Experimental investigation on the morphology of bubble curtains*

Among various geometries of bubbly flows, the bubble curtains forming a barrier with a large number of bubbles are attracting increasing attention as an eco-friendly method (strategy) to confine or guide the floating/submerged pollutants, such as the plastic particles, oil, and wastes in river and sea. In the present study, the laboratory-scale bubble curtains are experimentally investigated in water tunnel (with and without the freestream) with varying air flow rates. The morphological features of the bubble curtain are measured using the high-speed shadowgraphy (optical flow) and particle image velocimetry (PIV). They are used as a basis to draw some analytical modeling using the control volume analysis to explain the transition in the bubble-curtain shape. With a horizontal freestream (up to 0.3 m/s), we examine how the characteristics of the gas phase within the bubble curtain are modified by the crossflow. We will also report the liquid-phase flow entrained and/or guided by the bubble curtain under each condition.