Effect of landform on aerodynamic performance of high-speed trains in cutting under cross wind

The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e double-equation turbulent model. Results show that aerodynamic forces increase with the cutting leeward slope decreasing. The maximum adding value of lateral force, lift force, and overturning moment are 147%, 44.3%, and 107%, respectively, when the slope varies from 0.67 to -0.67, and the changes in the cutting leeward landform have more effects on the aerodynamic performance when the train is running in the line No. 2 than in the line No. 1. The aerodynamic forces, except the resistance force, sharply increase with the slope depth decreasing. By comparing the circumstance of the cutting depth H=-8 m with that of H=8 m, the resistance force, lateral force, lift force, and overturning moment increase by 26.0%, 251%, 67.3% and 177%, respectively. With the wind angle increasing, the resistance force is nonmonotonic, whereas other forces continuously rise. Under three special landforms, the changes in the law of aerodynamic forces with the wind angle are almost similar to one another.

Detached-eddy simulation of flow around high-speed train on a bridge under cross winds

In order to describe an investigation of the flow around high-speed train on a bridge under cross winds using detached-eddy simulation(DES), a 1/8th scale model of a three-car high-speed train and a typical bridge model are employed, Numerical wind tunnel technology based on computational fluid dynamics(CFD) is used, and the CFD models are set as stationary models. The Reynolds number of the flow, based on the inflow velocity and the height of the vehicle, is 1.9×10~6. The computations are conducted under three cases, train on the windward track on the bridge(WWC), train on the leeward track on the bridge(LWC) and train on the flat ground(FGC). Commercial software FLUENT is used and the mesh sensitivity research is carried out by three different grids: coarse, medium and fine. Results show that compared with FGC case, the side force coefficients of the head cars for the WWC and LWC cases increases by 14% and 29%, respectively; the coefficients of middle cars for the WWC and LWC increase by 32% and 10%, respectively; and that of the tail car increases by 45% for the WWC whereas decreases by 2% for the LWC case. The most notable thing is that the side force and the rolling moment of the head car are greater for the LWC, while the side force and the rolling moment of the middle car and the tail car are greater for the WWC. Comparing the velocity profiles at different locations, the flow is significantly influenced by the bridge-train system when the air is close to it. For the three cases(WWC, LWC and FGC), the pressure on the windward side of train is mostly positive while that of the leeward side is negative. The discrepancy of train's aerodynamic force is due to the different surface area of positive pressure and negative pressure zone. Many vortices are born on the leeward edge of the roofs. Theses vortices develop downstream, detach and dissipate into the wake region. The eddies develop irregularly, leading to a noticeably turbulent flow at leeward side of train.

Experimental Investigation on Flame Characterization and Temperature Profile of Single/Multiple Pool Fire in Cross Wind

An experimental study was carried out to investigate the flame characterization and temperature profile for single and multiple pool fire with the influence of cross wind.There were 13 test cases in total,categorized into circle and rectangle fuel pans,with diameter(or equivalent diameter)ranged from 50 mm to 300 mm.Kerosene was used for the fuel of pool fire.Some K-type thermocouples were arranged around the flame to monitor the flame temperature,while the flame tilt angle was measured based on the photograph of flame for different case.Firstly,it can be found that there are three phases,including preheating,steady burning and extinguishing phase,during the flame evolution.The maximum temperature near the fuel surface is~1040 K,which is higher than that of flame plume(~600 K),in the steady burning phase of circle single pool fire(D=300 mm),while the average burning rate is~1.525 g/s.In addition,the burning rates of all cases were measured and compared with the current predicted method.Typically,the flame morphology of single/multiple pool fire at different cross wind speed(ranging from 0 to 3.5 m/s)was analyzed,and it is found that the results for single pool fire agree with Thomas model and AGA model well,which are not suitable for multiple pool fire.Finally,the temperature profile of different case was measured with various wind speed.

