Experimental and quantitative investigation of a free round jet

Flow visualization, basic image processing and statistical treatment are used to investigate the flow characteristics of an axisymmetric free air jet having an initially uniform velocity profile. Vortical structures and their development in the transition zone of the jet are visualized for a range of Reynolds numbers from 1300 to 1700. It is shown the onset and growth of these structures which propagate downstream of the nozzle exit at approximately 0.65 of the velocity of the mean flow. The duration of this development mechanism, before reaching the zone of turbulence, is estimated at 7.6 x 10(-3). Near-field and intermediate-field region lengths, separation distance between two neighboring vortical structures, apparition frequency and jet Strouhal number are measured as functions of the Reynolds number. In particular, it is shown that the Strouhal number, which is estimated at 0.64 in our case, is independent of Reynolds numbers.