测雨雷达反演雨滴谱剔除垂直气流方法的研究

在测雨多普勒雷达反演雨滴谱中,垂直气流对反演结果影响较大(下沉气流大于1m/s时,直径误差超过40%)。用平均末速度法估计垂直气流速度,反演雨滴谱。与地面雨滴谱对比观测表明,消除垂直气流影响后测雨雷达反演的雨滴谱分布更加合理,和地面雨滴谱仪的一致性更好,平均相对偏差减小8%以上;从通过雨滴谱计算的雨强分析,大雨强时偏差减小得更明显,平均达到25%。说明这种方法在测雨雷达反演雨滴谱中具有重要参考价值。

卧式垂直气流分子筛吸附器内的流场分析

建立了以多孔管为气流分布器的卧式垂直气流分子筛吸附器结构的数学模型,并采用FLUENT软件对其内部速度场分布进行了数值计算分析。计算结果显示,进出口的计算压降值与实际运行监测情况相接近,分子筛床层的气流分布较均匀,该结构弥补了传统卧式吸附器气流分配不均匀的缺点。与以缓冲板为气流分布器的结构进行比较后发现,多孔管结构还能较好地解决吸附器壁面上容易产生边流现象的问题。

垂直气流电除尘深度提效技术研究

常规电除尘存在细颗粒粉尘难荷电、反电晕、二次扬尘等技术难题,限制了除尘效率的进一步提升。针对电除尘深度提效技术进行了研究,提出进口烟箱预收尘—电场尾部二维收尘—出口烟箱防逃逸电除尘深度提效工艺,研制了垂直气流方向的“W”形和梯形网状收尘装置,显著增大了电除尘收尘面积,解决了二次扬尘问题。垂直气流电除尘深度提效技术在630 MW燃煤机组工程应用结果表明:在保持电除尘外形尺寸、电场数量不变的情况下,出口烟尘浓度可控制在10 mg/m^(3)以下;电除尘出口烟尘浓度由改造前的14.4 mg/m^(3)降至6.5 mg/m^(3),提效幅度高达54.9%,与低低温电除尘技术提效幅度相当,可实现烟尘超低排放。

夏季索马里越赤道气流垂直结构的年代际变化

基于1950—2010年美国国家环境预报中心/国家大气研究中心(NCEP/NCAR)再分析月平均资料、哈得来中心月平均海温资料,定义夏季索马里越赤道气流(简称SMJ)垂直结构指数VS_1和VS_2,分别表征索马里越赤道气流全区一致、上下反相两种分布型。接着利用合成分析、奇异值分解方法探讨夏季索马里越赤道气流垂直结构的年代际变化,寻找可能影响其变化的环流因子和海温信号,并进一步分析垂直结构与亚洲夏季风活动的年代际关系,主要结论如下:(1)两个指数在年代际尺度上的阶段性变化特征十分显著,VS_1在20世纪80年代中期发生由负转正的年代际变化;VS_2在70年代初和90年代中期分别发生由负转正、由正转负的年代际变化。(2)合成分析表明,VS_1和VS_2的年代际变化与同期大气环流联系紧密,南极涛动可能是影响VS_1年代际变化的一个重要因子。(3)印度洋海温变化可能对夏季索马里越赤道气流两类垂直结构的年代际变化起调控指示作用。VS_1的年代际变化与夏季全印度洋海温增暖的趋势是一致的,VS_2与夏季南印度洋偶极型振荡事件关系显著。(4)高VS_1年代里,印度半岛至中南半岛夏季风偏弱,纬向水汽供应减少,降水偏少,东亚夏季风亦偏弱,使得华北地区纬向和经向水汽输送均偏弱,同时水汽辐合减弱,华北地区偏旱,而在江南地区由于水汽辐合,降水偏多;反之亦然。高VS_2年代,东亚季风区内中国西南、华南地区夏季风减弱,使得经向和纬向水汽输送均偏弱,水汽供应减少,因此华南、西南地区偏旱,日本地区夏季风偏弱,西风水汽输送亦偏弱,降水亦偏少,反之亦然。

