表面粗糙度对微细管内气体流动特性的影响

采用了表面粗糙度粘性系数模型对微细管内的气体流动进行数值模拟，以研究微管内壁表面粗糙度对微管内气体流动的影响。运用本文改进的表面粗糙度粘性系数模型，数值模拟与实验数据十分吻合。计算结果表明，进出口压力一定时，表面粗糙度对流场的压力、密度及温度分布的影响不大，但是对速度场的影响十分显著，表面粗糙度使气体流动速度减小，并使壁面附近的速度梯度减小，从而使通过管道的气体质量流量减小，在微管内的气体流动中，表面粗糙度的影响是不能被忽略的。     

Electroosmotic flow in slit microchannel containing salt-free solution

A theoretical study on the electroosmotic flow through a uniformly charged planar slit microchannel containing a salt-free solution is presented. Based on the exact analytical solutions for the electric potential distribution and the transient electroosmotic flow velocity, a systematic parametric study on the characteristics of the transient electroosmotic flow is then investigated. The results show that the general behavior of electroosmotic flow in a planar slit is similar to that in a cylindrical capillary; however, the characteristic time to reach the steady-state flow, the electroosmotic mobility and the correction factor to the Smoluchowski equation in a slit are larger than those in a cylinder with its diameter equal to the slit width. Furthermore, the osmotic pressure of counterion between two equally charged planar surfaces immersed in a salt-free solution is found to be always repulsive. In addition, the implications of these results on electroosmosis in a microchannel are discussed.     

Effect of Flow Structures on Turbulence Statistics of Taylor-Couette Flow in the Torque Transition State

Direct numerical simulations of Taylor-Couette flow from Re= 8000 to 25000 have been conducted to investigate changes of turbulence statistics in the transition of the Reynolds number dependency of the mean torque near Re= 10000. The velocity fluctuations are decomposed into the contributions of the Taylor vortex and remaining turbulent fluctuations. Significant Reynolds number dependencies of these components are observed in the radial profiles of the Reynolds stress and the transmission of the mean torque. The contributions of Taylor vortex and turbulent components in the net amount of mean torque are evaluated. The Taylor vortex component is overtaken by the turbulent counterpart around Re= 15000 when they are defined as the azimuthally averaged component and the remnants. The results show that the torque transition can be explained by the competition between the contributions of azimuthally averaged Taylor vortex and the remaining turbulent components.     

涂层表面粗糙性对流体噪声的影响

在铝合金回转体表面涂上一定粗糙度的低表面能涂层，涂层表面的不平度平均高度在６．３～１０．０μｍ时，涂层模型表面为光滑水力壁，这时表面粗糙所引起的那部分流噪声可忽略不计．在光滑（Ｒｚ＝３．２～６．３μｍ）的铝合金模型表面喷涂涂层后，涂层表面较粗糙（Ｒｚ＝１０．０～２０．０μｍ）时，同样在相应的频率范围内涂层模型仍有降噪的效果，而且对不同涂层材料其表面粗糙度对流噪声的影响也不相同．     

Heat Transfer in Porous Microchannels with Second-Order Slipping Boundary Conditions

Transport in Porous Media - The paper presents results of a study of forced convection in a vertical flat and circular microchannels incorporating porous medium under slip boundary conditions of...     

空泡流粘性效应研究

我们用激光多普勒技术(LDV)对钝头圆柱体、带小槽1.5度卵形头回转体、带背阶半球头回转体的绕流进行了测量。试验在600×600mm~2水洞中进行,雷诺数从0.75×10~5到6×10~5。给出了平均速度和脉动速度均方根值的分布并做了脉动速度的功率谱。得出了与过去热线流速计测量结果略有不同的结论。并且通过小槽内流动的测量对空泡的产生进行了分析。此外,本文提出一种捡测流动转捩现象的方法,用此法的实验结果与前人一致。     

The Effect of Downsizing on Hierarchical Work Flow Dynamics in Organizations

The objective was to determine the impact of the downsizing of management personnel on the flow of work throughout the organization, given that the quantity of workers (or technicians) must remain the same. In particular the objective of study was to assess the impact of downsizing on performance dynamics, where social factors such as power objectives of the management groups, job insecurity, and perceptions of fairness were not active variables in the process. Three groups of university students (19-33 in a group) were formed to play the Chaos Exercise in a three-level hierarchy. In the three experimental conditions, management groups were downsized during the game from 3 to 2 players, from 2 players to 1, or from 3 players to 1. Nonlinear dynamical structures were explored for each condition and at all three levels of hierarchy using production records generated by each group. Results showed chaos for two out of three conditions at the lowest level of the hierarchy, and usually a tendency toward asymptotic stabilization in middle management, although the functions themselves were markedly varied. The 2-to-1 condition, however, showed a tendency toward performance stabilization at the worker and middle management levels, but chaos at the top management level.     

