Oscillations, Waves, and Interactions - GWDG

The single bubble – a hot microlaboratory 149
Figure 9. Dynamics of a laser-produced spherical bubble in silicone oil of viscosity 4.85
poise observed at 75000 frames per second. Maximum bubble radius is about 2 mm.
3.1 Laser-bubble dynamics
The following figures present some examples of single bubble dynamics under various
circumstances. Figure 9 shows the free oscillations of a single spherical bubble
produced in silicone oil attaining a maximum bubble radius of about 2 mm, substantially
larger than the few 10 µm of acoustically trapped bubbles. The oscillation is
damped by the viscosity of the liquid and the bubble attains its equilibrium radius
after about four oscillations. The bright spot in the middle of the bubble is a result
of the backlight. In a nicely spherical bubble of this size the light traverses the bubble
undeflected and nearly undeflected along and near perpendicular incidence of the
illuminating light on the bubble surface.
Figure 10 shows the collapse of a single bubble near a solid wall. The sequence taken
at 300000 frames per second starts near the first collapse and shows the characteristic
protrusion of the bubble wall towards the surface. The liquid jet is hidden inside this
protrusion and is best visible in the rebound phase as a dark line inside the bright
spot at the center of the cavity where the backlight can pass undisturbed through
the smooth bubble surface. After some time the long tube of gas and vapour with
the jet inside gets unstable and decays into several tiny bubbles. The surface of the
bubble thereby reapproaches its spherical shape.
The formation and strength of a jet inside the bubble depends on the distance s
of the bubble center from the wall. To be more exact, the normalized distance or
stand-off parameter
γ = s
,
Rmax