均匀、振荡及组合流绕平板流动的尾迹研究

本文利用离散涡模型及改进的新生涡产生机制对三种不同来流绕平板的近尾迹进行数值研究。计算讨论了定常流中平板绕流流动的总体特性和近尾迹流场;对于简谐振荡来流,相应于K_c=2.0、4.0 和10.0 分别得到两种不同的尾迹形态。给出了小 K_c 数平板尾迹涡配对、运动的新模式而相应的阻力、惯性力系数计算比以前涡模拟结果更接近于 U 型管实验结果。对于流向组合来流本文模拟了涡锁定及其动力特性并于实验相符,给出了流向扰动对平板绕流流动的影响。     

小Kc数振荡流中圆柱绕流流场结构的数值分析

本文综合Chorin的涡方法、网格涡方法和泊松方程快速解法的优点,采用固定离散涡的数目和位置,随时间变化调整离散涡强度的计算方法,对Kc数在1到5之间,β数在10到1665之间圆柱在振荡流动中的流场结构进行了数值模拟。并与U型振荡水槽中的流场涡结构显示照片比较,计算结果表明,数值解在稳定性和收敛性方面都是比较好的。与显示照片相比,其符合程度也是令人满意的。     

用LDA测量U形水槽内的振荡流

本文介绍LDA用于测量U形水槽内的振荡流。水槽直管段为正方形,弯管段内侧弯面及外侧弯面是专门计算设计的。对于水平直管段、竖管段及弯管段共七个截面,测量了边界层外振荡流速的振幅分布。对于水平直管段上底面及下底面各三个截面,测量了边界层內振荡流速的振幅分布及相位分布。测量结果和无限长槽道的理论计算结果作了比较,二者基本符合。     

圆形月池流激振荡实验研究

采用基于经验模态分解(EMD)的本征模态函数(IMF)分析方法和对比研究的实验方 法,实验研究了圆形月池在均匀流条件下的流激振荡特性. 通过实验研究发现,尽管腔内的 流体在不同来流的条件下运动趋势有所不同,但归纳起来对于月池结构,其内部存在两类振 荡源,一类是腔内流体的固有振荡,该频率与腔体结构形式、尺寸、腔内流体深度有关,与 来流无关;另一类则是流体流经腔口时产生的流体动力振荡,该频率与来流特性、速度有关. 当二者频率相近时将会激起腔内流体的共振,即会有``活塞(piston)'现象产生. 实验中,还在腔体侧壁上布置了压力传感器,用来分析腔体侧壁受到的流体压力特性及 其变化趋势.     

流向强迫振荡圆柱绕流的涡脱落模态分析

通过求解采用ALE方法描述的运动坐标系Navier-Stokes方程组,分析均匀来流下雷诺 数为150的静止和流向振荡的圆柱绕流. 主要研究了强迫振荡频率和较大振幅比 (A/D=0.3-1.2)对圆柱升力、阻力变化特性以及涡脱落模态的影响. 研究表 明,流向振荡圆柱绕流存在多种涡脱落模态,如对称S以及反对称A-I, A-III, A-IV等多种形式;比较研究结果,拓展了各模态下对应的锁定区域,并将其分为5个 子区;A-I模态中圆柱受力较以前所知更复杂;通过分析计算结果,发现最大加速度 比Af_{c}^{2}/Df_{s0}^{2}可能是涡脱落模态(尤其是对称S模态)最有效的控制参数.     

均匀来流中旋转圆柱黏性绕流的数值研究

从不可压非定常Ｎ－Ｓ方程出发，首次数值求解了均匀来流中圆柱作周向旋转振荡的黏性绕流问题。探讨了旋转角速度振幅、振荡频率及Ｒｅ数等因素对流场结构及其非定常演化过程的影响，并根据计算结果，给出了在旋转振动频率。速度振幅平面内流场涡结构的分区图。     

弯曲渠道中的振荡流和二次流

本文以弯道理想不可压缩流动的流线和等势线为曲线坐标系给出了弯道内不可压缩粘性振荡流动的一阶解以及边界层流型下的二阶解,以直角弯道为例对弯道內的粘性振荡流动以及二次流的影响进行了讨论。     

振荡管流换热的理论解

本文从流体在管内振荡的运动方程和流体及管壁的能量方程出发,经过变量转换对常微分方程组进行求解,得到了计及管壁影响的振荡流体轴向换热的一般理论解。由这解,可以导出各种特殊条件下的表达式,包括已有的各种解析解。本解经数字化而制成各种图线,它们与已有的实验数据基本吻合。     

用管轴流速确定动脉中血液振荡流的速度剖面

本文通过求解圆管内血液振荡流的基本方程，求得圆管内血液流的速度与压力梯度之间的关系式，文章提出一种利用管轴外流速计算管内压力梯度，进而确定血液振荡流动速度分布的方法，该方法用于检测活体血管内血液振荡流的速度剖面，具有操作简单，精度较高的优点，最后，以人体颈动脉为例，讨论血液周期振荡流的速度分布特征，发现在任意时刻，除了邻近管壁速度迅速降为零之外，沿管截面速度分布相当均匀，呈现出与定常流不同的速度分布特征。     

