雷诺数对近壁面圆柱绕流和壁湍流相互作用结构特性的影响

该文采用流动显示和PIV对近壁面放置圆柱的流场进行了精细测量,重点研究了不同雷诺数下近壁区圆柱绕流与壁湍流的相互作用规律、尺度演化规律及标度律特性.当雷诺数从10 600降至4 800时,波数能量级串标度行为呈现从-5/3至-1变化规律.而联合概率密度分析发现随雷诺数的下降,大尺度结构出现的概率降低,而雷诺数在5 60...     

近壁水平圆柱绕流漩涡特性流场计算

该文运用计算机数值模拟了均匀流绕固定圆柱的流场.对3种模型进行了分析,分别是:孤立圆柱绕流、串列双圆柱绕流和并列双圆柱绕流.实验中主要模拟了雷诺数为20、40和100时的绕流流动,并得到流场的速度等值线图、速度欠量图和流线图.计算结果发现:当雷诺数为40时,流场有明显变化,有趋势但并没有形成明显的卡门涡街.     

用SST-DES和SST-URANS方法数值模拟亚临界雷诺数下三维圆柱绕流问题

基于剪切应力运输(shear stress transport,SST)的分离涡模拟(detached-eddy simulation,DES)在近壁面的流动区域采用SST模型,而在其他区域采用亚格子模型求解流场。本研究中分别应用SST-DES和SST-URANS方法对亚临界雷诺数Re=3900下的三维圆柱绕流进行了数值模拟,比较分析了两种数值方法下圆柱表面的时均压力分布、圆柱后方的漩涡脱落特征、圆柱下游流场的时均速度剖面分布等,并将数值模拟结果同前人物理试验比较,结果表明SST-DES方法在亚临界雷诺数下的三维圆柱绕流数值模拟问题上比SST-RANS方法具有更好的效果。     

展向周期振动的平板近壁湍流结构研究

通过直接数值模拟(DNS)对壁面作展向周期运动的槽道湍流进行研究,建立了槽道湍流数据库.通过改变振幅大小和振动周期,可以使壁面阻力明显减少.根据计算结果分析了减阻率和振动参数的关系.利用减阻后近壁湍流拟序结构的变化,研究了壁面展向周期振动减阻的内在机理,揭示了三种减阻过程中涡结构对近壁流体的上抛、下扫运动以及条带结构的影响规律.     

圆柱桥墩绕流试验研究

一个世纪以来,圆柱绕流一直是众多理论分析、实验研究及数值模拟的对象,但是由于圆柱周围三维水流的复杂性,迄今对该流动现象物理本质的理解仍是不完整的,特别是对于圆柱绕流流态与圆柱桥墩周围冲刷的关系问题,尚未形成系统的理论研究.利用超声波流速仪测量圆柱周围各测点的流速,得出圆柱桥墩绕流纵向、横向和垂向的三维时均流速分布,并对圆柱下游流态结构进行了初步的理论分析,为圆柱绕流流场和桥墩冲刷机理及防护研究提供了参考.     

有限元-有限差分法对振荡流加任意方向均匀来流中圆柱绕流的数值模拟分析

本文用有限元—有限差分混合法解不可压缩非定常N—S方程来直接模拟振荡流加任意方向均匀来流流场中圆柱绕流情况。该方法的基本思想为:在同一时间步的不同计算步中,用三阶迎风格式离散动量方程中的对流项,压力修正方程用有限元离散,离散后的方程用直接法解。本文计算了Re=800,K_c=4时,均匀来流与振荡流幅值之比等于0.8,其夹角分别为30°、45°和60°三种绕流情况。首次用该方法系统地计算分析了振荡流中在考虑较多因素时圆柱绕流的涡脱泻现象。重点探讨了有夹角均匀来流情况下振荡流场中圆柱近迹复杂的涡结构及其非定常演化过程。     

特征线算子分裂有限元的圆柱绕流大涡模拟

为研究圆柱绕流流场特性,将大涡模拟与特征线算子分裂有限元相结合,建立了大涡模拟特征线算子分裂有限元模型,对单圆柱和串列双圆柱绕流问题进行了数值模拟,所得结果与现有研究结果吻合较好。模拟结果表明:对单圆柱绕流,随着雷诺数的增大,圆柱近尾流区上下交替的涡旋逐渐靠近通过圆柱几何中心的水平线,且涡脱落位置逐渐靠近圆柱。对Re=1 000的串列双圆柱绕流,临界间距在圆柱直径的2.25~2.5倍之间;当两圆柱间距小于临界间距时,上游圆柱后方无明显涡旋脱落,间隙处压力较稳定;大于临界间距时,有涡旋脱落,上游圆柱尾流区上下表面交替出现强负压区。     

