Impact of Different Lip Thicknesses on Overexpanded Coaxial Jets

Abstract

In this work, the effects of lip thickness (LT) on coaxial supersonic jet decay at overexpansion level of NPR5 have been studied numerically. Studies have also been conducted on coaxial supersonic jets from main supersonic C-D nozzles and secondary convergent nozzles with LT of 5 mm (mid), 10 mm (thick) and 15 mm (ultra-thick). A coaxial jet with LT of 1.7 mm (thin lip) was also examined for comparability. Grid independence study and turbulence comparison analyses were conducted for the 1.7 mm lip based on experimental results from the literature. The evaluation included the primary jet centreline pitot pressure decline, Mach number contour, and the density contours. The findings demonstrate that the thick lip and ultra-thick lip coaxial jet mixing has greater advantages than the thin lip coaxial jet used in this investigation. Also, the thickness of the lips variation has a strong impact on the mixing of jets. Coaxial jets of LT of 10mm and 15mm achieve a mixing that is noticeably greater than the lip having thickness of 1.7mm jet. Axial centreline total pressure decay was studied to analyse shock structures, potential core length and characteristic decay. Velocity and streamline contours were also examined.