Conditional statistics of the passive scalar field of an axisymmetric turbulent jet in the turbulent ambient

The dynamics of an axisymmetric turbulent jet in an approximately homogeneous isotropic turbulent ambient with no mean flow is studied experimentally. The passive scalar field of the jet is measured using the planar laser-induced fluorescence technique. The statistics are conditioned on the jet centroid and are compared to those of the jet in a quiescent ambient. A two-region model for the jet structure in the turbulent ambient is proposed, based on the conditional statistics. In the first region, the mean scalar properties are self-similar and self-preserving despite the external disturbance. The entrainment and the mixing of the jet are reduced compared to those in a quiescent ambient. In the second region, the jet structure is destroyed, and the width growth stops due to the cessation of the entrainment. The relative turbulence intensity between the ambient and the jet characterizes the transition between the two regions and the critical value of 0.5 indicates the onset of breakup.