Numerical investigation on effects of trailing-edge modifications on rectangular sonic jets

Purpose The purpose of this study is to numerically investigate the effects of different trailing-edge modifications on the supersonic core length and jet decay behavior of rectangular sonic jet. Design/methodology/approach This paper discusses a numerical study using Realizable k-ε turbulent model of underexpanded sonic jets developed by rectangular nozzles of aspect ratio 2 with trailing-edge modifications at nozzle pressure ratios of 4 and 5. All results reported were obtained from steady-state simulations. Trailing-edge modifications include cut-outs on the wider side of the rectangular nozzle exit. Findings The comparison of numerical results with the experimental findings indicates substantial concordance. From the present results, it is found that three out of six nozzles with trailing-edge modifications, i.e. with non-inverted trailing-edge cut-outs (Mod 1, Mod 2 and Mod 3) are effective in increasing the entrainment of sonic rectangular jets with the surrounding fluid at both nozzle pressure ratios: at NPR 4 the supersonic core length reduces by 11.43%, 38.1% and 18.1% for Mod 1, 2 and 3, respectively, and at NPR 5 by 15.45%, 35.45% and 28.2% for Mod 1, 2 and 3, respectively. These nozzles produce shorter core, weaker shock and expansion waves and decays faster than the jet from the plain nozzle. Mod 2 shows the best mixing due to closely packed shock cells and weaker waves. The modified nozzles with inverted cut-outs namely Mod 4, Mod 5 and Mod 6 nozzles, tend to produce longer supersonic core than the non-inverted cut-outs, due to vortices rotating away from the jet core, resulting in relatively poor mixing. Mach number and turbulent kinetic energy contours reveal bifurcation and no axis switching, with jets spreading along the major axis for all modified nozzles. Originality/value Previous research focused on mainly experimental studies of high-aspect-ratio rectangular convergent-divergent nozzles with various trailing-edge modifications. Comprehensive CFD analysis of low-aspect-ratio rectangular convergent nozzles, considering different trailing-edge designs and nozzle pressure ratios, would be advantageous.