六盘山区地面碘化银发生器催化作业条件分析

利用数值模式模拟的1 km×1 km六盘山区2009年6月至2010年5月的垂直速度资料、宁夏173个加密自动气象站数据、云高观测资料等开展了六盘山区碘化银发生器催化作业条件研究。结果表明:有降水过程时,六盘山区2.0 km、2.5 km、3.0 km、3.5 km高度层均有明显上升气流;地面发生器释放的碘化银催化剂的有效扩散高度可达3000 m;降雪开始前6 h至降雪开始后12 h内,发生器作业点有明显上升气流,80%以上时间内上升气流速度分钟平均值大于0.3 m·s~(-1)。结合六盘山区云底、0℃层等特征层高度,综合分析得出了六盘山东西两侧及六盘山顶一年中不同时期开展碘化银发生器催化作业的适宜程度。

1.55μm激光雷达高原机场下击暴流探测应用研究

为了探究激光雷达在湿下击暴流天气时的风场探测效果和低空风切变识别能力,采用多元资料结合具体事件进行理论分析和数据验证的方法,利用西宁曹家堡国际机场的测风激光雷达数据,结合地面观测记录,对2021-05-18的一次湿下击暴流过程进行了分析和研究。结果表明,下击暴流具有复杂的风场结构,主体到达机场前,首先造成了超过14 m/s的外流,并与环境风耦合形成逆风切变辐合线,且最强外流区位于辐合线后侧1 km~2 km;下击暴流抵达跑道上空时,造成了地面辐散风场,辐散中心风速远小于外流边缘且垂直气流存在着剧烈变化,下击暴流共持续约10 min;测风激光雷达对雷暴云内部垂直气流分布、跑道区域下击暴流辐散风场的水平和垂直结构以及地面风场辐合线的形成和演变均有良好的识别效果,交互使用雷达不同探测模式和数据产品有利于机场低空风切变的监测和预警。该研究为激光雷达在下击暴流风切变预报和研究中的应用提供了参考。

垂直射流混合的三维湍流数值模拟

采用三维ＳＩＭＰＬＥ程序和ｋ－ε双方程湍流模型对三维受限垂直射流进行数值模拟，研究了不同的几何变量和流动参数对射流穿透和混合的影响。模拟结果表明，三维垂直射流最显著的流动特征是形成了流向旋涡。射流与来流的混合程度取决于旋涡的位置、作用范围和强弱。单股射流随动量比、旋涡强度和尺度的增加，混合增强。对于单排多股射流，喷孔间距直接影响旋涡涡心位置。密排射流，旋涡过于靠近下壁面，旋涡无法影响上面来流；但喷孔排列也不能过于稀疏，否则涡对靠的太近，旋涡对侧面影响不大。Ｓ／Ｈ和动量比不变，改变孔径Ｄ对射流穿透几乎无影响。这一重要结论说明Ｓ／Ｈ和Ｊ是决定多股受限射流穿透深度的最重要的量。

燃煤火力发电厂电除尘器超低排放技术改造路线研究

燃煤火力发电厂电除尘器提效改造,应回归于除尘本质,以多依奇公式及相关理论为根本,在最大限度增加收尘面积的同时,创造多依奇公式之所以成立的假设条件,为电除尘器找到一条行之有效的技术改造路线。高效电除尘器需要具备必要的收尘面积、粉尘充分荷电(正负电荷粉尘被充分吸附)、有效清灰及科学的振打制度、二次扬尘抑制4个条件有机结合缺一不可。污染废气除尘的实质是实现气固两相的分离,静电场仅是除尘机理中的一种且受粉尘特性影响较大。多场耦合除尘技术,即在原静电场除尘基础上集成了惯性、沉降、凝聚、微旋风、静电、过滤等机理实现气与尘两相分离的同时,配合适当的清灰方式和抑尘结构,从而最大限度减少二次扬尘,实现电除尘器的超低排放。

