并列圆柱绕流的格子Boltzmann数值模拟

采用非均匀不可压格子Boltzmann模型对低雷诺数下并列圆柱绕流进行了数值模拟,给出了数值计算结果,分析了间距g对圆柱尾流及升力、阻力的影响,并在此基础上得到了4种尾迹模式.此外,研究了流场的初始扰动对流动分岔现象的影响,发现在适当的扰动下可以很快得到同步同相的尾流.对Re=160和200下圆柱的升、阻力进行了对比,结果表明升力和阻力受间距g的影响大于雷诺数.     

较高Re数圆柱尾流的控制

引入一个窄条作为控制件，在Re=3.0×10 3~2.0×10 4范围内对圆柱尾流进行控制实验。窄条长度与柱体长度相同,厚 度为柱体直径的 0.015~0.025倍,宽度为柱体直径的0.18倍. 窄条的两个长边 与柱中心轴平行, 而且三者共面. 控制参数为窄条位置, 可由间距(窄条到柱轴)比λ/(0.5D)和风向角β (窄 条面与来流的夹角)确定. 采用流动显示和热线测量方法,对控制和未控制尾流的流动状态, 平均速度分布和脉动速度情况,以及作用于柱体和控制件的总阻力进行了研究和比较. 研究结果证明, 当窄条位于柱体尾流中一定区域内时, 可有效抑制柱体两侧的旋涡脱落.有效控制后的尾流湍流度也相应减小. 在不同Re数下,找出了有效抑制旋涡脱落的窄条位置区域, 并用动量积分估计了作用于柱体和窄条上的总阻力与光圆柱阻力的比值及其随风向角的变 化. 对λ/(0.5D)=2.9情况,得到了减阻的风向角区域(β=0°~40°与180°附近)以及最大减阻率32%.以上事实表明，在近尾流局部区域施加小的干扰,可改变较高Re数圆柱尾流的整体性质.     

网栅后湍流流动沿流程衰减特性的实验研究

应用ＬＤＶ测试技术对垂直方管内三种不同栅距的网所形成的湍流流动做了详细测量,网栅栅距Ｍ分别为１４ｍｍ,１０ｍｍ,６ｍｍ实验给出了管内不同位置湍流流动的各种参数沿流动方向的衰减规律,并就三种网栅进行比较分析,以探讨这种网栅流动所具有共同规律和在不同栅距对湍流结构及脉动大小的不同特点,从而对这种网栅所形成的湍流流结构较为清晰的了解。     

扭矩转化器（T／C）内部叶片流道流场的二维PIV实验研究

本文利用二维ＰＩＶ技术研究了汽车无级调连装置中扭矩转化器内部叶片流道流场的复杂流动,实验结果表明泵和透平在不同转速下,静子叶片流道中的流场体现出不同的流动特征,文中还对实验误差进行了分析,提出了减少误差的措施,通过叶栅流动理论分析说明了本文结果的可靠性。     

高超声速尾流及其气动、物理和化学性质(上)

高超声速飞行体再入大气层时,会在物体后面留下一条很长的电离尾流。尾流具有极其复杂的气动、物理和化学性质,不同流动状态的电离尾流,不仅具有不同的辐射特性,而且具有不同的雷达散射截面。这些现象及其性质为我们提供了识别飞行体的依据。 随着火箭、导弹和人造卫星再入大气层的成功,高超声速尾流已经得到了详细的研究。仅60年代初期美国的一些科研机构所发表的论文就约有200篇之多。1967年5月,北大西洋公约集团还在美国国立Co lorado大学召开了一次有关尾流的专家会议,详细讨论了高超声速尾流的流体物理问题。     

串列双圆柱绕流问题的数值模拟

本文运用有限体积方法,对绕串列放置的双圆柱的二维不可压缩流动进行了数值计算。为研究两圆柱不同间距对圆柱相互作用和尾流特征的影响,选取间距比Ｌ／Ｄ（Ｌ为两圆柱中心间的距离,Ｄ为圆柱直径）在１．５～５．０之间每隔０．５共八个有代表性的间距进行了计算模拟。计算均在Ｒｅ＝２００条件下进行。计算结果表明：对该绕流问题,流动特征在很大程度上取决于间距的大小。且间距存在一临界值,间距比从小于临界值变化到大于临界     

芯片封装焊球连接疲劳寿命预测分析--能量法和有效应变法之比较

研究了目前常用的两种芯片封装焊球连接的寿命预测方法一能量法和有效应变法。对焊球连接的材料本构关系进行了对比分析，并利用FORTRAN语言编制了相应的材料本构模型子程序，将其与有限元仿真工具ANSYS耦合，实现了将焊球连接的材料本构模型用户子程序导入到ANSYS的材料库。在此基础上模拟了三维芯片叠层球栅阵列尺寸封装的焊球结构，在热循环条件下(-40～ 125℃的工作状态，并分别利用能量法和有效应变法对焊球连接的寿命预测进行了比较分析，最后对两种方法作出了评价。     

圆柱尾流雷诺应力与平均运动变形率的空间弛豫效应

针对圆柱尾流中沿流向存在的Karman涡街周期性涡旋结构,对湍流雷诺应力与平均运动变形率之间的空间弛豫效应进行了实验研究.在回流式水槽中,放入不同直径的圆柱模型,获得不同雷诺数下的圆柱尾流,利用二维高时间分辨率粒子图像测速(TRPIV)技术测量圆柱尾流二维瞬时速度空间分布图像的时间序列.经过数字图像处理,获得二维雷诺应...     

