Vortical Structure of Turbulent Shear Flows Studied by Vortex Dynamics Simulation

1.本文用涡滴法模拟了带圆角的方涡环的演化过程，其中涡丝的连通性没有被显式地保持，以获得三维无粘涡运动的动力学不变量真正守恒的变形模式和外显式。模拟表明，不变量是保守的，直到它们的灾难性增加发生。动能被认为是讨论不变量守恒性的最严格判据。随着涡核半径的增大和角部曲率半径的增大，灾难性的扰动出现的时间也相应增加。得到了涡环的拓扑结构演化规律，并进行了讨论.对由两条平行线段和两个半径相同的圆弧连接而成的长短轴比为B的拟椭圆涡环的变形进行了涡动力学模拟 关于我们 2到20之间。变形有四个基本模式取决于纵横比：周期性的轴切换;分裂成两个涡环后的轴切换;分裂成两个涡环没有轴切换;分裂成三个涡环没有轴切换。最后两种模式预计将导致进一步的轴切换，并最终分裂成两个涡环在较长的时间。流动显示实验证实了这一点.用无粘涡动力学方法模拟了多个圆形涡环的相互作用，得到了符合Kolmogorov-5/3幂律的功率谱。涡度拟能谱与均匀湍流的耗散谱是等价的，在相同波数范围内，涡度拟能谱具有部分1/3幂律。这项研究是第一个显示-5/3功率谱的结果，几个，而不是很多，涡环的无粘相互作用。-5/3幂律的波数范围与涡环的数目及其初始形状有关，涡环核半径越小，波数范围越宽。高涡度区的均匀分布似乎对满足-5/3幂律是必不可少的。无粘涡运动的五个不变量，即。e.总能量、总动量、总角动量、总螺旋度和总涡量在允许的偏差内保持恒定，直到涡量趋于发散.采用涡滴法模拟了倾斜圆盘的非定常分离流动，得到了圆盘边缘分离形成的圆形涡环的三维涡结构演化。涡尾流的螺旋结构被证实的模拟在垂直于来流方向的平面内的涡量轮廓。少

1. Evolution of square vortex rings with rounded corners was simulated by a vortex blob method, in which the connectivity of vortex filaments is not explicitly maintained, to obtain patterns of deformation and the exetnt to which dynamical invariants of the three-dimensional inviscid vortex motion are really conserved. The simulation showed that the invariants were conserved until their catastrophic increase took place. The kinetic energy was found to serve as the most stringent criterion to discuss the conservation of the invariants. The time when the catastrophic bahavior appeared increased with increasing radius of core of the vortex blobs and with increasing radius of curvature of the corners. Evolution of topology of the vortex rings was obtained and discussed.2. A vortex dynamics simulation was made on the deformation of pseudoelliptical vortex rings which consists of two parallel line segments connected by two semicircles of the same radius, the major-to-minor axis ratio being b … More etween 2 and 20. The deformation had four fundamental patterns depending on the aspect ratio : the periodic axis switching ; the splitting into two vortex rings after the axix switching ; the splitting into two vortex rings without the axis switching ; the splitting into three vortex rings without the axis switching. The last two patterns are expected to lead to further axis switching and eventual splitting into two vortex rings at larer times. This was confirmed by a flow visualization experiment.3. An inviscid vortex dynamics simulation of interaction of several circular vortex rings produced the power spectrum which had a part of the Kolmogorov -5/3 power law. The enstrophy spectrum, which is equivalent to the dissipation spectrum in homogeneous turbulence, had a part of the 1/3 power law in the same wavenumber range. This study is among the first to show the -5/3 power spectrum as a result of the inviscid interaction of several, not many, vortex rings. The wavenumber range of the -5/3 power law slightly depends on the number of the vortex rings and their initial configuration, being wider for smaller radius of core of the vortex rings. A uniform distribution of high-vorticity regions appears to be essential to have the -5/3 power law. Five invariants of the inviscid vortical motion, i. e. The total energy, total momentum, total angular momentum, total helicity and total vorticity were maintained constant within tolerable deviations from the corresponding initial valves until vorticity tends to diverge.4. The unsteady separated flow around an inclined circular disk was simulated by the vortex blob method to obtain the evolution of three-dimensional vortical structures from circular vortex rings formed by the separation from the edge of the disk. A spiral structure of the vortical wake was confirmed by the simulation in terms of the vorticity contour in planes normal to the direction of the approaching flow. Less