旋转圆柱绕流流场特性分析

对雷诺数Re = 20000 ~ 90000、相对转速ɑ = 0 ~ 0.72的旋转圆柱后方流场进行了实验测量, 分析了旋转圆柱后方不同剖面处的速度分布规律和湍流度分布规律. 采用LES方法对旋转圆柱绕流问题进行了数值模拟, 分析旋转圆柱周围流场特性和自由剪切层变化规律, 最后通过理论模型对流场变化进行分析, 得出如下结论: 当圆柱逆时针旋转时, 同一雷诺数下随着相对转速的增加, 旋转圆柱尾迹区域下方速度突变处的位置随着相对转速的增加而上移, 而上方速度突变处的位置不变, 雷诺数的增加使旋转圆柱尾迹区域下方速度突变处位置有小幅度的下移. 通过数值模拟发现, 圆柱旋转之后, 圆柱后方下侧涡的位置明显上移, 且幅度较大. 下方的自由剪切层有明显的上移, 上方的自由剪切层位置变化较小. 最后通过理论分析发现, 圆柱后侧下方涡位置的上移对圆柱升力影响十分显著, 在高雷诺数、低相对转速的条件下, 旋转圆柱后侧下方涡位置的改变对旋转圆柱的升力、尾流区自由剪切层的变化起到了重要的影响.      

旋转式一孔测压管及其应用1）

由圆柱三孔型二元复合测压管的测速原理出发，提出用一孔测压管通过旋转实现平面气流速度大小与方向的自动测量，建立了相应的测试系统．通过大量实验，研究了该系统的性能．在多种回流和旋流流场测量中进行了应用．结果表明该系统测量原理正确，重复性好，精度高     

旋转式一孔测压管及其应用1）

由圆柱三孔型二元复合测压管的测速原理出发，提出用一孔测压管通过旋转实现平面气流速度大小与方向的自动测量，建立了相应的测试系统．通过大量实验，研究了该系统的性能．在多种回流和旋流流场测量中进行了应用．结果表明该系统测量原理正确，重复性好，精度高     

三角翼前缘涡的某些破裂形式及特性研究

基于流动显示和PIV技术测量的实验结果，对三角翼前缘涡破裂的一些形式和破裂特性进行了分析和讨论。通过PIV测量所得到的涡量分布证实了在螺旋破裂的情况下，涡核的螺旋方向与前缘涡的旋转方向相反，及双螺旋破裂形式的存在等。进而对螺旋波的形成机理提出了与有关文献不同的看法。     

亚临界雷诺数二维圆柱绕流边界层流场动态特性的实验研究

本文给出了关于亚临界雷诺数二维圆柱绕流动态特性的实验结果。应用热膜、热线和压力传感器测量了壁面剪切应力脉动、壁面压力脉动和流场的速度脉动,给出了壁面剪切应力脉动频率在驻点附近和分离前后变化的特征,计算了这些脉动量在圆柱面上任意两点间的相关特性。实验结果表明,在亚临界雷诺数二维圆柱绕流的边界层流场中存在着一个频率与涡脱落频率相同的整体同步脉动。     

慢扩张旋涡破裂位置的确定

在慢扩张的假设下给出一类旋涡发展的解析表达式,讨论了解的性质,在一定情况下会出现泡型区和涡破裂,讨论了扩张角及旋转速度对涡破裂位置的影响。     

激波在平板上诱导的旋涡强度的测量

运动激波通过两个等攻角平板后诱导出两个同向旋转的旋涡，这两个旋涡在随当地气流向下游运动的同时，绕涡核连线中心旋转。本文通过测量涡对的转动角度速度，获得了每个旋涡的强度。实验结果表明，由此测得的旋涡强度不同用于小攻角平板起动涡公式计算了起动涡强度。     

起始攻角附件三角翼涡破裂的演化特性研究

用数值方法求解Ｎ－Ｓ方程，并用“亚迭代”方法保证时间方向二阶精度，数值模拟了 ７５° 后掠三角翼非定常绕流，给出了详细的涡破裂起始攻角附近涡破裂的形成、发展和演化过程． 涡破裂从开始的螺旋破裂变为向泡状破裂演化的“过渡态”，然后发展到泡状破裂，再由泡状 破裂变为向螺旋破裂演化的“过渡态”，最终发展到典型的螺旋破裂形态．从计算结果中还发 现，当泡状破裂形成后破裂点前移速度明显减慢，同时当从泡状破裂向螺旋破裂演变时，破裂 点出现后移现象．可从最近相关的实验和数值模拟结果中发现这些现象的存在．     

