Bubble motion in a thin gap

The anomalous wake accompanying a penny-shaped air bubble of diameter 8 cm rising through a thin gap of water bound between glass plates inclined at 3 degrees relative to the horizontal. The image on the left is a schematic of the flow, and that on the right is a digitized image indicating the motion of particles suspended in the flow in the bubble frame of reference. Note the vigorous reversed surface flow and the bounding streamline, both of which are reminiscent of thermocapillary bubble motion in microgravity. A physical explanation and theoretical model of this peculiar flow structure is given by Bush, JFM (1997) .