Effect of Primary Nozzle Exit Diameter on Coaxial Subsonic Jet Mixing
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Abstract
Coaxial subsonic jets have paramount importance in a wide range of engineering fields involving combustion, propulsion and industrial fluid dynamics that require mixing characteristics. The diameter ratio and velocity fraction effects on the decay of coaxial subsonic jets are investigated through a numerical approach. Axial Mach number decay and jet flow field were investigated by analysing coaxial jets with different diameters of the primary nozzle of 6 mm, 9 mm and 12 mm and a fixed value of the secondary nozzle width of 6 mm. A single free jet equivalent to the primary nozzle of the coaxial nozzle was considered for comparison. The results indicate that the 6 mm diameter coaxial jet has better mixing than the other diameter jets studied in this work. The mixing characteristics of the co-flowing jet are found to be greatly affected by the variation of both the primary nozzle exit diameter and velocity fraction. A velocity fraction of 0.2 shows a clearly improved mixing efficacy over other values of velocity fraction. The results indicate that smaller diameter ratios promote enhanced mixing by enhanced shear interactions and larger diameter ratios entail long potential core lengths and reduced turbulence intensity. These findings provide important insights for the optimisation of jet configurations for improved mixing in practical applications.
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