Mesoscale circulation in the surface layer off the southern and western Sardinia Island in 2000-2002

Five oceanographic cruises were organized in the Sardinian Sea and Channel in May 2000, March 2001, September 2001, May 2002, and November 2002 to study the characterization of the water masses, Atlantic Water (AW) and Winter Intermediate Water (WIW), and their mesoscale variability. In the Sardinian Channel, an Algerian anticyclonic Eddy (AE) was observed in May 2000, along the Tunisian coast. This induced a greater minimum salinity in a wider and deeper layer than in November 2002, when no AE was observed. Some WIW was observed below it; nevertheless, no link could be established between AEs and WIW occurrences. In the Sardinian Sea, two AEs were observed during spring 2000, and a further two during spring 2002. One AE strongly influenced shelf circulation, in contrast to the other three that were off the continental slope. In the same area, during the end of September 2001, a vertical salinity inversion occurred in the first 30-50 m of depth over the whole sampling field, and a W-NW wind induced a coastal upwelling over the western Sardinian coast (south of 41° N). This upwelling increased the salinity from ∼20 to 30 m below the surface to the surface and, thereby led to a lower salinity close to the coast than offshore. This was in contrast to a classical upwelling. Consequently, in the Sardinian Sea, the general circulation, mainly driven by AEs, can meet the coastal wind-driven circulation.     

基于大涡模拟的旋风分离器内流场数值模拟研究

为了研究旋风分离器内流场的运动状况,借助Fluent软件,采用大涡模拟,基于曲线坐标系的SIMPLEC算法,对切向入口的Stairmand旋风分离器内流场进行了三维数值模拟研究。数值结果表明,大涡模拟适合于三维强旋流的流场模拟,分离器内部的流动空间可分为内、外2个流动区域,在不同的流动区域中,气体压力、速度场的分布有较大的差异。而且压力分布与速度分布不是绝对的轴对称分布。数值模拟结果对其设计优化研究有一定的应用价值。     

室内火灾烟气运动及机械排烟的大涡模拟

采用机械排烟是控制建筑火灾烟气扩散与蔓延的一种有效手段。利用大涡模拟方法,对建筑物室内火灾烟气运动及机械排烟进行了数值模拟。在室内后侧墙处有机械排烟口的条件下,模拟得到的烟气瞬时温度随时间的变化与实验相符合,计算出的烟气层高度也与实验相符合。通过数值模拟对室内机械排烟口的位置进行了优化选取,表明机械排烟口的不同位置对室内烟气运动有较大的影响。当火源位于房间地面中心时,在顶棚中心或左端中心实施机械排烟比在后侧墙处实施机械排烟可取得较好的排烟效果。这说明将排烟口布置在沿烟气运动趋势较强的路径且远离进风口处,可有效地控制室内烟气层的高度。     

Ozone Dry Deposition Velocities for Coastal Waters

Air-sea exchange rates for ozone were measured by the eddy correlation technique at a site on the north Norfolk coast in the UK. The average surface resistance to ozone uptake was found to be, r_s(O₃) = 1,000 ± 100 s m^-1. Micrometeorological measurements of trace gas fluxes to ocean surfaces are rare but a review of available measurements suggests that we can constrain sea water surface resistance for ozone to between 1,000 (Regener (1974), and this work) and 1,890 s m^-1 (Lenschow et al., 1982), yielding surface deposition velocities between 0.53 and 1.0 mm s^-1. These values are more than an order of magnitude greater than can be explained by laboratory determined mass accommodation coefficients for ozone to water. The importance of dry deposition with respect to process air-sea exchange models is highlighted. A trend in surface deposition velocity with wind speed was also observed supporting a surface chemical enhancement mechanism of ozone uptake which in turn is enhanced by near surface mixing processes.     

Ozone Deposition at a Forest Site in NE Bavaria

The dry deposition of ozone to aconiferous forest in northeastern Bavaria(southern Germany) was quantified during 1999with both the eddy correlation method and a bigleaf model. The model included parameterizationsof the atmospheric transfer resistances fromdirect measurements, stomatal resistance from aplant ecological model, and an estimation of thecuticle resistance as function of leaf wetness.Early in the season, the measured and themodelled deposition fluxes were in goodagreement, although the modelled fluxes tended tounderestimate the measured ones. Thisunderestimation was more pronounced in the latesummer, when high nocturnal fluxes werefrequently measured. The model parameterizationof the cuticle and the stomatal resistances didnot allow for such high fluxes. In these cases,the 24 hour average of the measured fluxes wereup to 4.5 times higher than the modelled ones.The reasons for these large discrepancies remainunknown. However, assigning the unaccounted partof the deposition to a nonstomatal surfacedeposition pathway, a new parameterization of therespective resistance yielded an average value of300 s m^-1. It exhibited a decreasing trendthrough the vegetation period.     