圆柱桥墩的绕流数值模拟

以西藏林芝八一大桥为模型,采用大涡模拟,得到了流场的压力云图、瞬时速度流线图、涡量图。结果表明:流体开始流过桥墩时,圆柱壁面压力最大点及最低点分别出现在前驻点与圆柱壁面上下两侧;流体充分流动,中间的圆柱压力最大点发生了变化;流体绕中间圆柱的流动特性同时受到上游圆柱与下游圆柱的作用;漩涡脱落圆柱向下游运动,受流体流动的影响与自身的剪切运动,涡能量不断减少,最后消失;运用大涡模拟能够很好的预测圆柱绕流问题,可以为高原实际工程的应用提供参考。     

圆柱桩群绕流包络线张角测试研究

参照单柱绕流现象建立了桩群绕流包络线张角的概念,通过有限深度均匀流水槽试验研究了不同圆柱桩群对均匀水流绕流包络线张角大小的影响规律,并进行了对比分析。结果表明:随着圆柱桩群阻流率、排架密度、桩群长度、桩群迎流角的增大,均匀水流绕流圆柱桩群包络线张角增大;不同流速的水流应对圆柱桩群绕流的反应不一,流速越大反应越剧烈。     

高速列车气动噪声的计算研究

通过对高速列车气动噪声产生的关键部位进行简化抽象,对其产生的噪声进行了数值分析。该文着重讨论了两个主要的简化模型,即二维后台阶问题以及三维圆柱绕流问题。对后台阶问题进行数值模拟时采用了NLAS和LES两种不同的方法,并同实验值进行了比较。对三维圆柱绕流问题则直接采用NLAS方法耦合FW-H声音传播方程进行了数值模拟。以此对高速列车气动噪声的机理进行了分析,并对适合于高速列车气动噪声计算的方法进行了选择。     

NUMERICAL SIMULATION OF AN OSCILLATING FLOW PAST A CIRCULAR CYLINDER IN THE VICINITY OF A PLANE WALL

Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D 〈 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D 〉 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frcqucncy and the vortex shedding frequency from an isolated stationary cylinder.     

不等直径串列圆柱绕流大涡模拟

为研究背负式海底管线中增设的小直径附属管线对主管线的水动力影响,将大涡模拟中经典Smagorinsky亚格子模型与特征线算子分裂有限元法结合,并引入出口对流边界条件,完善了基于特征线算子分裂有限元的大涡模拟方法。通过自编程序数值模拟Re=1 000的单圆柱绕流,计算结果与相关文献吻合较好,验证了该算法计算圆柱绕流的有效性,并分析了Re=1 000时不同直径比、间距比情况下的串列双圆柱绕流,根据流场的不同涡脱落形态及两圆柱平均阻力系数、升力系数随直径比、间距比变化的规律得到了不同直径比条件下的临界间距范围。达到临界间距后,流场由单一涡脱落状态转变为双涡旋脱落状态。最后分析了两圆柱平均阻力系数及升力系数在临界间距后急剧增加的原因,为背负式海底管线的布局优化提供了理论依据。     

CALCULATION OF VISCOUS FLOW AROUND CIRCULAR CYLINDER WITH THREE-DIMENSIONAL NUMERICAL SIMULATION

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｆｌｏｗａｒｏｕｎｄａｃｉｒｃｕｌａｒｃｙｌｉｎｄｅｒｉｓｖａｌｕａｂｌｅｉｎｏｉｌｃｏｍｐａｎｉｅｓｏｒｏｆｆｓｈｏｒｅｉｎｄｕｓｔｒｙｔｈａｔｒｅｌｙｉｎｍｏｓｔｃａｓｅｓｏｎｓｕｂｓｅａｐｉｐｅｌｉｎｅｏｒｒｉｓｅｒｓｔｏｔｒａｎｓｐｏｒｔｇａｓａｎｄｏｉｌｆｒｏｍｏｃｅａｎｇｒｏｕｎｄｓｔｏｌａｎｄｏｒｓｕｒｆａｃｅｐｌａｔｆｏｒｍ .Ｗｅｓｈｏｕｌｄｅｎｓｕｒｅｔｈａｔｔｈｅｓｅｏｆｆｓｈｏｒｅｓｔｒｕｃｔｕｒｅｓａｒｅｒｅｓｉｓ ｔａｎｔａｎｄｓｔａｂ…     

