A Numerical Study of the Effects of the Velocity Ratio on Coflow Jet Characteristics

Abstract

In this study, large eddy simulations (LES) of turbulent coflow jets are performed and designed to investigate the effects of the jet-to-coflow velocity ratio, Vr, on jet characteristics. A fully developed turbulent pipe flow at Re=10,000, based on the bulk velocity and pipe diameter, is employed as the jet outlet in this work. A comparison between laminar and turbulent jets is performed against the experimental results of a jet produced by a fully developed turbulent pipe flow. For the coflow jet, simulations with different jet-to-coflow velocity ratios (Vr = 3, 6, 12, and ∞) are performed to investigate the turbulence intensities and the decay of the centerline velocity of the jet. The results give two constant decay rates: Ku≈0.144 for single-phase jets and Ku≈0.133 for particle-laden jets. With a decrease in Vr (i.e., a higher coflow velocity), the results show a higher peak value and a larger droop rate for turbulence intensities. This study is then extended to investigate particle distribution under a two-way coupling regime, using a Lagrangian framework. The particle velocity and distribution along the jet centerline, and the particle clustering and radial probability distribution in the jet downstream domain are analyzed with the same coflow jet parameters. The particles tend to move faster and distribute preferentially in the center region with a decrease in Vr, which agrees with the increasing turbulence intensities along the jet centerline in the present work.