Effect of Bogie Cavity End Wall Inclination on Flow Field and Aerodynamic Noise in the Bogie Region of High-Speed Trains

Combining the detached eddy simulation(DES)method and Ffowcs Williams-Hawkings(FW-H)equation,the effect of bogie cavity end wall inclination on the flow field and aerodynamic noise in the bogie region is numerically studied.First,the simulation is conducted based on a simplified cavity-bogie model,including five cases with different inclination angles of the front and rear walls of the cavity.By comparing and analyzing the flow field and acoustic results of the five cases,the influence of the regularity and mechanism of the bogie cavity end wall inclination on the flow field and the aerodynamic noise of the bogie region are revealed.Then,the noise reduction strategy determined by the results of the simplified cavity-bogie model is applied to a three-car marshaling train model to verify its effectiveness when applied to the real train.The results reveal that the forward inclination of the cavity front wall enlarges the influence area of shear vortex structures formed at the leading edge of the cavity and intensifies the interaction between the vortex structures and the front wheelset,frontmotor,and front gearbox,resulting in the increase of the aerodynamic noise generated by the bogie itself.The backward inclination of the cavity rear wall is conducive to guiding the vortex structures flow out of the cavity and weakening the interaction between the shear vortex structures and the cavity rear wall,leading to the reduction of the aerodynamic noise generated by the bogie cavity.Inclining the rear end wall of the foremost bogie cavity of the head car is a feasible aerodynamic noise reduction measure for high-speed trains.

Resonance suppression and electromagnetic shielding effectiveness improvement of an apertured rectangular cavity by using wall losses

The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness （SE） of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall loss on the suppression of the resonance effect is investigated. For this purpose, an equivalent circuit model is employed to analyze the SE of an apertured rectangular cavity coated with an inside layer of resistive material. The model is developed by extending Robinson＇s equivalent circuit model through incorporating the effect of the wall loss into both the propagation constant and the characteristic impedance of the waveguide. Calculation results show that the wall loss could lead to great improvement on the SE for frequencies near the resonance but almost no effect on the SE for frequencies far away from the resonance.

Lattice Boltzmann simulation of natural convection in open end cavity with inclined hot wall

Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics （open cavity and inclined walls） is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 （air）. The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10^4 to 10^6 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method （FVM）. The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed.

Filling mode and regularity of vertical centrifugal casting process of titanium alloy in thin-walled cylinder cavity

The mold filling process of titanium alloy in a thin-walled cylinder cavity under vertical centrifugal casting process was studied by means of the hydraulic simulation experiments. Results show that the filling mode of the melt in the cylinder cavity varies with casting wall-thickness. When the casting wall-thickness is less than or equal to the thickness of the first layer during the filling process, the melts fill the cavity from the bottom to the top.When the casting wall-thickness is greater than the thickness of the first layer during the filling process, the melts first fill the largest radius parts of the cavity with a certain thickness of the first layer from the bottom to the top of the cavity, and then they fill the cavity from the larger radius part to the smaller radius part. The melt filling ability increases with the increment of the mold rotational speed and the pouring temperature. In another aspect, the melt filling ability rises with the decrement of the melt viscosity, and the melt with the better filling ability is prone to fill the cylinder cavity layer by layer.

Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Heat exchangers are utilized extensively in different industries and technologies.Consequently,optimizing heat exchangers has been a major concern among researchers.Although various studies have been conducted to improve the heat transfer rate,the use of a wavy wall in the presence of different types of heat transfer mechanisms has not been investigated.This study thus investigates the mixed heat transmission behavior of fluid in a horizontal channel with a cavity and a hot,wavy wall.The fluid flow in the channel is considered laminar,and the governing equations including continuity,momentum,and energy are all solved numerically.The numerical solution is stabilized by using a first-order multi-dimensional characteristic-based scheme in combination with a fifth-order Runge-Kutta method.The flow and heat transfer effects of varying Richardson numbers,Reynolds numbers,wave amplitude,wavelength,channel height,and cavity width are examined.The results indicate that the mean Nusselt number increases with an increase in Reynolds number,wave amplitude,and cavity width,while it decreases with an increase in Richardson number,wavelength,and channel height.The minimum Nusselt number is calculated to be 0.7,whereas the maximum Nusselt number is 27.09.The Nusselt number has only increased by 40%in the higher depths of the cavity,despite the Richardson number being 10,000 times larger.But this figure increases to 130%at lower depths.The mean Nusselt number is thus significantly influenced by channel height and cavity width.The influence of wave amplitude on the mean Nusselt number is twice that of wavelength.