刚性圆管中血液周期振荡流的切应力分布

本文通过求解圆管内血液振荡流的基本方程，求得圆管内血液流的压力梯度与切应力之间的关系式。在此基础上，详细讲座了圆管中轴向流速和切变率谐波的变化规律，指出流速谐波和切变率谐波的幅值都将随着谐波次数的增大而逐渐减小。为了使所得结果便于应用。文章通过管轴向中心线流速与压力梯度之间的关系式，进一步给出一种利用管轴向中心线流速计算管内切应力分布的简便方法。该方法用于检测活体血管内血液振荡流的切应力分布，具有操作简单，精度较高的优点。最后，以人体颈动脉为例，讨论血液周期振荡流的切应力的分布特性。发现在任意时刻，除了邻近管壁处切应力急剧增大到一定数值之外，沿管截面切应力分布相当均匀且接近于零，呈现出与定常流不同的切应力分布特征。     

Unsteady Flow of an Oscillating Porous Disk and a Fluid at Infinity

An exact analytic solution of the unsteady Navier–Stokes equations is obtained for the flow caused by the non-coaxial rotations of a porous disk and a fluid at infinity. The porous disk is executing oscillations in its own plane with superimposed injection or suction. An increasing or decreasing velocity amplitude of the oscillating porous disk is also discussed. Further, it is shown that a combination of suction/injection and decreasing/increasing velocity amplitude is possible as well. In addition, the flow due to porous oscillating disk and a fluid at infinity rotating about an axis parallel to the z-axis is attempted as a second problem. Sommario. Si studia il flusso non stazionario prodotto dall'oscillazione di un disco poroso in un fluido e si fornisce una soluzione analitica delle equazioni di Navier–Stokes. Si discute l'effetto di una suzione/iniezione e di una variazione sull'ampiezza della velocità' di oscillazione. Infine si studia il flusso dovuto alle oscillazioni non coassiali di un disco poroso e di un fluido all'infinito.     

一种测量TBM滚刀受力的实验方法研究

为探索测量TBM掘进机滚刀受力特性的方法,本文提出了一种能够测试滚刀三向受力的方案。选择滚刀装配体上的垫块作为弹性体,以粘贴应变片的方式实现测量。利用数值计算方法找出垫块底端面和侧端面对所测力敏感而对作用力位置变化不敏感的区域作为贴片位置,分析了锁紧楔块对测试结果的影响。对滚刀装配体在不同工况下的受力情况进行了数值分析和实验测试。结果显示,若根据数值计算选定的位置贴片,垫块底端面和侧端面桥路应变总值的实验和数值结果相对误差介于1.06%和5.62%之间。滚刀强烈振动或更换刀具后可能使中心轴与垫块之间受力位置发生变化,结果确定其影响不超过2.75%。该方案不仅可以测出三个力的信号,还可用于分析滚刀振动状态,特别是滚刀发生偏磨后,刀刃与岩石之间强烈摩擦,振动状态与未偏磨时必然不同,因此还可通过分析由该方法测得的动态信号来识别偏磨。     

散料在料仓内流动特性的实验研究

用振动筛测量多种散料的筛分尺寸，测量散料的容积密度、安息角，用应变直剪仪进行散料内摩擦角、壁面摩擦角的测量，分析了散料颗料的形状、尺寸对散料的安息角、内摩擦角、壁面摩擦角的影响。用示踪法进行了圆筒内散料重力场中颗粒流线和等时线的试验，以及出口直径与流量的关系、筒仓内散料高度对流量的影响的试验，流量与筒仓内散料高度关系的试验。分析了散料各物性参数对散料流动性的影响，为散料存贮和运输设备的结构设计提供实验依据。     

Instability of an Oscillating Cylinder in a Circulation Flow of Ideal Fluid

The problem of the stability of a circular cylinder in a circulation flow is considered under the condition that the cylinder can perform both free (free cylinder) and forced oscillations (cylinder on a spring). It is shown that this simple system can be unstable in the presence of flow vorticity. Particular cases of vorticity distributions which make it possible to obtain an analytic solution are considered. The case of weak monotonically decreasing vorticity of an arbitrary form is analyzed for an arbitrary relation between the densities of the cylinder and the fluid. It turns out that the instability can develop only for a cylinder whose density is greater than that of the fluid. An approximate method of solving this problem based on consideration of the energy balance in the system is constructed. This makes it possible to obtain an expression for the growth rates and explain the physical mechanism realizing the instability, which is associated with the possibility of energy transfer from perturbations in the critical layer to the cylinder oscillations.     

