共查询到19条相似文献，搜索用时 109 毫秒
1.
基于粒子图像测速技术(PIV)对小间距比比L/D=1.5工况下方形布置四圆柱在不同来流角角α(α=0°、15°、30°、45°)条件下的尾流流场特性进行了试验研究,分析了不同来流角度条件下四圆柱瞬时和时均尾流流场特征,获得了瞬时和时均速度矢量、涡量等值线、流线拓扑及雷诺应力分布随来流角度变化的规律。试验结果表明,来流角度对方形布置四圆柱尾流形态有显著影响。四圆柱瞬时尾流形态随来流角度增大可分为延伸体流动流态(α=0°)、尾流剪切层附着流态(α=15°、30°)及尾流剪切层共同脱落流态(α=45°)三种流态。当来流角度增大时,四圆柱下游断面平均流向速度分布由"W"形向"U"形转变,时均雷诺正应力及雷诺剪切应力等值线分布特征也会发生明显改变。 相似文献
2.
《中国海洋大学学报(自然科学版)》2016,(6)
为研究间距比对多柱体在湍流场下的互扰效应影响,利用Fluent软件模拟了雷诺数为3 900,柱间距比L/D为1.6~6.0情况下正方形排列四圆柱绕流过程。通过模拟得到了不同间距比下的升、阻力系数值以及涡量图,利用快速傅里叶变换法得到了漩涡脱落频率。结果表明,当柱间距比L/D为1.6~2时,4个圆柱后都没有漩涡脱落,随间距比增加,上游圆柱平均升力系数增大,平均阻力系数减小,下游圆柱平均升、阻力系数减小,斯特鲁哈数增大;当L/D为2~3.5时,随间距比增大,下游圆柱后开始出现漩涡脱落,平均升、阻力系数减小,斯特鲁哈数增大;当L/D为3.5~6时,随间距比增大,四个圆柱后都发生漩涡脱落,上游圆柱平均升、阻力系数减小,下游圆柱平均升力系数减小,平均阻力系数增大,斯特鲁哈数不变。L/D3.5时互扰效应逐渐增强,L/D3.5时互扰效应逐渐减弱;考虑到工程安全性和经济性,本文研究成果对于海洋工程设计具有一定的参考价值。 相似文献
3.
利用Fluent软件模拟雷诺数为200时不同间距比G/D和直径比d/D情况下的圆柱绕流现象。根据模拟结果分析G/D和d/D对圆柱体的涡脱落形态,大、小柱体的升力,阻力系数和St数的影响,结果表明涡脱落形态随着G/D和d/D的变化呈现不同的形式,在G/D小于临界间距比时呈现单一涡脱落形态,在G/D大于临界间距比时,呈现双旋涡脱落形态;临界间距比随着d/D增大而增大。在临界间距比附近大、小柱体的升力和阻力系数值及St数变化较大,大、小柱体的St数具有相同的变化规律,St随着d/D的增大而减小。 相似文献
4.
为研究低亚临界雷诺数Re情况下错列角度θ对不等直径双柱体绕流特性的影响,利用Fluent软件模拟了Re为3 900、间距比G/D为2.0、直径比D/d为0.5、θ=0°~180°之间9种角度的绕流过程,得到了流场涡量图、斯特鲁哈数St_1和St_2、平均阻力系数C_(d1)和C_(d2)以及平均升力系数C_(l1)和C_(l2)。研究结果表明,随着θ的从小到大,St_1先增大后减小,且在θ=30°和180°时有两个值,St_2在θ=120°~150°时明显小于其它角度;C_(d1)和C_(d2)的整体趋势都是先增大后减小,C_(l1)在θ=150°时取得极大值,C_(l2)在θ=30°时取得极小值。θ=0°时,两柱后方有单一涡脱落形态;θ=30°时,小柱后方有稳定漩涡脱落产生,大柱后方涡脱落受到干扰,且大柱有两个涡脱落频率;θ=45°~90°时,在间隙流的作用下,两柱后方均有漩涡脱落,尾流中有两列涡街;θ=120°~180°时,大柱后有稳定漩涡脱落,小柱涡脱落受到抑制。研究结果可为相关海洋工程设计提供参考。 相似文献
5.
针对双振子流致振动潮流能转换装置,基于ADINA软件对上游圆柱固定、下游圆柱横向振动的串列双圆柱流致振动,在不同工况下进行了数值模拟,并与文献和试验结果进行了对比分析,验证了该模拟方法的正确性并分析了不同因素(间距L=1.5 D~8.0 D、流速v=0.4~0.75m/s及相应流速v下的雷诺数Re=2.88×10~4~5.76×10~4)对下游圆柱流致振动的影响。结果表明,圆柱间距影响双振子尾流模式和下游振子振动形式;间距L=5 D~7 D范围内下游振子达到最大振幅,比单圆柱涡激振动增大50%。 相似文献
6.
