Planar laser-induced fluorescence study on the diffusion field of a round jet in a uniform counter-flow

Abstract

A turbulent jet in a uniform counter-flowing stream is known to show enhanced mixing efficiency in comparison with a conventional jet in stagnant ambient. In order to study the characteristics of the diffusion field of a passive scalar in the counter-jet, measurements of the velocity and concentration fields have been conducted by using particle image velocimetry and planar laser-induced fluorescence (PLIF) techniques. Experiments were carried out for three jet to counter-flow velocity ratios: 2.9, 4.0 and 5.1. Strong radial wandering of dyed jet fluid, which was confirmed by visual observation of the PLIF images, was found to cause the mean concentration for the jet in the counter-flow to decay in the downstream direction much faster than that for the jet in quiescent fluid, and to cause the rms concentration fluctuation as well as the rms velocity fluctuation to have a noticeable local maximum within the stagnating region. Another distinct indication of the jet wandering was the probability density function for concentration near the stagnation point, showing a distribution with a double peak that is typical of an intermittent and segregated passive scalar field.

This article is a modified version of the original article from the Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measurements, Mallorca, 16-18 September 2002, which appeared in ‘Engineering Turbulence Modelling Measurements 5’, Elsevier Science, ISBN 0-08-044114-9, ed W Rodi and N Fueyo.