环形截面螺旋管道内的粘性流动

根据张量分析,建立了非正交的曲线柱坐标系巾的N-S方程,采用摄动法求解环形截面螺旋管道内的粘性流动。结果表明:环形截面上存在二次流     

旋转方形截面螺旋管内流动与传热特性

利用数值计算方法研究了旋转矩形截面螺旋管内的粘性流动，分析了在离心力，科氏力共同作用下曲线管道中的二次流动结构、轴向流速分布、截面温度分布、摩擦系数比以及管道Nusselt数比随各参数的变化情况。计算结果表明：当旋转方向和主流方向相同时，旋转的作用与增大Dean数的作用相同，使得管道摩擦系数变大，管道换热效果增强，而当旋转方向和主流方向相反时，管道内流动结构变化十分明显，当F≈-1．2时(F为科氏力与离心力之比)，二次流出现类似于直扭管内的鞍状流动结构，轴向速度类似于静止直管内的流动结构，管道内的摩擦系数与静止直管内的摩擦系数大约相等，换热效果减至最弱；挠率对流动结构以及摩擦系数比和Nusselt系数比的影响效果与F有关。     

基于无网格Galerkin法求解矩形绝缘管道内的磁流体流动

无量纲磁流体流动控制方程中的哈特曼数较大将导致数值计算发散或误差过大。将无网格Galerkin法引入绝缘管道内的稳定磁流体流动计算中,针对磁流体控制方程中大哈特曼数导致计算误差大的情况,对无网格Galerkin法添加了稳定项。计算结果表明,同等条件下,添加了稳定项的无网格Galerkin法总体相对误差远小于标准无网格Galerkin法的结果,且可以计算哈特曼数最大达50000绝缘管道内的磁流体流动。     

自平衡端头载荷问题衰减率的分析与计算

给出了自平衡端头载荷问题应力衰减率分析的一种方法．用边界单元法求得了在端面自平衡载荷作用下，具有椭圆截面和矩形截面的弹性柱体内应力场的最小衰减率。计算结果表明：当椭圆截面的长短轴之比和矩形截面的长宽之比变化时，最小衰减率变化很小．     

环形截面螺旋管道内二次流动特性的研究

从曲线柱坐标系下的N-S方程出发,以曲率和挠率为小参数,采用摄动法求解了环形截面螺旋管道内的黏性流动,给出了完全二阶摄动解,结果表明：当挠率为零时,二次流表现为上下对称的四个涡;当挠率不为零,涡的对称性遭到破坏,二次涡的强度和个数受De数和环形截面内外径之比δ的影响,轴向速度最大值在De数较小时靠近管道的内侧,随着De数的增加,其最大值向外侧移动。     

管内定型流传热过程的有效能损失

对管道内充分发展对流传热过程的有效能损失进行了分析．根据定型流状态下定热流与定壁温换热条件的特点,经代数推演,得到了这两种条件下的表征换热状态、流动功耗以及黏性变化的无量纲形式的有效能损失关系式,适用于不同截面形状的管道内的层流与湍流工况下的有效能分析．     

汶川大地震后水坝建设中若干问题的思考

应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动 特性进行了分析．对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移 长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似 解．以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进 一步揭示了高压驱动下液体微管道流动偏离经典Hagen-Poiseuille(HP)理论的原因．     

高压下液体微管道流动的摄动分析

应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动特性进行了分析．对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似解．以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进一步揭示了高压驱动下液体微管道流动偏离经典Hagen-Poiseuille(HP)理论的原因．      

矩形截面管内电流变液的流动

基于伽辽金方法，导出了矩形截面直管内泊肃叶流动的一阶和二阶近似解．在此基础上，研究了电流变单链的变形问题，并得到了描述它形状的多项式函数．     

半椭圆和半圆环截面弯曲中心的分析解

本文利用对称截面悬臂梁在力作用下的弯曲解,推导出半椭圆截面和半圆环截面弯曲中心的分析解。在推导过程中算出了半椭圆截面扭转刚度的精确解,并在椭圆长短轴相等和圆环内半径趋于零的两种情况,分别给出半圆环截面弯曲中心的分析解。     

Results of direct numerical simulation of turbulent flow in a pipe of elliptical cross-section

Within the framework of the complete Navier-Stokes equations the turbulent flow in a pipe of elliptical cross-section with semiaxis ratio b/a = 0.5 is directly calculated for the Reynolds number Re = 6000 determined from the mean-flow velocity and the hydraulic diameter. The distribution of the average and pulsatory flow characteristics over the pipe cross-section are obtained. In particular, the secondary flow in the cross-section plane, typical of turbulent flows in noncircular pipes, is calculated. The equation for the longitudinal vorticity which determines the shape and intensity of the secondary flow is analyzed. In the balance equation for the pulsation kinetic energy the behavior of all the terms that characterize energy production, dissipation and redistribution over the pipe cross-section is described.     

Rarefied Poiseuille flow in elliptical and rectangular tubes

An isothermal steady rarefied gas flow in a long channel (tube) of elliptical or rectangular cross-section under the action of a given pressure gradient (Poiseuille flow) is studied on the basis of the Bhatnagar-Gross-Krook model. The solution is obtained using a conservative higher-order method. The velocity field in a channel cross-section is investigated as a function of the rarefaction degree and the cross-section geometry parameters. The main calculated function is the gas flow rate through the tube. The solutions obtained are compared with the available results.     

