Passive scalar mixing in a turbulent jet

The present work investigates passive scalar turbulent mixing by means of experimental optical techniques capable to simultaneously measure the instantaneous velocity and scalar fields in a non-intrusive way. In particular, passive scalar mixing of a water jet ejected from a pipe duct onto the surrounding quiescent pure fluid is studied by simultaneously using Particle Image Velocimetry for the velocity field and Planar-Laser Induced Fluorescence for the scalar field. The Reynolds numbers (Re) of the jet flow, based on the jet diameter and exit maximum velocity, is 23700 so a fully turbulent jet emerges from the pipe allowing investigating the mixing mechanisms driven by velocity fluctuations. In order to avoid diffusion to be important compared to advection, a scalar substance, Fluorescein sodium salt, with a Schmidt number equal to 2050 has been employed. This ensures turbulent transport to be investigated focussing on Reynolds fluxes, <ui’c’>, whose measure is the main aim of this work. A detailed and accurate description of these quantities is given, unveiling some new interesting features in the pipe jet near field, 0<x/D<17, where few experimental data are available for the scalar concentration field. At the end of the investigated region, the present data approach the Literature data for the self-similar region. © 2009 TSFP4 Symposium. All Rights Reserved.