Air quality nearby road traffic tunnel portals: BTEX monitoring

A monitoring campaign of BTEX （benzene, toluene, ethylbenzene, o- m- and p-xylene） was carried out nearby two tunnel portals in the urban area of Naples with the aim to verify air quality in this kind of urban sites. Sampling was carried out using the active adsorption technique. Sampling time was 1 h. Ambient temperature and traffic flow measurements were carried out during each sampling operation. The results indicate that average benzene concentrations at both sites exceed the limit value of 10 μg/Nm^3 established by the European Community （EC） （Dir. 2000/69）. Concentration levels of other BTEX are relatively high as well. A correlation between BTEX concentration and two wheeler vehicle flow was observed.

Study on Air Pollutant Concentration inside Railway Tunnels

This paper presents a one-dimensional unsteady flow model and a numerical procedure based on the model. Comparisons between the theory and full scale experiments in a railway tunnel show that the model is capable of produce precise predictions for piston wind and pollutant concentration in railway tunnels.

Capturing CO2 Emissions in the George C. Wallace Tunnel: A Case Study

This paper describes the design of a ventilation system to be paired with a carbon capture system. The ventilation system utilizes the geometry of the George C. Wallace tunnel, located in the City of Mobile, Alabama, USA to capture and redirect emissions to a direct air capture (DAC) device to sequester 25% of the total CO2 mass generated from inside the tunnel. The total CO2 mass rate for the westbound traffic between the week-day hours of 7 a.m. and 6 p.m. has been estimated between 2,300 to 3,000 lbs./hr. By sequestering these emissions, the overall surrounding air quality was shown to be improved to a level that mirrors that from the pre-US industrial era of 270 ppm.

Air Dam对整车气动性能的影响

为进一步提高整车气动性能,降低油耗,通过风洞气动试验,研究了air dam不同安装位置、高度和结构对整车风阻系数和前端进气的影响。结果表明:1在满足整车造型要求的基础上,air dam的安装位置应尽可能前移;2Air dam在拐角处的结构很关键,需要精心设计;3相对于安装位置而言,air dam的高度对前端进气量的影响较大,故在满足路阶和接近角要求的条件下,应尽量取较大值。

Design and Wind Tunnel Study of a Top-mounted Diverterless Inlet

Combined with a UAV of the shape like Global Hawk, a new inlet is advanced to obtain high performance in both Radar Cross Section(RCS) and aerodynamic drag. Efforts are made to achieve this goal such as adopting a top-mounted inlet configuration, utilizing the diverterless technique and putting forward a new shape of entrance. A design method is brought forward and verified by wind tunnel tests. Results indicate: (1) Despite the negative effect of the front fuselage and the absence of the conventional boundary diverter, the performance of the top-mounted diverterless inlet advanced here(Ma:0.50-0.70, α:-4°-6°,σ>0.975) is equivalent to that of conventional S shaped inlet with diverter; (2) The integration of the inlet with the fuselage is realized by the utilization of a special inlet section and the diverterless technique, which disposes the whole inlet in the shield of the head of UAV, improving the drag characteristics and the stealthy performance of the aircraft; (3) The bump which is equal to the local boundary layer thickness in height can divert the boundary layer effectively. As a result, no obvious low total pressure zone is found at the outlet of the inlet; (4) According to the experimental results, negative angle of attack is favorable to the total pressure recovery and positive angle of attack is favorable to the total pressure distortion, while yaw brings bad effects on both; (5) The design of cowl lip is of great importance to the inlet performance at yaw, therefore, further improvement of the inlet performance will rely on the lip shapes of the cowl chosen.

Evaluating Market Benefits of Transportation Tunnels—The Carmel Tunnels as a Case Study

Since opening in 2010, The Carmel Tunnels have redirected some of the traffic from within the City of Haifa in Israel. This paper studies the direct and indirect financial and environmental benefits of the Carmel Tunnels compared to alternative routes. Di-rect benefits for drivers include financial savings thanks to savings on time and gas. Indirect benefits for drivers and for the public include reduced air pollution, green-house gas emissions and noise. Results show significant positive benefits from using the Carmel Tunnels compared to various alternative routes (i.e., reference scenarios). During peak hours (8 am and 4 pm), when there is heavy traffic on the alternative routes, the total benefits increase by about 25% - 47%. Using tunnels for transportation allows, among other benefits, efficient use of underground land, redirecting traffic congestion from town centers, decreasing landscape damage due to major roads passing through open spaces, and reducing air pollution in residential areas.