速度谱低端法在MRR反演雨滴谱中的应用研究

针对微雨雷达(MRR)反演雨滴谱时,大气垂直气流影响较大(下沉气流达到1 m/s以上时,反演滴径的误差超过40%)以及如何剔除垂直气流的问题,应用速度谱低端法估计垂直气流,将降水粒子数密度最大处的速度作为速度谱的低端,并以此计算垂直气流的速度。为了检验这个垂直气流速度对MRR反演的修正效果,将与MRR放置在一起的Parsivel雨滴谱仪的测量值作为参考进行对比。大雨强条件下修正后的相对误差减小20%左右,中、小雨强时修正后的相对误差减小10%以上,说明用速度谱低端法计算的垂直气流可用于修正MRR的反演。

微降水雷达测量精度分析

利用数值模拟的方法,讨论了利用微降水雷达MRR(Micro Rain Radar)雷达功率谱密度反演降水参数时,MIE散射(米散射)效应、垂直气流(包括上升气流、下沉气流)对数浓度N、雷达反射率Z、雨强I、液态含水量LWC等参数的影响。MIE散射主要影响直径为1.20~4.00 mm的粒子,MIE散射效应影响的N、Z、I、LWC偏差的平均值分别为2.74 m-3 mm-1、1.47 d BZ、0.0061 mm h^(-1)、0.0004 g m-3。下沉气流使反演液滴直径偏大,上升气流使得反演的液滴直径偏小,下沉气流的影响更大,尤其是对低层影响大于高层。例如,在300 m高度上,当液滴直径为2.67 mm时,下沉气流为2.00 m s-1时,理论上反演的直径为8.07 mm,超出了MRR探测的阈值,其相对误差值能接近200%。下沉气流使得反射率谱向大粒子方向平移,且谱型展宽;上升气流则相反。将MRR资料与同步观测的THIES雨滴谱仪数据进行比对,分析MRR资料的可靠性。选取2015年4月1日01~12时(协调世界时)山东济南的一次降水过程,将MRR在300 m高度上反演的雷达反射率因子、雨强、数浓度、中值体积直径与雨滴谱仪资料进行对比。结果表明:两种仪器探测的Z、I、N、中值体积直径D0在时间序列上都有较好的吻合度,变化趋势和幅度相近,Z、I、D0的平均偏差分别为1.19 d BZ、0.34 mm h^(-1)、0.36 mm。MRR反演的I值偏大,而粒子直径偏小,分析了产生偏差的主要原因,除了探测系统偏差、分析方法本身存在的偏差外,上升气流导致的偏差不容忽视。这些结果初步验证了微降水雷达观测的功率谱密度及其反演方法的可靠性。

NCT系列热风烘茧装置试验

NCT系列热风烘茧装置解决了现行烘茧设备的气流方向不尽合理,部分载茧箔位排湿滞后及热气流短路而影响蚕茧解舒的保护。适干均匀程度的提高和能源消耗和降低等问题。其结构特点是改善了排湿布局,改进了热风管道,改变了茧车形式,以达到保护解舒、节能降耗、提高效率、减少占地、增大投入效益的目的。因此,该干茧装置是烘茧设备的一项重大技术革新。

