Numerical simulation on the temperature field in an equipment cabin of a high-speed railway train

With train speed increasing, the heat generation from its key equipment is growing as well and the cooling and ventilation of the equipment cabin become more and more important. In this paper, computational fluid dynamics (CFD) method is adopted to simulate the airflow and the temperature field in indoor and outdoor space of the equipment cabin when the train moves at 250 km/h in open space. The simulation results indicate that the surface temperature of the main heat generation equipment is not beyond the limit. When the train moves forward and backward, the maximum average surface temperature of the heat generation equipment is 56.5 °C and 71.7 °C, respectively, and the airflow rates of the fans in the equipment cabin are decreased by 9.1% and 5.2%, if compared to the rated value, respectively. Both forward and backward running conditions should be considered when designing the layout of the equipment and grilles. It is suggested that, the major heat generation equipment should be located in the middle of the cabin; the flow rate decrement of the cooling fan when the train moves at 250 km/h should be taken into account.     

Performance of three air distribution systems in VOC removal from an area source

Building-related health complaints and symptoms represent a significant occupational health problem. Elevated concentrations of various types of indoor pollutants, frequently associated with inadequate ventilation, have been implicated as a potential cause. The objective of this research is to model and evaluate the performance of several ventilation methods in pollutant removal from indoor environments. Pollutant sources are assumed to be at the floor level, one with a constant emission rate and the other a fast decaying source (volatile organic compound emissions from a wood stain). Three ventilation methods, namely displacement ventilation and two mixing systems using a side grille and ceiling square diffuser respectively are studied. A computer model has been applied to simulate the distributions and the time history of the pollutant concentrations in a mockup office. Experimental data of velocity, temperature, and tracer gas concentration distributions in the chamber with the displacement diffuser are obtained to validate the airflow model. Simulation results show that different ventilation methods affect the pollutant distributions within the room. When the pollutant sources are distributed on the floor and not associated with a heat source or initial momentum, displacement ventilation behaves no worse than perfect mixing ventilation at the breathing zone. Conventional “mixing” diffusers, on the other hand, could perform better or worse than a perfect mixing system. The computer model could be used for selecting appropriate ventilation systems to maximize indoor air quality for occupants.     

夏季空调房间气流组织的数值模拟

应用计算流体力学方法对夏季空调房间两种送风参数下的室内气流组织进行了数值模拟,给出了速度场和温度场的分布状况,通过对比分析,指出舒适性空调夏季采用较低的送风速度能使室内温度场和速度场分布更均匀。     

暖通空调气流组织数值模拟的特殊性

从计算流体力学CFD应用于暖通空调工程的角度，阐述了通风空调房间内气流组织数值计算的特殊性和难点，对风口模型、湍流模型、辐射模型、热源模型、计算收敛速度以及复杂物理条件的描述等作了分析和介绍，并提出了相应的对策或解决思路。     

空间站座舱工位送风的性能分析

分析了工位送风在空间站的适用性,确定了评价指标.建立了物理模型和数学模型,分析了不同工位送风量和送风速度对舱内乘员工位区空气质量的影响,得到了CO2浓度、空气龄、空气新鲜度比、局部换气效率和工位区风速分布,同时与无工位送风进行了对比.结果表明,工位送风在较小风量时就可以满足空气质量要求,符合航天器轻量化原则;在相同总风量下加大工位送风量后,工位区的性能指标均有所改善;在工位送风量一定情况下,送风速度提高有助于改善舱内的沉闷感.     

铁路客站无组织渗风现状调研及数值模拟研究

通过对全国16个大型铁路客站现场调研,总结了客站主要空间的无组织渗风现状及特点,归纳了目前控制无组织渗风的节能做法。通过调研发现,由于客站建筑及使用特点,大量的无组织渗风量增加了夏季空调和冬季供暖能耗,并且影响室内热舒适。通过数值模拟方法,分析了门斗和空气幕对客站无组织渗风的控制效果,并对各自控制无组织渗风的特性给出了评判和使用建议。     

