虚拟边界法研究正交双圆柱及串列双圆球绕流

把Goldstein等人提出的虚拟边界法推广到三维情况，研究了 Re=150时不同间距下正交双圆柱绕流，和Re=250时不同间距下串列双 圆球绕流流场. 对于正交双圆柱绕流，当间距比大于3，下游圆柱对上游圆柱尾流的影响只 限定在下游圆柱的尾流所扫过的范围之内；当间距比小于等于3，下游圆柱对上游圆柱尾流 的影响扩大，下游圆柱尾流扫过区上下出现两排三维流向二次涡结构. 对于串列圆球绕流， 研究发现，在小间距比(L/D≈ 1.5)的情况下，由于上下游圆球尾流区的相互抑 制消除了压力不稳定性，整个流场呈现稳 态轴对称特征；间距比为2.0时，周向压力梯度诱发出流体的周向输运，流场呈现稳态非对 称性，但流场中存在特定的对称面；间距比增大到2.5后，绕流场开始周期振荡，原有的对 称面依旧存在；在间距比3.5时下游圆球下表面的涡结构强度有所减弱，导致占优频率发生 交替；间距比增至7.0时，整个流场恢复稳态特征，两圆球尾部同时出现双线涡，这时流场 对称面的位置发生了变动.     

含有周期涡结构的湍流雷诺应力与平均速度梯度之间的迟滞效应

针对存在时空周期涡旋结构的湍流场，对湍流雷诺应力与平均速度梯度之间的空间迟滞效应进行了实验研究，发现二者流向相位差呈周期变化．在低速回流式水槽中，利用二维高时间分辨率粒子图像测速(TimeResolved Particle Image Velocimetry, TRPIV)技术，对Re=324的圆柱尾流流场进行测量．经过49个周期166个相位的8 215个PIV瞬时流场，经过周期相位平均，得到一个周期内不同相位典型的湍流雷诺应力和平均速度梯度的空间分布．利用湍流雷诺应力相位平均图像和平均速度梯度图像在不同时间相位下的空间互相关函数最大值对应的流向空间距离，得到湍流雷诺应力与平均速度梯度之间沿流向的空间相位差，并绘制流向相位差随周期相位的演变过程．本文验证了湍流复涡黏模型的合理性，为建立符合周期涡旋结构物理机理的湍流模型研究提供了实验依据．     

圆柱尾流雷诺应力与平均运动变形率的空间弛豫效应

针对圆柱尾流中沿流向存在的Karman涡街周期性涡旋结构,对湍流雷诺应力与平均运动变形率之间的空间弛豫效应进行了实验研究.在回流式水槽中,放入不同直径的圆柱模型,获得不同雷诺数下的圆柱尾流,利用二维高时间分辨率粒子图像测速(TRPIV)技术测量圆柱尾流二维瞬时速度空间分布图像的时间序列.经过数字图像处理,获得二维雷诺应...     

舵几何特征对桨-舵系统尾流场演化的影响

发生在桨和舵之间的干扰会影响螺旋桨尾流的演化,导致尾流场中的湍流在下游增强,恶化船舶的振动和噪声性能,深入分析舵几何参数对桨-舵系统尾流场演化的影响能够为推进器尾流场的调节和减振降噪提供新思路.因此,从弦长、剖面和梯形舵入手分析不同的舵几何参数对螺旋桨尾流场演化特性的影响,使用大漩涡模拟方法模拟流场中的湍流结构,对不同舵弦长、剖面下的螺旋桨尾涡结构演化进行了分析,在舵弦长、剖面影响螺旋桨尾流场演化的研究的基础上分析了梯形舵对螺旋桨尾涡结构的影响,进一步分析了梯形舵影响下的螺旋桨尾流场中湍动能的分布.结果表明舵的弦长和剖面均会影响螺旋桨尾流场的演化,这种影响表现为更大的弦长和更厚的剖面会促进螺旋桨梢涡在舵压力面上的偏移,更薄的舵剖面会带来更强烈的螺旋桨毂涡偏移;涡管轮廓和舵表面脉动压力的对比均表明梯形舵会促进螺旋桨尾流场沿逆舵梯度方向偏移,从而导致螺旋桨的尾涡结构在舵两侧及下游呈现不对称分布,桨-舵系统下游的湍流结构与螺旋桨尾涡-舵碰撞过程、螺旋桨尾涡-舵随边涡干扰过程、螺旋桨梢涡-螺旋桨毂涡干扰有关,偏移更大的螺旋桨尾涡结构会在尾流场中更早地引起湍动能增强.     