生命只有一次——你如何在突发性灾难中活下来

在人类死亡原因的排行表上,突发性的灾难死亡,正以惊人的速度向前五名冲刺。世界卫生组织总干事中岛宏博士指出,长期以来,人们对在家中、路上或工作所可能遇到的危险的认识不足以形成公众舆论。但是,漠视我们日常生活中的安全问题,就要使我们付出痛苦的代价。据新华社报道,4月6日由于遇上罕见的强大垂直气流,东方航空公司一架客机在空中短暂失控,剧烈的颠簸把未按要求扣好安全带的乘客抛向舱顶,造成两个死亡,数十人受伤;4月8日,北京狂风大作,两处巨型广告墙被掀塌,两人死亡.此与同时,马家堡小区的一座脚手架轰然倾斜,正在作业的北京一建三公司民工于成龙从8米高处摔下,死于医院。如果把时间逐渐前推,我们将会更容易地发现,死亡的阴影总是悄然袭向日常生活。河北唐山,一个营业面积不到30000平方米的小型商场起火,在并非营业高峰的时候,导致80人死亡;河南原丰,在轰轰烈烈的促销活动中,一架抛撒宣传品的直升飞机坠落街头,死伤状惨不忍睹。还有诸如汽车落崖、"巴士"相撞、飞机冲出跑道,火车倾覆、渡船失事、球场扰乱等等。而许多灾难事故就发生在你上班、旅行的路上,尤其是在大城市居住的人,或者经常使用各种交通工具的人,都随时可能成为科技"文明"无谓的牺牲品。损失无法估量,因为生命只有一次。如何在突发性灾难来临之际,尽量使自己活下来,

Laminar Forced Convection Heat and Mass Transfer of Humid Air across a Vertical Plate with Condensation

Condensation of humid air along a vertical plate was numerically investigated, with the mathematical model built on the full boundary layer equations and the film-wise condensation assumption. The velocity, heat and mass transfer characteristics at the gas-liquid interface were numerical analyzed and the results indicated that it was not reasonable to neglect the condensate film from the point of its thickness only. The condensate film thickness, interface temperature drop and the interface tangential velocity affect the physical fields weakly. However, the subcooling and the interface normal velocity were important factors to be considered before the simplification was made. For higher wall temperature, the advective mass transfer contributed much to the total mass transfer. Therefore, the boundary conditions were the key to judge the rationality of neglecting the condensate film for numerical solutions. The numerical results were checked by comparing with experiments and correlations.

Experimental detection of bubble-wall interactions in a vertical gas–liquid flow

Bubble motions and bubble-wall interactions in stagnant liquid were experimentally investigated by high-speed CCD and PIV technique with the main feature parameters such as E?tv?s numbers Eo = 0.98–1.10, Morton number Mo = 3.21 × 10^(-9)and Reynolds numbers Re = 180 ~ 190. The effect of bubble injecting frequency and the distance S between the gas injection nozzle and the wall on the statistical trajectory of bubbles, average velocity distribution of flow field and Reynolds shear stress were studied in detail. It was shown that the combination of bubble injecting frequency and the distance S caused different bubble motion forms and hydrodynamic characteristics.When the normalized initial distance was very little, like S*≈ 1.2(here S*= 2S/d_e, and deis the bubble equivalent diameter), bubbles ascended in a zigzag trajectory with alternant structure of high and low speed flow field around the bubbles, and the distribution of positive and negative Reynolds shear stress looked like a blob. With the increase of distance S*, bubbles' trajectory would tend to be smooth and straight from the zigzag curve. Meanwhile, with the increase of bubble injecting frequency, the camber of bubble trajectory at 20<y<60 mm had a slight increase due to the inhibitory effect from the vertical wall. Under larger spacing, such as S*≈ 3.6, the low-frequency bubbles gradually moved away from the vertical plane wall in a straight trajectory and the high-frequency bubbles gradually moved close to the vertical wall in a similar straight trajectory after an unstable camber motion. Under the circumstances, high-speed fluid was mainly distributed in the region between the wall and the bubbles, while the relative large Reynolds shear stress mainly existed in the region far away from the wall.