Effect of Shape on Inertial Particle Dynamics in a Channel Flow

Particle dynamics in a channel flow are investigated using large eddy simulation and a Lagrangian particle tracking technique. Following validation of single-phase flow predictions against DNS results, fluid velocities are subsequently used to study the behaviour of particles of differing shape assuming one-way coupling between the fluid and the particles. The influence of shape- and orientation-dependent drag and lift forces on both the translational and rotational motion of the particles is accounted for to ensure accurate representation of the flow dynamics of non-spherical particles. The size of the particles studied was obtained based on an equivalent-volume sphere, and differing shapes were modelled using super-quadratic ellipsoid forms by varying their aspect ratio, with their orientation predicted using the incidence angle between the particle relative velocity and the particle principal axis. Results are presented for spherical, needle- and platelet-like particles at a number of different boundary layer locations along the wall-normal direction within the channel. The time evolution and probability density function of selected particle translational and rotational properties show a clear distinction between the behaviour of the various particles types, and indicate the significance of particle shape when modelling many practically relevant flows.     

Electroosmotic flow of Eyring fluid in slit microchannel with slip boundary condition

In consideration of the electroosmotic flow in a slit microchannel, the con-stitutive relationship of the Eyring fluid model is utilized. Navier＇s slip condition is used as the boundary condition. The governing equations are solved analytically, yielding the velocity distribution. The approximate expressions of the velocity distribution are also given and discussed. Furthermore, the effects of the dimensionless parameters, the electrokinetic parameter, and the slip length on the flow are studied numerically, and appropriate conclusions are drawn.     

雷诺数对三角翼绕流的影响

应用染色液流动显示技术研究了雷诺数对６０°尖前缘三角翼前缘涡破裂位置、背风面流动结构等的影响，并详细分析了背风面流动随攻角的变化．     

考虑气动热对粘性系数μt影响的压气机流场计算

根据气动热影响叶片壁面附面层粘性系数tμ的理论,把考虑气动热对粘性系数tμ影响的粘性体积力计算方法运用于压气机叶栅三维粘性流场计算。计算时使用有限体积显式时间推进法解算Navier-Stokes方程,用Baldwin-Lomax模型模拟湍流流动。所得结果比不考虑气动热影响的三维计算结果更接近实验结果,能更真实地反映压气机叶栅流场的流动。     

Effect of Spherical Recesses on the Characteristics of Coanda Flow

Sub- and supersonic flows past curvilinear surfaces with spherical recesses are investigated. The Coanda flow was created by a jet flowing out from a plane convergent nozzle into a submerged space along the tangent to a circular cylinder. The forces exerted on the cylinder and the total and static pressure profiles in Coanda jet cross-sections were measured. It is shown that the spherical recesses increase the friction drag at both sub- and supersonic velocities.     

Simulation of the Effect of Water Injection on Volcanic Conduit Flow

The effect on the eruption process of water or steam injection into a volcanic conduit from an adjacent water-saturated stratum is studied. Both steady-state and unsteady processes are considered. The physical characteristics of these eruptions are identified. A mathematical model of such an eruption is proposed for the first time.     

Effect of Unsteady Wind Flow on Galloping of Tall Prismatic Structures

The galloping of tall prismatic cantilevertype structures due to unsteady wind is solvedanalytically. The unsteady wind was considered byadding a time varying wind speed component to the meanwind speed component. In reality, the time-varyingwind speed component is a random phenomenon that can bemodeled as a series of harmonic terms using thetransformation of the unsteady wind speed spectruminto the time domain. In doing this it is apparentthat the structure is subjected to multiharmonicexternal and parametric excitations due to theunsteady wind in addition to the nonlinearself-excited wind forces due to the steady wind speedcomponent. To have a clear insight into the unsteadywind effect, only one harmonic term is considered outof all the harmonic terms. The multiple-scale methodis used to study the effect of primary and secondaryresonances on the galloping response of the structure. Comparisons between the analytical results obtainedfrom the method of multiple scales and the numericalsolutions obtained from numerical integration indicate the accuracy of the analysis and thecomprehensive information obtained from the analyticalsolutions.     

