类升力体外形高超声速粘性绕流拓扑结构分析

采用交替方向隐式分解的隐式NND格式求解全N-S方程模拟“类升力体”外形在高超声速下的大攻角流动,给出了“类升力体”外形表面极限流线随攻角变化的拓扑结构及40°攻角下垂直于体轴的横截面流线拓扑结构。结果表明:类升力体外形三维流场结构十分复杂,攻角从0°～40°变化时,背风面表面极限流线依次由不分离、开式分离向起始于鞍、结点组合的高阶奇点的分离方式转化,翼面横向分离亦随攻角增大而增大;垂直于体轴的横截面流动拓扑结构与文献[2]给出的理论分析一致。     

弱界面端初始失效位置的试验初探

通过双材料受压试验研究了弱奇异性界面端的界面初始脱粘点的位置问题。实验材料采用钢和有机玻璃,根据弱奇异性要求和界面端应力分布特征,设计、制作了试件,并进行了初始脱粘实验。由实验发现楔形角为30°、45°和55°试件的界面初始脱粘点位置均在界面内部,脱粘是由有限应力引起的。63°是个临界角楔形角,大于63°试件,脱粘多会从界面端开始,即脱粘由奇异的界面应力引起的。此外界面正应力若为拉应力时,它对界面脱粘有很大的贡献。     

90°弯管内流动的理论模型及流动特性的数值研究

从三维不可压缩雷诺时均Navier-Stokes方程出发,对90°弯曲管道内湍流流动进行数值模拟。网格划分采用六面体网格,湍流模型为RNGk-ε模型,在近壁区采用两层壁面模型进行修正,流场的计算结果与实验数据吻合较好。在此基础上,本文数值研究了来流方向对流场结构和流动特性的影响。得出在弯管流场中发生了分离现象,且随着来流侧滑角的增大,分离区范围增大。此外,随着来流从同一侧滑角变换至同一攻角时,横截面的二次流图像中也从具有两个对称主涡变成只具有一个主涡的现象。     

考虑系留点垂向运动的飞艇系缆响应特性分析

为研究考虑系留点垂向运动的飞艇系缆的面内运动响应特性,将运动的飞艇作为系缆的边界条件处理,对系缆下端的系留点受到垂向激励时的系留飞艇系缆的运动状态进行了数值模拟,研究了系缆的动张力、运动情况。分析了飞艇攻角、系缆线密度等参数对系统的影响。研究结果表明:当系留点竖向简谐运动时,系缆上各点都做近似的简谐运动,在不同的线密度和攻角参数下,系缆各点的法向振幅分布不同,系缆可能处于二阶的振动状态;且随着系缆密度和攻角的增大,切向振幅增大,法向振幅减小;系留点激励还引起整个系统偏离平衡位置,这会引起飞艇动态高度的降低,在系留飞艇的高度控制中会有一定的影响。以上研究结果可为系留在舰船等运动中平台上的飞行器控制和系缆设计提供参考。     

基于涡粘性模型的翼型湍流流场熵产率计算

利用有限体积法实现了基于非正交同位网格的SIMPLE算法。基于熵分析方法,采用涡粘性模型求解湍流熵产方程,系统研究了湍流模型对二维翼型绕流流场熵产率的影响。通过计算NACA0012翼型在来流雷诺数为2.88×10⁶时,0°攻角~16.5°攻角范围内的翼型表面压力系数分布和升阻力特性,验证了算法及程序的正确性。结果表明,选择不同湍流模型时,翼型流场熵产的计算结果存在差异,湍流耗散是引起流场熵产的主要原因;翼型流场的熵产主要发生在翼型前缘区、壁面边界层和翼型尾流区域,流场熵产率与翼型阻力系数线性相关;当产生分离涡时,粘性耗散引起的熵产下降。     

钙质砂的胶结性及对力学性质影响的实验研究

对南海钙质砂进行了三轴实验研究,重点针对不同胶结情况下的力学性质,如不同胶结材料和含量的变化对强度和应力应变特性的影响等。研究表明,钙质砂具有与陆源砂不同的性质,它的内摩擦角高达48°,远大于一般陆源砂的35°左右;在低围压下钙质砂表现出剪胀性,但随围压增加剪胀性降低;利用硅酸盐水泥作为胶结材料效果较好;随着水泥含量的增加,钙质砂试样的强度增加。     

ZrN单层、多层、梯度层及复合处理层对不锈钢固体粒子冲蚀行为的影响

对比研究了离子镀ZrN单层、多层、梯度层及其与离子渗氮复合处理对2Cr13马氏体不锈钢抗大小攻角固体粒子冲蚀性能的影响规律,通过硬度、韧性、结合强度、动静态承载能力等特性的综合测试与分析,探讨了表面处理层对不锈钢固体粒子冲蚀行为的作用机制.结果表明,上述4种表面改性层均显著提高了2Cr13不锈钢表面的硬度和抗微切削能力,因而有效改善了2Cr13钢抗30°小攻角固体粒子冲蚀性能.经离子渗氮层上沉积ZrN梯度层的复合处理后,其硬度由表面至基材呈梯度分布,界面应力分布连续性好,承载能力和抗塑性变形能力高,多冲疲劳性能优,能够显著提高基材抗90°大攻角固体粒子的冲蚀能力.然而,ZrN单层、多层、梯度层的抗多冲疲劳性能较差,其抗大攻角固体粒子的冲蚀能力反而不及2Cr13基材.     