Simulation Experiment of Air Temperature Variation in Multi-film Covering at Night

In order to provide theoretical basis and data support for improving the production mode of covering,this study investigated the nighttime air temperature formed by multiple layers of films with tunnel sheds and small tunnel sheds as trial subjects.The experiment was carried out in four tunnel sheds with 0 or 2 small tunnel sheds covered by 0,1,2 and 3 layers of films,respectively in Jinan,Shandong Province in winter of 2018.The nighttime air temperatures of tunnel sheds and small tunnel sheds formed by 1,2,3 and 4 layers of plastic film were measured and analyzed to simulate the temperature environment of early-spring season.The results showed that there were little differences between the nighttime air temperatures inside the tunnel sheds which was installed 0-3-layer small tunnel sheds inside,and there were uncertainty in the values of the air temperatures inside and outside the tunnel sheds;and the nighttime temperature conditions were constantly improved with the number of plastic film layers increasing under the conditions of this study.The analysis indicated that the mechanism of raising the temperature surrounded by plastic film was not only due to its own thermal parameter (thermal conductivity).MATLAB fitting analysis results showed that the increment of nighttime temperature in multi-film coverings became smaller with the number of film layers increasing.In this study,the number of layers in multi-film covering should not exceed 5 layers.

高原地区隧道净空绝缘间隙修正

高原地区雷害频繁,电气外绝缘性能降低。修建高原铁路隧道需要对隧道净空绝缘间隙进行修正,其中隧道-架空接触网气隙间距是确定隧道净空间隙的重要依据,雷电冲击放电电压是确定该气隙最小间距的控制因素。国内外现有高海拔修正系列标准均不适用于3000 m以上地区,考虑放电基本特性和原理,在人工气候实验室搭建铁路隧道的典型结构,并模拟高原地区气候特点,研究300~700 mm 5个短间隙在243~4000 m 5个海拔条件下的正、负极性雷电冲击放电特性。基于大气实际参数提出了3种隧道净空绝缘间隙修正方法,建议在2、3、4 km海拔处分别按照340、390、440 mm进行隧道-架空接触网绝缘间隙修正,从而确定最小隧道净空高度。该方法可为高海拔地区铁路的电气化设计和改造提供指导,具有工程应用意义。

长距离地下综合管廊局部通风强化换热效果研究

现有的地下综合管廊通风散热方法主要为换气次数法。当管廊长度增加时,要满足规范规定的廊内温度不高于40℃的要求需要非常大的换气量,并会导致管廊前端区域过冷,整体散热效果并不好。本文提出了一种可用于长距离地下综合管廊的局部通风方式,使用CFD方法建立了局部通风数值模型,通过缩尺模型实验验证了其准确性。对增设射流风机后形成的局部通风气流组织进行了研究,结果表明,在总送风量相同的情况下,设置射流风机能够改善管廊局部热环境,在本文所研究工况下,局部截面平均温度降低了0.5℃。对比研究发现:管廊进口风量和射流风机风量之比对管廊内热环境影响不大;风机射流角度对管廊内热环境的优化具有显著影响,射流角度为90°时管廊后端截面平均温度相比0°、45°分别降低了0.41、0.33℃,90°为最优射流角度。

热位差对隧道掌子面热空气蔓延特性影响研究

为解决深埋高铁隧道内热空气对作业人员造成的热害问题,根据能量守恒定律推导热空气在隧道内蔓延时其前锋温度随距离变化的理论模型,运用CFD软件模拟某深埋高铁隧道不同工况下沿程空气温度变化情况。研究结果表明:不通风时,热空气蔓延前锋的温度变化呈现2个明显阶段,即T>297 K时的下降极快阶段和T<297 K时的逐渐平稳阶段;及时通风能够快速降低隧道温度,推荐大小里程侧风管出口距掌子面均为45 m,通风风速分别取20,15 m/s。研究结果可为进一步优化高铁隧道通风降温方式提供参考。

