Vortex-flow regimes

Abstract

Analysis of a considerable body of new data, based upon flow-visualization experiments, reveals a simple criterion for the occurrence of vortex breakdown at a fixed location in a tube: ReB ∼ Ω-3 R−1, where Ω is the circulation number, R the ratio of the radial to tangential velocities in the inflow region, and ReB the pipe Reynolds number at which vortex breakdown occurs. The constant of proportionality is found to be practically independent both of the pipe flare angle α and the type of breakdown observed (bubble, spiral, etc.) although the latter is shown to depend on ReB. Theoretical support for the experimental results is derived from the analysis of Benjamin (1962) combined with similarity arguments.

A weakly nonlinear mechanism for mode selection in swirling jets

“…The distinction between states was based on flow visualizations where dye was introduced on the vortex axis: the dye filament was either found to spread symmetrically and delineate a stagnant region (axisymmetric form) or to be deformed into a spiral configuration. Since then, spiral states have also been identified by Sarpkaya (1971), Faler & Leibovich (1977) and Escudier & Zehnder (1982) in tube experiments, and by Spall & Gatski (1991) in numerical simulations of the Navier-Stokes equations.…”

Synergistic Noise-By-Flow Control Design of Blade-Tip in Axial Fans: Experimental Investigation

“…First, the visualization of three-dimensional streamlines at the tip revealed the presence of a large bubble-type separation with the flow reversal being indicative of the critical bursting phenomenon (Lucca-Negro & O'Doherty, 2001). According to Leibovich (1982), the appearance of the vortex bursting in the bubble form can be interpreted as a consequence of a sufficiently large swirl level and this form of the vortex breakdown is increasingly steady with the level of swirl (Escudier & Zehnder, 1982, Inoue & Furukawa 2002. Second, the presence of a stagnation point along the vortex axis indicated the onset of the vortex collapse in accordance with the observation of Spall et al (1987), who first identified it as a necessary condition for the breakdown to appear.…”

“…The numerical investigation tool was based on an original parallel Finite Element flow solver (Corsini et al, 2005). Despite the steady-state conditions (Corsini et al, , 2010, RANS was adopted as an effective tool for this investigation because it is capable of capturing details of the vortex structures at the tip (Escudier & Zehnder, 1982, Inoue & Furukawa, 2002. One of the main findings was that in rotor AC90/6/TF, the leakage flow control that the aerodynamic appendages at the blade tip gave rise along the operating line, in the near-design operation, to a tip leakage vortex bursting.…”

Three-dimensional measurements of vortex breakdown

“…Only rare observations of a higher mode with |n| = 2 were made by Sarpkaya (1971) and Escudier and Zehnder (1982) in vortex tube experiments. Sarpkaya reported that extreme care for axisymmetry was essential in obtaining the |n| = 2 double helix mode.…”