Sidejet Strength and Mixing in Self-Excited Jets. [Abstract ONLY]
Sidejet Strength and Mixing in Self-Excited Jets.
Johnson, A. W.; Pitts, W. M.
American Physical Society. Annual Meeting, 46th.
November 21-23, 1993, Albuquerque, NM, 1993.
Bulletin of the American Physical Society, Vol. 28, No.
12, 2284, 1993.
jet induced flow; mixing; rayleigh light scattering
Absolutely unstable jet flows are known to produce
vigorous and intermittent lateral ejections of fluid, or
'sidejets'. Sidejet generation has been attributed to
the near-field interaction of axisymmetric vorticies,
streamwise vorticies, and lobes formed on the
axisymmetric ring vorticies by the Widnall instability.
Here we attempt to vary the strength of sidejets by
varying the intensity of the primary oscillating mode
associated with axisymmetric vorticies of self-excited
absolutely unstable round helium jets. The resulting
effects on the scalar mixing field have been documented.
The intensity of the oscillating mode was manipulated by
varying the velocity profile over a wide range of D/0.
Here, D is the nozzle diameter and 0 is the momentum
thickness of the velocity profile at the nozzle exit.
Profiles of jet concentration were measured using
Rayleigh light scattering (RLS). Simultaneous
concentration and velocity measurements were made using
hotwire probes and RLS in the near field. Strengthening
the oscillating mode increased the radial extent and
strength of the corresponding sidejets. Downstream
spreading and the virtual origin of the jet were also
dependent on sidejet strength. Qualitative results on
the temporal and spatial properties of sidejets in these
flows will also be presented.