椭圆截面弹体侵彻砂浆靶规律分析

为研究椭圆截面弹体侵彻混凝土靶规律,基于动态球形空腔膨胀理论,建立椭圆截面弹体侵彻受力模型,计算典型椭圆截面弹体阻力规律和侵彻砂浆靶深度。在此基础上,采用弹道炮发射平台,开展相同质量和长度的2种典型椭圆截面弹体及圆截面弹体垂直侵彻半无限砂浆靶实验。结果表明:理论模型能够反映椭圆截面弹体受力情况,并与实验研究结果吻合较好;椭圆截面弹体长短轴参数的改变对侵彻性能影响较为显著。     

Transient viscoelastic helical flows in pipes of circular and annular cross-section

Start-up helical flows for Oldroyd-B and upper-convected Maxwell fluids are studied in straight pipes of circular and annular cross-section. The differential form of the constitutive equation leads to partial differential equations which are second-order in space and time. Apart from the condition that the fluid is initially at rest another initial condition is required to complete the solution process. By comparing results derived from the integral form of the constitutive equation we show that an appropriate initial condition may be found. Numerical results for start-up rotational flow in pipes of annular cross-section are presented.     

Steady laminar flow of a power-law fluid in a curved pipe of circular cross-section with varying curvature

The steady laminar flow of power-law fluid through pipes of circular cross-section, whose center-line curvature varies locally, is analyzed theoretically. The flows, in three kinds of pipes whose center-lines are specified by

as examples of once, twice, and periodically-curved pipes, respectively, are discussed in comparison with Newtonian flow. The analysis is valid for any other two-dimensionally curved pipes, when the center-line curvature is small.     

A semi-analytical approach for temperature distribution in Dean flow

Numerical simulations of the flow field and heat transfer require the conjugate solution of the Navier–Stokes and energy equations, a highly compute-intensive process. Here a semi-analytical approach is proposed to solve the energy equation in curved pipes. It requires the flow velocity field, the wall temperature, and the temperature at only one point of the flow cross-section to provide the entire temperature field.     

在椭圆横截面弹体正侵彻下有限厚铝靶的破坏模式及响应特性

基于30 mm口径弹道炮平台,开展了3种不同椭圆横截面弹体在200~600 m/s撞击速度范围内正侵彻2A12铝靶的实验,获得了2A12铝靶的破坏形貌及弹体的剩余速度。在此基础上,建立了相应的数值模型,结合实验结果验证了所建模型的有效性,并系统分析了弹体横截面长短轴长度比对靶体的破坏情况及响应特性的影响。研究结果表明:弹体最大横截面面积是影响弹体剩余速度的主要因素,而弹体横截面长短轴长度比对弹体剩余速度的影响较弱;在圆形横截面弹体侵彻下靶体背部形成的花瓣大小和形状一致,空间分布均匀,而在椭圆横截面弹体侵彻下,随着弹体横截面长短轴长度比的增大,靶体背部形成的花瓣数量增加、尺寸变小,且在短轴方向的花瓣数量和靶体表面隆起高度均大于长轴方向的;靶体在圆形横截面弹体侵彻下的径向位移、径向应力和切向应力与其在椭圆横截面弹体侵彻下的显著不同,前者沿周向方向各点的变化规律基本一致,靶体处于简单的压缩状态,切向应力为零,而后者各点的应力状态与弹体横截面长短轴长度比和周向角密切相关,靶体受到压缩和剪切应力的耦合作用。     

椭圆截面弹体斜侵彻金属靶体弹道研究

为研究椭圆截面弹体对半无限金属靶体的侵彻弹道规律,基于14.5 mm弹道枪平台,开展了椭圆截面弹体在0°～20°倾角、850～950 m/s撞击速度下对2A12铝合金的斜侵彻试验。基于空腔膨胀理论及局部相互作用模型,建立了椭圆截面弹体侵彻弹道模型,并结合试验数据验证了模型的准确性。在此基础上,进一步分析了椭圆截面弹体长短轴之比、绕弹轴旋转角度、弹体撞击速度对侵彻弹道的影响规律。弹体长短轴之比为1.0时,弹体退化为尖卵形圆截面弹体,且椭圆截面弹体侵彻弹道稳定性随长短轴之比的增大而变弱,最优长短轴之比为1.0,即尖卵形圆截面弹体。椭圆截面弹体绕弹轴旋转一定角度后,侵彻弹道在平面曲线与空间曲线之间变化,当旋转角度为0°、90°时,侵彻弹道为二维平面弹道,当旋转角度在0°～90°之间时,侵彻弹道为三维空间弹道。当弹体撞击速度由800 m/s提升至1000 m/s时,椭圆截面弹体姿态角增量由18.6°降至17.8°。     

Steady laminar flow through thin curved pipes

Let R, τ denote, respectively, the radius of curvature and radius of torsion of the pipe (centre-line) and let a be a typical cross-sectional diameter.

The major part of the present paper addresses the case of flows through pipes of constant cross-section; (Re)²(a/R), Re(a/τ), (a/R) and (a/τ) all being small. Re is the Reynolds number for the flow. It is found that, even without further specifications of the details of the pipe, many important results can be obtained about the secondary flow which occurs and the pressure losses resulting from it. For example, it is shown that an important feature of such flows is valid for any corss-sectional shape; this was not obvious from previous works which treated only special cases having significant symmetries. Also, a new method for calculating the modified axial pressure gradient is presented which reduces dramatically the amount of work required therefor.

The remainder of the paper presents some results for similar flows through pipes of varying cross-section.     

Fluid flow through a network of thin pipes

We study the fluid flow through a network of intersected thin pipes with prescribed pressure at their ends. Pipes are either thin or long and the ratio between the length and the cross-section is considered as the small parameter. Using the asymptotic analysis with respect to that small parameter the effective behaviour of the flow is found. At each junction an explicit formula for computing the value of the pressure is found. The interior layer phenomenon in vicinity of the junction is studied. We generalize the junction formula on the case of adiabatic compressible flow.