Superaerodynamics, Mechanics of Rarefied Gases

Verification of the Flow Regimes Based on High-fidelity Observations of Bright Meteors

“…Columns are organized as follows: (1) the meteoroid ID; (2-3) the source height of the shock wave and the associated error; (4) the entry velocities (which are used to estimate the incoming gas flow velocity, as described in the main text); (5-8) the gas temperature, gas density, sound speed and Mach number upstream, respectively; (9-14) the downstream conditions in the following order: (9) gas temperature, (10) gas density, (11) Mach number, (12) sound speed, (13) gas velocity and (14) Table 3. Knudsen numbers, Reynolds numbers and meteoroid flow regime analysis: (1) event ID; (2-6) Knr as derived from the five possible masses discussed in Section 3; (7-11) the Re number using these five masses; the flow regime according to the classical scale (see the Introduction) and the scale described in Tsien (1946) as obtained from the JVB, IE and FM masses (12-13), and the masses derived from the infrasound detected signal (linear and weak shock period) (14-15). Figure 1 of Popova et al (2000).…”

“…Tsien (1946) noted the importance of these viscous effects and outlined a flow regime classification based on the comparison of the mean free path of the gas molecules (l) to the thickness of the boundary layer (δ). This scale is then described as in Tsien (1946): i) Free molecular regime, Kn>10;…”

A model of thermal conductivity for planetary soils: 1. Theory for unconsolidated soils

“…This configuration is observed when the pressure and/or when the particles are small (e.g., small typical pore dimension L). The opposite case (slip flow regime) [Shen, 2005;Tsien, 1946] is observed when l is much smaller than the typical pore dimension (e.g., large Figure 2. Schematic view of a contact between two nonspherical realistic natural grains (conductivity k sol ).…”

“…[17] First, when the pressure approaches zero (e.g., vacuum), Kn À1 tends to be extremely small and the effective gas conductivity tends to be zero (free molecular flow regime). Second, for intermediate pressures (and therefore intermediate Kn À1 , in the transitional regime [Shen, 2005;Tsien, 1946], e.g., where the gas thermal conductivity is strongly pressure-dependent and increases with increasing pressure), experiments and theoretical constraints Strieder, 1980, 1981;Pollard and Present, 1948;Shen, 2005] suggest that an expression of the form of equation (12) be used to determine k gas :…”

Numerical Analysis of Train Aerodynamic Drag of Vacuum Tube Traffic

“…铁路在国家的经济和社会发展中起到了至关重 要的作用。随着国家铁路网的建设和人民对时间要 求的提高，铁路还要面临进一步提速的问题。当列 车速度提高到 400 km/h 以上时，空气阻力将占到总 * 高铁联合基金重点(U1334205)和广东省教育厅青年创新人才类(2016 KQNCX172)资助项目。20180704 收到初稿，20181212 收到修改稿 阻力的 90%以上，严重影响列车运行的能耗问题 [1] ； 气动噪声随车速急剧增大， 严重影响周边居住环境； 横风等外界气候条件会加剧列车运行稳定性的安全 隐患 [2][3][4][5][6][7][8] 。诸如此类的问题对运行在常压下的高速列 车而言会接踵而来，那么构建真空运营环境的设想 应运而生。 目前，真空管道交通尚无全面的研究先例可 供参考。国外研究方面，对真空管道高速交通的 设想主要有两种：美国的 ETT 系统和瑞士的超高 速地铁。美国 ETT 公司只是对真空管道运输系统 的总体设想进行了介绍，并未对其列车空气动力 学问题进行深入研究；瑞士超高速地铁研究中只 包含了一小部分高速车辆与管道内的空气动力学 问题 [9][10] 。国内研究方面，西南交通大学牵引与动 力国家重点实验室成员、两院院士沈志云 [11] 认为， 真空管道技术可以很好地为"和谐号"高速列车 的进一步提速提供支撑。同时，ZHANG 等 [12][13][14][15] 对真空管道运行的可行性进行了全面系统的研 究。在数值计算方面，西南交通大学周晓等 [16] 采 用二维、定常、不可压缩湍流对真空管道内 6 种 阻塞比及 4 种速度运行的列车周围流场进行数值 模拟，得出了真空管道内阻塞比对列车空气阻力 的影响规律；列车是具有流线型复杂头型的三维 模型，且近地面运行，不能忽视其三维效应，青 岛科技大学贾文广等 [17] 运用三维模型，不可压缩 气体湍流数值模拟，分析在一定真空度、一定运 行速度、不同阻塞比下真空管道交通系统温度场 和压力场的耦合变化规律；华东交通大学的汤兆 平等 [18] 建立三维参数化模型，不考虑空气的可压 缩性，研究了管道压力、行驶速度、车头外形以 及阻塞比等参数对其空气阻力、气动升力的影响 规律；随着车速的不断提高，马赫数超过了 0.3， 同时在密闭管道内气体必然存在压缩效应，西南 交通大学刘加利等 [19][20] [21][22] / Kn L [21][22]…”