共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
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
3.
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
4.
In this study the basic characteristics of the dynamic response and vortex shedding from an elastically mounted circular cylinder in laminar flow is numerically investigated. The Reynolds number ranges from 80 to 160, a regime that is fully laminar. The governing equations of fluid flow are cast in terms of vorticity. The two-dimensional vorticity transport equation is solved using a vortex method. Effects of important parameters on the system response and vortex shedding are investigated; these include: mass ratio, damping ratio, Reynolds number and reduced velocity. The numerical results show that a decrease in either the mass ratio or damping ratio of the system can lead to an increase in both the oscillation amplitude and the reduced velocity range over which lock-in occurs. The results also suggest that the mass-damping parameter may characterize the system response adequately, although the effect of changing mass ratio appears to be a little more profound compared to damping ratio. Vorticity contour plots suggest that the vortex shedding occurs in the 2S mode, although a wake structure similar to the C(2S) mode appears at distances 15–20 diameters downstream in the lock-in region. The simulation results are in good agreement with previously published data. 相似文献
5.
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
6.
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
7.
The unsteady flow past a circular cylinder which starts translating and transversely oscillating from rest in a viscous fluid is investigated at a Reynolds numbers of R=103 and at a Strouhal number of π/4 and for the maximum oscillatory to translational velocity ratios between 0.1 and 1.0. This study is based on numerical solutions of the two-dimensional unsteady Navier–Stokes equations. The object of the study is to examine the effect of increase of velocity ratio on the near-wake structure as well as the hydrodynamic forces acting on the cylinder. For all velocity rates a periodic structure of vortex evaluation and shedding develops which is repeated exactly as time advances. Vortex dynamics close behind the body are affected by changing acceleration of the cylinder and a changeover from one mode to a different mode of vortex formation is observed with increase in velocity ratio. A comparison of the present results with the impulsively started translating case has been included to illustrate the effect of velocity ratio on drag at small values of velocity ratio. 相似文献
8.
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
9.
A. S. Ginevsky T. V. Pogrebnaya S. D. Shipilov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(5):627-631
A method is suggested for simulating axisymmetric laminar or turbulent flows formed during the motion of a vortex-ring bunch of given geometry and circulation toward a plane screen. Earlier, similar problems were simulated with the numerical solution of the Navier-Stokes equations for laminar flows. Turbulent flows have remained unconsidered until now. When a vortex ring approaches the screen, the secondary nonstationary flow is induced near the screen’s surface and this secondary flow causes the formation of the radial boundary layer (provided that air viscosity is taken into account). First, the medium spreads out from the critical point at the screen’s center with the negative pressure gradient along the radial coordinate and then detaches in the region of the positive pressure gradient. This radial wall flow and the corresponding boundary layer are considered in the quasi-stationary approximation. When the boundary layer detaches at successive instances, the flow is replenished with the radially moving secondary vortex rings whose circulations have the sign opposite to that of the circulation of the primary vortex ring. It is the interaction of the primary and secondary vortices that governs process dynamics, which differs substantially from that in the case when the formation of secondary vortices is disregarded. The suggested method is based on the method of discrete vortices (a perfect liquid) and the boundary-layer (laminar or turbulent) theory. During the development of the flow under investigation, the nonstationary ascending flow in the direction perpendicular to the screen’s plane is formed and then this flow decays and dissipates. Simulations for large Reynolds numbers corresponding to the formation of the turbulent boundary layer show that the velocity of ascending vortices in the plane of the initial vortex bunch is less than one-tenth of the initial velocity of the descending vortex ring. The boundary layer is introduced into calculations with the sole goal of determining the parameters of the secondary vortex rings formed during boundary-layer detachments. The interaction of the primary and secondary vortices is then considered within the framework of a perfect medium. Simulations for large Reynolds numbers corresponding to the formation of the turbulent boundary layer on the screen were correlated with the available data obtained in laboratory experiments for small Reynolds numbers. Qualitative agreement between the simulations and experiments is fairly satisfactory. The simulation for one combination of the circulation and vortex-ring geometry takes at most 10–15 min with the use of an average PC. 相似文献
10.
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
11.
