Bubble size and flow characteristics of bubbly flow downstream of a ventilated cylinder

Bubbly flows downstream of a ventilated cylinder in a water tunnel are experimentally studied. Emphasis is placed upon the relationship between bubble property and carrier flow parameters. Under no-ventilation condition, the pure-water wake flow is measured with particle image velocimetry technique. Bubbles are generated with ventilation and the bubbly flow is visualized using shadow image velocimetry. The separation and statistical treatment of bubbles in the captured images are accomplished with an in-house code. The influence of upstream flow velocity and air flow rate is examined. Sauter mean diameter of the bubbles and bubble velocity distribution are obtained. Instantaneous bubbly flow pattern is in accordance with the carrier flow characteristics. Across the high-vorticity region, bubbles experience a remarkable bubble size variation, large bubbles are annihilated. As for cross-sectional bubble size distribution, the tendency obtained with image processing agrees with the result obtained with the formula associating turbulent kinetic energy dissipation with bubble size. As upstream velocity increases, the percentage of small bubbles increases. Both bubble volume fraction and the most predominant bubble size increase with air flow rate. The percentage of large bubbles varies slightly with air flow rate.