Three-Dimensional Boundary Layer on a Permeable and Partly Permeable Surface of a Blunt Body

The solution is obtained of three-dimensional equations of laminar boundary layer for a permeable and partly permeable surface both in particular cases and in the most general case in which the flow exhibits no symmetry.     

Control of Velocity Profiles in a Boundary Layer

The control of average velocity in the turbulent boundary layer of a flat plate is investigated theoretically and experimentally. The control is exercised by injecting jets of air into the incident flow. Interpolation expressions are derived for the distribution of average velocities, dependent on the control parameters.     

MHD Boundary Layer Flow of a Power-Law Nanofluid Containing Gyrotactic Microorganisms Over an Exponentially Stretching Surface

This study focusses on the numerical investigations of boundary layer flow for magnetohydrodynamic (MHD) and a power-law nanofluid containing gyrotactic microorganisms on an exponentially stretching surface with zero nanoparticle mass flux and convective heating. The nonlinear system of the governing equations is transformed and solved by Runge-Kutta-Fehlberg method. The impacts of the transverse magnetic field, bioconvection parameters, Lewis number, nanofluid parameters, Prandtl number and power-law index on the velocity, temperature, nanoparticle volume fraction, density of motile microorganism profiles is explored. In addition, the impacts of these parameters on local skin-friction coefficient, local Nusselt, local Sherwood numbers and local density number of the motile microorganisms are discussed. The results reveal that the power law index is considered an important factor in this study. Due to neglecting the buoyancy force term, the bioconvection and nanofluid parameters have slight effects on the velocity profiles. The resultant Lorentz force, from increasing the magnetic field parameter, try to decrease the velocity profiles and increase the rescaled density of motile microorganisms, temperature and nanoparticle volume fraction profiles. Physically, an augmentation of power-law index drops the reduced local skin-friction and reduced Sherwood number, while it increases reduced Nusselt number and reduced local density number of motile microorganisms.     

晶界势垒对晶界层电容器性能的影响

本文从晶界势垒的角度研究了中间夹层的 Schottky 晶界势垒对晶界层电容的介电常数、工作电压等电性能的影响。对在空气中烧成和在还原气氛中烧成的 SrTiO_3晶界层电容器电性能的较大差别给予了一些解释。     

Supercapillary Architecture-Activated Two-Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer

Development of smaller, faster, and more powerful electronic devices requires effective cooling strategies to efficiently remove ever-greater heat. Phase-change heat transfer such as boiling and evaporation has been widely exploited in various water-energy industries owing to its efficient heat transfer mode. Despite extensive progress, it remains challenging to achieve the physical limit of flow boiling due to highly transitional and chaotic nature of multiphase flows as well as unfavorable boundary layer structures. Herein, a new strategy that promises to approach the physical limit of flow boiling heat transfer is reported. The flow boiling device with multiple channels is characterized with the design of micropinfin fences, which fundamentally transforms the boundary layer structures and imparts significantly higher heat transfer coefficient even at high heat flux conditions, in which boiling heat transfer is usually deteriorated due to the development of dryout starting from outlet regions and severe two-phase flow instabilities. Moreover, the approaching of physical limit is achieved without elevating pressure drop.     

SrTiO3独石化晶界层电容器研究

本文研究了低温烧结ＳｒＴｉＯ３晶界层瓷料系统中Ｂｉ２Ｏ３、Ｌｉ２Ｏ、ＳｉＯ２等掺杂剂对瓷料半导化及烧结特性的作用与影响，讨论了将这种瓷料应用于常规多层陶瓷电容器制作技术的工艺特点和技术关键。实验表明，利用晶界偏析技术制造ＳｒＴｉＯ３独石化晶界层电容器是一条可行性好的技术路线。     

Boundary Layer Flow on a Model Propeller

Flash photographs have been made of a model screw propeller under test in a towing tank, to show the areas of laminar and turbulent flow in the boundary layers over the blades. These areas may be defined from the surface patterns made by ejecting a liquid dye from fine holes in the rotating blade, and the change in extent of each region with change of Reynolds number is coupled with the scale effect evident in model tests.     

