Experimental study of the concentration field of discharge from a boat propeller

Abstract

Engines in boats and ships using total loss lubrication deposit a significant proportion of their lubricant and fuel directly into the water. Their impact on the Australian coastline and marine ecosystems is of great concern. The purpose of this study was to document the velocity and concentration field characteristics of a submerged swirling water jet emanating from a propeller in order to provide information on its fundamental characteristics. The properties of the jet were examined far enough downstream to be relevant to the eventual modelling of the mixing problem. Measurements of the velocity and concentration field were performed in a turbulent jet generated by a model boat propeller (0.02 m diameter) within a 0.4 m-wide and 0.15 m-deep flume, operating at 1,500 and 3,000 rpm in a weak co-flow of 0.04 m/s. The measurements were carried out in the Zone of Established Flow up to 50 propeller diameters downstream of the propeller. Results pertaining to radial distribution, self-similarity, standard deviation growth, maximum value decay and integral fluxes of velocity and concentration fitted with empirical correlations. Furthermore, propeller-induced mixing and pollutant source concentration from a two-stroke engine were estimated.