Experimental study on the effect of canyon cross wind on temperature distribution of buoyancy-induced smoke layer in tunnel fires

Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy induced smoke flow characteristics of pool fres,involving smoke movement behaviour and longitudinal temperature distribution of smoke layer.The canyon wind speed,longitudinal fre location and fre size were varied.Results show that there are two special smoke behaviours with the fre source positioned at different flow feld zones.When the fire source is positioned at the negative pressure zone,with increasing canyon wind speed,the smoke always exists upstream mainly due to the vortex,and the smoke temperature near the fire source increases frst and then decreases.However,when the fre source is located in the transition zone and the unidirectional flow zone,there is no smoke appearing upstream with a certain canyon wind speed.Meanwhile,the smoke temperature near the fre sources are decreases with increasing canyon wind speed.The dimensionless temperature rise of the smoke layer OT:*along the longitudinal direction of the tunnel follows a good exponential decay.As the canyon wind speed increases,the longitudinal decay rate of△T.*decreases.The longitudinal decay rate of AT*downstream of the fire is related to the fre location and canyon wind speed,and independent of the fire size.The empirical correlations for predicting the longitudinal decay of OT:*downstream of the fre are established.For a relatively large-scale fre,the longitudinal decay rate of AT:*upstream of the fire increases as the distance between the fire source and the upstream portal increases,especially for larger canyon wind speeds.

Numerical study on the restriction speed of train passing curved rail in cross wind

The results of numerical investigations of aerodynamic forces and moment coefficients of flow passing a simplified train geometry under different wind speeds are summarized. To compute numerically the different coefficients, the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations, combined with the κ-ε turbulence model, were solved using finite volume technique. The pressure-velocity fields were coupled using the SIMPLE algorithm. At each iteration the pressure correction was obtained by solving a velocity divergence-derived Poisson-like equation. With the computed aerodynamic forces, the formula of the restriction speed at which the train passed curved rail in cross wind was deduced to analyse the influences of aerodynamic forces on the restriction speed. Results of numerical investigations showed that aerodynamic lift and overturn moment increased more and more rapidly with train speed and wind speed. The enhancement trends showed nonlinear phenomena and enhanced risk in the course of train movement. When the train travels at a high speed and encounters a huge cross wind, the influence involved by nonlinear risk increment will extremely impair safety of train. The following conclusion can also be drawn: The effect of aerodynamic lift makes restriction speed reduce, however, the influences of aerodynamic drag to the limit train speed rest on the direction of wind flow. When the wind blows from inner rail to outer rail, aerodynamic forces shall reduce the restriction speed, by contraries, when the wind blows from outer rail to inner rail, aerodynamic forces shall increase the restriction speed.

NumericaI Computation of Flow over a Train in Cross-Wind

A finite different method is developed to predict the side force on a high speedtrain in a cross-wind at low yaw anglee. The k-εturbulence model with wallfunctions is employed. the solution algorithm is based on curvilinearnonorthogonal coordinates,covariant velocity components ,and staggered gridarrangement. The convective fluxes are described by the Power tow Scheme.A highly deformed grid generated with an elliptic grid generator is used aroundthe comero of the cross-section of the train. The results obtained comparepositively with wind tunnel experinients.

Experimental and Numerical Investigation on the Flow Characteristics around a Cross-Flow Wind Turbine

This study investigated the flow characteristics around a cross-flow wind turbine. A wind tunnel experiment (WTE) was performed to measure the flow characteristics past the wind turbine when operating at the optimal tip-speed ratio of λ = 0.4. In addition, computational fluid dynamics (CFD) simulations were performed for the flow field around the wind turbine that was operating at tip-speed ratios of λ = 0.1, 0.4, and 0.7. The CFD approach was validated against the WTE measurements. CFD results confirmed that with an increase in λ, the velocity deficit was generally increased in the leeward of the return side of the wind turbine, while it was generally decreased in the leeward of the drive side of the wind turbine. It was also confirmed that with an increase in λ, the turbulence kinetic energy was generally increased in the leeward of the return side of the wind turbine, while it generally decreased in the leeward of the drive side of the wind turbine.

