Experimental observations of vortex ring interaction with the fluid adjacent to a surface
Experimental observations of vortex ring interaction with the fluid adjacent to a surface
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发表时间：
1983-10
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通讯作者：
A. Cerra;C. Smith
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文献类型：
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作者：
A. Cerra;C. Smith
摘要：实验研究考察了初始层流涡环在静态环境中与固体表面和自由表面以及与发展中层流边界层下的固体表面碰撞时的破裂情况。流动相互作用可视化在水中使用染料和氢气泡技术，并记录与高速视频系统。当涡环接近表面时，所产生的流动相互作用看起来是混乱和湍流的，但实际上是一个非常有组织的粘性-非粘性过程，它迅速地将涡环的涡度分散在周围的流体中。所描述的流动相互作用综合了以下现象：（1）与涡环相反的二次涡量的产生;（2）涡环轨迹偏离经典理论预测的轨迹;（3）涡量有组织的扩散过程。涡度扩散的过程取决于涡环的初始雷诺数（Re sub 0）。对于非常弱的环，即Re小于350，涡度通过层流扩散分散。对于较强的环，涡度分散发生离散通过形成二次和三级涡环（SVR和TVR）通过粘性边界层过程。由于SVR和TVR与原始或主涡环的Biot-Savart型相互作用，涡度扩散继续进行。在这种相互作用过程中，SVR的直径被压缩，导致SVR的不稳定性，其特征在于方位波度。
Abstract : Experimental studies examined the breakdown of initially laminar vortex rings during impact with both solid and free surfaces in a quiescent environment, and with a solid surface beneath a developing laminar boundary layer. Flow interactions were visualized in water using dye and hydrogen-bubble techniques and recorded with a high-speed video system. When a vortex ring approaches a surface the resulting flow interaction appears to be chaotic and turbulent, but is actually a very organized viscid-inviscid process which rapidly disperses the vorticity of the vortex ring throughout the surrounding fluid. Described is the flow interaction which integrates the following phenomena: (1) generation of secondary vorticity of opposite sense to that of the vortex ring; (2) deviations in the trajectory of the vortex ring from that predicted by classical theory; and (3) the processes of organized dispersal of vorticity. The process by which vorticity dispersal occurs is dependent upon the initial Reynolds number (Re sub 0) of the vortex ring. For very weak rings, i.e. Re sub o less than 350, vorticity is dispersed by laminar diffusion. For stronger rings, vorticity dispersal occurs discretely through formation of secondary and tertiary vortex rings (SVR and TVR) via a viscous boundary layer process. Vorticity dispersal continues as a result of Biot-Savart-type interactions of the SVR and TVR with the original or primary vortex ring. During this interaction the diameter of the SVR is compressed, causing an instability in the SVR which is characterized by an azimuthal waviness.