基于LES的亚临界和超临界圆球绕流数值研究

三维圆球绕流是流体力学中的经典问题,国内外学者曾对此进行过许多研究,但大多局限于较低雷诺数。该文采用基于动力亚格子模型的大涡模拟对亚临界雷诺数(Re=10~4)和超临界雷诺数(Re=1.14×10~6)等高雷诺数下的圆球绕流进行了数值仿真计算。计算结果表明,得到的阻力时均值和经典Re-Cd曲线相吻合,相比于亚临界雷诺数,超临界雷诺数下近球面回流区剧烈收缩,阻力系数锐减;圆球尾流场明显偏离了中心轴(x轴),导致了侧向力的存在;球后有大尺度的规则涡从圆球表面脱落。     

串列布置下倒角柱体绕流数值模拟及水动力特性分析

为研究串列布置情况下,倒角变化对柱体绕流水动力特性的影响,该文采用大涡模拟方法研究了在雷诺数Re=3 900和间距比L/D=3条件下,6种不同倒角(R⁺=0.0、0.1、0.2、0.3、0.4和0.5)串列布置的柱体三维流场,模拟工作验证有效。分析了柱体后方水动力参数、瞬时流场和时均流场的变化情况,分析结果表明：随着倒角增大,上下游柱体的平均阻力系数C_d-ave变化趋势相反,上游柱体C_d-ave逐渐变小,而下游柱体的C_d-ave逐渐上升且均为负值;随着倒角增大,上下游柱体Sr数值相同并出现先增大后减少的趋势;两柱体之间的回流速度曲线下切深度明显增加,速度最小值出现处从下游柱体两侧向中心不断变化;串列布置下游柱体尾流宽度显著变小,在间距比L/D=3条件下,剪切层的初始分离均发生在上游柱体倒角转折处,并附着于下游柱体前端及两侧。该研究结果可为柱体绕流研究及相关工程应用提供参考。     

高雷诺数下双圆柱绕流的数值模拟

本文使用表面涡法研究高雷诺数下不同排列方式双圆柱绕流的流动状态，计算了双圆柱在并列、串列及级列的情况下的各种流动结构，涡街的变化及作用在圆柱上的受力情况。本文结果清楚地描述了双圆柱绕流复杂的流动状况，计算结果与实验显示的流动状况十分相似，斯特罗哈数和阻力系数与实验结果符合得很好。     

方柱绕流数值模拟

利用FLUENT中的RNG k-ε算法对长宽比H/B=1.5方柱绕流进行数值模拟,分别模拟了在雷诺数Re=800的亚临界条件下,4种不同情况下的流动。分别为:流体流过单个方柱,流体流过间距为1H,2H,3H的两并列方柱的流动。根据数值模拟结果,分别得出了4种流动状态下流场,壁面的升阻力系数。并对升力系数进行傅里叶变换,分析及归纳了方柱绕流旋涡脱落的规律。     

基于大涡数值模拟的海洋隔水管绕流分析

隔水管是深水油气开采中连接浮式平台与水下井口的通道,受复杂海洋工况影响会产生涡激振动而造成疲劳破坏,产生安全隐患。为了更为精确地分析海洋环境下隔水管的流动,建立了简化隔水管三维模型,采用大涡模拟方法开展了不同雷诺数下隔水管表面流动的研究。首先验证了该方法的可行性,然后对三维涡的结构表现、边界层内流体与壁面的分离位置、速度梯度的分布以及涡泄频率等进行了分析。结果表明,随着雷诺数的增加,三维涡能够较好地表征大涡到小涡的分布规律,可对分离点进行预测,其规律对后续减小隔水管的阻力的研究提供参考。     

基于能量比系数的圆柱栅绕流LES方法研究

圆柱阵列流场不但是工程上常见的流动换热结构,而且绕流问题与湍流涡发展研究密切相关。该文采用数值模拟算法研究了不同雷诺数下的单列圆柱栅绕流的不可压缩流动。比较了非定常RANS方程计算得到的湍动能和耗散率,引入湍流能量比系数对初始计算网格进行重新划分和局部加密,进而建立适宜于大涡模拟网格尺度,其结果与PIV和RANS结果进行对比。结果表明,在湍流流场区域能量比系数达到30%-40%的情况下,就可得到工程实际需要的精确计算结果,这大大减少LES算法所需要的计算网格总数和时间。     

