Bubbles Reduce Drag

Physicists in the lab have now confirmed under controlled conditions what shipbuilders have known for some time, that a shot of bubbles can help reduce the drag encountered by a ship moving through water. Detlef Lohse and his colleagues at the University of Twente in the Netherlands start with one of the classic fluid dynamics experiments, a Taylor-Couette cell, consisting of a bath of fluid held between two concentric cylinders, the inner of which rotates.

The drag effect of the fluid on this inner cylinder can be measured with great precision. By introducing a stream of bubbles at the base of the cell, the drag could be reduced by as much as 20%. Conversely, by introducing a stream of buoyant particles at the bottom, the drag was enhanced. In Japan, the largest shipbuilding nation in the world, the subject of bubble drag reduction is very hot. (Van den Berg et al., Physical Review Letters, 4 February 2005; contact Detlef Lohse, d.lohse@tnw.utwente.nl, 31-53-489-8076; http://www.tn.utwente.nl/pof/; see also http://www.fom.nl ; for related Japanese result, see http://www.nmri.go.jp/index_e.html)