Effect of Streamlined Nose Length on the Aerodynamic Performance of a 800 km/h Evacuated Tube Train

The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.

Aerodynamic Design of a Subsonic Evacuated Tube Train System

The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.

An Aerothermal Study of Influence of Blockage Ratio on a Supersonic Tube Train System

Evacuated tube transportation is an important development direction for the high-speed transportation technology of the future.However,a train running at supersonic speed in a closed tube can create an unstable aerothermal phenomenon,causing the temperature to rise sharply inside the tube and endangering the safe operation of trains and equipment.The blockage ratio is one of the key factors affecting the aerodynamic characteristics in the tube.In this paper,a 2 D axisymmetric model and Delayed Detached Eddy Simulation(DDES)based on the Shear Stress Transport(SST)k-ωturbulence model are used to study the aerothermal environment in the tube.The calculation method used in this paper was verified by a wind tunnel experiment.The aerothermal phenomenon and distribution of the flow field in the tube with different blockage ratios were compared and analysed.The results show that the aerothermal environment is significantly affected by the blockage ratio.A choking limit formed in the flow field will aggravate the aerodynamic phenomenon as the blockage ratio increases,which further deteriorates the aerothermal environment of the tube.Moreover,the existence of the choking limit,shock wave,and Mach disk make the flow field in the tube more complicated.

Numerical study on the influence of initial ambient temperature on the aerodynamic heating in the tube train system

The evacuated tube transportation has great potential in the future because of its advantages of energy saving and environmental protection.The train runs in the closed tube at ultra-high speed.The heat quantity generated by aerodynamic heating is not easy to spread to external environment and then accumulates in the tube,inducing the ambient temperature in the tube to rise gradually.In this paper,a three-dimensional geometric model and the Shear Stress Transport(SST)κ-ωturbulence model are used to study the influence of initial ambient temperature on the structure of the flow field in the tube.Simulation results show that when the train runs at transonic speed,the supersonic flow region with low temperature and low-pressure is produced in the wake.The structure of the flow field of the wake will change with the initial ambient temperature.And the higher the initial ambient temperature is,the shorter the low temperature region in the wake will be.The larger temperature difference caused by the low temperature region may increase the temperature stress of the tube and affect the equipment inside the tube.Consequently,the temperature inside the tube can be maintained at a reasonable value to reduce the influence of the low temperature region in the wake on the system.

Aerodynamic simulation of evacuated tube maglev trains with different streamlined designs

Based on the Navier-Stokes （N-S） equations of incompressible viscous fluids and the standard k-ε turbu- lence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag on a maglev train in an evacuated tube was made with ANSYS/FLOTRAN software under different vacuum pressures, blockage ratios, and shapes of train head and tail. The pressure flow fields of the evacuated tube maglev train under different vacuum pressures were analyzed, and then compared under the same blockage ratio condition. The results show that the environmental pressure of 1 000 Pa in the tube is the best to achieve the effect of aerodynamic drag reduction, and there are no obvious differences in the aerodynamic drag reduction among different streamline head shapes. Overall, the blunt-shape tail and the blockage ratio of 0.25 are more efficient for drag reduction of the train at the tube pressure of 1 000 Pa.

The approach to calculate the aerodynamic drag of maglev train in the evacuated tube

In order to study the relationships between the aerodynamic drag of maglev and other factors in the evacuated tube, the formula of aerodynamic drag was deduced based on the basic equations of aerodynamics and then the calculated result was confirmed at a low speed on an experimental system developed by Superconductivity and New Energy R＆D Center of South Jiaotong University. With regard to this system a high temperature superconducting magnetic levitation vehicle was motivated by a linear induction motor （LIM） fixed on the permanent magnetic guideway. When the vehicle reached an expected speed, the LIM was stopped. Then the damped speed was recorded and used to calculate the experimental drag. The two results show the approximately same relationship between the aerodynamic drag on the maglev and the other factors such as the pressure in the tube, the velocity of the maglev and the blockage ratio. Thus, the pressure, the velocity, and the blockage ratio are viewed as the three important factors that contribute to the energy loss in the evacuated tube transportation.

