INTERFEROMETRIC LASER IMAGING FOR SIMULTANEOUS SIZE AND VELOCITY MEASUREMENTS OF CAVITATING MICRO BUBBLES

With the aim to get the higher number of informations on cavitation phenomenon, whose comprehension seems to be really hard, a deep study focused on cavitation nuclei has been carried out, in particular on their size and velocity. To this aim have been utilized optical techniques such as PIV and ILIDS, which is the acronym for Interferometric Laser Imaging Droplet Sizing. The setup necessary to make use of this technique, to evaluate the size of transparent bubbles, is the same of a PIV-2D study. Its feasibility, until now, has been demonstrated especially in sprays of water droplets in air, where, thanks to the values of the relative refractive index and to spherical shape, an optimal light scattering can be obtained. This study plans to apply this technique to the air bubbles produced by incipient cavitation in marine propeller wake. Advanced image analysis methods on a single frame and on two consecutive frames allow to derive simultaneously cavitation bubble size and velocity.