Observation of Packets of Oblique T-S Waves Trailing a Turbulent Spot in a Radial Liquid Film Flow

Abstract

This report describes the behavior of wave packets trailing an isolated turbulent spot produced in the laminar region of a radial liquid film flow. The liquid film flow was formed by a water discharge to the atmosphere from a thin cylindrical gap between a pipe end and a disk surface. The turbulent spot was produced by a pulse-like jet injection into the laminar flow through a small hole in the disk, and was observed by high-speed photography. Furthermore, the evolution of a pulse-like disturbance, which was added to the basic flow, was analyzed by the finite difference method with VOF method. It was found that the strong turbulence of the spot results in the generation of a pair of oblique wave packets on both sides of the spot and the amplified wave packets break down to new turbulent patches. It was also found that the group velocity of the wave packet is 1.4 times as large as the phase velocity of oblique disturbance wave which is equal to the ordinary disturbance wave.