The Growth and Collapse of a Bubble between Parallel Flat Free Surfaces

Abstract

The growth and collapse of a bubble between two parallel flat free surfaces and the corresponding water column formation on the free surfaces have been investigated experimentally and numerically. In the experiment, a laser-induced bubble generated inside a plane water jet and the dynamical motion of free surfaces were observed with a high-speed video camera. The results are characterized by two dimensionless parameters: the ratio of the maximum bubble radius to the water jet width, Rmax * , and the ratio of the initial bubble offset from the center line of the jet to the water jet width, ε * .When a bubble is generated at the center (ε * = 0), water columns are formed on both free surfaces during the growth phase of a bubble, following the formation of crown-like shaped water columns during the second growth and collapse of a bubble. Since the bubble does not translates, it grows and collapses at the center of the jet. However, a water column due to the bubble growth when ε * ≠ 0 tends to be formed only on the nearer free surface to the bubble during its growth phase. Then in the collapse phase the bubble translates toward the other free surface far from the bubble accompanying with a liquid-jet formation toward it. The liquid-jet and the rebound shockwave from the bubble cause the water column formation on both sides of free surfaces. Numerical simulations are conducted for the growth and collapse phases using the boundary element method (BEM) and for the collapse phase using the ghost fluid method (GFM). The water column formation during the growth phase, a toroidal bubble deformation during the collapse phase, and the translation of the collapsing bubble are well simulated by BEM. The result of GFM shows shockwave emission from the rebounding motion of the bubble which causes the water column formation when the shockwave impacts on the free surface with large curvature.