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关键词： Boundary-layer transition   Boundary-layer instability   Wind-tunnel experiments   Angle of attack  

摘要： This paper investigates the effect of the angle-of-attack (AOA) on the windward boundary-layer stability over a blunt cone with a nose radius of 5 mm. We consider a free-stream Mach number of 6 and a unit Reynolds number of 4.0 x 107 m-1 and conduct both wind-tunnel experiments and stability analyses for AOAs ranging from 2 degrees-10 degrees at intervals of 2 degrees. The results suggest that, as the AOA increases, the pressure gradient across the spanwise range becomes more pronounced, and the windward-side boundary layer becomes thinner. Using bi-global stability analysis, two unstable three-dimensional modes (varicose and sinuous) are identified in the windward boundary layer at various AOAs. The most unstable mode is the varicose V1 mode, in which the amplitude peak is initially close to the windward centerline and gradually shifts to the centerline downstream. Hence, the primary unstable disturbance exhibits a "V-like" distribution along the streamwise direction, which is likely to cause the V-shaped transition front observed in the wind-tunnel experiments. The eN method based on bi-global analysis is used to predict the transition location along the centerline on the windward region of the cone. The results indicate that, as the AOA increases, the transition location shifts forward, in line with our experimental results. Moreover, linear stability theory accurately predicts the eigenfunction and growth rate of the V1 mode obtained from bi-global analysis. This indicates that linear stability theory can be used to predict transitions in the windward boundary layer of a blunt cone at large AOAs under the conditions studied in this paper.

关键词： Hypersonic   Boundary layer   Receptivity   Entropy wave   Vorticity wave  

摘要： Hypersonic boundary-layer receptivity to freestream entropy and vorticity waves is investigated using direct numerical simulations for a Mach 6 flow over a 5.08 mm nose radius cone. Two frequencies of 33 kHz and 150 kHz are considered to be representative of the first and second instability modes, respectively. For the first mode, wall pressure fluctuations for both entropy and vorticity wave cases exhibit a strong modulation yet without a growing trend, indicating that the first mode is not generated despite its instability predicted by linear stability theory. The potential reason for this is the absence of postshock slow acoustic waves capable of synchronizing with the first mode. By contrast, for the second mode, a typical three-stage boundary-layer response is observed, consistent with that to slow acoustic waves studied previously. Furthermore, the postshock disturbances outside the boundary layer can be decomposed into the entropy (density/temperature fluctuations) and vorticity components (velocity fluctuations), and the latter is shown to play a leading role in generating the second mode, even for the case with entropy waves where the density/temperature fluctuations dominate the postshock regions.

关键词： 前交叉韧带重建   步态分析   步态稳定性   肌肉协同模式   非负矩阵分解   压力中心  

摘要： 背景:现有研究初步总结了前交叉韧带重建患者步行时患侧腿肌肉活动与步态稳定性的潜在关联,然而存在观测肌肉类别不全、观测步行动作阶段不完整、未考量多块肌肉间协同作用等问题,亟待进一步完善该研究。目的:监测前交叉韧带重建患者步行时患侧腿部肌肉协同信息,分析肌肉协同信息与步态稳定性的关联。方法:招募24例男性前交叉韧带重建患者,年龄(21.66±4.09)岁,采集受试者步行时患肢的肌电数据与压力中心数据,采用非负矩阵分解算法提取患肢的肌肉协同元参与数量、肌肉协同元峰值激活用时及肌肉相对权重指标,并与压力中心指标进行相关性分析。结果与结论:①累计解析出6类肌肉协同元参与步行活动,其中肌肉协同元参与数量与患者步态压力中心横向位移距离、横向位移速度无显著相关性。在肌肉协同元峰值激活用时方面,主导步态承重反应期的协同元3峰值激活用时与患者步态压力中心横向位移距离、横向位移速度均呈显著负相关(r=-0.413,P=0.045;r=-0.470,P=0.020),其余类型协同元的峰值激活用时与患者步态稳定性指标无显著相关性。在肌肉相对权重方面,主导步态承重反应期的协同元1的股直肌与患者步态压力中心横向位移距离、横向位移速度均呈显著负相关(r=-0.592,P=0.005;r=-0.529,P=0.014);主导承重反应期的协同元3的股二头肌的相对权重与患者步态压力中心横向位移距离呈显著负相关(r=-0.428,P=0.037)。②结果表明,前交叉韧带重建患者的中枢系统会系统调节步行时患肢肌肉协同活动以提升步态稳定性,具体表现为:延长主导承重反应期肌肉协同元激活时间,增强股四头肌的激活程度,以增强患侧腿落地时膝关节离心收缩控制能力,提升膝关节稳定性;增强承重反应期股二头肌激活程度,以增加患侧腿落地时膝关节屈曲程度,增强下肢落地缓冲功能。

关键词： Hypersonic   Thermochemical non-equilibrium flow   Wall temperature effect  

摘要： During the re-entry of a hypersonic aircraft into the earth's atmosphere, the surrounding air experiences dissociation, ionization, and other complex chemical phenomena due to extreme temperature by shock wave. To ensure thermal safety, the thermochemical non-equilibrium effects resulting from real-gas behavior should be taken into account. In this paper, the characteristics of a double-cone hypersonic laminar flow, including distributions of wall pressure, heat flux, and species dissociation are numerically analyzed with incoming enthalpy of 9.65-21.77 MJ/kg. The thermochemical non-equilibrium flow at different enthalpy and wall temperatures is performed with two-temperature model and Park's seven chemical reaction model. It is found that the double-cone flow features complex shock-shock interactions to form triple points. The flow topology is further brought out from the analysis of streamlines. At the lowest incoming enthalpy with isothermal wall conditions, two foci points appear. While others highlight only one focal point. As the increment of incoming enthalpy, the heat flux and dissociation of nitrogen and oxygen also increase. An increasing wall temperature leads to a larger separation bubble and a lower value of heat flux and pressure peak, while massive dissociation occurs without obvious ionization under considered cases.

