Experimental and quantitative investigation of a free round jet

¹ Unit of Metrology in Fluid Mechanics and Thermal (03/UR/11-09), National School of Engineers of Monastir, Avenue Ibn Eljazzar, 5019 Monastir, Tunisia
² Thermal Centre of Lyon (CETHIL – UMR CNRS 5008), National Institute of Applied Sciences of Lyon, INSA de Lyon, 9 rue de la Physique, 69621 Villeurbanne Cedex, France

Corresponding author: yes.zaouali@laposte.net

Received: 23 February 2010
Revised: 18 May 2010
Accepted: 23 July 2010
Published online: 17 September 2010

Abstract

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 × 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.