Numerical simulation and analysis of aerodynamic drag on a subsonic train in evacuated tube transportation

The aerodynamic drag on a train running in an evacuated tube varies with tube air pressure, train speed and shape, as well as blockage ratio. This paper uses numerical simulations to study the effects of different factors on the aerodynamic drag of a train running at subsonic speed in an evacuated tube. Firstly, we present the assumption of a steady state, two dimensional, incompressible viscous flow with lubricity wall conditions. Subsequently, based on the Navier-Stokes equation and the k-c turbulent models, we calculate the aerodynamic drag imposed on the column train with a 3-meter diameter running under different pressure and blockage ratio conditions in an evacuated tube transporta- tion （ETT） system. The simulation is performed with FLUENT 6.3 software package. An analyses of the simulation re- sults suggest that the blockage ratio for ETT should be in the range of 0.25-0.7, and the tube internal diameter in the range of 2-4 m, with the feasible vacuum pressure in the range of 1-10 000 Pa for the future subsonic ETT trains.

A study on characteristics of shock train inside a shock tube

Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. lnside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates toward the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a computational fluid dynamics （CFD） analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube.

低真空管道列车关键气动问题研究进展

低真空管道列车系统结合应用了管道运输和磁浮推进技术,是一种颇具潜力的未来地面高速交通方式。列车在极狭长的管道空间内长距离往返,通常诱发以管内壅塞现象为主导的大尺度跨声速流动和多车干扰,导致气动阻力急剧增加和气动热环境恶化,从而面临突出的空气动力学问题。本文从管道全场和列车近场两个视角出发,对管道列车流动特征进行了总结,并对近年来国内外该领域气动力/热/噪声研究的进展进行了梳理。在此基础上,围绕管道列车全线多车运行热点问题,对运行速度、管道阻塞比、发车间隔、运行模式的选取进行了讨论。最后,展望了低真空管道列车气动研究领域未来发展方向,指出高效研究方法、多车运行流动干扰、多车运行气动热、长大管道气动噪声、减阻/降热/降噪技术等是今后需要重点研究的领域。

一种新型抗冲击曳光管设计与验证

根据某型现代小口径高炮武器系统曳光训练弹的研制要求,设计了一种新型抗冲击曳光管,对曳光管壳、曳光组件、曳光装药方案及曳光药剂抗冲击结构进行了优化,并对曳光管发火性能、动态发光强度和曳光时间进行了试验验证。结果表明,该曳光管在分别保常温(15℃,48h)、低温(-40℃,48 h)和高温(50℃,48 h)后,均能够满足动态发光强度不小于3 000 cd、曳光时间不小于6 s、曳光颜色为红色的技术指标要求,从而实现在弹丸4 000 m飞行轨迹上指示弹道的功能。

夹管训练结合渐进性盆底肌锻炼在前列腺增生切除术后军队退休干部患者膀胱功能康复中的作用

目的探讨夹管训练结合渐进性盆底肌锻炼在前列腺增生切除术后军队退休干部患者膀胱功能康复中的作用。方法选取空军军医大学第二附属医院2020年3月至2021年5月收治的行手术治疗的186例前列腺增生军队退休干部患者作为研究对象,依照信封随机法分为观察组和对照组,每组93例;对照组采用常规康复训练干预,观察组采用夹管训练结合渐进性盆底肌锻炼方案干预。在患者康复训练前及康复训练6个月后对治疗效果进行评价,包括临床疗效、控尿能力、尿动力学相关指标、国际前列腺症状评分、国际下尿路症候群症状(LUTS)评分、生活质量(QoL)评分、改良Barthel指数(MBI)、不良反应、泌尿道感染率及再次入院率。结果康复训练6个月后观察组临床疗效优于对照组(P<0.05),排尿、漏尿的次数少于对照组(P<0.05),恢复控尿的时间短于对照组(P<0.05),漏尿点压力(LPP)和最大尿道闭合压(MUCP)大于对照组(P<0.05),国际前列腺症状评分和LUTS评分低于对照组(P<0.05),MBI和QoL评分高于对照组(P<0.05),观察组泌尿道感染率和再次入院率低于对照组(P<0.05)。结论夹管训练结合渐进性盆底肌锻炼可有效促进前列腺增生切除术后军队退休干部患者的膀胱功能康复,具有较高的临床价值。

