Multi-cycle dynamics and vortex structures of the cavitation bubble in the circular tube

Revealing the bubble dynamics within the tube facilitates precise control of bubble positioning, thereby offering potential improvements in targeted drug delivery and the operational efficiency of inertial micropumps. This study focuses on an in-depth investigation of the multi-cycle dynamics of the cavitation bubble and the associated vortex behavior within a circular tube. The reliability and accuracy of the current model were validated through comparisons with three sets of experiments. A comprehensive analysis was conducted to investigate the effects of the relative position (δ) and tube diameter (γ) on bubble dynamics, vortex structures, and wall shear stress. The results show that the cavitation bubble exhibits different jet patterns depending on the δ: bidirectional jets occur at the pipe center (δ = 0), the unidirectional jet appears when the bubble is positioned off-center, and a high-speed unidirectional jet is observed near the tube port. The vortex structures induced by cavitation bubble collapse and their effects on wall shear stress exhibit significant variations under different γ. Two distinct regions are observed according to whether the localized high wall shear stress regions occur or not. The localized high wall shear stress is observed in the range 0.4 < γ ≤ 1.3, whereas no such high-shear regions are present when 1.3 < γ ≤ 1.6. As δ increases, the bubble collapse time in the first two cycles increases. In contrast, a decrease in γ leads to a reduction in the maximum bubble radius, while both the collapse time and peak wall pressure increase.