bubbly flow

Flow features resulting from air injection through a hole on an inclined hydrofoil in a free stream flow are investigated. The hydrofoil was oriented at different angles of inclination in the test section at the free stream velocity, 3, 5 and 7 m/s (Fn=30~70). The air jet emanating from the hole at various air injection rates (Cq) was characterized by high-speed imaging. Geometric features of the air jet, such as jet width, angle, effective diameter and thickness are measured from the high-speed images. Depending on Fn and Cq, several jet domains such as unstable jet, cloudy puff, buoyant-bifurcating jet, and stable-buoyant jet domains were observed upon air injection at Rn~1000 for various hydrofoil inclinations.

 The injection of air bubbles into the liquid phase of a freestream flow has several impacts on the flow structure, which depends on the volume and size of the bubbles. The effects of the bubble curtain on the sound wave attention are studied. The bubble curtain greatly suppresses sound waves at all frequency ranges. However, the sound attenuation rate varies along the frequency range. The insertion loss increases depending on the PVF of the bubbles, freestream velocity, and frequency range. 

Air injection in water has several engineering advantages, such as an air lubrication system, cavitation control, and noise reduction. This study investigates the effect of air injection rate and stream velocity on bubble layer volume fraction, thickness, and noise mitigation. Higher stream velocity promotes air bubble breaking and the formation of diverse air bubble patterns such as mono-dispersion bubbles and clustering bubbles. The insertion loss increases with stream velocity as higher flow velocity leads air bubbles to break and form bubble clusters, which is found to be more effective in reducing noise than a single bubble.