Author(s): W. D. Baines; D. L. Wilkinson

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Abstract: Release of a large volume of air into a rectangular duct on a slope produces a large air bubble which moves at constant velocity upward along the roof of the duct. Experiments reveal that the speed depends only on the duct slope for bubbles of large volume but it depends also on volume for bubbles below a given size. These observations agree well with a theory based on free-streamline potential flow. The measured and predicted frontal shape are also in accord. It is found that bubble height increases with volume for air volumes below a critical volume and above this value the height is constant. There is an abrupt decrease in bubble height at the rear of the bubble and this is associated with a turbulent dissipative region in the underlying flow. In large bubbles on gentle slopes where the flow beneath the bubble is uniform, the dissipative region takes the form of a hydraulic jump.

DOI: https://doi.org/10.1080/00221688609498539

Year: 1986