Study on three-dimensional expansion characteristics of four wall combustion-gas jets in confined liquid space

To explore further the launch mechanism of the new underwater launching technology proposed in this paper, the expansion characteristics of four wall combustion-gas jets in confined liquid space must be studied firstly. The experimental device is designed, and the high-speed digital photographic system is adopted to obtain the expansion sequence processes of Taylor cavities formed by the four wall jets. Meanwhile, the influence of the injection pressure on the axial expansion property of the four wall jets is discussed. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the turbulent flow process of the four wall jets expanding in liquid, and the temporal and spatial distribution laws of phase, pressure, temperature, and velocity and the evolution rules of vortices are illustrated in detail. Results show that, accompanied by the jets expanding downstream, the four wall combustion-gas jets get close to each other and achieve convergence eventually under induction of the interference effect between multiple jets. Meanwhile, the heads of the Taylor cavities separate from the observation chamber wall and offset to the central axis of the observation chamber with time going on. The numerical simulation results of the four wall combustion-gas jets coincide well with the experimental data.

Numerical Simulation of Interaction between Supersonic Flow and Backward Inclined Jets Surrounded by Porous Cavity

As one of supersonic mixing techniques, a supersonic mixing technique using a cavity and a porous wall has been proposed. The cavity and the porous wall generate the low speed region in the cavity, which enhances mixing the main flow with the jets. In this study, numerical simulations were conducted to clarify the effects of backward inclined jets on the mixing technique using a porous wall and a cavity. In the numerical simulations, three patterns of jet injections which combined normal jets with backward inclined jets were studied. As a result, the combination of a backward inclined jet and a normal jet generates the suction flow behind the backward inclined jet, which is useful for making the injected jets flow into the cavity. In addition, the introduction of backward inclined jets reduces the total pressure loss. On the other hand, the mass flow rate through the porous holes decreases with increase in the number of the backward inclined jets.

聚合物三腔微管挤出口模结构对胀大变形的影响

聚合物熔体的模内流动状态与模外胀大变形直接影响微挤出制品的成型质量。文中基于Carreau模型,采用数值模拟方法,研究了聚合物三腔微管挤出过程中口模壁厚差与空心度结构特征对胀大变形行为的影响。结果表明,影响挤出胀大变形程度的关键因素是口模出口附近的轴向速度分布;内外壁厚差会导致较大壁厚位置处对应的型坯厚度增大,而较小壁厚位置处的型坯厚度减小,壁厚差变化对薄壁区域壁厚变形影响较大,达到91.4%;空心度减小能提升口模出口附近轴向速度分布均匀性,减小了70.1%的变形程度;基于胀大变形规律逆向补偿设计了口模形状与尺寸,明显改善了制品成型质量。研究结果对聚合物多腔微管的口模结构优化设计具有理论意义与工程应用价值。

基于阻抗匹配的吸声方法

对于低中频声波入射,采用主动吸声方法可以获得较好的吸收性能,而对于高频声波入射则不能达到很好的吸收性能,为此,又提出了通过调节吸声材料后扬声器的表面阻抗来改变吸声系数的半主动吸声方法。将可控扬声器置于吸声材料后面,调节其表面阻抗,使其与空气的声阻抗达到最佳匹配,从而实现对吸声性能的有效调控。实验结果表明:半主动吸声方法可以在不断改变入射声波频率情况下对吸声系数进行有效调整,使吸声系数始终处于最大值。

