This paper describes an exploration of the behaviour and properties of swirling flow
through a constant-diameter pipe. The experiments reveal a complicated transition
process as the swirl intensity Ω is increased at fixed pipe Reynolds number Re ≈ 4900.
For Ω [les ] 1.09, the vortex was steady, laminar, axisymmetric, and developed slowly with
streamwise distance. The upstream velocity profiles were similar to those commonly
appearing in the literature in similar apparatus. Spiral vortex breakdown appeared
in the test section for 1.09 [les ] Ω [les ] 1.31 and was associated with a localized transition
from jet-like to wake-like mean axial velocity profiles. Further increase in Ω caused
the breakdown to move upstream of the test section. Downstream, the core of
the post-breakdown flow was unsteady and recovered toward jet-like profiles with
streamwise distance. At Ω = 2.68, a global transition occurred in which the mean
axial velocity profiles suddenly developed an annular axial velocity deficit. At the
same time, disturbances began to appear in the outer flow. Further increase in Ω
eventually led to an annulus of reversed axial flow and a completely unsteady vortex.
Vortical flow. Part 2. Flow past a sphere in a constant-diameter pipe
