The effect of single bubble-cluster in upward bubbly flow on large-scale vortex structure

At present, bubbly flow has been used for industrial applications such as reducing frictional resistance by introducing bubbles into the turbulent boundary layer at the bottom of the ship. To utilize air bubbles in high efficiency, we conduct experiments of upward bubbly channel flow in the vertical channel to investigate the interaction of the bubble-cluster formed in the wall shear layer and liquids. At present, it is confirmed that the large-scale vortex disappears under the bubble-cluster formation condition. In addition, we confirmed that vortex fraction begins to decrease around the time when the bubble-cluster passed the test section. Collating experiment with simulation results and analyzing three dimensional velocity field and bubble image, we estimated when and where bubble structure effect liquids. Because the velocity of bubble-cluster exists in wall-shear layer is slower than the advection speed, the bubble-cluster hardly affects large-scale vortex directly. Furthermore, by comparing the transition of the vortices upstream and downstream in the test section, transition and structure of the vortex throughout the whole channel were evaluated. As a results, we suggested the possibility that bubble-cluster inhibits the growth of vortex in the wall shear layer.