Instability of thin liquid layers between two pulsed laser induced cavitation bubbles

• Main Authors: Yen-Hung Chen, 陳彥宏
• Other Authors: Lin I
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/4z3437

博士 === 國立中央大學 === 物理研究所 === 97 === The interaction of two nearby pulsed laser induced expanding bubbles mediated with a thin liquid layer in a confined liquid sheet is investigated experimentally using high-speed photography under the optical microscope. The precise manipulation of dual laser beams for generating bubbles at the different laser energies, onset times, and bubble positions enables the study of the instability of the trapped liquid layer under the different condition of compression. The thin liquid layer trapped by the two symmetrically growing bubbles lubricates the nearby bubble surfaces and prevents the bubble coalescence. As the symmetry is broken by generating two bubbles at the different laser energies or the onset times, the lubrication layer becomes unstable. In the energy-asymmetric case, the explosive boiling leads to the bubble cluster formation which destabilizes the lubrication layer. The breakup of the thin lubrication layer perturbed by the boiling induced bubbles can be understood by studying the thin lubrication layer perturbed by a pulsed laser generated defect bubble, where the single defect bubble causes the bubble cluster formation. In the time-asymmetric case, the bubble cluster appears near the lubrication layer which spreads into the bubble under the pressure gradient. The thin liquid layer cannot be trapped anymore as the time-asymmetry is enhanced. The deformation of the thin liquid layer near a free bubble surface repelled by an expanding bubble is studied in the highly time-asymmetric case. The protrusion of the anisotropically expanding bubble toward the free bubble surface is shelled by a thin liquid layer. As decreasing the inter-bubble distance, the deformation structure of the repelled thin liquid shell transits from the single spike to the crown-shaped splash, where the liquid jets flowing through the junctions between the two bubbles become divergent and make the thin liquid layer break. The curvature of the free bubble surface affects the deformation structure, where flow through the highly curved bubble surface is focused. Therefore, it causes the sharp transition of the deformation structure. The localized flow through the highly curved free surface leads to the counter-jet formation on the other expanding bubble.