带化学反应的边界层流动问题中一类弱奇异Volterra积分方程的近似解

研究带化学表面反应的边界层流动问题导出的一类弱奇异Volterra积分方程的近似解。以一些化学反应的阶数为例求出解在零点的分数阶级数展开式及其■有理逼近。通过将发散积分解释为Hadamard有限部分积分,并借助数值积分方法导出解在无穷远点的带高阶对数项的渐近展开式。实际计算表明,给出的解在零点和无穷远点展开式的联合使用可以在整个半无限区间上高效地求解这类带化学表面反应的边界层流动问题。     

掺Nb的SrTiO_3内边界层高介电常数材料

掺 Nb 的 SrTiO_3内边界层高介电常数材料,其相对介电常数(?)值高达7.2×10~4,介电耗损角正切 tgδ<2.5×10~(-2),介电常数的温度系数α_r<2.0×10~(-3)K~(-1),电压系数α_v<5.0×10~(-3)V~(-1)。它不仅是制作电容器的极好材料,而且是压敏电阻材料,其微分电导 dI/dV 在小于击穿电压范围为:(1.15/V~(1/2))×10~(a+bV~(1/2))。材料的特性跟烧结后的晶粒尺寸、过量的 TiO_2和扩散杂质的选择有极其密切的关系。     

压力梯度作用下相干结构的演化

采用共振三波的一个周期作为湍流边界层近壁区相干结构的初值，用直接数值模拟方法对有压力梯度，包括定常压力梯度和变压力梯度作用下相干结构的演化进行了研究，得出其各种特性的变化与实验观测到的结果一致。压力梯度对相干结构初始扰动波的选择以及演化过程都起作用，相比之下对前者的作用更大。条纹结构和流向涡之间有某种内在的紧密的联系，可能是产生流向涡的起因。     

平行平板微通道流场在双电层和边界滑移条件下的解析解

讨论了双电层和边界滑移对微通道液体流动系统的影响.利用双电层动电效应理论对控制方程进行修正,同时引入Navier滑移边界条件考虑边界滑移现象,建立了两种壁面效应同时存在时微流动控制模型,得到了流场的解析解.结果显示,双电层效应抑制流动的发展,使流体在固/液边界附近区域产生回流;边界滑移虽能促进流动发展,但当这两种效应同时存在时,边界滑移的作用变为加强抑制流动,使回流现象更加显著.     

Investigation of Flow in the Vicinity of Porous Material on a Cylindrical Body Subjected to Flow

The results are given of an experimental investigation of the distribution of velocity components in a flow of air in the vicinity of a hemispherical permeable blunting of a cylindrical body under conditions of low injection intensity. A numerical simulation of the flow structure is performed for the parameters corresponding to those used in the experiments. Comparison of the results of physical and numerical simulation revealed a number of special features of flow in the boundary layer on a curved surface under conditions of its gasdynamic conjugation with the inner cavity.     

音速喷嘴喉径对边界层过渡影响研究

滞止压力0.1 ～2.5 MPa下,喉径1.921 ～12.444 mm范围内,21支音速喷嘴的518组流出系数测量结果表明:滞止压力对同一块音速喷嘴流出系数的影响可超过2.3％;2.721 mm音速喷嘴边界层的过渡出现在雷诺数0.48×106;喉径12.444 mm音速喷嘴的边界层过渡出现在雷诺数0.94 ×106,音速喷嘴边界层过渡雷诺数与喉径直接相关.基于测试结果,提出了流出系数与雷诺数之间的经验公式,该公式对流出系数预测偏差小于0.3％.此外,得到边界层过渡雷诺数与音速喷嘴喉径之间的经验公式,该公式外延到日本NMIJ-2013实验工况,预测结果与实验结果具有很好的一致性.     

热处理工艺对铜铝复合母线排界面性能的影响

使用五机架连轧工艺制备了铜铝复合母线排,通过不同热处理工艺对轧态产品进行处理,使用光学显微镜观察了铜铝界面层的形貌,使用显微硬度计测试了界面层的硬度分布,使用能谱对界面处的成分变化进行了分析。结果表明:温度对界面合金化层的影响作用较大;冷却方式对复合母排的力学性能影响较小,复合母排的表面布氏硬度低于铜层的硬度。     

逆压梯度下近壁湍流的喷射和扫掠

采用Fourier谱展开和紧致有限差分格式，选用两组共振三波为相干结构的初值，计算了其在零压和逆压梯度作用下的演化。对演化后期流场的2，4象限的运动进行了详细的分析。结果发现，在逆压梯度下，扫掠对雷诺应力的贡献要强于喷射。无论是在零压梯度还是逆压梯度下，uv和u2在法向的输运主要是靠Q2和Q4这两种运动来完成的。零压梯度下喷射部分对输运的贡献大于扫掠的部分。而在逆压梯度下喷射部分对输运的贡献明显减少，扫掠的作用要强于喷射。     

晶体生长的边界层效应—兼论光学实时观察法晶体生长技术

晶体生长边界层模型起源于流体动力学边界层模型，但两者又不完全相同，晶全生长边界层模型有两方面的含义：（１）在固－液界面处的、垂直于界面的，由杂质和组份构成的质量流决定晶体生长速度；（２）在界面附加溶度一侧的质量浓度流，其浓度分布是决定界面稳定性的基本参数。     