绕旋转圆柱流动涡尾流结构和临界状态特性

采用作者提出的基于区域分解，有限差分法与涡法杂交的数值方法，结合高阶隐式差分格式，和以修正的不完全ＬＵ分解为预处理器的共轭梯度法作求解器，系统地研究了雷诺数Ｒｅ＝１０００，旋转速度比α∈（０．５，３．２５）范围内，绕旋转圆柱从突然起到充分发展，长时间内尾流旋涡结构和阻力，升力系数的变化规律，计算所得流动图案与实验流场显示符合很好。数值试验证帝了临界状态的存在，并首次给出了临界状态时的旋涡结构特性。     

均匀来流中旋转圆柱黏性绕流的数值研究

从不可压非定常Ｎ－Ｓ方程出发，首次数值求解了均匀来流中圆柱作周向旋转振荡的黏性绕流问题。探讨了旋转角速度振幅、振荡频率及Ｒｅ数等因素对流场结构及其非定常演化过程的影响，并根据计算结果，给出了在旋转振动频率。速度振幅平面内流场涡结构的分区图。     

Compressible and confined vortex flow

The internal compressible flow of a thin vortex chamber was investigated experimentally by measuring the radial distribution of temperature and pressure, from which the velocity field was calculated. The bulk of the internal vortex was found to be described by u_θr^0.69 = constant. The total resistance of the vortex chamber to the flow was also investigated in the context of fluidic vortex diode behavior under conditions of compressible and choked flow. It was found that the vortex chamber choked at an upstream-to-downstream pressure ratio of about 6 and in doing so passed a mass flow rate of 28% of the equivalent one-dimensional ideal nozzle. The resistance of vortex chambers is known to be strongly influenced by the presence of reversed flow in the exit due to vortex breakdown. Schlieren photography of the swirling exhaust flow was used to show that, while vortex breakdown does occur, it can only do so after the flow has become subsonic downstream of the exit and cannot therefore influence the vortex chamber resistance.     

Obstacle-induced spiral vortex breakdown

An experimental investigation on vortex breakdown dynamics is performed. An adverse pressure gradient is created along the axis of a wing-tip vortex by introducing a sphere downstream of an elliptical hydrofoil. The instrumentation involves high-speed visualizations with air bubbles used as tracers and 2D Laser Doppler Velocimeter (LDV). Two key parameters are identified and varied to control the onset of vortex breakdown: the swirl number, defined as the maximum azimuthal velocity divided by the free-stream velocity, and the adverse pressure gradient. They were controlled through the incidence angle of the elliptical hydrofoil, the free-stream velocity and the sphere diameter. A single helical breakdown of the vortex was systematically observed over a wide range of experimental parameters. The helical breakdown coiled around the sphere in the direction opposite to the vortex but rotated along the vortex direction. We have observed that the location of vortex breakdown moved upstream as the swirl number or the sphere diameter was increased. LDV measurements were corrected using a reconstruction procedure taking into account the so-called vortex wandering and the size of the LDV measurement volume. This allows us to investigate the spatio-temporal linear stability properties of the flow and demonstrate that the flow transition from columnar to single helical shape is due to a transition from convective to absolute instability.     

槽道内涡波流场的POD分析

对槽道内涡波流场的瞬态速度矢量场进行了2DPIV测量实验,将2DPIV测量的矢量场数据进行POD分析,根据POD分解的各阶模态的能量比确定了表征涡波流场主导结构的前15阶模态。结果表明,POD分解的前15阶模态发现槽道内涡波流场是由槽道壁面剪切层诱导的涡列以及伴随的波状主流组成;流场中大尺度的涡旋发展为涡对,对波状主流的脉动频率产生影响;根据涡波流场中的驻点和鞍点,获取了流场的大尺度涡对、平均流场以及Helmholtz涡环等明显特征;最后根据POD分解的前15阶模态对槽道内涡波流场进行重组,重组流场表征了槽道内层流状态下波状主流的形态和涡旋共存的涡波结构以及驻点和鞍点的位置处涡旋的变化等主要特征,有效地剔除了PIV测量流场中的随机信息,保留了PIV测量流场的主导特征。     