基于成渝中线隧道参数CR450高速动车组气密性阈值分布特征研究

以成渝中线隧道特征为研究背景,利用一维可压缩不等熵流动模型的广义黎曼变量特征线方法,研究了CR450高速动车组单列车通过隧道和两列车中央等速交会时,车内外压力波特征及隧道长度、速度、不同时间间隔内最大压力变化量对气密阈值影响特性。研究表明:最不利隧道内车外压力波动幅值最大,随着隧道长度增加,车内压力波动幅值增大;单列车满足车内每3 s内最大压力时时间常数阈值基本在最不利隧道内最大,交会时基于气密性的最不利隧道与根据车外压力载荷得到的最不利隧道长度不同;单列车时间常数阈值随速度的增加而增加,两列车以430 km/h和450 km/h交会时,时间常数阈值基本相同;单列车头尾车和中间车满足13个压力标准时时间常数阈值最大分别为51 s和42 s,交会分别为88 s和92 s。

Development of the NWPU20 Micro Air Vehicle

This paper reports the design, construction, and operation of NWPU20 Micro Air Vehicle (MAV), which is the smallest that has, up to now, been developed in PR China. The miniaturization level in PR China makes smaller MAV, in our opinion, not possible to implement. The NWPU20 is a 20-centimeter span, battery powered, fixed-wing aircraft with an off-the-shelf color video camera that can transmit live video back to the ground station. The on-board electronic subsystems are smallest and lightest among the commercial products, including an 8-gram wireless video camera, an 8-gram receiver, a 5-gram electronic speed controller (ESC), two 4.5-gram fully proportional radio frequency control servos, and the total mass of NWPU20 is less than 80 grams. An experimental model was fabricated and tested in the Low Turbulent Flow Wind Tunnel (LTFWT) at Northwestern Polytechnical University (NWPU) to research low Reynolds number flow characteristics of the NWPU20. The result of the wind tunnel test shows that stall angle of attack of NWPU20 can reach 30°, which is higher than that of the general aircrafts, and the maximum lift-to-drag ratio of NWPU20 can nearly reach 6 at the angle of attack of 10°, which can satisfy design requirements of the NWPU20. A small-sized propulsion/torque testing system was developed to measure and analyze the propulsion and torque performances of the motor-propeller combination used in the NWPU20. A center of gravity (c.g.) testing apparatus was developed and used to adjust the c.g. of the NWPU20 so that it has good longitudinal static stability and control. The NWPU20 prototype has undergone successfully flight tests many times; it flies at 32 kilometers per hour, with an endurance of 15 minutes, and a maximum communications range of 300 meters. With the color video camera, NWPU20 successfully transmits real-time video back to the ground station. The success of NWPU20 proves preliminarily that 20-centimeter span micro air vehicle is feasible and usable.

基于时间自动机的动力调度岗位培训仿真机理建模

针对大型风洞群中压空气系统存在调度机理复杂、岗位人员素质要求高、系统实操培训代价大等问题,实施基于时间自动机的动力调度岗位培训仿真机理建模。通过混杂系统理论提出适合大型风洞群中压空气调度的扩展时间自动机模型,基于先来先服务策略构建资源申请、机组工作等队列,建立调度器、就地执行器等核心机理模型,并采用UPPAAL工具对模型进行验证。结果表明:该模型的建立不仅为岗位人员掌握设备结构原理、积累实操经验提供有效手段,而且为建立风洞试验调度仿真系统、合理有效实施风洞动力调度岗位培训打下了基础。

高流速、大流量无压洞掺气设施体形优化模型试验研究

高水头、大流量、高流速的泄水建筑物,往往需要设置掺气设施来降低空蚀破坏。结合新疆某水利枢纽工程实例,通过开展泄洪冲沙洞水工模型试验研究,对1号、2号掺气设施挑坎高度、通气孔面积、坡比及型式进行优化设计。结果表明:体形优化后,在各种工况下,掺气设施掺气效果良好,掺气空腔完整而稳定,坎下未出现较大回水等不利流态;通气孔通气顺畅,整体水流流态平顺,无水翅溅到洞顶等不利现象;沿程余幅均满足要求;过流能力和流量系数基本与原设计一致。研究结果可为类似工程的掺气设施体形研究提供指导与技术支撑。

