Experimental Investigation of the Influence of Air Bubbles on the Acoustic Radiation Efficiency of Turbulent Shear Flow

摘要

The objective of this program is to experimentally examine the interaction of a turbulent mean flow with entrained air bubbles. Particular attention has paid to the determination of the relative acoustic radiation efficiencies of bubbles undergoing simple harmonic oscillation and those undergoing splitting. There were three phases to this program: 1) Design and fabrication of a bubble injection system. Redesign and quieting of a turbulent jet facility. 2) Design and fabrication of a facility to study bubble formation noise. Acoustic and high speed observations were made and correlated with new theory developed in this program. 3) Experimental determination of the bubble splitting noise over a range of velocity. Stability theory is being used to explain the results. It can be concluded that splitting noise is the most potent noise source when it occurs. An average increase of 20 dB over single phase jet noise is common. The time scale of each noise pulse is independent of velocity, leading to the conjecture that the splitting process is triggered by turbulence, but the resulting unstable motion is a function of only bubble geometry. The peak sound pressure resulting from the formation of bubbles is dependent on the details of how the bubbles was formed. A simple model of this process correlated well with the measured data.