Indeterminate-origin nozzles to control jet structure and evolution

An indeterminate-origin (IO) nozzle consisting of a four-point tapered crown geometry is used to control jet structure and evolution. The near-field structure and flow field of round water jets were studied with particle image velocimetry (PIV) and laser-induced fluorescence (LIF) techniques. Typical jet Reynolds numbers (based on the nozzle diameter) are 5 000–10 000. The jet structures for IO nozzles are compared with those produced by conventional round nozzles. The IO nozzles introduce strong streamwise vortex pairs, which influence the near-nozzle structure and spreading by deforming the Kelvin–Helmholtz vortex rings. A pair of counter-rotating vortices forms at each valley plane, within the interior of the jet. Adjacent vortex pairs reorganize themselves and form another set of counter-rotating vortex pairs that propagate radially outwards from the jet. The evolution of these effects with streamwise distance and their implications are discussed.