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1.
为了深入研究亚临界雷诺数下光滑和沟槽圆柱绕流阻力及流场特性。采用SSTk-w模型对雷诺数Re分别为2×104,6×104,1×105和1.4×105的光滑圆柱和V型沟槽圆柱绕流进行三维流场数值模拟,首先以光滑圆柱绕流为算例与相关实验研究结果进行了对比,验证了SSTk-w方法的准确性,然后在不同雷诺数条件下,开展了V型沟槽圆柱绕流数值模拟研究;与光滑圆柱相比,V型沟槽圆柱具有较好的减阻效果,最大减阻率达28.4%;在相同雷诺数下,沟槽圆柱表面边界层分离点与光滑圆柱表面分离点相比更靠后。V型沟槽织构可有效改变尾流区旋涡脱落频率和尾流区湍流的发展,为隔水管减阻和提高隔水管柱系统的稳定性提供参考。 相似文献
2.
基于计算流体力学开源代码Open FOAM开展不同雷诺数(100≤Re≤3 900)下弯曲管体绕流流场三维数值模拟研究。对比分析不同雷诺数条件下弯曲管体的瞬时和时均流场特征,研究了弯曲管体不同位置处的时均压力系数和旋涡脱落频率。结果表明:当Re=100时,尾流中仅有展向涡存在;当300≤Re≤3 900时,流向涡出现且强度逐渐增加,展向涡减弱,随着局部曲率增大,沿弯管展向涡脱强度减小。随着雷诺数的增大,回流区沿流向的延伸尺度减小,但其沿展向的分布范围增大。沿弯管展向随着深度减小,前后驻点时均压力系数的绝对值递减,圆周时均压力系数变化幅度减小。在300≤Re≤3 900范围内,管体曲率会对展向涡脱频率产生一定影响。 相似文献
3.
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
4.
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
5.
自从人们对层流的圆柱绕流现象有了系列研究及清楚的认识后,人们逐渐把目光投向湍流的圆柱绕流,但相关研究主要关注于模拟湍流方法的数值格式和精度问题,而忽略了对高雷诺下圆柱绕流流场本身的认识及规律的总结。基于开源代码Open FOAM的大涡模拟方法以连续方程和Navier-Stokes方程为控制方程,选用Smargorinsky模式为亚格子应力模型,采用有限体积法和一次预测两次修正的PISO算法,对Re=3 900时三维圆柱绕流问题进行了数值模拟研究,并着重分析了其尾流特征和性质。数值计算结果表明:大涡模拟方法可以模拟出细致的流场结构,该雷诺数下的圆柱绕流具有很强的三维及湍流效应,在圆柱后方约一倍直径的范围内存在回流区域,在靠近圆柱壁面的尾流区域的速度剖面呈"U"型,远离壁面的速度剖面呈"V"型。瞬时速度剖面始终围绕着时均速度的周围脉动,且距离圆柱越远瞬时速度场的脉动范围越大。 相似文献
6.
不同倒角半径下方柱绕流的数值模拟及水动力特性研究 总被引：1，自引：0，他引：1
为了研究不同倒角半径对方柱绕流特性的影响,采用有限体积法,模拟了雷诺数Re为22 500、倒角半径为0.1D(D为方柱边长的长度)、0.2D和0.3D时方柱的绕流过程。方柱近壁面采用增强壁面函数,模型采用SST k–?湍流模型。根据模拟结果给出了不同倒角半径下方柱的流场涡量图以及阻力系数Cd和升力系数Cl;利用快速傅里叶变换法得到斯托罗哈数St。结果表明,倒角半径的增加改变了方柱的分离点,使得尾流区长度增加,旋涡尺度减小;Cd和Cl的振动幅值呈现先减小后增大的趋势,倒角半径为0.1D和0.2D时方柱受力较小,不存在倒角时方柱受力较大,倒角半径为0.3D时方柱受力最大;随着倒角半径的增加,柱体截面形式越接近圆形,斯托罗哈数逐渐增大,漩涡脱落频率更快。 相似文献
7.
《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
8.