高尔夫球绕流流场数值研究

采用基于Smagorinsky-Lilly亚格子模型的大涡模拟方法模拟了 一个直径为42.6 mm, 布有均匀凹坑的高尔夫球的绕流流场, 证实了其尾涡分离点比光滑球的 分离点远, 其绕流阻力较小. 模拟了自转速度为100 rad/s的正旋和逆旋的高尔夫球, 发现它 们的尾流分布更不均匀, 并因此产生了垂直于来流方向的压力, 压力大小不受自转方向的影 响; 并发现带有旋转效应的凹坑高尔夫球受到的阻力系数增大; 自旋对于球的上下面压力有 明显影响.     

绕栅中水翼空化流动的数值和实验研究

采用数值计算和实验研究的方法研究了绕水翼和栅中水翼的非定常空化流动. 实验采用高速录像技术分别观察了绕水翼和栅中水翼云状空化形态随时间的变化, 测量了升阻力, 并对测量数据进行了频率分析. 计算时空化模型选用了能比较准确描述旋涡空化非定常特性的Kubota模型, 湍流模型采用能准确捕捉流场非定常特性的FBM模型. 计算模型的可靠性用实验结果进行验证. 结果表明, 计算与实验的结果基本一致, 相比绕单个水翼的空化流动, 绕栅中水翼的空穴厚度比较薄, 翼型近壁处的逆压梯度较小, 反向射流的速度较小, 且水汽混合区速度梯度较小, 空穴的脱落周期变长, 平均升阻力系数较小      

The oseen flow of finite clusters of spheres and the wake effect on the drag factor

In this paper, the wake effect on drag factor in the axisymmetric Oseen flow of the finite clusters of equally spaced spheres with same size is studied. Putting the Oseen lets on the centres of all the spheres, the series solution of the problem is obtained. By truncating the infinite series and applying the collocation method to solve a set of the linear algebraic equations, the approximate solution of the Oseen flow of finite clusters of spheres and the drag factor for each sphere are presented. The effect of the sphere number and spacing on the drag factor of each sphere under different Reynolds numbers are calculated and the wake effect as well as the shielding effect and the end effect are revealed. The influence of various parameters on the effects is considered and compared with the corresponding results of the Stokes flow. The convergence of the method is also studied numerically in this paper.     

Drag of a rotating sphere

We consider the problem of steady incompressible viscous fluid flow about a rotating sphere, with the flow specified on a sphere of finite radius, which reduces to the solution of the complete Navier-Stokes equations.The dimensionless stream functions and circulai velocity are sought in the form of series in powers of the Reynolds numbers, which converge for small values of this number. Recurrence formulas are derived for determining the coefficients of these series. The pressure, rotational resistance torque, and drag are determined. It is established that the rotating sphere has higher drag than a stationary sphere. The leading term of the series in powers of the Reynolds number for the drag and resistive torque is calculated.     

同轴圆柱间滑移旋转流动问题的同伦解析解

从理论上研究了具有延伸柱面的同轴圆柱间滑移流动问题.通过引入适当的相似变换将控制方程组转化为一类非线性边值问题, 利用同伦分析方法首次获得问题的近似解析解, 分析讨论滑移参数、雷诺数和内外筒半径比对流动的影响.结果表明: 滑移边界参数对剪切应力有较大的影响, 滑移边界小的流体对壁面和边界层内流场施加了更大的剪切力; 增大雷诺数Re, 能增大内筒的壁面剪切力和扭矩; 内外筒半径比对流动结构也有较大的影响, 内筒半径固定, 增大外筒半径能够减少内筒的纵向剪切力.      

高超声速尾迹流场稳定性数值研究

通过数值模拟, 对高超声速尾迹流场进行了研究, 对其尾迹流动的失稳过程进行了分析.选取计算模型为圆球,Ma= 6.0, Re = 1.71\times 10^6(Re以球头半径为参考长度). 通过数值模拟,首先得到的流动是稳定解,在底部发展出一个主分离区和一个二次分离区,流动是轴对称状态. 不添加任何扰动继续进行计算,发现底部流场缓慢发展出微弱的非定常流动. 随后,该现象继续发展,出现明显的结构失稳,得到了无量纲周期为12.0的周期解. 给出了高超声速圆球绕流尾迹结构的周期性演化过程,对其涡系结构的演化及奇点特征进行了分析. 研究表明该数值模拟方法可用于底部流动稳定性问题的研究,同时证实了高超声速底部流动也存在流动不稳定性.      

