Influence of injection pressure ratio on the mean flow characteristics of secondary dual injection control nozzle

This article presents an experimental study to investigate the effects of fluidic injection on the mixing characteristics of a slightly over-expanded jet with NPR of 4 and Mach number of 1.6. The experiments were performed with two injectors placed at the nozzle exit and run at an injection pressure (IP) of 1.0, 1.5 and 2.0 bar. The free jet (FJ) without injection was regarded as reference case. To determine the development of the jet, measurements of normalized total-pressure were made along the centreline and in the radial directions at different downstream positions. The measured potential-core lengths were 8.36D e , 8.86D e , 8.28D e , and 6.35D e for FJ, IP 1.0, IP 1.5, and IP 2.0, respectively. The core length is increased by 5.98 % on IP 1.0, decreased by 0.95 % on IP 1.5 and by 24.04 % on IP 2.0 compared to FJ. This is due to weak interaction, with the relatively low injection momentum, which is the reason for the long core in IP 1.0. As the injection pressure increases, the shear-layer is more developed, more entrainment and more spreading and mixing are achieved.