关键词： 透平压缩一体机   控制系统   保护系统   解决方案  

摘要： 随着现代工业的不断发展,透平压缩一体机作为一种具备节能、高效和可靠等特点的新型设备,展现出广阔的应用前景。但是透平压缩一体机的控制与保护系统设计实现还没有成熟的控制模式。为实现透平压缩一体机的高效、稳定、安全运行,本文针对其控制与保护系统设计进行了研究。文中提出在该系统中应用可编程逻辑控制器(PLC),并详细阐述了PLC在系统硬件和软件设计中的具体应用。研究表明,PLC可实现对透平压缩一体机运行状态的实时监控和过程控制优化,确保系统可靠、灵活、高效运行。本研究充分展示了PLC在透平压缩一体机控制与保护系统设计与实现中的重要作用,为该设备的进一步研发与应用提供了重要参考。

关键词： 回转体   壁面脉动压力   转捩   湍流  

摘要： 采用嵌入式齐平安装的柔性壁面脉动压力传感器阵列,在声学风洞中测量了两种大尺度回转体模型的边界层转捩区频率–空间谱及其谱峰特征和湍流区壁面脉动压力并分析其相似性,得到以雷诺数为频率分段点的转捩区和湍流区壁面脉动压力拟合模型,模型具有一定的适用性。结果表明,回转体艏部转捩区局部雷诺数为5.27×10^(5)~1.1×10^(6),转捩状态由起始到完全发展在转捩特征谱频段的脉动压力带级增加36 dB,特征谱峰无量纲中心频率为0.2基本不变;湍流区壁面脉动压力无量纲频谱在0.1~10范围,符合Smol’yakov模型随无量纲频率的变化规律;相同模型和不同尺度回转体模型湍流区壁面脉动压力无量纲频谱,分别在0.4~4和0.1~10范围,存在3~4 dB和4 dB的尺度效应,且模型尺度大,无量纲谱高。

关键词： 配送效率   智能网联外卖柜   物联网   工业一体机   等离子体消毒   微信小程序  

摘要： 随着外卖行业的持续发展,后疫情时代货物的无接触配送方式逐渐成为消费者的配送新选择。为实现无接触外卖存取的智能化监控与管理,设计了以工业一体机为控制核心的网联外卖柜。系统硬件设计包括柜体的机械结构、控制模块、传感器模块三部分,系统软件设计包括柜体交互应用以及用户微信小程序。该系统能够实现对外卖物品的暂存、消毒、保温、监控及管理等功能,确保外卖等物资安全送至用户处,减少外卖配送人员的等待时间,提高配送效率。经验证,该智能网联外卖柜运行稳定,具有广阔的应用前景。

关键词： 药典委员会   中医基础理论   通用名称   医学名词   名词术语   《中华人民共和国药典》   通用译名   中西药  

摘要： 医学名词应使用全国科学技术名词审定委员会公布的名词。中医基础理论术语、中医临床诊疗术语、腧穴名称与部位、耳穴名称与定位均遵照相应的国家标准执行。没有通用译名的名词术语于文内第1次出现时应注明原词。中西药名以中国药典委员会编写的最新版本《中华人民共和国药典》和《中国药品通用名称》为准。确需使用商品名时应先注明其通用名称。

关键词： TurbSim   脉动风场   气动特性  

摘要： 为开展脉动风场下气动性能数值仿真研究,本文介绍了一种TurbSim/Fluent耦合脉动风场仿真方法。将网格节点信息与求解时间步长导入TurbSim,通过时间迭代得到整个计算域的三维脉动风场。并进行仿真验证,结果发现:当速度入口为湍流脉动风场时,模型时均气动阻力系数与均匀风场相比增大了6.74%,且模型尾流结构也有明显差异。使用脉动风场进行数值仿真对精确流场解析具有重要意义。

关键词： 残差网络   轨道角动量   大气湍流   涡旋光束   自由空间光通信  

摘要： 轨道角动量(OAM)模式的准确识别是大气湍流信道中基于轨道角动量的光通信面临的主要难题。为实现OAM模式的高精度识别,提出了一种基于双通道残差网络实现湍流信道下的OAM模式识别。首先,通过涡旋调制的方法进一步放大相邻阶OAM之间的差异,并设计了改进残差神经网络模型的结构,又将单通道数据输入设计为双通道数据输入,分别将原光束和调制后的光束输入,提高模型的识别精度并保留光束的原本结构。最后,设计了一种基于OAM的通信系统用于验证该方法的可行性。光束传播仿真实验结果表明,改进后的模型训练需要样本数量降低为600,其模型的识别精度达到93%以上。通信系统模拟仿真传输彩色图像的实验结果表明,通过该方法展现出图像的较高保真度,有力地证明了双通道残差网络模型的实用性和有效性。