STRUCTURE AND STABILITY OF VORTEX RINGS
STRUCTURE AND STABILITY OF VORTEX RINGS
复制标题
DOI：
10.1017/s0022112072001041
复制
发表时间：
1972-01-01
影响因子：
3.7
通讯作者：
MAXWORTHY, T
中科院分区：
文献类型：
--
作者：
MAXWORTHY, T
描述了对实验产生的涡环的一系列观察。使用染料和氢气泡技术观察流场、环速度和生长速率。研究发现，稳定环的形成和增长方式使得它们的大部分涡量分布在整个流体体积中，该流体体积大于可见染料核心并随其移动。当涡量从该移动的流体体扩散到外部无旋转流体中时，它会产生两个影响。它导致一些具有新获得的涡度的流体被夹带到气泡的内部，而其余的则被留下并导致尾流中环涡度的出现。研究发现，在高雷诺数下，这些稳定环的平移速度 U 变化为 t−1，其中 t 是从下游无穷远虚拟原点开始运动开始测量的时间。提出了一个简单的理论模型，它解释了观察到的稳定流的所有这些特征。雷诺数更高的环变得不稳定，并在尾流中释放出更多的涡量。在某些情况下，这个脱落过程中会出现一个新的更稳定的漩涡，并且以比以前更小的漩涡继续存在。最终，环运动停止，因为其所有涡量都沉积到尾流中并通过粘性扩散扩散。对沿共同路径行进的两个几乎相同的环之间相互作用的观察表明，与普遍看法相反，环不会相互来回传递，而是后面的环被夹带到前面的环中。只有当后面的环的速度比其伙伴的速度高得多时，它才能从连接过程中出现并留下移动较慢的环。
A series of observations on experimentally produced vortex rings is described. The flow field, ring velocity and growth rate were observed using dye and hydrogen-bubble techniques. It was found that stable rings are formed and grow in such a way that most of their vorticity is distributed throughout a fluid volume which is larger than and moving with the visible dye core.As the vorticity diffuses out of this moving body of fluid into the outer irrotational fluid, it has two effects. It causes some of the fluid, with newly acquired vorticity, to be entrained into the interior of the bubble, while the rest is left behind and accounts for the appearance of ring vorticity in a wake. It was found that the velocity of translation U of these stable rings varies as t−1, at high Reynolds number, where t is the time measured from the start of the motion at a virtual origin at downstream infinity. A simple theoretical model is presented which explains all of these features of the observed stable flow. Rings of even higher Reynolds number become unstable and shed significantly more vorticity into the wake. Under some circumstances a new more stable vortex emerges from this shedding process and continues with less vorticity than before. Eventually, the ring motion ceases as all of its vorticity is deposited into the wake and is spread by viscous diffusion. Observations of the interaction between two nearly identical rings travelling a common path showed that, contrary to popular belief, rings do not pass back and forth through one another, but that the rearward one becomes entrained into the forward one. Only when the rearward ring has a much higher velocity than its partner can it emerge from the joining process and leave a slower-moving ring behind.