Control of jet structure by crown-shaped nozzles

Flow visualization and hot-wire anemometry were used to examine the effects of indeterminate-origin nozzles on flow in the near field of an otherwise axisymmetric air jet. Flow structure was investigated under both unforced and forced conditions where the forcing frequency corresponded to a Strouhal number based on diameter of 0.51. Time-averaged views of the unforced flow showed significant deviations of the jet from axisymmetry. Phase-averaged slices of forced flow strobed with a copper vapor laser revealed strong variations in entrainment along different azimuthal planes. Also, the phase-averaged visualizations showed repeatable coherent longitudinal vortex structures attached to the larger-scale vortex rings normally observed in round jets.