A pattern-recognition technique, applied to multi-point
simultaneous velocity measurements obtained with 45°
X-wire anemometer probes, is used to extract and
characterize the underlying organized motions, i.e. coherent
structures, within the near-wake region of a turbulent round
jet discharged perpendicularly from a pipe into
a crossflow. This flow has been found to be quite complex owing to its
three-dimensional nature and the interactions between several flow regions.
Analyses of the underlying coherent structures, which play an important
role in the physics of the flow,
are still rare and are mostly based on flow-visualization techniques. Using
a pattern-recognition technique in conjunction with hot-wire measurements,
we recently examined the wake regions of the pipe and jet at levels near
the tip of the pipe, and found that Kármán-like vortex
structures in the wake of the pipe are locked to similar
structures in the jet-wake. In this paper we expand upon our previous
work and characterize these structures throughout the wake of the jet
up into the region of the bent-over jet – a region where they
have not been identified previously. The complex
geometry of these structures in the wake of the jet as well as their
interaction with the bent-over jet are discussed. The results show
that these structures split before they link to similar structures
on the opposite side of the symmetry plane in the jet region. The
results further suggest that the vorticity due to the structures in
the wake of the jet contributes to the motion of the well-known
counter-rotating vortex pair.