基于行车试验的高铁路基面动应力幅值概率分布规律及设计值研究

高速列车荷载作用下路基动应力的大小直接影响到路基沉降变形及长期动力稳定性,现很多高铁线路路基动力响应数据仍处于“信息孤岛”状态,信息共享不充分和综合再分析不够,较难获得更具普遍意义和价值的路基动应力响应规律。鉴于此,采用现场实测、调研收集和数理统计分析的方法研究高速列车荷载作用下路基面动应力大小及概率分布规律,探讨《高速铁路设计规范》中路基面设计动应力幅值计算公式的适应性,并提出高铁路基面设计动应力幅值的计算公式。主要结论如下：①高铁无砟、有砟轨道路基面动应力幅值均服从正态分布,并统计获得了其特征值(均值μ、标准差δ,“3δ规则”的上下限值);②路基面动应力幅值与列车速度的关系：对于高铁无砟轨道,当v≥150km/h,路基面动应力幅值基本保持不变;当v≥150km/h时,动应力幅值随速度线性增加。对于高铁有砟轨道,动应力幅值随速度增大而线性增加。高速无砟、有砟轨道路基面动应力幅值的速度影响系数α分别为0.0015和0.0012;高铁无砟铁路轴重系数β=0.074,约为普通和高速有砟铁路β值的1/3～1/2;③提出高铁无砟、有砟轨道路基面设计动应力幅值计算公式分别为σdl=0.119P,v<150km/h,σdl=0.119P［(1+0.0015(v-150)］,v≥150km/h(无砟)和σdl=0.27P(1+0.0012v) (有砟)。研究成果可为高铁路基设计参数取值提供参考及其设计动应力幅值计算公式的修订提供依据。     

高速铁路列车检修库热风系统数值模拟与改进

以京沪高速铁路某列车检修库为例,利用CFD技术,对检修库联合供暖设计方案中列车底部热风系统的实施效果进行了模拟。结合8个典型算例,对检修库内空气速度分布、温度分布、热舒适度指标PMV分布及列车表面的热流密度进行了模拟,确定了合理的送风口位置和最佳的送风参数。     

Recent developments of high-speed railway bridges in China

China’s high-speed railway (HSR) construction industry has been experiencing a golden period of opportunities in the recent decades. Due to the necessity of protecting arable lands and the advantage of rapid construction, bridges (elevated structures) are predominantly used in China’s HSRs, which must meet the critical small settlement requirement. This article first reviews the main technical standards of small- to medium-span HSR bridges, where their comparison with the Japanese standard and International Union of Railway standards is highlighted. Then, the long-span HSR steel bridges are described and discussed case by case. Based on the engineering practice of HSRs, the main achievements and key technologies of HSR bridges in China are provided, followed by the opportunities and challenges of the current and future developments of HSR bridges.     

Distribution of exhaled contaminants and personal exposure in a room using three different air distribution strategies

The level of exposure to human exhaled contaminants in a room depends not only on the air distribution system but also on people's different positions, the distance between them, people's activity level and height, direction of exhalation, and the surrounding temperature and temperature gradient. Human exhalation is studied in detail for different distribution systems: displacement and mixing ventilation as well as a system without mechanical ventilation. Two thermal manikins breathing through the mouth are used to simulate the exposure to human exhaled contaminants. The position and distance between the manikins are changed to study the influence on the level of exposure. The results show that the air exhaled by a manikin flows a longer distance with a higher concentration in case of displacement ventilation than in the other two cases, indicating a significant exposure to the contaminants for one person positioned in front of another. However, in all three cases, the exhalation flow of the source penetrates the thermal plume, causing an increase in the concentration of contaminants in front of the target person. The results are significantly dependent on the distance and position between the two manikins in all three cases. PRACTICAL IMPLICATIONS: Indoor environments are susceptible to contaminant exposure, as contaminants can easily spread in the air. Human breathing is one of the most important biological contaminant sources, as the exhaled air can contain different pathogens such as viruses and bacteria. This paper addresses the human exhalation flow and its behavior in connection with different ventilation strategies, as well as the interaction between two people in a room. This is a key factor for studying the airborne infection risk when the room is occupied by several persons. The paper only takes into account the airborne part of the infection risk.     

A numerical investigation of three different thermosyphon solar water heating systems

This work presents a theoretical evaluation of the performance of three types of thermosyphon solar water heating (TSWH) systems with flat-plate collectors considering different weather conditions. The flat-plate solar collectors considered are the absorber–pipe lower bond configuration (Type I), the absorber–pipe side bond configuration (Type II) and the absorber–pipe upper bond configuration (Type III). The performance of the three heaters have been investigated numerically under the same conditions. The average values of the energetic and exergetic efficiencies, for one of the weather conditions are: 39.47% and 18.21% for Type I, 34.86% and 15.45% for Type II, 32.28% and 13.8% for Type III. This study reveals that, the thermal performances obtained with Type I TSWH is always greater than the two others, and that this configuration leads to an improvement in the efficiency–temperature rise couple, followed by Type II TSWH system.     