计及UPFC最优配置的电力系统鲁棒调度协同优化策略

统一潮流控制器(UPFC)应用于潮流调控时,计及UPFC调控参数的交流潮流计算是非凸、非线性问题,且多台装置间的非线性交叉耦合特性也会直接影响优化配置方案。为此,基于UPFC的潮流调控特性,构建了计及UPFC的松弛型交流潮流二阶锥规划模型;计及风电的不确定性,协同考虑UPFC的规划和电力系统的调度问题,建立了计及UPFC最优配置的电力系统鲁棒协同优化模型,并采用列和约束生成算法进行求解。以IEEE RTS-24节点系统为算例进行仿真分析,结果表明所提协同优化策略有效提升了UPFC配置方案的适应性,提高了系统运行经济性和风电消纳能力,增强了系统运行调控的灵活性。

基于瞬变电磁法的煤层风氧化带探查

煤层风氧化带的发育对煤矿的生产组织和安全回采影响巨大,针对准格尔煤田东部隆起带煤层风氧化带圈定的技术难题,研究了瞬变电磁法探查煤层风氧化带的可行性。首先对研究区正常地层与煤层风氧化区的电阻率测井曲线进行了分析,总结了正常区与煤层风氧化区的电性差异,并以电阻率测井曲线构建了煤层风氧化区地电模型;然后采用MAXWELL软件对理论模型的瞬变电磁响应进行了数值模拟,发现在煤层风氧化区瞬变电磁反演电阻率断面表现为浅部低阻层变厚、低阻异常幅值减小的异常特征,可以以此来圈定煤层风氧化区的分布范围;最后在数值模拟的基础上,在串草圪旦煤矿开展了现场试验,结合钻探情况对试验数据从瞬变电磁反演电阻率断面和平面2个角度进行了分析,结果表明瞬变电磁法探测划分风氧化带是可行的。

高速受电弓安装形式对列车气动性能的影响

受电弓作为高速列车上不可或缺的部件,其结构特性直接影响高速列车整车气动性能。采用数值仿真方法,基于三维稳态SST k-ω模型,分析高速受电弓不同安装形式对高速列车气动性能的影响以及各节车辆气动阻力的变化规律,并进一步研究其横风环境适应性。研究结果表明:当高速列车在明线运行时,高速受电弓不同安装形式对整车气动性能影响较小,但受电弓所在车辆的气动阻力变化较大;与闭口-升前弓工况相比,受电弓开口-升前弓时整车气动阻力减小2.10%,其中第6节车气动阻力减小6.06%;在横风条件下,受电弓开口-升前弓时整车横风稳定性能较优,与开口-升后弓工况相比,整车横向力与倾覆力矩分别降低2.52%和3.48%,其中第6节车横向力和倾覆力矩分别减少11.13%与18.50%。因此,在明线有无横风条件下,受电弓安装形式为开口-升前弓的气动性能均最优,且升前弓能改善受电弓后区域的流场结构,从而达到改善整车气动性能的目的。

桥上轿车并行超车的风致安全评价及横向运动控制

为厘清并行超车过程中“风-车-桥”的气动交互干扰及其对轿车侧风稳定性的影响,采用空气动力学与系统动力学耦合方法建立了侧风环境下桥上轿车分别超轿车和货车的风致安全评价模型,揭示了轿车超车过程中气动侧力和气动横摆力矩的变化规律及作用机理,基于线性二次最优控制的路径跟踪模型分析了轿车超车过程中有、无控制作用时侧偏运动和横摆运动的差异。结果表明,“风-车-桥”气动交互干扰形成的高速低压区和低速低压区对行车安全有显著影响,影响程度与被超车类型及所在车道有关:轿车超轿车时,在迎风侧第1车道超其他车道轿车时为较危险工况;轿车超货车时,在迎风侧第1车道超其他车道货车及在第2车道超第1车道货车时为较危险工况。研究结果可为提升桥梁风致行车安全能力提供参考。

高速汽车侧风稳定性控制

针对汽车在侧风环境中容易失稳的问题,基于模型预测控制(model predictive control,MPC)理论提出了一种分层式直接横摆力矩控制(direct yaw moment control,DYC)策略,以使得汽车突遇侧风干扰时能够较好地维持稳定性。上层控制器依据MPC理论精确计算并输出必要的横摆力矩,以确保车辆稳定行驶并将其传递给下层控制器;下层控制器接收到横摆力矩后,将横摆力矩精确地分配到每个车轮上。为验证所设计的MPC直接横摆力矩控制器的性能,采用Carsim与Simulink联合仿真平台进行仿真,并与基于滑模控制理论的控制器进行对比分析。结果表明:本研究提出的基于MPC的控制器,控制效果优于滑模控制器,有效提高了汽车的侧风稳定性。

