SEARCH FOR LARGE-SCALE COHERENT STRUCTURES IN THE NEARLY SELF-PRESERVING REGION OF AN AXISYMMETRIC TURBULENT JET.

In an attempt to explore the existence of large-scale coherent structures in the self-preserving region of an axisymmetric free air jet, a 2. 54 cm air jet at a Reynolds number Re//D equals 4. 6 multiplied by 10**4 has been investigated for x/D greater than 40 via both long and short time-averaged space-time correlation measurements. Conventional space-time correlation data with probe separations in the streamwise direction by as much as 25 diameters suggest the existence of large-scale coherent structures centered off the jet axis. The radial extent of these structures is about three local jet diameters, and the azimuthal extent is about a quadrant of the cross-section. Time series of short time-averaged correlations between longitudinal velocity fluctuations obtained with two arrays of hot-wires separated in the streamwise direction strongly support the existence of these structures.