7.
《中国海洋大学学报(自然科学版)》2016,(7)
管线附近的水动力因素是底床局部冲刷形成的主要原因。基于开源程序OpenFOAM和分离涡紊流模拟方法建立三维数值水槽,数值模型的计算结果与同条件的物理实验结果基本一致。在此基础上,对水流作用角为30°、45°、60°和90°及间隙比为0、0.1、0.3、0.5水流作用下,管线周围的流场结构进行分析,探讨水流作用角和间隙比对管线附近三维水流结构的影响规律。结果表明:随着作用角的增大,管前涡流范围逐步缩小至管线附近,管后涡流范围逐步向下游延伸,且管后涡漩尺度、回流范围与尾涡紊动区域逐步增加,尾涡中心逐步远离管线,且轴向水流逐渐减弱;管后尾涡的产生、脱落,涡旋尺度大小受管线与底床间隙比e/D的影响明显,e/D=0时管线后尾涡的脱落形态不明显;e/D0.3时,类似圆柱扰流,管后尾涡形态变化不明显。 相似文献
8.
《中国海洋大学学报(自然科学版)》2015,(5)
多柱体系统在石油开采逐渐向深海发展的过程中得到广泛的应用,由于波浪、流对多柱体的影响易导致其破坏。因此研究多柱体系统绕流具有重大价值。目前多不等直径多柱体绕流的研究还有待深入。本文利用Fluent模拟雷诺数Re=3 900,G/D为0.1~2.5,d/D为0.5、1.0情况下并列双圆柱的绕流过程,并根据模拟结果分析G/D和d/D的变化对大、小柱体涡脱落形态、升力系数Cl、阻力系数Cd和St值的影响。结果表明,随着G/D变化,涡脱落形态会呈现出不同的形式,绕流参数值也随之发生变化。当0G/D≤0.2时,柱后只有一个涡脱落,为单一涡脱落区,升、阻力系数值存在突变,St值小于单柱St值;当0.2G/D≤0.5~1.0时,柱后出现交替的偏斜流,为偏斜流区,升、阻力系数随着G/D的增大而减小,St值在两个极值之间变化;当0.5~1.0G/D≤2.5时,柱后有成对的涡旋,为双旋涡脱落区,升阻力系数值趋于稳定,St值稳定在0.2左右。偏斜流区与双旋涡脱落区之间的临界间距比G/D随着d/D的增大而增大;不等直径情况下,间隙流偏斜对大柱的影响小于对小柱的影响。 相似文献
9.
两层粘性流体中圆柱体受迫振荡数值模拟 总被引：1，自引：1，他引：1
研究两层粘性流体中无限长水平圆柱体的受迫振荡问题。在湍流模式下,采用VOF方法追踪两层流体的内界面,基于动网格技术模拟圆柱体的运动边界,对均匀流中横向振荡圆柱体的绕流场进行了数值模拟。计算受迫振荡圆柱体的升力系数、阻力系数随时间的演化曲线和圆柱体的尾涡分布,以及圆柱体的受迫振荡激发两层流体内界面的扰动,并与均匀流体的情况进行了比较分析。研究表明,流体的两层分层效应对受迫振荡圆柱体的升阻力系数和尾涡分布特性都有显著影响,在水下输油气管道涡激振动特性的工程评估中,应考虑流体的密度分层效应。 相似文献
10.
为研究潮流能水轮机尾流场流动特性及涡结构组成,基于DDES(Delayed Detached Eddy Simulation)模型对不同流速和转速的4种工况下水轮机尾流场进行数值模拟,并进一步探究其尾流场空间涡结构的变化特性。结果表明,水轮机的数值模拟结果与试验结果能够较好吻合。对比不同工况下的尾流场模拟结果可知:水轮机尾流区域流动复杂,延迟分离涡模拟方法能有效模拟水轮机旋转过程中产生的叶尖涡、叶尖脱落涡、轮毂涡等不同涡结构,并能完整观察到叶尖涡的产生、脱落、失稳、破碎过程。转速一定时,流速越大,叶尖脱落涡、轮毂涡的发展距离越远;流速一定时,转速越大,涡的发展距离越短。本文数值模拟计算结果可为实际海况中潮流能阵列水轮机的布局提供可靠依据。 相似文献
11.
