旋转方式对并列双圆柱绕流特性的影响

基于层流模型,使用有限体积法对并列旋转双圆柱绕流进行数值模拟计算。首先计算雷诺数为100时静止单圆柱绕流与旋转单圆柱绕流的流动性能,并与参考文献结果进行比较,验证计算的可靠性;然后,分析了两圆柱在中心间距比为3.0时圆柱不同旋转方式与旋转速度比对双圆柱绕流流动性能的影响。结果表明:逆流向旋转比顺流向旋转的临界转速更小,对涡旋脱落的抑制效果更好;两种旋转方式下时均升力系数绝对值均随旋转速度比的增大而增大;逆流向旋转下时均阻力系数随旋转速度比的增大而减小,顺流向旋转下时均阻力系数随旋转速度比的增大先增大后减小。     

不同间距比下粗糙度对并联双圆柱绕流的影响

利用ANSYS-Workbench大型有限元软件建立了二维模型,在Fluent的工作环境下,探究了不同间距下不同柱体粗糙度对并联双圆柱的升力系数、阻力系数的影响。采用SST k-ω湍流模型,雷诺数控制在1×10~6,并联双圆柱的间距比T/D分别为1.5、2.0、2.5、3.0,进行了柱体表面粗糙度Rh在0、0.1%D、0.3%D、0.5%D、0.8%D和1%D时的数值模拟。结果表明:间距比为1.5时,阻力系数达到最大,升力系数上下波动峰最高;在同一间距比下,随着粗糙度的增加,阻力系数先增大后减小,粗糙度在0.5%D时阻力系数达到最大;并联双圆柱由光滑面发展到粗糙面,阻力系数会发生突变,证明了光滑柱面下的阻力系数最小和升力系数的波动峰值最小。基于以上研究,可以将结论应用于以后圆柱绕流的理论研究和桥梁墩柱的工程建设中。     

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。     

高雷诺数下串列双圆柱绕流的影响因素研究

针对串列双圆柱绕流问题进行了数值研究,利用Fluent软件建立二维数值模型,探究了不同柱体间距、不同柱体表面粗糙度对串列双圆柱阻力系数、升力系数、St数的影响。采用SST k-ω湍流模型,对雷诺数为1×10~6,柱体间距L/D分别为1.75、1.90、2.20、2.50,表面粗糙度Rh在0~0.5%D范围内的串列双圆柱进行数值模拟。结果表明:柱体间距L/D在1.75~2.50范围内,光滑柱体表面下,St数、后柱平均阻力系数会随着柱体间距的增加而增大;同时,柱体间距对升力系数振幅也存在极大影响。改变柱体表面粗糙度,会使柱体间距为1.75的串列双圆柱前柱平均阻力系数在Rh=0.2%D时降低7%,而各柱间距下的后柱平均阻力系数会随粗糙度的增加而减小。研究成果能够为河道桥梁建设和圆柱绕流理论研究提供基础数据。     

低雷诺数条件下并列三圆柱绕流的尾流模式和水动力系数研究

该文应用浸入边界法对雷诺数Re(28)100和间距比T/D(28)1.1-5.0条件下的等间距并列三圆柱绕流进行了数值模拟。研究发现,尾流模式与无量纲圆柱间距比T/D密切相关,在所研究的间距比范围内共出现六种尾流模式,分别为:单体尾流模式(T/D(28)1.1-1.2)、偏斜尾流模式(T/D(28)1.3)、第一类Flip-Flopping(FF1)尾流模式(T/D(28)1.4-1.5)、第二类Flip-Flopping(FF2)尾流模式(T/D(28)1.7-2.3)、同步尾流模式(T/D(28)2.5-3.2)和调制尾流模式(T/D(28)3.3-5.0)。通过分析近尾流的涡量图、升阻力系数时程曲线和不同圆柱所受升力的相位差,详细研究了各个尾流模式的特点和联系。     

直径变化对三圆柱绕流的影响

数值研究了直径变化对三圆柱绕流的影响.在上游布置一个直径在d/D=0.15～2.0范围变化的圆柱,再以并列形式布置两个直径为D的圆柱.用有限元法对不等直径三圆柱的二维绕流进行数值模拟,分别求出在不同直径比下的流场分布和各个圆柱的升、阻力系数以及Strouhal数.结果发现:在直径比的变化过程中,流场可分为五类;升、阻力系数和Strouhal数的变化都有一定规律.     

高雷诺数下并列双圆柱绕流的DES法三维数值模拟

该文采用基于S-A的DES方法对雷诺数为104且不同间距比下并列双圆柱的湍流模型进行了三维数值模拟,取间距比T/D为1.1、1.5、2.0、3.0和4.0(T为两圆柱中心之间的距离,D为圆柱直径)。数值模拟研究了流场形态,升阻力系数及升力频谱,发现了不同间距比下的各种紊流形态及流体动力情况,它们与实验结果一致且显示了明显的三维特性,同时这也验证了DES方法在高雷诺数柱群数值模拟方面的准确性。     

流体中相互靠近两圆柱的水动力特性数值研究

该文采用基于动态网格技术的CFD数值方法,对黏性流体中两物体相互靠近时的水动力特性进行了研究。首先对比分析了无黏流场和黏性流场中圆柱的受力特性,然后分析了不同间隙比、不同靠近速度、不同背景流场下黏性流场中圆柱的受力特性。数值模拟结果表明:当来流速度为零时,阻力系数随着间隙比的减小而增大,随靠近速度的增大而增大;当来流速度不为零时,阻力系数随着来流速度的增大而增大;当来流速度与靠近速度之比较大时,圆柱受力出现较为明显的振荡。     

