EXPERIMENTAL INVESTIGATION OF TURBULENCE PROPERTIES IN THE INTERFACE REGION OF VARIABLE-DENSITY JETS

The global evolution of variable density turbulent jets is now quite well documented, showing that the entrainment of external fluid into these jets is considerably modified by density variations. But, to our knowledge, no specific study has so far been devoted to the intermittent region of such flows. For constant density flows, the radial evolutions of the velocity variances are known to follow the so-called Phillips' relations in this interface region. The main objective of the present work is to investigate whether density variations affect properties of the interface. It is found that Phillips' relations are also valid in the presence of large-density variations, albeit their extent is slightly different. In relation to this, the structure of turbulence is almost unchanged, even in the outer region where large-scale structures are dominating the flow mixing properties, and departure from isotropy for the Reynolds stresses is rather similar for all jets within the range of density ratios considered here. Therefore, except in the very near-field region, most of the influence of density variations can be taken into account by considering only the different evolutions of the flow characteristics on the jet axis. The implication of our results for various aspects associated with these flows, such as in modeling, is also discussed. (C) 1995 American Institute of Physics.