Void fraction of dispersed bubbly flow in a narrow rectangular channel under rolling conditions

• The void fraction in narrow rectangular channel in rolling motion is studied.
• The void fraction and volumetric gas flow rate oscillate with rolling motion.
• The time-averaged void fraction is getting smaller under rolling condition.
• A new correlation for predicting void fraction under rolling motion was given.

Rolling motion, as a typical ocean condition, can induce additional force and change the states of a two-phase flow system. Visualized experiments was carried out on void fraction of air–water flow in a narrow rectangular channel (40 × 3 mm2) under ambient temperature and pressure as well as rolling conditions of 5°-8s, 10°-8s, 15°-8s, 15°-12s, 15°-16s (rolling amplitude-rolling period). The results showed that the void fraction oscillates periodically in rolling motions due to the induced changes in phase distribution and the slip of the interface. In addition, rolling motion gives rise to the reduction of the time-averaged void fraction. The fluctuation amplitude of the void fraction increased with the increase in rolling amplitude and the decrease in rolling period. The distribution parameter under rolling condition was obtained and compared with that under steady state. The influence coefficient K was defined by taking the rolling Reynolds number and gas Reynolds number into consideration. A new correlation for predicting the void fraction was given based on the experimental data.