细长体背风面横向非对称分离的研究

用数值模拟方法研究了超声速情况下，无限长细长体背风面的涡结构。数值模拟的出发方程和计算格式分别为全Ｎ－Ｓ方程和二阶空间精度的ＴＶＤ格式。数值结果给出了圆锥、半球柱体和椭圆锥在不同攻角下的流场结果。结果表明圆锥在攻角α＝１５°，２０°和２５°时背风面呈现明显的稳定非对称横向分离，而半球柱体和椭圆锥在３２．５°和２５°时背风面均未出现非对称的横向分离结构。     

偏转矢量喷流对双三角翼前缘涡破裂影响的实验研究

本文应用染色液流动显示技术对后缘偏转喷流情况下76°/40°双三角翼前缘涡破裂位置的变化进行了观测,实验结果表明偏转喷流主要推迟与喷流方向相同一侧前缘涡的破裂,而使另一侧前缘涡破裂略有提前.随着喷流偏转角度的增大,喷流使两前缘涡破裂位置差逐渐增大.另外,随着模型攻角的增大,前缘涡涡核与双三角翼翼面的夹角逐渐增大,导致偏转喷流的作用逐渐减弱.     

不同网格拓扑对细长体绕流计算的影响研究

分别运用扇形(Fan)、阶梯形(Ladder)、交界面形(Interface)网格对细长体小攻角对称、大攻角对称、大攻角非对称绕流流场进行了数值研究．通过涡核位置、涡簇显示、物面压力分布、轴向力分布等的计算结果比较了三种网格的计算精度．数值实验表明：细长体分离涡流场对边界层网格非常敏感,应严格控制边界层网格的正交性;随着攻角增大,流场对网格特性的敏感性有增高的趋势;阶梯形网格可能会对流场带入非物理性扰动,交界面网格对流场捕捉有不连续现象;将三种网格得到的物面压力、侧向力、流动分离位置与实验值进行对比,发现扇形网格误差最小、交界面网格误差最大;大攻角非对称流动时,扇形网格计算的侧向力有整体向细长体头部压缩的趋势,涡脱落位置靠前,第二个及第三个极值更大,说明非对称现象有向尾部发展的趋势．     

层状两相流动的基本方程式

本文将两相流动的雷诺方程沿深度方向进行平均,出求了平均后的运动方程、连续方程和能量方程式,在适当的物理假定下,简化得到可适用于考虑固-液流动及气-液流动两种情况下的两相层状流动基本方程.     

高超声速层流尾迹的数值模拟

本文利用无波动、无自由参数、耗散的差分格式(NND格式),通过求解NS方程,数值模拟了高超声速层流尾迹的流动,清晰地给出了主激波、拐角膨胀波、迹激波及自由剪切层,所得流场物理量的分布与实验结果甚为一致。计算发现了底部迴流区由起始向定常的发展中,在瞬时流线图上经历了极限环形成、胀大、缩小、再胀大最后消失的演变过程。     

Gas-particle two-phase turbulent flow in a vertical duct

Two-phase gas-phase turbulent flows at various loadings between the two vertical parallel plates are analyzed. A thermodynamically consistent turbulent two-phase flow model that accounts for the phase fluctuation energy transport and interaction is used. The governing equation of the gas-phase is upgraded to a two-equation low Reynolds number turbulence closure model that can be integrated directly to the wall. A no-slip boundary condition for the gas-phase and slip-boundary condition for the particulate phase are used. The computational model is first applied to dilute gas-particle turbulent flow between two parallel vertical walls. The predicted mean velocity and turbulence intensity profiles are compared with the experimental data of Tsuji et al. (1984) for vertical pipe flows, and good agreement is observed. Examples of additional flow properties such as the phasic fluctuation energy, phasic fluctuation energy production and dissipation, as well as interaction momentum and energy supply terms are also presented and discussed.

Applications to the relatively dense gas-particle turbulent flows in a vertical channel are also studied. The model predictions are compared with the experimental data of Miller & Gidaspow and reasonable agreement is observed. It is shown that flow behavior is strongly affected by the phasic fluctuation energy, and the momentum and energy transfer between the particulate and the fluid constituents.     

