Multi-scale analysis of bubbly flows

✍ Scribed by Kazuyasu Sugiyama; Shu Takagi; Yoichiro Matsumoto

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 407 KB
• Volume: 191
• Category: Article
• ISSN: 0045-7825
• DOI: 10.1016/s0045-7825(01)00309-7

✦ Synopsis

Bubbly ¯ow has multiple structures in time and spatial scales. The macro-scale ¯ow structure in bubbly ¯ow is aected by both the mezzo-scale and micro-scale phenomena. It is well known that a very small amount of surfactant can drastically change the terminal velocity of a bubble. When the liquid is contaminated, the bubble motion is aected by the Marangoni eect due to the variation of surface tension along the bubble surface caused by the gradient of the contaminant concentration. The numerical results reveal that the drag coecient increases due to the Marangoni eect and the drag coecient of a contaminated bubble approaches that of a rigid particle. The behavior of rising bubbles in quiescent liquid is simulated by the direct numerical simulation (DNS), as the sample of a bubbly ¯ow, where the mezzo-scale phenomena in bubbly ¯ow is clearly observed. The Navier±Stokes equation is solved by the ®nite dierence method (FDM) and the bubble motion is tracked with the rectangular grid system. The turbulent energy in the surrounding liquid increases with the void fraction. The relation between drag coecient, Reynolds number and void fraction is investigated at the moderate Reynolds number. Present results of the void fraction dependence on the drag coecients show an interesting agreement with the experimental and theoretical ones.