关键词: 浮升气泡, Front Tracking Method方法, 界面形态, 数值模拟, 流体动力学

Abstract: A single bubble driven by buoyance rising through a sudden expansive channel was simulated by Front Tracking Method (FTM). Firstly, the influence of the width ratio of the narrow channel and the wide channel on shape and rising velocity of bubble was investigated. It was found that the morphology of bubble interface presented different characteristics in the three parts, i.e., the narrow channel, the expansion part and the wide channel, respectively. When the bubble left the expansion, the surrounding fluid flowed from both sides of the bubble into the bottom area, causing both sides of the bubble to be squeezed, the bubble reached the highest aspect ratio. With the increase of the channel width ratio, the flow field of the bubble was less inhibited by both sides of the wall, and the maximum aspect ratio of the bubble decreased. When Wn/We reached over 4/6, the influence of expansion segment can be ignored. Then the influence of Eotvos number Eo and Mo number were analyzed. At low Eo, when the Mo number reduced, the bubble was more likely to deform, the aspect ratio of the bubble decreased and the bubble?s rising speed increased. When the Eo number increased, the deformation became more serious when the bubble rised. Changing the position of the bubble relative to the narrow channel at the initial moment also affected the shape of the bubble. When the initial position of the bubble was close to the single side wall, due to the low flow velocity of the surrounding fluid near the wall, the bubbles would be stretched horizontally while moving, and the bubble deformed badly in the horizontal direction. Asymmetrical pressure distributions occurred on the left and right sides of the bubble level. The pressure on the side of the bubble near the wall surface was lower, making the movement path of the bubble in the narrow channel appear to swing left and right. After leaving the expansion part, the movement of bubbles gradually stabilized due to the absence of wall constraint on the bubbles. When the bubble was far away from the expansion part, the influence of the wall surface decreased. After 2.3 times from the expansion part, it can be considered that the bubble enters a stable rising state.

Key words: buoyancy-driven bubble, Front Tracking Method, bubble shape, direct numerical simulation, fluid dynamics