晶体生长的边界层效应—兼论光学实时观察法晶体生长技术

晶体生长边界层模型起源于流体动力学边界层模型，但两者又不完全相同．晶体生长边界层模型有两方面的含义：（1）在固-液界面处的、垂直于界面的、由杂质和组份构成的质量流决定晶体生长速度；（2）在界面附加溶液一侧的质量浓度流，其浓度分布是决定界面稳定性的基本参数．特征扩散长度是表征垂直于界面的质量流的一个重要参数．对熔体晶体生长而言，理论估计此值在0．04～0．4cm之间．光学实时观察法晶体生长技术是一种研究晶体生长过程的新颖方法．它能有效地区分扩散-平流和扩散-对流两种不同的生长状态，其实验测得的KNbO3熔体生长的特征扩散长度值为0．01～0．1cm之间．应用此方法实时观察到胞状结构的形成和发展，也证实了界面附近的质量浓度流是决定界面稳定性的一个重要参数．     

Impact of nocturnal planetary boundary layer on urban air pollutants: measurements from a 250-m tower over Tianjin, China

It is well known that nocturnal planetary boundary layer (NPBL) has important effects on urban air pollutants. However, the direct measurements of the interactions between the NPBL height and urban air pollutants are normally difficult, because such measurements require continuous vertical profiles of air pollutants and meteorological parameters. This paper provides an unique data, which temperature, NPBL, NO(x) and O(3) concentrations are measured at a 250-m meteorological tower in the city of Tianjin, China (a much polluted city located in central-eastern China). The results are analyzed to study the trend of NPBL and the impacts of NPBL on air pollutants in the city. The results show that the measured NPBL height ranges from 100m to 150m. The measurement of 10-year trend of the NPBL height suggests that the averaged NPBL height increases by about 20% between 1995 and 2006. The results also show that the NPBL height has important effects on air pollutants. This study suggests that NO(x) and O(3) concentrations are strongly anti-correlated inside of the NPBL height. During nighttime, NO(x) is directly emitted from the surface and is limited to inside of NPBL (40m), resulting in high NO(x) concentrations near the surface. The high NO(x) concentrations depress O(3), producing low O(3) concentrations near the surface. The measurements of vertical gradient of O(3) show that about 30-50ppbv of O(3) concentrations are chemically destroyed due to the surface emission of NO(x) during nighttime, suggesting that NPBL plays important roles in regulating the diurnal cycle of O(3) at the surface.     

The Effect of Radiation on the Spatial Distribution of the Temperature of Subsonic Flows of Induction Plasma

Results are given of measurements of the temperature characteristics of subsonic flows of air and oxygen plasma, generated by a VGU-4 100-kW induction plasmatron developed at IPM RAN (Institute of Problems of Mechanics of the Russian Academy of Sciences). The values of absolute intensity of spectral lines of oxygen and nitrogen atoms are used to measure the average (over the plasma jet diameter) temperature of atomic level populations (hereinafter referred to as atomic temperature) as a function of the parameters of the mode of generation, namely, the gas pressure in the range from 25 to 200 GPa and the power of anode supply within 29–72 kW. The distributions of the atomic temperature of plasma (T _a ) along the jet are obtained for some modes of generation. The radial distributions of the atomic temperature are obtained for some modes of generation of air and oxygen plasma. Their comparison with the temperature profiles obtained by the calculation of flows of equilibrium plasma in a discharge channel reveals a divergence for values of temperature on the flow axis exceeding 8000 K.     

A Novel Approach to Identify the Thermal Conductivities of a Thin Anisotropic Medium by the Boundary Element Method

A common difficulty arises in characterizing the anisotropic properties of a thin sheet of anisotropic material, especially in the transverse direction. This difficulty is even more phenomenal for measuring its mechanical properties on account of its thickness. As the prelude of such investigation, this paper proposes a novel approach to identify the thermal conductivities of an unknown thin layer of anisotropic material. For this purpose, the unknown layer is sandwiched in isotropic materials with known conductivities. Prescribing proper boundary conditions, one may easily measure temperature data on a few sample boundary points. Therefore, the anisotropic thermal conductivities can be calculated inversely. For the inverse analysis, the boundary element method (BEM) is employed to combine with the conjugate gradient method (CGM). For verifying our analysis, numerical experiments were carried out. The obtained results have shown great computational efficiency and accuracy in identifying the thermal conductivities of the thin anisotropic layer.