Numerical study of the effects of velocity ratio on co-flow jet characteristics

Abstract

In this study, large eddy simulations (LES) of turbulent coflow jets are performed, aiming at investigating the effects of jet-to-co-flow velocity ratio on the jet characteristics. A fully developed turbulent pipe flow at Re=10000 is employed at the jet outlet in the present work. It is generated in a straight pipe with a validated adequate length to achieve fully developed stage. For the co-flow jet, simulations with different jet-to-coflow velocity ratios (Vr =3, 6 and 12) are performed to investigate the decay of centreline velocities and turbulence intensities of the jet. Results show a decreasing trend of the velocity decay rate, together with the increasing trends for the peak value and decay rate of turbulence intensities, when the velocity ratio decreases (i.e. higher co-flow velocity). This study is then extended to investigate the probability distribution of passive particles within the jet. It is acquired at above-mentioned different velocity ratios in the particle-laden co-flow jets. The results show a negative correlation between the velocity ratio and particle concentration. The particles have a more concentrated distribution with the decrease of Vr, which agrees with the variation of turbulence intensities in the present work.