HIGH-SPEED PHOTOGRAPHY OF THE BUBBLE GENERATED BY AN AIRGUN

High-speed photography has been used visually to study the shape, surf ace, turbulence and behaviour of an underwater oscillating bubble gene rated by an airgun. The source was a BOLT airgun with a chamber volume of 1.6 cu.in., placed in a 0.85 m(3) tank at 0.5 m depth. Near-field signatures were also recorded in order to compare the instant photogra phs of the oscillating bubble with the pressure field recorded about 2 5 cm from the gun. Estimations of the bubble-wall velocity and bubble radius estimated from high-speed film sequences are also presented, an d are compared with modelled results. The deviation between the modell ed and measured bubble radii was at most 9%. In order to check the cap acity for transmission of light through the bubble, a concentrated las er beam was used as illumination. We found that the air bubble is a st rong scattering medium of laser light, hence the bubble is opaque.