风-车-桥气动干扰作用下的汽车纵横向协调控制

为提高跨海大桥上轿车的风致行车安全能力,采用合成风和动网格耦合方法建立了轿车超越集装箱货车的瞬态分析模型,揭示了“风-车-桥”气动交互作用机理及其对轿车气动特性的影响规律。采用五次多项式插值算法建立了超车轨迹规划模型,基于模糊逻辑的双PID控制方法与径向基神经网络的滑模控制方法设计了纵横向协调控制器,开展了轿车超车过程的路径跟踪能力分析及行驶稳定性评价。研究结果表明:风-车-桥的气动干扰大小与行驶车道及位置有显著关系,纵横向协调控制器的路径跟踪控制精度和鲁棒性较好,轿车侧风稳定性提高效果明显。

表面横向风流作用下煤体的内部燃烧蔓延规律

煤的自燃特性使其在开采、存储和运输过程中存在火灾事故隐患,极大地阻碍了煤炭行业的可持续发展.通过自主搭建的敞车载运煤燃烧蔓延模拟实验装置,分析在表面横向风流作用下的松散煤体内部高温区域演变以及气体蔓延规律.结果表明,表面横向风流明显加快了本文实验煤样内部高温区域蔓延速度,相比无风状况下,高温蔓延速度加快了0.3倍(风流1 m·s^(-1)时)和0.5倍(风流2 m·s^(-1)时),高温区域峰值温度升高了120±20℃;受表面横向风流影响,燃烧蔓延路径向风流流动方向偏移;在风流0 m·s^(-1)时,燃烧的高温点O2体积分数快速下降阶段所经历的时间随纵深的增加逐渐增大,风流作用会加剧煤氧反应.研究成果可为煤炭在运输与储存过程煤火灾害形成规律研究提供参考借鉴.

改进MUSIC算法的超声波测风方法研究

针对传统超声波测风装置测风精度不高、抗噪声能力弱,提出了一种改进多重信号分类(multiple signal classification,MUSIC)算法的超声波测风方法。采用一种弧形6阵元超声波传感器阵列的测风结构,推导其阵列流型;在此基础上,添加小波阈值降噪算法提高信号信噪比,降低噪声信号协方差矩阵的秩;再使用PHAT加权广义互相关时延估计算法以提高时延估计的准确性,同时根据时延关系对传统MUSIC算法矢量矩阵进行改进;最后通过MUSIC算法实现对风速风向的测量。理论分析与仿真结果表明:改进后的MUSIC算法具有较好的抗噪性能和较高的风参数测量精度,测量风速绝对误差达到0.15 m/s,风向绝对误差达到2°,可以应用于对风参数要求较高的场景。

CFOSAT与MetOp卫星散射计12.5 km产品反演风速交叉验证分析

按照30 min和50 km的时空窗口,对2021—2022年同期在轨的中法海洋卫星(China-France Oceanography SATellite,CFOSAT)微波散射计(SCATterometer,简记为“CSCAT”)与MetOp(Meteorological Operational)卫星A、B、C星先进散射计(Advanced SCATterometer-A/B/C,ASCAT-A/B/C)反演海面风速进行交叉配对,进而对匹配数据进行降雨和陆地质控、匹配数据相关分析、相对误差和风速分布偏差分析,结果如下:(1)质量控制后CSCAT与ASCAT-A反演风速相关系数为0.94~0.97,均方根误差为0.82~1.89 m·s^(-1)。(2)2 m·s^(-1)以下风速段CSCAT比ASCAT-A/B/C大30%~70%,2~21 m·s^(-1)风速段CSCAT比ASCAT-A小0~5%,2~3 m·s^(-1)风速段CSCAT较ASCAT-B/C大3%~30%,4~17 m·s^(-1)风速段CSCAT比ASCAT-B/C小2%~10%。(3)2021年中国近海整体风速CSCAT大于ASCAT-A,其中1月,东海、南海、菲律宾及以东海域CSCAT比ASCAT-A大0.5~1.5 m·s^(-1);7月,黄海、南海CSCAT比ASCAT-A大1.0~1.5 m·s^(^(-1)),与中国近海2021年各月平均风速变化相吻合,表明卫星间风速交叉验证可以很好地揭示卫星间风速的差异。