烟气输运和水喷淋相互作用的大涡模拟研究

本文应用大涡模拟方法，并结合Smagorinsky亚格子尺度模型，数值研究了烟气输运和水喷淋的相互作用问题。为了有效地模拟烟气输运过程，文中采用低马赫数近似下的三维可压缩Navier-Stokes方程和组分方程进行求解，并采用有限差分法数值计算了滤波后的控制方程。对于燃烧过程扣所产生的热释放，采用Lagrangian粒子携带热量的近似方法来模拟，这些运动粒子进一步用来标识烟气的输运过程，同时还近似模拟了水喷淋和热气流的相互作用过程。文中数值计算了燃烧火源所形成的热气流和烟气输运过程，以及与水喷淋的相互作用，并探讨了喷水装置的喷水量、喷射角和水颗粒直径对流动特性的影响。     

复杂山区地形水利水电液氨施工泄漏研究

水电工程中液氨泄漏扩散对周围居民的危害很大,疏散区域划分成为重要的防护措施,但在复杂地形条件下确立准确的疏散区域成为难题。为解决这一难题,通过现场调查所得数据,采用大涡模拟方法对泄漏气体扩散进行模拟,分析氨的泄漏扩散在大气中的扩散规律,研究泄漏气体的扩散动力学演化过程及影响范围,计算泄漏事故中不同时间段影响范围,得出时间序列上的爆炸危险区域和有毒气体影响区域,最后总结分析制定安全防护距离的影响因素,为周边居民安全防护策略提供参考。     

气流清扫的超音速喷管气动设计及其性能的对比分析

目的 提出使用拉瓦尔喷管产生高速气流清扫固体表面附着的水膜。方法 设计中心轴对称锥形喷管(Taper-A)、中心轴对称Sivell法喷管(Sivell-A)、中心轴对称短化喷管(MLN-A)和二维锥形型线喷管(Taper-2D),建立包括外流场的LES数值仿真模型,并进行仿真,分析研究外流场结构,并基于韦伯数判据,分析超音速喷管的清扫性能。结果 喷管短化设计方法可以将喷管长度缩短50%。外流场速度呈波动衰减趋势,特征线法喷管的气流膨胀更充分。缩短喷管长度会减小内流场的附面层厚度,因此MLN-A在速度波动中的能量耗散较少;喷管过长也会降低清扫性能,MLN-A和Taper-2D在xL>2区域的最大等效水膜厚度小于0.2 μm,但MLN-A有效清扫面积比Taper-A的喷管提高15%以上,清扫性能最优。结论 喷管短化设计方法可以有效缩短喷管。喷管结构对清扫性能影响较大。MLN-A喷管的清扫性能最优。     

高速列车隧道会车流场的CFD分离涡数值模拟

目的研究高速列车隧道会车压力波及列车尾流特性。方法建立某型高速列车三节车模型,采用脱体涡方法数值模拟两列车以350km/h在隧道内等速会车的流场。数值模拟的空间离散化压力项、密度项及修正的湍流黏度项使用二阶迎风格式,动量项使用有界中心差分格式,时间离散采用预处理二阶精度差分格式,用壁面函数处理隧道壁,使用雷诺时均法作方法对比。计算列车车头、侧墙及尾车等部位的压力时间历程,然后使用傅里叶变换对尾车测点进行频谱分析,最后对尾流中不同位置的湍流强度进行分析。结果头车所受压力波动最为剧烈,中间车次之,尾车最小。列车侧墙同一垂向位置不同高度压力变化相差不大。列车尾涡主频在3.85Hz附近,其可能对列车横向振动有一定的影响。结论尾涡是两个不断向后发展的中等强度涡旋,在充分发展段,其湍流强度会有一个较为明显的抬升,之后逐渐减弱。会车侧涡流由于横向发展较为迅速,导致其强度较小且减弱速度较快。     

基于光谱分析仪的通量-梯度法测量小型池塘水-气界面温室气体交换通量

小型池塘作为内陆水体的一部分,是被忽视的温室气体重要排放源.本研究主要利用通量-梯度方法测量长江三角洲地区的一处小型池塘水-气界面温室气体(CO_2和CH_4)交换通量.结果表明:1零梯度测试结果显示本套通量-梯度系统测量H_2O、CO_2和CH_4通量的精度分别为7.525 W·m-2、0.022 mg·(m2·s)-1、0.054μg·(m2·s)-1,并且在正常实验观测期间3种气体(H_2O、CO_2和CH_4)的通量值分别有84%、80%和94%的结果高于零梯度测试精度,以上结果可以保证本套通量-梯度系统具有足够的精度测量池塘水-气界面温室气体交换通量;2通量-梯度计算结果表明此小型池塘在夏季为CO_2和CH_4的排放源,其排放通量平均值分别为0.038 mg·(m2·s)-1和0.889μg·(m2·s)-1,其中CH_4排放通量远高于内陆湖泊甲烷排放通量的中值,说明小型池塘的温室气体排放量是估算内陆水体温室气体排放量特别是CH_4排放量中不可忽视的重要量值,本研究结果可为准确估算区域温室气体排放量提供科学参考.