Computational investigation of mixing and thrust characteristics of Mach 1.64 jets issuing from contoured and straight CD nozzles

The present study investigates the mixing and thrust characteristics of Mach 1.64 jets issuing from a contoured (De Laval) nozzle and a straight convergent-divergent nozzle under overexpanded, correctly expanded, and underexpanded operating conditions. Computational simulations were performed using the SST k – ω turbulence model at NPRs of 3, 4, 4.51, 5, and 6. The numerical methodology was validated against published computational results before being used to examine jet centerline decay, jet-core length, radial jet spread, turbulent kinetic energy, shock-cell structure, and thrust characteristics. The results showed that the De Laval nozzle produced a shorter jet core than the straight CD nozzle at NPRs 3, 4, 4.51, and 5, with reductions of 10.81%, 12.00%, 16.00%, and 2.13%, respectively. The maximum reduction was observed at the design condition (NPR 4.51). However, the De Laval nozzle at NPR 6 resulted in a core extension of about 3.45%, indicating better preservation of axial momentum. For NPRs 3–5, the De Laval nozzle showed a radial jet spread 5–9% higher than the straight CD nozzle. For NPR 6, the spread characteristics of both nozzles were similar. The Mach and turbulent kinetic energy contours depict the formation of shock-cell structures, shear-layer growth, and entrainment of surrounding fluid into the jet. The De Laval nozzle also produced higher thrust than the straight CD nozzle for all the operating conditions investigated, with thrust improvements of 5.3%, 3.0%, 2.4%, 2.1%, and 1.8% at NPRs 3, 4, 4.51, 5, and 6, respectively. The results of the study show that the De Laval nozzle provides improved jet mixing for overexpanded and correctly expanded conditions with a thrust advantage over the straight CD nozzle over the range of NPRs considered.