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

The global evolution of variable density turbulent jets is now quite w ell documented, showing that the entrainment of external fluid into th ese jets is considerably modified by density variations. But, to our k nowledge, no specific study has so far been devoted to the intermitten t region of such flows. For constant density flows, the radial evoluti ons of the velocity variances are known to follow the so-called Philli ps' relations in this interface region. The main objective of the pres ent work is to investigate whether density variations affect propertie s of the interface. It is found that Phillips' relations are also vali d in the presence of large-density variations, albeit their extent is slightly different. In relation to this, the structure of turbulence i s almost unchanged, even in the outer region where large-scale structu res are dominating the flow mixing properties, and departure from isot ropy for the Reynolds stresses is rather similar for all jets within t he range of density ratios considered here. Therefore, except in the v ery 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 resu lts for various aspects associated with these flows, such as in modeli ng, is also discussed. (C) 1995 American Institute of Physics.