不等直径串列圆柱绕流大涡模拟

为研究背负式海底管线中增设的小直径附属管线对主管线的水动力影响,将大涡模拟中经典Smagorinsky亚格子模型与特征线算子分裂有限元法结合,并引入出口对流边界条件,完善了基于特征线算子分裂有限元的大涡模拟方法。通过自编程序数值模拟Re=1 000的单圆柱绕流,计算结果与相关文献吻合较好,验证了该算法计算圆柱绕流的有效性,并分析了Re=1 000时不同直径比、间距比情况下的串列双圆柱绕流,根据流场的不同涡脱落形态及两圆柱平均阻力系数、升力系数随直径比、间距比变化的规律得到了不同直径比条件下的临界间距范围。达到临界间距后,流场由单一涡脱落状态转变为双涡旋脱落状态。最后分析了两圆柱平均阻力系数及升力系数在临界间距后急剧增加的原因,为背负式海底管线的布局优化提供了理论依据。     

多孔方型人工鱼礁绕流的数值模拟研究

数值模拟得到了5种不同来流速度(0.1 ～0.8 n/s)下的多孔方型人工鱼礁周围的水流场.过礁体中心的铅垂面上速度分布表明:①不同来流速度下,上升流的最大速度和平均速度均分别为来流速度的0.74倍和0.12倍,上升流最大高度均为礁体高度的2.6 ～2.7倍,背涡区的长度和高度均分别为礁体高度的4倍和1.25倍;②在靠近礁体背流面形成水流方向与来流方向相一致的透水区.过礁体中心的水平面上速度分布表明:①不同来流速度下,背涡区的长度和宽度均分别为礁体宽度的4倍和1.8倍;②在鱼礁内部形成水流方向杂乱的旋涡区.本研究还初步比较了多孔方型人工鱼礁绕流与无孔方型人工鱼礁绕流的流场效应异同点.     

明渠不恒定分离流数值模拟及试验验证

本文应用平面二维不恒定流数学模型成功地模拟了不恒定分离流的回流。通过与相应的明渠不恒定分离流的试验结果比较,流动图案、回流长度及正反向最大流速均相吻合,从而证明本文所依据的数学模型是正确的。     

Numerical simulation of flow past twin near-wall circular cylinders in tandem arrangement at low Reynolds number

Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of 0.25 ≤ G/D ≤ 2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.     

Numerical simulation of flow past circular duct

The Renormalization Group(RNG)k-ε turbulence model and Volume of Fluid(VOF)method were employed to simulate the flow past a circular duct in order to obtain and analyze hydraulic parameters.According to various upper and bottom gap ratios,the force on the duct was calculated.When the bottom gap ratio is 0,the drag force coefficient,lift force coefficient,and composite force reach their maximum values,and the azimuth reaches its minimum.With an increase of the bottom gap ratio from 0 to 1,the drag force coefficient and composite force decrease sharply,and the lift force coefficient does not decreases so much,but the azimuth increases dramatically.With a continuous increase of the bottom gap ratio from 1 upward,the drag force coefficient,lift force coefficient,composite force,and azimuth vary little.Thus,the bottom gap ratio is the key factor influencing the force on the circular duct.When the bottom gap ratio is less than 1,the upper gap ratio has a remarkable influence on the force of the circular duct.When the bottom gap ratio is greater than 1,the variation of the upper gap ratio has little influence on the force of the circular duct.     