间歇性经口至食管管饲法联合康复训练对脑卒中后吞咽障碍患者的影响研究

目的:研究间歇性经口至食管管饲法联合康复训练对脑卒中后吞咽障碍患者病耻感、营养状态及吞咽功能的影响。方法:选取2019年1月—2021年12月南阳市第二人民医院收治的150例脑卒中后吞咽障碍患者作为研究对象,按照随机分配原则分为实验组和对照组,每组各75例。对照组患者接受常规护理治疗模式,实验组患者行间歇性经口至食管管饲法联合康复训练模式,比较两组患者治疗效果,比较干预前、干预后两组患者病耻感程度、吞咽功能评分及营养状态评分情况。结果:干预后,实验组患者病耻感程度评分均低于对照组患者,差异有统计学意义(t=73.613、177.429、30.003,P<0.05)。干预后,两组患者洼田饮水试验评分、标准吞咽功能评定量表(SSA)评分均低于干预前,差异有统计学意义(P<0.05)。实验组患者干预后营养风险筛查2002(NRS2002)评分低于对照组患者,差异有统计学意义(t=8.717,P<0.05)。结论:间歇性经口至食管管饲法联合康复训练应用于脑卒中后吞咽障碍患者中,对于改善患者吞咽功能具有显著的临床效果,且能够降低患者的病耻感,改善患者的营养状况,减少不良反应的发生。

护理专案在心脏外科术后获得性吞咽障碍患者中的应用效果

目的 探讨护理专案在心脏外科术后获得性吞咽障碍患者行吞咽康复训练中的应用效果。方法 采用便利抽样法,选取2021年7月—2023年6月在厦门大学附属心血管病医院住院的60例心脏外科术后发生获得性吞咽障碍患者为研究对象。将实施护理专案前的30例患者设为对照组;将给予护理专案后的另外30例患者设为观察组。比较2组患者康复训练执行率、鼻饲管平均留置天数及吞咽障碍并发症(主要为显性误吸及吸入性肺炎)发生率。结果 观察组吞咽障碍康复训练执行率为90.00%,高于对照组的20.00%,差异有统计学意义(P <0.05);观察组鼻饲管平均留置天数短于对照组,吞咽障碍并发症总发生率低于对照组,差异有统计学意义(P <0.05)。结论 护理专案可提高护理人员吞咽障碍康复执行率,降低患者鼻饲管平均留置天数,有效促进心脏外科术后吞咽障碍患者康复进程,改善患者预后。

静脉输液治疗培训盒联合同步投影在留置针冲封管培训中的应用

目的探讨一种静疗教学培训盒联合同步投影在留置针冲封管培训中的应用。方法选取2021年7月至2022年6月南昌市第一医院各个科室定期参与静疗专科培训的300名护士作为研究对象,采用随机数字表法将其分为试验组和对照组,每组各150名。两组均按照《临床静脉导管维护操作专家共识》实施操作技术教学,试验组运用新型静疗培训盒装置联合同步投影进行留置针冲封管维护培训。比较培训前后两组的理论知识、留置针维护冲封管操作考核、1 min找错训练结果及护士对于培训的满意度。结果试验组的理论知识成绩高于对照组,差异有统计学意义(P<0.05);试验组的操作成绩高于对照组,差异有统计学意义(P<0.05);试验组的1 min找错训练得分及满意度高于对照组,差异有统计学意义(P<0.05)。结论结合静疗教学培训盒联合同步投影在留置针冲封管培训,能提高专科护士的专科理论知识,工作坊的自主操作模式让专科护士准确掌握对留置针使用不同输液接头进行冲封管操作的规范性,大大提高了专科护士对培训的满意度。

真空管道列车动态运行气动特性研究

研究真空管道列车瞬态气动特性能为建设多态耦合真空管道列车实验平台提供参考。建立了三维真空管道列车模型,采用剪切应力运输(Shear Stress Transport,SST)k–ω湍流模型求解流场,通过对比不同时刻列车匀速和加速时的气动阻力、压力分布及流场特性,揭示了加速度对真空管道列车气动阻力的影响机制。研究结果表明:头车和尾车气动阻力主要受管道壅塞和尾部激波脱离的影响,在非壅塞状态下,尾车阻力增长缓慢而头车阻力基本不变。相比于加速工况,匀速工况启动速度较大,斜激波反射造成列车表面压力波动,波动幅值随时间逐渐降低。加速时头车压缩前方空气过程较缓慢,前驱激波强度较低,头车气动阻力和周围压力的变化滞后于列车运行速度的变化,且加速度越小滞后效果越明显。在匀速运行阶段,壅塞段和尾部激波段长度与运行时间成正比。