内壁扩张角度对冲压旋转爆轰燃烧室工作特性影响的数值研究

为研究内壁扩张角度对冲压旋转爆轰燃烧室工作特性的影响,构建了内壁扩张角度从0°~6°变化的5种扩张型燃烧室,基于乙烯-空气对带有凹腔结构的冲压旋转爆轰燃烧室进行三维数值模拟,分析了不同扩张角度下燃烧室的流场特征。计算结果表明:采用扩张型流道可有效减弱新鲜燃料层内的提前燃烧现象,随着扩张角度增大,爆轰波波头高度增加,爆轰波传播稳定性增强;扩张型流道对爆轰波后燃烧产物起到整体加速作用,并未起到整流作用;凹腔结构中涡核中心随着扩张角度的增大逐渐向凹腔后缘壁面移动,回流进入凹腔底部的新鲜燃料增多,凹腔对主流区新鲜燃料卷吸作用增强;采用扩张型流道后,燃烧室凹腔段总压增益和燃烧室出口总压均随扩张角度的增大而降低。

空腔部分填充的轻钢复合墙体耐火性能研究

为提升内填充轻钢复合墙体的抗火性能,开展了2块双层石膏板覆面岩棉内填充非承重轻钢复合墙体的抗火试验研究,探究了不同填充层布置对墙体抗火性能的影响。试验结果表明:相较于空腔全填充墙体,龙骨无填充墙体受火过程中热翼缘温升更慢、冷热翼缘温差更小;龙骨无填充墙体的承重抗火性能优于空腔全填充墙体的承重抗火性能。同时,在荷载比为0.27的条件下,相较于空腔全填充墙体,龙骨无填充墙体的耐火极限提升了11.5%左右,且龙骨无填充墙体的施工更为简便。因此,可考虑采用墙柱无填充的构造形式来代替内填充构造以提升该类墙体承重抗火性能。此外,所建立的轻钢复合墙体受火传热模拟方法适用于龙骨无填充、空腔全填充等不同构造形式的墙体,可为后续轻钢墙体抗火研究提供参考。

办公建筑干挂光伏幕墙构造优化

综合我国不同气候区和太阳能资源区,遴选5座典型城市,运用EnergyPus能耗模拟软件对办公建筑通风式和封闭式两种空腔的光伏幕墙进行能耗仿真。以全年净能耗为目标,优化光伏幕墙朝向和空腔厚度,并采用夏季、冬季高峰周空腔温度对仿真结果进行补充验证。结果表明,通风式光伏幕墙有利于降低建筑夏季冷负荷,封闭式光伏幕墙有利于降低冬季热负荷;夏热冬暖地区通风光伏幕墙空腔厚度越小,节能效果越好;其他地区最佳空腔厚度为30~50mm;封闭式光伏幕墙随空腔厚度增大,节能效果降低。严寒、寒冷、夏热冬暖地区光伏幕墙宜设置在南向,其他地区最佳朝向为西向。

大型薄壁空心构件精密校形工艺研究

针对航天领域大型薄壁空心构件在连续热挤压过程中产生的不良变形问题,提出了充压镦形精密校形工艺。以具有轴向弯曲缺陷的单腔和多腔铝合金挤压件为研究对象,首先,利用有限元仿真探索了关键工艺参数对校形结果的影响,确定了校形后误差值与校形压缩量之间的变化关系。在此基础上,根据校形产品形状设计充压镦形模具,开展空心构件精密校形试验。结果表明,经充压镦形校正后的空心构件具有高度形状精度,满足生产制造标准。充压镦形技术不仅可用于单腔大型薄壁空心构件的精密校形工作,而且可适用于铝合金大尺寸异形多腔构件,有助于满足未来空心构件制造中多样化型号所带来的高效率和高精度要求。

支气管内置管泵药治疗厚壁空洞型肺结核的临床效果

目的探究支气管内置管泵药治疗厚壁空洞型肺结核的临床效果。方法选取赣州市第五人民医院2019年10月至2020年12月收治的60例厚壁空洞型肺结核患者作为研究对象,按照抽签法分为观察组和对照组,每组各30例。对照组采用常规抗结核化疗治疗,观察组在常规抗结核基础上加用支气管内置管泵药治疗。比较两组的痰结核菌转阴率、空洞闭合率、复发率、不良反应。结果两组治疗1个月后的痰结核菌转阴率比较,差异无统计学意义(P>0.05);观察组治疗2个月后的痰结核菌转阴率高于对照组,差异有统计学意义(P<0.05);而治疗6个月后,两组患者的痰结核菌均转阴,差异无统计学意义(P>0.05);治疗1个月后,两组的空洞闭合率比较,差异无统计学意义(P>0.05),而治疗2、6个月后,观察组空洞闭合率为90.00%、93.33%,均高于对照组的43.33%、56.67%,差异有统计学意义(P<0.05);随访1年,两组的厚壁空洞型肺结核复发率比较,差异无统计学意义(P>0.05);两组不良反应总发生率比较,差异无统计学意义(P>0.05)。结论支气管内置管泵药治疗厚壁空洞型肺结核疗效显著,可促进痰找结核菌转阴,提高空洞闭合率,复发率低,无明显不良反应。

