 mg/L,微气泡射流气浮装置处理1 kg含油污水时能耗仅为6.53×10^(-4) kW·h,较溶气气浮能耗降低35%以上。

2022年“2.13”冀中大雪过程多源气象资料分析

利用常规观测资料、era5再分析资料、风廓线雷达产品、地基GPS/MET大气可降水量(precipitable water vapor,PWV)等,对2022年2月13日冀中大雪过程进行了详细分析。①降雪发生之前的36 h内PWV呈增长态势,0~12 h上升最快,12~36 h呈缓慢上升趋势。②降水量和PWV呈一定正相关关系,降雪期间PWV变化平稳,随着PWV出现连续下降,降水结束。③风廓线雷达的水平风向风速演变对降雪的预报有一定指示意义:3000 m突然出现20 m/s的西南低空急流,随着20 m/s的西南低空急流向下延伸至2500 m高度,降雪增强。④降雪之前,0.5 m/s及以上的正速度首先出现在1500 m以上,当2000 m以下突然出现1.0 m/s以上的正速度后,0~3 h内降雪发生。⑤1000 m以下垂直速度增加到1.5 m/s及以上时,降雪增强。⑥降雪期间C_(n)^(2)(大气折射率结构常数)一直稳定在-180~-165 dB,C_(n)^(2)值小于-180 dB时,最大探测高度降至3500 m以下,整层垂直速度小于0.5 m/s,预示降雪结束。

凹坑下城镇中低压燃气管道水平喷射火研究

城镇埋地中低压燃气管道周围人口密集,一旦发生全管径破裂,凹坑条件将加剧水平喷射火行为的复杂及危险性.利用Fluent模拟分析了不同凹坑尺寸及管压下火焰长度、等效宽度及长宽比变化规律,得到了火焰长度及等效宽度与无量纲热释放速率关系式.结果表明:火焰长度随着热释放速率增加与凹坑尺寸减小而增大,坑口尺寸较小时,火焰长度大于开放空间;坑口尺寸增大到一定程度时,火焰长度小于开放空间火焰长度.等效宽度随热释放速率的增大而增大,且当等效宽度增长到凹坑开口尺寸后,增长速率变缓并趋于稳定,同时火焰长度有明显增长.火焰长宽比呈现先减小后增大趋势,随着凹坑尺寸增大,长宽比减小且均小于开放空间.

MILD粉体燃烧技术研究进展与关键问题分析

MILD燃烧是一种在中度或极度低氧环境下发生的温和燃烧模式,兼具高燃烧热利用率和极低NOx排放的优势,国际燃烧领域认为它是拥有巨大应用潜力的清洁燃烧技术之一。自1990年左右开展相关研究以来,对于实现气体燃料的MILD燃烧的相关技术已相对成熟,而关于煤粉和生物质等固体燃料的MILD燃烧机制和实现条件的研究仍相对缺乏。基于高动量氧化剂射流来实现内部再循环,不再需要外部高温预热来建立MILD燃烧,极大拓宽了MILD燃烧的应用范围。从颗粒弥散、受热、着火、燃烧、污染物等方面概述了MILD粉体燃料燃烧的基础特性,由于颗粒的不均匀弥散和反应,煤粉等碳基固体燃料的MILD燃烧进程较气体燃料更复杂。高速射流MILD燃烧在增加点火延迟的同时也扩展了点火区和反应区,需要对燃烧各阶段的特征和机理开展系统研究。介绍了固体燃料MILD燃烧理论设计和装备研发领域所取得的研究成果,建议通过高精度数值模拟,改进现有燃煤锅炉燃烧器、调节工艺参数以匹配MILD燃烧模式,增加焦炭颗粒的停留时间以提高燃烬率,提高燃烧稳定性并抑制包括细颗粒物在内的各类污染物排放。基于互联能源系统的整体方法,推进MILD燃烧与各类新型燃烧技术的耦合研究,尤其加强煤粉、生物质与氢、氨等可燃气体共燃特性研究,助力能源转型。探究粉体MILD燃烧中的湍流两相流特征、湍流相间传热作用以及湍流-化学耦合作用是加深对粉体MILD燃烧理解的关键,涉及多变量分析和高精度模拟,是未来研究的重点和难点。

逆向喷流对可回收火箭气动特性的影响研究

可回收火箭返回时,需要依靠发动机进行点火减速制动,为得到逆向喷流条件下箭体气动性能的变化规律,通过对低空和高空两次点火过程进行数值仿真,分析来流马赫数和攻角对箭体气动性能的影响,同时开展单喷管、多喷管喷流条件下的仿真研究。结果表明,低空状态,逆向喷流会导致全箭轴向力系数绝对值减小,且喷流数目越多,轴向力系数绝对值越小。小攻角条件下,逆向喷流会引起全箭压心大幅前移,随着开机台数增加,压心前移越多。高空条件下,喷流膨胀区和来流存在强烈的相互干扰,导致轴向力系数减小明显,其绝对值在0.04以内,0°~10°攻角内箭体法向力系数绝对值小于0.1,随着来流静压增加,法向力系数绝对值小于0.1的攻角区间减小。

愈创木酚与环戊醇烷基化-加氢脱氧制备高密度低冰点生物航油

以木质纤维素为原料合成高密度低冰点生物航油,可以实现绿色低碳发展。报道了一种以木质素衍生物愈创木酚和半纤维素衍生物环戊醇为原料,经过烷基化和加氢脱氧制备高密度低冰点燃料的工艺路线。筛选出硅铝比为100的USY分子筛作为烷基化反应的催化剂,在优化工况下愈创木酚的转化率可达到97.7%,双环和三环产物的总产率为93.9%。筛选出HZSM-5和Pt/C的组合催化剂催化烷基化产物加氢脱氧,在260℃反应12h,可以实现烷基化产物96.4%的转化率,双环烷烃的产率为27.7%,三环烷烃的产率为63.8%。加氢脱氧终产物的密度为0.89 g/mL,冰点低于-65℃。该研究为木质纤维素衍生物合成高性能喷气燃料提供了一种简单高效的方法。

TCP+MFE+JET三联作测试工艺技术研究与应用

针对低压、低渗非自喷油层求取油层产能、压力、收集有代表性产液样品资料难的问题,研究开发了TCP+MFE+JET三联作测试工艺管柱。经现场应用表明,该工艺不仅解决了上述问题,而且缩短了油气井测试周期,降低了试油成本。

台风“暹芭”(2203)残涡陆上维持并引发大范围降水过程的成因

利用中国气象局上海台风研究所最佳路径数据、 FNL 0.25°×0.25°再分析资料和NOAA 0.5°×0.5°全球日降水数据分析了登陆台风“暹芭”残涡长时间维持并且产生大范围降水的成因。结果表明,第一阶段(2022年7月3-4日)“暹芭”残涡维持的主要水汽来源是偏南风低空急流,第二阶段(2022年7月5-6日)主要是偏南风低空急流和边界层东风急流共同作用,这使得大气可降水量达到罕见的75 mm。双低空急流的耦合形成的垂直风切变和水汽辐合为暴雨的发生和维持提供了良好的动力条件。冷空气开始入侵“暹芭”残涡后,在其西侧近地面形成冷池,这使得“暹芭”残涡逐渐变性为温带气旋,斜压动能发生显著增长。利用位势散度诊断发现,由于“暹芭”残涡不断北上接近副热带高空西风急流增大了高低层垂直风切变,高空冷涡携带的冷空气侵入“暹芭”残涡使其斜压性增大,边界层东风急流使得850hPa以下层结不稳定度显著增大,这为暴雨的发生和维持提供了不稳定能量条件。