Multiphase Flow Fields in In-situ Air Sparging and its Effect on Remediation

In-situ air sparging (IAS) is used for the clean-up of soil and groundwater that are contaminated with volatile organic compounds in relatively permeable subsurface environments. In this study, we investigated the secondary groundwater and gas flow fields that develop in the vicinity of single and multiple air sparging wells. The purpose is to evaluate their effects on contaminant plume migration and thus, remediation. Governing equations describing multiphase flow and contaminant transport in a three-dimensional domain were formulated and solved using the Galerkin finite element technique. Trichloroethylene was selected as a target contaminant. The increase in air injection contributed to an increase in the size of the IAS cone of influence and the gas saturation levels within the cone. This reduced the groundwater velocity within the cone and increased the zone of detour of groundwater around the air sparging wells. This outcome was quantified and compared under several IAS operations. Different soil permeability characteristics also affected the groundwater and gas flow patterns, and this impacted the remedial performance of the IAS system. Under high ambient groundwater velocity, an air sparging system that uses a single injection well caused the detour of contaminant plumes around injection wells, regardless of air injection rates, and failed to meet the remedial goal specified here. This system was successful for relatively low ambient groundwater velocity environments used here. An IAS system with multiple injection wells was effective in capturing and remediating the detoured contaminant plume, and showed superior performance when compared to a single injection well IAS system. Using IAS simulation, we also analyzed the impact of injection rates on site remediation using single or multiple wells. Design criteria that are based on the results of this study would be useful in enhancing the performance of the IAS systems.     

Effect of a Dispersed Admixture on the Flow Pattern and Heat Transfer in a Supersonic Dusty-Gas Flow Around a Cylinder

A mathematical model of two-phase (gas-solid particle) flow which takes into account particle-particle collisions and the feedback effect of the admixture on the gas parameters is proposed. The dispersed phase is described by a kinetic equation of the Boltzmann type and the carrier gas by modified Navier-Stokes equations. Using this model, a supersonic uniform dusty-gas flow past a cylinder is calculated. The fields of the macroparameters of the admixture and the carrier medium are obtained. The dependence of the heat transfer at the stagnation point on the relative particle size and the free-stream admixture concentration is studied in detail. The ranges of these parameters on which particle collisions and the feedback effect of the admixture on the carrier-gas flow are important are found.     

Effect of Microturbulent Flow on Gallium Crystal Growth from the Melt

The results of experiments on gallium crystal growth under conditions of microturbulent flow in the melt in a nonuniform vibration field are discussed. The vibration field in the conducting melt is generated by superposing profiled constant and oscillating magnetic fields. Among the features of the flow is the onset of intense small-scale turbulent flow which homogenizes the heat and concentration fields in the melt in the neighborhood of the growing crystal. High values of the transport coefficients, in particular, the effective thermal conductivity and diffusion coefficients, which ensure a high degree of supercooling of the melt in the neighborhood of the crystallization front, and a kinetic mechanism of single-crystal growth are recorded.     

Modeling the Effect of Freestream Turbulence on Unsteady Boundary Layer Flow

We present a new version of the two-equation turbulence model, which makes it possible to calculate continuously the entire flow range from laminar to turbulent, including transition, in the case of a time-periodic, high-turbulence-level freestream. The influence of the parameters characterizing the harmonic fluctuations of the external velocity and the freestream turbulence intensity and scale on the parameters of the flat-plate flow are analyzed. A comparison of the numerical solutions with the experimental and theoretical data indicates the possibility of describing the wall flow properties on the basis of a quasi-stationary turbulence model, as the Reynolds number varies from low to high values.     

多孔介质结构对渗流惯性效应的影响规律研究

本文通过局部展开算法研究了多孔介质中排列结构对非线性渗流规律的影响．计算结果表明：规则排列结构的渗流标度律和渗流方向相关,然而非规则排列结构的渗流标度律不依赖于渗流方向而只依赖于多孔介质的几何结构．伴随着排列结构的非规则程度增强,不同方向的渗流阻力变化规律的差异性减小．当流场输运区域较为复杂且不存在较宽直通道时,渗流阻力在较宽雷诺数范围内体现出较为明显的标度律特性．周期性强非规则排列结构中不同区域大小的模型却具有相似的渗流阻力的标度律特性,同时标度律特性与孔隙度的大小相关性不大．阻力非线性标度律由多孔介质结构的不同而取值为2至3之间．