床面上直立圆柱的三维湍流数值模拟

从数值预报桥墩等结构物床面局部冲刷的角度发展绕直立圆柱的三维湍流的数值模拟技术. 基于Wilcox的k-ω两方程湍流模式，采用基于有限体积法的压力修正SIMPLE算法, 计算了绕床面直立圆柱的三维湍流流场，分析了光滑和粗糙床面两种情况下的流动情况. 通过系列的验证计算，表明该计算模型能够比较准确地反映不同外来流条件下绕直立圆柱的流场. 计算结果揭示了床面粗糙度对绕圆柱的湍流流动的影响.     

横摆角下汽车尾部湍流特征量的PIV试验分析

汽车尾部湍流场是汽车压差阻力的主要来源,在HD-2汽车模型风洞中,首先使用测力天平和测压系统,对横摆角工况下汽车模型的气动六分力和纵对称截面48个测点的表面压力进行了测量,然后利用PIV测量技术对模型在横摆角分别为0°、15°的尾部湍流场进行了测量,获得该模型尾流场的速度场、涡量场和雷诺应力流场信息,通过计算得出尾流场区域空间相关系数和湍流积分尺度。结果表明:在横摆角工况下,汽车模型尾部涡流的结构呈现向上发展的趋势;尾流场拖拽涡的范围和强度的增大导致了模型气动力出现较大的增加;湍流积分尺度的变化表明,尾部涡流区的分离噪声与涡流分离位置有关,在汽车尾部造型设计中,要尽量推迟尾部涡流的分离。     

近床面水平圆柱局部冲刷二维数值模拟

为研究近床面水平圆柱的局部冲刷问题，基于N-S方程和有限体积法，在FLUENT中通过二次开发建立了局部冲刷二维数值模型。模型采用标准κ-ε紊流模型来计算水平圆柱周围的流场，同时借助FLUENT软件中的自定义函数功能提取床面剪应力参数来计算该时刻的推移质输沙率及床面节点位移变化值，然后运用动网格技术来模拟床面地形的变化，通过物理模型试验来进行模型验证。结果表明，计算结果与试验结果基本一致，从而证实了冲刷模型的准确性。     

倾斜圆柱结构涡激振动研究进展

圆柱结构涡激振动现象在生活中十分常见, 如海洋工程中的管道、土木工程中的高耸建筑、桥梁斜拉索, 核工程中的热交换器等频繁受到涡激振动影响, 诱发结构的疲劳损伤, 甚至破坏失效. 现阶段, 人们对垂直来流作用下圆柱结构涡激振动机理已有较为全面的认识. 然而, 当圆柱倾斜置于流场中, 结构后缘的尾流形态与垂直放置差异显著, 结构与流体的耦合作用机理更为复杂. 为简化倾斜圆柱涡激振动问题, 提出了不相关原则, 来流速度被分解为垂直圆柱结构轴向和平行圆柱结构轴向的两个速度分量, 仅考虑垂直结构轴向速度分量的影响, 忽略平行结构轴向速度分量的影响. 近年来, 针对倾斜圆柱涡激振动及不相关原则的适用性, 出现了大量实验和数值模拟研究成果. 为了深化对倾斜圆柱结构涡激振动相关机理的认知, 本文全面阐述了倾斜圆柱结构涡激振动响应规律、尾迹流场模式和流体力特性等方面的研究进展, 分析了不相关原则的适用范围, 探讨了倾斜圆柱结构涡激振动抑制措施, 并对今后该领域的研究进行了力所能及的展望.      

矩形槽道内表面活性剂减阻流体场特性

采用粒子图像测速仪对矩形槽道内表面活性减阻流体在流动方向(x方向)与壁 面垂直方向(y方向)所在平面的流场进行了测量，分析了速度、涡量、速度脉 动相关量在流场内的瞬态分布，以及对500幅相同工况的流场进行了统计平均. 结 果显示: 与牛顿流体相比, 表面活性剂减阻流体接近于层流流动，横向速度脉动被大幅 减弱，导致湍流输运减弱，雷诺应力远远小于水. 减阻流体流向速度脉动呈条带 特征，沿流动方向发展，反映了减阻流体不同于水的湍流输运特征.     