Investigating the initiation and propagation processes of convection in heavy precipitation over the western Sichuan Basin

Heavy precipitation events occur often over the western Sichuan Basin in summer, near the transition zone between the Sichuan Basin and the steep terrain of the Tibetan Plateau. One such event -- a heavy precipitation process that occurred on 18-20 August 2010, with clear nocturnal peaks -- is chosen as a case to tentatively explore how the convection associated with convectivescale precipitation is initiated and propagated. By utilizing the vertical momentum equation from the viewpoint of separating perturbation pressure into dynamic and thermal parts, it is demonstrated that the vertical momentum is induced by the imbalance of several forces, including the dynamic/buoyant part of the perturbation pressure gradient force and the buoyancy force, with the latter dominating during the nocturnal-peak period. Although a negative value of the dynamic perturbation pressure gradient force partly offsets the positive buoyant forcing inside the strong updraft, the pattern of vertical motion tendency is largely attributable to its buoyancy because of its larger magnitude. Relative to the buoyancy component, the dynamic part of the vertical perturbation pressure gradient is also examined, revealing a smaller order of magnitude. Thus, it is the thermal effect that should be responsible for the initiation and propagation of convection. As for the convective-scale precipitation, it always presents a trailing morphology relative to the strong leading-side updraft. Furthermore, overlapping strong signals of vertical motion and its tendency point towards strong precipitation in the future.

An Investigation on the Void Fraction for upward Gas-Liquid Slug Flow in Vertical Pipe

In order to investigate the influence of the entrance effect on the spatial distribution of phases, the experiments on gas-liquid two-phase slug flow in a vertical pipe of 0.03m ID were carried out by using optical probes and an EKTAPRO 1000 high speed motion analyzer. It demonstrates that the radial profile of slug flow void fraction is parabolic. Influenced by the falling liquid film, the radial profile curve of liquid slug void fraction in the wake region is also parabolic. Since fully turbulent velocity distribution is built up in the developed region,the void fraction profile in this region is the saddle type. At given superficial liquid velocity, the liquid slug void fraction increases with gas velocity. The radial profiles of liquid slug void fraction at different axial locations are all saddle curves, but void fraction is obviously high around the centerline in the entrance region. The nearer the measuring station is from the entrance, the farther the peak location is away from the wall.

Tropical Cyclone Tilts Under Vertically Varying Background Flows:Preliminary Results Based upon TCM4 Simulations

The characteristics of tropical cyclone(TC) tilts under vertically varying background flows were preliminarily examined in this study based on numerical simulations with the Tropical Cyclone Model version 4(TCM4).The tilt magnitudes presented a linearly decreasing tendency in the simulation with the environmental wind speed vertically varying throughout the troposphere and in the simulation with the vertical wind shear concentrated in the lower troposphere,while the vortex tilt showed a linearly increasing tendency in magnitude in the simulation where the vertical shear was concentrated in the upper troposphere.The change in tilt magnitude was found to be related to the evolution of the penetration depth near the eyewall.When the shear was concentrated in the lower troposphere,the vortex tended to tilt downshear right during the early integration and underwent more precession processes.When the shear was concentrated in the upper troposphere,the vortex rapidly tilted downshear left during the early simulation and vortex precession was less frequently observed.The storms simulated in all experiments were finally in downshear-left tilt equilibrium.

Analysis of Flow Structure and Calculation of Drag Coefficient for Concurrent-up Gas-Solid Flow

This study investigates the heterogeneous structure and its influence on drag coefficient for concurrent-up gas-solid flow. The energy-minimization multi-scale (EMMS) model is modified to simulate the variation of structure parameters with solids concentration, showing the tendency for particles to aggregate to form clusters and for fluid to pass around clusters. The global drag coefficient is resolved into that for the dense phase, for the dilute phase and for the so-called inter-phase, all of which can be obtained from their respective phase-specific structure parameters. The computational results show that the drag coefficients of the different phases are quite different, and the global drag coefficient calculated from the EMMS approach is much lower than that from the correlation of Wen and Yu. The simulation results demonstrate that the EMMS approach can well describe the heterogeneous flow structure, and is very promising for incorporation into the two-fluid model or the discrete particle model as the closure law for drag coefficient.

Analysis of atmospheric turbulence in the upper layers of sea fog

Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. Turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.

Local Flow Regime Transition Criteria of Gas-Liquid Two-phase Flow in Vertical Upward Tube with a Horizontal Rod

The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are ana- lyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.