Numerical study in the developing region of coaxial axisymmetric confined jet

Abstract

The flow characteristics in the developing region of coaxial axisymmetric confined . - jets were studied numerically. The computer programme used for this purpose employed finite volume discretisation of Na'vier-Stokes equations and a twoequation (k-i;) turbulence modeL After"sUffiCiert1testing against bench-mark experimental and analytical data, the computer programme was used for the prediction of coaxial jet. The present study is confined to jets of a fixed diameter ratio of 2.48. To study the effect of boundary layer at primary jet exit, four different velocity profiles were considered. The Reynolds number and the velocity ratio were kept unchanged for these four cases and were taken to be 3.28 X 104 and 0.023, respectively. Then, for the same Reynolds number, the flow development was studied for four different velocity ratios viz., 0.05, 0.1, 0.2 and 0.5. Finally, the Reynolds number was increased to 3.28 X 105 and for a velocity ratio of 0.5 computations were made for two inlet profiles. It is found that recirculation phenomena; growth rate of jet and turbulence intensity distinctly depend on the shear layer of velocity profile at primary nozzle " exit. However, pressure is rather insensitive to inlet profile variation. For higher velocity ratios (>0.023) recirculation does not occur and the turbulence intensity is found to be suppressed. It is further 's~en "that the flow assumes a self preserving profile in the later part of the developing region.