Observation of von Kármán vortex street in a droplet breakup

Abstract

We report the first observation of von Kármán vortex street in a droplet breakup induced by shock waves and high-speed fluid after the shock. To obtain these data, a novel experimental system is used to record the interaction between the droplet and shock wave and the following fluid. Details of flow fields and transients are also presented and discussed. Based on high-speed shadowgraphs, a Strouhal number of 0.28 ± 0.09 with a Reynolds number of 2817 is obtained, which is in good qualitative agreement with earlier experiments on the von Karman vortex street. The results suggest that the vortex-induced vibration may dominate the oscillation in the horizontal direction, which would result in resonance when the frequency of the oscillating flow matches the natural frequency of the droplet, thereby enhancing the deformation and breakup of the droplet. Our data may be useful to benchmark related multiphase flow models or nonlinear theories.

Torques and angular momenta of fluid elements in the octonion spaces

“…It can be considered as the result of two torques, W i 1(1) and W i 1 (2) , applied simultaneously to a cylinder. Herein the amplitude, frequency, and phase value of the torque, W i 1 (1) , are different from that of the torque, W i 1(2) , respectively. In a word, when the torque applied to the fluid changes, the angular momentum of the fluid element will alter, transforming the vortex street accordingly.…”

“…The difference of torques between two sides is close to zero. It can be considered as the result of two torques, W i 1(1) and W i 1 (2) , applied simultaneously to a cylinder, with W i 1(2) = −W i 1 (1) . In other words, the amplitude and frequency of the torque, W i 1 (1) , are equal to that of the torque, W i 1 (2) , respectively, although their phase values are reversed.…”

“…It can be regarded as the result of two torques, W i 1(1) and W i 1 (2) , applied simultaneously to a cylinder. Herein, the frequency of the torque, W i 1 (1) , is equal to that of the torque, W i 1 (2) . But the amplitudes of the two torques are different from each other, while their phase values are reversed.…”

“…(b) Vortex street. In the experiment of Karman vortex street, 1 besides the divergence of angular momentum of the fluid elements, the torque, that the fluid is subjected to, has an important influence on the direction of motion of the fluid, flowing through the surface of a cylinder. (c) Cloud pattern.…”