近壁湍流脉动的概率分布函数

采用大涡模拟方法，模拟槽道湍流，获得了不同雷诺数情形下的槽道流大涡模拟数据库．在此基础上，获得了流向和垂向脉动速度的概率分布函数，并运用假设检验，分析了其与正态分布的定量差别．进一步计算了流向和垂向脉动速度的偏斜度、平坦度，讨论了二者在粘性子层、过渡区和对数律区的变化．同时，讨论了粘性子层、过渡区和对数律区流向和垂向脉动速度概率分布函数的特点及其与湍流猝发的高速流下扫和低速流喷发事件的关系．最后，分析了雷诺数对流向、垂向脉动速度分布的影响。     

静水中正方形孔口的有障碍浮射流(Ⅱ)--流场特性分析

在数值计算成果的基础上，对正方形阻力盘浮力射流的流场进行了分析和总结，基于轴线流速的变化规律将盘后流场分为3个区域：回流区、过渡区和自相似区．验证了竖直方向流速自相似性的存在．根据给出的轴线流速的变化图也可以区分盘后3个区域的位置，同时发现各工况在自相似区域的轴线流速沿同一规律曲线变化，采用Chen和Rodi对流速的表示方法，得到了所有工况下自相似区域轴线流速的分布公式，给出了典型工况下阻力盘后不同高度位置处的压强场等值线变化过程，发现盘后各负压中心区域的产生、膨胀、破裂和消失。     

泄爆诱导的湍流、旋涡和外部爆炸

基于k-s湍流模型和Eddy-dissipation燃烧模型，采用同位网格SIMPLE算法，对充满甲烷。氧气预混气的带导管柱形泄爆容器向空气中泄爆的情形进行了数值模拟．根据计算结果。分析了泄爆后外流场中可燃云团、火焰和压力的变化过程．结果表明。外部爆炸是因射流火焰点燃高压区中的可燃云团。从而引起的剧烈湍流燃烧所致．同时还讨论了外流场湍流和涡量的分布特征．射流火焰进入外部可燃云团后，湍流主要分布在平均动能梯度较大的区域。而不在火焰阵面上．涡量分布主要受斜压效应的影响，在压力和密度梯度斜交区域．其值较大．     

复合材料大层数层压矩形截面杆的扭转问题分析

本文根据有效弹性模量理论［１］，采用三维八节点等参数有限元和整体—局部方法，对复合材料大层数矩形厚截面层压杆的扭转问题及其自由边缘效应进行了分析研究，通过算例计算给出了剪切应力在横截面内的分布规律、杆的扭转变形及其在自由边缘区域层间应力的分布情况·由于本文的分析方法可根据需要仅在应力梯度较大的局部区域，按单层逐层划分单元或在单层内再细化单元，以求得单层内精确的应力场和位移场，因此能显著节约计算量与机时，为具有大层数层压杆的扭转强度计算提供了一种有效的方法·     

轴向变速运动弦线的非线性振动的稳态响应及其稳定性

研究具有几何非线性的轴向运动弦线的稳态横向振动及其稳定性．轴向运动速度为常平均速度与小简谐涨落的叠加．应用Hamilton原理导出了描述弦线横向振动的非线性偏微分方程．商接应用于多尺度方法求解该方程．建立了避免出现长期项的可解性条件．得到了近倍频共振时非平凡稳态响应及其存在条件．给出数值例子说明了平均轴向速度、轴向速度涨落的幅值和频率的影响．应用Liapunov线性化稳定性理论，导出倍频参数共振时平凡解和非平凡解的不稳定条件．给出数值算例说明相关参数对不稳定条件的影响．     

