三角形排列圆柱绕流尾流模式及其流体力特性

该文采用基于嵌入式迭代浸入边界法对等边三角形排列的三圆柱绕流进行了数值模拟研究,其中上游为一个圆柱,下游为并列两圆柱,雷诺数为Re?100,间距比为L*?1.0-6.0。依据流体力特性和旋涡排列的不同,将尾流模式分为6种,分别为单体模式(L*?1.0-1.4)、偏斜模式(L*?1.5-1.9)、FF(Flip-Flopping)模式(L*?2.0-2.5)、反相模式(L*?2.6-2.8和3.5-4.1)、同相模式(L*?2.9-3.4和4.2-4.5)和共同脱涡模式(L*?4.6-6.0)。其中,偏斜模式下,下游两圆柱的间隙流会稳定偏向其中一个圆柱,使得两圆柱的尾流宽度不同,对应的阻力均值也不相等。在上游圆柱剪切层的作用下,FF模式中间隙流偏斜方向切换的时间间隔要明显大于相同雷诺数下并列双圆柱绕流时的情况。为深入研究各尾流模式的特性,分析了不同模式下三圆柱流体力系数的变化情况及其原因。当1.9?L??4.6时,上游圆柱的剪切层进入下游两圆柱的间隙,使得下游两圆柱出现相互吸引。当4.8?L??5.5时,下游两圆柱与上游圆柱脱落旋涡的作用不一致,使得下游两圆柱的流体力系数不相等。     

上游圆柱固定条件下串列三圆柱涡激振动响应和尾流特性

应用基于嵌入式迭代浸入边界法对雷诺数Re=100下串列三圆柱涡激振动进行了数值模拟,其中上游圆柱固定不动,中游和下游圆柱仅作横向振动。三圆柱间距相同,间距比L~*= 1.2、2.0和5.0,折合流速U_r=3.0-25.0,质量比m~*=2.0。研究发现,各间距比下,串列三圆柱存在强烈的相互作用,中游和下游圆柱的振幅明显大于单圆柱涡激振动的情况。随着L~*的增大,圆柱振幅整体上减小,除个别工况外,下游圆柱的振幅均大于中游圆柱的情况。当间距比较小(L~*=1.2、2.0)时,St数随折合流速的增加而缓慢减小;当间距比较大(L~*=5.0)时,St数几乎不再随折合流速变化,固定在St=0.15上。对尾流的研究发现,当振幅较小时,上游圆柱的剪切层将三圆柱包裹在一起,尾流与绕流时相似,表现为经典的卡门涡街;当振幅较大时,上游圆柱的旋涡/剪切层撞击/重附着于下游圆柱上,圆柱之间存在强烈的相互作用,尾流表现为并排的两列旋涡。     

并列旋转双圆柱流动特性的数值模拟

该文基于k - ε湍流模型,采用Galerkin有限元法对并列旋转双圆柱的绕流特性进行了数值模拟,计算的雷诺数为 1550.为了考查两圆柱旋转和间距的相互作用,文中采用三种间距比分别是T/D = 1.2,1.6和3.0 (T 为两圆柱中心之间的距离,D为圆柱直径) 和一系列不同的旋转速度比 (|α| ≤ 2).计算显示,当 |α| = 0,即圆柱不转动时,对应三种间距有三种典型的流型,单钝体流型对应小间距、偏流对应中等间距和对称流对应大间距;当 |α| 达到临界值时,涡脱落得到了有效的抑制,流动趋于稳定,升力系数和阻力系数的脉动值趋于零;平均升力系数和阻力系数随着 |α| 的增大分别增大和减小.     

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。     

多圆柱绕流旋涡脱落和流场形态概论

当流体绕多个圆柱流动时,圆柱的个数、相对位置和大小都明显影响着绕流流场结构。基于已有研究成果,归纳总结了流场中放置双圆柱、三圆柱、四圆柱和流场中主圆柱附近放置1个或2个附属小圆柱时,随圆柱相对位置变化,流场结构和旋涡脱落状态的演变规律。双圆柱相对位置分串列、并列和错置3种,其绕流流态按间距比和水流攻角对旋涡脱落形态的影响划分,流态在临界间距比上下变化很大;三圆柱呈“品”字布置,当间距比小于临界值时,出现明显的偏流现象,大于临界值后不再出现偏流现象;三圆柱呈倒“品”字布置,在任何间距比下,流动状态相对于来流几乎都是对称分布的;四圆柱绕正方形排列,实验研究发现上游两圆柱后没有旋涡形成和脱落,下游两圆柱旋涡脱落反相同步,而数值模拟得到上下游柱后都有明显的涡脱落;主圆柱尾流中存在附属小圆柱时,调整小圆柱的位置能够有效抑制尾流中的旋涡脱落。     