TBM隧道在不同围岩条件下的数值模拟分析

通过利用ANSYS有限元分析软件,对TBM法隧道施工的过程进行数值模拟分析,结合隧道的工程地质情况,通过分析其应力应变的状态,提出了ANSYS模拟TBM在不同围岩条件下开挖隧道时围岩应力变化的可行性,得出了TBM隧道在不同围岩条件下的一些基本特征。     

室内空气流动数值模拟的风口模型综述

介绍了目前国际上对室内空气流动进行数值模拟时采用的风口模型方法,并提出了应用于房间空气流动数值模拟的风口模型新思路。     

论高铁候车大厅空气调节净化的重要性

针对高铁候车大厅当前的空气环境,尤其是在特定环境下易受到严重污染的区域,结合国家室内环境标准要求,人们对生活环境质量需求日益增高,从空气调节的工作原理、流程及空气净化技术,分析了当前形势下如何提高高大空间空气质量及空气净化的必要性。     

预测压气法隧道施工中的漏气量的模型研究

在阐述压气法隧道施工原理的基础上,建立了水–气二相流模型来模拟压气法隧道施工过程中超压空气驱替隧道周围土体的孔隙水的水–气二相流过程。该模型同时考虑了土体中气相和水相的流动以及水相和气相相互作用的影响,比较符合水–气二相渗流过程的物理意义。通过工程算例,计算出不同施工进度下开挖面和隧道混凝土衬砌上的空气损失速率以及空气入流对隧道周围土体渗流场的影响,结果表明:在均质的地质条件下,开挖面上的漏气速率一般为常数,而衬砌上的漏气速率将随着隧道长度的增加而线性增大。最后,提出了利用水–气二相流模型进一步提高压气法隧道施工的漏气量的数值模拟精度,需要深入研究的两点意见。     

Fast simulation of temperature distribution in air conditioned rooms by using proper orthogonal decomposition

Real-time control of air conditioning needs dynamic models of temperature distribution and air velocity field in rooms. Complete models, based on computational fluid dynamics (CFD), give this information, but they are too time-consuming for real-time applications. Therefore, a reduced model is needed. In mixed convection, when the air temperature has negligible variations, the velocity field may be considered fixed. In this case, the size of a CFD model may be reduced by solving only the energy balance equation, then putting this equation in the form of state-space and finally by reducing its order by proper orthogonal decomposition (POD). This algorithm was applied to a room equipped with a fan coil. Four fixed airflow fields, corresponding to negligible air temperature variation, were considered, resulting in four airflow patterns: the air jet sticks to the ceiling and reaches the opposite wall, the air jet falls before reaching the opposite wall, the air jet reaches the ceiling without extending along it, and the air jet falls before reaching the ceiling. The reduced model obtained from these airflow patterns was validated by comparing with CFD results for step variation of inlet temperature. As the order of the reduced model is always lower than seven, it may be used for real-time control applications.     

工位空调送风气流微环境评价

模拟了三种送风速度下送风气流在人体活动区形成的速度场、温度场及PMV的分布，结果表明人员活动区存在送风不均匀和温度分层现象，有助于解决吹风感；PMV值在 1和-1之间，可以满足人体热舒适要求。     

大型集中空调水系统调试浅析——以京沪高速铁路上海虹桥站为例

总结了大型集中空调水系统调试过程中需要注意和解决的几个问题,对传统大管径空调水系统冲洗方法提出了质疑,对调试过程中的水流量分配提出了自己的观点,希望为大型集中空调水系统的调试提供一种新的思路和方法.     

Performance evaluation of ductless personalized ventilation in comparison with desk fans using numerical simulations

The performance of ductless personalized ventilation (DPV) was compared to the performance of a typical desk fan since they are both stand-alone systems that allow the users to personalize their indoor environment. The two systems were evaluated using a validated computational fluid dynamics (CFD) model of an office room occupied by two users. To investigate the impact of DPV and the fan on the inhaled air quality, two types of contamination sources were modeled in the domain: an active source and a passive source. Additionally, the influence of the compared systems on thermal comfort was assessed using the coupling of CFD with the comfort model developed by the University of California, Berkeley (UCB model). Results indicated that DPV performed generally better than the desk fan. It provided better thermal comfort and showed a superior performance in removing the exhaled contaminants. However, the desk fan performed better in removing the contaminants emitted from a passive source near the floor level. This indicates that the performance of DPV and desk fans depends highly on the location of the contamination source. Moreover, the simulations showed that both systems increased the spread of exhaled contamination when used by the source occupant.     

水系统中三例气塞故障的分析

对工程中遇到的三例水系统气塞故障加以总结，分析其原因，认为气塞是建筑水系统常见故障，应从设计、施工、运行管理三方面加以重视。