磁场、多孔性和各向异性动脉壁有多处狭窄段时对血液流动的影响

建立一个血液流动的数学模型:多孔介质在磁场作用下,血液流过一段有多处狭窄段的弹性动脉;用一个各向异性的弹性圆柱形管道模拟动脉,用粘性不可压缩的导电流体表示血液,动脉有轻微的局部性狭窄,形成一段内腔局部变窄的动脉,并完成该模型的数学分析.详细阐述了血管壁参数对血液流动的影响,参数包括纵向和圆周向的粘弹性应力分量Tt和Tθ、血管壁的各向异性度γ、血管及其周边结缔组织的总质量M、完全栓管中粘性约束的贡献C和弹性约束的贡献K,并用图形表示壁面剪切应力的分布、径向和轴向的速度等.还研究了狭窄形状参数m、渗透率常数κ、Hartmann数Ha和血管狭窄区的最大高度δ,对血液流动特征的影响.研究表明,流动受到周边结缔组织(动脉壁运动)的影响式微,血管壁的各向异性度,是确定动脉材料的一个重要指标.进一步发现壁剪切力分布,随着Tt和γ的增加而增加,随着Tθ,M,C和K的增加而减少.壁面剪切应力分布的传播,以及壁面处阻力阻抗的传播,栓管与自由管相比要低得多;狭窄段咽喉处的剪切应力分布特性,完全栓管和自由管正相反.靠近中心线的俘获区大小,随着渗透率κ的增加而增大;随着Hartmann数Ha的增加而减小.最后,狭窄段非对称时,逐渐形成...     

轴向复合载荷作用下变截面悬臂弹性立柱后屈曲分析

基于轴线可伸长弹性杆的几何非线性理论，建立了同时作用端部轴向集中荷载和沿轴线作用分布轴向载荷的变截面弹性悬臂柱的后屈曲控制方程．采用打靶法直接求解了所得强非线性边值问题，给出了截面线性变化的圆截面柱的二次平衡路径及其过屈曲位形曲线．     

MILU—CG方法和绕旋转圆柱流动的数值研究

本文采用以修正的不完全ＬＵ分解作预处理器的共轭梯度法（ＭＩＬＵ＿ＣＧ），结合高阶隐式差分格式，改进了作者（１９９２）提出的基于区域分解、有限差分法与涡法杂交的数值方法（ＨＤＶ）·系统地研究了雷诺数Ｒｅ＝１０００，２００，旋转速度比α∈（０５，３２５）范围内，绕旋转圆柱从突然起动到充分发展，长时间内尾流旋涡结构和阻力、升力系数的变化规律·计算所得流线与实验流场显示相比，完全吻合·首次揭示了临界状态时的旋涡结构特性，并指出最佳升阻比就在该状态附近得到     

功能梯度棒-弹簧系统的一维约束热应力

求解了功能梯度棒-弹簧系统的一维约束热应力问题.假设棒只存在轴向应变且线膨胀系数和弹性模量与位置坐标是呈幂函数变化,通过得到描述问题的方程组,进而得到棒热应力分布的解析解.结果经退化可得到均匀棒以及功能梯度棒若干问题的解析解.数值算例分析了功能梯度参数等对热应力的影响.     

锥形血管入口区域内管壁应力分析

本文对锥形血管入口区域的流动进行了探讨，导出了压力分布、轴向和径向的速度分布以及流场的切应力分布、管壁应力分布等公式，进行了相应的数值算例的研究和分析，还着重讨论了血管锥度角对管壁应力、压力分布等的影响。     

Investigation of physiological pulsatile flow in a model arterial stenosis using large-eddy and direct numerical simulations

Physiological pulsatile flow in a 3D model of arterial stenosis is investigated by using large eddy simulation (LES) technique. The computational domain chosen is a simple channel with a biological type stenosis formed eccentrically on the top wall. The physiological pulsation is generated at the inlet using the first harmonic of the Fourier series of pressure pulse. In LES, the large scale flows are resolved fully while the unresolved subgrid scale (SGS) motions are modelled using a localized dynamic model. Due to the narrowing of artery the pulsatile flow becomes transition-to-turbulent in the downstream region of the stenosis, where a high level of turbulent fluctuations is achieved, and some detailed information about the nature of these fluctuations are revealed through the investigation of the turbulent energy spectra. Transition-to-turbulent of the pulsatile flow in the post stenosis is examined through the various numerical results such as velocity, streamlines, velocity vectors, vortices, wall pressure and shear stresses, turbulent kinetic energy, and pressure gradient. A comparison of the LES results with the coarse DNS are given for the Reynolds number of 2000 in terms of the mean pressure, wall shear stress as well as the turbulent characteristics. The results show that the shear stress at the upper wall is low just prior to the centre of the stenosis, while it is maximum in the throat of the stenosis. But, at the immediate post stenotic region, the wall shear stress takes the oscillating form which is quite harmful to the blood cells and vessels. In addition, the pressure drops at the throat of the stenosis where the re-circulated flow region is created due to the adverse pressure gradient. The maximum turbulent kinetic energy is located at the post stenosis with the presence of the inertial sub-range region of slope −5/3.     