《中国海洋工程》2021,(4)
Helical strake is a widely-used device for passive flow-induced vibration(FIV) control of cylindrical structures. It is omnidirectional and can effectively reduce FIV response amplitude. Studies on the passive FIV control for cylindrical structures are mainly concerned with a single isolated cylinder, while the influence of wake interference between multiple cylinders on FIV suppression devices is less considered up to now. In engineering applications,multiple flexible cylinders with large aspect ratios can be subjected to complex flow forces, and the effects of wake interference are obvious. The FIV suppression effect of helical strake of a common configuration(17.5 D pitch and0.25 D height, where D is the cylinder diameter) in two staggered cylinders system is still unknown. This paper systematically studied the FIV response of multiple cylinders system fitted with the helical strakes by model tests.The relative spatial position of the two cylinders is fixed at S = 3.0 D and T = 8.0 D, which ensures the cylindrical structures in the flow interference region. The experimental results show that the helical strakes effectively reduce the FIV response on staggered upstream cylinder, and the suppression efficiency is barely affected by the smooth or straked downstream cylinder. The corresponding FIV suppression efficiency on the downstream cylinder is remarkably reduced by the influence of the upstream wake flow. The wake-induced vibration(WIV) phenomenon is not observed on the staggered downstream cylinder, which normally occurs on the downstream straked cylinder in a tandem arrangement. 相似文献
12.
In the present study, flow characteristics were investigated experimentally using particle image velocimetry technique (PIV) in a gap between a solid cylinder and a shroud to reveal the effect of shroud diameter (Ds) and porosity (β) on the vortex shedding mechanism of the cylinder. Porosity (varied from β = 0.3 to 0.7) and diameter ratio (D/Ds = 0.4, 0.5 and 0.6) were main parameters examined at a Reynolds number of Re = 5000. For the porosity values of β ≤ 0.5, it is observed that vortex formation of the cylinder occurs only in the gap and shroud produces its own wake flow patterns. Penetrating flow through the shroud extends the shear layers on the both sides of the shroud through the downstream direction and prevents the interaction of shear layers in the near wake region. The diameter ratio and the porosity are impactful on the wake flow patterns in outer region of the shroud since they are determinant of the penetrating flow rate. Force measurements were also performed in the air tunnel in order to reveal the effect of shroud on the drag coefficient of cylinder. It is found that the drag coefficient of the cylinders are reduced significantly by shrouds when compared with that obtained from the bare cylinder case. However, the drag coefficient of the cylinder together with the shroud is higher than the bare cylinder for all cases since the shrouds enlarge the area exposed to the flow. 相似文献
13.
The flow patterns in the near wake of a cylinder (either circular or square in shape, D=25 mm) placed in the proximity of a fully developed turbulent boundary layer (thickness δ=0.4D) are investigated experimentally using particle image velocimetry (PIV). The effects of changing the gap height (S) between the cylinder bottom and the wall surface, over the gap ratio range S/D=0.1–1.0, have been investigated. The results show that both the ensemble-averaged and instantaneous flow fields are strongly dependent on S/D. The flow patterns for the two types of cylinders share many similarities with respect to the change in S/D, such as the reduced recirculation length and increased velocity fluctuation in the near wake with increasing S/D, as well as the trend of suppression of vortex shedding at small S/D and onset of vortex shedding at large S/D. However, developments of the shear layers, in terms of wake width, flow curvature, etc., are considerably different for these two types of cylinders. In general, the wake development and momentum exchange for the square cylinder are slower those for the circular cylinder at the same gap ratio. Correspondingly, it is shown that the periodic vortex shedding is delayed and weakened in the case of square cylinder, as compared to that of the circular cylinder at the same S/D. 相似文献
14.
Necati Mahir 《Ocean Engineering》2009,36(5):357-367
In this study, two- and three-dimensional numerical simulations were performed to investigate the effect of the flow structure in the wake of a square cylinder placed near a plane wall by applying a fully implicit finite-difference method to the Navier-Stokes equations. The gap ratio between the cylinder and the wall, G/D, was varied from 0.2 to 4 for the Reynolds numbers of 175, 185 and 250. The role of the 3D structure on the lift and drag coefficients and Strouhal number was investigated. The results were compared with those of the 2D numerical simulations. The deviations of the 3D flow structure of the cylinder-wall pair from that of a single cylinder were also reported. At Re=250, B type secondary vortices were determined in the wake region. At Re=175 and 185, transition from A type vortex to fully periodic B type vortices was observed when the cylinder was brought closer to the wall. 相似文献
15.
A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.
相似文献16.
