Influence of primary nozzle exit diameter on mixing dynamics of correctly expanded coaxial sonic jets

Abstract The current study explores the effects of primary nozzle exit diameter (PNED) and velocity ratio (VR) on the decay and mixing behaviour of coaxial, correctly expanded sonic jets using numerical simulations. Coaxial jets with 3 mm lip and three primary nozzle exit diameters of 6 mm, 9 mm, and 12 mm were examined while ensuring a constant secondary nozzle width of 6 mm. A singular free jet, which corresponds to the primary nozzle of the coaxial configuration, was utilized for comparative analysis. The axial Mach number decay and jet flow characteristics were systematically investigated to elucidate the dynamics of mixing. The findings indicate that the coaxial jet with a 6 mm primary nozzle demonstrates the most efficient mixing performance among the configurations assessed. Both PNED and VR significantly influence the behaviour of the coaxial jet. Notably, a velocity ratio of 0.2 was identified as yielding the highest mixing efficiency in comparison to the alternative velocity ratios. The simulations effectively captured the principal flow characteristics and aligned well with the empirical results. This investigation provides significant insights for the optimization of coaxial jet designs, particularly in contexts that necessitate effective mixing and regulated jet behaviour within aerospace, propulsion, and industrial applications.