半U形隧道火灾补气速度和最高烟气温升的机器学习预测

半U形隧道是考虑火灾发生在水下隧道变坡点前而简化得到的隧道结构,通过理论推导很难建立有关烟气运动参数预测模型。因此,借助于FDS数值模拟和机器学习对320组火灾工况进行模拟分析和机器学习预测。结果表明:纵向风速的增大对于空气补充速度会有一定的抑制效果,BP神经网络在测试集和训练集上的预测效果较其他机器学习模型更为精确,决定系数R~2能够达到0.99;通过Shap值对影响隧道内空气补充速度的特征因素按重要性从高到低排序依次为高度效应、热效应、风效应;最高烟气温升受风速影响,坡高小则温升随风速减小剧烈,坡高大时风速影响不显著,并且相较于其他机器学习方法,BP神经网络和理论计算均能准确预测烟气最高温升,R~2均大于0.9。研究结合数值模拟与机器学习,为高效预测隧道火灾动力学行为及通风排烟系统优化设计提供了新方法。

瓦斯隧道压入式通风风管漏风对瓦斯分布的影响

压入式通风风管漏风对瓦斯隧道施工中的瓦斯分布规律影响颇大。以何家坡高瓦斯隧道通风为工程背景,采用计算流体动力学(computational fluid dynamics,CFD)方法模拟风管漏风工况下的瓦斯隧道通风案例,分析漏风面积与漏风位置对隧道瓦斯分布的影响规律。结果表明:风管出风口的射流作用导致掌子面靠近风管一侧无瓦斯聚集,而掌子面与出风口之间的涡流作用导致该区域出现大量瓦斯聚集;风管漏风面积越大,漏风处上游涡流强度和下游射流强度越大,因此上游瓦斯聚集程度与下游瓦斯稀释程度越明显,两者均随着漏风面积的增加呈线性增加;风管漏风位置越靠近掌子面漏风处上游瓦斯聚集的程度越明显,瓦斯聚集的增量随轴向距离呈指数减小的关系,风管位置越远离掌子面漏风处下游瓦斯的稀释与扩散程度越显著,瓦斯浓度减小的程度随轴向距离呈指数增大的关系。研究成果可为瓦斯隧道施工中的瓦斯监测及传感器布置提供一定的理论借鉴。

Air Plasma Mitigation of Shock Wave

Shock wave is a detriment in the development of supersonic aircrafts;it increases flow drag as well as surface heating from additional friction;it also initiates sonic boom on the ground which precludes supersonic jetliner to fly overland. A shock wave mitigation technique is demonstrated by experiments conducted in a Mach 2.5 wind tunnel. Non-thermal air plasma generated symmetrically in front of a wind tunnel model and upstream of the shock, by on-board 60 Hz periodic electric arc discharge, works as a plasma deflector, it deflects incoming flow to transform the shock from a well-defined attached shock into a highly curved shock structure. In a sequence with increasing discharge intensity, the transformed curve shock increases shock angle and moves upstream to become detached with increasing standoff distance from the model. It becomes diffusive and disappears near the peak of the discharge. The flow deflection increases the equivalent cone angle of the model, which in essence, reduces the equivalent Mach number of the incoming flow, manifesting the reduction of the shock wave drag on the cone. When this equivalent cone angle exceeds a critical angle, the shock becomes detached and fades away. This shock wave mitigation technique helps drag reduction as well as eliminates sonic boom.