球形空腔内爆炸壁面荷载特性研究

为研究球形空腔内部爆炸条件下空腔壁面反射超压的变化规律,对不同半径球形空腔内爆炸进行了数值模拟分析。结果表明,采用1 mm的网格尺寸模拟计算得到的球形空腔内壁面荷载更加接近试验值。随着空腔半径与装药半径之比逐渐增大,空腔内壁面荷载的峰值逐渐减小,且脉宽逐渐增大。

基于试验研究的有空腔幕墙保温系统竖向火特性仿真模拟

针对有空腔幕墙保温系统竖向燃烧进行分析,研究其温度场分布及火焰蔓延规律。通过应用FDS软件建立相关模型进行竖向火蔓延仿真模拟,并与试验研究结果进行对比分析,发现仿真模拟结果与试验结果有良好的吻合度,能够应用该仿真模拟进行更多工况的空腔竖向燃烧研究。另外模拟结果表明空腔内部保温材料燃烧温度能够达到850℃左右时能够引燃,对铝塑板幕墙有较大威胁,会增加空腔内部空气流通,增加火灾蔓延风险。

典型薄壁窄槽深盲腔钛合金铸件工艺数值模拟及优化

聚焦于钛合金铸件,尤其是薄壁窄槽深盲腔结构件的熔模真空离心铸造技术,鉴于钛合金具有较高的化学活性,易与多种大气成分发生反应,因此对型壳材料的选择及其干燥过程提出了严格要求。然而,由于窄槽深盲腔型壳受限于干燥条件,浇注过程中易产生冷隔、欠铸、气缩孔等缺陷,导致其铸件质量的稳定性未能满足服役标准。针对这一问题,采用铸造模拟仿真技术,对金属液充型行为进行精确分析,以确保薄壁区域按序填充,并优化离心铸造中的补缩路径和气体逸散通道,有效解决了密集气孔的问题,实现复杂钛合金铸件的稳定批量生产。

金丝球焊近壁键合技术

在引线键合工艺应用中,由于球焊键合工艺具有键合方向灵活、键合速度快等优势,在半导体芯片的封装互联领域被广泛应用。针对金丝球焊键合工艺中的近壁键合问题进行了研究,从键合方式、劈刀设计两个方面进行优化、改进,制定了两种不同的解决方案,并分析了两种方案的应用局限性。

预制剪力墙全灌浆套筒连通腔工艺与坐浆工艺对比研究

预制剪力墙全灌浆套筒连通腔工艺与坐浆工艺对比分析:制作12个预制剪力墙,将其等分为2组,在预制剪力墙上埋设套筒,每组试件分别进行预制剪力墙全灌浆套筒连通腔操作和预制剪力墙坐浆套筒连通腔操作,利用振动传感器对腔内混凝土进行振动测试,采集浆料振动能量值,通过对腔内浆料进行超声波检测,采集腔内浆料孔隙率。结果显示:预制剪力墙全灌浆套筒连通腔工艺浆料振动能量值和孔隙率低于坐浆工艺。由此可知:预制剪力墙全灌浆套筒连通腔工艺浆料饱和程度高于坐浆工艺,并且浆料孔隙率低于坐浆工艺,故在实际工程中应优先考虑采用全灌浆套筒连通腔工艺。

建筑外墙外保温层脱落原因及预防措施分析

文章结合某学院项目,分析了外墙外保温层脱落的原因,并阐述了建筑外墙外保温层脱落的预防措施,包括更换保温形式、加固保温层、消除热桥效应、采用无空腔满粘构造等,旨在增强建筑外墙保温体系的可靠性,发挥保温隔热功能,避免保温板脱落,从而为广大师生提供安全、舒适的室内外环境。