高海拔输电线路走廊风场实测及湍流特性研究

在海拔高度为4 500 m的西藏那曲镇高山平原地貌建立了两两间距为10 m、20 m和30 m的4点位同步脉动风速实测系统,获得了持续1.5年的高海拔地区连续大风风速样本,10 min平均风速和脉动风速最大值分别达到33.6 m/s和45.0 m/s以上,实测顺风向湍流强度和横风向湍流强度的均值分别为0.134和0.123,介于DL/T 5551-2018《架空输电线路荷载规范》规定的A类地貌和B类地貌湍流强度之间。基于任意两个测点的同步脉动风速,计算了顺风向脉动风速分量沿导线方向的空间相关系数及湍流积分尺度,广义极值模型可以较好地反映高风速样本湍流积分尺度的概率分布。实测样本风速越高,湍流积分尺度均值越大,当样本风速限值取8.0 m/s和20.0 m/s时,湍流积分尺度均值相差22.5%。20.0 m/s以上高风速样本的湍流积分尺度均值为106.96 m,约为DL/T 5551-2018《架空输电线路荷载规范》规定值50 m的2.1倍,导地线风荷载增大约6.1%,即高海拔高山平原地貌导地线风荷载可能会被低估。

基于星载合成孔径雷达图像交叉谱的全球海浪特征研究

星载合成孔径雷达(Synthetic Aperture Radar, SAR)因其全天时、全天候的观测能力,为全球海洋动力环境要素研究提供了重要数据支撑。然而,SAR海浪成像是非线性过程,现有理论中的近似求解会导致海浪谱反演的信息缺失。SAR图像交叉谱技术的提出一定程度上突破了这一限制,能够很好地量化海浪谱特性及海浪传播方向。本研究延续前人系列成果,利用最新提出的面向径向海浪的图像谱强度,开展不同尺度海浪随局地风速的变化趋势分析,并基于雷达视向图像谱强度提取了谱峰波数,进而结合欧洲空间局环境遥感卫星先进合成孔径雷达波模式在开阔大洋获取的近400万景SAR图像,分析了谱峰波数的全球分布特征,为量化全球风浪耦合过程提供新视角,揭示了海浪与风速耦合关系的空间分布与季节变化规律。

G3铜陵长江大桥交叉索防碰减振措施研究

G3铜陵长江公铁大桥主桥为主跨988 m的斜拉-悬索协作体系桥,每个索面布置了6对交叉索,交叉索间距较小,最小间距仅0.152 m,斜拉索在风荷载作用下,极可能会在交叉索区域发生碰撞。本文建立了G3铜陵长江公铁大桥主桥的有限元分析模型,计算了列车荷载、温度变化等日常荷载作用下交叉索处相对位移情况,研究了百年风荷载激励下交叉索碰撞情况,发现发生碰撞的交叉点均集中于最外侧的斜拉索上,为此研发了一种防撞装置,计算表明在18#交叉索处设置该措施可有效避免交叉索发生碰撞。

气溶胶污染物跨楼层传播特性数值研究——建筑热羽流影响

太阳辐射力和水平来流惯性力引起的壁面热羽流会对建筑表面的污染物跨楼层扩散传播产生明显影响。采用风洞实验和数值模拟,研究6层居民建筑在不同强度热羽流影响下,气溶胶污染物沿建筑立面不同楼层扩散分布特性。采用理查德森数Ri表示建筑立面热羽流的强弱。研究表明,建筑立面的热羽流对气溶胶污染物的扩散分布有明显影响。当Ri<2.28时,污染物主要向迎风面近地面聚集,导致近地面污染物浓度较高;当Ri≥2.28时,污染物向高处扩散,将引起严重的污染物跨楼层扩散传播风险。