Direct numerical simulation was conducted to investigate the flow past a slotted cylinder at low Reynolds number (Re) of 100. The slotting of cylinder affects the boundary layer separation, vortex formation position, recirculation region length and wake width, which are determined by the type of slit. The streamwise slit (SS1), T-shaped slit (SS3) and Y-shaped slit (SS4) act as passive jets, while the transverse slit (SS2) achieves an alternate self-organized boundary layer suction and blowing. The flow rate in slits fluctuates over time due to the alternate vortex shedding and fluctuating pressure distribution around the cylinder surface. One fluctuation cycle of flow rate is caused by a pair of vortices shedding for SS2, SS3 and SS4, while it is created by each vortex shedding for SS1. The wall shear stress and flow impact on the slit wall partly contribute to the hydrodynamic forces acting on the slotted cylinder. Taking into account the internal wall of slit, the transverse slit plays the best role in suppressing the fluid forces with drag reduction of 1.7% and lift reduction of 17%. 相似文献
12.
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
13.
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
14.
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
15.
基于Fluent流体计算平台,运用大涡模拟方法对亚临界雷诺数Re=3900下“X”形排列五圆柱体结构群三维绕流特性进行研究,主要分析来流攻角α与间距比L/D两个关键参数对五圆柱体结构群的尾流区三维涡结构演化与流体力系数的影响,并揭示其内在流动互扰机理。研究表明:来流攻角和间距比的变化对五圆柱体结构群流动控制及互扰效应的影响显著。在小间距比工况下,观察到柱体群间隙区域内流体高速流动的现象,导致五圆柱体之间的互扰作用十分强烈。间隙流对中间圆柱体和下游圆柱体有较强的冲击作用,对其表面的流体力分布特性有显著的影响。另外,大间距比工况下,当α=0°与L/D≥5.0工况时,柱体群尾流效应强于其间隙流效应。当α=22.5°与L/D=7.0时,位于下游与中间处的圆柱体流体绕流特性存在较大差异。而当α=45°与L/D≥6.0时,位于上游与中间处的圆柱体尾流区均会产生正负交替的漩涡结构。 相似文献
16.
This paper discusses numerical results from three-dimensional large eddy simulations of an oscillating cylinder under prescribed movements in uniform flow. Six cases,namely pure in-line,pure cross-flow and two groups of 'Figure of Eight' oscillation patterns are under investigation at Reynolds number Re=24000. The 'Figure of Eight' pattern in each group is with identical shape but opposite orbital directions. The numerical results on hydrodynamic forces,higher order force components,and vortex shedding mode... 相似文献
17.
A numerical study of vortex-induced rotations(VIRs) of an equivalent triangular cylinder, which is free to rotate in the azimuthal direction in a uniform flow, is presented. Based on an immersed boundary method, the numerical model is established, and is verified through the benchmark problem of flow past a freely rotating rectangular body.The computation is performed for a fixed reduced mass of m~*=2.0 and the structural stiffness and damping ratio are set to zero. The effects of Reynolds number(Re=25-180) on the characteristics of VIR are studied. It is found that the dynamic response of the triangular cylinder exhibits four distinct modes with increasing Re: a rest position,periodic rotational oscillation, random rotation and autorotation. For the rotational oscillation mode, the cylinder undergoes a periodic vibration around an equilibrium position with one side facing the incoming flow. Since the rotation effect, the outset of vortex shedding from cylinder shifts to a much lower Reynolds number. Further increase in Re leads to 2 P and P+S vortex shedding modes besides the typical 2 S pattern. Our simulation results also elucidate that the free rotation significantly changes the drag and lift forces. Inspired by these facts, the effect of free rotation on flow-induced vibration of a triangular cylinder in the in-line and transverse directions is investigated. The results show that when the translational vibration is coupled with rotation, the triangular cylinder presents a galloping response instead of vortex-induced vibration(VIV). 相似文献
18.
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
19.
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
20.
An experimental study on vortex-induced motions (VIM) of a deep-draft semi-submersible (DDS) was carried out in a towing tank, with the aim to investigate the VIM effects on the overall hydrodynamics of the structure. In order to study the fluid physics associated with VIM of the DDS, a comprehensive numerical simulation was conducted to examine the characteristics of vortex shedding processes and their interactions due to multiple cylindrical columns. The experimental measurements were obtained for horizontal plane motions including transverse, in-line and yaw motions as well as drag and lift forces on the structure. Spectral analysis was further carried out based on the recorded force time history. These data were subsequently used to validate the numerical model. Detailed numerical results on the vortex flow characteristics revealed that during the “lock-in”, the vortex shedding processes of the upstream columns enhance the vortex shedding processes of the downstream columns leading to the rapid increase of the magnitude of VIM. In addition to the experimental measurements, for the two uniform flow incidences (0° and 45°) investigated, comprehensive numerical data of the parametric study on the VIM characteristics at a wide range of current strength will also serve as quality benchmarks for future study and provide guidance for practical design. 相似文献