Toward a Vortex Breakdown Condition for Swirling Annular Jets

Vortex breakdown is a significant phenomenon in science and technology. In spite of extensive research, the question of the underlying mechanisms for vortex breakdown still lacks a definite answer. The uncertainty of the governing principles for vortex breakdown is revealed by lfie common use of a variety of different parameters to describe the degree of swirl. In this paper, a theoretical discussion on the suitahility of three kinds parameters was conducted, and it was found that one appears to be the natural one if the flow is primarily a swirling channel flow, but if the jet character of the flow is dominant, another one appears to be the most suitable. CFD simulations were performed for a channel with an annular inlet considerably smaller than the channel width. For this case the jet character of the flow should predominate and it was found that the parameter, which theoretically appeared to be best suited for jet flows, indeed was less dependent of the detailed inflow geometry than the others.