Influence of induced magnetic field on peristaltic flow in an annulus

This paper looks at the influence of the induced magnetic field on peristaltic transport through a uniform infinite annulus filled with an incompressible viscous and Newtonian fluid. The present theoretical model may be considered as mathematical representation to the movement of conductive physiological fluids in the presence of the endoscope tube (or catheter tube). The inner tube is uniform, rigid, while the outer tube has a sinusoidal wave traveling down its wall. The flow analysis has been developed for low Reynolds number and long wave length approximation. Exact solutions have been established for the axial velocity, stream function, axial induced magnetic field, current distribution and the magnetic force function. The effects of pertinent parameters on the pressure rise and frictional forces on the inner and outer tubes are investigated by means of numerical integrations, also we study the effect of these parameters on the pressure gradient, axial induced magnetic field and current distribution. The phenomena of trapping is further discussed.     

Peristaltic motion of a Jeffrey fluid under the effect of a magnetic field in a tube

This study is concerned with the analysis of peristaltic motion of a Jeffrey fluid in a tube with sinusoidal wave travelling down its wall. The fluid is electrically conducting in the presence of a uniform magnetic field. Analytic solution is carried out for long wavelength and low Reynolds number considerations. The expressions for stream function, axial velocity and axial pressure gradient have been obtained. The results for pressure rise and frictional force per wavelength obtained in the analysis have been evaluated numerically and discussed briefly. The significance of the present model over the existing models has been pointed out by comparing the results with other theories. It is further noted that under the long wavelength approximation, the retardation time has no effect in the present analysis.     

Effects of temperature dependent viscosity on peristaltic flow of a Jeffrey-six constant fluid in a non-uniform vertical tube

This paper deals with the influence of heat transfer and temperature dependent viscosity on peristaltic flow of a Jeffrey-six constant fluid. The two-dimensional equations of Jeffrey-six constant fluid are simplified by making the assumptions of long wave length and low Reynolds number. The arising equations are solved for temperature, velocity profile and axial pressure gradient using regular perturbation method and homotopy analysis method. The integration appeared in the pressure rise is treated numerically to find the solution. The expressions for pressure rise, temperature, pressure gradient and stream functions are sketched for various embedded parameters and interpreted. The graphical results are also presented for five different wave shapes.     

Effects of an induced magnetic field on the peristaltic flow of a third‐order fluid

In this article, we carry out the effect of an induced magnetic field on the peristaltic transport of an incompressible conducting third order fluid in a symmetric channel. The flow analysis has been developed for low Reynolds number and long wave length approximation. Analytical solutions have been established for the axial velocity, stream function, magnetic force function, and axial‐induced magnetic field. The effects of pertinent parameters on the pressure rise per wavelength are investigated by using numerical integration. Besides this, we study the effect of these parameters on the pressure gradient and axial induced magnetic field. The phenomena of trapping and pumping are also discussed. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010     

Investigation of secondary flow and the related instability on an infinite yawed cylinder with Schubauer’s ellipse as section

