Abstract
The formation, development and breakdown of a Tollmien-Schlichting wave packet have been investigated in a radial liquid film flow. The liquid film flow was formed of water discharged to the atmosphere from a narrow cylindrical gap between the end of a vertical pipe and the surface of a horizontally placed disk. The wave packet was generated artificially by an extremely weak pulselike jet, which was injected into the laminar region of the liquid film flow through a small hole in the disk, and observed by means of high-speed photography. In addition to the observation, downstream development of the linear wave packet was calculated on the basis of a linear stability theory. For both the shape of the linear wave packet and the manner of the wave packet spreading outward on the way downstream, the calculation gave a good agreement with the experimental result. The group velocity of the wave packet was about 1.4 times as large as the phase velocity of the ordinary T-S wave. The experimental observation enabled us to make clear the process of breakdown of the wave packet to a turbulent spot and the process of formation of a pair of the oblique T-S wave packets trailing along behind the turbulent spot.
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