基准排放因子更新对隧道需风量的影响研究

为解决交通车辆持续更新导致的城市隧道内通风系统设计浪费和运营闲置,研究基准排放因子更新对隧道需风量的影响,并建立2种应对车辆更新的基准排放因子计算方法.首先,通过理论分析明确需风量计算式中随时间更新的关键参数为基准排放因子;随后,根据定量分析得到基准排放因子和纵坡-车速系数更新对需风量的影响;最后,结合国外理念和实际设计经验,提出2种考虑时间更新的基准排放因子计算方法.研究结果表明:我国道路隧道通风设计规范在制定基准排放因子时参考了世界道路协会(PIARC)通风报告,并分析得到了参考理由;与2000年相比,2021年的CO、NOx和PM基准排放限值分别降低了81.6%、76.7%和97.9%;建立了使用机动车污染物排放限值作为基准排放因子的最不利设计方法,计算出2018年各污染物基准排放因子(CO为0.0011 m^(3)/(辆·km),PM为0.4610 m^(2)/(辆·km)),相比于2014年《细则》分别降低84.3%和77.0%.建立并验证了基准排放因子计算方法,为城市道路隧道通风系统设计提供参考.

低压超声速磨料空气射流喷嘴结构

硬岩隧道掘进刀具磨损严重、换刀频繁是限制高效掘进的主要因素,低压磨料空气射流辅助刀具破岩是突破硬岩隧道掘进技术瓶颈的可行性思路,为实现辅助高横移速度刀具破岩,提出了矩形喷嘴。矩形喷嘴能有效提高磨料在移动方向集束性,进而减小切缝宽度,提高切缝深度。为明确矩形喷嘴对磨料加速及破岩的影响规律,采用加长扩张段长度和截面近似等效设计了圆形喷嘴及矩形喷嘴;然后基于数值方法确定了喷嘴扩张段长度对气体及磨料加速的影响,并对比分析了喷嘴不同断面形状对磨料加速和分布特征的影响。最后通过开展低压磨料空气射流冲蚀破碎花岗岩实验,研究了喷嘴结构和横移速度对冲蚀效果的影响,分析了不同断面形状喷嘴的切割效率,确定了适用辅助刀具破岩的最佳喷嘴结构。数值结果表明压力2 MPa时,加长扩张段长度,气固两相能量转化更充分,磨料加速更充分,但随着喷嘴扩张段持续加长,磨料速度提升不明显;相比圆形断面喷嘴,矩形断面喷嘴对磨料加速稍差,但仍能将磨料加速至300 m/s,且经矩形喷嘴加速的磨料在自由流域呈扁平矩形分布,有效提高了磨料在刀具横移方向的集束性。实验表明圆形喷嘴扩张段加长,岩石冲蚀深度不断增加,当扩张段长度为145 mm时,花岗岩冲蚀深度分别为23.90、20.23 mm,扩张段长度持续加长,岩石的冲蚀深度提高并不显著。当横移速度为0.02 m/s时,喷嘴C_(4)、R_(1)、R_(2)切割玄武岩深度分别为3.35、12.15、8.25 mm,花岗岩深度分别为5.2、14.9、11.5 mm;横移速度为0.30 m/s时,喷嘴C_(4)、R_(1)切割玄武岩深度分别为0.8、3.0 mm,花岗岩深度分别为1.0、3.6 mm。对比喷嘴C_(4),和数值模拟结果相同,矩形喷嘴能使磨料聚能、磨料利用充分,切割效率较优。且喷嘴R_(1)的切割效率最好,喷嘴结构最优。研究结论将为磨料空气射流辅助刀具破岩提供理论和技术支撑。

高速铁路隧道内气室参数对列车表面气动效应的影响

应用三维、可压缩、非定常Navier−Stokes方程和有限体积法,以单线隧道人行通道下方布置单个气室为例,分析隧道内气室参数对列车表面气动压力和横向力的影响。研究结果表明:隧道中加设气室后列车表面压力峰值增大,且当气室位于隧道前部、气室纵向长度较长、气室入口面积较大时,列车表面压力峰值增大更明显;当隧道长156 m、气室位于隧道前部、气室长度L为50 m、气室入口面积A为1.2 m^(2)、车速为400 km/h时,列车表面瞬变压力的正负峰值分别比无气室时的正负峰值大0.2 kPa和0.18 kPa;列车所受横向力在车头经过气室入口时产生波动,且波动时间随着气室长度的增大而延长,气室入口面积增大使横向力波动更为剧烈;安装气室后,列车所受横向力峰值通常低于其自身重力的1%,因此,列车发生倾覆概率较低。