3-D numerical investigation of the wall-bounded concentric annulus flow around a cylindrical body with a special array of cylinders

Concentric annulus flow around a combinational cylindrical body with a special array of cylinders at five high Reynolds numbers is investigated numerically using Fluent 6.3.26 in this paper. The numerical results show a good agreement with the experimental data in regard to the axial velocity of the flow. This study focuses on the flow structure and the hydrodynamic characteristics based on the velocity distribution, the pressure distribution, streamlines and vectors under 1-D, 2-D and 3-D conditions. Meanwhile, some global parameters including the pressure coefficient, the drag coefficient and the lift coefficient are analyzed. Numerical results show that the high velocity region and the reverse wake zone with low velocity exist in some spaces due to the disturbance of the cylindrical body. Negative pressures appear in some regions. Neither a wide area vortex nor the vortex shedding appears in the wall-bounded domain. The drag along the axial direction is the main force acting on the cylindrical body in the pipe domain. The annulus flow around the cylindrical body is analyzed to reveal the hydrodynamic characteristics of the complex turbulent concentric annulus flow field due to the multi-effects in the pipeline.     

绕二维对称水翼的通气空泡流数值研究

本文通过有限体积离散方法求解Reynolds平均Navler—Stokes方程,采用VOF法追踪气一液两相交界面。研究了在高压低速来流,即本质上不发生自然空化的条件下,绕二维对称水翼的非定常通气空泡流动。分析了物理参数——通气方向角和攻角,对通气空泡外形、稳定性及水动力参数的影响。计算结果表明：在通气空泡的形成过程中,通气方向角存在着一个临界值,使得空泡形态由片状空泡过渡到超空泡;特定的参数组合将会诱发空泡表面出现波动现象。而且,当攻角做周期性变化时,水动力参数的变化也随之满足周期性规律,且出现阶段性振荡。     

基于转捩SST模型的钝尾缘水翼绕流数值计算与分析

边界层转捩是影响水翼绕流水动力学特性的关键因素之一。为了探究γ-Reθt转捩模型在低湍流度来流下水翼边界层转捩及尾涡脱落预测中的适用性,本文基于耦合γ-Reθt转捩模型和SST k-ω模型的转换SST模型,对0°攻角的NACA0009钝尾缘水翼绕流进行了数值计算。分析了转捩SST模型对网格尺度的敏感性,预测了边界层和尾迹区流场及不同雷诺数下水翼尾涡脱落特征,并与实验数据和SST k-ω模型计算结果进行了对比。结果表明:随近壁面第一层网格尺度y+的增大,水翼边界层转捩位置沿流向后移,最大y+值小于1时,预测的转捩位置趋于一致;与SST k-ω模型相比,转捩SST模型可以求解层流边界层,避免了在边界层和尾迹区对涡黏系数的过高预测,得到的边界层厚度和水翼尾迹区流动参数与实验结果更为接近;转捩SST模型可以较准确预测水翼尾涡脱落频率随雷诺数增大而增加的变化趋势,水翼尾涡脱落频率预测值与实验结果的最大相对误差为6.2%。     

Numerical modeling of flow and scouring around a cofferdam

When planning river hydraulic structures, the analysis of the hydrodynamic and bed elevation change is of great importance, particularly the assessment of the scour depth around a cofferdam. In this study, the flow field variation and the corresponding scour depth was simulated using two-dimensional hydrodynamic analysis and a bed-load transport model. The hydrodynamic model used the streamlined upwind Petrov–Galerkin (SUPG) finite element scheme to solve the Reynolds-averaged turbulent flow equations. Based on the results of flow field analysis, the bed-load transport model was able to simulate the scour hole development, where it was shown that velocity gradients dramatically increase due to the existence of hydraulic structures. The applicability of the model was tested by simulating the velocity field and bed elevation changes around the cofferdam constructed during the Lock and Dam No. 26 replacement project in the Mississippi River. The model created in this study is able to estimate the maximum scour depth, determine the configuration of the cofferdam to suggest changes to reduce any local scour, and suggest if protection materials around the cofferdam are needed.     