利用计算流体力学软件Fluent开展了三维动波浪壁圆柱绕流的数值模拟,建立了三维运动波浪壁圆柱模型,通过C语言自编程序实现波浪壁面的运动控制,并保证壁面变形时网格的高质量。在来流速度u=0.125 m/s、雷诺数Re=12 500的情况下,开展了动波浪壁波动速度w=0、0.062 5、0.125、0.187 5 m/s四个工况的计算分析,并比较了不同波动速度对流场结构、升力、阻力特性的影响。结果表明:动波浪壁圆柱能有效抑制流动的分离,消除交替脱落的尾涡,从而消除周期振荡的升力;在消除卡门涡街的同时,圆柱后驻点处的涡量值随波动速度增加而增加,其原因在于波形移动加大了壁面流体的速度,从而减小了圆柱前后的压力差,减小了阻力;随着波动速度的增大,平均阻力系数呈明显下降趋势,当波动速度为来流速度的1.5倍时,平均阻力系数相对于光滑圆柱下降了53.76%。 相似文献
9.
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
10.
《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
11.
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12.
In this study, the Navier-Stokes equations and the pressure Poisson equation for two-dimensional time-dependent viscous flows are solved with a finite difference method in a curvilinear coordinate system. With this numerical procedure, the vortex shedding flow past a circular cylinder near a wall is investigated. The flow is calculated for a broad range of gap ratios for different Reynolds numbers ranging from 80 to 1000. Based on the numerical solutions, the vortex shedding is observed using various methods, and the mechanism for the vortex shedding suppression at small gap ratios is analyzed. The critical gap ratio at which the vortex shedding is suppressed is identified at different Reynolds numbers. 相似文献
13.
The incompressible viscous shear flow past a circular cylinder is analyzed by solving two-dimensional Navier-Stokes equations and pressure Poisson equation using a finite difference method. The shear flow is calculated for Reynolds numbers from 80 to 1000, and shear parameters up to 0.25. The numerical results indicate that the vortex shedding persists at the shear parameters up to 0.25 for the present Reynolds number range. The Strouhal number and the drag coefficient decrease as the shear parameter increases. There is a transverse force acting from the high velocity side toward the low velocity side in the shear flow. 相似文献
14.
-The hydrodynamic forces on a smooth inclined circular cylinder exposed to oscillating flow were experimentally investigated at Reynolds number (Re) in the range 40000-200000 and Keulegan-Capenter number (KC) in the interval from 5-40. In the test, Re number and KC number were varied systematically. The inertia force coefficient (Cu) and the drag force coefficient (CD) in Morison equation were determined from the measured loads and the water particle kinematics. In this analysis a modified form of Morison equation was used since it uses the normal velocity and acceleration. Thus, the applicability of the Cross Flow Principle was assumed. This principle, simply stated, is as follows: the force acting in the direction normal to the axis of a cylinder placed at some oblique angle with the direction of flow is expressed in terms of the normal component of flow only, and the axial component is disregarded. Both the total in-line force coefficient (CF) and transverse force (lift) coefficient (Cf) were analyzed 相似文献
15.
The flow about a circular cylinder placed centrally inside a channel is studied numerically with an unstructured collocated grid finite volume method based on the primitive variable formulation. The distance between the channel walls is allowed to vary to change the blockage ratio. Simulations are carried out over a range of Reynolds numbers that are consistent with the two-dimensional assumption. The study confirms that transition to vortex shedding regime is delayed when the channel walls are close to the cylinder because of the interaction between the vortices from the channel wall and cylinder wake. In the unsteady vortex shedding regime, the wake pattern is opposite to the classic Karman street in respect of the positions of the shed vortices. The cylinder drag coefficient and Strouhal number are considerably increased at smaller gaps while the root-mean-squared lift coefficient is significantly decreased. Several important flow parameters are correlated with the input parameters, namely Reynolds number and blockage ratio. 相似文献
16.
不同倒角半径柱体绕流数值模拟及水动力特性分析 总被引：3，自引：1，他引：2
为研究倒角半径变化对柱体绕流水动力特性的影响,本文使用Fluent软件,采用大涡模拟对雷诺数Re=3 900下的6种不同倒角半径的三维柱体进行了研究。在模型验证基础上,分析了由方柱渐变到圆柱过程中后方流场速度的时均特性及瞬时涡脱落变化规律,给出了不同倒角半径下的升、阻力系数值及无量纲涡脱频率St数。分析结果表明:平均阻力系数随倒角半径的增加而降低,在倒角半径为0.2D时下降速率最大,相较方柱降幅达到50%;升力系数均方根在倒角半径为0.1D~0.2D时变化最显著,减小约93%; St数随倒角半径增加而增大,在倒角半径为0.4D时可达到最大值;回流区长度随倒角半径的增加呈先增大后减小的趋势,其长度在倒角半径为0.2D时达到最大;尾涡宽度在倒角半径为0.0D最大,后随倒角半径增加逐渐下降,且当倒角半径大于0.2D以后变化不大。本文研究结果可为柱体绕流研究及相关工程应用提供参考。 相似文献
17.
