An Acoustic Study of Gaseous Micro-Bubbles In Boundary Layers and Propeller Wakes

Abstract

This report deals with exploratory tests to measure the nature of the free gas which occurs in natural water due to the dynamic disturbance of a ship. Acoustic attenuation measurements serve to show that micro gas bubbles are evolved from dissolved gases by the shear dynamics of a boundary layer and that the rate of evolution increases as some function of the intensity and duration of the disturbance and of the pressure, viscosity, and gas content of the water. The tests were conducted in the Laboratory, in large scale simulations of a ship's boundary layer and propeller, and in wakes of actual ship propeller's. These exploratory tests indicate the need for more extensive tests in sea water under a wide variety of naval operating conditions. Such tests are necessary to a better determination of the role that these bubbles play in cavitation and acoustic detection problems.