Abstract
This study follows our previous report (Zhang et al., Phys. Fluids, vol. 31, 2019, 034105) by describing the formation and evolution of the engulfment flow in the cross‐shaped channel. First, the flow regimes were studied by planar laser induced fluorescence (PLIF). Results show the formation of a spiral vortex in the center of the chamber and the appearance of a well‐mixed zone inside the spiral vortex. Second, we proposed a novel experimental method to analyze the residence time of the fluid in the chamber, and discover an unexpected trapping region inside the well‐mixed zone. There is almost no fluid transport into or out of this region. Furthermore, three‐dimensional numerical simulation is used to reveal the origination of this trapping region. Simulation results reveal that the fluid recirculates in the trapping region and the flow feature is caused by the bubble‐type vortex breakdown.