| Summary: | 碩士 === 國立中正大學 === 物理學系暨研究所 === 101 === Two gas bubbles are produced simutaneously with a moderate separation
by laser induced ablation on micron-sized carbon particles suspended in 460
torr N2 environment. Each gas bubble is produced with the generation of
a shock shell. The pressures p of the shock front at differet distances d are
measured, and p is shown to decay following p ∼ d^-3 as the shock shell
propagates outward, which agrees the theory of shock wave. The evolution
of a single gas bubble is presented. The effect of self-acting behavior on the
single bubble is neglected due to the differnt time scale with that of two
bubbles interaction. In the case of two bubbles interaction, the p-d diagram
is used to estimate the pressure of the shock front as the shock shell enters
the gas bubble. This shock pressure is compared with the estimation from
the speed of shock shell, which shows that the intensity of the shock shell
hardly decreases by collision under the present explosion energy. During the
evolution of two bubbles interaction, the small-scale fluctuations are observed
on the compressed surface of the gas bubble after the shock shell-gas bubble
collision. The growth rate of the fluctuations is measured to be linear and is
shown to agree with the theory of RM instability. As the alignment of the
bubbles is rotated slightly in horizontal plane, the ”fluctuating surface” is
observed, which represents the 3D structure of RM instability. A surprising
phenomenon is observed that there is a density drop at the intersection of
the shock shells, and it lasts for a long time. The possible mechanism is due
to the overlapping of the rarefaction waves.
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