Numerical simulation of wave interacting with a submerged cylinder using a 2D RANS model

A 2D RANS numerical model (IH2VOF) is employed to study wave interacting with a circular cylinder with a diameter of 0.02 m in a water depth of 0.27 m, with a wave period of 1.08 s and a wave height of 0.047 m. The influence of the wall proximity on the forces is analyzed for ratios between the pipe (i.e. circular cylinder) distance from the bottom and the pipe diameter varying from 0.04 to 1.5. Results of lift forces and streamlines are compared with the experimental results of Jarno-Druaux et al. (1995) and good agreement is found. Lift, drag and inertia coefficients are also compared with experimental results and the same trend of fundamental quantities with the gap between the cylinder and the bottom was obtained with the model giving slightly larger values. Finally, the influence of the method to estimate the drag and inertia coefficients in the force calculated using Morison equation is analyzed and Morison method shows the better agreement.     

三维圆柱绕流数值模拟湍流方法的选择

研究湍流模拟方法对三维圆柱绕流数值模拟精度的影响,分别采用雷诺平均法（RANS）中的κ-ω模型、SST模型以及大涡模拟法（LES）对亚临界区内雷诺数Re=3 900时的三维圆柱绕流进行数值计算,分析了圆柱体表面的受力、圆柱后流场时均速度特性与瞬时涡量分布情况。结果表明,当流体流过圆柱表面时,圆柱表面出现的与流速方向相反的负压力差区域使流体从圆柱表面分离,引起了不稳定的周期性交替脱落的湍流涡泄,从而在圆柱表面产生周期性波动的升力,同时在圆柱后近流场区域形成回流区。研究还发现,LES法对圆柱体的受力以及流场时均速度特性的模拟效果要优于κ-ω模型与SST模型;相较于前人利用浸入边界法得到的模拟结果,LES法的模拟精度也有了较大提升;同样,通过对瞬时流场涡量等值线图的分析,并与已有的模拟结果进行对比,发现LES法不但可以从整体上表现出漩涡的周期性脱落,而且对流场中不同位置的、复杂的小尺度湍流涡泄也描述得非常细致,得到的自由分离剪切层长度与湍流涡泄的卷曲度更符合湍流涡泄的特征。所以,在亚临界区,LES法对湍流的模拟效果相对较好。     

FLOW PAST TWO ROTATING CIRCULAR CYLINDERS IN A SIDE-BY-SIDE ARRANGEMENT

Measurements were performed using Particle Image Velocimetry(PIV) to analyze the modification of flow by the combined effects of the rotation and the Reynolds number on the flow past two rotating circular cylinders in a side-by-side-arrangement at a range of 425 ≤ Re≤ 1130,0 ≤α≤ 4(α is the rotational speed) at one gap spacing of T / d =1.11(T and d are the distance between the centers of two cylinders and the cylinder diameter,respectively).A new Immersed-Lattice Boltzmann Method(ILBM) scheme was used to st...     

Numerical simulation of flow past twin near-wall circular cylinders in tandem arrangement at low Reynolds number

Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of 0.25 ≤ G/D ≤ 2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.     

Large-eddy simulation of the flow past both finite and infinite circular cylinders at Re =3900

The flow past a finite circular cylinder with a height-to-diameter ratio of 1.5 and an infinite circular cylinder of the same diameter at a Reynolds number Re= 3 900 is investigated using the large eddy simulation(LES). The objective of the present study is to explore the differences of the flow mechanisms between the finite and infinite circular cylinders. It is shown that the free end of the finite circular cylinders affects the wake region significantly. The mean drag coefficient and the fluctuating lift coefficient of the finite circular cylinder are smaller than those of the infinite circular cylinder. The three-dimensional separation and the separated shear layer instability of the finite circular cylinder can obviously be observed. The existence of an arch vortex in the average flow downstream of the free end is demonstrated.     

大直径圆筒筒内填料抗倾机理

根据试验结果及分析，圆筒内填料抗倾模式随筒径的增大而变化。筒径由小到大，筒内填料抗倾模式由重力式逐渐向过渡式、平面挡土墙式变化。大圆筒的抗倾能力，除应考虑筒内壁与填料间的摩擦力，还应计及作用在筒壁上填料侧压力所起的抗倾作用。