基于Stereo-PIV技术的三维发卡涡结构定量测量研究

发卡涡是湍流相干结构研究中最为关注的内容,实现发卡涡三维结构的定量测量并进行流体动力学分析,对深入研究湍流相干结构、实现湍流精准控制等具有重要意义.本研究通过对合成射流装置进行合理控制,使得层流边界层中产生了规则的人造发卡涡结构,进而用体视图像粒子测速仪(Stereo-PIV)锁相实验技术对发卡涡结构所在的三维空间流场进行了定量测量,并得到了一个完整周期内形成的发卡涡三维结构的空间流场. 结果发现,重构所得的三维发卡涡结构质量较高, 实验技术和方案具有可行性.发卡涡结构所在空间流场情况,符合目前人们对于发卡涡、高低速条带、喷射和扫掠事件的常规认识. 此外,对近壁二次流向涡、展向涡量集中区域的展向涡头和强剪切区域、与低速喷射流体相关的汇聚流动和发散流动等有了更细致的认识.同时, 也探讨了"基于二维脉动流场的相关特征去重构发卡涡三维流场"的可行性.为进一步定量探究发卡涡结构的形成演化、不同涡结构的融合及二次诱导等壁湍流相干结构问题提供思路.      

Improvements on bed‐shear stress formulation for pier scour computation

This paper introduces an improved formula for the bed‐shear stress by applying the vorticity effect and its application in a 3D flow and sediment model to estimate scouring around bridge piers. Up to now, the sediment transport formulae used for computing pier scour were developed based on the general scouring in unobstructed flow. The capability for numerical models to predict local scour around bridge piers was severely restricted by the sediment transport formulae. The new formula introduced in this paper can take into account vortices that affect the local scour process by adding some terms into the classic bed‐shear stress equation. The 3D numerical model system used in this study consists of three modules: (a) an unsteady hydrodynamic module; (b) a sediment transport module; and (c) a Fation module. The hydrodynamic module is based on the 3D RANS equations. The sediment transport module is comprised of semi empirical models of suspended load and non‐equilibrium bed load. The bed‐deformation module is based on the mass balance for sediment. The model was used to simulate pier scour in tree different test cases: (1) a circular pier; (2) a square pier; and (3) a rectangular pier, by applying the ordinary sediment equation and the newly introduced sediment equation. Results of both numerical simulations were compared against laboratory measured data and also in case 1 with result of Olsen and Melaaen (J. Hydraul. Eng. 1993; 119 (9):1048–1054). Comparisons show that the new sediment formula could predict the scour more accurately than the ordinary one. Copyright © 2010 John Wiley & Sons, Ltd.     

Scour Hole Influence on Turbulent Flow Field around Complex Bridge Piers

Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its sides are observed and have been measured. It is shown that these flow patterns also cause sediment entrainment. Vortex flow behind the PC and amplification of turbulence intensity along its sides near the downstream region can be other reasons for the scour hole (SH) development. Turbulence intensities and Reynolds shear stresses are presented and discussed. A comparison is made between the flow field measured with the equilibrium SH and that measured on the fixed flat-bed. The results show that the flow field around the PC is considerably influenced by the development of the SH. The extent of the wake region at the rear of the PC is about 1.4 times larger for the fixed bed (FB) than for the scoured bed (SB). Moreover, the size of the core of high turbulent kinetic energy K, as well as the maximum values of K behind the column for the FB case is larger than that of the SB case. When a scour hole develops, the flow below the PC around the piles is considered to be the main cause of the scour. This is the first time that these observations about the flow and turbulence field around a complex bridge pier are reported and analyzed. In addition to improving the understanding of the flow structure, the present detailed measurements can also be used for benchmarking and verification of numerical models.     

