Turbulent vortex breakdown at high Reynolds numbers

This paper deals with vortex breakdown in noncavitating swirling flows in tubes at high Reynolds numbers (Re = U0D0/nu as high as 3 x 10(5) or gamma = Gamma/nu as high as 175,000). Breakdown in slender vortices of high intensity begins with a rapidly spinning spiral at a point dictated by the prevailing flow and boundary conditions. The nascent spiral bursts into turbulence shortly after its inception, i.e., the breakdowns occurring at relatively low gamma or Reynolds numbers are bypassed at sufficiently high Reynolds numbers. Additional findings concern the core bifurcation, the random reversals in the sense of the spiral windings, and the absence of a reversed-flow region. The core meandering and stagnation-point darting are quantified and discussed in light of extensive velocity, turbulence, and spectrum measurements.