Axisymmetric vortex breakdown Part 1. Confined swirling flow

Abstract

A comparison between the experimental visualization and numerical simulations of the occurrence of vortex breakdown in laminar swirling flows produced by a rotating endwall is presented. The experimental visualizations of Escudier (1984) were the first to detect the presence of multiple recirculation zones and the numerical model presented here, consisting of a numerical solution of the unsteady axisymmetric Navier-Stokes equations, faithfully reproduces these phenomena and all other observed characteristics of the flow. Further, the numerical calculations elucidate the onset of oscillatory flow, an aspect of the flow that was not clearly resolved by the flow visualization experiments. Part 2 of the paper examines the underlying physics of these vortex flows.

Multiple helical modes of vortex breakdown

“…Later studies, by e.g. Lopez (1990Lopez ( , 2006 and Sørensen, Naumov & Mikkelsen (2006), confirmed and extended the observations of Escudier, but did not detect new breakdown states. In a recent study we focused the investigation on higher aspect ratios, with H/R D going from 3.3 to 5.5, and compared the observed critical Reynolds numbers to values obtained from numerical simulations (Sørensen et al 2009).…”

Solitary waves with recirculation zones in axisymmetric rotating flows

“…We point out that in all these successful calculations the divergence of the tube (at least in the region where a separation bubble was observed experimentally) was carefully modelled. In the case of a confined geometry, where the boundary conditions are obvious, Lopez (1990) has shown excellent agreement with the relevant experiments.…”

Axisymmetric vortex breakdown. Part 3 Onset of periodic flow and chaotic advection

“…At low rotation rates the flow is steady and axisymmetric vortex breakdown is possible. This regime has been explored experimentally (Vogel 1968 ;Escudier 1984), as well as numerically (Lugt & Abboud 1987;Lopez 1988Lopez , 1990) and the dynamics of the steady flow is understood (Brown & Lopez 1990). Vortex breakdown in the cylinder flow is a result of the production of an azimuthal component of vorticity which induces a reversed flow on the axis and hence, by continuity, a local divergence of the streamtubes in the neighbourhood of the reversed axial flow.…”