基于光滑粒子流体动力学(SPH)方法,开发了能够准确描述水流作用下圆柱强迫振动特性的数学模型。通过引入适合于无网格粒子法的开边界算法,来模拟出入流边界条件,建立了具有造流功能的SPH数值水槽。圆柱及计算域的上下边界均采用修正的动力边界条件进行模拟。借助于粒子位移矫正和压力修正算法,避免了圆柱周围流体粒子压力大幅震荡以及结构下游区域出现空腔等非物理性现象。使用典型的圆柱绕流数据,验证了所建SPH模型的计算性能,研究了固定圆柱在低雷诺数情况下的尾涡脱落模式和升阻力变化规律。明确了低雷诺数下强迫振动圆柱在频率锁定以及非锁定区间内的升力变化规律,量化了升力与外界激励频率之间的关系。 相似文献
18.
The incompressible viscous uniform and shear flow past a circular cylinder is studied. The two-dimensional Navier-Stokes equations are solved by a finite element method. The governing equations are discretized by a weighted residual method in space. The stable three-step scheme is applied to the momentum equations in the time integration. The numerical model is firstly applied to the computation of the lid-driven cavity flow for its validation. The computed results agree well with the measured data and other numerical results. Then, it is used to simulate the viscous uniform and shear flow over a circular cylinder for Reynolds numbers from lO0 to lO00. The transient time interval before the vortex shedding occurs is shortened considerably by introduction of artificial perturbation. The computed Strouhal number, drag and lift coefficients agree well with the experimental data. The computation shows that the finite element model can be successfully applied to the viscous flow problem. 相似文献
19.
Muk Chen Ong Torbjørn Utnes Lars Erik Holmedal Dag Myrhaug Bjørnar Pettersen 《Coastal Engineering》2010
High Reynolds number flows around a circular cylinder close to a flat seabed have been computed using a two-dimensional standard high Reynolds number k–ε turbulence model. The effects of gap to diameter ratio, Reynolds number and flat seabed roughness for a given boundary layer thickness of the inlet flow upstream of the cylinder have been investigated. Hydrodynamic quantities and the resulting bedload transport have been predicted, and the vortex shedding mechanisms have been investigated. Predictions of hydrodynamic quantities around a cylinder located far away from the bed (so that the effect of the bed is negligible) are in satisfactory agreement with published experimental data and numerical results obtained for the flow around an isolated cylinder. Results for lower Reynolds number flows have also been computed for comparison with the high Reynolds number flow results. Overall it appears that the present approach is suitable for design purposes at high Reynolds numbers which are present near the seabed in the real ocean. 相似文献
20.
柱体绕流问题是流体力学领域一个非常经典的问题。当流体流经柱体时,由于黏性的存在,会发生许多复杂的流动现象,如流动分离、涡旋周期性生成与脱落等,经常被作为标准验证算例。同时,柱体绕流广泛存在于实际工程中,并在一定工况下可能对工程产生巨大危害,因此对柱体绕流进行深入研究具有重要意义。研究中,拟将一种无网格类方法——半隐式移动粒子方法(moving particle semi-implicit method,简称MPS)引入到柱体绕流问题的数值研究中,并对不同雷诺数下二维方柱绕流问题进行数值模拟。首先,使用基于MPS方法自主开发的MLParticle-SJTU求解器,结合入口边界条件和出口边界条件,模拟了雷诺数Re分别为40、200和1 000时均匀来流条件下的方柱绕流。随后,将模拟的绕流结果与文献中试验和数值计算结果进行了对比,结果吻合较好,并且在雷诺数为200和1 000时,可以清晰地捕捉到方柱尾流中的卡门涡街现象,验证了MPS方法在柱体绕流问题模拟上的有效性和适用性。 相似文献