Investigation of Microbubble Boundary Layer Using Particle Image Velocimetry

Particle tracking velocimetry has been used to measure the velocity fields of both continuous and dispersed phases, in a microbubble turbulent boundary layer, in a channel flow. Hydrogen and oxygen microbubbles were generated in the flow by electrolysis. The average size of the microbubble radius was 15 μm. Significant drag reductions (above 40%) were observed, when the accumulation of microbubbles took place in a critical zone within the buffer layer. The z-component of the mean vorticity field was derived from the measured velocity fields. There is a decrease in the magnitude of the vorticity, leading to a smother transition from the viscous to the buffer layer. This indicates the increase of the viscous sublayer thickness, as also observed in investigations of drag reduction by polymer and surfactant injection in liquid flows.