透水框架的三方柱绕流数值分析

针对四面六边透水框架按高度分层后形成等边三角形布置的三方柱绕流问题进行了数值模拟,分析不同间距比l/d=1.5,2,3,4,5,7下流场分布和各方柱的升、阻力系数以及斯特劳哈尔数的特性。研究结果表明:当l/d=1.5~7时,B,C柱尾流场经历了近处漩涡掺混到近处漩涡分离,远处漩涡掺混到远处漩涡分离,最后形成各自独立的方柱绕流;在l/d=2时,各方柱的平均阻力系数明显减小,并且通过对流场分析发现此间距比下对水流的减速效果最明显;由于B,C柱的存在与单方柱绕流有很大区别:在流场方面,l/d=1.5时,B,C柱限制A柱边界层剪切带的卷起,随间距比的增加这种现象逐渐消失;在动力特性上,A柱的阻力系数明显小于单方柱绕流情况。斯特劳哈尔数Sr随间距比的增大而逐渐增大并趋近于单方柱绕流的值。     

Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters

The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.     

月牙肋岔管水流数值模拟研究

随着电力需求的不断增长,抽水蓄能电站的建设日益受到重视,其调峰平谷功能成为电力系统不可缺少的重要组成部分.结合江苏某抽水蓄能电站岔管部分的设计要求,对带有月牙肋板的岔管水流进行模拟研究,采用SIMPLE方法进行迭代计算,通过求解三维κ-ε紊流方程,较好地模拟了水流的流速场,并且通过物理模型试验得到了验证,从而肯定了数值模拟的合理性.     

Numerical simulation of viscous flow past an oscillating square cylinder using a CIP-based model

The flow past an in-line forced oscillating square cylinder at Reynolds number of 200 is studied using an in-house code, named constrained interpolation profile method developed in Zhejiang University(CIP-ZJU). The model is established in the Cartesian coordinate system using the CIP method to discretise the Navier-Stokes equations. The fluid-structure interaction is treated as a multiphase flow of the liquid and solid phases to be solved simultaneously. An immersed boundary method is used to deal with the boundary of the solid body. The CFD model is first applied to the computation of the flow past a fixed square cylinder for its validation. Computations are then performed for the flow past a square cylinder oscillating in the streamwise direction. Considerable attention is paid to the symmetric and anti-symmetric modes of the vortex shedding in the oscillating square cylinder wake. Various oscillation amplitudes and frequencies are simulated and their effects on the vortex shedding modes are analyzed via Lissajous patterns of the unsteady lift coefficient. The relationship among the lift coefficient, the drag coefficient and the lock-on range is also investigated quantitatively.     

液体管道高频水力瞬变过程的数值模拟

目前在液体管道高频水力瞬变分析中,人们通常采用经典的拟稳态摩阻模型进行分析.但这种方法针对管壁切应力具有拟稳态特性的缓慢瞬变的分析是可行的,而对高频瞬变流动过程而言却不能准确预测水击压力波具体的衰减过程以及出现的波形畸变现象.介绍了一种新的考虑瞬时加速度对高频水力瞬变过程影响的非恒定摩阻模型,并结合特征线法给出了其数值解法,最后通过实例验证了该模型能比经典的拟恒定摩阻模型更为准确地模拟液体管道中高频瞬变流压力波的衰减和波形畸变.该模型对计算机的要求和计算耗时与经典的拟稳态摩阻模型相差不大,是一种具有良好工程应用潜力的液体管道高频瞬变分析数学模型.     

配水器流场的数值模拟

用数值方法模拟注水井中所用配水器内的三维粘性流场,计算不同规格水嘴在不同注水流量下的总压损失情况,并对流场进行分析。研究了总压损失与水嘴直径和注水流量之间的关系,得出了二者间的影响方程,为油田注水井分层流量调配提供依据。     

三组元比例控制器内流场的数值模拟

运用计算流体力学软件CFX对三组元比例控制器内的三维粘性流场进行数值模拟,计算在不同注入流量、不同入口尺寸及是否有混流段等多种情况下三组元比例控制器的内泄漏情况,并对流场进行分析。研究了内泄漏量与注入流量、入口尺寸及有无混流之间的关系,得出了这几种情况对内泄漏的影响规律,为三组元比例控制器的比例控制精度的优化提供必要的参考。