A Numerical Study on Mixing Characteristics of Underexpanded Sonic Twin Jets

Twin jets, such as aircraft systems and combustors, find use in many engineering and practical applications. The study of supersonic flow at the exit of twin nozzles is of great interest to scientists and engineers to comprehend the jet-to-jet interaction and flow physics. The present numerical study investigates the mean flow field and mixing characteristics of underexpanded sonic twin jets using Reynolds-Averaged Navier-Stokes (RANS) equations based SST K-ω turbulence model. The numerical simulations are performed under various nozzle pressure ratios (NPR) ranging from 2 to 6; the NPR is defined as the stagnation pressure upstream of the nozzle to the back pressure downstream of the nozzle. The simulated results are validated with the qualitative and quantitative experimental results. Good overall agreements regarding shock cell structures, velocity decay and radial velocity profiles can be observed. However, the shear layer thickness determined from the present turbulence model showed a wider spread, hence slightly over-estimating the jet mixing behavior. In addition, the results show that the length of the supersonic core increases with NPR till 4. The increase in the core is attributed to the mutual interaction between the twin jets, resulting in a reduced entrainment rate.