高雷诺数下圆柱绕流与大振幅比受迫振动的数值模拟

利用CFD方法,研究较高雷诺数下圆柱绕流及圆柱大振幅比横向受迫振动特性。在Navier-Stokes方程和k??湍流模型的基础上,对圆柱绕流分别进行了二维与三维的数值模拟,得到了圆柱绕流的升力系数和漩涡发放频率数等结果。研究结果表明,三维模拟的升力系数均小于二维模拟结果。利用Fluent的动网格技术进行大振幅比圆柱横向受迫振动的研究,得到圆柱在不同振动频率时的升力系数及漩涡发放规律和圆柱在特定振幅及频率下的"锁定"区间。     

串列双圆柱涡激振动响应的数值模拟

该文利用动网格技术对雷诺数Re=100的串列双圆柱的涡激振动响应特性进行了详尽的数值研究。研究了上游圆柱固定,下游圆柱横向振动时,不同间距比(L/D=2-5)和折合流速(Ur=2.4-12)对上、下游圆柱的升阻力特性、涡激振动响应特性和圆柱间干扰效应的影响;以及下游圆柱双自由度(横向和流向振动)涡激振动响应特性。研究发现:随着间距比的增大,下游圆柱开始进入"锁定区间"的Ur减小,且下游圆柱的涡激振动对上游圆柱的影响逐渐减弱,但上游圆柱对下游圆柱的干涉效应一直存在。对于不同间距比,在折合流速Ur=7.2附近,下游圆柱的升阻力系数具有很明显的"跳跃"现象,并出现阻力峰值,且不同间距比的下游圆柱都在Ur=7.2时获得最大振幅且幅值相近,这意味着下游圆柱可能在此折合速度下被完全诱导,当下游圆柱被完全诱导振动后,间距比对圆柱振幅的影响较小。不同的折合流速下,小间距比(L/D=2)和大间距比(L/D=5)的尾流会表现出不同的流动形式和"2P"、"2S"等涡脱形式。下游圆柱双自由度振动时,流向振动相对横向振动振幅较小。     

Vortex shedding in the flow around two side-by-side circular cylinders of different diameters

In this paper,the 3-D turbulent flow around two side-by-side circular cylinders of different diameters,at sub-critical Reynolds number(Re=3 900),is numerically simulated by the large eddy simulation(LES).The spacing ratios(T/D)between the two cylinders are considered in four cases(T/D=1.2,1.5,1.8 and 2.7)to study the vortex shedding and turbulent properties in the flow field.The main results are focused on the drag and lift coefficients,the vortex shedding frequency,the coherent structure,and the scale properties.It is shown that when T/D is equal to 1.2,the vortex shedding of the main cylinder is strongly suppressed by the small cylinder,the drag and lift coefficients of the main cylinder are smaller than those in other three cases.While T/D is equal to 1.5,the vortex shedding of the main cylinder can be improved,the drag and lift coefficients of the main cylinder are larger than those in other three cases.The empirical mode decomposition(EMD)method is applied to decompose the velocity signals traced by the LES.It is shown that there is a linear relationship between the mean period and the mode in the semi-log coordinates.The vortex shedding period of the main cylinder is consistent with the period of the restructured coherent structures quantitatively.     

Flow characteristics of the two tandem wavy cylinders and drag reduction phenomenon

This paper presents an extensive numerical study of 3-D laminar flow around two wavy cylinders in the tandem arrangement for spacing ratios (L/Dm ) ranging from 1.5 to 5.5 at a low Reynolds number of 1...     

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...     

双圆柱在不同排列方式下绕流流态模拟

双圆柱绕流伴随着流动分离、旋涡生成与脱落、旋涡间相互干扰等复杂问题,其流动形态和流动特征受圆柱相对位置影响。使用FLUENT流体软件,选取间距比1.75,2.5和4,在二维层流模型下,模拟了双圆柱串列、30°夹角错置、60°夹角错置和双圆柱并列绕流,分析了双柱绕流流态、旋涡脱落形态、升力、阻力系数随圆柱相对位置改变而变化的规律,并对比已有的试验成果和模拟成果,为桥梁建设和圆柱绕流理论研究提供了基础数据。     

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.     

高雷诺数下双圆柱绕流的数值模拟

本文使用表面涡法研究高雷诺数下不同排列方式双圆柱绕流的流动状态，计算了双圆柱在并列、串列及级列的情况下的各种流动结构，涡街的变化及作用在圆柱上的受力情况。本文结果清楚地描述了双圆柱绕流复杂的流动状况，计算结果与实验显示的流动状况十分相似，斯特罗哈数和阻力系数与实验结果符合得很好。     

Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters

The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.     

亚临界雷诺数下波浪型圆柱绕流的数值模拟及减阻研究

采用大涡模拟数值方法对亚临界雷诺数Re=3000下波浪型圆柱的绕流现象进行研究分析。研究结果表明,波浪型圆柱的三维尾迹涡结构能得到很好的控制,它在轴向方向呈现周期性正负涡的交替分布特性。随着幅值的增大,波浪型圆柱表面的自由剪切层得以延展,使得旋涡的脱落发生在波浪型圆柱下游较远处,从而达到减阻的目的。波浪型圆柱与普通直圆柱相比,其幅值对平均阻力系数及脉动升力系数的减少及尾迹控制有着更重要的影响,最大减阻可达16%。