Computational Analysis of Lip Geometry Influence on Subsonic Rectangular Co-Flow Jet Mixing Efficiency for Primary Jet Aspect Ratio 1.5

The effect of lip thickness on the jet decay and mixing characteristics of rectangular coaxial subsonic jets at a Mach number of 0.6 has been investigated numerically. The aspect ratio of the primary nozzle is maintained as 1.5. The study analyzes jet flows emerging from rectangular coaxial nozzle with lip thicknesses of 1mm, 5mm, and 10mm. Detailed assessments of axial and radial total pressure distributions were carried out, along with the analysis of total pressure contours at various downstream locations to understand the influence of lip geometry on jet evolution. The potential core length for the lip thickness of 1mm, 5mm and 10mm extends up to X/D H = 8.28, 7.47 and 3.43 respectively. The results reveal that lip thickness plays a crucial role in governing the rate of jet spreading and mixing. It was observed that the 10mm lip thickness case promotes faster core decay and enhanced mixing due to impinging secondary jet towards primary jet in the intermediate zone, while the 1mm and 5 mm configurations maintained a more coherent jet core over longer distances. The radial pressure profiles and contours revealed key features of the axis-switching phenomenon, highlighting the transformation between the major and minor axis. This study provides insights into how rectangular nozzle lip design can be effectively tailored to control jet behavior in applications involving efficient mixing, noise control, or flow shaping in aerodynamic and propulsion systems.