Statistical description of the bubble cloud resulting from the injection of air into a turbulent water jet

Abstract

The final bubble size distribution, resulting from the break-up of an air jet injected into the central axis of a fully developed, high Reynolds number turbulent water jet has been measured using a Phase Doppler Particle Analyzer (PDPA). The shape of the final size distribution is shown to depend not only on the dissipation rate of turbulent kinetic energy, ϵ, but also on the global void fraction, α H. It has been shown that such a dependence can be expressed as a function of two dimensionless numbers, namely the jet Weber number, W en= ρU J 2 D J/ σ, and the ratio between the initial bubble's size and the critical diameter, D 0/ D c. The statistical properties of the time and distance separating two bubbles of the same diameter, after the turbulent break process is complete, have also been measured. The probability density function of the inter-arrival time between two consecutive bubbles was found to follow an exponential distribution with intensity factor, λ, depending on the number density of bubbles of a certain diameter and on the velocity of the flow.