极端温度下高速铁路钢管混凝土拱桥行车安全

研究目的:为研究温度荷载作用下桥梁结构产生的变形对桥上行车安全性的影响,以成贵高铁某钢管混凝土拱桥为研究对象,基于ANSYS建立大跨桥梁-轨道精细化有限元模型,分析不同温度荷载作用下结构变形规律。在此基础上,将桥梁-轨道结构有限元模型导入SIMPACK中进行联合仿真,构建列车-轨道-桥梁耦合振动分析模型,最后从列车运营安全性与舒适性方面讨论不同温度荷载作用和不同车速下列车动力响应指标的变化规律。研究结论:(1)桥梁上挠温致变形引起的轨道附加不平顺比下挠更不利;(2)组合温度作用下,行车安全性指标仅轮重减载率出现超限,建议将其作为高速铁路桥上行车安全的主要评价指标;(3)温度梯度是导致轮重减载率出现超限的重要原因,实际工程中分析温度作用对列车行车安全的影响时,应考虑温度梯度的作用;(4)垂向Sperling指标对温度作用十分敏感,为保障行车舒适性,列车在极端温度条件下行驶时应控制车速;(5)本研究成果可为钢管混凝土拱桥的行车安全性评价提供参考。

真空管道磁悬浮列车气动特性及激波效应三维研究

近年来,真空管道列车系统以其减阻降噪、高速运行的特点成为高速列车新的研究方向。真空管道列车运行环境复杂多变,对管道内部气动特性及流场结构的研究在真空管道列车的设计和优化中尤为重要。研究基于SST k-ω湍流模型及大涡模拟方法,采用三维数值模型对阻塞比为0.15的真空管道磁悬浮列车系统在马赫数为0.490~0.980的来流条件和0.3~0.1 atm的管道压力下进行稳态和非稳态模拟,得到列车周围外部流场的气动特性,详细阐述了列车尾流激波的形成和传播。根据不同来流马赫数和压力条件将流场分为3类典型工况,并沿流动方向将流场分为5个区域分析流场特性。结果表明,随着来流马赫数从0.490增加到0.654,尾车肩部开始出现激波。随着来流马赫数进一步增加至0.817,尾流区域出现斜激波、“X”型激波结构等复杂流动现象,不同来流马赫数条件下跨声速流场中的气流马赫数分布相似,压力系数呈现梯度分布。激波与尾涡、边界层相互干涉与融合,成为尾流流场的主要结构。研究成果可为真空管道列车不同来流速度和不同真空度情况尾流激波抑制以及气动阻力优化设计提供工程指导。

二维管道列车交会激波特性分析

列车在低真空管道内运行可以极大的减少阻力,但同时面临激波效应等难题。建立二维管道仿真模型,采用可压缩非定常SST k-ω湍流模型并结合滑移网格技术,研究不同起始交会距离、速度、时间下管道内激波演变规律。结果表明:两车相距较远时,列车前方壅塞区段向前推进,壅塞长度随时间线性递增,正激波相互扰动时,阻力/压力绝对值激增;两头车交会时,阻力/压力绝对值再次激增达到最大值,随列车的运行又急剧下降到相对平稳状态,交会过程中阻力/压力沿车尾方向先降低后增大。车尾区域存在激波、膨胀波相互交叉干涉现象,波系较为复杂,沿车尾方向激波反射强度减弱。随交会距离的增加,列车行驶在短、中长隧道(<1500 m)阻力/压力变化剧烈,长隧道(>1500 m)阻力/压力变化幅值较小。随速度的增加,列车前方壅塞区段长度缩短,阻力/压力绝对值增大,车尾激波串长度增加,强度减弱。

真空管道高速列车系统中管道压力分布研究

针对真空管道内列车运行对管道压力分布的影响,本文建立了单车运行和两车交汇的真空管道交通系统模型,通过Fluent湍流模型和重叠网格划分技术,得到真空管道交通系统的压力场,分析了压力场的变化规律。结果表明,列车运行速度和阻塞比对管道内压力分布影响较大,管道真空度影响较小,列车表面压力分布受列车运行速度影响较大。两车交汇时,真空管道内压力分布变化较大,达到110kPa/s。该研究为真空管道高速列车系统中管道压力设计提供了理论指导。