Measurements of entrainment and mixing in turbulent jets

Abstract

Entrainment and mixing were investigated in the self-similar far field of a steady, axisymmetric, momentum-driven, free turbulent jet fluid concentration field. Results show that the entrainment and mixing processes in the jet display a roughly periodic organization characterized by temporal and spatial scales approximately equal to the local large scales of the flow. It is found that instantaneous radial profiles of the jet fluid concentration do not resemble the mean profile, indicating that the mean profile is a poor representation of the mixed fluid states in the jet. The instantaneous profiles show that unmixed ambient fluid is transported deep into the jet, and that the mixed fluid composition can be fairly uniform within large regions. The probability of finding unmixed ambient fluid on the jet centerline is found to increase markedly at intervals typically separated by the local large-scale time of the flow. These results are interpreted in terms of a simple conceptual picture for the large-scale organization of entrainment and mixing in the far field of turbulent jets.