Visualization of the large-scale motion of a plane jet.

The passage of turbulent large scale structures in a plane air jet was observed from the contortions of the turbulent/non turbulent interface made visible by the use of smoke wires in the non turbulent entraining flow. For the self preserving region, these structures were found to be highly three dimensional, displaying considerable streamwise vorticity in the trailing region. No periodicity was observed and no correlation could be detected between the occurrence of these structures across the centreline. The engulfment of the entraining non turbulent fluid takes place predominantly in the trailing region of the coherent structures. Even though the details remain to be established, this study reveals that the large scale coherent structures in the self preserving region of the plane jet are highly complex. (A)