Numerical solution of the turbulent flow of an incompressible fluid in curved planar and axially symmetrical channels

The governing equations for axially symmetric flow, where the Reynolds stresses are expressed by scalar turbulent viscosity, are the Reynolds equations. The turbulence model k, ? is used in the well-known form for fully developed turbulent flow.The numerical method, a continuation of the MAC system¹, is adapted so that even for high Reynolds cell numbers precision (δx²) can be achieved for the steady flow. Irregular cells join the rectangular network on the curved surface. Von Neumann's stability condition of the linearised numerical system is investigated. Special problems concerning the numerical solution of the turbulence model equations are stated and a special procedure is worked out to ensure that the fields k, ? do not converge to physically meaningless values. The program for the computer is universal in that the boundary problems can be assigned by input data.As an example, an axially symmetrical diffuser with an area ratio of widening 1.40 is computed. Fields of velocity and pressure at the wall as well as fields v_T and k are assessed. The results are compared with an experiment. The conclusion is that this method is suitable for the problems mentioned in this study as well as for unsteady flow.     

双圆诱导不可压缩势流的几个精确解

Lagally(1929)给出了两个静止圆在均匀来流中的扰动速度势精确解。本文通过使用 Apollonius 保角变换,将两圆外部区域变为圆环内部区域,并在变换平面上用 Fo-urier 级数方法求解 Laplace 方程,从而得出双圆扰动势流的另外三个精确解。它们分别对应于静止流体中两圆膨胀(收缩)、沿连心线相向(相背)运动和垂直连心线反向运动(错动)所诱导的速势场。     

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．     

Sidewall flow stability in the MHD channel flows

The velocity distribution between two sidewalls is M-shaped for the MHD channel, flows with rectangular cross section and thin conducting walls in a strong transverse magnetic field. Assume that the dimensionless numbersR _m ?1,M, N? 1, and σ* and that the distance between two perpendicular walls is very long in comparison with the distance between two sidewalls. First, the equation for steady flow is established, and the solution of M-shaped velocity distribution is given. Then, an equation for stability of small disturbances is derived based on the velocity distribution obtained. Finally, it is proved that the stability equation for sidewall flow can be transformed into the famous Orr-Sommerfeld equation, in addition, the following theorems are also proved, namely, the analogy theorem, the generalized Rayleigh's theorem, the generalized Fjørtoft's theorem and the generalized Joseph's theorems.     

Theoretical analysis of using airflow to purge residual water in an inclined pipe

ＩｎｔｒｏｄｕｃｔｉｏｎＰｕｒｇｉｎｇｒｅｓｉｄｕａｌｌｉｑｕｉｄｉｎａＵ＿ｓｈａｐｅｄｐｉｐｅｌｉｎｅｉｓｃｈａｌｌｅｎｇｅｆｏｒｃｈｅｍｉｃａｌａｎｄｔｒａｎｓｐｏｒｔａｔｉｏｎｉｎｄｕｓｔｒｙ[1].Ｍａｎｙｔｅｃｈｎｉｑｕｅｓｈａｖｅｂｅｅｎｅｍｐｌｏｙｅｄｔｏｐｕｒｇｅｏｕｔｒｅｓｉｄｕａｌｗａｔｅｒ[2 ],ｂｕｔｎｏｎｅｈａｖｅｂｅｅｎｃｏｍｐｌｅｔｅｌｙｓａｔｉｓｆａｃｔｏｒｙ .Ｏｎｅｐｏｓｓｉｂｌｅｍｅｔｈｏｄｆｏｒｄｏｉｎｇｔｈｉｓｈａｓｂｅｅｎｔｏｂｌｏｗａｇｒｅａｔｑｕａｎｔｉｔ…     

Solution of the Incompressible Unsteady Navier–Stokes Equations Only in Terms of the Velocity Components

A method which uses only the velocity components as primitive variables is described for solution of the incompressible unsteady Navier–Stokes equations. The method involves the multiplication of the primitive variable-based Navier–Stokes equations with the unit normal vector of finite volume elements and the integration of the resulting equations along the boundaries of four-node quadrilateral finite volume elements. Therefore, the pressure term is eliminated from the governing equations and any difficulty associated with pressure or vorticity boundary conditions is avoided. The equations are discretized on four-node quadrilateral finite volume elements by using the second-order-accurate central finite differences with the mid-point integral rule in space and the first-order-accurate backward finite differences in time. The resulting system of algebraic equations is solved in coupled form using a direct solver. As a test case, an impulsively accelerated lid-driven cavity flow in a square enclosure is solved in order to verify the accuracy of the present method.     

A collocated finite volume method for predicting flows at all speeds

An existing two-dimensional method for the prediction of steady-state incompressible flows in complex geometry is extended to treat also compressible flows at all speeds. The primary variables are the Cartesian velocity components, pressure and temperature. Density is linked to pressure via an equation of state. The influence of pressure on density in the case of compressible flows is implicitly incorporated into the extended SIMPLE algorithm, which in the limit of incompressible flow reduces to its well-known form. Special attention is paid to the numerical treatment of boundary conditions. The method is verified on a number of test cases (inviscid and viscous flows), and both the results and convergence properties compare favourably with other numerical results available in the literature.