Dynamic interaction of fixed dual spheres for several configurations and inflow conditions

The changes in force characteristics as well as the shedding patterns for various dual sphere configurations are studied. The Reynolds numbers considered are 300, 600 and two different inflow conditions are used: steady and pulsating. The sphere formations are defined by the separation distance D₀ between the spheres and the angle between the line connecting the centres of the spheres and the main flow direction, γ. The position of one of the spheres is varied in the range 0°–90° using a 15° increment. Two separation distances are studied; 1.5D and 3D. The method used for the simulations is the Volume of Solid (VOS) approach, a method based on Volume of Fluid (VOF). A major conclusion from this work is that the sphere interaction alters the wake dynamics by obstructing the vortex shedding (generating a steady wake or a wake with lower Strouhal number) and by changing the direction of the lift force so that it in most cases is directed in the plane containing the sphere centres. The results also show that changing the inflow condition gives the same relative change in drag and lift as for a single sphere. The drag is substantially reduced by placing the sphere downstream in a tandem arrangement and slightly increased in a side-by-side arrangement. However, the effect is decreased by increasing separation distance and increasing Reynolds number.     

Interaction between two spheres placed in tandem arrangement in steady and pulsating flow

The interaction among two spheres in tandem formation are studied for a Reynolds number of 300 using both steady and pulsating inflow conditions. The purpose is to further investigate the force characteristics as well as the shedding patterns of the two spheres as the separation distance is changed from 1.5 to 12 sphere diameters. The method used for the simulations is the volume of solid (VOS) method, an approach based on the volume of fluid (VOF) method. Comparisons with other computational methods have shown VOS to accurately resolve the flow field around solid spheres. The results show that the separation distance plays a significant role in changing the flow patterns and shedding frequencies at moderate separation distances, whereas effect on drag is observed even at a separation distance of 12 diameters.     

The creeping motion of multiple spherical liquid drops

This paper deals with the drag factor of the multiple spherical liquid drops in the creeping motion by means of the Sampson singularities and collocation technique. The drag factors of the drops are calculated under distinct conditions: different number of liquid drops in the chain and different sphere spacing. From the results the influence of the viscosity ratio on the shielding effect and end effect are revealed. The convergence of the method is also studied in this paper.In this paper the collocation technique developed by Gluckman et al. in treating the rigid sphere case is applied to deal with the creeping motion of multiple spherical liquid drops which has improtant applications in bioengineering and chemical engineering. Writing the general solutions in inner and outer regions of the spheres and satisfying the kinematic and dynamic matching conditions at the collocation points on the interfaces, a set of linear algebraic equations is obtained to determine the unknown coefficients in the solutions. By means of any matrix inversion technique the approximate solutions are presented. In the first section of this paper the mathematic formulation of the problem is given and then in the second section the numerical results are introduced and analysed.     

The stokes flow of the rotating double spheres and multiple spheres

In this paper the expressions for a kind of new rotlets in Stokes flow are derived. By means of superposition of this new rotlets, the drag moment for rotating double spheres and multiple spheres along the smae axis are presented. It has been demonstrated that drag moment for each sphere is the linear function of its angular velocity.     

Stokes flow past finite coaxial clusters of spheres in a circular cylinder

Solutions are presented for the Stokes flow past finite axial assemblages of up to 9 spheres in an infinitely long cylindrical tube for a wide range of sphere spacings and sphere to cylinder diameter ratios. General solutions are constructed from the fundamental solutions to the governing equation in both the cylindrical and spherical coordinate systems. No-slip boundary conditions are enforced on the tube surface by constructing the Fourier transform of the general disturbance created by the spheres, as detected on the cylinder wall. The boundary conditions are then applied on the sphere surfaces by a previously developed series truncation technique.The calculated drag forces and zero-drag velocities demonstrate the interparticle interaction effects, the sphere-wall interactions, and the effects of wall damping on the inter-particle shielding phenomenon.     

THE METHOD OF CONTINUOUS DISTRIBUTION OF SINGULARITIES TO TREAT THE STOKES FLOW OF THE ARBITRARY OBLATE AXISYMWETRICAL BODY

This paper deals with the Stokes flow of the arbitrary oblate axisymmetrical body by means of constant density and quadratic distribution function approximation for the method of continuous distribution of singularities. The Sampson spherical infinite series arc chosen as fundamental singularities. The convergence, accuracy and range of application of both two approximations are examined by the unbounded Stokes flow past the oblate spheroid. It is demonstrated that the drag factor and pressure distribution both conform with the exact solution very well. Besides, the properties, accuracy and the range of application are getting belter with the improving of the approximation of the distribution function. As an example of the arbitrary oblate axisymmetrical bodies, the Stokes flow of the oblate Cassini oval are calculated by these two methods and the results are convergent and consistent. Finally, with the quadratic distribution approximation the red blood cell, which has physiologic meaning, is considered and for the first time the (orresponding drag factor and pressure distribution on the surface of the cell are obtained.