École Nationale Supérieure de
Techniques Avancées

Abstract

Air entrainment is a complex phenomenon that has multiple applications in the environment and in the industry like wave breaking or aeration in chemical reactors. Air entrainment is due to the surrounding gas phase around the plunging jet. When it impacts the free surface, it creates a plume of bubbles of different sizes with a considerable inter-facial area, enhancing exchanges of heat and mass between air and water. We develop an experimental setup to study the impact of a circular vertical turbulent jet on the free water surface. Understanding the complexity of multi-phase turbulent flow remain a major challenge in fluid dynamics, with major practical implications. In this report, we present an experimental framework to study the mechanism and characteristics of air entrainment by a jet. We identify three regimes of the flow under the free surface : no entrainment below a critical impact speed, incipient entrainment with a dilute plume, and continuous entrainment with a dense plume. We characterize the effects of the impact velocity and length of the jet on the plume depth and bubble size distribution. We measure the water velocity fields of the three regimes using Particle Image Velocity (PIV), adapting classic algorithm to the case of a two-phase flow. Finally, we explore the effects of adding surfactant on the bubble plume properties and flow field.