3D tangentially injected swirling recirculating flow in a nozzle with a slotted‐tube—Effects of groove parameters

A numerical prediction for 3D swirling recirculating flow in an air‐jet spinning nozzle with a slotted‐tube is carried out with the realizable k–ε turbulence model. The effects of the groove parameters on the flow and yarn properties are investigated. The simulation results show that some factors, such as reverse flow upstream of the injector, vortex breakdown downstream of the injector, corner recirculation zone (CRZ) behind the step and vortex ring in the groove caused by the groove geometric variation, are significantly related to fluid flow, and consequently to yarn properties. With increasing groove height, the length of the CRZ increases, while the initial vortex ring in the groove decreases and a same direction rotating vortex forms in the bottom of the groove. Similarly, as the groove width increases, the extent of both vortex breakdown in downstream of the injectors and the vortex ring in the groove increases slightly, whereas the CRZ lengths in stream‐wise direction decrease. Some factors, such as the negative tangential velocities, the size of the vortex rings in the grooves and the CRZ, are constant for nozzles with different groove lengths. Copyright © 2009 John Wiley & Sons, Ltd.     

EXPERIMENTAL STUDY ON QUANTITATIVE MEASUREMENT OF THREE-DIMENSIONAL STRUCTURE OF HAIRPIN VORTEX BY STEREO-PIV 1)

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.     

Eclatement tourbillonnaire dans une cavité rotor–stator cylindrique

The rotating flow inside an enclosed cylindrical rotor–stator cavity is studied. Within a certain range of governing parameters, vortex breakdown phenomenon can arise along the axis. Very recent papers exhibiting some particular three-dimensional effects, have concentrated new interest on this topic. The study is carried out by a numerical resolution of the 3D Navier–Stokes equations, based on spectral approximations. Three-dimensional behaviours of the flow and in the structure of the associated vortex breakdown are numerically exhibited for the first time in a cavity of large axial aspect ratio.     

Study of vortex breakdown by particle tracking velocimetry (PTV) Part 3: Time-dependent structure and development of breakdown-modes

This third part of the study deals with the time-dependent nature of vortex breakdown. The results show the unsteady velocity and vorticity field of the initiation and development of breakdown and transition between both predominant breakdown modes, the bubble and the spiral. During the development to breakdown, the generated amount of circumferential vorticity follows the theoretical prediction by Brown and Lopez (1990). This confirms the idea of positive feedback as the key-mechanism leading to vortex breakdown. We regard the bubble-type as the fundamental breakdown type, that is stationary and nearly axisymmetric. The circumferential vorticity is distributed in a form of an elliptical vortex-ring-like structure. Starting from this stage, an increase of volume flux to a higher Reynolds number leads to the transition to the spiral-type with an initial stretching of the vortex ring-like structure and a subsequent change to an asymmetric circumferential vorticity distribution. This in combination with the inductive effect causes the front stagnation point to be deflected radially away and later to rotate around the centerline. Consequently the approaching vortex core is radially deflected in opposite direction and evolves in a spiral path. The idea of a second positive feedback-mechanism gives a possible explanation for the transition. Following this theory the asymmetry of circumferential vorticity will trigger itself at a certain degree by the interaction with the inductively affected stagnation point and its influence on the approaching vortex core. This self-enhancing process will finally lead to the spiral-type breakdown in which the radial distance between rotating stagnation point and deflected vortex core is of the order of the characteristic vortex core radius. The reversed transition from the spiral to a stable bubble-type can be regenerated by decreasing the Reynolds number down to the value that corresponds to the stable bubble state. The flow structure evolves nearly in the time-reversed way as during transition from bubble towards the spiral.     

Applications of 2D helical vortex dynamics

In the paper, we show how the assumption of helical symmetry in the context of 2D helical vortices can be exploited to analyse and to model various cases of rotating flows. From theory, examples of three basic applications of 2D dynamics of helical vortices embedded in flows with helical symmetry of the vorticity field are addressed. These included some of the problems related to vortex breakdown, instability of far wakes behind rotors and vortex theory of ideal rotors.