Flow around submerged structures subjected to shallow submergence over plane bed

The results of an experimental investigation on the flow field around submerged structures on horizontal plane beds, measured by an acoustic Doppler velocimeter (ADV), are presented. Experiments were conducted for various conditions of submergence, having submergence factors ranging from 1.0 to 2.0 and average flow velocity ranging from 0.25 to 0.51 m/s. The Froude number and the Reynolds number of the approaching flow for different runs are in the range of 0.18–0.42 and 50 000–76 500, respectively. The vertical distributions of time-averaged three dimensional velocity components and turbulence intensity components at different radial distances from the submerged structures are plotted. Deceleration and acceleration of the approaching flow around the submerged body are evident from the vertical distributions of the horizontal velocity component, whereas the lifting and diving nature of the flow are indicated by the vertical velocity component distributions. The vertical distributions of the horizontal velocity component indicate reduction of 30% of the non-dimensional time-averaged horizontal velocity component magnitude for the cylinder of diameter 11.5 cm in comparison to the cylinder of diameter 10 cm. Also, there is an increase of 10–25% in the horizontal velocity component at different radial sections. The flow is three dimensional in the downstream of the submerged structure. The velocity and the turbulent intensity components are also well predicted by FLUENT. The flow characteristics in the wake and the induced bed shear stress are also analyzed with FLUENT.The profiles of non-dimensional shear velocity deviate from the log law in the wake and the far downstream directions. The scour prone regions may be identified from the profiles of the induced bed shear stress around the submerged structure.     

Flow Field Around Single and Tandem Piers

The present study provides a comparison between the flow pattern around two circular piers in tandem and a single pier set up on a moderately rough flat bed in a laboratory flume. Velocities are measured by an Acoustic Doppler Velocimeter (ADV). The contours of the time-averaged velocity components, Reynolds shear stresses, turbulence intensities and turbulence kinetic energy at different planes are presented. Streamlines and vectors are used to study the flow features. The analysis of power spectra around the piers is also presented. The results show that the presence of downstream pier changes the flow structure to a great extent, particularly in the near-wake region. Within the gap between the two piers, a stronger and substantial upflow is shaped. However, a weaker transverse-deflection is formed in comparison with that in the single pier. Near the bed, the velocity of flow approaching the downstream pier decreases to 0.2–0.3 times of the approach mean velocity (U ₀) due to the sheltering effect of the upstream pier. In the wake of downstream pier, the flow structure is completely different from the one in the wake of single pier. In comparison with the single pier, the values of turbulence kinetic energy and turbulence intensities show a considerable decrease around the tandem piers. In tandem piers, the high values of turbulence characteristics are found near the downstream pier. There is a recirculation zones just upstream of the sheltered pier close to the bed and another behind that pier near the free surface. The results show a decrease in the strength of vortical structure in the wake of tandem piers in comparison with single pier. It is shown that the formation of flow with different Reynolds number along the flow depth due to the effect of bed roughness, as well as pier spacing, can influence the type of flow regime of tandem case. In addition to enhancing the flow structure indulgence, the present detailed measurements can also be used for verification of numerical models.     

透水床面明渠湍流时空平均特征的大涡模拟与分析

基于大涡模拟数据,研究了理想粗糙透水床面明渠湍流的时空平均特性. 考虑到空间异构性,对比分析了不同位置的时空平均流速、雷诺剪应力、构造剪应力、脉动幅度的垂线分布. 结果表明:第一,顶层床面之上,空间异构性的影响较小,不同位置的双平均流速符合类似的对数分布,但由于透水床面影响,卡门常数较不透水床面小;在床面附近,空间异构性影响较大,不同位置的双平均流速分别符合线性分布与多项式分布;在透水河床内部,靠近底层球孔的双平均流速为上部球孔双平均流速的1.55 倍. 第二,床面之上,雷诺剪应力占总剪应力的95% 以上,占有主体地位;床面附近,紊动较大,构造剪应力不能忽略,其值大约占总剪应力的15%.由于流场的各向异性,纵向与垂向的脉动幅度有所差异.     

桥墩-冰塞-局部冲刷相关问题研究进展

桥梁建设改变了河流的边界条件、水流条件和河床泥沙的运动状态,冬季河流中有冰塞出现时则产生相互影响作用.近年来,基于冰塞稳定性力学分析,开展了桥墩影响下冰塞稳定性研究,所得桥墩影响下冰塞稳定性判别公式计算结果和实测资料能够较好得吻合;研究了桥墩对河道卡封以及临界流凌密度的影响,计算得到的临界流凌密度与实验值较为接近;介绍了明流、冰盖下桥墩周围局部冲刷等方面的相关研究工作,得出了冰盖条件下桥墩局部最大冲刷深度的回归经验公式,结果表明该公式具有很好的适用范围.对冰塞条件下桥墩附近局部冲刷问题探索性地开展了试验研究,研究表明,冰塞条件下的局部冲刷与冰盖条件下有着很大不同,不仅冲刷深度要大的多,而且桥墩周围局部冲刷过程与冰塞厚度变化相关.在冰塞条件下,桥墩处的最大冲刷深度和最大冲刷长度均随流速增大而增大,冲刷坑尾部淤积沙丘高度也受到流速的影响.就相关研究难点和今后需要进一步开展的研究工作进行了分析和展望.      

