Jet Dynamics of Co-Axial Dual Compressible Jets for Different Exit Velocity Ratios

Abstract

The flow characteristics of jets emerging from a dual co-axial nozzle are investigated using Reynolds Averaged Navier Stokes calculations. The development of double shear layer from a dual compressible jet is compared with three exit velocity ratios, keeping a constant value for core exit velocity. The flow characteristics such as centreline velocity, velocity profiles in the jet development region, potential core length, turbulent kinetic energy fields, Vorticity, Mach number variation etc. are predicted from CFD simulations. The effect of secondary flow in the reduction of the growth rate of the primary shear layer, elongation of the primary potential core and the momentum transfer rate of the co-axial jet is compared. The core and secondary potential cores and the shear layers established between them are resolved together with the high turbulence regions between the shear layers. More over, vorticity in the vicinity of the primary and secondary nozzles in the three directions and the subsequent vortex dynamics studied. It is observed that the exit velocity ratio and inflow conditions have significant influence on physical mechanisms taking place within these jets. Co-axial jets exhibit complicated flow structures, depending on the mean-velocity ratio between the two streams. The study indicates that RANS calculations employing linear two-equation turbulence modelling, can predict the flow characteristics of co-axial dual jets reasonably well.