Experimental results are presented in the paper of two elastically supported rigid circular cylinders subjected to steady flows in a flume. The two cylinders were initially placed at various tandem and staggered positions with one in the wake of the other when subject to the steady flows. The in-line centre-to-centre distance varied from 2 to 5 diameters whilst the cross-flow distance from 0 to 2 diameters. The nominal Reynolds numbers were in the sub-critical regime and ranged from 1.12 × 104 to 5.52 × 104, and the nominal reduced velocities from 1.78 to 8.77. The damping ratio of the test set-up is low at 0.003 which gives a combined mass-damping parameter of 0.0046. Both the cylinders were free to respond in both the in-line and the cross-flow directions. The cylinder motion was measured simultaneously with the hydrodynamic loading in the two directions. It was found that the motion trajectories of the downstream cylinder show qualitative difference depending upon whether it is in tandem with the upstream cylinder or in the wake with a transverse offset. The VIV response of the downstream cylinder is dependent upon the reduced velocity of the upstream cylinder and its own reduced velocity based upon the actual mean wake velocity. The drag amplification of the downstream cylinder in the wake appears to be fundamentally different from that of a single VIV cylinder in isolation. Furthermore, unlike the two fixed cylinders in cross flow, the downstream cylinder undergoing VIV no longer experiences a marked non-zero mean lift. The upstream cylinder is largely unaffected by the downstream cylinder when the initial spacing is greater than 3 diameters. On the other hand, the motion response of and the fluid loading on the downstream cylinder are strongly influenced by the upstream cylinder in the spacing range tested. 相似文献
17.
The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already known that a sharp edge square cylinder would undergo galloping if it is subjected to uniform flow. In this study the influence of the wake of a fixed circular cylinder on the response of a downstream square cylinder at different spacing ratios (S/D = 4, 8, 11) is experimentally investigated. The subject appears not to have received previous attention. The lateral displacements, lift forces and the pressure data from gauges mounted in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 7.7 × 102 to 3.7 × 104.In contrast to that for two circular cylinders in tandem arrangement, the freely mounted downstream square cylinder displays a VIV type of response at all spacing ratios tested. There is no sign of galloping or wake induced galloping with the square cylinder. With increase at the spacing ratio the cross-flow oscillations decrease. It is shown that the vortices arriving from the upstream fixed circular cylinder play a major role on the shedding mechanism behind the downstream square cylinder and cause the square cylinder to shed vortices with frequencies above Strouhal frequency of the fixed square cylinder (St = 0.13). The VIV type of oscillations in the downstream square cylinder is most probably caused by the vortices newly generated behind the square cylinder. 相似文献
18.
基于计算流体力学(CFD)开源代码OpenFOAM开展了不同雷诺数(Re=100、1500和3900)和倾斜角度(-60°≤α≤60°)工况下倾斜圆柱绕流流场的三维数值模拟,研究倾斜圆柱绕流的三维瞬时及时均尾流流场、流线拓扑、升阻力系数与旋涡脱落频率随雷诺数及倾斜角度变化的规律,探讨在顺流向及逆流向情况下独立性原则对倾斜圆柱绕流的适用性。研究结果表明:随着圆柱倾角的增大,倾斜圆柱尾流产生较为明显的轴向流,尾流旋涡脱落受到明显抑制,细碎旋涡逐渐消失,尾流宽度随之减小;随着雷诺数的增大,圆柱尾流涡管发生明显的变形,展向掺混使得大量细碎旋涡产生,呈现出明显的三维特性。在不同雷诺数下,阻力系数均值、升力系数均方根及无量纲涡脱频率在一定倾角范围内符合独立性原则。 相似文献
19.
《中国海洋工程》2020,(4)
A vortex-induced vibration(VIV) experiment on three side-by-side risers subjected to a uniform flow was carried out in a combined wave-current flume. The dynamic features of interference effect on three side-by-side risers were investigated by varying fluid velocity and inter-riser spacing. The distributions of dimensionless displacement,dominant frequency, and displacement trajectory of the model risers were measured using mode decomposition and wavelet transform techniques. The coupled interference of inter-riser fluid to adjacent risers at different spacings was disclosed by introducing the "interference ratio" concept. The results show that at spacings smaller than 6.0 D, the three model risers display appreciable deviations in their displacement responses in cross-flow or in-line direction,attributable to the strong proximity disturbance and wake interference between the risers. When the spacing is increased to 8.0 D, wake interference still makes great difference to the dynamic response of the risers in both directions. As reduced velocity increases, the three risers show higher agreement with an isolated riser in overall dominant vibration frequency in CF direction than that in IL direction at all spacings and the side risers, although symmetrically placed, do not vibrate symmetrically, as a result of the steady deflection of clearance flow within the riser group. Interference effect results in a remarkable unsteady mode competition within the risers; quantitation of the interference levels for the three risers at different spacings with interference ratio revealed that under low flow velocities and large spacing ratios, clearance flow constitutes a non-neglectable interferer for three side-by-side risers. 相似文献