Bubble Formation from an Air Jet Injected into a Turbulent Boundary Layer

(On a Single Bubble)

Abstract

The diameter of small bubbles separated from an air jet injected into a turbulent boundary layer from a nozzle on the wall is evaluated. There exist three patterns of bubble separation that are dependent on the jet velocity, i.e., single bubble, coalesced bubbles, and a continuous air jet. The mechanism of bubble separation from the jet is theoretically considered for the single-bubble region. First, the bubble volume is calculated when the force separating the bubbles, such as the drag or lift from the free stream, overcomes the surface tension acting on the wall. Then the total volume of the separating bubble is obtained by adding the volume supplied from the nozzle until the final separation. The diameter of a single bubble was measured for various experimental conditions. The results are well approximated by the results obtained from the theoretical considerations described in the present study.