水动力试验和流噪声测试

在模型表面上涂敷低表面能涂层会降低航行体阻力和噪声．因此，对水筒中流噪声的测量数据重复性、误差和数据的可信度等，必须有正确的测量和分析方法．在相同时期内，用相对比较法，从模型内测量同一模型的流噪声，其测量数据的重复性好，误差小于２ｄＢ．在８ｋＨｚ４０ｋＨｚ频率范围内，水筒中环境所造成的背景噪声小，这时信噪比大，噪声的测量能较好地反映出涂层的降噪效果．而低频时≤５ｋＨｚ，循环系统引起较高的背景噪声，可能会掩盖涂层的降噪效果．但低频时，相对比较法中，噪声的降低确是涂层引起的结果．     

Numerical Study of the Flow Behind a Rotary Oscillating Circular Cylinder

A numerical study is performed of flow behind a rotationally oscillating circular cylinder in a uniform flow by solving the two-dimensional incompressible Navier-Stokes equations. The flow behavior in lock-on regime and the timing of vortex formation from the oscillating cylinder are studied. When the frequency of excitation of the cylinder is in the vicinity of the natural vortex formation frequency, a lock-on vortex formation regime appears. As the excitation frequency being increased relative to the natural frequency the initially formed vorticity concentration switches to the opposite side of the cylinder. The effects of oscillating frequency and amplitude on the vortex structures formed in the near wake of the cylinder are also investigated. Based on the present calculated results, some complicated vortex patterns are identified and are consistent with the previous experimental visualizations.     

桩柱水流作用力实验测量技术研究

桩柱的绕流水流作用力一直是工程设计中所关注的问题。为了精确地测量模型试验中竖直桩柱在不同来流夹角下的水流作用力,基于力的平衡原理,设计并制作了一种新的桩柱水流作用力试验测量装置,并采用标准砝码模拟水流作用力,验证了该测量装置在不同来流工况下的测量精度。结果表明:桩柱受不同来流夹角的水流作用力时,该装置都具有相当高的测量精度,可满足模型试验要求。因此,该测量方法可用于竖直桩柱在水平或斜向水流作用下模型试验中水流作用力的试验研究。     

Simulation of a Viscous Flow Around an Oscillating Cylinder at Low Keulegan-Carpenter Numbers

A finite difference simulation method for a viscous flow around a circular cylinder sinusoidally oscillating at low Keulegan-Carpenter numbers is presented. Navier-Stokes equations in finite difference form are solved on a moving grid system, based on a time dependent coordinate transformation. Evolution with time of the flow structures induced by a circular cylinder performing sinusoidal oscillations in a fluid at rest, by means of stream lines, pressure contours and vortex shedding is studied in detail at Keulegan-Carpenter numbers, Kc = 9.4 and 14. The time dependent drag and lift are also explained.     

Numerical simulation of viscous oscillatory flow past four cylinders in square arrangement

The results of a numerical study of the viscous oscillating flow past four circular cylinders, for a constant frequency parameter equal to 50 and KC ranging between 0.2 and 10, are presented. The cylinders were placed on the vertices of a square, two sides of which were perpendicular and two parallel to the oncoming flow, for pitch ratios, P/D, ranging between 2 and 5. The finite-element method was employed for the solution of the Navier-Stokes equations, in the formulation where the stream function and the vorticity are the field variables, whereas the pressure distribution throughout the computational domain was obtained from the solution of Poisson’s equation. When the Keulegan-Carpenter number is lower than 4, the flow remains symmetrical with respect to the horizontal axis of symmetry of the solution domain and periodic at consecutive cycles. As KC increases to 4, the flow becomes aperiodic in different cycles, although symmetry with respect to the horizontal central line of the domain is preserved. For KC equal to 5, asymmetries appear intermittently in the flow, which are eventually amplified as KC increases still further. These asymmetries, in association with the aperiodicity of flow in different cycles, lead to an almost chaotic configuration as KC grows larger. For characteristic cases the flow pattern and the time histories of the in-line and transverse forces exerted on the cylinders are presented. The mean transverse forces acting on the cylinders, the r.m.s. values of the in-line and transverse forces, together with the drag and inertia coefficients of the in-line force, were evaluated for each pitch ratio in the range of Keulegan-Carpenter numbers examined and are presented in diagrams.     

Application of Differing Forcing Function Models on Simulated Flow Past an Oscillating Cylinder in a Uniform Low Reynolds Number Flow

A Computational Fluid Dynamics (CFD) model is presented for the uniform viscous two dimensional flow past an oscillating cylinder at low Reynolds number. Numerical simulations are made to study the effect of differing forced induced oscillation mechanisms with a large range of cylinder forcing frequencies. In the first case sinusoidal velocity slip boundary conditions are adopted for the cylinder surface to simulate cylinder oscillation. The implication suggests that no modification or additional term need to be added to the Navier-Stokes equations. In the second case this time extra body force terms which are assumed to account for velocity effects due to cylinder movement are included in the Navier-Stokes equations with the imposition of same boundary conditions. Drag and lift coefficients are extracted from present numerical results and other detailed computations of these coefficients are made at a Reynolds number of 80 and an amplitude-to diameter ratio 0.14. The results are found to be in agreement with each other at low force driving frequencies below and near lock-in. However, differences are found at higher frequencies above lock-in. Agreement are also found with experimental results at some frequency ranges.