温度对液氢绕水翼非定常空泡流影响的数值研究

该文基于均质多相流理论,采用RNG k-模型和修正系数Zwart空化模型对液氢绕NACA0015水翼非定常空化流动进行数值模拟。模拟了非定常空泡云的生长、断裂、涡状空化团脱落和破裂的周期性过程,模拟中考虑了热力学效应,并分析了温度对空泡流场特性的影响。研究结果表明:在相同空化数和来流速度下,空泡周期随温度增高而变长,升、阻力系数的波动周期随温度增高而增加,但其时均值的随温度增高而减小。     

外流问题的外边界条件设计

粘性外流计算原则上要求在无限大的外空间进行，巨大的计算区要求巨大的计算机资源。本文利用一般绕流问题在远区流动尺度大，因而雷诺数大的特点对远外处的流动近似地用位势流代替，从而在较小的流体边界条件上建立了“开边界条件”，由此大大缩小了计算工作量。     

Numerical study on influence of structural vibration on cavitating flow around axisymmetric slender body

The unsteady behaviors of cloud cavitating flow would lead to structural vibration and deformation that conversely affect its development. The present paper aims to preliminarily discuss the influences of structural vibration on the development of the cavitating flow. Simulations of a slender body are carried out under different vibration amplitudes and frequencies. The results show that the structural vibration causes alternate variation of local attack angle at the head of the body, and thus changes the development of cavitation and re-entrant jet. On the downstream side, the length and thickness of the cavity are larger than that on the upstream side due to larger area of negative pressure. For a large vibration amplitude, alternate variations of the local attack angle change the adverse pressure gradient at the closure of the cavity, and then affect the development of the re-entrant jet, so that the phenomena of local shedding of the cavitation happen, compared with global shedding in the case of no structural vibration. For a frequency larger than 0.05, transverse speed of the vibration is suggested to be a dominant factor in controlling the behavior of the cavitating flow besides the local attack angle, since it causes local cavitating phenomena.     

亚临界雷诺数下波浪型圆柱绕流的数值模拟及减阻研究

采用大涡模拟数值方法对亚临界雷诺数Re=3000下波浪型圆柱的绕流现象进行研究分析。研究结果表明,波浪型圆柱的三维尾迹涡结构能得到很好的控制,它在轴向方向呈现周期性正负涡的交替分布特性。随着幅值的增大,波浪型圆柱表面的自由剪切层得以延展,使得旋涡的脱落发生在波浪型圆柱下游较远处,从而达到减阻的目的。波浪型圆柱与普通直圆柱相比,其幅值对平均阻力系数及脉动升力系数的减少及尾迹控制有着更重要的影响,最大减阻可达16%。     

Numerical investigation of a swirling flow under the optimal perturbation

The nonlinear evolution of 3-D instability of a viscous swirling flow, namely, the Oseen vortex, is addressed by direct numerical simulation with a Reynolds number equal to 5000. The global optimal perturbation is considered as the initial perturbation. In axisymmetric cases, three flow regimes are found: (1) the linear growth; (2) the decay of perturbation energy; (3) secondary energy growth. The linear energy growth, which is characterized by the amplification of radial perturbations, is arrested by the interaction between the vortex ring and the Oseen vortex core. The development of the vortex structure is also investigated for non-symmetric flows.

     

辽宁中部平原区土壤入渗量影响因素分析

本文通过对辽宁中部平原地区的大洼、灯塔、东港、凌海、石佛寺、浑蒲等六大灌区的入渗补给实验,对影响各灌区的土壤渗漏特性进行了分析研究,进而分析了辽宁中部平原区土壤入渗量影响因素。     

Numerical investigation of a thermally inhomogeneous flow in a reservoir

Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 2, pp. 9–13, February, 1994.     

双锥头型回转体空化特性实验研究

该文以双锥头型回转体为研究对象,开展了攻角0°–6°、空化数0.3–1.0范围内共计20个工况的水洞实验,获得了空泡形态和回转体表面压力分布;根据实验观测结果,提出了四种类型的流型划分,研究了各类型空泡流状态下的表面压力特征,给出了不同空化数和攻角下的空泡流流型图;对空泡长度进行了定量判读,分析了小空化数下重力对空泡长度的影响,获得了空泡长度、迎背流面空泡长度差随攻角、空化数的变化规律。     

Numerical investigation of non-cohesive seabed response around a mono-pile by crossing wave-current