PIV measurements of flow in and around scour holes

Two sets of experiments related to the scour of cohesionless sediment by planar turbulent jets are presented and discussed. The first set of experiments measures the growth of the scour hole and downstream dune as a function of time. Measurements reveal a bedform that is nearly self-similar and whose growth in time is governed by a power-law relationship. The bedform is well represented by three linear segments with slopes near the angle of repose of the sediment. The second set of experiments uses Particle Image Velocimetry to characterize the mean velocity field in the scour hole and above the dune. For this set of experiments, a series of successively larger roughened fixed-bed models was used in place of the mobile bed. The measurements reveal the presence of strong recirculation in the hole and an attached wall jet on the main slope. Discussion of the utility of the present fixed-bed measurements in estimating shear stress along the bed and related application to predictive modeling of hydraulic scour is provided. Discussion of the technical challenges of similar mobile-bed measurements is also given.     

Turbulent flow structure at concordant and discordant open-channel confluences

Models of flow at river-channel confluences that consist of two concordant confluent channels with avalanche faces dipping into a scour zone are limited because this morphology may be the exception rather than the rule in nature. In this paper the mean and turbulent flow structure in the streamwise and vertical directions at both concordant and discordant laboratory confluences were examined in order to determine the effect of bed discordance on the flow field, and to assess its influence on sediment transport. Instantaneous velocities were measured with a laser Doppler anemometer using a dense spatial sampling grid. The spatial distribution of normal stress varies with bed geometry as bed discordance generates a distortion of the mixing layer between the confluent streams. Turbulent shear stress is larger in the discordant bed case and its peak is associated with the position of the mixing layer whereas for concordant beds the zone of mixing is characterised by a decrease in the Reynolds shear stress. Quadrant analysis also revealed differential dominating quadrants between the two bed geometries which will influence sediment transport routing and, consequently, the resulting bed morphology. These results highlight the need for significant modifications to current models of confluence flow dynamics in order to account for the bed configuration.We would like to thank Phil Fields of the Earth Sciences workshop at Leeds for his skillful construction of the confluence model and continued help during the course of this research. The LDA facility has been funded through grants from the UFC, NERC and University of Leeds. PB thanks NSERC for financial support and the Fonds FCAR for funding an eight month study-visit held at the Department of Earth Sciences, University of Leeds. AGR acknowledges the financial support of NSERC whilst JLB is grateful for the award of a Nuffield Science Foundation Fellowship which facilitated the preparation of this paper. We thank two anonymous reviewers for their constructive criticisms that helped clarifying the paper.     

一种新的往复流试验平台及其泥沙冲刷试验研究

本文提出一种可以模拟潮流运动的自动化控制水槽。该水槽可以时控制往复流两端的水位,实现流的往复运动,并可以按计算机要求实现水位的稳定或渐变。本文同时利用该水槽进行了圆柱开桥墩周围的测试数据、照片为基础、分析了不同水流条件下圆柱形桥墩周围的床面冲刷情况。试验发现在桥墩附近,水流的旋滚运动及旋涡系是造成床面冲刷的主要原因,另外对于往复流情况,桥墩附近床面受到的冲刷比固定水位冲刷时要严重,也更为复杂 。     

Coupling between countercurrent gas and solid flows in a moving granular bed: The role of shear bands at the walls

We extended the standard approach to countercurrent gas–solid flow in vertical vessels by explicitly coupling the gas flow and the rheology of the moving bed of granular solids, modelled as a continuum, pseudo-fluid. The method aims at quantitatively accounting for the presence of shear in the granular material that induces changes in local porosity, affecting the gas flow pattern through the solids. Results are presented for the vertical channel configuration, discussing the gas maldistribution both through global and specific indexes, highlighting the effect of the relevant parameters such as solids and gas flowrate, channel width, and wall friction. Non-uniform gas flow distribution resulting from uneven bed porosity is also discussed in terms of gas residence time distribution (RTD). The theoretical RTD in a vessel of constant porosity and Literature data obtained in actual moving beds are qualitatively compared to our results, supporting the relevance under given circumstances of the coupling between gas and solids flow.