共查询到18条相似文献，搜索用时 93 毫秒
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通过数值模拟方法与物理模型实验,对不同间隙比情况下的海底管线绕流特性进行研究。数值模拟采用有限差分法对标准k-ε湍流方程和控制方程进行离散,利用GMRES算法求解离散方程,模拟绕流流场。物理模型实验中采用超声测速仪ADV系统测取不同断面的流速分布情况,分别分析不同间隙比情况下的漩涡运动特性。同时分析各垂直断面不同间隙比时尾流流速变化情况,数值模拟结果与实验结果吻合较好,本文成果为进一步研究海底管线的防护措施打下基础。 相似文献
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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
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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
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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
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为了研究真实海洋表面马蹄波特性以及对建筑物的作用,通过物理模型实验研究了马蹄波的波形特征参数以及马蹄波对圆柱体的作用。实验中通过对浪高仪采集的波面升高时间历程曲线进行分析得出了不同水深情况下马蹄波的垂向几何特征,并通过快速傅里叶变换得出了马蹄波波幅谱的特征,研究了马蹄波各组成波波幅沿空间的变化从而得出了圆柱存在对马蹄波演化的影响,同时给出马蹄波绕射形成的波面分布和不同频率谐波在圆柱周围的分布,讨论了马蹄波不同于Stokes波对圆柱作用的特征。结果表明,马蹄波波形受水深影响较大,水深越浅,马蹄波的波面形状越接近椭圆余弦波。圆柱体的存在干扰了马蹄波不稳定的增长,使其在接近圆柱时呈下降趋势,导致不稳定幅值最大值的位置提前并且出现在偏离圆柱迎浪点的侧表面,从而使圆柱受到侧向力的作用。 相似文献
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圆柱绕流作为流体力学领域中的经典问题,近年来得到了广泛的关注和研究。开展振荡流下二维圆柱的水动力特性和漩涡发放形态研究将为认识和理解圆柱绕流特性提供重要参考。基于RANS方程,采用k-ωSST湍流模型,首先通过对比雷诺数10 000时均匀流下的受迫振动试验数据,验证了研究方法的可行性,进而开展了振荡流下圆柱绕流的数值模拟,对比讨论了5种KC数下流体力系数变化情况及漩涡脱落模式,并开展了升力系数时历分析。结果表明:在低振幅、低频率下,小KC数时激励力系数变化较大,大KC数时流态趋向于均匀流,激励力系数变化较小。在大KC数时可以观察到较为明显的2S脱落模式,升力系数在每一周期内出现两次振幅调制现象,小KC数时流体变化较快,规律性相对较弱。 相似文献
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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
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Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially. 相似文献
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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
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《Applied Ocean Research》2004,26(3-4):147-153
A numerical study of the effect of the width of the computational domain on viscous oscillatory flow past a circular cylinder has been conducted, for Keulegan–Carpenter numbers ranging between 0.1 and 6 at a fixed frequency parameter equal to 50. The finite element method was used for the solution of the Navier–Stokes equations, in the formulation where the stream function and the vorticity are the field variables. Simulations for blockage ratios in the range between 0.10 and 0.50 were performed assuming frictionless flow at the outer boundaries, the blockage ratio being defined as the cylinder diameter divided by the width of the solution domain. The first set of simulations was carried out for a constant stream function along the horizontal boundaries. Then the procedure was repeated, for stream function values at the outer boundaries derived from the irrotational solution around a circular cylinder. This boundary condition relieves considerably the blockage effect on the flow pattern and on the drag coefficient of the in-line force. 相似文献
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低雷诺数下圆柱涡激振动的二维有限元数值模拟 总被引：2，自引：0，他引：2
采用有限元方法求解原始变量的二维不可压粘性流体的N-S方程,计算了雷诺数从90到150范围内圆柱绕流引起的涡激振动,完整地再现了流固耦合系统从不共振到频率锁定,再到脱离锁定的过程,成功地预测到了涡激振动的“拍”和“锁定”现象,并与A nagnostopou los和B earam an的试验结果进行了比较。计算涡激振动时用ALE方法分析圆柱和流体的耦合作用,圆柱振动被简化为质量-弹簧-阻尼系统。 相似文献
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《Ocean Engineering》2004,31(3-4):269-304
The paper seeks to apply the methodology of matched asymptotic expansions to obtain analytical solutions for hydrodynamic properties of a circular cylindrical platform (truncated circular cylinder) in extremely shallow water. By matching potentials of the fluid flows outside and under the cylinder bottom with the inner flow near its edge the radiation problems are solved for heave, surge and pitch motions. Closed asymptotic formulae are derived for all hydrodynamic coefficients of the floating cylinder, which include the first-order terms in the gap height. The formulae are discussed and shown to compare well with numerical results published in literature. 相似文献
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在势能流及微小振幅波理论假设下,采用复合边界元素法(CBEM)数值解析规则波通过单根外壁透水cosine-type型同心圆柱结构物绕射。将cosine-type外壁不透水条件改为透水外,并在内部设有一半径为b的不透水内圆柱共同组成同心圆柱,为了验证CBEM数值模式正确性与可行性,将其退化成圆柱,均得到合理结果。数值计算条件包含波浪正向入射凸端、透水参数及绕射参数,探讨波浪通过单根cosine-type同心圆柱体四周水面波动变化情况,并与双重圆筒同心圆柱作比较。计算结果显示结构物外壁采用透水型式,可以大幅降低cosine-type同心圆柱体四周整个波浪绕射场的水面波动。 相似文献
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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