Growing Process and Structure of Axisymmetric Vortex Breakdown (Experiments on the Bubble Growing Process)

Abstract

This study investigates the developmental process of an axisymmetric (bubble type) vortex breakdown. In the the preceding reports, the growing process of the bubble was discussed, based on the inviscid linear theory of the internal wave. In this study, experiments on the unsteady swirling pipe flow are conducted to confirm the theoretical results concerning the growing process. The generation of a group of internal waves by the abrupt change of the upstream boundary condition, its propagation and dispersion are measured by a Laser-Doppler-Velocimeter, and the obtained data are compared with the results of the inviscid theory. The growing process of a bubble is clearly visualized by the method of intermittent injections of dye, and also examined by numerical analysis of the Navier-Stokes equations. The obtained results of the growing process showed a good agreement with the theory.