A continuously unstable precessing flow within a short cylindrical
chamber following
a large sudden expansion is described. The investigation relates to a nozzle
designed
to produce a jet which achieves large-scale mixing in the downstream field.
The inlet
flow in the plane of the sudden expansion is well defined and free from
asymmetry.
Qualitative flow visualization in water and semi-quantitative surface flow
visualization
in air are reported which identify this precession within the chamber.
Quantitative
simultaneous measurements from fast-response pressure transducers at four
tapping
points on the internal walls of the nozzle chamber confirm the presence
of the
precessing field. The investigation focuses on the flow within the nozzle
chamber
rather than that in the emerging jet, although the emerging flow is also
visualized.Two flow modes are identified: a ‘precessing jet’ mode which
is instantaneously
highly asymmetric, and a quasi-symmetric ‘axial jet’ mode.
The precessing jet mode,
on which the investigation concentrates, predominates in the geometric
configuration
investigated here. A topologically consistent flow field, derived from
the visualization
and from the fluctuating pressure data, which describes a three-dimensional
and
time-dependent precessing motion of the jet within the chamber is proposed.
The surface
flow visualization quantifies the axial distances to lines of positive
and negative
bifurcation allowing comparison with related flows involving large-scale
precession
or flapping reported by others. The Strouhal numbers (dimensionless frequencies)
of
these flows are shown to be two orders of magnitude lower than that measured
in the
shear layer of the jet entering the chamber. The phenomenon is demonstrated
to be
unrelated to acoustic coupling.
This mail survey of 136 public relations practitioners in Washington State reveals that public relations tasks are most easily sorted into two — those of manager or technician. Factor analysis suggests that earlier study divisions into four distinct roles are hard to defend because of role overlap. This study suggests the need to rework the Broom and Smith public relations role scale.
Focusing on the function played by individuals in public relations organizations, this study tested an updated version of James Grunig's indices for public relations models, a measure that compares, among other things, whether communication is more one- or two-way. A sample of 136 public relations professionals, surveyed in Washington State, demonstrated two clear functions for one- and two-way communication. The study finds limited support for Grunig's indices but suggests rewriting some measure items and adding new items to improve the indices.
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