Evolution of vortex structures in an open deep cavity under pulsatile flow conditions: An experimental study
Experiments have been conducted to investigate the vortex dynamics in a deep open cavity driven by pulsatile flows. Physiological flow waveforms have been examined for mean Re ranging from 200 to 1000 and Wo of 10.2, 12.4, and 17.6, with Strouhal numbers (Str, as a function of Re and Wo) ranging from 0.065 to 0.98. Results show that a two-primary-vortex system develops, similar to a steady driven cavity flow, but it exhibits more dynamic behaviors as it evolves during a cycle. Five stages of vortex evolution are defined: generation, traveling, merging, stretching, and weakening. As Re increases, the first three stages occur faster and earlier in a cycle, allowing more time for the top primary vortex to interact with the rear wall and for the bottom vortex to develop. The opposite trend is found as Wo increases. While the flow strength increases with Re, the vortex patterns are more correlated with Str, which is proportional to the Wo square and inversely proportional to Re: vortices are symmetric at low Str, but become more distorted at high Str. A critical Str exists beyond which the bottom vortex would not develop inside the cavity. Results also suggest that an increasing Wo causes a more significant increase in the in-cavity vortex strength and flow unsteadiness compared to an increasing Re. The peak flow unsteadiness inside the cavity occurs at a later phase compared with that of the main flow. The normalized mass flux ratio and the normalized cavity kinetic energy are both linearly proportional to the Strouhal number.