FLOW CHARACTERISTICS AND SHEAR-LAYER VORTEX SHEDDING OF DOUBLE CONCENTRIC JETS

The characteristics of the flow structure and shear-layer vortex shedd ing of double concentric jets separated by a disk are studied experime ntally, Average flow patterns in the prepenetration, transition, and p enetration regimes are measured. In the prepenetration regime, five ch aracteristic flow structures are identified in the shear layer evolvin g from the edge of the circular disk: laminar, subcritical, transition al, supercritical, and fully turbulent modes, Periodic vortices with s mall fluctuations shed intermittently along the subcritical shear laye r, The transitional shear layer is characterized by chaotic motion, Pe riodic turbulent vortices shed intermittently in the supercritical she ar layer, The Strouhal number of the subcritical vortex shedding incre ases with the increase of annulus Reynolds number. It is constant in t he supercritical mode, With the increase of central jet Reynolds numbe r, the Strouhal number increases to a maximum at a central/annular Rey nolds number ratio of 0.11 and then decreases, The Taylor's integral l ength scale of the subcritical shear-layer vortex shedding decreases r apidly with the increase of annulus Reynolds number. It remains consta nt at about 0.4 disk diameters in the supercritical mode. The Reynolds stresses of the shear layer and the stagnation point are presented an d discussed. At the maximum Strouhal number of shear-layer vortex shed ding in the prepenetration regime, the turbulent kinetic energy attain s a maximum in the shear layer and at the stagnation point.