This paper presents the principal results of a theoretical investigation of the secondary flow and the related instability performed in the laminar incompressible boundary layer on an infinite uniform yawed solid cylinder with Schubauer’s ellipse of axial ratio 2·96:1 as the section normal to the leading edge. The secondary flow profiles and the value of the instability criterion are obtained at different points of the wing section and for various angles of sweepback. It is found that in favourable pressure gradients and at pressure minimum, the secondary flow profiles have negative values. In regions of adverse pressure gradients after the pressure minimum the secondary flow changes sign from negative to positive values and have points of inflexion. The change of sign starts from the surface and extends to the edge of the boundary layer downstream. At some points in adverse pressure gradients the secondary flow profiles have double points of inflexion and values of both signs simultaneously. It is found that an adverse pressure gradient produces more powerful secondary flow than a favourable pressure gradient of the same strength. It is also found that the values of the instability criterion increase with the increasing sweepback whether the pressure gradient is favourable or adverse. At every point of the wing section, there are two values of the criterion for a given sweepback. The effect of adverse pressure gradient on the variation of the criterion is much more pronounced than that of a favourable pressure gradient. It is also seen that the flow is intermittently laminar and turbulent for low values of the chordwise free stream Reynolds number and for low values of sweepback and consists of an irregular sequence of laminar and turbulent regions.     

Direct numerical simulation of the turbulent flow in an elliptical pipe

The turbulent flow in a pipe with an elliptical cross section is directly simulated at Re = 4000 (where the Reynolds number Re is calculated in terms of the mean velocity and the hydraulic diameter). The incompressible Navier-Stokes equations are solved in curvilinear orthogonal coordinates by using a central-difference approximation in space and a third-order accurate semi-implicit Runge-Kutta method for time integration. The discrete equations inherit some properties of the original differential equations, in particular, the neutrality of the convective terms and of the pressure gradient in the kinetic energy production. The distributions of the mean and fluctuation characteristics of the turbulent motion over the pipe’s cross section are computed.     

SOME REMARKS AID PROBLEMS CONCERNING THE GEOGRAPHY OF FANO 4-FOLDS OF INDEX AND PICARDNUMBER ONE

The two-dimensional steady flow of a viscous incompressible fluid in a diverging symmetrical channel is examined. The paper exploits a new series summation and improvement technique (i.e. Drazin and Tourigny, 1996). The solutions are expanded into Taylor series with respect to the corresponding Reynolds number and the bifurcation study is perfomed. Parameter ranges for the Reynolds number, where no, one or two solutions of the given type exist, are computed.     

Pressure and flow in two dimensional numerical bifurcation models

The finite element method has been used to solve the Navier-Strokes equations for steady flow conditions in bifurcations. The results are presented as pressure, velocity and streamline plots at different Reynolds number. The three bifurcations considered have rigid walls and bifurcation angles of 0°, 20° and 180°. For the bifurcation with branch angles 0° and 20° there is flow separation along the inner wall of the outlet branches and large spatial pressure variations, these phenomena being more pronounced at the higher Reynolds numbers. For the bifurcation with a branch angle of 180° the high pressure gradients occured at the outer corner and for the high Reynolds number a vortex formation developed downstream of this corner.     

Nonlinear mathematical analysis for blood flow in a constricted artery under periodic body acceleration

This study analyses the pulsatile flow of blood through mild stenosed narrow arteries, treating the blood in the core region as a Casson fluid and the plasma in the peripheral layer as a Newtonian fluid. Perturbation method is employed to solve the resulting coupled implicit system of non-linear partial differential equations. The expressions for shear stress, velocity, wall shear stress, plug core radius, flow rate and longitudinal impedance to flow are obtained. The effects of pulsatility, stenosis depth, peripheral layer thickness, body acceleration and non-Newtonian behavior of blood on these flow quantities are discussed. It is noted that the plug core radius, wall shear stress and longitudinal impedance to flow increase as the yield stress and stenosis depth increase and they decrease with the increase of the body acceleration, pressure gradient, width of the peripheral layer thickness. It is observed that the plug flow velocity and flow rate increase with the increase of the pulsatile Reynolds number, body acceleration, pressure gradient and the width of the peripheral layer thickness and the reverse behavior is found when the yield stress, stenosis depth and lead angle increase. It is also recorded that the wall shear stress and longitudinal impedance to flow are considerably lower for the two-fluid Casson model than that of the single-fluid Casson model. It is found that the presence of body acceleration and peripheral layer influences the mean flow rate and mean velocity by increasing their magnitude significantly in the arteries.