Air Bubble Entrainment by Breaking Bow Waves Simulated by a 2D+T Technique

Abstract

Experimental studies of air entrainment by breaking bow waves are essential for advancing the understanding of these flows and reating valid models. This experimental research is part of a larger project whose broad goal is to improve our understanding of the dynamics of breaking bow waves including the entrainment of air bubbles into the flow and the generation of turbulence and vorticity.

A mechanical wave maker creates waves similar to those formed at the bow of a moving ship, utilizing the 2D+T approximation. The rimary mechanisms for air entrainment are the impact of the plunging wave jet and individual droplets in the splash region on the free surface. The air entrainment process is observed in small scale stationary model experiments, and the air bubbles are entrained in spatially periodic bubble clouds. The specific objectives of this project are to develop a shadowgraph technique for measurement of bubble size distributions and motions and to measure and analyze the void fraction as a function of the equivalent forward speed of the ship model. Three key bubble characteristics that will be emphasized and studied in particular detail are bubble distributions and motions, void fractions and relationships between the properties of bubble and the geometrical characteristics of the wave. The air entrainment in ship bow waves simulated by a 2D+T technique and the methods used to analyze these phenomena are all novel aspects of this particular study and should provide a valuable set of data and analyses for the study of breaking bow wave mechanics.