串列条件下静止圆柱对振动圆柱的流致振动影响试验研究

利用圆柱群的流致振动进行海洋能发电是当前可再生能源研究的热点之一。由于多柱体绕流存在强烈的相互干扰作用,其流致振动与单圆柱有着明显的区别且运行过程中必然存在某些柱体损坏或停机的现象,对相邻圆柱产生巨大的影响。利用自循环水槽对串列条件下静止圆柱对振动圆柱的流致振动影响进行试验研究。考虑两种工况:(1)上游圆柱固定,下游圆柱可沿横流向自由振动;(2)下游圆柱固定,上游圆柱可沿横流向自由振动。结果表明:对于工况(1),当2.0≤L/D≤4.0时,固定上游圆柱对下游圆柱的振动响应起增强作用,当5.0≤L/D≤7.0时,固定上游圆柱对下游圆柱的振动响应起抑制作用;对于工况(2),当2.0≤L/D≤3.0时,固定下游圆柱对上游圆柱的振动响应起增强作用,当L/D=4.0时,固定下游圆柱对上游圆柱的振动响应起抑制作用。随着间距比的增大,振动圆柱的涡激振动(vortex induced vibration,VIV)上端分支范围逐渐减小。相比于工况(1),工况(2)中上游圆柱的振动响应对间距比更为敏感。     

浅水圆柱绕流流动模式探讨

数值求解了二维浅水方程和RNG k-ε流模型,模拟了不同稳定性系数S和圆柱中心间距G下的单圆柱、两圆柱和三圆柱的尾流流动模式,研究了底部摩擦力对尾流结构的影响。结果表明:随着S增大,尾流在底部摩擦力的作用下趋于稳定,大尺度涡结构逐渐消失。单圆柱尾流区依次出现了涡街（VS）尾流、不稳定漩涡（UB）尾流和稳定漩涡（SB）尾流。多圆柱尾流除了受S数影响外,还与G密切相关。随着G的增大,两圆柱背后依次出现了单钝体绕流、偏转尾流和对称尾流,三圆柱背后则依次出现了单钝体绕流、偏转尾流、对称尾流和非对称尾流。此外,数值结果还表明多圆柱尾流结构不同于单圆柱,多圆柱并排使得尾流更加不稳定。     

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。     

壁面对并列双圆柱尾迹影响的实验研究

用压强传感器和PIV对近壁并列双圆柱尾迹频谱和涡结构进行了测量,来研究壁面对其尾迹特性的影响.实验在循环水槽内进行,雷诺数为1696(基于圆柱直径D),壁面边界层厚度为6.6D.两个重要的特征参数T/D和G/D(T为两圆柱中心间的距离,G为下圆柱与壁面间的距离)分别为:T/D=1.151和1.604;G/D=0～1.811.结果显示,对于T/D=1.151,当G/D为0.302～1.811时,两圆柱尾迹表现为base-bleed流动模式,随着G/D的增加,尾迹强度逐渐增强,尺寸逐渐减小.对于T/D=1.604,当G/D大于临界值时出现biased流动模式,随着G/D的增加,两圆柱的尾迹尺寸以及上圆柱的斯特鲁哈数St变化很小;当G/D小于临界值时,随着G/D的减小,两圆柱的尾迹尺寸都逐渐减小,上圆柱的St逐渐增加.     

