EXPERIMENTAL INVESTIGATIONS ON CAVITATIONS OF MARINE PROPELLERS USING QUANTITATIVE IMAGE-BASED METHODS

Abstract

Cavitations associated with marine propellers have been a major issue in naval architecture and marine propulsion. Among them, sheet and bubble cavitations are especially impactful in ship propulsion, structural vibration and noise, and propeller damage. Even though numerical simulations are becoming more and more powerful in computing complex flows like cavitating propeller flows, their modelings and resulting data still need to be validated by experiments. Due to the fact that most of the experimental methods for cavitations of marine propellers are only qualitative, this paper develops a quantitative image-based method to extract from cavitation images data useful to the validations of the numerical results. The experimental methodology and setup consist of a phase-locked imaging system incorporated with a dynamometer installed in a cavitation tunnel. Series of images at the same phase for unsteady and quasi-steady sheet cavitations, and bubble cavitation are acquired and then processed and analyzed with different algorisms and procedures developed in light of the respective characteristics of these cavitations. The experimental data provide not only quantitative comparisons, validations, and even calibrations to the numerical modelings and results, but also physical insights such as the correlation of sheet cavitation with propeller dynamics.