The interaction between waves and currents in the ocean often complicates the flow field around structures. In this study, a three-dimensional integrated numerical model was established to investigate the seabed response and liquefaction around a mono-pile under different wave–current interaction angles. In the present model, the Reynolds-averaged Navier–Stokes equations were used to simulate the flow field, and the Biot's poro-elastic theory was adopted to calculate the seabed response caused by crossing wave-current loading. Unlike previous studies, the load on the mono-pile was considered, and the wave–current interaction angle was extended to 180°, which was more in line with practical engineering problems. The numerical results were in a good agreement with the experimental measurements. The results indicated that waves interacted with currents in a large angle could result in a large momentary liquefaction depth of the seabed. The parametric studies proved that the position of the front and two sides of the pile was relatively safer compared with that of the leeside of the pile, and the surface of the seabed downstream of the pile was liable to liquefy.     

桥台局部冲刷坑内水流运动的三维数值模拟

局部冲刷是河道中丁坝、桥台等破坏的重要因素。这些建筑物周围绕流流场和泥沙运动十分复杂,对冲刷的机理及平衡条件的研究还有待于进一步深入。文中采用k-ε模型对桥台周围平衡冲坑内的流场进行了三维数值模拟,计算结果正确反映了建筑物周围的流速分和紊动动能的分布;根据流场分布分析了冲坑内的旋涡分布规律及其与冲刷的关系,阐述了主旋涡向螺旋旋涡的转化以及冲坑内水流的能量耗散机理。冲坑内的床面切应力的分布反映了床面冲刷平衡条件,数值模拟得到的床面切应力分布表明颗粒运动受到斜坡上重力作用的影响,同时在紊动剧烈的区域还受到旋涡的影响。     

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。     

框架墩式码头结构绕流数值模拟

基于FLUENT软件,针对不同方柱排列组合进行绕流数值模拟,得到不同间距比时各方柱水流阻力系数及三维流场情况,探寻框架墩式结构水流力分布规律。计算结果表明,简单的双方柱串、并联时,方柱阻力变化较有规律;双排并列三方柱绕流时,第一排方柱阻水作用显著,处于尖角位置的方柱绕流参数呈现对称现象,各方柱阻力明显增大,但阻力变化已无规律可循;当上下横撑间距为3倍横撑直径时,相互间影响已经较小;处于上游第一排横撑的水流阻力系数与单方柱时基本相同,第二排横撑所受水流阻力明显减小,与水流方向一致的纵撑其水流阻力可忽略不计。     

The effect of free surface on cloud cavitating flow around a blunt body

In this study, the effect of the free surface on the cloud cavitating flow around a blunt body is investigated based on the water tank experiment and the CFD method. Numerical results are in good agreement with experimental data, and the mesh independence of the methods is verified. The cavity evolution process includes the cavity growth, the re-entrant jet, the cavity shedding, and the collapse, which can all be observed from the water tank experiment. The effects of the free surface on the cavity length, the thickness, and the cavity evolution period are analyzed by comparing the difference between the cavitating flows on the upper and lower sides of the body. This study also examines the effect of the distance between the free surface and the model through a series of water tank experiments and numerical simulations. The cavity stability and asymmetry, as well as the thickness and the velocity of the re-entrant jet inside the cavity, which varies with the submerged depth, are discussed with consideration of the effect of the free surface. The effect of the free surface on the cavitating flow around the blunt body is enhanced with the decrease of the submerged depth.     

混流式水轮机内三维定常湍流数值研究

基于 k-ε紊流模型和三维时均N-S方程,进行了混流式水轮机全流道的三维定常湍流计算.捕捉到了水轮机过流部件内的流场和非最优工况下转轮通道及尾水管内的旋涡结构与演化特征等流动信息.结果表明,水轮机的全通道CFD分析能够较为准确地预测出水轮机过流部件内的性能参数及内部流场结构,所得到的结果对进行水轮机的水力设计或改型优化设计等研究具有重要的指导意义.     

导流板对海底管道绕流影响的数值模拟与试验研究

采用试验研究和数值模拟相结合的方法为对海底管道添加导流板后的绕流特性进行了研究。数值模型利用有限体积法进行离散,湍流模型采用标准kε湍流模型。通过对比分析,数值模拟结果与试验结果吻合较好。同时对不同间隙比下导流板对迎流面前驻点、流速分布、管道表面压力分布、升阻力系数及床面剪应力的影响进行了分析,为海底管道冲刷及防护技术的进一步研究奠定了基础。