近平板圆柱体气动力雷诺数效应

该文通过风洞试验对水平板附近圆柱气动力特性进行了研究。实验中圆柱平板间隙比G/D=0-2.0,雷诺数范围为1.9×10~5-4.5×10~5,涵盖了亚临界、临界与超临界区。研究发现,G/D=0和0.05时,在该实验雷诺数范围内圆柱气动力没有雷诺数效应,圆柱上侧始终处于湍流分离状态;G/D≥0.1后,气动力存在明显雷诺数效应,但G/D并不影响临界雷诺数的数值。当0.1≤G/D≤0.4时,圆柱上侧边界层首先发生湍流转变;而当G/D≥0.5时圆柱下侧边界层首先发生湍流转变。亚临界区内,G/D≥0.5的圆柱尾流出现周期性涡脱;而小间隙比下,圆柱涡脱被平板抑制。临界与超临界区域内,各间隙比下圆柱尾流中都无周期性涡脱存在。     

低雷诺数下并列双波浪柱尾迹干扰效应数值模拟

该文针对雷诺数Re=100下不同波长参数(/mλD=2、4、6和8)、不同间距比(1.5/3.5m≤L D≤)的并列双波浪柱后尾迹复杂的三维流动结构及干扰效应进行了数值研究。研究表明:三维并列双波浪柱在较小的间距比/1.5mL D=时,波峰对波谷排列的并列波浪柱后尾迹呈现明显偏置双稳流动结构,而波峰对波峰排列工况下基本呈现单一波浪型钝体后尾迹流动结构(尤其是在大波长/mλD=6和8时);当间距比/3mL D≥时,随着波长/mλD的增大,上下波浪柱各自呈现单波浪柱后尾迹流动结构;较大波长的三维波浪形状更好地组织了后尾迹三维流动结构,减少了并列双波浪柱后尾迹的相互干扰,从而减阻减振明显,最高减阻可达14.5%,脉动升力系数上下游波浪柱均趋于0.1。该研究可为近海工程的多立管结构及悬索桥的拉索振动抑制等提供理论支持。     

WAKE PATTERNS OF FLOW PAST A PAIR OF CIRCULAR CYLINDERS IN SIDE-BY-SIDE ARRANGEMENTS AT LOW REYNOLDS NUMBERS

A flow past two side-by-side identical circular cylinders was numerically investigated with the unstructured spectral element method. From the computational results at various non-dimensional distances between cylinder centers T/D and the Reynolds number Re, a total of nine kinds of wake patterns were observed: four steady wake patterns, including single bluff-body steady pattern, separated double-body steady pattern and transition steady pattern for sub-critical Reynolds numbers and biased steady pattern for super-critical Reynolds numbers, and five unsteady wake patterns, including single bluff-body periodic pattern, biased quasi-steady pattern, quasi-periodic (flip-flopping) pattern, in-phase-synchronized pattern and anti-phase-synchronized pattern. Time evolution of lift and drag coefficients corresponding to each unsteady wake pattern was given.     

串列双圆柱在规则波中的压力分布

本文通过实验研究，测定了串列双圆柱在规则波中柱表面压力，分析了定常压力和脉动压力沿柱周向的分布，对并列、串列双圆柱的升力进行了适当的讨论，结果表明，两柱的压力分布、升力均与两柱间距有关。     

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...     

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。     

WALL EFFECTS ON FLOWS PAST TWO TANDEM CYLINDERS OF DIFFERENT DIAMETERS

Flows past two tandem cylinders of different diameters placed centrally in a channel with fixed centre-to-centre spacing 6D and diameter ratio are simulated based on the Lattice Boltzmann Method(LBM).In all the simulations,the diameter of the smaller cylinder is chosen as the characteristic length.The Reynolds number based on the average inflow velocity is 20-120 and studies are over the range of blockage ratio 2-8.In both Small-Big Arrangement(SBA)and Big-Small Arrangement(BSA),the effects of the channel width and Reynolds number on the flow structures and force coefficients are studied.Results show that the flows in BSA are more regular than those in SBA for the same flow fields.In BSA with and,the force coefficients all fluctuate with constant amplitudes and a coupled frequency,the coupled frequency becomes small as the blockage ratio decreases and by an exact test we give out the relation of the blockage ratio and Strouhal number.As the blockage ratio decreases to 2,there exist pitchfork bifurcations in both SBA and BSA,and results show that the critical Reynolds numbers of pitchfork bifurcations for SBA and BSA are both between 60 and 80.In SBA with,the flow structure has a static asymmetric mode.It is found that the channel width has also an effect on the critical spacing where the flow changes from single body mode into co-shedding mode.By an accurate survey on flows past two cylinders with equal diameters placed inside a channel with the width,the relation between channel width and the critical spacing is given and results show that the critical spacing increases as the channel width increases.     

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。     

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...