NEAR-FIELD CHARACTERISTICS OF A TURBULENT COFLOWING JET

The near-field evolution of the velocity and concentration fields for an axisymmetric jet flow of CFC-12 issuing into a coannular jet flow of air is presented. Results based on measurements of the time resolved velocity (two components) and (separately) the concentration, obtained using laser anemometry and Rayleigh scattering systems, show that the transport of momentum and mass in the near field depends on the large scale structure which forms in the shear layer at the edge of the jet. The type of instability and hence the flow development is shown to depend primarily on the ratio of the coflow to jet velocity (m), density ratio, and the jet exit velocity profile. Specifically, for velocity ratios less than and greater than unity, the statistical properties of the velocity and concentration fields are compatible with the existence of an annular vortex ring with positive vorticity for m < 1 and negative vorticity for m > 1. For a velocity ratio equal to unity, the results are consistent with the presence of pairs of counter-rotating vortices that are typical of a wake flow. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.